Patent ID: 11933642
Assignee: HITACHI ASTEMO, LTD.
Field: Measurement (Instruments)
Classification: CPC G  H | IPC G  H

Claim 11:
12. A displacement detection system using a two-wire stroke sensor, the displacement detection system comprising:
an LC oscillation circuit including a coil whose inductance changes in accordance with a stroke amount of a shock absorber of a straddle type vehicle and an oscillation unit provided with a capacitor and an amplifying element;
an interface unit serving as a signal output unit that outputs an alternating current signal having a current waveform to a first wire and a power supply input unit to which a direct current power supply voltage is input;
a current and voltage conversion unit configured to convert the alternating current signal having the current waveform into an alternating current signal having a voltage waveform; and
an electronic control unit including a detection unit configured to detect the stroke amount by observing a frequency of the alternating current signal having the voltage waveform after the conversion,
wherein the interface unit includes
a first constant current circuit that is connected between the first wire and a second wire and is configured to output an alternating current signal having a current waveform to the first wire when the first constant current circuit is switched between an ON state and an OFF state based on an alternating current signal having a voltage waveform obtained from the LC oscillation circuit,
a second constant current circuit that is connected between the first wire and the second wire and is constantly turned on, and
a smoothing capacitor that is connected between the second wire and a reference potential line and is configured to generate a power supply voltage of the oscillation unit,

wherein the first wire serves as a current signal output line that outputs the alternating current signal having the current waveform and a direct current power supply voltage input line to which the direct current power supply voltage is input,
wherein the interface unit includes an input and output terminal to which the first wire is connected, that inputs the direct current power supply voltage, and that outputs the alternating current signal having the current waveform,
wherein a connection point between the second constant current circuit and the first wire is provided at a position farther away from the input and output terminal than a connection point between the first constant current circuit and the first wire,
wherein a constant current amount of the second constant current circuit is set to be larger than a constant current amount of the first constant current circuit,
wherein each of the first constant current circuit and the second constant current circuit is configured with at least one constant current diode,
wherein the interface unit includes at least one Zener diode connected between the second wire and a reference potential line,
wherein a total current obtained by adding currents flowing out from the first constant current circuit and the second constant current circuit flows to the reference potential line via the Zener diode to generate a predetermined constant voltage at two ends of the Zener diode, and a surplus current exceeding a current amount required to generate the constant voltage flows to the reference potential line, and
wherein the constant voltage generated by the Zener diode is smoothed by the smoothing capacitor to generate the power supply voltage of the oscillation unit.