Wheel speed sensor

Abstract

A wheel speed sensor for a motor vehicle can be supplied with an operating voltage by a control device. The control device has a load resistance with a load resistance value. An operating voltage can be at a voltage input by the control device. An electrical circuit is designed to determine a turn-on or a turn-off voltage value according to the load resistance value. An operation control is designed to transfer the wheel speed sensor into a normal operation using the operating voltage, when the turn-on voltage value is exceeded, and to transfer the wheel speed sensor into an emergency operation using the operating voltage, when a turn-off voltage value is not met. In emergency operation only a low constant signal level is emitted.

Claims

1. A wheel speed sensor for a wheel of a motor vehicle, comprising: a control device which applies an operating voltage to the wheel speed sensor; a load resistor of the control device with a load resistance value; a voltage input to which the control device can apply the operating voltage; an electrical circuit to determine a switch-on voltage value on the basis of the load resistance value; an operational controller which changes the wheel speed sensor to normal operation when the switch-on voltage value is reached by the operating voltage and to emergency operation when a switch-off voltage value is reached by the operating voltage; and wherein the electrical circuit determines a difference V.sub.B between the switch-on voltage value and the switch-off voltage value on the basis of: V.sub.B=(I.sub.HI.sub.RESET)*R.sub.L, where R.sub.L is the load resistance value, I.sub.RESET is a current value which is independent of the speed, during emergency operation of the wheel speed sensor, and I.sub.H is a maximum current value during normal operation of the wheel speed sensor.

2. The wheel speed sensor of claim 1, wherein during emergency operation the wheel speed sensor has a current value output which is independent of the speed.

3. The wheel speed sensor of claim 2, wherein, the wheel speed sensor current value output is a constant current value.

4. The wheel speed sensor of claim 1, wherein the electrical circuit determines the switch-on voltage value on the basis of the switch-off voltage value.

5. The wheel speed sensor of claim 1, wherein during normal operation the wheel speed sensor has a current value output which depends on a speed of the wheel.

6. The wheel speed sensor of claim 1, wherein the electrical circuit determines at least one of the switch-on voltage value V.sub.B,EIN and the switch-off voltage value V.sub.B,AUS on the basis of: V.sub.B,AUSV.sub.B,EIN=(I.sub.HI.sub.RESET)*R.sub.L, where R.sub.L is the load resistance value, I.sub.RESET is a current value which is independent of the speed, in particular a constant current value, during emergency operation of the wheel speed sensor, and I.sub.H is a maximum current value during normal operation of the wheel speed sensor.

7. The wheel speed sensor of claim 1, further comprising a programming interface for inputting the load resistance value.

8. The wheel speed sensor of claim 1, wherein the electrical circuit determines the switch-off voltage value on the basis of the load resistance value.

9. A method for controlling a wheel speed sensor for motor vehicle, comprising: applying an operating voltage to a voltage input of the wheel speed sensor with a control device; determining a switch-on voltage value on the basis of a load resistance value of a load resistor for the control device; changing the wheel speed sensor to normal operation with an operational controller when the operating voltage reaches a switch-on voltage value; changing the wheel speed sensor to emergency operation with the operational controller when the operating voltage reaches a switch-off voltage value; and determining a difference V.sub.B between the switch-on voltage value and the switch-off voltage value on the basis of: V.sub.B=(I.sub.HI.sub.RESET)*R.sub.L, where R.sub.L is the load resistance value, I.sub.RESET is a current value which is independent of the speed, during emergency operation of the wheel speed sensor, and I.sub.H is a maximum current value during normal operation of the wheel speed sensor.

10. The method of claim 9, wherein during emergency operation the wheel speed sensor has a current value output which is independent of the speed.

11. The method of claim 10, wherein the wheel speed sensor current value output is a constant current value.

12. The method of claim 9, wherein during normal operation the wheel speed sensor has a current value output which depends on a speed of the wheel.

13. The method of claim 9, further comprising determining the switch-on voltage value on the basis of the switch-off voltage value with an electrical circuit.

14. The method of claim 9, further comprising determining the switch-off voltage value on the basis of the load resistance value with an electrical circuit.

15. The method of claim 9, further comprising determining at least one of the switch-on voltage value V.sub.B,EIN and the switch-off voltage value V.sub.B,AUS on the basis of: V.sub.B,AUSV.sub.B,EIN=(I.sub.HI.sub.RESET)*R.sub.L, where R.sub.L is the load resistance value, I.sub.RESET is a current value which is independent of the speed, in particular a constant current value, during emergency operation of the wheel speed sensor, and I.sub.H is a maximum current value during normal operation of the wheel speed sensor.

16. The method of claim 9, further comprising inputting the load resistance value with a programming interface.

17. The wheel speed sensor of claim 1, wherein the current value is a constant current value.

18. The method of claim 9, wherein the current value is a constant current value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are illustrated in the drawings and are described in more detail below. In the drawings:

(2) FIG. 1 shows a schematic illustration of a wheel speed sensor according to one embodiment;

(3) FIG. 2 shows a schematic illustration of a wheel speed sensor arrangement according to one embodiment; and

(4) FIG. 3 shows a schematic voltage/current graph for illustrating the operating ranges of the wheel speed sensor.

DETAILED DESCRIPTION

(5) FIG. 1 shows a schematic illustration of a wheel speed sensor 100 according to one embodiment. The wheel speed sensor 100 comprises a voltage input 101, an electrical circuit 103 and an operational controller 105.

(6) The wheel speed sensor 100 for sensing a speed of a wheel of a motor vehicle, a control device being able to apply an operating voltage to the wheel speed sensor 100, and the control device having a load resistor with a load resistance value, can be designed with: the voltage input 101 to which the control device can apply the operating voltage; the electrical circuit 103 which is designed to determine a switch-on voltage value on the basis of the load resistance value; and the operational controller 105 which is designed to change the wheel speed sensor 100 to normal operation when the switch-on voltage value is reached by the operating voltage and which is designed to change the wheel speed sensor 100 to emergency operation when a switch-off voltage value is reached by the operating voltage.

(7) The motor vehicle may be a passenger motor vehicle, a heavy goods vehicle, an automobile, a motorcycle, an electric motor vehicle or a hybrid motor vehicle, such as a hybrid vehicle. The wheel speed sensor 100 may also comprise a Hall sensor, a magnetoresistive sensor and/or an optical sensor. The wheel of the motor vehicle may also comprise a magnetic transducer ring and/or a perforated disk edge. Furthermore, a functionality of the wheel speed sensor 100 may be restricted or deactivated during emergency operation of the wheel speed sensor 100.

(8) The load resistance value may be an internal resistance value or a source resistance value of the control device. For example, the load resistance value is 10, 35, 50, 75, 100, 115 or 300. Furthermore, the wheel speed sensor 100 may comprise a sensing device for sensing the load resistance value. The wheel speed sensor 100 may also comprise a programming interface or an actuation element, such as a dual in-line package (DIP) switching element, for setting the load resistance value. The load resistance value may also be prestored in a memory of the wheel speed sensor 100.

(9) The operating voltage may be 1 V, 5 V, 10 V, 12 V, 15 V, 20 V, 25 V, 30 V, 35 V, 40 V, 45 V or 50 V. The switch-off voltage value may be predetermined. For example, the switch-off voltage value is 1 V, 2 V, 3 V, 4 V, 5 V, 6 V, 7 V, 8 V, 9 V or 10 V. Furthermore, the switch-on voltage value may be 0.5 V, 1 V, 2 V, 3 V, 4 V, 5 V, 10 V, 12 V, 15 V, 20 V, 25 V or 50 V.

(10) In one embodiment, the electrical circuit 103 is formed by a processor.

(11) In another embodiment, the wheel speed sensor 100 during emergency operation is designed to output a current having a current value which is independent of the speed, in particular a constant current value.

(12) In another embodiment, the wheel speed sensor 100 during normal operation is designed to output a current having a current value which depends on a speed of the wheel.

(13) FIG. 2 shows a schematic illustration of a wheel speed sensor arrangement 200 according to one embodiment. The wheel speed sensor arrangement 200 comprises the wheel speed sensor 100 and a control device 201 having a load resistor 203 which has the load resistance value R.sub.L.

(14) A voltage V.sub.B is applied between the connecting poles, such as the voltage input 101, of the wheel speed sensor 100. The entire system or the wheel speed sensor arrangement 200 is supplied with a voltage U.sub.B by a motor vehicle battery, such as a vehicle battery. The internal resistance of the control device 201 is represented by the load resistor 201 having the load resistance value R.sub.L. During normal operation, a current I from the wheel speed sensor 100 is modulated onto the current levels I.sub.L/I.sub.H, as in the case of a wheel speed sensor 100 or standard sensor without a log function, or I.sub.L/I.sub.M/I.sub.H, as in the case of a wheel speed sensor 100 having a log function.

(15) FIG. 3 shows a schematic voltage/current graph 300 for illustrating the operating ranges of the wheel speed sensor 100. The voltage/current graph 300 shows the operating ranges normal operation and undervoltage of the wheel speed sensor 100, the current I being plotted against the voltage V.sub.B.

(16) If the voltage V.sub.B falls below the switch-off voltage value V.sub.B,AUS, such as a switch-off threshold, a correct method of operation of the wheel speed sensor 100 can no longer be ensured. In order to avoid a malfunction, the wheel speed sensor 100 can change to a constant undervoltage current level I.sub.RESET. This operating state is left again only when the voltage V.sub.B exceeds a switch-on voltage value V.sub.B,EIN, such as a switch-on threshold. The implementation of a difference V.sub.BV.sub.B,AUSV.sub.B,EIN, such as voltage hysteresis, makes it possible to avoid continuous and unwanted switching-on and switching-off of the wheel speed sensor 100 if V.sub.B is permanently in the range of the switch-off threshold V.sub.B,AUS.

(17) The difference V.sub.B or the voltage hysteresis depends on the load resistance R.sub.L and is calculated according to the following relationship:
V.sub.B=(I.sub.HI.sub.RESET).Math.R.sub.L

(18) According to one embodiment, the greatest possible load resistance value R.sub.L which occurs in the application can be assumed for the interpretation of the difference V.sub.B or the voltage hysteresis in order to enable sufficient robustness of the wheel speed sensor 100 with respect to undervoltage strength. Since different control devices 201 differ in terms of their load resistance value, a wheel speed sensor 100 installed in a system having a control device 201 with a low load resistance may have a high voltage hysteresis, such as a high difference V.sub.B, and a high switch-on voltage V.sub.B,EIN.

(19) According to another embodiment, the difference V.sub.B or the voltage hysteresis and therefore the switch-on voltage V.sub.B,EIN can be programmable. Therefore, the voltage hysteresis V.sub.B and therefore the switch-on voltage V.sub.B,EIN can be individually set for each application in a manner optimally adapted to the control device 201. This makes it possible to achieve improved robustness of the wheel speed sensor arrangement 200 or of the overall system with respect to low voltage levels.

(20) The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the scope of the following claims.