The present invention is directed to accelerator control systems, and more particularly to an accelerator control system that controls vehicle speed and power via electronic means by creating a direct relationship between the accelerator pedal position and drivetrain power.
Internal combustion engines having mechanical accelerator control systems are known in the art. In these mechanically-based systems, there is a mechanical connection between the accelerator pedal and the portion of the engine that controls power and vehicle speed. In the case of throttled spark ignition engines, there is usually a mechanical connection between the accelerator pedal and the throttle, allowing the user to control power by throttling at the air intake. The throttle position and intake manifold depression in this system, in conjunction with a carburetor or electronically controlled fuel injection system, controls the power by adjusting the air/fuel ratio via mechanical means.
In the case of diesel engines, there is no air intake throttle. However, diesel engines usually have governors to control power by adjusting the amount of fuel injected into the engine. A mechanical connection between the accelerator pedal and an input to the governor allows the user to control the speed and power.
Although the mechanical controls (e.g., mechanical intake air/throttle controls, mechanical governors) allow the engine to operate adequately, the control characteristics of these structures are mechanically defined and limited. These definitions often compromise optimal engine control characteristics. Examples of part-load engine control at a constant indicated horsepower (IHP) in the prior art is shown in FIGS. 1A and 1B. FIG. 1A is a diagram showing conventional part-load control constant power in a throttled spark ignition engine, while FIG. 1B is a similar diagram for a diesel engine with a conventional max/min governor.
With respect to FIG. 1A, the roughly horizontal lines in the Figure indicate the amount of net power that is generated for a given throttle position by varying the engine speed (in rpm""s). As can be seen from the curvature in the horizontal lines, the drivetrain power tends to vary for a fixed throttle position as the engine speed changes due to the mechanical limitations in the engine control system. Similarly, FIG. 1B shows lines for part-load control of a diesel engine using a different type of controls; as can be seen in the FIG., the amount of power does not remain consistent for a given load as the engine speed changes, particularly when the engine operation switches to idle. Although the characteristics are acceptable, they are not ideal because of the mechanical limitations mentioned above.
With the introduction of electronic engine controls, however, there exists greater flexibility in optimizing part-load engine control characteristics by avoiding mechanically-imposed definitions and limitations. There is a need for an accelerator control strategy that takes advantage of this flexibility.
Accordingly, the present invention relates to a method and system for generating and providing a constant power, part-load accelerator control strategy using electronic communication with the vehicle engine and powertrain. The invention takes advantage of the design freedom and lack of mechanical limitations provided by electronic engine controls and electronic communication systems by freely adjusting engine operational parameters to optimize engine control characteristics.
More particularly, the constant power, part-load engine control method of the invention optimizes the engine control characteristics by adjusting the torque and engine speed as the transmission ratio varies to keep the driveshaft power at a selected constant level for a given accelerator pedal position. A fuel table corresponding to this constant power, part-load control characteristic is generated to define the fuel quantity needed to maintain the driveshaft power at the selected level based on the engine speed and engine torque. By adjusting the engine speed and engine torque when the transmission ratio changes so that the driveshaft power for a given accelerator pedal position is constant, transmission shifts for both manual and automatic transmissions can be made more smoothly. Also, the invention allows modification of the accelerator pedal position versus power characteristics so that the relationship is not limited to a linear relationship.