Method for operating a drive device for a motor vehicle and corresponding drive device

Abstract

A method for operating a drive device for a motor vehicle, said method includes: permanently supplying an entire exhaust gas of a drive aggregate of the drive device to a turbine of an exhaust gas turbocharger of the drive device via a variable turbine geometry and providing compressed air by means of a compressor coupled with the turbine for the drive aggregate; operating in at least one operating mode of the drive device in each operating point of the drive aggregate an electric machine, which is mechanically operatively connected with the turbine and the compressor, as a generator for braking the turbine; and braking the turbine by means of the electric machine the stronger the further a throttle flap arranged fluidly between the compressor and the drive aggregate is opened, while maintaining the operating point of the drive aggregate constant.

Claims

1. A method for operating a drive device for a motor vehicle, said method comprising: permanently supplying an entire exhaust gas of a drive aggregate of the drive device to a turbine of an exhaust gas turbocharger of the drive device via a variable turbine geometry and providing compressed air by means of a compressor coupled with the turbine for the drive aggregate; operating in at least one operating mode of the drive device in each operating point of the drive aggregate an electric machine, which is mechanically operatively connected with the turbine and the compressor, as a generator for braking the turbine; and braking the turbine by means of the electric machine the stronger the further a throttle flap arranged fluidly between the compressor and the drive aggregate is opened, while maintaining the operating point of the drive aggregate constant.

2. The method of claim 1, wherein the variable turbine geometry is closed the further the further the throttle flap is opened.

3. The method of claim 1, wherein the turbine is braked by means of the electric machine the stronger the further the variable turbine geometry is closed.

4. The method of claim 1, wherein a brake power of the electric machine, a position of the variable turbine geometry and an opening degree of the throttle flap is selected in dependence on the actual operating point of the drive aggregate.

5. The method of claim 4, wherein the brake power, the position of the variable turbine geometry and the opening degree of the throttle flap are determined by means of at least one of a characteristic curve and an open loop control.

6. The method of claim 5, wherein an efficiency of the drive device is an input variable in the open loop control.

7. The method of claim 6, wherein an efficiency of the drive aggregate is an input variable in the open loop control.

8. The method of claim 4, wherein when the throttle flap is fully opened, the brake power of the electric machine and the position of the variable turbine geometry are selected so that the drive aggregate is operated at a greatest possible efficiency.

9. The method of claim 1, wherein the drive aggregate is operated with a defined fuel-air-ratio which is kept constant by closing the variable turbine geometry when the throttle flap is opened.

10. The method of claim 1, wherein electrical energy provided by means of the electric machine is used for driving a further electric machine which is mechanically operatively connected with the drive aggregate.

11. A drive device for a motor vehicle, said drive device comprising: a drive aggregate; an exhaust gas turbocharger having a turbine, said turbine permanently receiving an entire amount of exhaust gas generated by the drive aggregate via a variable turbine geometry; a compressor coupled with the turbine, said drive aggregate receiving compressed air compressed by means of the compressor; an electric machine mechanically operatively connected with the turbine and the compressor; and a throttle flap arranged fluidly between the compressor and the drive aggregate, wherein in at least one operating mode of the drive device the drive device is configured to operate the electric machine as a generator in each operating point of the drive aggregate for braking the turbine, and to brake the turbine by means of the electric machine the stronger the further the throttle flap is opened while maintaining the operating point of the drive aggregate constant.

Description

(1) Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which the sole FIGURE shows a schematic representation of a drive device for a motor vehicle.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(2) Throughout all the FIGURE, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the FIGURE are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

(3) The FIGURE shows a schematic representation of a drive device 1 for a motor vehicle. The drive device 1 has a drive aggregate 2, in the here shown exemplary embodiment an internal combustion engine. The drive device 1 also has an exhaust gas turbocharger 3 and optionally a charge air cooler 4. The exhaust gas turbocharger 3 has a compressor 5 and a turbine 6. These are coupled with each other via a shaft 7, preferably rigidly and/or permanently. On the shaft 7 also an electric machine 8 engages, which can insofar be used for driving or supporting the exhaust gas turbocharger 3.

(4) The turbine 6 has a variable turbine geometry 9, which is can generally be referred to as a cross-section-adjustment element upstream of the turbine 6. However, particularly preferably the variable turbine geometry 9 is a guide wheel of the turbine 6 and thus has multiple adjustable guide vanes. The turbine 6 serves for driving the compressor 5 via the shaft 7. For this purpose exhaust gas, which is generated by the drive aggregate 2, is supplied to the turbine 6.

(5) In the here shown exemplary embodiment the entire exhaust gas generated by the drive aggregate 2 is supplied to the turbine 6, i.e., that the exhaust gas turbocharger 3 is configured without a waste gate. Rather all cylinders 10 of the drive aggregate 2 are connected fluidly to the turbine 6, in particular respectively via at least one outlet valve 11 and/or a exhaust manifold 12. The exhaust gas generated by the drive aggregate 2 flows through the turbine 6, wherein kinetic flow energy and/or enthalpy is withdrawn from the exhaust gas. Subsequently the exhaust gas is discharged in the direction of the arrow 14 towards an external environment 14.

(6) The energy withdrawn from the exhaust gas by means of the turbine 6 is used for driving the compressor 5. The compressor serves for compressing air, for example fresh air, which was withdrawn from the external environment 14. The air flows thus in the direction of the arrow 15 into the drive device 1 and moves though the compressor 5 and optionally the charging air cooler 4 in the direction of the drive aggregate 2. Fluidly provided between the compressor 5 and the drive aggregate 2, in particular downstream of the charging air cooler 4, is a throttle flap 16 of the drive aggregate 2. By means of the throttle flap 16 the air mass flow conducted to the drive aggregate 2 can be adjusted. In particular when the drive aggregate 1 is operated at partial load the throttle flap 16 is usually partially closed. Correspondingly throttle losses occur, which are to be avoided. For this purpose it is provided that while maintaining the operating point of the drive aggregate 2 constant the throttle flap 16 is further opened in order to more efficiently use the ambient pressure of the air present in the external environment 14. As a result however the air mass flow increases in the direction of the derive aggregate 2 so that simultaneously also the exhaust gas counter pressure increases between the drive aggregate 2 and the turbine 6.

(7) As a result of increasing the exhaust gas counter pressure the power of the turbine 6 increases so that for operating the compressor 5 a higher power is available. Correspondingly the air mass flow would further increase and the exhaust gas pressure would further increase. However because at the same time the operating point is kept constant, i.e., for example because the fuel mass flow into the drive aggregate 2 remains constant, the fuel-air-ratio may change, and may in particular deviate from a stoichiometric ratio. In order to avoid this the variable turbine geometry 9 is further closed also while the operating point of the drive aggregate remains the same. This however causes a further power increase of the turbine 6.

(8) In order to prevent that the compressor 5 is impinged with a greater power and correspondingly the air mass flow is further increased the excessive power is withdrawn by means of the electric machine 8. For this purpose the electric machine 8 is operated as a generator so that the turbine 6 and thus the compressor 5 can be braked with the electric machine 8. The herby generated electrical energy can for example be supplied to an onboard network of the motor vehicle and/or for driving a further electric machine 17.

(9) The further electric machine 17 is for example mechanically operatively connected with the drive aggregate 2 so that by means of the drive device 1 a greater torque can be provided. However this can tin turn influence the operating point of the drive aggregate 2 so that depending on the circumstances a further adjustment of the position of the variable turbine geometry 9 and/or a stronger braking of the turbine 6 by means of the electric machine 8 is required.