1. Field of the Invention
The present invention generally relates to braking systems on diesel powered vehicles that use engine brake systems in addition to vehicle service brakes and more particularly relates to control integration of the former with the latter.
2. Background Art
The heavy-duty diesel engine of a modern highway tractor-trailer commonly includes an engine brake system that is a compression release engine braking system. This supplements service brakes when the tractor-trailer is being operated on declining road surfaces in hilly and mountainous areas. The system manipulates exhaust valves to release air compressed during a compression stroke of one or more engine cylinders to the exhaust system while fuel input to the engine is off. This eliminates the normal expansion within the cylinder and causes the engine to act as an air compressor that is driven by the tractor""s rear drive wheels.
Typically, a vehicle driver uses his throttle to activate the engine brake. By removing foot pressure from the throttle pedal after reaching the crest of a hill, the engine brake system automatically activates to retard the downhill speed of the vehicle. This extends service brake life while benefitting engine operation and minimizing tire problems. The system is also activated to limit vehicle speed while it is operating under cruise control to assist in clutchless transmission gear shifting and to retard the vehicle without service brake application.
A dash-mounted, multiposition switch provides means for controlling the amount of braking power desired. For a six-cylinder engine with a compression release braking system, such a switch typically selects two, four or six cylinders to provide low, medium and high braking power respectively. More accurately, a low, medium, or high brake power curve is being selected since engine brake power is proportional to engine speed along each of these curves. The incremental control of braking power is necessary for driver control of vehicle deceleration or for limiting brake power based on traction conditions. This switch also provides means for disabling the engine brake system, for example, while driving an unloaded vehicle under poor traction conditions or where there are noise restrictions. Furthermore, anti-lock brake systems disable the engine brake under severe braking situations. The engine brake acts only on the rear drive wheels of the tractor and may affect vehicle-handling characteristics under this braking condition.
The foregoing describes an engine brake system that has found primary application on diesel-powered highway tractor-trailers while they are being driven in mountainous areas, where there are downhill sections of road. Usage of the system during urban driving situations depends on driver habits and traffic density. In heavy traffic, the current system encourages the driver to follow traffic closely since he can use his throttle foot for both acceleration and moderate deceleration. This eliminates the need for moving his foot between the throttle and brake pedals. In a vehicle coast situation, however, fuel economy is minimized since the driver fuels the engine above idle to keep the engine brake deactivated. Engine brake systems can be integrated with the service brakes by use of a cruise control brake switch. This activates the engine brake system upon application of the brake pedal. However, braking power is not proportional to the brake pedal application since the dash-mounted switch sets the power level. If the dash-mounted switch is set too high, abrupt braking occurs.
The present invention provides a new mode of engine brake control that minimizes service brake wear and maximizes fuel economy during vehicle coasting by integrating the engine brake system with the service brakes. In this mode, the engine brake system is the first source of vehicle braking power, is initiated by brake pedal application only, gives engine brake power proportional to brake pedal motion, and then supplements the vehicle service brakes until disengagement for conditions mentioned earlier.
The present invention includes an engine brake control system that is integrated with the vehicle service brakes for use with a diesel engine having a plurality of cylinders. The vehicle has the following minimum controls: a throttle pedal, a clutch pedal and a brake pedal. The system includes an engine brake power selector that is settable to select one of a plurality of levels of engine brake power. It also includes an engine brake mode selector that is settable for the following modes of engine brake and service brake operation: 1) The engine brake control system is disabled. 2) Zero throttle activates the engine brake control system and engine brake power is determined by the engine brake power selector setting. 3) The brake pedal activates the engine brake control system. as well as the service brakes, and engine brake power is determined by brake pedal position and limited by the engine brake power selector setting.
The system also includes a brake pedal position slide switch having a pedal-actuated common contact wiper in continuous contact with a base contact. As the brake pedal is displaced, the contact wiper is displaced to engage and/or disengage additional slide contacts to close or open combinations of electrical circuits that cause various engine brake power levels proportionate to pedal travel.
An engine computer having a plurality of inputs, outputs, and control algorithms is needed for proper engine operation in both unfueled brake and fueled power mode. Electrical inputs are required from the engine brake mode selector, engine brake power selector, and the brake pedal position slide switch. Also needed are electrical inputs from other sensors or switches typical for control of compression brake mechanisms and not limited to: a throttle position sensor, a clutch pedal position switch, and an engine speed sensor. The engine brake must be disabled for proper engine operation whenever the throttle is not zero, the clutch is disengaged, or the engine speed is at idle.
The intent of the first embodiment of this invention is to use existing inputs, outputs, and algorithms for engine brake and power control without modification. The conventional dash-mounted switch is replaced by the engine brake mode selector and the engine brake power selector. The brake pedal position slide switch is added. The second embodiment requires changes to the engine computer input configuration and minor logic changes that provide functional and system integration advantages.