Rotation angle detection device and electric power steering system including the same

Patent metadata

Field	Value
Publication number	US-9625249-B2
Application number	US-201314104510-A
Country	US
Kind code	B2
Filing date	Dec 12, 2013
Priority date	Dec 12, 2012
Publication date	Apr 18, 2017
Grant date	Apr 18, 2017

Abstract

Rotation angle computation modes include a normal mode and a simple mode. In normal mode, a rotation angle of an input shaft is computed based on output signals from first and second magnetic sensors, which are sampled at two sampling timings. In simple mode, the rotation angle of the input shaft is computed based on the output signals from the first and second magnetic sensors, which are sampled at one sampling timing, and an amplitude ratio between the output signals from the magnetic sensors set in advance. After a power supply is turned on, the rotation angle is computed in the simple mode until a condition that the rotation angle of the input shaft can be computed in the normal mode even if the immediately preceding value of the rotation angle of the input shaft is not present is satisfied. Then, the rotation angle is computed in the normal mode.

First claim

What is claimed is:

1. A rotation angle detection device comprising:
a plurality of sensors used to detect a rotation angle of a rotary body;
a first rotation angle computation unit that computes the rotation angle of the rotary body with use of a first plurality of output signals from a first set of two sensors among the plurality of the sensors, and samples the first plurality of output signals at a prescribed number of different timings, the prescribed number being two or more;
a second rotation angle computation unit that computes the rotation angle of the rotary body with use of a second plurality of output signals from a second set of two sensors among the plurality of the sensors, and samples the second plurality of output signals at one sampling timing; and
a selector that selects one of the first rotation angle computation unit and the second rotation angle computation unit, as a computation unit used to compute the rotation angle of the rotary body, based on the first plurality of output signals from the first set of two sensors when the selector selects the first rotational angle computation unit and based on the second plurality of output signals from the second set of two sensors when the selector selects the second rotational angle computation unit.

2. The rotation angle detection device according to claim 1 , wherein the selector is configured such that the first rotation angle computation unit computes the rotation angle of the rotary body after a power supply is turned on, and
the selector selects the second rotation angle computation unit as the computation unit used to compute the rotation angle of the rotary body until a condition is satisfied that the first plurality of output signals from each one of the sensors of the first set of two sensors differ from each other, and selects the first rotation angle computation unit to compute the rotation angle of the rotary body when the condition is satisfied and after the condition is satisfied.

3. The rotation angle detection device according to claim 1 , wherein the selector is configured such that the selector selects the first rotation angle computation unit as the computation unit used to compute the rotation angle of the rotary body when a condition is satisfied that the first plurality of output signals from each one of the sensors of the first set of two sensors differ from each other, and selects the second rotation angle computation unit as the computation unit used to compute the rotation angle of the rotary body when the condition is not satisfied.

4. The rotation angle detection device according to claim 1 , wherein:
a condition is satisfied that the number of multiple expressions obtained by operating each of the first plurality of the output signals used by the first rotation angle computation unit to compute the rotation angle of the rotary body is smaller than the number of unknown quantities included in the multiple expressions; and
the first rotation angle computation unit is configured to compute the rotation angle of the rotary body by solving simultaneous equations constituted of the multiple expressions after setting the number of unknown quantities included in the multiple expression equal to or smaller than the number of multiple expressions obtained by operating each of the first plurality of output signals used by the first rotation angle computation unit to compute the rotation angle of the rotary body by setting predetermined unknown quantities among the unknown quantities included in the multiple expressions to be equal to each other.

5. The rotation angle detection device according to claim 4 , further comprising:
a multipolar magnet that rotates in accordance with rotation of the rotary body, and that has a plurality of magnetic poles, wherein
the plurality of the sensors is a plurality of magnetic sensors that respectively output sinusoidal signals having a predetermined phase difference in accordance with rotation of the multipolar magnet,
the first rotation angle computation unit is configured to compute the rotation angle of the rotary body with use of four output signals from the first plurality of the output signals being sampled at a prescribed number of different timings from the first set of two sensors among the plurality of the sensors, the four output signals being sampled at two different timings,
the multiple expressions are constituted of four expressions obtained by operating the four output signals, each of the expressions including an amplitude and the rotation angle of the rotary body as the unknown quantities, and
the first rotation angle computation unit sets the number of unknown quantities included in the multiple expressions equal to or smaller than the number of multiple expressions obtained by operating each of the first plurality of output signals used by the first rotation angle computation unit to compute the rotation angle of the rotary body, by setting, among the unknown quantities included in the four expressions, the amplitudes of two output signals of the first plurality of output signals from each one of the two sensors of the first set of two sensors, sampled at different sampling timings, equal to each other.

6. The rotation angle detection device according to claim 5 , wherein the second rotation angle computation unit is configured to compute the rotation angle of the rotary body with use of the second plurality of output signals being sampled at one sampling timing from the second set of two sensors among the plurality of sensors, the second plurality of output signals being sampled at the one sampling timing, and an amplitude ratio between the second plurality of output signals from the second set of two sensors, the amplitude ratio being set in advance.

7. The rotation angle detection device according to claim 4 , further comprising a multipolar magnet that rotates in accordance with rotation of the rotary body, and that has a plurality of magnetic poles, wherein
the plurality of the sensors is a plurality of magnetic sensors that respectively output sinusoidal signals having a predetermined phase difference in accordance with rotation of the multipolar magnet,
the first rotation angle computation unit is configured to compute the rotation angle of the rotary body with use of six output signals from the first plurality of the output signals being sampled at a prescribed number of different timings from the first set of two sensors among the plurality of the sensors, the six output signals being sampled at three different timings,
the multiple expressions are constituted of six expressions obtained by operating the six output signals, each of the expressions including an amplitude, the rotation angle of the rotary body, and a piece of information regarding a magnetic pole width of each of the magnetic poles of the multipolar magnet as the unknown quantities, and
the first rotation angle computation unit sets the number of unknown quantities included in the multiple expressions equal to or smaller than the number of multiple expressions obtained by operating each of the first plurality of output signals used by the first rotation angle computation unit to compute the rotation angle of the rotary body, by setting, among the unknown quantities included in the six expressions, the amplitudes of three output signals of the first plurality of output signals from each one of the two sensors of the first set of two sensors, sampled at different sampling timings, equal to each other, and all the pieces of the information regarding the magnetic pole width included in the six expressions are the same.

8. An electric power steering system comprising:
a plurality of sensors used to detect a rotation angle of a rotary body;
a sampl

Assignees

• Jtekt Corp

Inventors

• Takaki Takeshi
• Kariatsumari Yuji
• Shimizu Yoshinobu

Classifications

• B62D5/0463

  calculating assisting torque from the motor based on driver input · CPC title

• B62D6/10

  characterised by means for sensing {or determining} torque · CPC title

• G01B7/30 Primary

  for measuring angles or tapers; for testing the alignment of axes · CPC title

• G01D5/244 Primary

  influencing characteristics of pulses or pulse trains; generating pulses or pulse trains · CPC title