EP0377717A4 - Supercharging method and apparatus using tailored boost pressure - Google Patents

Abstract

An internal combustion engine (20) has a supercharger (50) for providing boost pressure tailored to engine speed. The supercharger (50) is controlled or specifically designed such that boost presure for engine speeds above a predetermined level is equal to or less than the maximum permissible boost and boost pressure for engine speeds thereabove is less than maximum permissible boost. The supercharged engine has high, low engine speed torque while maintaining nearly naturally aspirated power at higher speeds. The design requires few modifications to the naturally aspirated base engine.

Description

SUPERCHARGING METHOD AND APPARATUS USING TAILORED BOOST PRESSURE

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of U.S. Patent Application Serial No. 208,072 filed June 17, 1988, entitled "Supercharging Method and Apparatus Using Tailored Boost Pressure."

TECHNICAL FIELD

The present invention relates to a method and apparatus for supercharging an internal combustion engine, and more specifically, to a method and apparatus for supercharging wherein the boost pressure is tailored to engine speed to provide an engine giving improved driveability, performance and economy, particularly in a passenger car application.

BACKGROUND ART

Supercharging internal combustion engines has been practiced for many years. Although supercharging can be accomplished using one of several intake manifold pressure-enhancing devices, such as blowers, screw compressors, dynamic compressors, and turbochargers, the application of supercharging techniques for past and present internal combustion engines has centered around turbocharging. In the mid to late 1970's, application of turbochargers to internal combustion engines was seen as a method of improving fuel economy while achieving the performance of a larger displacement, naturally aspirated engine.

While engine turbocharging has produced some improvements, certain limitations have also been recognized. Specifically, turbocharging has not produced the low engine speed torque desired. In addition, compression ratios have had to be lowered to accommodate high engine speed performance and resulting detonation which would be experienced at compression ratios acceptable in a naturally aspirated engine. Moreover, high octane fuels have been required because of potential detonation problems. Further, engines have had to be designed to operate with very rich WOT (wide open throttle) mixtures to control peak turbine inlet temperatures to avoid turbocharger damage as well as helping to avoid detonation.

Indeed, one of the primary objectives of the engine designer has been to optimize the variables of compression ratio, spark timing, octane requirements, air/fuel ratio and allowable boost pressure for various engine speeds. An example of such a teaching is shown in the patent to Jan E. Rydquist, et al., U.S. Patent No. 4,467,607, wherein the maximum permissible charge pressure as a function of engine speed (assuming the other variable parameters of compression ratio, air/fuel ratio, and spark timing have been optimized) is plotted in FIGURE 2, for a given fuel quality and knock security margin. The turbocharger control system is then designed such that boost pressure may be achieved to closely follow the engine knock boundary as defined by the maximum permissible charge pressure. Thus, it is clear that the current state of the art is directed at maximizing boost pressure, with the constraint of detonation, over the entire engine speed range.

In view of the deficiencies encountered in engine turbocharging, such engines have primarily been designed to appeal to a very narrow market, namely, those drivers interested in "high" performance. To accommodate the desires of these drivers, turbochargers have been incorporated in engine design with the understanding that the engines would provide peak performance at high rpm usage. Therefore, peak boost pressure is accomplished at high engine rpm and the necessary adjustments are made, by way of lowering the compression ratio and use of high octane fuels to accommodate such high boost pressures. Further, large capacity turbines and compressors have been incorporated to extend the engine performance at high engine speeds. As a result, thermal loads on internal engine components have increased, thereby requiring use of more expensive materials as well as a larger radiator capacity. Further, maximum gas mass flow is considerably greater, thereby requiring larger air cleaners, air meters, catalytic converters, exhaust system components and the like.

While attention has been directed to improving low engine speed performance, the main thrust of recent developments has been to satisfy market demands for increases in high engine speed performance. Such developments have resulted in an overall increase in the cost of the power system with no appreciable increase in fuel efficiency. Thus, a system, namely supercharging, which began as an effort to increase efficiency, has led strictly to a means of increasing performance at rather high engine speed operation and with substantial additional expense to the overall system. While such systems have met with success in the very limited market to which they are directed, these engine systems do not provide those characteristics which are sought by the vast majority of drivers. Because the supercharged or turbocharged engines are designed to provide maximum power at high engine speeds, with relatively low torque at low-to-moderate engine speeds, such a configuration is not generally acceptable to the average driver who prefers good driveability, that is, good acceleration from stop, relatively easy city traffic maneuvering, safe on-ramp acceleration, and the like, without the necessity of high engine speed operation.

While these characteristics have, in the past, been satisfied by the use of large displacement naturally aspirated engines, such engines produce more maximum power than is actually needed (and rarely used), and, of course, are accompanied by unnecessarily high engine friction and pumping losses, and therefore are less efficient. With the fuel economy requirements now in place (with the outlook for future requirements even more severe), manufacturers have been obliged to move to smaller and smaller engines which, to date, have not produced optimum driveability characteristics. DISCLOSURE OF THE INVENTION

The present invention overcomes many of the deficiencies identified in the prior art referred to above. The invention incorporates a supercharger which is controlled to provide a tailored boost or intake manifold pressure to produce optimum driveability characteristics, that is, good acceleration in low to mid-range engine speeds, relatively easy city traffic maneuvering and the like, without the necessity of high engine speed operation, while providing adequate maximum power for the average motorist.

In accordance with one embodiment of the invention, an internal combustion engine comprises a combustion chamber wherein an air/fuel mixture is ignited. A supercharger is provided for boosting the pressure to the combustion chamber to provide a predetermined boost pressure at low engine speed and a decreasing boost pressure with increases in engine speed. Herein, boost pressure shall mean gauge pressure (psig) and shall be used interchangeably with the term intake manifold pressure.

Thus, in accordance with one embodiment of the present invention, a relatively high boost pressure is provided at low engine speed, but the supercharger is controlled or specifically designed such that the profile of engine intake manifold pressure versus engine rpm has generally a negative slope with increases in engine speed. As a result, an engine so supercharged has very high, low engine speed torque while maintaining adequate maximum power at higher engine speeds. In accordance with a further embodiment of the invention, a sensor is provided for measuring engine speed or any parameter indicative of engine speed. A controller controls the supercharged in response to the sensor such that at engine speeds up to 40% maximum engine speed, the boost pressure to the combustion chamber is equal to or less than maximum permissible boost pressure. For engine speeds above 40% maximum engine speed, the boost pressure is controlled to be less than the maximum permissible pressure. The controller may be designated to maintain the boost pressure of a constant margin below maximum permissible boost or at on increasing margin so that the boost pressure diverges from (becomes continuously less than) maximum permissible boost with increases in engine speed.

Therefore, the present invention envisions the application of a drastically tailored boost characteristic to relatively small displacement engines. Minimal changes to the base (naturally aspirated) engine, air inlet, exhaust system or engine cooling system are made. Maximum boost pressure is applied at low engine speed and little or no boost is applied at high engine speed. By selecting the final drive ratio, the additional torque at low engine speed can be used to achieve improved performance or improved fuel economy, compared to the naturally aspirated base engine, or any combination of performance and fuel economy.

Because of the application of boost pressure in the manner envisioned by the present invention, maximum boost is sufficiently low that detonation is avoided, permitting the use of relatively low octane gasoline. Further, additional equipment, such as intercoolers or other components for cooling the boost charge are not required. Maximum gas flow and fuel flow are no greater than that in the base engine. Thus, larger air cleaners, air meters, catalytic converters, exhaust system components, fuel lines, fuel pump and the like are unnecessary. Further, maximum thermal loads are only marginally greater than the naturally aspirated engine; thus, no special materials or components are required, and larger radiator capacity is not needed. Therefore, the distinction between the current state of the art and the present invention is clear. The objective of the present state of art of turbocharging, including the teachings in the Rydquist, et al. patent referenced above, is to provide the maximum allowable boost pressure while avoiding detonation, thereby obtaining the maximum power output from the engine. In contrast, the present invention teaches providing the maximum permissible boost only at low engine speeds, to provide driveability, and rapidly decreasing boost with increasing engine speed. This teaching allows the engine designer to optimize the variable parameters such as compression ratio, spark timing and air/fuel ratio, much as he would do with a naturally aspirated engine for high engine speed operation.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and for further details and advantages thereof, reference is now made to the following detailed description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a partially broken away section view of an in-line engine adapted in accordance with the present invention; FIGURE 2 is a top plan view of the assembly of

FIGURE 1;

FIGURE 3 is a partially broken away end view of the pressure increasing component of the present invention showing the engine parameters used in control of the pressure increasing device;

FIGURE 4 is a block diagram further illustrating the control unit illustrated in FIGURE 3;

FIGURE 5 is a diagram showing the relationship between engine boost, or intake manifold pressure in relation to engine speed for varying throttle positions for the present invention;

FIGURE 5a is a diagram showing the relationship between the maximum permissible boost pressure of a specified engine and the boost pressure according to one embodiment of the present invention;

FIGURE 6 is a diagram showing an alternative to the relationship shown in FIGURE 5 for engine boost pressure in relation to engine speed;

FIGURE 7 is a diagram showing boost pressure versus engine speed (percent) for the preferred range of operation for the present invention;

FIGURE 8 is a diagram showing engine boost pressure in relation to engine speed for the present invention and for prior art turbocharged engines; and FIGURE 9 is a diagram showing the relationship of engine torque to engine speed for an engine modified according to the present invention in comparison to naturally aspirated engines; and

FIGURE 10 is a diagram showing relative tractive effort in relation to relative vehicle speed for an engine modified according to the present invention.

DETAILED DESCRIPTION

The present invention envisions the use of a supercharger, used in conjunction with an internal combustion engine, which is controlled or specifically designed to provide a tailored boost, or intake manifold pressure to produce optimum driveability characteristics. Such characteristics include good acceleration from stop, acceleration in engine low to mid-range speeds, relatively easy city traffic maneuvering but without the necessity of high engine speed operation.

A primary embodiment is illustrated in the accompanying drawings and described herein and incorporates the use of a turbocharger as the supercharging unit for boosting intake manifold pressure. It is to be understood that the illustration in the primary embodiment of the use of a turbocharger is merely one of a number of variable pressure making devices which may be used in the practice of the present invention. Thus, although the primary embodiment shows the use of a turbocharger, any supercharging device may be used. The terms supercharging device or supercharger will be understood to encompass any variable pressure making device used with internal combustion engine, including, but not limited to, turbochargers, screw compressors, blowers (both internal and external compression positive displacement compressors), dynamic compressors and the like. Thus, the present invention is not limited to the use of turbochargers but will be understood to encompass other variable pressure making devices which are well known now, or which may be developed in the future.

Further, in the primary embodiment discussed below, reference is made to a variable inlet geometry turbocharger used to vary the speed of the turbine and compressor rotors to thereby vary the boost pressure. However, it will be understood that the present invention is not limited to the use of variable inlet geometry to accomplish the present invention.

Specifically, the use of other means for varying the boost pressure may be incorporated, such as the use of a waste gate design, as well other methods of varying boost pressure as taught in the practice of the present invention.

Referring now to FIGURE 1, a partially broken away section view is shown of an in-line engine adapted in accordance with the present invention. FIGURE 2 is a top plan view of the assembly of FIGURE l. As is shown in FIGURES 1 and 2, an in-line four cylinder engine 20 includes the standard components such as cylinder 22 with a crankshaft 24 for driving piston 28 via connecting rod 26. Each piston has an exhaust valve 30 and an intake valve (not shown) which are operated in the conventional way by a camshaft and associated structure.

The present invention is to a method and apparatus for supercharging such an engine where such supercharging is tailored to the speed of the engine. As shown in the embodiment illustrated in FIGURES 1 and 2, such supercharging may be accomplished by using a turbocharger 50 having a compressor housing 54 mated to a turbine housing 52 and having a compressor and turbine rotor 58 and 56, respectively, mounted for rotation therein. A compressor inlet 62 is provided for receiving incoming air or an air/fuel mixture and a turbine exhaust 60 is provided for exhausting spent gases from the turbocharger. As in usual turbocharger designs, the compressor has an outlet 68 which communicates with intake manifold 80 for delivery of air or an air/fuel mixture to cylinders 22. Exhaust from cylinder 22 is communicated through the exhaust valves 30 and by way of an exhaust manifold 66 to the inlet to turbine 52. For purposes of the present invention, a turbocharger of the design shown in U.S. Patent No. 4,179,247, issued December 18, 1979, in the name of Norbert L. Osborn and entitled "Turbocharger Having Variable Area Turbine Nozzles", may be used. The disclosure in such patent is incorporated by reference in the present application for all purposes. Because the structure of this patent is incorporated herein by reference, a detailed discussion of the specific structure is not included here. However, the turbocharger structure disclosed in such patent teaches the use of a variable area inlet geometry with nozzle vanes mounted circumferentially in the inlet between the inlet to the turbine and the turbine rotor. As is shown in FIGURE 3, the area of these nozzles are controlled by the movement of vanes 82 positioned within the inlet to the turbine rotor and such vanes are controlled by an appropriate mechanical controller 84. The vanes are operated to rotate and thereby increase or decrease the inlet area to the turbine rotor. This change in inlet area varies the velocity of the gases directed against the turbine rotor and thus varies the output power of the rotor. Controller 84 is controlled by a proportional controller 90 as described below.

Referring still to FIGURE 3, the specific control of the turbocharger according to the present invention is illustrated. As can be seen in FIGURE 3, controller 84 controls a control rod 92 which is in turn connected at its distal end to an extension 94 having one of the vanes 82 attached thereto. Movement of control rod 92 and extension 94 operates to rotate interconnecting linkage which simultaneously rotates each of the vanes 82 to increase or decrease the velocity of exhaust gases which impinge turbine 56. Controller 84 is controlled by a proportional controller 90 which is illustrated in greater detail in FIGURE 4. In one embodiment of the invention, controller 90 is a microprocessor including a conversion system for receiving analog input from a plurality of sensors 100, 102 and 104 for conversion to digital format usable by the microprocessor. The microprocessor may be of the general type now used in automotive engine management systems. Proportional controller 90 also includes an amplification system for amplifying the signal provided from the microprocessor for controller unit 84. The microprocessor may be programmed to control the turbine output power by way of nozzle area changes, and thus the boost, or intake manifold pressure provided by the turbocharger compressor as provided for in the present invention.

As shown in FIGURE 4, sensors 100, 102 and 104 are provided to measure engine speed, throttle position and intake manifold pressure, respectively, and provide the corresponding analog reading to the proportional controller 90 where they are converted to the digital form for use by the microprocessor. While the example of FIGURES 3 and 4 show measurement of intake manifold pressure, measurements of other parameters indicative of manifold pressure could be substituted such as air mass flow to the cylinders, fuel flow, or engine torque.

Each of the sensors produce an analog signal which is transmitted to respective analog to digital converters 106, 108 and 110, respectively. The signals produced by each of these sensors is transformed within the corresponding analog to digital converter into a series of digital words which represent the numerical value of the parameter being measured.

The digitized signal produced by the analog to digital converters are conveyed to a microprocessor 120 which is included within proportional controller 90. Microprocessor 120 receives the digital signals which represent the parameters being measured by sensors 100, 102 and 104. The microprocessor evaluates the combination of signals received by means of an appropriate algorithm and produces therefrom a signal which controls the operation of the turbocharger in accordance with the present invention. The output signal produced by microprocessor 120 is transferred to a digital to analog converter 122 which produces a corresponding nozzle control signal. The output of the digital to analog converter 122 is connected to a control unit driver circuit 124 which amplifies the nozzle control signal. The amplified signal is transmitted to the nozzle area controller 84 for selectively positioning the nozzle vanes 82. The driver circuit 124 not only provides amplification for the nozzle control signal, but also isolates the proportional controller 90 from the controller unit 84 as well as from any spurious signals generated in the region of the proportional controller.

The proportional controller 90 and sensors 100, 102 and 104 of the present invention utilize a technology which has previously been developed for automotive engine control directed to spark timing and fuel metering. Existing systems of this nature are described in an the SAE text entitled, Engine and Driveline Control Systems; New Developments and Trends, Sp-739, dated February, 1988. The information in this text is incorporated herein by reference for all purposes. In operation of the control system, manifold pressure is read and compared to the desired pressure as determined by the particular algorithm in conjunction with the engine speed. Where the desired pressure is less than or greater than the desired pressure, the controller makes appropriate changes in the position of the nozzle vanes, closing the vanes to increase pressure and opening the vanes to decrease pressure, to produce the desired boost. The control process is of course continuous.

In accordance with the present invention, boost pressure is controlled in conjunction with engine speed such that the turbocharger provides a predetermined boost pressure at low engine speeds and a continuously decreasing boost pressure with increases in engine speed resulting in an increasing security margin with respect to detonation. An illustrative example of this relationship is shown in FIGURE 5. From FIGURE 5, it can be seen that in one embodiment of the invention, boost pressure is at its maximum at relatively low engine speed, for example, 1,200 to 1,600 rpm at wide open throttle. In the example illustrated in FIGURE 5, boost pressure at this engine speed at wide open throttle, would be on the order of 9 psig boost pressure. With increases in engine speed, the pressure making device is controlled or designed such that the boost pressure is reduced. As shown in the example, boost pressure is continuously decreased with increases in engine speed such that at high engine speeds, on the order of 4,800 rpm, boost pressure is between one and two psig. The system may be set such that at higher engine speeds, boost pressure becomes zero or is negative. FIGURE 5 also shows boost pressure versus engine speed for part throttle operation. Specifically, lines 132, 134 and 136 illustrate this relationship for 90%, 80% and 70% of wide open throttle. In a further embodiment of the invention, not only does the boost pressure decrease with increases in engine speed, the reduction is such that for values of engine speed below 40% of maximum engine speed, boost pressure is at or below maximum permissible boost and for engine speeds above this level, boost pressure is less than maximum permissible boost pressure by a specified margin. In one embodiment, this specified margin is a constant. In yet another embodiment, the engine boost is controlled such that the boost pressure diverges from (that is, becomes continuously less than) maximum permissible boost pressure with increases of engine speed. Maximum permissible boost pressure is that maximum pressure allowable (allowing for an adequate security margin from detonation) when considering fuel quality or octane, compression ratio, spark timing and the air/fuel ratio. For further discussion with regard to the maximum permissible boost pressure, versus the independent variables such as compression ratio, spark timing, and exhaust gas temperature constraint, reference is made to the SAE

Paper No. 890458, entitled "Development and Experimental Study of a 1.1 Liter Turbocharged Intercooled Carburettor Engine", by Z. Filipi, Stojan Petrovic and Milan Popovic. In the present invention, the controller operates to provide boost pressure at the maximum permissible level below 40% maximum engine speed but limits boost pressure above this level. This 40% level is significant in that it marks the advent of increasing potential for engine damage caused by detonation. By limiting boost above this level, the possibility of engine damage is substantially reduced. Moreover, at and below 40% maximum engine speed, maximum driveability (e.g., maximum torque) is desired as this rpm region represents engine speeds at which most driving occurs. This is to be contrasted with the prior art, such as that shown in the patent to Rydquist, et al., wherein a turbocharged engine is designed to perform as closely as possible to a maximum permissible charge pressure at various engine speeds. In the present invention, for engine speeds greater than a predetermined level, boost pressure is below the allowable maximum and, in one embodiment, diverges from the maximum permissible boost pressure for higher engine speeds. This relationship is depicted in FIGURE 5a wherein line 138 represents the base value of maximum permissible charge pressure as a function of engine speed. As is well known in the art, after having fixed these parameters and working within the constraints to avoid detonation and to maintain the exhaust gas temperature below a specified level, the maximum permissible boost pressure can be empirically determined.

Such a base value of maximum permissible boost pressure is represented in FIGURE 5a by line 138 which is representative of a four cylinder 2.1 liter turbocharged engine designed to be driven on leaded 97RON petrol and produced in the standard version with conventional charge pressure control, a maximum power of 114kW DIN with a maximum torque of 240 Nm DIN. These specifications are taken from the above referenced patent to Rydquist, et al. , and are provided for exemplary purposes only. Line 130' in FIGURE 5a then represents the boost pressure for varying engine speeds. In this example, at engine speeds of up to 40% of maximum engine speed, the boost pressure is below maximum permissible pressure and for engine speeds above such predetermined level, the boost pressure is less than maximum permissible pressure. More specifically, in accordance with the present invention, at engine speeds up to 40% of maximum engine speed, the boost pressure should be set at equal to or below the maximum permissible pressure and for engine speeds above such predetermined level, the boost pressure should be less than the maximum permissible boost.

In accordance with a more specific embodiment of the invention, above the predetermined engine speed level, the boost pressure may be maintained at a constant margin below the maximum permissible pressure, and in yet a further embodiment of the invention, for engine speeds above 40% maximum engine speed, the boost pressure diverges from maximum permissible pressure. In this embodiment, an increasing margin is provided between maximum boost and maximum permissible boost pressure, with increases in engine speed.

As a result, the benefits of the present invention, namely the avoidance of detonation, permitting the use of relatively low octane fuel and the reduction in the need for additional cooling of the engine is provided. The design eliminates the need for larger engine components which would be required in engines designed for full boost pressure of high engine speeds, such as larger air cleaners, air meters, catalytic converters and exhaust system components. Significantly, the present design avoids the possibility of major engine damage which may occur as a result of detonation at high engine speeds. It will be noted that the controller and the microprocessor therein are designed such that the profile of boost pressure versus engine speed has generally a negative slope, although it may be other than a constant slope, with increases in engine speed. In one embodiment, the profile of boost pressure versus engine speed is below the maximum permissible boost at speeds above the predetermined level by a constant margin. In yet another embodiment, the boost pressure diverges from the maximum permissible boost with increases in engine speed. These variations are achieved by control through the microprocessor of the position of the turbine inlet nozzle vanes 82 thereby varying the velocity of the exhaust gases impinging such turbine rotor and in turn varying the output power of the turbine rotor and thus the boost pressure provided by the compressor to the intake manifold. It will be appreciated, of course, that other methods of control of the turbocharger, or other superchargers used, may be readily employed to vary the intake manifold pressure.

It will be understood that although the above disclosure refers to the control of the boost pressure in conjunction with the engine speed, such control can be provided in conjunction with any parameter indicative of engine speed. For example, such control can be made to correspond to the alternator speed, distributor speed, number of spark events, as well as others. Similarly, control can be based on fuel consumption taken in conjunction with the speed of the vehicle and gear ratio such than the same result is accomplished as described above with respect to controlling the boost pressure in accordance with engine speed. It will be understood that the present invention is intended, and does, cover the use of any parameter indicative of engine speed for purposes of controlling the boost pressure as described herein.

Further, it will be understood that an engine designer may choose to provide certain plateaus where engine boost is not decreased but is maintained level or slightly increased to tailor torque, but with the overall profile being the reduction in boost pressure with increases in engine speed. Such a design is shown in FIGURE 6 wherein the engine is controlled such that boost pressure is decreased in accordance with curve 140 with increases in engine speed, with such curve having plateaus or other variations 142 and 144 although maintaining an overall decrease in boost pressure with increases in engine speed. This and similar arrangements are considered within the scope of the present invention.

The present invention has as its objective to provide a predetermined boost pressure at low engine speeds with a decreasing or lesser intake manifold pressure at higher speeds. As can be seen from FIGURE 7, an optimum region of operation may be defined for wide open throttle. This region is defined such that at 30% of maximum engine speed, the boost pressure is between approximately 4 and 11 psig, with boost pressure being between approximately 0 and 4 psig at 100% engine speed. Thus, for an engine having a maximum speed of 5,000 rpm, boost would be between approximately 4 and 11 psig @ 1,500 rpm, ranging to approximately 0 to 4 psig at approximately 5,000 rpm. FIGURE 8 compares the profile of boost pressure in relation to engine speed as contemplated in the present invention with that presently used in turbocharged engines. As shown in FIGURE 8, the shaded area shown by numeral 180 depicts the boost pressure versus engine speed according to the present invention whereas the area depicted within the boundaries outlined by line 182 shows present turbocharging profiles. The area depicted within the boundaries outlined by line 184 shows past turbocharging profiles. Specifically, in present and past designs, turbochargers have been controlled to increase boost pressure from low engine speeds to a maximum boost pressure and to maintain the boost pressure at elevated levels through increases in engine speed. This is contrasted to the present invention wherein boost pressure is at its highest level at low engine speeds and thereafter is reduced.

Substantial benefits are achieved when the present invention is incorporated. First, because of the application of boost pressure as envisioned in the present invention, maximum boost at the various engine speeds will be sufficiently low that detonation is avoided, permitting the use of relatively low octane gasoline. Further, additional equipment, such as intercoolers or other components for cooling the boost charge are not required although some applications of the present invention may incorporate them. Maximum gas flow may only be marginally greater than that of the base engine. Thus, larger air cleaners, air meters, catalytic converters or exhaust system components are unnecessary. Further, maximum thermal loads are only marginally greater than in the naturally aspirated engine; thus, no special materials or components, or greater capacity engine cooling components, are necessary.

However, the low engine speed torque produced by operating the engine according to the present invention is substantially increased over the naturally aspirated engine. Referring to FIGURE 9, a representation is shown comparing the torque of a typical 2.5 liter naturally aspirated 4-cylinder engine, a typical 2.5 liter 4-cylinder engine operated in accordance with the present invention using a turbocharger, and a typical 3.0 liter naturally aspirated 6-cylinder engine. The torque, in pound-feet of the 2.5 liter naturally aspirated 4-cylinder engine is depicted by curve 150. The torque for the same engine modified in accordance with the present invention is depicted by the curve 152, and the torque produced by the 3.0 liter naturally aspirated 6-cylinder is depicted by curve 154. The curve 152 is calculated torque for engine speed at wide open throttle using boost pressure as shown in FIGURE 5.

The 4-cylinder naturally aspirated engine produces enough maximum torque (and horsepower) at high engine speed operation for the needs of the average driver. On the other hand, the 6-cylinder naturally aspirated engine provides good low engine speed torque but more high engine speed torque (and horsepower) than is used under normal driving conditions. The shaded area 156 defines a torque or power range which provides overall good driveability, that is good low engine speed torque coupled with sufficient high engine speed power. As can be seen, this performance is achieved by the present invention which is represented by curve 152.

As can be seen, the present invention improves the torque of the 4-cylinder naturally aspirated engine to a level substantially equal to that of the 6-cylinder naturally aspirated engine in the low speed range while maintaining adequate but only slightly improved torque in the high speed range. This arrangement is ideally suited to the driveability demands for the average driver wherein the engine should have high, low engine speed torque (such as near 170 pound-feet) while maintaining adequate maximum torque (near 105 pound- feet) at higher rpm. However, these improvements are accomplished with minimum additional expense and modification to the 4-cylinder engine, as mentioned above.

By selecting a final drive ratio, the additional torque can be used to achieve either improved driveability or improved fuel economy, compared to the base engine, or any combination of improved performance and improved fuel economy. For example, FIGURE 10 plots the relative tractive force for the 2.5 liter, naturally aspirated 4-cylinder engine (curve 150) with curves 160, 162 and 164 showing the relative tractive effort produced by the same engine modified in accordance with the present invention using relative drive ratios of 1.00, 1.10 and 1.20, respectively. Thus, it can be seen that the tractive effort can be tailored, with corresponding affect on fuel economy. Thus, the present invention incorporates the use of a supercharger of any design which is controlled or designed to provide a tailored boost pressure to provide optimum driveability characteristics but without the necessity of high engine speed operation and without substantial modification to the naturally aspirated base engine to which the supercharging is applied. In the invention, a supercharger is provided for boosting the pressure in the intake manifold. A control structure is provided for controlling the supercharger to provide a predetermined boost pressure at low engine speed but with a lower boost pressure with higher engine speeds. Alternatively, a boost device may be designed that automatically provides the boost versus engine speed characteristics taught herein. Thus, a substantially high boost pressure is provided at low engine rpm but the supercharger is controlled or designed such that the profile of engine intake manifold pressure versus engine speed has substantially a negative slope with increases in engine speed. As a result, the engine has a very high, low engine speed torque while maintaining adequate maximum power at higher engine speeds. Only minimal changes to the engine, air inlet or exhaust systems are necessary. This is a result of the fact that maximum boost pressure is applied at low engine speed and little or no boost is applied at high engine speed. Thus, maximum boost pressure when considered with engine speed, is sufficiently low that detonation is avoided, permitting the use of lower octane gasoline. Further, additional equipment, such as intercoolers or other components for cooling the boost charge are not required. Maximum gas flow is no greater than that in the base engine. Thus, larger air cleaners, air meters, catalytic converters or exhaust system components are unnecessary. Further, maximum thermal loads are only marginally greater than in the naturally aspirated engine; thus, no special materials or components are required.

Although preferred embodiments of the invention have been described in the foregoing detailed description and illustrated in the accompanying drawings, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions of parts and elements without departing from the spirit of the invention. Accordingly, the present invention is intended to encompass such rearrangements, modifications and substitutions of parts and elements as fall within the spirit and scope of the invention.

Claims

I CLAIM :

1. An internal combustion engine comprising: a combustion chamber wherein an air/fuel mixture is ignited to drive said engine, a supercharger for boosting the pressure to said combustion chamber, a sensor for sensing any parameter indicative of engine speed, a controller for controlling said supercharger in response to said sensor such that at engine speeds up to a predetermined engine speed, the boost pressure to the combustion chamber is equal to or less than maximum permissible boost pressure and for engine speeds thereabove, the boost pressure is less than maximum permissible pressure.

2. The internal combustion engine according to Claim 1 wherein said controller controls the boost pressure for engine speeds above 40% maximum engine speed such that the boost pressure is less than the maximum permissible pressure by a constant margin.

3. The internal combustion engine according to Claim 1 wherein said controller controls the boost pressure at engine speeds above 40% maximum engine speed such that the boost pressure is less than and diverges from maximum permissible pressure.

4. The internal combustion engine according to Claim 1 wherein said decrease in pressure to the combustion chamber is substantially uniform from approximately 30% maximum engine speed to 100% maximum engine speed. 5. The internal combustion engine according to Claim 1 wherein said boost pressure to the combustion chamber at engine speeds of between 30% and 100% of maximum, is less than those values defined by a line from the coordinates 11 psig at 30% to 4 psig at 100% and greater than those values defined by a line from the coordinates 4 psig at 30% to 0 psig at 100%.

6. An internal combustion engine comprising: a combustion chamber for receiving an air/fuel mixture for ignition therein, a supercharger for boosting the pressure to said combustion chamber, a sensor for sensing engine speed or throttle position, or any parameter indicative of engine speed or throttle position, and a controller for controlling said supercharger in response to said sensor such that at engine speeds up to 40% maximum engine speed, the boost pressure to the combustion chamber is equal to or less than maximum permissible boost pressure and for engine speeds above 40% maximum engine speed, the boost pressure is less than the maximum permissible pressure by a predetermined margin.

7. The internal combustion engine according to Claim 6 wherein the margin between the maintained boost pressure and the maximum permissible pressure increases with increasing engine speed.

8. The internal combustion engine according to Claim 6 wherein the margin between the maintained boost pressure and the maximum permissible boost pressure is a constant for increasing engine speeds.

9. The internal combustion engine according to Claim 6 wherein said boost pressure to the combustion chamber at engine speeds of between 30% and 100% of maximum, is less than those values defined by a line from the coordinates 11 psig at 30% to 4 psig at 100% and greater than those values defined by a line from the coordinates 4 psig at 30% to 0 psig at 100%. 10. An internal combustion engine comprising: a combustion chamber wherein an air/fuel mixture is ignited, and supercharger means for boosting the pressure to said combustion chamber such that the profile of engine intake manifold pressure versus engine speed has substantially a negative slope with increases in engine speed and is below the maximum permissible boost pressure for engine speeds above 40% maximum engine speeds.

11. The internal combustion engine according to Claim 10 wherein said boost pressure to the combustion chamber at engine speeds of between 30% and 100% of maximum, is less than those values defined by a line from the coordinates 11 psig at 30% to 4 psig at 100% and greater than those values defined by a line from the coordinates 4 psig at 30% to 0 psig at 100%.

12. In an internal combustion engine having combustion chambers wherein an air/fuel mixture is ignited and having supercharger means for selectively boosting the pressure to the combustion chambers, the improvement comprising: controlling said supercharger means to provide a predetermined boost pressure at low engine speed and a substantially continuously decreasing boost pressure with increases in engine speed which is below the maximum permissible boost pressures for engine speeds above 40% maximum engine speed.

13. The method of Claim 12 further comprising decreasing the pressure to the combustion chamber uniformly from approximately 30% to 100% of maximum engine speed.

14. The method of Claim 12 further comprising controlling said boost pressure such that at engine speeds of between 30% and 100% of maximum, the boost is less than those values defined by a line from the coordinates 11 psig at 30% to 4 psig at 100% and greater than those values defined by a line from the coordinates 4 psig at 30% to 0 psig at 100%.

15. In an internal combustion engine having one or more combustion chambers wherein an air/fuel mixture is ignited and having supercharger means for selectively boosting pressure to the combustion chambers, the improvement comprising: controlling said supercharger means to provide a higher boost pressure at low engine speed than at high engine speed, and controlling said supercharger means to provide a boost pressure at engine speeds above 40% maximum engine speed at a level below the maximum permissible boost pressure.

16. The method of Claim 15 further comprising controlling said boost pressure such that at engine speeds of between 30% and 100% of maximum, the boost is less than those values defined by a line from the coordinates 11 psig at 30% to 4 psig at 100% and greater than those values defined by a line from the coordinates 4 psig at 30% to 0 psig at 100%.

17. An internal combustion engine comprising: a plurality of cylinders, each having intake and exhaust valves, said intake valves communicating with an intake manifold, and each cylinder having pistons oveable therein, fuel and air supply means for supplying an air/fuel mixture to said cylinders, ignition means for igniting said air/fuel mixture, supercharger means for boosting the pressure in said intake manifold, and control means for controlling said supercharger means to provide boost pressure which is below the maximum permissible boost pressure for engine speeds above 40% maximum engine speed.

18. An internal combustion engine according to Claim 17 wherein the boost pressure at engine speeds above 40% maximum engine speed is below the maximum permissible boost pressure by a constant margin.

19. The internal combustion engine according to Claim 17 wherein the boost pressure for engine speeds above 40% maximum engine speed is below the maximum permissible boost pressure by an increasing margin for increasing engine speeds.

20. The internal combustion engine according to Claim 19 wherein said boost pressure to the combustion chamber at engine speeds of between 30% and 100% of maximum, is less than those values defined by a line from the coordinates 11 psig at 30% to 4 psig at 100% and greater than those values defined by a line from the coordinates 4 psig at 30% to 0 psig at 100%.