METHOD FOR OPERATING A MOTOR VEHICLE

Description

[0001] The invention relates to a method for operating a motor vehicle. Furthermore, the invention relates to a motor vehicle.

[0002] Motor vehicles are increasingly powered by electric motors. So-called hybrid vehicles also feature an internal combustion engine, whereby the vehicle can be powered by both the electric motor and the internal combustion engine. This is practical because the range of electric vehicles is rather short compared to vehicles equipped with internal combustion engines due to the limited capacity of their energy storage systems.

[0003] To increase the range of electric vehicles, it has proven useful to recover or recuperate the kinetic energy released during braking. Document DE 11 2012 000 892 T5 discloses a braking device for a motor vehicle whose electric motor can be operated as a generator. This converts the kinetic energy of the motor vehicle during braking into electrical energy, which is used to charge an electrical energy storage device in the motor vehicle.

[0004] Document EP 1 431 623 A1 discloses a method for controlling a hybrid vehicle, comprising recovering residual kinetic energy from an electric machine when a clutch is opened to disconnect the electric machine from the drive train.

[0005] The problem underlying the present invention is to provide a method for operating a motor vehicle which is improved compared to the prior art, in particular with regard to the operating time of the electrical energy storage device and the efficiency of the motor vehicle.

[0006] The object is achieved according to the invention by a method for operating a motor vehicle, wherein the motor vehicle comprises an electric machine and a coupling device which couples the electric machine to a drive train in a first coupling state and decouples the electric machine from the drive train in a second coupling state, wherein the method comprises the following steps: a) detecting coupling information indicating whether the coupling device is in the first or second coupling state, b) evaluating a recuperation condition, the fulfillment of which depends 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.

[0007] The method advantageously ensures that, in the event of the electric machine being decoupled from the drivetrain, any rotational energy stored in a rotor of the electric machine is not lost due to dissipation or friction within the electric machine, but is recovered. The mechanical energy stored in the rotor is converted into electrical energy by the electric machine, which operates as a generator in this process step, and can thus be used for various purposes. This can improve the efficiency of the motor vehicle.

[0008] If the coupling device is operated in the first coupling state, i.e., if the electric machine is coupled to the drive train, then the electric machine can be used as an electric motor to drive the motor vehicle. The electrical energy required for this can be provided by an electrical energy storage device. A torque of the electric machine can be transmitted to the wheels of the motor vehicle via the components of a drive train. In particular, the drive train can comprise a drive shaft, which can be designed as a cardan shaft, and the coupling device. In addition, the drive train can comprise a differential coupled to the drive shaft, wherein two output shafts coupled to the differential are each connected to a wheel of the motor vehicle.

[0009] If, on the other hand, the coupling device is operated in the second coupling state, the electric machine is decoupled from the drive train and can therefore no longer be used to drive the motor vehicle. In this case, however, the rotor of the electric machine may still be rotating, particularly if the electric machine was used immediately beforehand to drive the motor vehicle. In this case, the recuperation condition may be met, in which case the electric machine can then be used as a generator. However, fulfillment of the recuperation condition may also depend on further conditions. For example, it may only be fulfilled if the electric machine has a certain minimum speed, since otherwise recuperation may not be efficient under certain circumstances.Additionally or alternatively, the fulfillment of the recuperation condition can depend on a predicted time, which indicates how long the coupling device is expected to be in the second coupling state. If the electric motor is only briefly uncoupled, it may be advantageous to maintain rotation.

[0010] In the method according to the invention, it can be provided that a control device is provided for the motor vehicle, wherein the control device can bring the coupling device from the first to the second coupling state and vice versa by controlling an actuator, in particular an electromechanical actuator. The control device can further be configured to store the coupling state thus set and / or to detect it by sensors. The evaluation of the recuperation condition can be carried out by the control device. In this case, it can be expedient if this information about the coupling state of the coupling device, stored or detected by the control device, is evaluated as part of the evaluation of the recuperation condition.

[0011] It is conceivable that the electric motor can also be operated as a generator in the first coupling state if a further recuperation condition is met. This further recuperation condition can be met when the vehicle is decelerated or when a brake pedal of the motor vehicle is depressed. This enables the kinetic energy of the motor vehicle to be converted into electrical energy by the electric motor operating as a generator and fed into the electrical energy storage device. The evaluation of the further recuperation condition can also be carried out by the control device.

[0012] The method according to the invention provides that at least one piece of operating information relating to the operating state of the motor vehicle is recorded, wherein the fulfillment of the recuperation condition additionally depends on the operating information. One piece of operating information can relate to the speed of the electric machine, wherein the recuperation condition can only be fulfilled if the speed is greater than a predetermined speed limit. For example, the speed limit can be one revolution per minute. If the speed of the electric machine is lower than the limit, then recuperation is not effective because the rotational energy stored in the electric machine is too small to allow energy recovery through recovery. The speed can be recorded by a sensor on the electric machine.

[0013] One piece of operating information relates to the speed of the vehicle. For example, it may be appropriate for the recuperation condition to not be met when the vehicle is stationary. If, for example, the vehicle is at a red light and is about to start moving, the rotational energy stored in the electric motor can be used, for example, for the vehicle's starting process, which is why the electric motor should not be decelerated.

[0014] Further operating information can relate to the charge level of the energy storage device. If the energy storage device is fully charged, recuperation of the energy stored in the electric motor would not be appropriate. Instead, the rotor of the electric motor can be decelerated using friction in the electric motor or the drive train.

[0015] Further operational information concerns the predicted start of the combustion engine. If such a start is imminent, the energy stored in the electric motor can be used to start the combustion engine instead of for recuperation. Alternatively, the recuperated energy can, of course, be used for other electronic systems in the vehicle.

[0016] The method according to the invention can provide for at least one piece of vehicle information relating to the operating state of the motor vehicle to be acquired, wherein, upon fulfillment of a coupling condition dependent on the vehicle information, the coupling device switches to the second coupling state when the coupling device is in the first coupling state. If the coupling condition is fulfilled, the coupling device switches to the second coupling state, i.e., the electric motor is decoupled from the drive train. For example, the vehicle information can relate to the actuation of the brakes, wherein, for example, during an emergency braking maneuver, the coupling device switches from the first to the second coupling state, i.e., the electric motor is decoupled from the drive train.

[0017] The vehicle information can be identical to the operating information or include it. In this case, the same information can cause the coupling device to switch to the second coupling state, and the electric motor can then, after the coupling state has changed, operate as a generator for recuperation. This can be useful, for example, if the motor vehicle is a hybrid vehicle and is powered by the combustion engine, or if the vehicle is "coasting" in the decoupled state.

[0018] The method according to the invention can provide for the motor vehicle to be driven by the electric motor when the coupling device is in the first coupling state and a drive condition is met. The drive condition can be met, for example, when a driver of the motor vehicle presses the accelerator pedal. The evaluation of the drive condition can also be performed by the control device.

[0019] In the method according to the invention, the energy recovered by the electric machine when the recuperation condition is met can be used to charge the electrical energy storage device or another electrical energy storage device. This can extend the operating life of the electrical energy storage device, since the energy thus stored can be reused to drive the motor vehicle or to operate other electrical components.

[0020] In the first coupling state, the electric machine can be coupled to a component of the drivetrain via a transmission, wherein the transmission translates the speed of the electric machine to the speed of this component of the drivetrain. The speed of the electric machine can be greater than the speed of this component of the drivetrain, i.e. the transmission ratio of the transmission is greater than 1 when the component is driven by the electric machine. This makes it possible to use a relatively small and fast-rotating electric machine for the drive, the torque of which is increased with the help of the transmission. The transmission can, for example, be designed as a planetary gear that is coupled to the drive shaft or the drivetrain via a shaft connected to the electric machine.

[0021] The invention further relates to a motor vehicle comprising an electric machine, a coupling device which couples the electric machine to a drive train in a first coupling state and decouples the electric machine from the drive train in a second coupling state, and a control device, wherein the control device is configured to control the operation of the electric machine according to the method according to one of the preceding claims.

[0022] As already mentioned, the control device can be configured to control the coupling device via an actuator, in particular an electromechanical actuator, or to switch it from the first coupling state to the second coupling state and vice versa. The control device can expediently be configured to detect and / or store the current coupling state. Furthermore, the control device can be configured to detect and, if necessary, evaluate a charge state of the electrical energy storage device.

[0023] A further development of the motor vehicle according to the invention can consist in that a transmission couples the electric machine in the first coupling state to a component of the drive train, wherein the transmission translates the speed of the electric machine to the speed of this component of the drive train, wherein the speed of the electric machine is greater than the speed of the component of the drive train.

[0024] The features described for the method according to the invention can be transferred to the motor vehicle according to the invention with the advantages mentioned.

[0025] Further advantages and details of the invention will become apparent from the exemplary embodiments described below and from the drawings, which schematically show: Fig. 1 shows an embodiment of a motor vehicle according to the invention, and Fig. 2 shows a flow chart of an embodiment of the method according to the invention.

[0026] Fig. 1 shows a schematic diagram of a motor vehicle 1. The motor vehicle 1 comprises an electric machine 2 which can be coupled to a component 5 of a drive train 4 of the motor vehicle 1 via a coupling device 3. In the exemplary embodiment shown, the component 5 of the drive train 4 is a drive shaft designed as a cardan shaft. The drive train 4 further comprises the wheels 6 of the motor vehicle 1. The wheels 6 are connected to the component 5 of the drive train 4 by a differential gear (not shown). Further components of the drive train 4 are not shown for reasons of clarity. The motor vehicle 1 also comprises an electrical energy storage device 8 in which energy is stored, in particular for driving the motor vehicle 1.

[0027] 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 to the component 5 of the drive train 4 via the coupling device 3. 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 storage device 8 into kinetic energy of the motor vehicle 1. In this case, the electric machine 2 serves as the drive motor for the motor vehicle 1. The coupling between the electric machine 2 and the component 5 of the drive train 4 is achieved via a transmission 12, which is designed to translate the rotational speed of the electric machine 2 to the rotational speed of the component 5 of the drive train 4, with the electric machine 2 rotating faster than the component 5.In the second coupling state, the electric machine 2 is decoupled from the component 5 of the drive train 4 by the coupling device 3.

[0028] For the motor vehicle 1, it is provided that rotational energy possibly stored in a rotor of the electric machine 2 can be recuperated or recovered for various purposes in the second coupling state, i.e., when the electric machine 2 is decoupled from the drive train 4, by operating the electric machine 2 as a generator. Details of this are explained below.

[0029] In Fig. 2A flowchart of a method for operating the motor vehicle 1 is shown. In step S1, vehicle information relating to the operating state of the motor vehicle 1 is acquired. This information can indicate, for example, whether emergency braking is being performed or whether the motor vehicle 1 is to be driven by an internal combustion engine 11, which is coupled to the drive train 4 for this purpose.

[0030] In step S2, the control device 7 evaluates a coupling condition dependent on the vehicle information. If the coupling condition is met, then in step S3, a control device 7 controls an electromechanical actuator 9, which brings the coupling device 3 into the second coupling state. Furthermore, the control device 7 stores the current coupling state of the coupling device 3.

[0031] If, however, the coupling condition is not met, then in step S4, the control device 7 detects the coupling state of the coupling device 3 using a sensor (not shown). Alternatively, the detection can occur if the control device 3 has already previously stored the current coupling state. In step S5, the control device 7 then checks whether the coupling device 3 is in the first or second coupling state.

[0032] If the coupling device 3 is in the first coupling state, the method is repeated from step S1 in order to monitor the vehicle information and the coupling state during further driving operation.

[0033] If the coupling device 3 is in the second coupling state, either because it was placed in the second coupling state in step S3 or because this coupling state was detected in step S5, then operating information is detected in step S6, wherein the operating information relates, among other things, to the rotational speed of a rotor of the electric machine 2, which is detected by a sensor 10 and transmitted to the control device 7.

[0034] In step S7, the control device 7 evaluates a recuperation condition that depends 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 subcondition is already ensured by checking the coupling state in step S5 or by actively selecting the second coupling state in step S3 in step S7, so that a repeated check of the coupling state can, in principle, be dispensed with. As will be explained later, it is possible, however, for the control device to continue monitoring the vehicle information in the background, for example, and to change the coupling state depending on this, independently of the method steps shown.Therefore, it may be advantageous to explicitly check again in step S7 whether the coupling device is in the second coupling state.

[0035] Furthermore, the recuperation condition in step S7 is only met if the rotational speed of the electric machine 2 is greater than a predetermined speed limit. The speed limit can be, for example, one revolution per minute. Recuperation is not appropriate if the rotational energy stored in the rotor of the electric machine 2 is too low.

[0036] In addition, further operating information can be evaluated, on which the fulfillment of the recuperation condition in step S7 may depend. The further information may, for example, relate to the speed of the motor vehicle 1 and / or the charge state of an electrical energy storage device 8. In particular, recuperation would not be appropriate if the electrical energy storage device is fully charged.

[0037] If the recuperation condition is not met, the method is terminated in step S8 and can be repeated, for example, immediately or after a certain waiting time from step S1. If the recuperation condition is met, then in step S9 the electric machine 2 is operated as a generator. The energy stored in the rotor of the electric machine 2 is recovered and is advantageously not lost through friction. The energy recuperated in this way is used to charge the electrical energy storage device 8 of the motor vehicle 1. It is also conceivable that the recuperated energy is used for other consumers of the motor vehicle 1, such as an air conditioning system or the like.

[0038] Throughout the entire process, the driving operation of motor vehicle 1 is monitored in the background by control device 7. During this monitoring, a feedback condition is evaluated; if the feedback condition is met, coupling device 3 is switched from the second coupling state to the first coupling state. This occurs, for example, when coupling device 3 is in the second coupling state and electric motor 2 is to be used to drive motor vehicle 1.

[0039] For the sake of completeness, it should be mentioned that in the method, the operation of the electric machine 2 as a generator can occur not only when the coupling device 3 is in the second coupling state, but equally when it is in the first coupling state. In this case, kinetic energy of the motor vehicle 1 is converted into electrical energy by operating the electric machine as a generator, which is particularly useful when braking the motor vehicle 1. The electrical energy generated or recovered in this way is fed, for example, to the electrical energy storage device 8, thereby charging it. The operating time of the energy storage device 8 is thereby extended and the efficiency of the motor vehicle 1 is thus improved.

Claims

1. Method for operating a motor vehicle (1), comprising an electric machine (2) and a coupling apparatus (3), which, in a first coupling state, couples the electric machine (2) to a drivetrain (4) and, in a second coupling state, decouples the electric machine (2) from the drivetrain (4), wherein the method comprises the following steps: a) registering an item of coupling information, which specifies whether the coupling apparatus (3) is in the first or second coupling state, b) analyzing a recuperation condition, the fulfillment of which depends on the coupling information, wherein the recuperation condition is fulfilled or can only be fulfilled if the coupling apparatus (3) is in the second coupling state, and c) braking the electric machine (2) by operating the electric machine (2) as a generator if the recuperation condition is fulfilled, wherein at least one item of operating information relating to the operating state of the motor vehicle (1) is registered, wherein the fulfillment of the recuperation condition is additionally dependent on the operating information, characterized in that the operating information relates to the speed of the motor vehicle (1) and / or a predicted starting of an internal combustion engine (11) of the motor vehicle (1).

2. Method according to claim 1, characterized in that the operating information describes the speed of the electric machine (2) and the recuperation condition can only be fulfilled if it is greater than a predetermined speed limit value.

3. Method according to claim 1 or 2, characterized in that at least one item of vehicle information relating to the operating state of the motor vehicle (1) is registered, wherein, if a coupling condition dependent on the vehicle information is fulfilled, the coupling apparatus (3) changes into the second coupling state if the coupling apparatus (3) is in the first coupling state.

4. Method according to any one of the preceding claims, characterized in that the motor vehicle (1) is driven by the electric machine (2) if the coupling apparatus (3) is in the first coupling state and a drive condition is fulfilled.

5. Method according to any one of the preceding claims, characterized in that the electric machine (2), if it is used as a generator upon fulfillment of the recuperation condition, charges at least one electrical energy store (8).

6. Method according to any one of the preceding claims, characterized in that in the first coupling state, the electric machine (2) is coupled via a transmission (12) to a component (5) of the drivetrain (4), wherein the transmission (12) converts the speed of the electric machine (2) to the speed of this component (5) of the drivetrain (4), wherein the speed of the electric machine (2) is greater in this case than the speed of this component (5) of the drivetrain (4).

7. Motor vehicle comprising an electric machine (2), a coupling apparatus (3), which, in a first coupling state, couples the electric machine (2) to a drivetrain (4) and, in a second coupling state, decouples the electric machine (2) from the drivetrain (4), and a control apparatus (7), wherein the control apparatus (7) is configured to control the operation of the electric machine (2) in accordance with the method according to any one of the preceding claims.

8. Motor vehicle according to claim 7, characterized in that a transmission (12) couples the electric machine (2) in the first coupling state to a component (5) of the drivetrain (4), wherein the transmission (12) converts the speed of the electric machine (2) to the speed of this component (5) of the drivetrain (4), wherein the speed of the electric machine (2) is greater than the speed of the component (5) of the drivetrain (4).