JPH01173875A - Rotating speed sensor - Google Patents

Abstract

PURPOSE:To accurately measure even a slow rotating speed by setting the magnetic path of permanent magnets oppositely to the teeth of a hub rotor and detecting leak magnetic flux from the magnetic path by a magneto- resistance element. CONSTITUTION:The magnetic path 8 is set by the permanent magnets 7 and 7 oppositely to the peak parts 5 and bottom parts 6 of the teeth 2-1, 2-2... of the hub rotor 1 fitted on a rotary shaft 10. The magneto-resistance element 9 detects the leak magnetic flux from part of the magnetic path which passes through the magnetic path 8 and hub rotor 1. When a peak art 5 faces the magneto-resistance element 9, the magnetic resistance is small, but when a bottom part 5 faces the element, the resistance is large, so that the output variation corresponds to the rotating speed. The rotating speed is therefore detected as frequency variation and variation in amplitude is small, so the rotating speed is accurately measured even when the speed is slow.

Description

[Detailed Description of the Invention] L4 Existing Items The present invention relates to a rotation speed sensor that measures the rotation speed of a rotating shaft using a magnetic resistance element. The purpose is to provide a rotational speed sensor that can measure rotational speed, and a magnetic path is set by permanent magnets placed opposite the peaks and valleys of the teeth of a hub rotor, which is coaxially attached to the rotating shaft whose rotational speed is to be measured. However, it is constructed by comprising a magnetic resistance element that detects magnetic flux leaking from the magnetic path, and measuring the rotational speed of the rotating shaft based on the output j of the magnetic resistance element.

[Industrial Application Field] The present invention relates to a rotational speed sensor that measures the rotational speed of a rotating shaft using a magnetoresistive element.

Conventional sensors that use pink-up coils to measure the rotational speed of rotating shafts have been put into practical use for detecting wheel speeds of automobiles, but they have not been able to accurately measure at low speeds. Therefore, there was a need to develop a technology that could perform accurate measurements without being affected by rotational speed.

BACKGROUND OF THE INVENTION [Background Art] It has been put into practical use to detect the running speed of an automobile and measure the rotational speed of an axle in order to operate an anti-skid system. FIG. 10 is a diagram showing a schematic configuration thereof.

The hub rotor 1 is coupled to rotate coaxially with the engine drive shaft, and has, for example, 72 teeth 2-1, 2-2...
Cut around the edges. The hub rotor l is made of soft iron. The pickup coil 3 is connected to the tooth 2 of the hub rotor 1.
-1.2-2... are opposed to each other with a gap therebetween, and have a permanent magnet and a core 4 inside the coil. When the pink-up coil 3 is fixed and the hub rotor l is rotated, the coil
As the air gap between the rotors changes in size, the magnetic flux φ caused by the permanent magnet changes over time, and an alternating current voltage is generated in the pickup coil. This voltage is given by the formula dφ/dt. Since this AC voltage has a frequency change proportional to the rotation of the rotor, that is, the running speed of the vehicle, the running speed can be directly read by converting the output of the pink-up coil 3 into frequency and voltage. FIG. 11 is a diagram showing the output of the pickup coil 3, where the solid line is for high speed and the dotted line is for low speed. References for the above structure are "Car Electronics" by Shiga et al., p. 126, Sankai Tori.

[Problems to be Solved by the Invention] As can be seen from Fig. 11, the rotational speed of the shaft rotating at low speed has a small alternating current amplitude.
Speeds below /II result in inaccurate values being detected or even impossible to measure. This cannot be handled due to the principle of operation.

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks and provide a rotational speed sensor that utilizes a magnetoresistive element to accurately measure even slow rotations of a rotating shaft.

[Means for Solving the Problems] FIG. 1 is a diagram showing the principle structure of the present invention. In Fig. 1, 1 is a hub rotor, 2-1.2-2- is a tooth of the hub rotor, 5 is a tooth peak, 6 is a tooth trough, 7 is a permanent magnet,
8 is a magnetic path, 9 is a magnetoresistive element, and 10 is a rotating shaft.

The present invention has the following configuration. That is, the hub rotor 1 is coaxially attached to the rotating shaft IO whose rotational speed is to be measured.
The peaks 5 and valleys 6 of the teeth 2-1 and 2-2--
A magnetic path 8 is set by a permanent magnet 7 provided facing the magnetic path 8, and a magnetic resistance element 9 is provided for detecting magnetic flux leaking from the magnetic path 8, and the rotational speed of the rotating shaft 10 is determined by the output of the magnetic resistance element 9. It is to measure.

[Function] In the configuration shown in FIG. 1, between the permanent magnets 7.7 there is a magnetic path 8 and the teeth 2-1°2-2 of the hub rotor 1.
configured via. Therefore, the magnetic flux leaking from a part of the magnetic path passing through the magnetic path 8 and the hub rotor is detected in the magnetic resistance element 9 disposed between both magnets 7. Then, an output is obtained from the detection terminal No. 18 and used as a rotational speed detection signal. When the hub rotor 1 rotates about the shaft 10, the magnetic flux seen from the magnetoresistive element 9 changes, so the magnetoresistive element 9, ie the output at the detection signal terminal, also changes. At this time, when the magnetoresistive element 9 and the ridges 5 of the teeth of the hub rotor 1 directly face each other, the magnetic resistance is small, and when the troughs 6 of the teeth face each other, the magnetic resistance becomes large. The rotational speed can be determined by the change in output from the detection signal terminal of the magnetoresistive element.

At this time, the output change can be detected as a frequency change corresponding to the rotation speed, and since there is no change in amplitude, even when the rotation speed is slow, it can be accurately detected as a gradual frequency change.

Embodiment 1 FIG. 2 is a diagram showing the configuration of a first embodiment of the present invention. In Fig. 2, the permanent magnet 7 has a magnetic pole 7a on the hub rotor side.
, 7b: It is divided into two parts as shown in 7c and 7d, and the divided 4It poles are magnetized with a pinch of the teeth apart so that they face the peaks and troughs of the teeth of the hub rotor. The magnetoresistive element 9 can be placed at an intermediate position 8A of the magnetic path 8 (not necessarily at the center position between both permanent magnets 7.7) with a gap or a cut in the magnetic path. The magnetic path 8 between the permanent magnets is made of soft iron, for example. As the magnetoresistive element 9, for example, four elements connected in a bridge are used as shown in FIG. In FIG. 3, each element is connected to a substrate 1.
1 by vapor deposition using thin film technology. Then, terminals are drawn out using pads 12-1 to 12-4 for bridge connection, and direct current is supplied from the direct current voltage source 13. When the magnetic flux passing through the magnetoresistive element group 9 by 1lTI changes, the DC resistance changes, the balance of the bridge collapses, and an AC signal can be taken out from the terminal 14. Next, the amplifier 15 amplifies the signal.

In this embodiment, the teeth of the hub rotor are divided into two parts, so that one of the divided teeth may be missing in places where vibrations are applied, such as when used for detecting the speed of an automobile.
Preparations are made so that rotational speed detection will not be affected even if the

FIG. 4 is a diagram showing output signals when the hub rotor is rotated, for example, in the right direction, with time plotted on the horizontal axis. Time t
Before 0, the hub rotor rotated at a nearly constant speed, so
The amplitude was constant at 70 mV, for example, but since it approached stopping after time t0, it can be seen that the amplitude did not change and the repetition frequency changed gradually.

FIG. 5 is a diagram showing the configuration of a second embodiment of the present invention. In FIG. 5, 16-1 and 16-2 each indicate a signal detection circuit using a magnetoresistive element. Further, 16-3 indicates a signal synthesis circuit, which is a circuit for synthesizing the outputs of two signal detection circuits. At this time, the signals from each magnetoresistive element are summed, and differentially amplified in response to a disturbance magnetic field such as external earth's magnetism.

By using the circuit 16-3, only the desired detection signal can be extracted by human output.

FIG. 6 shows a third embodiment of the present invention in which the magnetic path is constructed from the magnet itself. The magnetic path can be constructed with a single permanent magnet, making it simple.

FIG. 7 shows a fourth embodiment of the present invention, in which a yoke divided into two parts is covered at the tip of a permanent magnet. Since the material of the permanent magnet is easily damaged by impact, the tip is made of magnetic metal.

In FIG. 6 and FIG. 7, there is no significant difference in effectiveness regarding the operation of the magnetoresistive element.

Next, FIG. 8 is a diagram showing the amplitude of the output signal shown in FIG. 4 when the forward rotation of the hub rotor is temporarily stopped and then the rotation direction is reversed. This difference in level occurs because the teeth of the hub rotor facing the magnetic poles of the permanent magnets 7 are magnetized to N or S poles and approach or leave the magnetoresistive element 9, but when the rotation direction is reversed, the teeth of the hub rotor face the opposite direction. This is because it happens. Electrical circuits have been extremely insufficient to correct this. Therefore, as shown in the fifth practical example of FIG. 9, the magnetization directions of the two permanent magnets are made to have the same polarity with respect to the teeth of the hub rotor. In that case, the magnetization of the hub rotor teeth will have the same polarity everywhere, so
There is no difference in the magnitude of the output signal depending on the rotation direction of the hub rotor.

[Effects of the Invention] According to the present invention, since the rotational speed of the hub rotor is detected by converting it into a change in leakage magnetic flux using a magnetoresistive element, even in the case of a slow rotational speed, the repetition frequency of the AC signal can be adjusted. Can be accurately measured as a change. Since the magnetic path between the magnets is a closed magnetic path, it is magnetically stable, and the leakage magnetic flux for the magnetoresistive element is also stable, making it possible to easily increase the detection sensitivity.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle configuration of the present invention, FIG. 2 is a diagram showing the configuration of the first embodiment of the present invention, FIG. 3 is a diagram showing an example of the magnetoresistive element in the first embodiment, and FIG. The figure shows the output signal of the example shown in Figure 2, and Figure 5.
Figures 6 and 7 are diagrams showing the configurations of the second, third, and fourth embodiments of the present invention, and Figure 8 shows changes in the output signal shown in Figure 4 when the rotation of the hub rotor is reversed. 9 is a diagram showing the configuration of a fifth embodiment of the present invention, FIG. 1O is a diagram showing the configuration of a conventional device, and FIG. 11 is an output waveform diagram according to FIG. 10. 1-Hub rotor 2-L2-2-teeth 3-pink-up coil 4-permanent magnet and coil 5-crest 6-trough 7...-permanent magnet 8-magnetic path 9...magnetic resistance element 10-rotation axis patent applicant
Eisuke Suzuki, Representative of Fujitsu Co., Ltd., Patent Attorney, Principle of the Invention #I Figure 1 Figure 1 Precedent Figure 2 Figure 3 Relationship between sensor outputs Figure 4 1 Hub rotor Figure 5 '113 1 row Figure 6 41! P example Fig. 7 Time Fig. 8 Fig. 5%' False I cut Fig. 9 Haf'0-even Conventional same as above

Claims (1)

[Claims] Teeth (2-1) (2-2) of a hub rotor (1) coaxially attached to a rotating shaft (10) whose rotational speed is to be measured.
For ..., a magnetic path (8) is set by permanent magnets (7) and (7) provided opposite to each other at the peaks (5) and troughs (6), and leakage from the magnetic path (8) is established. A rotational speed sensor comprising: a magnetoresistive element (9) that detects the magnetic flux generated by the magnetoresistive element;