Vehicles have been developed to perform an engine idle-stop when idle-stop conditions are met and then automatically restart the engine when restart conditions are met. The engine may be restarted with assistance from a starter motor, for example. Such idle-stop systems enable fuel savings, reduction in exhaust emissions, reduction in noise, and the like. Vehicle systems may include a parking brake, in addition to wheel brakes, to assist in keeping the vehicle stationary when parked, in particular, when parked on an incline. During an engine restart on an incline, the engagement of the parking brake may be coordinated with the cranking of the engine to prevent the vehicle from rolling backwards.
One example of such coordination is illustrated by Hiyoshi et al. in U.S. 2010/0076656 A1. Therein, a parking brake device is actuated prior to an automatic start of the engine, and an engine starter is operated only after it has been confirmed that the brakes are being held. The brakes are released after a predetermined amount of time has elapsed since the restart of the engine.
However, the inventors herein have identified a potential issue with such an approach. As one example, the parking brake device of Hiyoshi et al. uses a compressed air flow to apply the braking force. The need for a compressor to provide the compressed air adds component costs to the vehicle system.
In one example, component costs may be reduced by using an electronically actuated parking brake (also referred to as an electric brake or eBrake) in place of the compressed air-based brake device of Hiyoshi. A current drawn from the vehicle's existing electrical supply may be used to apply and/or release the electric brake to assist in keeping the vehicle stationary when parked. However, since operation of the electric brake requires a current to be drawn, the electric brake and the starter motor cannot be operated simultaneously. For example, if the vehicle operator releases his foot from a wheel brake pedal while requesting parking brake assistance, the starter motor may be operated to restart the engine (in response to the brake pedal release) at the same time as the electric brake is engaged. As such, the electrical supply of the vehicle (e.g., battery) may not be able to provide sufficient current to operate both the starter motor and the brake, leading to degraded engine restart quality and degraded brake assistance.
Thus, in one example, some of the above issues may be at least partly addressed by a method of operating a vehicle engine coupled to a transmission and an electrically-actuated brake. In one embodiment, the method comprises, limiting current supplied to one of a starter and an electric parking brake in response to a request to supply current, or while current is being supplied, to the other of the starter and the electric parking brake. In this way, during some conditions, current may be directed to the starter to crank the engine before current is supplied to apply the electric brake. During other conditions, application of the electric brake may be completed before current is directed to operate the starter motor.
In one example, directing current sequentially to the starter motor and the electric brake may include selecting an order of limiting the current based on a timing of the brake request (that is, a request to supply current to the electric brake) relative to the restart request (that is, a request to supply current to the starter motor). As such, an electric brake request may be inferred, for example, in response to a vehicle operator pressing an ebrake button on the vehicle's dashboard. An engine restart request may be inferred, for example, in response to a vehicle operator releasing a wheel brake pedal. For example, when the restart request is received after the electric brake request, current supplied to the starter may be limited. Alternatively, if the restart request is received before the electric brake request, the current supplied to the electric brake may be limited.
In this way, by directing current to the starter and the electric brake sequentially, both the starter motor and the electric brake can be operated without draining excess current from the vehicle system's electrical supply, thereby improving the quality of the engine restart as well as the parking brake assist.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.