It is well known that a vehicle engine may stall under driving conditions that impose a heavy load on the engine. For example, engine stall may occur while driving the air conditioner compressor, the radiator fan, the power steering pump and the alternator for generating electric power to operate accessories such as car audio systems and air conditioner blowers.
In a conventional control system for preventing engine stall, engine parameters, including engine speed, and other operating conditions of automotive components affecting engine operation are monitored and checked against patterns known to lead to engine stall. When the engine operating parameters match or closely correlate predetermined patterns for engine stall, the control system performs a stall-preventive operation. In a known stall-preventive operation, additional torque is provided to the engine by means of an auxiliary device which is driven by a power source other than the engine itself.
Those skilled in the art will recognize that a conventional starter motor can be used as an electric motor to provide additional engine torque via an electromagnetic clutch. A disadvantage of using such a conventional starter motor to prevent engine stall is the complexity associated with the hysteresis operation necessary to prevent hunting in the starter motor operation. Additionally, a stall-preventive control system using a conventional starter motor to prevent engine stall includes a separate alternator to charge a vehicle's battery and source its electrical loads. This imposes additional costs and under-the-hood fit and function obstacles.
Similarly, an alternator can be used as an electric motor to drive the engine via a power transmission belt stretched between the alternator pulley and a pulley attached to the engine output shaft. A disadvantage of using a conventional alternator is that it requires a belt tensioning system. Moreover, a separate starter motor is necessary to crank the engine during ignition.
In the area of vehicle electrical systems, there continues to be a need for an electronic control system with fewer major assemblies to prevent engine stall. What is needed is a cost-effective system for preventing engine stall that fits comfortably under the hood of a vehicle.