Dual motor power system and control method for pure electric vehicle

A dual motor power system for a pure electric vehicle, comprising:

• first and second motors;
• a transmission coupled with the first and second motors in a manner that the first motor is able to output power with a single gear ratio and the second motor is able to output power with two gear ratios, the transmission comprising a single synchronizer for controlling the two gear ratios of the second motor;
• and
• a control system configured to determine a torque distribution between the first and second motors and an engaging position of the synchronizer and to control operations of the first and second motors and the synchronizer;
• wherein the control system is configured to determine the torque distribution between the first and second motors and the engaging position of the synchronizer by the steps of:
• (1) a step of establishing a torque distribution relation of the first and second motors, wherein a required torque of vehicle at wheel, required torques of the two motors at wheel, a transmission path efficiency for the two motors and the gear ratio of the second motor are all involved in determining the torque distribution relation;
• (2) a step of establishing a relation between a synchronized efficiency of the power system and working points of the first and second motors, each working point being expressed by a torque and a speed;
• (3) an optimization step in which the following concrete ergodic optimization actions are taken, with the synchronized efficiency of the power system as the optimization objective and with the torque distribution of the first and second motors and the gear ratio of the second motor as parameters to be optimized:
• within a range defined between upper and lower torque thresholds for the operations of one motor of the first and second motors under current vehicle speed, a torque of the one motor of the first and second motors is changed stepwise with a certain torque step;
• a torque of the other motor of the first and second motors is determined based on the torque distribution relation of the first and second motors;
• and
• the synchronized efficiency of the power system is determined based on the torques of the first and second motors so that an optimal synchronized efficiency of the power system is ergodically searched out, and optimal working points of the first and second motors and a corresponding gear ratio of the second motor are determined.