Method for operating a motor vehicle

Abstract

A method for operating a motor vehicle, including an electric machine and a coupling device, which, in a first coupling state, couples the electric machine to a drivetrain and, in a second coupling state, decouples the electric machine from the drivetrain, wherein the method includes the following steps: a) registering an item of coupling information, which specifies whether the coupling device is in the first or second coupling state, b) analyzing a recuperation condition, the fulfillment of which is dependent on the coupling information, wherein the recuperation condition is fulfilled or can only be fulfilled if the coupling device is in the second coupling state, and c) braking the electric machine by operating the electric machine as a generator if the recuperation condition is fulfilled.

Claims

1. A method for operating a motor vehicle, comprising an electric machine and a coupling device, which, in a first coupling state, couples the electric machine to a drivetrain and, in a second coupling state, decouples the electric machine from the drivetrain, wherein the method comprises the following steps: a) registering an item of coupling information, which specifies whether the coupling device is in the first or second coupling state, b) analyzing a recuperation condition, the fulfillment of which is dependent on the coupling information, wherein the recuperation condition is fulfilled or can only be fulfilled if the coupling device is in the second coupling state, and c) braking the electric machine by operating the electric machine as a generator if the recuperation condition is fulfilled; wherein the drivetrain comprises the wheels of the vehicle; wherein at least one item of operating information relating to the operating state of the motor vehicle is registered, wherein the fulfillment of the recuperation condition is additionally dependent on the operating information; and wherein the at least one item of operating information relates to one or more of a charge state of at least one energy accumulator of the motor vehicle and a predicted starting of an internal combustion engine of the motor vehicle.

2. The method as claimed in claim 1, wherein the operating information describes the speed of the electric machine and the recuperation condition can only be fulfilled if it is greater than a predetermined speed limiting value.

3. The method as claimed in claim 2, wherein at least one item of vehicle information relating to the operating state of the motor vehicle is registered, wherein if a coupling condition dependent on the vehicle information is fulfilled, the coupling device changes into the second coupling state if the coupling device is in the first coupling state.

4. The method as claimed in claim 2, wherein the motor vehicle is driven by the electric machine if the coupling device is in the first coupling state and a drive condition is fulfilled.

5. The method as claimed in claim 2, wherein the electric machine, if it is used as a generator upon fulfillment of the recuperation condition, charges the at least one electrical energy accumulator.

6. The method as claimed in claim 2, wherein in the first coupling state, the electric machine is coupled via a transmission to a component of the drivetrain, wherein the transmission converts the speed of the electric machine to the speed of this component of the drivetrain, wherein the speed of the electric machine is greater in this case than the speed of this component of the drivetrain.

7. The method as claimed in claim 1, wherein at least one item of vehicle information relating to the operating state of the motor vehicle is registered, wherein if a coupling condition dependent on the vehicle information is fulfilled, the coupling device changes into the second coupling state if the coupling device is in the first coupling state.

8. The method as claimed in claim 7, wherein the motor vehicle is driven by the electric machine if the coupling device is in the first coupling state and a drive condition is fulfilled.

9. The method as claimed in claim 7, wherein the electric machine, if it is used as a generator upon fulfillment of the recuperation condition, charges the at least one electrical energy accumulator.

10. The method as claimed in claim 7, wherein in the first coupling state, the electric machine is coupled via a transmission to a component of the drivetrain, wherein the transmission converts the speed of the electric machine to the speed of this component of the drivetrain, wherein the speed of the electric machine is greater in this case than the speed of this component of the drivetrain.

11. The method as claimed in claim 1, wherein the motor vehicle is driven by the electric machine if the coupling device is in the first coupling state and a drive condition is fulfilled.

12. The method as claimed in claim 11, wherein the electric machine, if it is used as a generator upon fulfillment of the recuperation condition, charges the at least one electrical energy accumulator.

13. The method as claimed in claim 11, wherein in the first coupling state, the electric machine is coupled via a transmission to a component of the drivetrain, wherein the transmission converts the speed of the electric machine to the speed of this component of the drivetrain, wherein the speed of the electric machine is greater in this case than the speed of this component of the drivetrain.

14. The method as claimed in claim 1, wherein the electric machine, if it is used as a generator upon fulfillment of the recuperation condition, charges the at least one electrical energy accumulator.

15. The method as claimed in claim 1, wherein in the first coupling state, the electric machine is coupled via a transmission to a component of the drivetrain, wherein the transmission converts the speed of the electric machine to the speed of this component of the drivetrain, wherein the speed of the electric machine is greater in this case than the speed of this component of the drivetrain.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Further advantages and details of the invention result from the exemplary embodiments described hereafter and on the basis of the drawings. In the schematic figures of the drawings:

(2) FIG. 1 shows an exemplary embodiment of a motor vehicle according to the invention, and

(3) FIG. 2 shows a flow chart of an exemplary embodiment of the method according to the invention.

DETAILED DESCRIPTION

(4) FIG. 1 schematically shows a motor vehicle 1. The motor vehicle 1 comprises an electric machine 2, which can be coupled via a coupling device 3 to a component 5 of a drivetrain 4 of the motor vehicle 1. In the exemplary embodiment shown, the component 5 of the drivetrain 4 is a driveshaft designed as a propeller shaft. The drivetrain 4 furthermore comprises the wheels 6 of the motor vehicle 1. The wheels 6 are connected by a differential gear (not shown) to the component 5 of the drivetrain 4. Further components of the drivetrain 4 are not shown for reasons of comprehensibility. The motor vehicle 1 moreover comprises an electrical energy accumulator 8, in which energy is stored, in particular to drive the motor vehicle 1.

(5) The coupling device 3 is operable in a first coupling state and a second coupling state. In the first coupling state, the electric machine 2 is coupled via the coupling device 3 to the component 5 of the drivetrain 4. In this case, the electric machine 2 can be used as an electric motor to drive the motor vehicle 1, i.e., it converts electrical energy stored in the electrical energy accumulator 8 into kinetic energy of the motor vehicle 1. The electric machine 2 is used in this case as a drive motor for the motor vehicle 1. The coupling between the electric machine 2 and the component 5 of the drivetrain 4 takes place in this case via a transmission 12, which is designed to convert the speed of the electric machine 2 to the speed of the component 5 of the drivetrain 4, wherein the electric machine 2 rotates faster than the component 5. In the second coupling state, the electric machine 2 is decoupled by the coupling device 3 from the component 5 of the drivetrain 4.

(6) It is provided for the motor vehicle 1 that rotation energy possibly stored in a rotor of the electric machine 2 can be recuperated and/or reclaimed for various purposes in the second coupling state, i.e., upon decoupling of the electric machine 2 from the drivetrain 4, by operation of the electric machine 2 as a generator. Details in this regard will be explained hereafter.

(7) FIG. 2 shows a flow chart of a method for operating the motor vehicle 1. An item of vehicle information relating to the operating state of the motor vehicle 1 is registered in step S1. This information can specify, for example, whether full braking is carried out or whether the drive of the motor vehicle 1 is to be performed by an internal combustion engine 11, which is coupled for this purpose to the drivetrain 4.

(8) In step S2, the control device 7 analyzes a coupling condition dependent on the vehicle information. If the coupling condition is fulfilled, in step S3, a control device 7 activates an electromechanical actuator 9, which brings the coupling device 3 into the second coupling state. Moreover, the control device 7 stores the present coupling state of the coupling device 3.

(9) In contrast, if the coupling condition is not fulfilled, in step S4, the control device 7 registers the coupling state of the coupling device 3 by way of a sensor (not shown). Alternatively, the registration can take place in that the control device 3 has already previously stored the present coupling state. In step S5, the control device 7 subsequently checks whether the coupling device 3 is in the first or in the second coupling state.

(10) If the coupling device 3 is in the first coupling state, the method is thus repeated from step S1, to monitor the vehicle information and the coupling state in the further driving operation.

(11) If the coupling device 3 is in the second coupling state, whether because it was put into the second coupling state in step S3 or because this coupling state was recognized in step S5, an item of operating information is registered in step S6, wherein the operating information relates, inter alia, to the speed of a rotor of the electric machine 2, which is registered by a sensor 10 and transmitted to the control device 7.

(12) In step S7, the control device 7 analyzes a recuperation condition dependent on the operating information and the coupling state of the coupling device 3. The recuperation condition can only be fulfilled if the coupling device 3 is in the second coupling state. In the exemplary embodiment shown, the fulfillment of this partial condition is already ensured in step S7 by the check of the coupling state in S5 or by the active selection of the second coupling state in S3, respectively, so that a further check of the coupling state can be omitted in principle. As will be explained hereafter, however, it is also possible that the control device still monitors the vehicle information in the background, for example, and can change the coupling state in dependence thereon, independently of the method steps shown. It can therefore be advantageous to explicitly check again in step S7 whether the coupling device is in the second coupling state.

(13) Moreover, the recuperation condition is only fulfilled in step S7 if the speed of the electric machine 2 is greater than a previously defined speed limiting value. The speed limiting value can be one revolution per minute, for example. A recuperation is not expedient if the rotational energy stored in the rotor of the electric machine 2 is excessively small.

(14) In addition, further items of operating information can be analyzed, on which the fulfillment of the recuperation condition in step S7 can depend. The further items of information can relate, for example, to the velocity of the motor vehicle 1 and/or the charge state of an electrical energy accumulator 8. In particular, a recuperation would not be expedient if the electrical energy accumulator is fully charged.

(15) If the recuperation condition is not fulfilled, the method is thus ended in step S8 and can be repeated from step S1, for example, immediately or after passage of a specific waiting time. If the recuperation condition is fulfilled, in step S9, the electric machine 2 is then operated as a generator. In this case, the energy stored in the rotor of the electric machine 2 is reclaimed and advantageously is not lost due to friction. The energy recuperated in this matter is used to charge the electrical energy accumulator 8 of the motor vehicle 1. Moreover, it is conceivable that the recuperated energy is used for further consumers of the motor vehicle 1, for example, for an air conditioner or the like.

(16) During the entire method sequence, the driving operation of the motor vehicle 1 is monitored in the background by the control device 7. During this monitoring, a feedback condition is analyzed, wherein if the feedback condition is fulfilled, the coupling device 3 is brought from the second coupling state into the first coupling state. This takes place, for example, if the coupling device 3 is in the second coupling state and the electric machine 2 is to be used to drive the motor vehicle 1.

(17) For the sake of completeness, it is to be noted that in the method, the operation of the electric machine 2 as a generator can take place not only if the coupling device 3 is in the second coupling state, but rather similarly also if it is in the first coupling state. In this case, kinetic energy of the motor vehicle 1 is converted by the operation of the electric machine as a generator into electrical energy, which is expedient in particular during braking of the motor vehicle 1. The electrical energy thus generated and/or reclaimed is supplied, for example, to the electrical energy accumulator 8, whereby it is charged. The operating time of the energy accumulator 8 is thus extended and thus the efficiency of the motor vehicle 1 is improved.