Borgwarner, Inc. v. New Venture Gear, Inc. (237 F. Supp. 2d 919, 2002)

MEMORANDUM ORDER

BOBRICK, United States Magistrate Judge.

Plaintiff BorgWarner charges defendant New Venture Gear with infringing U.S. Patents Nos. 5,407,024 (“patent 024”); 5,485,894 (“patent 894”); 6,000,488 (“patent 488”); and 6,062,330 (“patent 330”). This matter was referred to this Magistrate Judge for the purposes of conducting a Markman hearing and construing the disputed claims of the patents-in-suit. See Markman v. Westview Instruments, Inc., 52 F.3d 967, 979 (Fed.Cir.1995). The patents-in-suit deal with four-wheel drive systems employing active-on-demand transfer cases that automatically control the amount of torque transferred to front and rear wheels. A transfer case is an auxiliary transmission designed to permit the drive from the engine of a vehicle to be operatively split to both the front and rear driving axles. The patents-in-suit disclose a transfer case design that is electronically controlled by a microcontroller.

I. TECHNOLOGY

The microcontroller transfer case is the substance of these patents. Four-wheel drive allows vehicles to operate better on slippery road surfaces, or in off-road conditions. Compared to two-wheel drive systems, however, four-wheel drive systems can result in lower gas mileage, and decreased handling and performance in certain situations. Thus, a part-time four-wheel drive system has the advantage of allowing the operator to select the drive system based on the driving conditions at hand. The operator engages the four-wheel drive system by lever or switch and, within the transfer case, a clutch is engaged that locks the front and rear drive shafts together. The speed of the front and rear wheels becomes equal.

In an on-demand four-wheel drive system, the clutch in the transfer case engages and disengages automatically. This can be an advantage over the part-time, operator-initiated system because it is thought that the operator will not always know when driving conditions call for, or do not call for, four-wheel drive. On-demand transfer cases can be active or reactive. A reactive transfer case employs a mechanical system, such as a viscous clutch, which engages, or reacts, when there is a difference is speed between the front and rear drivelines. A viscous coupling is basically a drum filled with a thick fluid that houses several closely fitted, thin steel discs. One set of the discs is connected to the front wheels and the other to the rear. As one axle begins to demand more torque, the fluid ■ heats up and its viscosity changes. This change in viscosity affects the discs and torque is split according to the actual .demands of the axles.

Active on-demand transfer cases employ sensors that monitor traction needs and automatically adjust the delivery of power to the wheel. Sensors may monitor various factors — such as vehicle speed, wheel slip, accelerator pedal angle, or braking— for which a passive system cannot account. The reaction is quicker than in the passive systems, and some handling problems are eliminated as a result. While this can be an advantage, it can also be a disadvantage in some off-road conditions where the shift might be too abrupt. In addition, as it is a more complex system, it can be more costly.

The patents-in-suit describe an active on-demand system. BorgWarner states that its: “transfer cases have primary and secondary output shafts which drive the primary and secondary axles, front and rear output speed sensors, a modulating clutch to transfer torque from the rear output to the front output when necessary, a drive and a driven sprocket, a chain connecting the two sprockets, a planetary reduction gear for high and low range, and a dog clutch for selecting the range.” (.Plaintiffs Markman Brief, at 7). Borg-Warner goes on to explain some of this as follows:

The modulating clutch is a friction plate clutch that includes plates that rotate with the primary output shaft and plates that rotate with the secondary output shaft. The plates are interleaved together so that when the plates are engaged (i.e., pressed together) torque is transferred from the primary output to the secondary output. The amount of torque transferred will vary with the amount of engagement. The patents-in-suit teach that the clutch actuator can be electromagnetic, hydraulic, or pneumatic.

A microcontroller controls the amount of clutch engagement and disengagement, The microcontroller is' programmed with a control strategy that uses information about vehicle and road conditions to determine when to engage and disengage the modulating clutch. More specifically, the microcontroller first determines the amount of slip (i.e. the difference in rotational speeds) between the front and rear drivelines in determining whether to engage the clutch. A certain amount of slip is acceptable, and in fact, in cornering situations is required. However, when the slip exceeds a certain amount, vehicle handling and performance are affected adversely. The microcontroller determines when the amount of slip is too much. Specifically, the microcontroller receives signals from sensors that are indicative of the rotational speed of the front and rear drivelines. These sensors can be located in the transfer case or at the wheels. From these signals, the microcontroller is able to determine the slip or the speed difference between the front and the rear drivelines.

Once the amount of slip has been determined, the microcontroller uses that information to determine whether the modulating clutch should be engaged or disengaged. Specifically, the amount of slip is compared to a predetermined amount of allowed slip. If the actual slip is greater than the predetermined amount, the microcontroller generates a signal that causes the modulating clutch to be engaged a discrete amount. The microcontroller then repeats its analysis. If the slip is still above the predetermined amount, the amount of engagement of the modulating clutch is increased again. However, if the slip is below the predetermined of threshold amount, the modulating clutch is disengaged by a discrete amount. Thus, the torque is increased and decreased in a stepwise manner. This incremental engagement and disengagement control is a closed loop control strategy that is repeated over and over again as long as the vehicle is in the on demand mode. The constant monitoring and stepwise clutch engagement and disengagement result in an on demand four-wheel drive system that operates without any driver input. In fact, the driver is unaware of this constant monitoring and engagement/disengagement process.

The patents-in-suit disclose that one technique for applying the incremental control strategy is to use pulse width modulation (“PWM”) to control the amount of engagement applied by an electrical clutch actuator. In PWM, the voltage is pulsed to the electrical device to control the amount of power applied. For example, applying five volts to an electrical device will impart about one-half the power that ten volts will provide. However, the same x-educed amount of power can be generated with ten volts by leaving it on for 50% of the time, i.e., turning it on and off so that the electrical device receives five volts instead of ten. This method of power application is called PWM because pulses of full voltage are used, but the width of the pulse (i.e., the time duration of the pulse) is adjusted to affect the overall average power.

Other vehicle operating conditions that can be utilized by the BorgWarner control strategy include the vehicle speed, throttle position (i.e., acceleration), brake application, and steering angle (i.e., cornering). The control strategy may utilize the vehicle speed by varying the predetermined amount of allowed slip depending on the vehicle speed. The control strategy may also utilize acceleration. Specifically, a throttle position sensor may be used to determine the throttle position that is indicative of the acceleration. The throttle position is used to determine if the clutch should be engaged to provide better acceleration. The control strategy may further utilize a brake sensor to determine if the vehicle is braking. The control strategy may use information about the steering angle for modifying the measured amount of slip to account for cornering.

The patents-in-suit also disclose that a minimum standby clutch engagement may be utilized in the on demand transfer case system. This standby engagement establishes a minimum torque transfer amount through the modulating clutch. The minimum engagement is sometimes called “touch off torque” or “preload.” The purpose of the minimum engagement is to provide faster reactions time to prevent wind up or clunking that otherwise occurs when engagement begins.

(.Plaintiff’s Markman Brief, at 7-10). Obviously, NVG parts company with BorgWarner at significant junctures in this explanation of the patents-in-suit. Specifically, there are twelve claim terms in the three patents-in-suit which are in dispute. For three days beginning September 10, 2002, this court held a Mark-man hearing at which the parties presented their respective interpretations of the twelve patent claims at issue. See Markman v. Westview Instruments, Inc., 52 F.3d 967, 979 (Fed.Cir.1995) (en banc), aff'd. 517 U.S. 370, 116 S.Ct. 1384, 134 L.Ed.2d 577 (1996). The parties presented their cases for their interpretations of these twelve claim terms and the court must construe those claim terms in accord with the following applicable law.

II. CLAIM CONSTRUCTION STANDARDS

In Markman, the Federal Circuit held, and the Supreme Court affirmed, that it is the courts’ responsibility as a matter of law to construe the claims of patents for the jury. 52 F.3d at 979. Claim construction is “the process of giving proper meaning to the claim language,” the fundamental process that “defines the scope of the protected invention.” Abtox, Inc. v. Exitron Corp., 122 F.3d 1019, 1023 (Fed.Cir.1997). Claim construction analysis must begin with the words of the claim, which define its scope. Teleflex, Inc. v. Ficosa North America Corp., 299 F.3d 1313, 1324 (Fed.Cir.2002). “[T]he language of the claim frames and ultimately resolves all issues of claim interpretation.” Abtox, Inc. v. Exitron Corp., 122 F.3d 1019, 1023 (Fed.Cir.1997).

The words used in the claims are interpreted in light of the intrinsic evidence of record, including the written description, the drawings, and the prosecution history, if in evidence. Teleflex, 299 F.3d at 1324. The intrinsic evidence may provide context and clarification about the meaning of claim terms. Id. In the absence of an express intent to impart a novel meaning to claim terms, there is a “heavy presumption” that a claim term carries its ordinary and customary meaning. Teleflex, 299 F.3d at 1325. The ordinary meaning of a claim term may be determined by reviewing a variety of sources, including the claims themselves, other intrinsic evidence including the written description and the prosecution history, and dictionaries and treatises. Id. (citations omitted). In all cases, however, the ordinary meaning must be determined from the standpoint of a person of ordinary skill in the relevant art. Id. In this case, the parties inform us that one of “ordinary skill” in the art is a person with a Bachelor of Science Degree in engineering, with several years of experience in building and designing transfer cases. At the Markman hearing, the parties indicated, however, that expert testimony would not be necessary to their presentations, and neither had their expert attend the proceedings. Nevertheless,, the parties referred throughout the proceedings to interpretations based on the understanding of one skilled in the art. While it is true that both sides included reports from their respective experts, those reports' — obviously — simply supported the interpretations the parties advanced. In a situation where the parties call upon the court to interpret a dozen intricate claims, some of which are interrelated, in an area outside the court’s expertise, live testimony, with opportunity for cross-examination and questions from the court would have been of real value.

Of all the intrinsic evidence, courts have indicated that the specification is the “single best guide to the meaning of a disputed term.” Vitronics, Corp. v. Conceptronic, Inc., 90 F.3d 1576, 1582 (Fed.Cir.1996). “Usually, it is dispositive.” • Id. In Teleflex, the court indicated that “[o]ne purpose for examining the specification is to determine if the patentee has limited the scope of the claims.” 299 F.3d at 1325. As an example of such an instance, the court said “an inventor may choose to be his own lexicographer if he defines the specific terms used to describe the invention with reasonable clarity, deliberateness, and precision.” Teleflex, 299 F.3d at 1325. In addition, the specification may be consulted to resolve ambiguity if the ordinary and customary meanings of the words used in the claims are not sufficiently clear to allow the scope of the claim to be determined form the words alone. Id. “The patentee may demonstrate an intent to deviate from the ordinary and accustomed meaning of a claim term by including in the specification expressions of manifest exclusion or restriction, representing a clear disavowal of claim scope.” Id.

On the other hand, while the claims must be read in view of the specification, limitations from the specification are not to be read into the claims. Id. at 1326. “That claims are interpreted in light of the specification does not mean that everything expressed in the specification must be read into all the claims.” Raytheon Co. v. Roper Corp., 724 F.2d 951, 957 (Fed.Cir. 1983). Quoting SRI International v. Matsushita Electric Corp., 775 F.2d 1107, 1121 (Fed.Cir.1985), the Teleflex court sought to explain this seeming contradiction:

If everything in the specification were required to be read into the claims, or if structural claims were to be limited to devices operated precisely as a specification-described embodiment is operated, there would be no need for claims. Nor could an applicant, regardless of the pri- or art, claim more broadly than that embodiment. Nor would a basis remain for the statutory necessity that an applicant conclude his specification with “claims particularly pointing out and distinctly claiming the subject matter which the applicant regards as his invention.” 35 U.S.C. § 112. It is the claims that measure the invention.

299 F.3d at 1326. The Teleflex court distilled these concerns to hold that “claims take on their ordinary meanings unless the patentee demonstrated an intent to deviate from the ordinary and accustomed meaning of a claim term by redefining the term or by characterizing the invention in the intrinsic record using words or expressions of manifest exclusion or restriction, representing a clear disavowal of the claim scope.” 299 F.3d at 1327. Not surprisingly, with such language as their guide, the parties have engaged in a rather spirited disagreement over the role of the specification in the construction of the claims.

More recently, the Federal Circuit addressed this seemingly ambiguous area of law in Texas Digital Systems, Inc., 308 F.3d 1193 (Fed.Cir.2002), where it held that:

the intrinsic record also must be examined in every case to determine whether the presumption of ordinary and customary meaning is rebutted. Indeed, the intrinsic record may show that the specification uses the words in a manner clearly inconsistent with the ordinary meaning reflected, for example, in a dictionary definition. In such a case, the inconsistent dictionary definition must be rejected. In short, the presumption in favor of a dictionary definition will be overcome where the patentee, acting as his or her own lexicographer, has clearly set forth an explicit definition of the term different from its ordinary meaning. Further, the presumption also will be rebutted if the inventor has disavowed or disclaimed scope of coverage, by using words or expressions of manifest exclusion or restriction, representing a clear disavowal of claim scope.

308 F.3d at 1204 (emphasis added, citations omitted). It would appear, then, that the intrinsic record, including the specification, would generally “trump” the claim language in construing the claim. The court, however, went on to caution:

Consulting the written description and prosecution history as a threshold step in the claim construction process, before any effort is made to discern the ordinary and customary meanings attributed to the words themselves, invites a violation of our precedent counseling against importing limitations into the claims. For example, if an invention is disclosed in the written description in only one exemplary form or in only one embodiment, the risk of starting with the intrinsic record is that the single form or embodiment so disclosed will be read to require that the.claim terms be limited to that single form or embodiment. Indeed, one can easily be misled to believe that this is precisely what our precedent requires when it informs that disputed claim terms should be construed in light of the intrinsic record. But if the meaning of the words themselves would not have been understood to persons of skill in the art to be limited only to the examples or embodiments described in the specification, reading the words in such a confined way would mandate the wrong result and would violate our proscription of not reading limitations from the specification into the claims.

308 F.3d at 1204-05 (emphasis added, citations omitted). It would seem, however, that there will always be a tension in claim construction between reference to the claim language and reference to the specification, especially given what the Federal Circuit itself suggests is misleading precedent.

That being said, there are four patents involved in this dispute, with twelve disputed claim interpretations. The parties briefed these disputes prior to the commencement of the three-day Marlcman hearing. Unfortunately, at least one of the disputes raised at the hearing had not been briefed by the parties. In addition, some of the parties’ claim interpretations were changed either during or following the hearing, rendering much of the exposition that went on prior to the change of no import. Following the hearing, the parties were given one more opportunity to set forth their arguments in post -Marlcman briefs. Based on this record, then, the court endeavors to interpret the disputed claims.

III. CONSTRUCTION OF DISPUTED CLAIMS

A. Patent ’024

1. “Incrementally Engaging and Disengaging”

Claims 1, 23, 33, 62, 64, and 66 of patent ’024 recite that the modulating clutch is incrementally engaged when a measured speed difference between the primary and secondary drivelines is greater than a predetermined amount and is incrementally disengaged when the speed difference between these drivelines is below that amount. The parties’ dispute is over the meaning of the phrase “incrementally engaging and disengaging.”

BorgWarner: NVG:

‘Incrementally engaging and disengaging” is a closed loop control strategy that incrementally increases the clutch engagement when the slip is above a predetermined amount and incrementally decreases — the clutch engagement when the slip is below that amount. This incrementally engaging and disengaging is done in discrete steps, which may be the same or different sizes. (Plaintiff’s Markman Brief, at 14). ‘Incrementally engaging and disengaging” means discrete steps that are fixed (pre-set prior to using the system). The size of the step is not dependent on the magnitude of the wheel slip and therefore not continuously variable. (Markman Reply Brief of NVG, at 8).

The issue regarding this claim distills down to the definition of “incrementally”: whether it can describe steps of varying sizes or must mean step of fixed sizes. As noted above, we begin with the “heavy presumption” that a claim term carries its ordinary and customary meaning. Teleflex, 299 F.3d at 1325. To discern the ordinary and customary meaning of a term we may look to dictionary definitions of the word. Kopykake Enterprises, Inc. v. Lucks Co., 264 F.3d 1377, 1382 (Fed.Cir. 2001). Dictionaries, as noted earlier, may always be relied on by the court to determine the meaning of the claim terms “so long as the dictionary definition does not contradict any definition found in or ascertained by a reading of the patent documents.” Id., quoting Vitronics, 90 F.3d at 1584 n. 6.

In this case, the parties offer a buffet of dictionary definitions. BorgWarner’s sampling is geared toward a definition of “increment” as “the finite increase of a variable quantity.” Webster’s New Twentieth Century Dictionary, at 926 (2nd ed.1978). Accordingly, BorgWarner argues that the “ordinary and customary meaning of the word ‘incrementally’ refers to stepwise changes and that these changes may be variable (or different) sizes.” (Plaintiff’s Markman Brief, at 15). Not surprisingly, NVG’s selections refer to changes in steps of fixed or constant sizes. For example, NVG points to the Oxford Modem English Dictionary’s definition of increment as “an increase or addition, esp. one of a series on a fixed scale.” (Markman Brief of NVG, at 10, citing Oxford Modem English Dictionary, at 539 (1992)). From the court’s perspective, the difference is merely one of context.

BorgWarner argues that words in a claim are entitled to their broadest dictionary definition, citing Rexnord Corp. v. Laitram Corp., 274 F.3d 1336, 1342 (Fed. Cir.2001). (Plaintiff’s Post Markman Brief, at 2). We cannot disagree that, generally, an increment could be of “variable quantity,” as BorgWarner argues, of different sizes. There is a specific context here, however, which a definition such as that of the Oxford Modem English Dictionary addresses. Beyond that, we are not really resolving the issue of what “increment” means, but what “incrementally” means as used to describe “engaging and disengaging.”

We are dealing with “increment” as the root of the adverb “incrementally,” which is used to modify “engaging” and “disengaging.” While the noun “increment” may refer to a single, step, addition, or unit of increase which may be of any size, the adverb “incrementally” must be applied to the process of engaging and disengaging. Then, we are not speaking of an “increment,” but a potential series of increments. Once the size of an increment is determined, “incrementally” would refer to a series of steps or additions of that determined size: one increment following another. Ordinarily and customarily, one might refer to such a process as occurring “in increments of ...,” followed by a single amount, as in “increments of 5.” It is doubtful, or would at least be rare, that the phrase would ever be followed varied amounts, as in “increments of 5, 7, and 10.”

As BorgWarner describes that process, once the microcontroller determines the amount of slip, it compares it to a predetermined amount of allowed slip. If the actual slip is greater than the predetermined amount, the microcontroller causes the modulating clutch to be engaged a “discrete” amount, and the analysis is repeated. If the slip is still above the predetermined amount, the amount of engagement of the modulating clutch is increased again; if the slip is below the predetermined of threshold amount, the modulating clutch is disengaged, again by a “discrete” amount. Certainly, these “discrete amounts” would be “increments,” but to suggest they would be of a random or variable size would be counterintuitive. If they could be, the analysis spoken of could simply be performed a single time and the slip corrected for in whatever “increment” was called for. According to BorgWarner, such a single step correction is “very apparent to the driver and undesirable.” (.Plaintiffs Markman Brief, at 8-9 n. 5). It would seem that at least one supposed innovation of the patents-in-suit, the unnoticed correction of slippage, would be defeated by the interpretation BorgWarner advances here.

This dispute, then, is resolved by the ordinary and customary meaning of “incrementally engaging.” Clearly, the “increments” by which the clutch engages or disengages must be of the same size. “Incrementally engaging and disengaging” means discrete, fixed steps.

2. “Clutch Means”, “Modulating Clutch Means”, and “Adjustable Clutch Means”

Claims 1, 23, 33, 59, 62, and 64 all recite some form of modulating clutch means. For example, Claim 1 recites:

a transfer ease having a primary output shaft adapted to drive said primary wheels, a secondary output shaft adapted to drive said secondary wheels, modulating clutch means for selectively transfemng torque from said primary output shaft to said secondary output shaft and substantially inhibiting torque transfer from said primary output shaft to said secondary output shaft.

Claims 23, 33, 62, and 64 all include similar limitations, which may be phrased “clutch means” or “adjustable clutch means.” The use of the term “means” in each of the claim limitations, along with the recitation of a function, such as “selectively transferring torque ...” raises the issue of the applicability of 35 U.S.C. § 112, paragraph 6, which deals with means-plus-function” claims. The parties’ disagreement over the interpretation of this claim concerns the applicability of interpretation rules. ‘means-plus-function”

BorgWarner:

“Modulating clutch means” is a clutch that can transfer different amounts of torque from the primary output shaft to the secondary output shaft. The “modulating clutch means” may be a disk-pack-frietion-plate clutch. The “modulating clutch means” does not include an actuator and may be actuated by any type of acceptable actuator. (Plaintiff’s Markman Brief, at 20).

NVG:

A means-plus-function element, properly interpreted under § 112 ¶ 6 to be the structure described in the specification that performs the recited function, or its equivalent. The structure for performing the function must include clutch assembly 124, which includes an electromagnetic ball/ramp actuator, the drive and driven sprockets 160 and 166 and chain 164. (Markman Brief of NVG, at 16).

The use of the word “means” triggers a presumption that the inventor used the term advisedly to invoke the statutory mandate for “means-plus-function” clauses. Allen Engineering Corp. v. Bartell Industries, 299 F.3d 1336, 1347 (Fed. Cir.2002). This area of patent law is a bit counterintuitive from the court’s perspective. According to the Federal Circuit:

[t]he question whether a claim element triggers section 112(6) is ordinarily not a difficult one. Claim drafters conventionally use the preface “means for” (or “step for”) when they intend to invoke section 112(6), and there is therefore seldom any confusion about whether section 112(6) applies to a particular element.

Greenberg v. Ethicon Endo-Surgery, Inc., 91 F.3d 1580, 1583 (Fed.Cir.1996). It would seem to be a well-settled and simple rule and, consequently, it is puzzling why the patent in this case would employ the terminology if it was not meant to invoke § 112, ¶ 6. That is what BorgWarner claims the patent does here, however, thereby creating the confusion which “sel-domly” occurs.

True, there are two circumstances, however, in which courts have allowed that the presumption is not controlling. First, if a claim element employs the word “means” but recites no corresponding function, then § 112 ¶ 6 is not applicable. Allen Engineering, 299 F.3d at 1347. Second, even if the claim recites a function, if it also recites sufficient structure or material for performing that function, § 112 ¶ 6 does not apply. Id. It is this second circumstance that BorgWarner hopes to take advantage of in this case: according to it, a “modulating clutch means” is a structure sufficient to perform the stated functions of “selectively transferring torque ... and substantially inhibiting torque ...” from the primary output shaft to the' secondary output shaft. NVG disagrees, but the difficulty here seems to be that both sides have support in the applicable case law.

Part of the problem here stems from somewhat murky, or at least less than specific, case law. As already noted, the court in Allen Engineering held that § 112 ¶ 6 did not apply if the claim element “recites sufficient structure or material for performing that function.” 299 F.3d at 1347. Then, the court went on to state that “[a] claim term recites sufficient structure if the term, as the name for the structure, has a reasonably well-understood meaning in the art.” Id. In this case, we would be hard-pressed to disagree with BorgWarner that the term “modulating clutch” has a well-understood meaning in the art. Understandably, then, BorgWarner argues that “[t]he clear reasoning of Allen Eng’g dictates that ‘modulating clutch means for ... ’ does not invoke § 112 ¶ 6 because it recites structure that has a reasonably understood meaning in the art.” (Plaintiffs Post Markman Hearing Brief, at 10).

While the language of Allen Engineering might appear to allow such an argument, we feel it skips a step. The court was relying in part on Watts v. XL Systems, Inc., 232 F.3d 877 (Fed.Cir.2000), which stated that “[a]s an aid in determining whether sufficient structure is in fact recited by a term used in a claim limitation, this court has inquired into whether the term, as the name for structure, has a reasonably well understood meaning in the art.” 232 F.3d at 880-81 (emphasis added). As such, we begin with the term, and we first query whether that term has a reasonably well understood meaning in the art. Certainly, “modulating clutch” is such a term. The analysis is not complete, however: the term may have a reasonably understood meaning, but it must “be understood by one skilled in the art as being adequate to perform the recited function. ” Budde v. Harley-Davidson, Inc., 250 F.3d 1369, 1377 (Fed.Cir.2001). Based on the court’s reading of these cases, it is not enough that the term at issue simply have a reasonably well understood meaning in the art, as it is understood, it must also be adequate to perform the recited function.

With this understanding in mind, we can review what evidence the parties have compiled to support their contentions as to whether “modulating clutch” is a sufficient structure to perform the recited function. They rely, essentially, on expert reports (Plaintiffs Markman Brief, at 20-21; Markman Brief of NVG, at 20-21) although, as noted above, neither party presented expert testimony at the Markman hearing. As a result, the court is left to choose between dry statements, neither of which is subject to questioning from the court or cross-examination. According to BorgWarner, a “modulating clutch means” is a structure sufficient to perform the stated functions of “selectively transferring torque ... and substantially inhibiting torque ...” Its expert, John Starkey explains that:

A “clutch” is a device that provides an interruptible torque connection between two rotating elements. A “clutch” can use positive contact, friction, magnetic forces, or fluid pressure to transfer torques between two elements. A “modulating clutch” is an even more specific type of clutch that can transfer different amounts of torque. The dictionary definition of modulate is “to vary the amplitude.” This is exactly what the modulating clutch does, i.e., vary the amount of torque transferred from none to full capacity. Such clutches use magnetic fields, fluid pressure, or friction plates to transfer the torque.

(Plaintiffs Markman Brief, at 20-21, citing App. V, Ex. A, pp. 6-7). NVG argues that this structure — the modulating clutch — cannot perform the function without an “actuator” which turns the clutch on and off, relying on its expert, Jeffrey Stein. (Markman Brief of NVG, at 20, citing Ex. 9a, ¶ 54). In his report, Mr. Stein stated:

a “friction clutch with multiple plates”is insufficient to perform the claimed function. One reason ... is because the thisfsic] “friction clutch” requires an actuator in order to “selectively” transfer torques (or as stated in some of the claims, “modulate” or “adjust” torque levels). Dr. Starkey’s “friction clutch with multiple plates”... would fail to perform this function this structure is missing an actuation mechanism (e.g. the electromagnetic actuation mechanism described in the specification). Additionally, the recited function requires that the torque is selectively transferred from the primary output shaft to the secondary output shaft .... a “friction clutch” alone cannot accomplish this function — a chain and sprocket assembly is necessary to transfer torque from the “friction clutch” to the secondary output shaft.

(Id). Indeed, another of BorgWarner’s experts — in patent law if not transfer cases — Gerald Bjorge, testified — tentatively, as he put it “that the term modulating clutch means by itself would not recite enough structure to be a nonmeans plus function element.” (Markman Brief of NVG, Ex. 16, at 72). This automotive engineering version of “he said, he said” culminated at the deposition of BorgWar-ner’s expert, who testified as follows:

Q: Now, what components make up that friction clutch with multiple plates?

A: The components which transmit the torque through the clutch.

Q: Can the friction plates transmit torque without an actuator of some type?

A: Clearly they need other enabling components to transmit the torque, but they are the ones that transmit the torque through the clutch.

(Markman Brief of NVG, App., Ex. 11 at 123-24). This is the type of thing that just goes back and forth and, unfortunately, the court did not have the opportunity to question the experts, and perhaps force them to commit to one position, at the Markman hearing. Significantly, though, for our purposes, the plaintiffs expert testimony stops short of asserting that the “modulating clutch” is sufficient to perform the recited function. Considering all the evidence, and the varying opinions, it appears that, while “modulating clutch” may have a well understood meaning in the art, it is not a sufficient structure to perform the recited function. Accordingly, we find that § 112, ¶ 6 is applicable.

Construction of a means-plus-function limitation involves two steps. First, the court must identify the claimed function. Cardiac Pacemakers, Inc. v. St. Jude Medical, Inc., 296 F.3d 1106, 1113 (Fed.Cir.2002)(citing Telemac Cellular Corp. v. Topp Telecom, Inc., 247 F.3d 1316, 1324 (Fed.Cir.2001)). The court must construe the function of a means-plus-function limitation to include the limitations contained in the claim language, and only those limitations. Cardiac Pacemakers, 296 F.3d at 1113. The court may neither narrow the scope of the function beyond the claim language, nor broaden the scope of the claimed function by ignoring clear limitations in the claim language. Id. Here, “modulating clutch means” must be interpreted to be the structure set forth in the specification that performs the claimed function of “selectively transferring torque from said primary output shaft to said secondary output shaft and substantially inhibiting torque transfer from said primary output shaft to said secondary output shaft.”

Second, the court must determine what structure, if any, disclosed in the specification corresponds to the claimed function. Id. In order to qualify as corresponding, the structure must both perform the claimed function, and clearly associate the structure with performance of the function. Id. The court does this — or at least attempts to — from the perspective of a person of ordinary skill in the art. Id.

The parties, with some reliance on their respective experts, direct the court to two different structures disclosed in the specification that purportedly perform the claimed function. BorgWarner submits that:

the components that actually transfer torque and inhibit the transfer of torque are the components of the disc pack clutch assembly 150 described in the specification. Those components include interleaved friction plates or discs 152, clutch hub 155, and annular housing 156.

(Plaintiff’s Markman Reply Brief, at 14 (citing Patent ’024, col. 8, Is. 52-58)). NVG claims that this interpretation ignores the requirement that torque be selectively transferred, and that it be transferred between the two shafts. As NVG would have it:

The specification makes clear that the claimed function is performed by the clutch assembly 124 (including bali/ramp device), the chain drive sprockets 160 and 166, and the drive chain 164. The specification states that these components transfer torque from the primary out put shaft 40 to the secondary output shaft 26 of the transfer case when energized, as is required by the claims.

(Markman Brief of NVG, at 21 (citing Patent ’024, col. 9, Is. 34-42)). BorgWar-ner criticizes this interpretation as confusing the performance of the function with the enablement of that performance. Through several rounds of briefing, the parties offer no response to these respective criticisms.

In Asyst Technologies, Inc. v. Empak, Inc., 268 F.3d 1364 (Fed.Cir.2001), upon which BorgWarner. relies, the court attempted to differentiate between a structure that actually performed a recited function, and one that merely enabled the pertinent structure to operate as intended. In that case, the recited function was “receiving and processing digital information ...” and the disputed structure was the line that transferred the information. Obviously, the line did not “receive and process” but merely enabled that function by transmitting, so it was found not to be pertinent structure. 268 F.3d at 1370-71. BorgWarner fails to expound upon the purported analogy to its position, however. (.Plaintiffs Markman Brief, at 14). The function at issue is the selective transfer of torque between the two shafts. The structure cited by NVG is directly involved in the function, along with the clutch. If “transferring” were part of the function in Asyst, we suspect the line would be pertinent structure. Accordingly, we must find that the structure for performing the function must include clutch assembly 124, which includes an electromagnetic ball/ ramp actuator, the drive and driven sprockets 160 and 166 and chain 164.

We must address one final point regarding this claim dispute. After two rounds of briefing, BorgWarner came up with a new argument at the Markman hearing and in its post -Markman hearing brief: that NVG’s interpretation violates the doctrine of claim differentiation. Under the doctrine of claim differentiation, there is a presumption that each claim in a patent is different in scope, especially if “there is a dispute over whether a limitation found in a dependent claim should be read into an independent claim, and that limitation is the only meaningful difference between the two claims.” Ecolab, Inc. v. Paraclipse, Inc., 285 F.3d 1362, 1375 (Fed. Cir.2002). BorgWarner submits that claim 1, an independent claim, must be broader that its dependent claims, such as claim 10. It argues that NVG’s interpretation — that the “modulating clutch” of claim 1 must have a “electromagnetic ball/ramp actuator” — renders claim 1 impermissibly narrower than claim 10.

The doctrine of claim differentiation, however, only guides the court’s interpretation of the claims, it is not a “hard and fast rule of construction.” Kraft Foods, Inc. v. Int’l Trading Co., 203 F.3d 1362, 1368, (Fed.Cir.2000). Indeed, it is settled law that independent claims containing means-plus-function limitations do not have the same literal scope as dependent claims reciting specifically the structure that performs the stated function. Medtronic, Inc. v. Advanced Cardiovascular Systems, Inc., 248 F.3d 1303, 1313 (Fed.Cir.2001). In Laitram Corp. v. Rexnord, Inc., the court held that “[a] means-plus-function limitation is not made open-ended by the presence of another claim specifically claiming the disclosed structure which underlies the means clause or an equivalent of that structure.” 939 F.2d 1533, 1538, (Fed.Cir.1991). Thus, claim differentiation will not be applied to a situation where, as here, a dependent claim recites the only structure disclosed in the specification that could correspond to the means claimed in the independent claim. Accordingly, our interpretation of this claim, then, remains unchanged: the -structure for performing the function must include clutch assembly 124, which includes an electromagnetic ball/ramp actuator, the drive and driven sprockets 160 and 166 and chain 164.

3. “Means for Determining a Desired Speed Difference”

Claim 52 reads, in part, “means for determining a desired speed difference between said primary output shaft speed and said secondary output shaft speed.” The parties agree that this limitation is a “means-plus-function” element under § 112 ¶ 6. The dispute is over what structure is disclosed in the specification for performing the function of “determining a desired speed difference ...”

BorgWarner:

“Means for determining a desired speed difference between said primary output shaft speed and said secondary output shaft speed” is circuitry within a microcontroller for determining a desired speed difference between said primary output shaft speed and said secondary output shaft speed. {Plaintiffs Markman Brief at 23).

NVG:

A means-plus-function element, properly interpreted under § 112 ¶ 6 to be the structure described in the specification that performs the recited function, or its equivalent. That structure is a microprocessor with specific circuitry (i.e., programmed with a specific algorithm) that determines the desired .speed threshold based on (1) whether the brakes are on or off and (2) whether the transfer case is in high or low gear. {Markman Brief of NVG, at 23).

As we interpret the parties’ presentations, the dispute here is whether the claim can be interpreted as broadly as a general “circuitry within the microcontroller” or whether it must be interpreted to include specific programming of that microcontrol-ler circuitry. According to BorgWarner, the structure that is disclosed in the specification for performing the recited function is circuitry within the microcontroller, which is described in detail in column 13, lines 52-68, of Patent ’024. (App.I, p. 27.). As BorgWarner -explains:

It is commonly known among those of ordinary skill in the art that the circuitry of the microcontroller stores and implements the control programs and routines, as well as facilitates the computations, analyses, and generation of output signals. The specification states that “the microcontroller utilizes an interrupt driven program which functions with four internal loops having distinct cycle times.” During the steps of one of the routines performed by the microcon-troller, “the maximum allowable drive shaft speed difference” is determined. Also, “a process step 254 determines the maximum allowable wheel speed difference (which is indicative of wheel slip) for the present vehicle speed inferred from the speed of the drive shaft which is rotating more slowly.” Furthermore, this “desired speed difference” is the “threshold” slip value “below which the system does not take action to correct for wheel slip and above which the system begins to correct for wheel slip.”

(Plaintiff’s Markman Brief, at 23-24). NVG submits that the structure that performs the recited function is a microcon-troller programmed with the specific algorithm disclosed in the specification.

In WMS Gaming, Inc. v. International Game Technology, 184 F.3d 1339 (Fed.Cir. 1999), the court dealt with a means-plus-function limitation involving a microcomputer. As the court explained:

The structure of a microprocessor programmed to carry out an algorithm is limited by the disclosed algorithm. A general purpose computer, or microprocessor, programmed to carry out an algorithm creates “a new machine, because a general purpose computer in effect becomes a special purpose computer once it is programmed to perform particular functions pursuant to instructions from program software.” The instructions of the software program that carry out the algorithm electrically change the general purpose computer by creating electrical paths within the device. These electrical paths create a special purpose machine for carrying out the particular algorithm.

184 F.3d at 1348. The court held that, “[i]n a means-plus-function claim in which the disclosed structure is a computer, or microprocessor, programmed to carry out an algorithm, the disclosed structure is not the general purpose computer, but rather the special purpose computer programmed to perform the disclosed algorithm.” 184 F.3d at 1349.

In this case, NVG contends that the only “disclosed algorithm” for determining the desired speed difference employs brake and gear information:

The maximum allowable wheel speed difference for a given vehicle speed (which is indicative of wheel slip) is determined from that part, i.e., Part A, B, C, or D of Section 1 of Table II which corresponds to the then current operating conditions of the vehicle, i.e., whether the brake switch is activated, and whether the transfer case is in high or low gear.

(Patent ’024, col. 17, Is. 33-39). Under WMS Gaming, then, the disclosed structure must be interpreted as the microcon-troller programmed with a specific algorithm that determines the desired speed threshold based on (1) whether the brakes are on or off and (2) whether the transfer case is in high or low gear.

BorgWarner argues that the specification also states that the desired speed difference is related to the vehicle speed and the identity of the overrunning shaft, and “may also be dependent upon, for example, steering angle and braking.” (Plaintiffs Markman Reply Brief, at 15 (citing Patent ’024, col. 2, Is. 46-49)). BorgWarner also submits the specification contains still other algorithms that can be used, including one involving steering angle (col. 10, 1.64-col. 11, 1.2). CPlaintiffs Markman Reply Brief at 15 n. 15). At this point, the parties once again descend into a “he said, she said” battle: NVG claims these are not algorithms; Borg-Warner says they are.

Through several rounds of briefing, unfortunately, neither party expounds on their algorithm position, or offers any support for their positions beyond conclusory assertions. (Plaintiffs Markman Reply Brief, at 15 n. 15 (“the specification of the patents in suit makes clear that there are many algorithms that can be used to determine the desired speed difference”); Post Markman Hearing Brief of NVG, at 10 (describing BorgWarner’s citations as “merely part of the Summary” portion of the specification — despite the fact that not all cited portions were in the Summary, and “not an algorithm that performs the claimed function”); Plaintiffs Post Mark-man Hearing Brief, at 13 (“The specification discloses multiple algorithms that may be used by the microcontroller to determine the desired speed difference ... ”)). The parties leave the court to speculate as to what a person skilled in the art would make of all these putative algorithms; whether such an individual would understand they were to employ them to program the microcontroller to determine the desired speed difference. Based on the record the parties have developed, however, the court is constrained to find the only algorithm to be found in the patent-as opposed to lists of possible influencing factors which BorgWarner cites-determines the desired speed threshold based on (1) whether the brakes are on or off and (2) whether the transfer case is in high or low gear. Accordingly, the disclosed structure must be interpreted as the microcontroller programmed with that specific algorithm.

4. “Means for Controlling Operation of Said Clutch Means in Response to Predetermined Conditions”

Claim 59 provides, in part:

[i]n an adaptive four-wheel drive system including a torque distributing system for four-wheel drive operation having a primary drive and. secondary drive line, clutch means associated with said secondary drive line, and means for controlling operation of said clutch means in response to predetermined conditions, a method for controlling clutch operation comprising:

determining primary drive line speed, determining secondary drive line speed,

determining the speed difference between said primary drive line speed and said secondary drive line speed, comparing a desired speed difference and said determined speed-engaging said clutch at a predetermined rate ...

disengaging said clutch at a predetermined rate ...

Again, the parties are in agreement that this is a “means plus function” claim limitation under § 112 ¶ 6, but differ as to the function which the claim recites.

BorgWarner:

“Means for controlling operation of said clutch means in response to predetermined conditions” is circuitry within a microcontroller for controlling the operation of the modulating clutch in response to predetermined conditions. (Plaintiff’s Markman Brief, at 25).

NVG:

A means-plus-function element, properly interpreted under § 112 ¶ 6 to be the structure described in the specification that performs the recited function, or its equivalent. The structure is a programmed microcontroller and the electromagnetic ball/ ramp clutch actuator. (Markman Brief of NVG, at 25).

According to BorgWarner, the structure identified in the specification for performing the recited function is, again, the circuitry within the microcontroller set out in Patent ’024, col. 13, Is. 52-68:

It is commonly known among those of ordinary skill in the art that the circuitry of the microcontroller stores and implements the control programs and routines, as well as facilitates the computations, analyses, and generation of output signals. (App. I, pp. 27-35, col. 13, line 52 col. 29, line 15; App. V, Ex. A, p. 10.) The specification states that “the microcontroller utilizes an interrupt driven program,” during which routines are performed “which monitor the Hall effect sensors 170, 176 and 180 compute the vehicle speed, control the locking hubs 16, enable, operate and disable the electromagnetic clutch assembly 124.” (App. I, p. 27, col. 13, lines 56-57, 63-66.) Further, “[t]he transfer case includes a modulating electromagnetic clutch controlled by the microcontroller.” (App. I, p. 21, col. 2, lines 3 5-36.). As set forth in the specification, the “predetermined conditions” of the claim limitation include the speeds of the output shafts of the transfer case, throttle information, and brake information.

(.Plaintiff’s Markman Brief, at 25-26). The relevant portion of the specification indicates that the microcontroller determines if there is a slip condition by comparing the speeds of the output shafts and, if it exceeds the threshold amount, generates a signal that causes the clutch to begin engaging. The microcontroller again performs the comparison, repeating the process until the slip drops below the threshold amount, at which time the micro-controller then generates a signal that causes the clutch to begin disengaging. This, as BorgWarner would have it, is the function of controlling the operation of the clutch. (Plaintiffs Markman Brief at 26).

NVG adds to the microcontroller the “electromagnetic ball/ramp actuator.” NVG’s position is based on its contention that the “means for controlling operation of said clutch” must not only perform the microcontroller computations, but must also engage and disengage the clutch. (Markman Brief of NVG, at 25).

BorgWarner argues that claim 59 is a “method” claim, with specific rules for its interpretation — an argument that first appears in its reply brief. (Plaintiff's Mark-man Reply Brief, at 15-16). According to BorgWarner, because the “means for controlling” element is in the preamble of the claim, it need not perform all six actions that follow, i.e., determining primary drive line speed, determining secondary drive line speed, determining the speed difference between said primary drive line speed and said secondary drive line speed, comparing a desired speed difference and said determined speed, engaging said clutch at a predetermined rate, and disengaging said clutch at a predetermined rate. BorgWarner relies on Vaupel Textilmaschinen v. Meccanica Euro Italia, 944 F.2d 870, 879-80 (Fed.Cir.1991) for the proposition that:

Structural language in the preamble of a method claim merely defines the general environment for the method and does not dictate how the steps of the method must be performed. Indeed, the steps that comprise the method need not be performed by any of the elements recited in the preamble.

(Plaintiffs Markman Reply Brief at 15-16). In Vaupel, the court was considering the issue of infringement of a patent for a weaving method and a machine. In the preamble language of that particular patent, were the terms “breast beam” and “breast plate,” which the district court concluded were used “only to fix the direction of movement of the woven fabric on the loom” and not to constitute claim limitations. 944 F.2d at 880. The appellate court agreed, finding that:

“[b]reast beam” and “breast plate” -are not structural limitations of Claims 1 and 2; as used in Claims 1 and 2, they indicate a reference point to fix the direction of movement of the woven fabric from the loom.

Id. The appellate court also concluded that the weaving steps of the claim need not be carried out in the specific manner or order appearing in the preferred embodiment. Id.

Does this holding apply here? Unfortunately, BorgWarner does not trace the analogy from a weaving to a “means for controlling operation of said clutch means in response to predetermined conditions ...” and the court is unwilling, without more from BorgWarner, to make such a leap. We do not read Vaupel as holding that the preamble can never limit the claim, as that would be contrary to case law. In C.R. Bard, Inc. v. M3 Systems, Inc., 157 F.3d 1340 (Fed.Cir.1998), the court indicated that the preamble could indeed limit the scope of a claim, as well as simply state the intended use or purpose of the invention. 157 F.3d at 1350. Here, BorgWarner seems to argue that the while the first four steps following the preamble — determining primary drive line speed, determining secondary drive line speed, determining the speed difference between said primary drive line speed and said secondary drive line speed, comparing a desired speed difference and said determined speed- — must be performed, the last two — engaging and disengaging the clutch — need not be. That proposition is very difficult to draw from the Vaupel holding to the extent that Vaupel stated that the steps might be performed in a different manner or order- — but performed nonetheless — and BorgWarner’s arguments to the contrary, both on paper and at the Markman hearing have been con-clusory and unconvincing. As a result, we must find that the structure must perform the stated steps, and therefore, must be interpreted as a programmed microcon-troller and the electromagnetic ball/ramp clutch actuator.

5. “Predetermined Rate”

Claim 59 recites, in part, “engaging said clutch at a predetermined rate to transfer torque from said primary drive line to said secondary drive line” and “disengaging said clutch at a predetermined rate to substantially inhibit torque transfer from said primary driveline to said secondary driveline.” The dispute regarding this claim is over the meaning of the term “rate.”

BorgWarner:

A “predetermined rate” is a preset time for each step of the clutch engagement and disengagement. (.Plaintiff’s Markman Brief, at 27).

NVG:

A pre-set change in the dutch engagement or disengagement per pre-set time interval. (Markman Brief of NVG, at 27).

Here, the parties claim to agree that a rate is defined as a relationship between two variables, but apparently disagree as to what those two variables are. BorgWar-ner contends that they are the number of times the clutch engagement is changed— a potential number of steps — and a period of time. NVG, on the other hand, argues that the rate must involve the force or pressure of clutch engagement and a period of time.

BorgWarner defines “predetermined rate” as a pre-set number of steps that can occur per a unit of time. In the specification, it is explained each step lasts 30 milliseconds before the engagement level can be changed. As a result, in BorgWar-ner’s interpretation, the clutch engagement may be changed at a rate of 200 times per minute. NVG adds to this ratio the “amount of clutch engagement,” interpreting the rate to involve the act of engagement, the pressure or force of the engagement, and the time period. At the same time, NVG allows that the term “rate” refers to a relationship between only two variables. (Post Markman Hearing Brief of NVG, at 12). This would allow for BorgWarner’s interpretation: the variables would be the number of engagement steps and the period of time. Clutch force or pressure would be a third variable. Accordingly, we construe this claim as the number of engagement steps that can occur per a unit of time.

B. Patent ’894:

“A Plurality of Predetermined Values”

Claim 17 recites of Patent ’894 recites, in'part:

a microcontroller for determining operating values including the difference between the speeds of said primary drive line and said secondary drive line and the identity of one of said drive lines overrunning the other of said drive line, comparing said operating values with a plurality of predetermined values and engaging said clutch in increments when said predetermined values are exceeded by said operating values and disengaging said clutch in increments when said predetermined values exceed said operating values.

Claim 11 recites a microcontroller that performs substantially the same operations.

BorgWarner:

“Plurality of predetermined values” is a predetermined difference between the speeds of the output shafts and a determination of which shaft is overrunning (i.e., rotating the fastest), and the mi-crocontroller causes the clutch to engage when the slip is greater than the amount of the predetermined difference. (Plaintiffs Markman Brief, at 20).

NVG:

A microcontroller having circuitry and predetermined information (i.e., determined beforehand) to (1) determine operating values, (2) perform a comparison between at least two operating values with at least two pre-set values and based on this comparison, (3) engage the clutch assembly when both pre-set values are judged to exceed said both operating values; and (4) disengage the clutch assembly when both operating values ex-eeed both pre-set values. (Markman Brief of NVG, at 29).

The parties had some difficulty, on paper and at the hearing, with this particular dispute, to the extent that it is unclear exactly what the dispute is about. Certainly, even in a patent claim, that meaning of the phrase “plurality of predetermined values” is self-evident. In ordinary language, at least, it would refer to at least two values that are set prior to comparison with operating values. Once the parties begin arguing over the interpretation, however, the problems begins.

BorgWarner’s interpretation of the disputed claim term starts with the “operating values,” which BorgWarner says are determined by the microcontroller, and include (1) the speed difference between the output shafts and (2) a determination of which shaft is overrunning. (Plaintiffs Markman Brief, at 29 (citing Patent ’894, col. 30, Is. 33-42)). BorgWarner then explains that these operating values are compared with a “plurality” of “predetermined values,” meaning, not surprisingly, “two or more predetermined values.” (.Plaintiffs Markman Brief, at 29-30). NVG argues that “a person of ordinary skill in the art would understand from the plain wor