1. Field of the Invention
The present invention relates to a control system for stopping and starting the engine of a vehicle, which is typically a hybrid vehicle having an engine and a motor as driving sources.
2. Description of the Related Art
Recently, in order to economize on fuel for driving the engine, reduce exhaust gas generated by fuel combustion, and the like, hybrid vehicles have been developed, in which an engine and a motor which can generate power (called a “motor generator”, hereinbelow) are coupled with the power transmission mechanism which is coupled with driving wheels of the vehicle. In such a hybrid vehicle, (i) while the vehicle is running, the driving power is assisted using the motor generator according to need, and (ii) the power input via the driving wheels during deceleration is transmitted to the motor generator, and the motor generator performs regeneration so as to convert the deceleration energy into regenerated energy which is stored in a storage battery as electrical energy.
When a hydraulic automatic transmission is employed in the above-explained hybrid vehicle, the working oil pressure in the transmission mechanism of the automatic transmission is secured by a hydraulic pump driven by the engine. However, if the engine is stopped while the vehicle is stopped so as to wait until the traffic light turns green, the hydraulic pump is also stopped so that the necessary working oil pressure of the transmission mechanism cannot be secured.
In consideration of these circumstances, hybrid vehicles having an electric oil pump in addition to the above-explained hydraulic pump (called a mechanical oil pump, hereinbelow) have been developed, so as to secure the working oil pressure in the transmission mechanism even when the engine is stopped. If the working oil pressure is secured even when the engine is stopped, it is possible to prevent the supply of the oil pressure from being delayed at the starting of the vehicle.
In the vehicle having both the mechanical and electric oil pumps, a specific oil pressure must be secured using the electric oil pump while the engine is stopped, in consideration of the object for providing the electric oil pump. If the specific oil pressure is not secured for some reason during the operation of the electric oil pump, when the engine is restarted, the specific oil pressure is secured by the operation of the mechanical oil pump, where the mechanical oil pump is operated after the engine speed is increased. In this case, a shock may be produced when the clutch is engaged. Therefore, it is very important to confirm that the hydraulic system of the automatic transmission has no anomalies. If an abnormal portion is found, it is also very important how it is handled.
As an example of related known art, an engine stop control system may be applied to a vehicle, in which the engine is stopped under specific stopping conditions, and the engine is restarted under specific restarting conditions, and when the engine is automatically stopped, the electric oil pump is driven so as to continuously supply working fluid to the automatic transmission. In this system, it is determined whether the current state satisfies the working conditions of the electric oil pump, and if it is determined that the working conditions are not satisfied, automatic engine stop control, which is performed when the specific stopping conditions are satisfied, is prohibited (refer to Japanese Unexamined Patent Application, First Publication No. 2000-45807). Here, the working conditions for the electric oil pump are (i) the electric oil pump is in a normal state, the state of charge in a battery used for driving the electric oil pump is equal to or greater than a specific value, and (iii) the motor driven system for the electric oil pump is in a normal state.
However, in the above-explained known art, if the specific working oil pressure is not secured due to elements other than the electric oil pump (e.g., increase of clearance in the mechanical oil pump or valves, and degradation of seal members), then the automatic engine stop control is performed. Accordingly, when the engine is restarted, a shock may be produced when the clutch of the automatic transmission is engaged, as explained above.