Cummins Engine Co. v. General Motors Corp. (299 F. Supp. 59, 1969)

FRANK A. KAUFMAN, District Judge.

This is an action for infringement of certain claims of United States Letters Patent No. 3,110,293, issued November 12, 1963, on an application of Neville M. Reiners filed May 24, 1961 (the Reiners patent). Plaintiff, Cummins Engine Company, Inc. (Cummins) is an Indiana corporation and has its principal place of business at Columbus, Indiana, where it manufactures diesel engines, primarily for use in trucks made by other manufacturers. Cummins is the owner of the entire right, title, and interest in and to the patent in suit and has been since the patent issued. Defendant, General Motors Corporation (General Motors), is a Delaware corporation and has its principal offices in Detroit, Michigan, and has numerous manufacturing, sales and service facilities located throughout the country. General Motors manufactures Toro-Flow engines at its GMC Truck and Coach Division in Pontiac, Michigan, and this division also has a regular and established place of business in Silver Spring, Maryland. Those ToroFlow engines are the accused engines in this proceeding. Defendant, McCallBoykin Truck, Inc. (McCall-Boykin), is a Delaware corporation having its principal place of business in Baltimore, Maryland, where it sells and services the .accused Toro-Flow engines.

FINDINGS OF FACT

A. Diesel and Gasoline Engine Technology.

The Reiners patent in suit concerns the open chamber type of diesel (or compression-ignition) engines. This class of diesel engines is characterized by a mode of combustion involving the direct injection of fuel into the cylinders of the engine. In other respects, however, the class shares certain common operating features with all other classes of diesel engines. On a broader level, the diesel engine itself differs from its predecessor, the conventional gasoline (or spark-ignition) engine, in some respects and is similar or identical in others. In order to assess the significance of the Reiners patent as it applies to one class of diesel engines, it is helpful to examine the similarities and differences that run through gasoline and diesel engine technology.

1. The Four-Stroke Cycle.

Basic to all these engines is a common four-stroke power cycle operating with the same fundamental elements- — a piston, connecting rod, crankshaft, and cylinder head with intake and exhaust valves. Basic also is the kinematics, or mechanical operation, of the engines.

Figure 1 shows diagramatically the operation of the four-cycles of the internal combustion engine. During the first (or intake) stroke, the piston moves downward and the intake valve opens with the exhaust valve closed. The downward motion of the piston causes air, which is at normal atmosphere pressure, to be sucked into the cylinder. The intake valve is then closed, with the exhaust valve remaining closed, at the start of the second (or compression) stroke, thus trapping the air in the cylinder; the piston moves upward and compresses this trapped air between the top face of the piston and the cylinder head. During the compression stroke, combustible fuel is injected into the cylinder, and at or near the end of this stroke the fuel-air mixture is ignited. With the intake and exhaust valves remaining closed, the heat of combustion raises the temperature and pressure within the cylinder; this correspondingly expands the trapped gases and drives the piston downward, initiating the third (or power) stroke. The downward motion of the piston acts through the connecting rod to rotate the crankshaft of the engine. The energy thus delivered to the crankshaft can be used to drive the equipment coupled to the engine (usually through a clutch and transmission arrangement). All the useful power of the engine is derived from the third stroke of the cycle. Near the end of this stroke, the exhaust valve opens and, as the piston moves upward during the fourth (or exhaust) stroke, the spent gases are forced out of the cylinder through the exhaust port. This clears the cylinder for another intake stroke and thereby completes the four-stroke cycle.

2. Combustion System Designs.

The differences between the gasoline and diesel engines are manifested in the second stroke of the cycle. In a diesel engine, the fuel is ignited by the heat generated from highly compressing the trapped air. Because a diesel engine utilizes the heat of compression to ignite the fuel, a relatively high degree of compression is required. The ratio of the volume of the air before compression (which is equal to the volume of the cylinder and is called the displacement) to the volume of the air at the end of the compression stroke when it is squeezed into a small space (defined as the clearance volume) is, for diesels, usually 16:1 or more. Ignition takes place when, as the piston approaches the top of the compression stroke, a determined amount of fuel is injected under high pressure into the clearance space and is mixed with the highly-compressed, very hot air (see Figures 2, 3). In order to achieve proper combustion, the injection of the fuel, the mixing of the fuel with the compressed hot air and the ignition must all occur within a very short period of time, on the order of about Vsooth second.

On the other hand, in a gasoline engine, the fuel and air are premixed in a carburetor and intake manifold and the combustible mixture is then drawn into the cylinder during the intake stroke. When the piston is at the top of the compression stroke, the air-fuel mixture is ignited by an electrical spark. Combustion thus does not depend exclusively on compression, and this allows the gasoline engine to operate with significantly lower compression ratios, usually of the order of 8:1 or about half the compression ratio of a diesel engine (see Figures 2 and 3).

The higher compression ratio in the diesel engine of course means that there is a higher expansion ratio of the gases during the power stroke. More power per cycle can thus be generated, all other things being equal, and this adds to the efficiency of the diesel engine. At the same time, the higher cylinder pressures in a diesel engine mean that the principal engine parts including the cylinder head, cylinder blocks, pistons, connecting rods, crankshaft and associated bearings must be stronger and heavier than the smaller parts in a gasoline engine; and a design problem exists to minimize the extra weight and cost of these parts. Differences in cylinder pressures are, however, differences of degree only since the kinematics of the diesel and gasoline engines are basically the same. Knowledge of developments in gasoline engine design to accommodate high pressures is therefore adaptable to diesel engine design, and it is undisputed that an engineer skilled in the art would have no difficulty in designing the engine parts to withstand whatever additional pressures are encountered.

Differences in the modes of combustion, however, create an additional problem for the diesel engine designer that cannot be solved by reference to the gasoline engine art. Because in a diesel engine the fuel must be injected, thoroughly mixed with the air and ignited within a very small period of time and in a small space, the clearance volume of the cylinder must be accurately designed and matched with an appropriate injector spray. Tolerances of error in both design and machining must be minimized, and as the compression ratio is increased for a given displacement this problem is accentuated.

Some diesel designers have attempted to alleviate this problem by using a divided combustion chamber into which all or part of the fuel is injected or directed to mix with the air and to burn partially before being expelled through a passageway into the engine cylinder where it acts as a catalyst for combustion. Though proper combustion is thereby facilitated, pumping losses and heat losses are increased, so engine efficiency and fuel economy are sacrificed to some extent.

The diesel engines of the patent are characterized as being of the open chamber type. In such engines, the fuel is injected directly into the cylinder as the piston nears the top of the compression stroke. In order to achieve proper combustion, the fuel must be atomized into fine droplets, the spray must be dispersed and the droplets must penetrate into the clearance volume. A common combustion chamber design, in widespread use long before the Reiners patent, is based on a Mexican Hat, or Hesselman, chamber. This arrangement is illustrated in Figure 4. The cone-shaped combustion chamber is, in effect, grafted out of the top of the piston, with the sides of the piston reaching, at the top of the compression and exhaust strokes, practically to the cylinder head. During the intake stroke, the air entering the cylinder is given a rotational movement around the cylinder axis due to the shape and location of the intake ports and manifolding. This effect is called “swirl,” and its particular properties influence the choice of the angle and position of the cone in the Mexican Hat. As the piston approaches top dead center on the compression stroke, the rate of swirl accelerates; at the same time, the peripheral (top) portion of the piston forces air radially inward. This latter effect is called “squish”. Also to be considered in designing this combustion system is the type of injector to be used: the pressure of the fuel injection, along with the location and sizes of the orifices in the injector, must be chosen and matched with the chamber design. It can be seen that there are many interdependent variables that have to be considered, both by themselves and in relation to each other, before an optimum design can be achieved. The state of the art at present (and, a fortiori, the state of the prior art) is such that there is no exact mathematical formulation that can yield the best working design; instead, there must be resorted to extensive cut-and-try experimentation. Also, some sophisticated minor design improvements — e.g., recessing the valves to decrease the amount of metal in contact with the burning gasses — may be attempted by further experimentation. It should be emphasized that all of this was thoroughly described in journals of the trade and in common use in the prior art long before the Reiners patent was filed.

3. The Stroke-to-Bore Ratio.

Commercial pressures to develop engines with more power in a smaller package induced diesel and gasoline engine designers to adopt a variety of techniques to achieve more compact machines. These methods included utilizing better lightweight materials, streamlining, and using the “V” cylinder design. Another technique was to reduce the ratio of the length of the stroke to the diameter of the cylinder for a given displacement. This relationship is called the stroke-to-bore ratio (s/b) and an engine is said to be “undersquare” when the bore is less than the stroke (i.e., s/b > 1) and “oversquare” when the bore is greater than the stroke (i.e., s/b