Method and device for determining wheel slip information of an electrically driven wheel of a motor vehicle

Abstract

A method and a device for determining wheel slip information of an electrically driven wheel of a motor vehicle, according to which during travel, the speed (nE-motor) of an electric motor driving the wheel is detected and the detected speed (nE-motor) of the electric motor is used to determine the wheel slip information.

Claims

1. A method for determining wheel slip information of an electrically driven wheel comprising: a motor vehicle, according to which during travel, when a wheel speed sensor for the electrically driven wheel fails, a speed (n.sub.E-motor) of an electric motor driving the wheel is calculated from a current profile and/or a voltage drop and/or from information about control of the motor, and the calculated speed (n.sub.E-motor) of the electric motor is used to determine the wheel slip information, wherein the wheels of an axle are driven via a common electric motor and an axle differential, and a speed difference (Δn) between the wheels of the axle caused by the axle differential is detected, wherein a theoretical wheel speed (n.sub.wheel,theo) is determined from the calculated speed (n.sub.E-motor) of the electric motor, the speed difference (Δn), and a gear ratio and axle differential ratio (i.sub.G, i.sub.A) for both wheels of the axle, and in that an actual wheel speed (n.sub.wheel,actual) of the wheels of the axle is determined from a current driving speed (V.sub.vehicle) of the motor vehicle, wherein when the theoretical wheel speed (n.sub.wheel,theo) of one or more wheels deviates from the actual wheel speed (n.sub.wheel,actual), it is determined as wheel slip information that the wheel in question or both wheels of the axle is/are slipping.

2. The method according to claim 1, wherein each electrically driven wheel is assigned a separate electric motor.

3. The method according to claim 2, wherein the theoretical wheel speed (n.sub.wheel,theo) of the wheel is calculated according to the formula $n_{\mathrm{wheel},\mathrm{theo}}=\frac{n_{E\text{-}\mathrm{Motor}}}{i_G}$ and the actual wheel speed (n.sub.wheel,actual) of the wheel is calculated according to the formula $n_{\mathrm{wheel},\mathrm{left},\mathrm{actual}}=\frac{V_{\mathrm{vehicle}}}{\pi d_{\mathrm{wheel}}}$ wherein d.sub.wheel=diameter of the wheel.

4. The method according to claim 1, wherein the theoretical wheel speed (n.sub.wheel,theo) of the wheels of the axle is calculated according to the formula $n_{\mathrm{wheel},\mathrm{theo}}=\frac{1}{2}\left(\frac{n_{E\text{-}\mathrm{motor}}}{i_G{i}_A}\pm \Delta n\right)$ and the actual wheel speed (n.sub.wheel,actual) of the wheels of the axle is calculated according to the formula $n_{\mathrm{wheel},\mathrm{actual}}=\frac{V_{\mathrm{vehicle}}}{\pi d_{\mathrm{wheel}}},\mathrm{wherein}{d}_{\mathrm{wheel}}=\mathrm{diameter}\mathrm{of}\mathrm{the}\mathrm{wheel}.$

5. The method according to claim 1, wherein the actual wheel speed (n.sub.wheel,actual) deviates from the theoretical wheel speed when the following applies to the wheel speeds:
n.sub.wheel,actual≤0.9 n.sub.wheel,theo or n.sub.wheel,actual≥1.1n.sub.wheel,theo.

6. The method according to claim 2, wherein the actual wheel speed (n.sub.wheel,actual) deviates from the theoretical wheel speed when the following applies to the wheel speeds:
n.sub.wheel,actual≤0.9 n.sub.wheel,theo or n.sub.wheel,actual≥1.1 n.sub.wheel,theo.

7. A device for determining wheel slip information of an electrically driven wheel of a motor vehicle when a wheel speed sensor for the electrically driven wheel fails, comprising: an electric motor for driving the wheel, the wheel speed sensor assigned to the wheel, and a regulating/control unit configured for calculating a speed (n.sub.E-motor) of the electric motor, wherein the current motor vehicle speed (V.sub.vehicle), the output signals of the wheel speed sensor, the speed (n.sub.E-motor) of the electric motor, and at least one of a voltage, current, or control signal for the electric motor, are provided as input signals to the regulating/control unit, wherein the regulating/control unit is configured to determine wheel slip information using the input signals when the wheel speed sensor fails, wherein one or more wheels of an axle are driven via a common electric motor and an axle differential, and a speed difference (Δn) between the wheels of the axle caused by the axle differential is detected, wherein a theoretical wheel speed (n.sub.wheel,theo) is determined from the calculated speed (n.sub.E-motor) of the electric motor, the speed difference (Δn), and a gear ratio and axle differential ratio (i.sub.G, i.sub.A) for both wheels of the axle, and in that an actual wheel speed (n.sub.wheel,actual) of the wheels of the axle is determined from a current driving speed (V.sub.vehicle) of the motor vehicle, wherein when the theoretical wheel speed (n.sub.wheel,theo) of one or both wheels deviates from the actual wheel speed (n.sub.wheel,actual), it is determined as wheel slip information that the wheel in question or both wheels of the axle is/are slipping.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Further advantages and possible uses of the present invention will be apparent from the following description in conjunction with the exemplary embodiment depicted in the drawing.

(2) In the drawing:

(3) FIG. 1 is a schematic representation of a motor vehicle designed to illustrate the method for determining redundant wheel slip information of an electrically driven wheel of a motor vehicle.

DETAILED DESCRIPTION

(4) FIG. 1 shows a schematic representation of a motor vehicle designated as a whole by reference number 10. In the present case, the rear wheels 12-1 and 12-2 are driven by an electric motor 14, and the wheels 12-3 and 12-4 of the front axle are not driven. Between the wheels 12-1, 12-2 of the rear axle, an axle differential designated by reference number 16 is arranged in a known manner. In addition, each wheel 12-1, 12-2, 12-3, 12-4 of the motor vehicle 10 is assigned a wheel speed sensor 18-1, 18-2, 18-3, and 18-4, in order to determine which wheel is slipping and by how much. The system is controlled based on this information, i.e., the wheel that is slipping is typically braked.

(5) If, e.g., wheel speed sensor 18-1 should fail, slip control of the wheel 12-1 would no longer be possible. As a consequence, particularly with respect to future functions such as piloted or (partially) autonomous driving, for example, such functions would have to be deactivated at least for a short time, because the failure of the wheel speed sensor 18-1 on wheel 12-1 would mean that slip control is no longer possible, and thus the motor vehicle 10 might be placed in a safety-critical driving situation.

(6) This is exactly where the invention comes in: As shown in FIG. 1, a regulating/control unit 20 is provided, to which the output signals of the wheel speed sensors 18-1, 18-2, 18-3, and 18-4 are provided as input variables, along with the current vehicle speed V.sub.vehicle (cf., reference number 22), the speed n.sub.E-motor of the electric motor 20 (cf., reference number 24), and the speed difference Δn between the wheels 12-1, 12-2 of the rear axle (cf., reference number 26) caused by the axle differential 16, as indicated schematically.

(7) For the following explanation of the method, it is assumed that the wheel speed sensor 18-1 assigned to the left rear wheel 12-1 has failed.

(8) In a first method step, the regulating/control unit 14 then calculates the theoretical wheel speed n.sub.wheel,left,theo of the left rear wheel 12-1 that is induced by the power output from the electric motor 16:

(9) $n_{\mathrm{wheel},\mathrm{left},\mathrm{theo}}=\frac{1}{2}\left(\frac{n_{E\text{-}\mathrm{motor}}}{i_G{i}_A}\pm \Delta n\right)$
wherein in the present case, since no gearing is arranged between the electric motor 16 and the axle differential, i.sub.G=1 and the value of the axle differential ratio i.sub.A is stored in the control unit.