Method for operating an electric or hybrid vehicle with shiftable transmission and electric or hybrid vehicle

Abstract

At least one electric motor is employed for propelling an electric or hybrid vehicle with a shiftable transmission. Upon reaching a shift threshold, a shift operation is performed in the transmission of the vehicle, wherein a value specifying the shift threshold is varied depending on at least one parameter. As the at least one parameter, a speed is used, at which a power provided by the at least one electric motor for propelling the vehicle has a maximum.

Claims

1. A method for operating a vehicle with all electric or hybrid power and having a shiftable transmission, in which at least one electric motor is employed for propelling the vehicle, comprising: performing a shift operation in the shiftable transmission of the vehicle upon reaching a shift threshold specified by a value varied depending on at least one parameter, the at least one parameter including a speed at which a power, provided by the at least one electric motor for propelling the vehicle, reaches a maximum prior to dropping below the maximum.

2. The method according to claim 1, wherein the shift operation is performed when an acceleration of the vehicle under full load of the at least one electric motor is requested by a driver of the vehicle or by a control system of the vehicle.

3. The method according to claim 1, wherein the value specifying the shift threshold is changed when the at least one electric motor is operated in a continuous operating mode in which operational damage to the at least one electric motor and/or at least one component associated with the at least one electric motor is avoided.

4. The method according to claim 1, further comprising obtaining a data value specifying the speed by at least one of computation and from a map.

5. The method according to claim 4, wherein by using the data value, at least one variable is taken into account, which is associated with at least one of an electric energy storage and an electric power source of the vehicle and which influences the speed, at which the power provided by the at least one electric motor for propelling the vehicle has the maximum.

6. The method according to claim 5, wherein the at least one variable which is taken into account includes at least one of a voltage, a voltage under load, a state of charge, a state of health and a temperature.

7. The method according to claim 4, wherein by using the data value, at least one of a temperature of the transmission, a temperature of the at least one electric motor, a temperature of power electronics, and a derating of high voltage components or semiconductor elements of the vehicle is considered as a variable, which influences the speed, at which the power provided by the at least one electric motor for propelling the vehicle has the maximum.

8. The method according to claim 3, further comprising supplying the data value to a control device, which effects the shift operation.

9. A vehicle, comprising: at least one electric motor configured to propel the vehicle; a shiftable transmission configured to perform a shift operation upon reaching a shift threshold; and a control device configured to vary a value specifying the shift threshold depending on at least one parameter, including a speed, as the at least one parameter, at which a power, provided by the at least one electric motor, reaches a maximum prior to dropping below the maximum.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects, advantages, features and details will become more apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings of which:

(2) FIG. 1 is a graph, in which the progression of the torque and the power of an electric motor of a vehicle is shown related to the speed of the electric motor in different states of charge of a battery supplying the electric motor with electric energy;

(3) FIG. 2 a further graph, in which power curves of the electric motor depending on the battery voltage and a power curve for the continuous operation of the electric motor are shown; and

(4) FIG. 3 is a block diagram of components of the vehicle and a communication path, via which a data value specifying the kink speed can be communicated to a transmission controller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(5) Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.

(6) In a graph 10 shown in FIG. 1, the progression of the torque and the power progression of an electric motor 12 of a vehicle 14 (cf. FIG. 3) as a function of the speed in different states of charge of a battery 16 of the vehicle 14 are shown. On an abscissa 18 of the graph 10, the speed of the electric motor 12 in revolutions per minute [1/min] is indicated, on a first ordinate 20 its torque in Nm is indicated and on a second ordinate 22 its power in kW is indicated.

(7) A first curve 24 illustrates the progression of the torque of the electric motor 12 with increasing speed if the battery 16 of the vehicle 14 has a high, in particular maximum state of charge. According to the first curve 24, the torque first remains constant and then drops upon reaching a certain speed 26. A further curve 28 illustrates the progression of the power delivered by the electric motor 12 if the battery 16 has the high state of charge. Correspondingly, the power reaches a maximum 30 at the speed 26. The speed 26, at which the torque output by the electric motor 12 decreases or the power reaches the maximum 30, is also referred to as kink speed, as the curve 24 abruptly bends down or kinks at this speed.

(8) This kink speed is dependent on various influencing variables. The influence of the state of charge of the battery 16 is illustrated in the graph 10. Correspondingly, a third curve 32 in the graph 10 describes the progression of the torque and a fourth curve 34 in the graph 10 describes the progression of the power of the electric motor 12 if the battery 16 has a low, in particular minimum state of charge. Here, the torque already collapses at a lower speed 36 and also the power, which can be delivered by the electric motor 12, reaches its maximum 38 earlier, namely at this lower speed 36. The variation of the kink speed caused by the altered state of charge of the battery 16 is illustrated by an arrow 40 in FIG. 1.

(9) The realization that the kink speed varies depending on a plurality of influencing variables in the vehicle 14, is presently utilized to vary a shift threshold, thus a speed of the electric motor 12, at which an automatic shift operation is performed in a transmission 42 of the vehicle 14 (cf. FIG. 3). Thus, it can be ensured that upon full-load acceleration or maximum acceleration of the vehicle 14, the power maximally being able to be provided by the electric motor 12 is always exploited.

(10) In FIG. 2, in a further graph 44, the power progression of the electric motor 12 depending on the voltage of the battery 16 is illustrated. A first curve 46 in the graph 44 illustrates the power of the electric motor 12 plotted on an ordinate 48 in kW depending on the speed of the electric motor 12 plotted on an abscissa 50 in revolutions per minute.

(11) The first curve 46 has a maximum 52. Upon reaching a shift speed 54 corresponding with this maximum 52, a shift operation is performed by a transmission controller 56 of the vehicle 14 (cf. FIG. 3) in the transmission 42. In the power train, a new subsequent speed 58 appears, which is lower than the shift speed 54.

(12) A second curve 60 in FIG. 2 illustrates the power progression of the electric motor 12 of the vehicle 14 at a medium voltage of the battery 16. A maximum 62 of this second curve 60 is at a lower speed than the shift speed 54. Thus, if at this medium voltage of the battery 16 or such a source voltage the same shift speed 54 would be used, thus, the shift operation would not be effected upon reaching the maximum 62 of the power, but only at a higher speed. Thereby, a power potential of the electric motor 12 would remain unutilized in the electric or hybrid operation of the vehicle 14.

(13) The graph 44 in FIG. 2 shows a third curve 64 indicating the power of the electric motor 12 at a still lower voltage of the battery 16. Correspondingly, a maximum 66 of this third curve 64 is at a still lower speed than at the medium voltage position of the battery 16 according to the curve 60.

(14) Furthermore, it is apparent from FIG. 2 that the maximum 62 of the second curve 60 is lower than the maximum 52 of the first curve 46 and the maximum 66 of the third curve 64 is lower than the maximum 62 of the second curve 60.

(15) In order to optimally exploit the available mechanical propulsion power in the electric drive operationor in the electrically assisted hybrid drive operationwith regard to the maximum acceleration, presently, the shift speed 54 or the shift threshold is therefore varied. Namely, if the source voltage, presently thus the voltage of the battery 16, decreases due to discharge thereof, thus, the power maximum of the electric motor 12 shifts towards lower speeds. Correspondingly, then, the shift speed 54 is decreased such that the power maximum of the electric motor 12 is further in the available speed range.

(16) If the electric motor 12 is heavily loaded, thus for instance operated under full load, thus, overheating of the magnets and windings used in it occurs. Furthermore, power electronics 68 associated with the electric motor 12, the battery 16 as well as lines 70 may overheat, which connect the battery 16 to the power electronics 68 and the power electronics 68 to the electric motor 12 (cf. FIG. 3). In order to protect the mentioned component parts in such a case, the power delivered by the electric motor 12 is reduced by supplying less current to it. A corresponding continuous operating mode 72 of the electric motor 12 is illustrated in the graph 44 in FIG. 2 by a fourth curve.

(17) In this continuous operating mode 72, the electric motor 12 can continuously provide power without overheating of the electric motor 12 or of the further components possibly affected by overheating having to be feared. As is apparent from the graph 44, the power maximum of the electric motor 12 shifts towards higher speeds related to the shift speed 54 if it is operated in the continuous operating mode 72. Correspondingly, in this operating state, the shift speed 54 is shifted to higher values such that the power maximum of the electric motor 12 is further in the available speed range.

(18) Based on FIG. 3, it can be illustrated how the communication in the vehicle 14 can proceed in order to effect the corresponding variation of the shift speed 54. Control devices of the vehicle 14 such as for instance the transmission controller 56, a battery management system 74 and a motor controller 76 are connected to each other via a suitable communication path, for instance a CAN bus system 78.

(19) Presently, the currently prevailing speed 26, 36 (cf. FIG. 1) is determined by the power electronics 68, at which the power maximum is available for the electric drive propulsion. A signal 80 specifying this respective kink speed is communicated to the transmission controller 56 via the CAN bus system 78. The transmission controller 56 utilizes this information for adapting the shift speed 54 to the respectively present maximum power curve.

(20) By determining the kink speed of the electric motor 12 depending on influencing variables as the load voltage, the state of charge and the temperature of the battery 16, the temperature of the electric motor 12, the temperature of the transmission 42 and/or the temperature of the power electronics 68 in a first step, only this individual parameter, namely the kink speed, has to be used in a second step. In the second step, then, the shift characteristics are displaced depending on the kink speed by the transmission controller 56. This consideration of the kink speed for controlling the shift characteristics is particularly low in effort since the kink speed determined by the power electronics 68 already considers the described influencing variables.

(21) In alternative embodiments, the kink speed can also be determined by a different control device than the power electronics 68, for instance by the battery management system 74 or by the motor controller 76.

(22) Since the vehicle 14 is presently formed as a hybrid vehicle, the motor controller 76 presently controls an internal combustion engine 82 of the vehicle 14. However, the displacement of the shift threshold or shift speed 54 depending on the kink speed, thus the speed 26, 36, can also be employed in a vehicle 14 formed as an electric vehicle.

(23) A description has been provided with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase at least one of A, B and C as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).