JPS6135362A - Vehicle speed sensor - Google Patents

Abstract

PURPOSE:To obtain performance which is not affected by secular voltage variation and is stable against variation in source voltage by comparing variation in the voltage at the connection point between two magneto-resistance element with variation given a phase difference through a delay element. CONSTITUTION:Variation of a magnetic field during the rotation of a permanent magnet joined with a shaft rotating coaxially with the driving shaft in the transmission of a vehicle is detected as voltage variation at the connection point between a couple of magneto-resistance elements 12 and 13 to detect the rotating speed of the shaft. Then, voltages applied to the elememts 12 and 13 are obtained by stabilizing a battery voltage VBATT' through a resistor 10 and a Zener diode 11. For the purpose, the voltage variation at the connection point 10 between the elements 12 and 13 is divided through resistances 14 and 15 and inputted to the plus-side input terminal of a comparator 19, and also inputted to the minus-side input terminal through the primary delay element consisting of a resistance 16 and a capacitor 18, so that the output of the comparator 19 is used as a detection output.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a vehicle speed sensor, and more particularly to an improvement in a vehicle speed sensor that utilizes changes in the resistance value of a magnetoresistive element in response to changes in a magnetic field.

[Background of the invention]

Conventionally, in detecting vehicle speed, it has been considered promising to rotate a magnet and detect changes in the magnetic field as changes in the resistance value of a magnetoresistive element in terms of environmental resistance and noise resistance.

By the way, the applicant of the present invention previously filed a patent application in 1682-1982.
In No. 08, changes in the magnetic field are detected as changes in the resistance value of a magnetoresistive element.As a vehicle speed sensor, the change in voltage at the junction between two magnetoresistive elements arranged at right angles is detected at a certain threshold. We proposed a method that determines the direction of the magnetic field by comparing the values.

However, in the above case, when the voltage at the junction between the two magnetoresistive elements changes over time due to changes in the magnetoresistive elements by more than the voltage generated by the change in resistance due to the change in the magnetic field of the magnetoresistive elements, the threshold is reached. The disadvantage is that it cannot be detected because the value is fixed. As a countermeasure for this,
The AC coupling method is considered to take out the change in the resistance value of the magnetoresistive element caused by the change in the magnetic field, but when it is done in this way, it also directly responds to changes in the applied voltage, so when the applied voltage changes, This creates a new problem of malfunction. Therefore, when a vehicle speed sensor is mounted on a vehicle and current is supplied from the battery, an expensive circuit configuration is required to ensure stable performance even when the voltage fluctuates when the engine starts. .

[Purpose of the invention]

The present invention has been made in view of the above, and its purpose is to be able to avoid the influence of voltage fluctuations over time at the junction point of two magnetoresistive elements, and to be able to resist fluctuations in power supply voltage. The object of the present invention is to provide a vehicle speed sensor that exhibits stable performance.

[Summary of the invention]

A feature of the present invention is that the voltage applied to a pair of magnetoresistive elements that detect changes in the magnetic field during rotation of a permanent magnet connected to a shaft that rotates in synchronization with a drive shaft in a vehicle transmission is connected to a battery voltage resistor. and a Zener diode, the voltage change at the junction of the pair of magnetoresistive elements divided by resistance is input to one input terminal of the comparator, and the other input terminal of the comparator is input to the input terminal of the comparator. , the electrical change is inputted via a first-order delay element, and the output of the comparator is used as a detection output.

[Embodiments of the invention]

Hereinafter, the present invention will be explained by the embodiments shown in FIGS.
This will be explained in detail using figures.

FIG. 1 is a longitudinal sectional view showing an embodiment of the vehicle speed sensor of the present invention. In Fig. 1, 1 is a boushing, 2 is a shaft that receives rotation of a rotating body proportional to the vehicle speed, and 3 is a holder connected to the shaft 2. The holder 3 holds an annular magnet 4, and the shaft 2 is The magnet 4 is designed to rotate around the shaft 2 as it rotates.

The magnet 4 is formed into an annular shape with a portion cut out, and the magnetic field in the vicinity thereof changes as the magnet screw 140 rotates.

A magnetoresistive element group 5 is provided to detect this magnetic field, and this magnetoresistive element group 5 is composed of two magnetoresistive elements arranged so that their directions intersect perpendicularly to each other. The voltage at the junction of the two magnetoresistive elements is made to change in accordance with the change. The amount of change is transmitted through a circuit provided on the ceramic substrate 6, a lead frame 7, and a lead wire 8 to an external instrument panel (placed inside the vehicle interior) to inform the driver of the speed of the vehicle. 9 is a bearing of the shaft 2. In addition, the vehicle speed sensor bar shown in FIG.
It is attached to the extension part of the vehicle's transmission.

FIG. 2 is a circuit diagram showing one embodiment of the electric circuit of the vehicle speed sensor of the present invention. In Fig. 2, reference numerals 12 and 13 indicate magnetoresistive elements, and when a rotating magnetic field is applied due to the rotation of the magnet 4 in Fig. 1, the resistance value changes, and the voltage at junction A becomes a sine wave with a period equal to the change in the magnetic field. Changes to Comparator 19 divides this voltage between resistors 14 and 15.
The voltage is input to the + side input terminal of the converter 19, and this voltage is input to the one side input terminal of the converter 19 via a first-order delay element consisting of a resistor 16 and a capacitor 18. That is, a signal delayed in multiple phases from the input signal of the + side input terminal is inputted. These are compared by the comparator 19, and the comparator 19 outputs a pulse having a waveform having a period equal to the change in the magnetic field with a duty ratio of 50.

By the way, the voltage at the junction A of the magnetoresistive elements 12 and 13 not only changes with changes in the magnetic field, but also changes with the power supply voltage V.
It also changes depending on the fluctuation of cc.

Therefore, when the amount of variation due to vcc becomes larger than the hysteresis width determined by the resistors 14 and 15, a pulse is output from the comparator 19, resulting in a malfunction. Therefore, in FIG. 2, in order to keep vcc as constant as possible, a stabilized voltage Vcc is obtained from the battery voltage Vbat* using a resistor 10 and a Zener diode 11.

However, like during cranking, the battery voltage Vb
When *+* varies from 12V to 6■, the Zener current flowing through the Zener diode 11 changes significantly, so the Zener voltage vcc also changes, albeit weakly. Furthermore, during cranking, the battery voltage Vbm
As shown by curve 8 in Figure 3, tt decreases to near the Zener voltage Vcc shown by the curve in the figure, so the Zener current becomes extremely small and the Zener voltage Vcc
fluctuates as shown in the 6 curves in FIG.

Incidentally, when cranking, unless the engine of the vehicle is started, cranking will be completed within several seconds after the key switch of the vehicle is turned on. Therefore, by preventing the comparator 19 from outputting pulses for only a few seconds after the key switch is turned on, the vehicle running sensor can be prevented from malfunctioning. Therefore, in the embodiment shown in FIG. 2, the time constant defined by the resistor 16 and the capacitor 1B is set to several seconds, which is approximately the same as the cranking time. Therefore, for several seconds after the key switch is turned on and power is supplied to the vehicle speed sensor according to the present invention, the + side terminal of the comparator 19 is connected to the junction point A based on the power supply voltage fluctuation shown by the curve C in FIG. A voltage is input to one side of the input terminal of the comparator 19, and a voltage that rises as shown in curve d in FIG.
The output from 9 is output after the voltage input to the one side input terminal becomes stable. That is, no pulse is output from the comparator 19 until the voltage input to one side input terminal of the comparator 19 becomes stable after the key switch is turned on, and the influence of cranking can be avoided.

In this way, even if the power supply voltage is stabilized with a simple circuit consisting of the resistor 10 and the Zener diode 11, the voltage input to the one side input terminal of the comparator 19 during cranking is stabilized by the resistor 16 and the capacitor 18. Since the delay is made by the time specified by , it is possible to avoid the influence of fluctuations in the power supply voltage during cranking.

〔Effect of the invention〕

As explained above, according to the present invention, since the amount of change in voltage itself at the junction of two magnetoresistive elements is compared with the voltage with a phase difference added by a delay element, it is possible to This has the effect of being able to avoid being affected by voltage fluctuations, and exhibiting stable performance against power supply voltage fluctuations.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of the vehicle speed sensor of the present invention, FIG. 2 is a circuit diagram showing an embodiment of the electrical circuit of the vehicle speed sensor of the present invention, and FIG. 3 shows the operation of FIG. It is a time chart for explanation. 2... Shaft, 3... Holder, 4... Magnet, 5... Magnetoresistive element group, 6... Board, 7...
Lead frame, 8...Lead wire, 10.14-16
...Resistor, 11...Diode, 12.13...
・Magnetic resistance element, 17.18... Capacitor, 19・
··comparator.

Claims (2)

[Claims] 1. Changes in the magnetic field during rotation of a permanent magnet connected to a shaft that rotates coaxially with a drive shaft in a vehicle transmission are detected by at least a pair of magnetoresistive elements provided near the permanent magnet and having a voltage applied to both ends. In a vehicle speed sensor configured to detect the rotational speed of the shaft by detecting a voltage change at a junction point of the pair of magnetoresistive elements based on a change in resistance, the voltage applied to the pair of magnetoresistive elements is a battery voltage. It is assumed that the voltage change at the junction of the pair of magnetoresistive elements is stabilized by a resistor and a Zener diode, and the resulting voltage is divided by the resistance and inputted to one input terminal of the comparator, and the voltage change at the junction of the pair of magnetoresistive elements is input to one input terminal of the comparator, A vehicle speed sensor characterized in that the voltage change is input to a terminal via a first-order delay element, and the output of the comparator is used as a detection output. 2. The first-order delay element has a delay time equal to or longer than the time required for cranking the vehicle.
Vehicle speed sensor described in section.