A hybrid powertrain may be powered by a combination of an engine and an electric machine, such as an electric motor. The electric machine may improve drivability by compensating for the fluctuation in the engine torque output during transmission shifts. The hybrid powertrain may further include an energy storage module to power the electric machine. In order to efficiently utilize the onboard fuel and energy stored in the energy storage module, a vehicle torque demand may be distributed (or arbitrated) strategically among the engine and the electric machine.
Attempts to address torque arbitration include arbitrating the torque based on engine characteristics. One example approach is shown by Simon, J R. et al. in U.S. US2009/0204280. Therein, the torque request to an engine and a motor is controlled by a predetermined calibration based on the capabilities of the engine and the motor.
However, the inventors herein have recognized potential issues with such systems. As one example, when operating the vehicle on a predetermined route, such as in a race, vehicle weight may affect vehicle performance. For example, low vehicle weight is preferred to maximize vehicle propulsion. The vehicle weight may be reduced by arbitrating a high level of engine torque to increase the consumption of the onboard fuel. Further, burning excess fuel during regenerative braking can recharge the energy storage module and extend the range of the electric assist from the electric machine. Ideally, the depletion of the energy in the energy storage device and the onboard fuel may be coincident with the end of the race. Depleting the battery before the end of the race may result in additional battery weight with no power benefit. Depleting the onboard fuel early in the race may result in loss of electric assist and reduced torque output.
In one example, the issues described above may be addressed by a method comprising operating a hybrid powertrain to provide a torque to vehicle wheels over a predetermined drive route; and arbitrating the torque between an engine and an electric machine based on a vehicle mass. In this way, the highest power to weight ratio on average over a predetermined route may be achieved.
As one example, an optimal torque arbitration among the engine and the electric machine may be determined by optimizing a cost function constructed based on a vehicle model. As an example, the torque arbitration may be optimized to achieve a maximum vehicle speed. As another example, the torque arbitration may be optimized to achieve an optimal velocity profile. The vehicle model may include multiple functions for calculating a vehicle acceleration based on inputs including an amount of onboard fuel. By including the amount of onboard fuel into the vehicle model, the effect of vehicle mass variation during the race is accounted for when solving the optimization problem for the optimal torque arbitration. Parameters of the vehicle model (that is, coefficients and formats of the multiple functions of the vehicle model) may be updated at the end of each race based on track data acquired during the race and previous races as well as previous non-racing vehicle operation. The track data may include an engine torque output, an electric motor torque output, a vehicle speed, a battery state of charge, and an onboard fuel amount at each location during the track. By updating the vehicle model, mechanical and environmental changes of the vehicle system are accounted for in the determination of the optimal torque arbitration. For example, the mechanical change may include wearing or adjustment of the vehicle's mechanical system; and the environmental change may include variation in weather and road condition.
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.