Torque sensor and motor-driven power steering apparatus using thereof

• US 20040016305A1
• Filed: 02/26/2003
• Published: 01/29/2004
• Est. Priority Date: 07/25/2002
• Status: Abandoned Application

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Yamada, Masamichi, Matsumoto, Masahiro
• Application Number:
  US10/373,661
• Publication Number:
  US 20040016305A1
• Time in Patent Office: Days
• US Class Current: 73/862.331
• CPC Class Codes: G01L 3/104 involving permanent magnets
• CPC Class Codes: G01L 3/105 involving inductive means G01L3/102, G01L3/104 take precedence
• CPC Class Codes: G01L 3/109 involving measuring phase difference of two signals or pulse trains
• CPC Class Codes: G01L 5/221 to steering wheels, e.g. for power assisted steering

Abstract

A torque sensor includes input and output axes coupled through a torsion bar, magnetic media attached to the input and output axes and having magnetic tracks magnetized at a predetermined pitch and magnetic detection elements disposed opposite to the magnetic media to be sensitive to the magnetic tracks. At least two magnetic tracks for detection of torque are formed with a magnetic phase difference in each of the magnetic media attached to the input and output axes.

Claims

1. A torque sensor including magnetic media attached to input and output axes coupled through a torsion bar, respectively, and each having magnetic tracks magnetized at a predetermined pitch and magnetic detection elements disposed opposite to each of said magnetic media and sensitive to said magnetic tracks, whereby torque is detected on the basis of output signals of said magnetic detection elements, comprising:

at least two magnetic tracks formed in each of said magnetic media attached to said input and output axes with a magnetic phase difference in order to detect torque.

3. A torque sensor according to claim 1, wherein the magnetic phase difference of said two magnetic tracks of each of said magnetic media is {fraction (1/4)} of the magnetization pitch.

5. A torque sensor according to claim 1, wherein each of said magnetic media includes not only two magnetic tracks having a magnetic phase difference equal to {fraction (1/4)} of the magnetization pitch but also magnetic tracks having magnetization pitches which are twice and quadruple as large as said two magnetic tracks.

7. A torque sensor according to claim 1, wherein each of said magnetic media includes not only at least two magnetic tracks having the magnetic phase difference but also magnetic tracks for identifying the number of at least four or more periods of a magnetization pattern in said at least two magnetic tracks.

9. A torque sensor according to claim 1, wherein each of said magnetic media includes at least two magnetic tracks having the magnetic phase difference and a plurality of magnetic tracks representing the gray code.

11. A torque sensor according to claim 1, wherein said magnetic detection elements corresponding to said magnetic tracks of each of said magnetic media are disposed in substrates formed for each of said magnetic media separately.

13. A torque sensor according to claim 1, wherein said magnetic detection elements corresponding to said magnetic tracks of each of said magnetic media are disposed in a substrate formed for each of said magnetic media separately and each of said substrates includes means for automatically adjusting a gap between said magnetic detection elements and said magnetic tracks.

15. A torque sensor according to claim 1, wherein a substrate for supporting said magnetic detection elements includes magnetic write heads disposed in said substrate to magnetize said magnetic tracks to be read out by said magnetic detection elements onto said magnetic medium.

17. A torque sensor according to claim 1, wherein two or more magnetic tracks formed in each of said magnetic media contains magnetic tracks having magnetization directions different from those of said magnetic tracks and said magnetic detection elements corresponding to said magnetic tracks having said different magnetization directions use magnetic detection elements each sensitive to a particular magnetization direction.

2. A torque sensor including first and second axes coupled through a torsion bar, a first magnetic medium rotated together with said first axis and having magnetic tracks magnetized at a predetermined pitch, a second magnetic medium rotated together with said second axis and having magnetic tracks magnetized at a predetermined pitch, first magnetic detection elements disposed to be sensitive to said magnetic tracks of said first magnetic medium, and second magnetic detection elements disposed to be sensitive to said magnetic tracks of said second magnetic medium, whereby torque is detected on the basis of output signals of said first and second magnetic detection elements, comprising:

at least two magnetic tracks formed in each of said first and second magnetic media at equal magnetization pitch and with a magnetic phase difference.

4. A torque sensor according to claim 2, wherein the magnetic phase difference of said two magnetic tracks of each of said magnetic media is {fraction (1/4)} of the magnetization pitch.

6. A torque sensor according to claim 2, wherein each of said magnetic media includes not only two magnetic tracks having a magnetic phase difference equal to {fraction (1/4)} of the magnetization pitch but also magnetic tracks having magnetization pitches which are twice and quadruple as large as said two magnetic tracks.

8. A torque sensor according to claim 2, wherein each of said magnetic media includes not only at least two magnetic tracks having the magnetic phase difference but also magnetic tracks for identifying the number of at least four or more periods of a magnetization pattern in said at least two magnetic tracks.

10. A torque sensor according to claim 2, wherein each of said magnetic media includes at least two magnetic tracks having the magnetic phase difference and a plurality of magnetic tracks representing the gray code.

12. A torque sensor according to claim 2, wherein said magnetic detection elements corresponding to said magnetic tracks of each of said magnetic media are disposed in substrates formed for each of said magnetic media separately.

14. A torque sensor according to claim 2, wherein said magnetic detection elements corresponding to said magnetic tracks of each of said magnetic media are disposed in a substrate formed for each of said magnetic media separately and each of said substrates includes means for automatically adjusting a gap between said magnetic detection elements and said magnetic tracks.

16. A torque sensor according to claim 2, wherein a substrate for supporting said magnetic detection elements includes magnetic write heads disposed in said substrate to magnetize said magnetic tracks to be read out by said magnetic detection elements onto said magnetic medium.

18. A torque sensor according to claim 2, wherein two or more magnetic tracks formed in each of said magnetic media contains magnetic tracks having magnetization directions different from those of said magnetic tracks and said magnetic detection elements corresponding to said magnetic tracks having said different magnetization directions use magnetic detection elements each sensitive to a particular magnetization direction.

19. A torque sensor including magnetic media attached to input and output axes coupled through a torsion bar, respectively, and each having magnetic tracks magnetized at a predetermined pitch and magnetic detection elements disposed opposite to each of said magnetic media and sensitive to said magnetic tracks, whereby torque is detected on the basis of output signals of said magnetic detection elements, comprising:

at least two magnetic tracks disposed in each of said magnetic media and having a magnetic phase difference;

magnetic tracks disposed in each of said magnetic media to be able to identify the number of at least four or more periods of a magnetization pattern in said at least two magnetic tracks; and

an operation unit for calculating torque exerted on said input and output axes from detection signals of said magnetic tracks having said magnetic phase difference and detection signal of said magnetic tracks disposed to be able to identify the number of at least four or more periods.

20. A torque sensor comprising a rotational axis of which a rotational angle is detected by electromagnetic induction operation and a distortion sensor disposed in said rotational axis to detect torque exerted on said rotational axis and be driven by utilizing electric power produced by said electromagnetic induction operation.

21. A torque sensor for detecting torque exerted between first and second axes coupled through a torsion bar on the basis of a torsional angle produced in said torsion bar, comprising:

at least one or more moving coils rotated together with said first or second axis and disposed to produce electromagnetic induction by a magnetic field perpendicular to said first or second axis; and

at least one or more fixed coils fixedly mounted relatively to said first or second axis and disposed to produce electromagnetic induction by a magnetic field perpendicular to said first or second axis.

22. A torque sensor according to claim 21, comprising, as said fixed coil, at least two or more fixed coils disposed to produce electromagnetic induction by magnetic fields having directions different from each other.

23. A torque sensor according to claim 21, comprising a distortion sensor for detecting torque exerted on said first and second axes, fixed-coil driving means for applying an AC voltage to said fixed coil in a mode of a period 1, storing means for inducing an AC voltage in said moving coil by said application of the voltage to said fixed coil and converting the AC voltage into a DC voltage to store it, and moving-coil driving means for applying an output of said distortion sensor to said moving coil in form of AC voltage by means of electric power stored in said storing means, whereby said AC voltage is induced by the application of the AC voltage to said moving coil to take out a torque output signal.

24. A torque sensor according to claim 21, comprising detection means for detecting a torsional angle of said torsion bar, frequency conversion means for converting an output of said detection means into a frequency, means for applying a voltage having an output frequency of said frequency conversion means to said moving coil, and means for producing an induced voltage in said fixed coil by said application of said voltage to said moving coil and measuring a frequency of said induced voltage.

25. A torque sensor according to claim 21, comprising means for measuring a ratio of voltages induced in at least two or more fixed coils.

26. A motor-driven power steering apparatus which transmits rotation of a steering wheel to wheels through a rotational axis and detects at least torque of said rotational axis so that a motor for assisting operation of the steering wheel is controlled on the basis of the detected signal, wherein

said detection of said torque is performed by providing a plurality of magnetic tracks each having a phase difference in a plurality of magnetic drums provided in two rotational axes coupled through a torsion bar and by means of a contactless magnetic encoder system.

27. A motor-driven power steering apparatus which transmits rotation of a steering wheel to wheels through a rotational axis and detects at least torque of said rotational axis so that a motor for assisting operation of the steering wheel is controlled on the basis of the detected signal, wherein

said detection of said torque is performed by detecting distortion of said rotational axis and taking out the detected signal by means of electromagnetic induction from a moving coil provided in said rotational axis to at least two fixed coils disposed around said rotational axis.