The invention relates to a drive train for a motor vehicle with an internal combustion engine that is supercharged by a supercharger for supplying a pre determinated torque to the drive train. The internal combustion engine has an inlet side, and the supercharger is connected to the inlet side of the internal combustion engine via an air mass flow line without a throttle valve. The drive train has at least one electric machine that can be operated as a generator. Secondary air is blown into the outlet side of the internal combustion engine upstream of a catalytic converter to yield desirable effects on the exhaust gas as described in the prior art. However, the secondary air blown into the outlet side of the internal combustion engine upstream of the catalytic converter also affects the charge pressure and results in excess torque of the internal combustion engine. To compensate for the excess torque of the internal combustion engine, the drive train of the subject invention also has a control unit that is configured to cause the electric machine to operate in a generator mode while the supercharger is operating as a secondary air pump.
The invention is based on the realization that the air system of the internal combustion engine need not have additional throttle valves with correspondingly complex regulating systems to be employed when the supercharger is used as a secondary air pump, provided that the drive train of the motor vehicle also has an electric machine that can be operated as a generator. Instead, the excess torque generated by the operation of the supercharger as a secondary air pump is “tolerated”, i.e. the internal combustion engine is operated with higher torque than the torque actually predefined by the driver of the motor vehicle, for example by means of the accelerator pedal. However, the driver of the motor vehicle does not notice this higher torque because at the same time at least one electric machine is operated as a generator with a load that is just enough to precisely compensate the excess torque. Thus, the drive train supplies only the torque that is predefined by the driver of the motor vehicle even though the internal combustion engine is operated with a torque that is higher than the torque predefined by the driver of the motor vehicle. The excess torque is converted into electrical energy by the electric machine that is operated as a generator.
The invention requires only very slight modifications to the air system of the internal combustion engine. More particularly, the air system of the internal combustion engine has an outlet or branch downstream of the supercharger and connected to the secondary air system. In addition, the software in a corresponding control unit is changed to cause the drive train to function as described herein.
As a result, the secondary air pump can be dispensed with and corresponding costs saved. In particular, there is no need for further measures in the inlet side air system of the internal combustion engine, such as additional throttle valves or the like. As a result, it is possible, for example when starting the motor vehicle in the morning, that is to say when the catalytic converter is cold and secondary air therefore has to be blown in, to provide an electrical starting process that discharges a battery so that supercharging can be carried out through the operation of the electric machine as a generator.
The video shows the torque effect by climbing capability of a 4WD vehicle.
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