Method and control for a drive system having four-wheel drive

A method for operating a drive train comprising an internal combustion engine as a primary drive and an electric machine as a secondary drive, wherein the electric machine of the secondary drive is detachably mounted, together with an inverter and a controller, on a vehicle axle of a vehicle, the method comprising:

• actuating the electric machine of the secondary drive and at least one switchable element in order to minimize drag losses of the electric machine of the secondary drive during operation of the vehicle by way of the internal combustion engine over an entire vehicle speed range of the vehicle and to provide a defined connection time for the electric machine of the secondary drive,
• dividing the vehicle speed range of the vehicle into multiple ranges,
• wherein a first range of the multiple ranges starts from the stationary state of the vehicle and the electric machine of the secondary drive, and
• wherein the at least one switchable element is actuated differently and the electric machine of the secondary drive is selectively coupled or uncoupled from the vehicle axle depending on which of the multiple ranges the vehicle is operating in,
• wherein the first range of the vehicle speed extends up to a defined speed of the vehicle in accordance with a WLTC cycle, the defined speed being a vehicle speed at which the defined connection time is possible, wherein the electric machine of the secondary drive is uncoupled from the vehicle axle within the first range;
• wherein, in a second range of the multiple ranges, the electric machine of the secondary drive is actuated such that it rotates at a preset speed, wherein the electric machine of the secondary drive remains uncoupled from the vehicle axle while in the second range, and
• wherein in a third range of the multiple ranges of the vehicle speed, which includes an overall maximum speed of the vehicle, the electric machine of the secondary drive is coupled to the vehicle axle and rotates at the speed of the vehicle axle.