Sensor arrangement for the precise detection of relative movements between an encoder and a sensor

• US 7,830,278 B2
• Filed: 08/01/2007
• Issued: 11/09/2010
• Est. Priority Date: 08/01/2006
• Status: Active Grant

• Current Assignee: Continental Teves AG & Co. OHG (Continental AG)
• Original Assignee: Continental Teves AG & Co. OHG (Continental AG)
• Inventors: Rink, Klaus, Lohberg, Peter
• Primary Examiner(s): JEANGLAUDE, JEAN BRUNER
• Application Number:
  US12/375,081
• Publication Number:
  US 20090278711A1
• Time in Patent Office: 1,196 Days
• Field of Search: 341/11, 341/155, 738/617.7, 734/88, 324/165, 324/202, 324/251, 324/252, 324/207.21, 324/166, 324/207.22, 324/207.25
• US Class Current: 341/11
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: G01P 3/487 delivered by rotating magnets
• CPC Class Codes: G01P 3/489 Digital circuits therefor

Abstract

A sensor arrangement and a method for the precise detection of relative movements between an encoder and a sensor, including an encoder, which has an incremental scale having a plurality of scale subdivisions (λ), and a sensor which is magnetically coupled to the encoder via an air gap and includes at least two magnetic field sensor elements (SE1, SE2) which are arranged offset with respect to one another by a defined distance (Δx) in the direction of the relative movement, the magnetic field sensor element output signals (V₁, V₂) having been shifted relative to one another by a relative-speed-dependent time difference with regard to the detection of a scale subdivision (λ) or a defined part of a scale subdivision (N,S), the sensor having a signal processing circuit which comprises an interface module which generates a sensor output signal (I_S3,I_S4) including at least one speed signal based upon the time difference.

Claims

1. A sensor arrangement for detection of relative movement between an encoder and a sensor, said sensor arrangement comprising:

an encoder having an incremental scale defining a plurality of scale subdivisions (A), and

a sensor which is magnetically coupled to the encoder via a n air gap and comprises at least two magnetic field sensor elements which are arranged offset with respect to one another by a defined distance (Δ

x) in a direction of the relative movement,

output signals (V₁, V₂) of the magnetic field sensor elements having been shifted relative to one another by a relative-speed-dependent time difference with regard to detection of a scale subdivision (λ

) or a defined part of a scale subdivision (N,S),

wherein the sensor includes a signal processing circuit which comprises an interface module that generates a sensor output signal (I_S3,I_S4) comprising at least one speed signal on the basis of the time difference,

wherein the signal processing circuit comprises a signal conditioning unit which generates at least one respective movement signal from the magnetic field sensor element output signals (V₁,V₂),

wherein the interface module comprises a modulator and at least one current source, the modulator being configured to drive the at least one current source at least on the basis of the movement signals and generating the sensor output signal (I_S3,I_S4) in the form of a substantially periodic injected current signal having two counting pulses for each signal period, which counting pulses are each generated from the movement signals in a counting pulse unit and a temporal offset (Δ

t) of which, from a rising edge of a first counting pulse to a rising edge of a second counting pulse, depends on the relative-speed-dependent time difference between the magnetic field sensor element output signals (V₁,V₂),

wherein the signal processing circuit has a movement direction unit which drives the modulator of the interface module on the basis of the movement direction information provided by the signal conditioning unit in such a manner that an additional information signal generated from at least one item of additional information in an additional information unit follows the second, lagging counting pulse at a defined interval of time irrespective of the direction of movement of the encoder and irrespective of the order, which is generated thereby, of the two counting pulses generated from the magnetic field sensor element output signals (V₁,V₂).

2. The sensor arrangement as claimed in claim 1, wherein the incremental scale of the encoder has at least one scale subdivision of a defined length for coding an item of position information, said defined length differing from a length of other scale subdivisions of the encoder.

3. The sensor arrangement as claimed in claim 1, wherein the sensor is connected to an electronic control unit (ECU) by means of at least two lines.

4. The sensor arrangement as claimed in claim 3, wherein the sensor is supplied with electrical power by the at least two lines.

5. The sensor arrangement as claimed in claim 1, wherein the lengths of the scale subdivisions (λ

) are different depending on the location in the direction of relative movement.

6. The sensor arrangement as claimed in claim 1, wherein the signal conditioning unit also generates at least one of the following items of additional information from at least one of the magnetic field sensor element output signals (V₁,V₂) and provides it for further processing:

(i) an item of movement direction information, (ii) an item of information relating to magnetic field strength in the air gap, (iii) a self-diagnosis parameter, or (iv) any combination thereof.

7. The sensor arrangement as claimed in claim 1, wherein the interface module additionally generates the sensor output signal (I_S3,I_S4) on the basis of additional information pulses of a defined time duration or additional information pulse pauses of a defined time duration being generated at defined times for each signal period on the basis of a binary value of the additional information in the pulse pause between the individual counting pulse and a counting pulse of a following signal period or in the pulse pause between the second counting pulse and a first counting pulse of the following signal period, an amplitude of the additional information pulses differing from the amplitude of the counting pulses.

8. The sensor arrangement as claimed in claim 1, wherein the at least two magnetic field sensor elements (SE1, SE2) are anisotropic magnetoresistive sensor elements and the sensor additionally has at least one bias magnet, and in that, with reference to a spatial cartesian coordinate system (x,y,z), a scale area of the encoder which is detected by the sensor is arranged substantially parallel to an x-y plane, a magnetization direction of the bias magnet is arranged substantially parallel to an x-axis, and a respective sensor area of the magnetic field sensor elements is arranged substantially parallel to an x-y plane, the magnetic field sensor elements being arranged at a distance from a scale surface which is different in a z-direction.

9. The use of a sensor arrangement as claimed in claim 1 in motor vehicles as a wheel rotational speed detection system.

10. A method for precise detection of relative movement between an encoder and a sensor in a sensor arrangement comprising an encoder, which has an incremental scale having a plurality of scale subdivisions (λ

), and a sensor which is magnetically coupled to the encoder via an air gap and comprises at least two magnetic field sensor elements (SE1, SE2) which are arranged offset with respect to one another by a defined distance (Δ

x) in a direction of relative movement of the encoder, said method comprising the steps of;

shifting output signals (V₁, V₂) of the magnetic field sensor elements relative to one another by a relative-speed-dependent time difference with regard to the detection of a scale subdivision (λ

) or a defined part of a scale subdivision (N,S);

generating an individual sensor output signal (I_S3,I_S4) comprising a speed signal pattern from the two magnetic field sensor element output signals (V₁,V₂) on the basis of the time difference using a signal processing circuit, wherein the step of generating the speed signal pattern for a respective signal period comprises generating a first counting pulse and a lagging, second counting pulse each with a defined amplitude and a defined duration by the signal processing circuit, when a first defined amplitude threshold (V_T) and a second defined amplitude threshold (−

V_T) are exceeded and undershot in direct succession by a respective one of the magnetic field sensor element output signals (V₁,V₂) with respect to the relative-speed-dependent time difference; and

coding additional information in the form of at least one additional information bit that is obtained from at least one of the magnetic field sensor element output signals (V₁,V₂) in the signal processing circuit, the at least one additional information bit being respectively coded, once for each signal period, in the form of successive additional information pulses with a defined second amplitude and a defined time duration or in the form of corresponding additional information pulse pulses in a pulse pause following a lagging, second counting pulse.

11. The method as claimed in claim 10, further comprising the step of transmitting the sensor output signal (I_S3,I_S4) in the form of an injected current signal, to an electronic control unit (ECU) to which the sensor is connected by means of at least two lines.

12. The method as claimed in claim 11, further comprising the step of calculating a relative speed between the encoder and the sensor in the electronic control unit (ECU), for each signal period of the sensor output signal (I_S3, I_S4), from a temporal offset between a first counting pulse and a lagging, second counting pulse or from a time duration (Δ

t) of an individual counting pulse.

13. The method as claimed in claim 11, wherein the sensor arrangement is in the form of a wheel rotational speed detection system, and a method for indirectly detecting a loss of tire pressure, which has recourse to the sensor output signal (I_S3,I_S4), is carried out in the electronic control unit.

14. The method as claimed in claim 10, further comprising the step of identifying the corresponding scale subdivision (λ

) or a corresponding scale subdivision segment (N,S) of the encoder, the detection of which by the sensor can be assigned to the respective signal period, in the electronic control unit (ECU) from a respective period duration of the sensor output signal (I_S3, I_S4) and is used to generate an item of position information.

15. The method as claimed in claim 10, further comprising the steps of:

detecting a mean magnetic field strength in the air gap;

transmitting the mean magnetic field strength in the form of additional information, to the electronic control unit (ECU) in which an imaging error of the scale subdivision, with which the sensor output signal (I_S3,I_S4) is respectively encumbered with respect to one period,

determining the imaging error based upon the mean magnetic field strength in the air gap;

evaluating a reference characteristic curve which is stored electronically and indicates the relationship between the standardized air gap length and the imaging error and the standardized field strength; and

evaluating the respective period duration of the sensor output signal (I_S3,I_S4) to determine and/or calculate an item of position information taking into account the imaging error.