Apparatus for determining rotational position of a rotatable element without contacting it

• US 5,880,586 A
• Filed: 07/22/1996
• Issued: 03/09/1999
• Est. Priority Date: 11/22/1994
• Status: Expired due to Term

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Winner, Hermann, Dukart, Anton, Steinlechner, Siegbert, Zabler, Erich
• Primary Examiner(s): Patidar, Jay M.
• Application Number:
  US08/682,642
• Time in Patent Office: 960 Days
• Field of Search: 324/207.2, 324/207.21, 324/207.23, 324/207.25, 324/251, 324/160, 324/163, 324/165, 324/173-175, 324/252, 338/32 R, 338/32 H, 327/3, 702/145, 340/670-672
• US Class Current: 324/207.2
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: G01R 33/077 Vertical Hall-effect devices

Abstract

The apparatus for determining rotational position of a rotatable element without contacting it includes a sensor device having two Hall or AMR sensor elements for sensing a magnetic field of magnetic field strength (B) generated by or influenced by the rotational position of the rotatable element and for producing output signals according to the magnetic field and thus the rotational position of the rotatable element. In order to easily detect the absolute rotational position of the rotatable element, the sensor device is constructed and positioned with respect to the rotatable element so that in every rotational position the field lines from the rotatable element extend at right angles to the sensor structures defined by the direction of an alternating current in the sensor elements. Using different embodiments of an electronic evaluation circuit, the direction components of the magnetic field are evaluated to determine the rotational position by comparing the input current to one of the sensors and the sum of the output signals of the respective sensor elements. Either sinusoidal or rectangular alternating voltages or direct voltages are input to the sensor elements.

Claims

1. An apparatus for determining rotational position of a rotatable element without contact with the rotatable element, said apparatus comprising

a sensor device having at least two sensor elements for sensing a magnetic field of magnetic field strength (B) generated by the rotatable element or influenced by rotation of the rotatable element and for producing output signals according to said magnetic field, said sensor elements having sensor outputs;

and

evaluation circuit means for evaluating said output signals including

means for supplying said at least two sensor elements with respective alternating currents (I₁, I₂) that are 90°

out of phase in accordance with formulae Ia and Ib;

space="preserve" listing-type="equation">I.sub.1 =Io cos(ω

t) (Ia)

space="preserve" listing-type="equation">I.sub.2 =Io sin(ω

t) (Ib)

to produce respective output voltages (U_H1, U_H2) at said sensor outputs according to formulae IIa and IIb;

space="preserve" listing-type="equation">U.sub.H1 =C.sub.1 B.sub.1 cos(Kα

) I.sub.1 (t) (IIa)

space="preserve" listing-type="equation">U.sub.H2 =C.sub.2 B.sub.2 sin(Kα

) I.sub.2 (t) (IIb)

wherein t is time, ω

is frequency in reciprocal time units, Io is a constant and is a maximum current value for I₁ and I₂, C₁ =C₂ =C=another constant and B₁ =B₂ =B=an additional constant magnetic field strength value, such that C₁ B₁ and C₂ B₂ are maximum voltage values and are equal, α

is an angle of rotation of the rotatable element and K is a constant such that Kα

is the phase factor;

means (23) for summing said output voltages (U_H1, U_H2) to form a sum signal; and

a phase comparator (25) for producing a rotational position signal proportional to the rotational position of the rotatable element from the sum signal and said alternating current supplied to one of the at least two sensor elements.

2. The apparatus as defined in claim 1, wherein said at least two sensor elements consist of two Hall sensors (6,7).

3. The apparatus as defined in claim 2, wherein said means for producing said magnetic field is included in said rotatable element (2), said two Hall sensors (6,7) are oriented vertically and parallel to an axis of rotation of the rotatable element and are positioned with respect to the rotatable element (2) so that field lines of said magnetic field from the rotatable element extend at right angles to Hall structures of said Hall sensors defined by a current direction of the alternating currents supplied to said Hall sensors (6,7) in any rotational position of said rotatable element so that directional components of said field lines resulting from a change in said rotational position of said rotational element can be determined in said evaluation circuit means.

4. The apparatus as defined in claim 3, wherein said two Hall sensors (6,7) are offset by 90°

in said sensor device so that said output voltages (U_H1,U_H2) are arranged in a plane extending at right angles to said axis of rotation and each of said output voltages detects ones of said directional components of said field lines differing by 90°

.

5. The apparatus as defined in claim 4, wherein the rotatable element is a rotational shaft (1) including a permanent magnet (2) positioned rotationally symmetrically on an end of the rotatable element adjacent the sensor device so that said output voltages (U_H1,U_H2) at said sensor outputs are given by formulae 1 and 2:

space="preserve" listing-type="equation">U.sub.H1 =C.sub.1 I.sub.1 (t) B cos(α

) (1)

space="preserve" listing-type="equation">U.sub.H2 =C.sub.2 I.sub.2 (t) B sin(α

) (2),

wherein said U_H2 is offset by 90°

from U_H1, said C₁ =C₂ and C₁ and C₂ are material constants for the Hall sensors and B is a magnetic field strength value perpendicular to a plane of the Hall sensors when said field strength is the same at both of said Hall sensors.

6. The apparatus as defined in claim 2, further comprising a micromechanically machinable semiconductor wafer including said Hall sensors (6,7) and at least a part of said evaluation circuit means integrated therein, wherein said Hall sensors are arranged so that a wafer plane of the semiconductor wafer is at right angles to an axis of rotation of the rotatable element and so that a current flow direction of said alternating currents in said semiconductor wafers is vertical to the wafer plane.

7. The apparatus as defined in claim 6, wherein said semiconductor wafer is made of silicon.

8. The apparatus as defined in claim 1, wherein said at least two sensor elements consist of two AMR sensors offset rotationally by 45°

.

9. The apparatus as defined in claim 8, further comprising means for determining said rotational position according to formula (3)

10. The apparatus as defined in claim 9, further comprising a micromechanically machinable semiconductor wafer including said AMR sensors and at least a part of said evaluation circuit means integrated therein, wherein said AMR sensors are arranged so that a wafer plane of the semiconductor wafer is at right angles to an axis of rotation of the rotatable element and so that a current flow direction of said alternating currents in said semiconductor wafers is vertical to the wafer plane.

11. The apparatus as defined in claim 1, wherein said rotatable element is a shaft of a motor vehicle.

12. An apparatus for determining rotational position of a rotatable element without contact with the rotatable element, said apparatus comprising

a sensor device having two sensor elements (30,31) for sensing a magnetic field of magnetic field strength (B) generated by the rotatable element or influenced by rotation of the rotatable element and for producing sensor output signals according to said magnetic field, said sensor elements having sensor outputs at which said sensor output signals appear;

and

evaluation circuit means for evaluating said output signals including

means (28,29) for supplying said two sensor elements with respective rectangular currents having an angular frequency (ω

), pulse duty factors of 50% and phase differences of one-fourth of a period, to produce respective output voltages at said sensor outputs;

means (32,33) for amplifying said output voltages to form amplified output voltages;

means (34) for summing said amplified output voltages to form a sum signal;

means (35) for filtering the sum signal to form a filtered sum signal; and

a phase comparator (36) for producing a rotational position signal according to the rotational position of the rotatable element from the filtered sum signal and said rectangular current supplied to one of the two sensor elements.

13. The apparatus as defined in claim 12, wherein said means (28,29) for supplying said two sensor elements with respective rectangular currents comprise two delay flipflops and a clock generator and said two sensors are AMR sensors or Hall sensors.

14. An apparatus for determining rotational position of a rotatable element without contact with the rotatable element, said apparatus comprising

a sensor device having two sensor elements (30,31) for sensing a magnetic field of magnetic field strength (B) generated by the rotatable element or influenced by rotation of the rotatable element and for producing sensor output signals according to said magnetic field, said sensor elements having sensor outputs at which said sensor output signals appear;

and

evaluation circuit means for evaluating said output signals including

means (28,29) for triggering said two sensor elements with a direct voltage (V_s) to produce respective output voltages (U_a1,U_a2) at said sensor outputs given by formulae IVa and IVb;

space="preserve" listing-type="equation">U.sub.a1 (Kα

)=C V.sub.s cos(Kα

) (IVa)

space="preserve" listing-type="equation">U.sub.a2 (Kα

)=C V.sub.s sin(Kα

) (IVb);

wherein is an angle of rotation of the rotatable element, K is constant such that K is the phase factor and C is another constant;

means (51) for amplifying a difference between said respective output voltages (U_a1,U_a2) to form an amplified difference signal, said means for amplifying having respective inputs connected to respective switch terminals;

means (48a, 48b, 50,

     49) for periodically alternately switching said respective output voltages (U_a1, U_a2) between said respective switch terminals;

means (52) for filtering the amplified difference signal to form a filtered difference signal; and

a phase comparator (36) for producing a rotational position signal according to the rotational position of the rotatable element from the filtered difference signal and a switching signal supplied by said means for switching said respective output voltages.

15. The apparatus as defined in claim 14, wherein said means (52) for filtering comprise switched-capacitor filters.

16. The apparatus as defined in claim 14, wherein said means (48a, 48b, 50, 49) for periodically switching said respective output voltages (Ua1, Ua2) comprise electronic switches (48a,48b) controlled by a divider circuit (49) clocked by a clock generator (50).