High-Resolution Steering Angle Sensor

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High-Resolution Steering Angle Sensor

1.

INTRODUCTION

Recently, demands for the safety of vehicles are increasing in the field of automobiles, and the electronic stability
control (ESC) system for vehicle attitudes which has beendeveloped in response to such demands is expanding its
applications. The ESC system stabilizes, when a vehicle
begins to skid at the time of turning, the behavior of thevehicle instantly by automatic controlling of the brake andthe engine output. Thus, the accuracy of the vehicle information such as speed, acceleration and steering angle isdirectly linked to the accuracy of vehicle control. For thisreason, high precision and high reliability are required forthe sensors that detect these vehicle information.
The product presented here is a steering angle sensor
for the ESC system, and, to satisfy the above mentioned
requirements, Furukawa Electric has developed a noncontact steering angle sensor of its proprietary design
adopting an electromagnetic induction principle. SeeFigure 1.

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Magnetic ﬂux of coil����� ��∝����������������� ���������������������������������������������������������������������������������������������������������������������������������������� ������������������������������������������������������������������������������Figure 2

Basic principle.

2.2 Detection Principle
Practical configuration of the product is such that a plate
conductor of changing width is situated on the coil, andthe plate conductor is fixed to a rotor that rotates in synchronization with the steering shaft. As the steering shaft
rotates, the shielding area of the plate conductor for themagnetic flux generated by the coil changes, thus causing a change in the coil inductance that corresponds tothe steering rotation angle. See Figure 3.

Figure 1

2.

Appearance of the developed product.

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DETECTOR STRUCTURE

2.1 Basic Principle
The product developed here has adopted a detection
principle of electromagnetic induction, in which a change
in a coil inductance due to shielding of magnetic flux isdetected. When a plate conductor is inserted in the regionof magnetic flux generated by the coil, an eddy current
will flow to shield the magnetic flux, so that by changing
the shielding area of the plate conductor, a change in thecoil inductance is caused as illustrated in Figure 2, andthe steering angle can be detected from this inductancechange.

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Detection principle.

Furukawa Review, No. 30

200628

High-Resolution Steering Angle Sensor

3.

ing angle to the electronic control unit (ECU) before turning the ignition switch OFF.

FEATURES

3.1 High Resolution
In the conventional optical sensor of encoder type, its resolution improves as the slits on the rotator that interrupts
the photodiode light beam increase in number. But,because the slit width must be decreased to increase theslit number in the tight space, there is a certain limit ofresolution due to processing difficulties.
In contrast with this, the resolution of the product developed here can reach a level higher than 0.1° by improving
the performance of signal processing which the total resolution depends on.
3.2 Low Hysteresis
The product has a structure such that the plate conductor
is directly fixed on to the rotor that rotates in synchronization with the steering shaft, so that there exists no transmission loss of rotation signals to the sensing head,enabling steering angle detection of high precision andlow hysteresis. See Figure 4.
For reference's sake, in the sensor adopting magnetoresistive (MR) elements it is necessary to acquire twotypes of signals with different periods to detect absolutesteering angles. And, to change the signal period, rotation
period of the permanent magnet for signal detection has
to be changed usually using a gear. Moreover, the magnet has to be located on the center of a rotator that faces
the MR element, and, because the steering shaft penetrates the rotor (i.e. rotator), the gear is linked with therotor, and the magnet is located on the rotation center ofthe gear. Such a structure, however, tends to have a large
hysteresis because a mechanical loss in rotation transmission is generated due to the gear.

3.4 High Reliability
The product has high reliability due to its structure of noncontact type necessitating no mechanical contacts in thesensing head. The product has passed a severe rotational
endurance test of five million rotations at 300 rpm in theheat cycle environments.
3.5 Self-Diagnosis Function
The product is provided with a variety of self-diagnosis
functions as shown below, and in case an abnormality isdetected by the sensor itself, the signal contaminated withpossible errors is interrupted from outputting, and thesensor immediately shift to a warning mode. This function
securely prevents malfunction of the host system.
1. Coil disconnection
2. Open/short of electric circuits
3. Outreaching the guaranteed temperature
4. Over-rotation due to deviations from the neutral position of rotation

4.

PRODUCT SPECIFICATIONS

Table 1 shows the main specifications of the product.
Table 1

Product specifications.

Item

Specification−40〜85�℃

Operating temperature
Rated operating voltage

5V

Relative angular detection range±750°

Absolute angular detection range±225°

Angular resolution�����������������������Angular hysteresis

within ±1°

Rotation speed limit

5 rps（1800°/s）

Current consumption

40 mA or lessOuter dimensions������������Unit weight

Figure 41°(thickness)

18 mm(outer dia.)

65 mm(inner dia.)

25 mm(total length)

91 mm
77 g

Structure of detector head.

3.3 Instantaneous Detection of Absolute Angles
Upon turning the ignition switch ON, the product instantaneously redetermines the absolute angle of the steering
shaft, so that it is not necessary to store the value of steer-For more information, please contact:
Engineering Management Division, Automotive
Products Business Group, Electronics and Automotive
Systems Company
TEL: +81-595-85-2026
FAX: +81-595-85-2431

Furukawa Review, No. 30

200629