When a driver removes their foot from the accelerator pedal—often referred to as a “tip-out”—it is desirable to provide a smooth deceleration which is consistent from one tip-out to another. To ensure smoothness and consistency, the engine and motor in a hybrid electric vehicle must work together to deliver a requested torque profile to the input of the transmission. In some hybrid vehicle designs, the engine and motor are on the same physical shaft, yet the torque delivery characteristics are not identical. Moreover, it is not uncommon to find controlling algorithms for the engine and motor operating in different microcontrollers connected by a communication bus, or in some cases running in separate software within the same microcontroller.
The physical differences in delivery, coupled with delays resulting from the software structure, can produce both magnitude and phase errors in the delivery of the combined torque. The end result is that the torque delivered to the transmission input can be quite different from that which is expected. For example, there may be significant peaks or dips, or oscillations because of the combined delivery errors, producing variations in the tip-out response. Therefore, a need exists for a system and method for controlling a vehicle powertrain that addresses these issues.