JPH1096617A - Car height sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a car height sensor having small measurement error. SOLUTION: A threshold signal generating circuit stores a reception level characteristic indicating reception level of ultrasonic wave receiver 11 according to the stroke between ultrasonic wave transmitter/receiver 10, 11 and a reflection plate which is obtained in advance by tests. The threshold signal generating circuit also generates patterned threshold signals N which has nearly equal pattern to the reception level characteristics and smaller value than the reception level at every threshold signal generating timing from the moment inputting a transmission timing pulse J. The threshold value of comparing part corresponding to the half time of the cumulative time from the moment generating the timing pulse J in the threshold signal N becomes one corresponding to the reception level of the stroke to be measured and the level of the comparing part of the threshold signal N is made smaller than the reception level so that an amplified signal M that is, a reception signal L is surely detected and improvement of the measurement accuracy is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle height sensor used for a vehicle suspension system or the like.

[0002]

2. Description of the Related Art As an example of a conventional vehicle height sensor, there is a vehicle height sensor proposed by the present applicant in Japanese Patent Application Laid-Open No. Hei 8-170677. This vehicle height sensor is provided with an ultrasonic reflecting surface on a cylinder side fixed to an axle side, and an ultrasonic transmitter / receiver on a piston rod side displaceable with respect to the cylinder so as to face the ultrasonic reflecting surface. A shell (enclosing member) fixed to the piston rod side so as to cover one side (upper side) of the cylinder in a substantially cylindrical shape, and an ultrasonic receiver after transmitting the ultrasonic wave by the ultrasonic transmitter. The time (ultrasonic transmission / reception time) up to the point in time at which the received signal becomes equal to or larger than a predetermined threshold value is measured, and based on this measurement data, the relative stroke between the cylinder and the piston rod, and thus the vehicle height Is to be detected.

[0003]

By the way, in the above-described vehicle height sensor, the ultrasonic wave propagation path between the ultrasonic wave transmitter / receiver and the ultrasonic wave reflecting surface is surrounded by a cylindrical shell, and the inside of the shell is (Hereinafter, referred to as an ultrasonic path space), a standing wave is generated, and an ultrasonic resonance phenomenon occurs. Due to this resonance phenomenon, for example, as shown in FIG. 7, the size (reception level of the ultrasonic receiver) of the ultrasonic wave is wavy (reception level) according to the distance (stroke) between the ultrasonic transmitter / receiver and the ultrasonic reflecting surface. Approximately sin wavy)
(Reception level characteristics of ultrasonic waves). Note that the reception level characteristics are determined by the shape of the shell (enclosing member).

[0004] In a stroke region where the reception level is low, as shown in FIG. 7, portions A and B (a portion where the transmitted wave is weakened by a reflected wave of the inner wall of the shell), as shown in FIG. The signal (received signal) received by the device becomes smaller, for example, from the solid line C to the dotted line D. For this reason,
A point (detection point) that is equal to or larger than a threshold used for reception determination of the ultrasonic receiver changes from point E to point F, for example, and a measurement error (in FIG. 8, an error of one cycle of the ultrasonic frequency) is reduced. Will happen.

[0005] The present invention has been made in view of the above circumstances, and has as its object to provide a vehicle height sensor having a small measurement error.

[0006]

In order to achieve the above object, the present invention provides an ultrasonic transmitter / receiver provided on one of a vehicle body side and an axle side, a vehicle body side and an axle side. A reflecting surface provided on the other side to reflect ultrasonic waves from the transmitter to the receiver, and a surrounding member provided to surround a propagation path of the ultrasonic waves from a radial direction, A vehicle height sensor that detects a vehicle height based on an ultrasonic transmission / reception time required from a transmission time of the device to a time when a reception signal of the receiver is equal to or greater than a predetermined threshold, and the vehicle height sensor in the internal space of the surrounding member. Storage means for storing in advance the reception level characteristics of the ultrasonic waves corresponding to the distance between the transmitter / receiver and the reflecting surface; and the threshold value having a pattern substantially equivalent to the reception level characteristics and a value smaller than the reception level characteristics. Shows Characterized by providing a threshold value generating means for generating a signal.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An operation control method according to an embodiment of the present invention will be described below with reference to FIGS. FIG.
2 and FIG. 2, the shock absorber 1 has a cylinder 2 and a shell case 3 surrounding the cylinder 2 and holding the cylinder 2. This shell case 3
Is fixed to the axle side (not shown) of the vehicle. A piston (not shown) is slidably housed in the cylinder 2, and a piston rod 4 is attached to the piston. The piston rod 4 projects outside from the end of the shell case 3. A body mounting eye 5 is fixed to an end of the piston rod 4. As described above, the shock absorber 1 is interposed between the vehicle body and the axle side, and expands and contracts according to the vertical movement of the vehicle body.

A cylindrical dust cover 7 is attached to the end of the piston rod 4 via a jig 6. The dust cover 7 extends to the axle side so as to cover the shell case 3, and protects the piston rod 4 and the shell case 3 from flying stones. A sensor attachment jig 8 is attached to the jig 6 inside the dust cover 7 with bolts 9. An ultrasonic sensor 12 including ultrasonic transmitters / receivers 10 and 11 is mounted on the sensor mounting jig 8. A reflection plate 13 (reflection surface) is attached to an end of the shell case 3, and an ultrasonic wave from the ultrasonic transmitter 10 is transmitted to the ultrasonic receiver 11.
To be reflected. In the present embodiment, the dust cover 7 surrounds the propagation path of the ultrasonic wave, and forms a surrounding member.

As shown in FIG. 3, a driving circuit 14 and a transmission timing generating circuit 15 are connected to the ultrasonic transmitter 10 in this order. The transmission timing generation circuit 15
A transmission timing pulse J indicating the measurement timing is output to the drive circuit 14, a propagation time measurement circuit 16, which will be described later, and a threshold signal generation circuit 17. The drive circuit 14 generates an ultrasonic wave (transmission signal) K from the ultrasonic transmitter 10 every time the transmission timing pulse J is input. Note that the shock absorber 1 expands and contracts due to the loading of luggage and running on uneven roads, and the vehicle height changes.
As shown in FIG. 5, the measurement cycle (transmission timing pulse J
Is the length between two transmission timing pulses J when transmitting continuously. ) Is extremely short, so that even when the vehicle height level changes due to running on an uneven road or the like, the vehicle height value can be reliably detected.

The ultrasonic receiver 11 includes an ultrasonic receiver 11
The amplifier circuit 18 amplifies a signal (received signal) L received by the amplifier and outputs the amplified signal as an amplified received signal M, and a comparison circuit 19 are connected in this order. The threshold signal generation circuit 17 is connected to the comparison circuit 19. The threshold signal generation circuit 17 determines the size (ultrasonic wave) of the ultrasonic wave according to the distance (stroke) between the ultrasonic wave transmitter / receivers 10, 11 and the reflector 13 as shown in FIG. A characteristic (reception level characteristic) indicating the reception level of the receiver 11 is stored (storage means). Further, the threshold signal generating circuit 17 has a pattern (threshold signal) N having a pattern substantially equal to the reception level characteristic and having a value smaller than the reception level.
Is generated every predetermined time (a time period extremely shorter than the frequency of the ultrasonic wave; hereinafter, referred to as a threshold signal generation time) from the time when the transmission timing pulse J is input, and is output to the comparison circuit 19 (threshold generation means). ). Here, the threshold signal generation circuit 17 also serves as storage means and threshold generation means.

The comparison circuit 19 compares a reception signal L (amplified reception signal M) sent from the ultrasonic receiver 11 via the amplification circuit 18 with a comparison part (described later) of the threshold signal N for each threshold signal generation time. When the magnitude of the amplified reception signal M is larger than the magnitude of the predetermined portion of the threshold signal N, the ultrasonic detection signal P is output to the propagation time measuring circuit 16. In this case, the portion of the threshold signal N to be compared with the amplified reception signal M (comparison portion) as the cumulative time from the time of generation of the transmission timing pulse J increases.
Takes the right part in FIG. The propagation distance of the ultrasonic wave is twice the stroke as the ultrasonic wave reciprocates with respect to the reflecting plate 13.
As the comparison portion, a portion corresponding to a stroke position corresponding to half the accumulated time is selected for each threshold signal generation time. By selecting the comparison part in this way,
The comparison part (threshold) of the threshold signal N corresponds to the reception level of the stroke to be measured, and the size of the comparison part of the threshold signal N becomes a value smaller than the reception level. For example, when the vehicle height (stroke) is in the area A ₀ of the area A, _VA is used as the comparison part (threshold), and the vehicle height (stroke) is G in the area G.
When in ₀ part V _G is used as a comparison portion (threshold), and when the vehicle height (stroke) is in the B ₀ partial area of the B portion, V _A is used as a comparison portion (threshold).
In the comparison for each threshold signal generation time, the accumulated time is twice as long as the distance between the ultrasonic transmitter / receivers 10 and 11 and the reflector 13 to be measured (the reciprocating amount of the ultrasonic wave). Until the time required for propagation is reached, the ultrasonic receiver 11 does not receive an ultrasonic wave, but noise is present. Therefore, the threshold signal N is set to a value larger than the noise.
By receiving the noise, it is prevented that a normal ultrasonic wave is erroneously detected.

When the propagation time measuring circuit 16 receives the ultrasonic detection signal P from the comparison circuit 19, the propagation time measuring circuit 16 obtains the time from the input of the first transmission timing pulse J to the input of the ultrasonic detection signal P. Is output to the tV conversion circuit 20. tV
The conversion circuit 20 outputs a voltage corresponding to the width of the time pulse signal Q. Note that the distance (stroke) to be measured, and thus the vehicle height, can be obtained from the output voltage.

In the vehicle height sensor configured as described above,
When the threshold signal generation circuit 17 receives the transmission timing pulse J as shown in FIG. 6, a signal (threshold signal N) having a value substantially smaller than the reception level in a pattern substantially equivalent to the reception level characteristic is generated. Occurs every hour. And
The comparison circuit 19 compares the amplified reception signal M and a comparison part of the threshold signal N for each threshold signal generation time. At this time, the ultrasonic wave is transmitted from the ultrasonic transmitter 10 and then the ultrasonic receiver 11
, The magnitude of the amplified reception signal M is small (for noise), and the ultrasonic detection signal P is not output. When the ultrasonic wave reaches the ultrasonic receiver 11, the amplified reception signal M is substantially compared with the threshold signal N (comparison portion). As the magnitude of the threshold signal N at this stage, a threshold signal N (comparison portion) having a smaller magnitude than the reception level at the distance (stroke) to be measured is used.
For this reason, even if the reception level at the distance (stroke) to be measured is, for example, the portion A or the portion B in FIG. 4, the detection point is not changed, and it is detected that the ultrasonic wave has been properly received. Thus, the ultrasonic reception signal J is output at a highly accurate timing, so that the measurement accuracy can be improved.

In the prior art, there is an apparatus for stabilizing the measurement by feeding back the received signal J. However, the time required for the feedback is not required, and the measurement can be accelerated accordingly. In addition, since a circuit for feedback becomes unnecessary, the circuit configuration is simplified, and accordingly, the failure rate is reduced and the cost of the device can be reduced.

In the above-described embodiment, a reflection plate 13 is separately provided to the shell case 3 as the reflection surface. However, the present invention is not limited to this, and the end of the shell case 3 is formed flat as a reflection surface. You may.

[0016]

Since the present invention is a vehicle height sensor constructed as described above, the time required for the ultrasonic wave to propagate through the distance between the transmitter / receiver and the reflecting plate is reduced by the transmission time via the reflecting surface. A threshold of a portion corresponding to a half of the threshold signal, which corresponds to a half of the accumulated time from the transmission point of time of the transmitter, which is related to a relationship of being 1/2 of the ultrasonic transmission / reception time between the receiver and the reception signal. By performing the comparison, the threshold value to be compared with the received signal corresponds to the reception level in the portion to be measured, and the magnitude of the threshold value is set to a value smaller than the reception level. Is reliably detected,
As a result, measurement accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a vehicle height sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a mounting state of a transmitter / receiver of the vehicle height sensor of FIG. 1;

FIG. 3 is a block diagram schematically showing the vehicle height sensor of FIG. 1;

FIG. 4 is a diagram showing a relationship between a reception level of the vehicle height sensor of FIG. 1 and a threshold signal.

FIG. 5 is a diagram schematically showing a relationship between a vehicle height level change and a measurement cycle.

FIG. 6 is a timing waveform chart showing the operation of the vehicle height sensor of FIG. 1;

FIG. 7 is a diagram illustrating a relationship between a reception level and a threshold value in an example of a conventional vehicle height sensor.

FIG. 8 is a diagram illustrating a decrease in a received signal in a stroke region where the reception level is low.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Ultrasonic transmitter 11 Ultrasonic receiver 13 Reflector 15 Transmission timing generation circuit 17 Threshold signal generation circuit (storage means, threshold signal generation means) 19 Comparison circuit

Claims (1)

[Claims] An ultrasonic transmitter / receiver provided on one of a vehicle body side and an axle side of a vehicle, and an ultrasonic wave transmitted from the transmitter provided on the other of the vehicle body side and the axle side. A reflecting surface for reflecting to the receiver, and an enclosing member provided so as to surround the propagation path of the ultrasonic wave from the radial direction, the reception signal of the receiver from the time of transmission of the transmitter is a predetermined threshold or more A vehicle height sensor that detects the vehicle height based on the ultrasonic transmission / reception time required until the time when the ultrasonic wave corresponding to the distance between the transmitter / receiver and the reflection surface in the internal space of the surrounding member. Storage means for storing reception level characteristics in advance, and threshold value generation means for generating a signal indicating the threshold value having a value substantially smaller than the reception level characteristics in a pattern substantially equivalent to the reception level characteristics. Toss Vehicle height sensor.