Device for Calibrating Two Electric Motors Mounted on One Axle in Two-Axle Motor Vehicles

Abstract

A device for calibrating two electric motors mounted on one axle in two-axle motor vehicles includes at least one electronic control unit configured to check whether predefined conditions for a switchover from torque control to rotational speed control are met. If met, the at least one electronic control unit is configured to switch to rotational speed control for a predefined period of time. A torque-dependent characteristic map with correction values is created on the basis of this difference. The target torques are corrected by the correction values during torque control after rotational speed control has been deactivated.

Claims

1.-9. (canceled)

10. A device for calibrating two electric motors mounted on one axle in two-axle motor vehicles comprising: at least one electronic control unit, wherein while the vehicle is in motion the at least one control unit is configured to: check whether predefined conditions for a switchover from torque control to rotational speed control are met, and if met: switch to rotational speed control for a predefined period of time; and during the period of time in which rotational speed control is active: acquire and save the target torques of the two electric motors, and form a difference between the acquired target torques of the two electric motors, wherein a torque-dependent characteristic map with correction values is created on the basis of this difference, and the target torques are corrected by the correction values during torque control after rotational speed control has been deactivated.

11. The device according to claim 10, wherein the conditions met include at least one of the following: that the current rotational speeds of both electric motors are the same, that the vehicle speed is less than a predefined vehicle speed, that the steering wheel is in a straight position or within a predefined tolerance range, and that the yaw rate of the vehicle is within a predefined range of values.

12. The device according to claim 11, wherein the vehicle speed is determined by the rotational speed of the electric motors.

13. The device according to claim 12, wherein a value close to the current actual rotational speed is selected as the target rotational speed value for the two rotational speed controllers of the electric motors.

14. The device according to claim 13, wherein the target torques of the electric motors are output from the rotational speed controllers of the electric motors.

15. The device according to claim 14, wherein a torque-dependent characteristic map or a characteristic curve with correction values is created from previously stored target torque values, wherein the correction values are added to the target torque values of the torque control during the period of time of torque control.

16. The device according to claim 15, wherein the frequency of execution of the second step is limited to activation within a predefined period of time.

17. A method for calibrating two electric motors mounted on one axle in two-axle motor vehicles having at least one electronic control unit, the method comprising: while the vehicle is in motion, checking whether predefined conditions for a switchover from torque control to rotational speed control are met, and if met: switching to rotational speed control for a predefined period of time, while the vehicle is in motion, and during the period of time in which rotational speed control is active: acquiring and saving the target torques; and forming a difference between the acquired target torques of the two electric motors, wherein a torque-dependent characteristic map with correction values is created on the basis of this difference, wherein the target torques are corrected by the correction values during torque control after rotational speed control has been deactivated.

18. A non-transitory computer readable storage medium storing a program, which when executed performs the method according to claim 17.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 shows, in a schematic illustration, an overview of the components of the invention in a single-axle drive; and

[0025] FIG. 2 is a flowchart of the calibration.

DETAILED DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 illustrates a vehicle with single-axle drive having a first, left-hand electric motor EM1 for individual wheel drive on the rear axle HA, and having a second, right-hand electric motor EM2 for individual wheel drive on the rear axle HA. Alternatively, it is also possible for a vehicle driven via the front axle or an all-wheel drive vehicle to be provided with the invention since said invention is directed to two electric motors EM1 and EM2 arranged on one axle, irrespective of the position on the vehicle. The vehicle according to FIG. 1 represents a road-coupled hybrid or electric vehicle. The vehicle has at least one electronic control unit 1, in particular as or in an engine control device. The control unit 1 is configured in such a way, by means of a correspondingly programmed function module (computer program product) for example, that the following method according to the invention, which is represented in FIG. 2 as a flowchart, can be carried out therewith while driving:

[0027] In a first step S1, the control device 1 checks whether switching to rotational speed control is possible for a predefined, short period of time under predefined conditions while the vehicle is in motion.

[0028] The conditions to be met are:

[0029] S11: the currently detected rotational speeds of both electric motors EM1 and EM2 are the same, which is the case when driving straight ahead without slip, i.e. Nist_EM1=Nist_EM2

[0030] S12: the vehicle speed is below a maximum permitted vehicle speed of, for example, 30 km/h or less. The vehicle speed can be determined from the rotational speed N of the electric motors EM1 and EM2. It must therefore be the case that N≤Nmax, wherein Nmax can be determined from the vehicle speed and vice versa. The maximum vehicle speed can be specified by a person skilled in the art according to the electric motors EM1 and EM2 used or other conditions.

[0031] S13: the steering wheel is in a straight position or within a tolerance range of, for example, ±2 degrees, wherein the tolerance range can likewise be specified by a person skilled in the art. The straight position can be supported, for example, by means present in the vehicle, e.g. “steer by wire”.

[0032] S14: the yaw rate, that is to say the vehicle rotational speed about the Z-axis, must not exceed a predefined value N_z_max. This value too can be chosen by a person skilled in the art according to the application and should be as low as possible.

[0033] If all conditions are met (yes), the second step S2, namely the actual calibration, is carried out. For this purpose, rotational speed control is activated for a predefined, short time Δt. During this time Δt, the difference between the target torque of the first electric motor and the target torque of the second electric motor is determined:

ΔMsoll=Msoll_EM1_N_Regler−Msoll_EM2_N_Regler

[0034] On the basis of the difference values, a characteristic map or a characteristic curve is created, which specifies correction values ΔMsoll(Msoll) based on current target torques. After this, calibration is complete and it is possible to switch back to torque control. During torque control, the correction values ΔMsoll(Msoll) are respectively added to the target torques of the two electric motors MSoll_EM1 and MSoll_EM2.

[0035] If one of the conditions is not met (no), then step S1 is carried out again, i.e. rotational speed control and thus calibration are not activated until all conditions S11-S14 are met again.