Hitherto, there is known a control device for a vehicle that performs so-called “idle stop”, in which supply of fuel is stopped to automatically stop an engine, under predetermined conditions such as when the vehicle is temporarily stationary while waiting for a traffic light to change, for example, for the purpose of improving fuel efficiency, reducing gas emission, or the like.
In a vehicle including an engine, in general, a hydraulic pressure (referred to as “shifting hydraulic pressure”) of working fluid (ATF) required to control a hydraulic pressure to be supplied to an automatic transmission is secured by a mechanical oil pump driven mechanically by the engine. In the case where idle stop is performed, however, the mechanical oil pump is of course stopped at the same time as the engine is stopped, and thus the shifting hydraulic pressure cannot be secured. That is, the shifting hydraulic pressure is reduced in a hydraulic pressure control circuit provided in the automatic transmission, resulting in an insufficient hydraulic pressure. Consequently, a forward clutch (which may be referred to simply as “clutch”) is disengaged or half-engaged with a first gear (so-called “low gear”) among forward gears (speed shift gears) kept in-gear (engaged) in the transmission. Re-starting the engine in this state is very inconvenient because the clutch is likely to slip or a clutch engagement shock may be caused because a hydraulic pressure which has been abruptly raised by operation of the mechanical oil pump and which is under no control is supplied to the forward clutch as an engagement hydraulic pressure.
Thus, in the related art, in order to secure the shifting hydraulic pressure during idle stop, an electric oil pump driven by a motor is provided separately from the mechanical oil pump, and is activated at the same time as the engine is automatically stopped. An example of this technique is disclosed in Patent Literature 1.
Patent Literature 2 discloses a control device for a vehicle that compulsorily re-starts an engine immediately after the engine is automatically stopped, upon detecting a fault (faulty drive) of an electric oil pump activated at the same time as the engine is automatically stopped. This aims at minimizing a reduction in shifting hydraulic pressure accompanied by engine stop by compulsorily starting the engine to drive the mechanical oil pump immediately after the engine is automatically stopped, because the shifting hydraulic pressure cannot be secured if the electric oil pump cannot be activated because of a fault.    Patent Literature 1 JP-A-2006-170399    Patent Literature 2 JP-B-4226543
In the control device according to the related art described in Patent Document 2 discussed above, the engine is immediately compulsorily started when a fault of the electric oil pump is detected irrespective of whether or not a hydraulic pressure (shifting hydraulic pressure) of working fluid required to control a hydraulic pressure to be supplied to the automatic transmission is secured. However, the shifting hydraulic pressure is not always secured when the engine is compulsorily started along with a fault of the electric oil pump, and the engine may be re-started with the shifting hydraulic pressure not secured (that is, at an insufficient hydraulic pressure). In such a case, a clutch engagement shock or clutch slipping may be caused as described above, which may inconveniently result in a reduction in durability of the automatic transmission. In this case, the durability of the automatic transmission may be gradually progressively reduced each time the vehicle becomes temporarily stationary to wait for a traffic light to change before a user finds the fault of the electric oil pump to have the electric oil pump repaired at a service station or the like.
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