JP3648698B2 - Vehicle height sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle height sensor used in a vehicle suspension device or the like.
[0002]
[Prior art]
As an example of a conventional vehicle height sensor, there is a vehicle height sensor previously proposed by the applicant of the present invention in Japanese Patent Laid-Open No. 8-170677. This vehicle height sensor is provided with an ultrasonic reflection surface on the cylinder side fixed to the axle side, and an ultrasonic transmitter / receiver is provided on the piston rod side that is displaceable with respect to the cylinder so as to face the ultrasonic reflection surface. Provided with a shell (enclosure member) fixed to the piston rod side so as to cover one side (upper side) of the cylinder in a substantially cylindrical shape, and after the ultrasonic transmitter transmits ultrasonic waves, the ultrasonic receiver Measure the time (ultrasonic transmission / reception time) until the time when the received signal becomes equal to or greater than a predetermined threshold value, and based on this measurement data, the relative stroke between the cylinder and piston rod, and the vehicle height To detect.
[0003]
[Problems to be solved by the invention]
By the way, in the vehicle height sensor described above, the ultrasonic propagation path between the ultrasonic transmitter / receiver and the ultrasonic reflection surface is surrounded by a cylindrical shell, and the inside of the shell (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 of the ultrasonic wave (the reception level of the ultrasonic receiver) varies in a wave-like manner (in accordance with the distance (stroke) between the ultrasonic transmitter / receiver and the ultrasonic reflection surface). It has a characteristic that changes to an approximately sin wave shape (reception level characteristic of ultrasonic waves). The reception level characteristic is determined by the shape of the shell (enclosure member).
[0004]
Then, in the stroke region where the reception level is small, such as A part and B part in FIG. 7 (the part where the transmission wave is weakened by the reflected wave etc. of the shell inner wall), the ultrasonic receiver receives as shown in FIG. The signal to be received (reception signal) becomes smaller as indicated by a solid line C to a dotted line D, for example. For this reason, a point (detection point) that is equal to or higher than a threshold used for reception determination of the ultrasonic receiver changes as indicated by a point E to a point F, for example, and a measurement error (in FIG. 8, one period of the ultrasonic frequency). Error).
[0005]
The present invention has been made in view of the above circumstances, and provides a vehicle height sensor that can detect an ultrasonic signal appropriately and reliably and has little measurement error in response to an ultrasonic resonance phenomenon occurring in the internal space of the surrounding member. The purpose is to do.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an ultrasonic transmitter / receiver provided on one of the vehicle body side and the axle side of the vehicle and the other of the vehicle body side and the axle side of the vehicle. A reflection surface that reflects the ultrasonic waves from the transmitter to the receiver; and an enclosing member that is provided so as to surround the propagation path of the ultrasonic waves from the radial direction, and is received by the receiver from the transmission time of the transmitter. A vehicle height sensor for detecting a vehicle height based on an ultrasonic transmission / reception time required until a signal becomes equal to or higher than a predetermined threshold, wherein the transmitter / receiver-supervisor is caused by a resonance phenomenon in an internal space of the surrounding member. Threshold generation means for generating a signal indicating the threshold based on the reception level characteristic of the ultrasonic wave according to the distance between the sound wave reflecting surfaces is provided.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an operation control method according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2, the shock absorber 1 has a cylinder 2 and a shell case 3 that holds the cylinder 2 so as to surround the cylinder 2. The shell case 3 is fixed to the axle side (not shown) of the vehicle. A piston (not shown) is slidably accommodated in the cylinder 2, and a piston rod 4 is attached to the piston. The piston rod 4 protrudes from the end of the shell case 3 to the outside. A body mounting eye 5 is fixed to the 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.
[0008]
A cylindrical dust cover 7 is attached to the end of the piston rod 4 via a jig 6. The dust cover 7 extends toward the axle so as to cover the shell case 3 and protects the piston rod 4 and the shell case 3 from flying stones and the like. A sensor mounting jig 8 is attached to the inside of the dust cover 7 of the jig 6 with bolts 9. An ultrasonic sensor 12 including ultrasonic transmitters / receivers 10 and 11 is attached to the sensor mounting jig 8. A reflection plate 13 (reflection surface) is attached to the end of the shell case 3 so that the ultrasonic wave from the ultrasonic transmitter 10 is reflected to the ultrasonic receiver 11. In the present embodiment, the dust cover 7 surrounds the ultrasonic wave propagation path, and constitutes a surrounding member. Since the present embodiment includes the surrounding member in this way, as described in the paragraph “0003”, a standing wave is generated inside the surrounding member (dust cover 7), and the ultrasonic resonance is generated. Due to this resonance phenomenon, the size of the ultrasonic wave (reception by the ultrasonic receiver 11) depends on the distance (stroke) between the ultrasonic wave transmitter / receiver 10, 11 and the reflector 13 (ultrasonic reflection surface). Level) has a characteristic that changes in a wave shape (substantially sin wave) (acoustic wave reception level characteristic).
[0009]
As shown in FIG. 3, a drive circuit 14 and a transmission timing generation circuit 15 are connected to the ultrasonic transmitter 10 in this order. The transmission timing generation circuit 15 outputs a transmission timing pulse J indicating the measurement timing 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. The shock absorber 1 expands and contracts due to the loading of the luggage and traveling on the uneven road, and the vehicle height changes. As shown in FIG. 5, the measurement cycle (transmission timing) is compared with the vehicle height change speed. The length between two transmission timing pulses J when transmitting pulses J continuously is extremely short.) Even when the vehicle height level changes due to running on uneven roads, the vehicle height value is reliably detected. Can be done.
[0010]
An amplification circuit 18 that amplifies a signal (reception signal) L received by the ultrasonic receiver 11 and outputs it as an amplified reception signal M and a comparison circuit 19 are connected to the ultrasonic receiver 11 in this order. A threshold signal generation circuit 17 is connected to the comparison circuit 19.
The threshold signal generation circuit 17 determines the size of the ultrasonic wave (ultrasonic wave) according to the distance (stroke) between the ultrasonic transmitter / receiver 10 and 11 and the reflector 13 as shown in FIG. characteristic indicating the reception level) of the receiver 11 (reception level characteristics) that are stored. Further, the threshold value signal generation circuit 17 generates a predetermined signal (threshold value signal) N having a pattern substantially equivalent to the reception level characteristic and a value smaller than the reception level, from the time when the transmission timing pulse J is input. It is generated every time (very short time compared to the frequency of the ultrasonic wave, hereinafter referred to as threshold signal generation time) and output to the comparison circuit 19 (threshold generation means). That is, the threshold signal generation circuit 17 has a horizontal axis (stroke amount) for a threshold signal N shown as in FIG. 4, for example, with the horizontal axis representing the stroke amount and the vertical axis representing the voltage value corresponding to the magnitude of the ultrasonic wave. Is generated for each portion corresponding to the sound speed and the predetermined stroke amount determined by the predetermined time, and is output to the comparison circuit 19. In other words, the threshold value signal generation circuit 17 generates ultrasonic waves according to the distance between the transmitter / receiver 10 and 11 and the reflection plate 13 (ultrasonic reflection surface) due to a resonance phenomenon in the internal space of the surrounding member (dust cover 7). The threshold value signal N based on the reception level characteristic is generated. Here, the threshold signal generating circuit 17 constitutes a threshold generating means .
[0011]
The comparison circuit 19 compares a reception signal L (amplification reception signal M) sent from the ultrasonic receiver 11 via the amplification circuit 18 with a comparison portion (described later) of the threshold signal N for each threshold signal generation time. When the magnitude of the amplified received signal M becomes 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 to be compared with the amplified received signal M in the threshold signal N as the accumulated time from the time when the transmission timing pulse J occurs [distance (stroke) from the ultrasonic transmitter 10] increases. The (comparison part) takes the part on the right side in FIG. Then, the propagation distance of the ultrasonic wave is twice as long as the ultrasonic wave reciprocates with respect to the reflecting plate 13, so that the comparison portion has a stroke corresponding to half of the accumulated time. A portion corresponding to the position is selected for each threshold signal generation time. By selecting the comparison portion in this manner, the comparison portion (threshold value) of the threshold signal N corresponds to the reception level of the stroke to be measured, and the size of the comparison portion of the threshold signal N is received. The value is smaller than the level.
For example, when the vehicle height (stroke) is in the A ₀ portion of the A portion region, V _A is used as the comparison portion (threshold), and when the vehicle height (stroke) is in the G ₀ portion of the G portion region, the comparison is made. V _G is used as the portion (threshold), and V _A is used as the comparison portion (threshold) when the vehicle height (stroke) is in the B ₀ portion of the region B.
In addition, in the comparison for each threshold signal generation time, the ultrasonic wave has a distance that is twice the distance between the ultrasonic transmitter / receiver 10 and 11 and the reflector 13 to be measured (reciprocal ultrasonic wave). The ultrasonic receiver 11 does not receive the ultrasonic wave until the time required for propagation [and thus the distance (stroke) corresponding to the time] is reached, but noise occurs. By setting the value to a larger value and receiving noise, it is prevented from erroneously detecting that a normal ultrasonic wave has been received.
[0012]
When the propagation time measurement circuit 16 receives the ultrasonic detection signal P from the comparison circuit 19, the propagation time measurement circuit 16 obtains the time from the first transmission timing pulse J input time to the ultrasonic detection signal P input time, and corresponds to this time. A time pulse signal Q having a width is output to the tV conversion circuit 20.
The tV conversion circuit 20 outputs a voltage corresponding to the width of the time pulse signal Q. It should be noted that the distance (stroke) to be measured and the vehicle height can be obtained from this output voltage.
[0013]
In the vehicle height sensor configured as described above, when the threshold signal generation circuit 17 inputs the transmission timing pulse J as shown in FIG. 6, the value is smaller than the reception level in a pattern substantially equivalent to the reception level characteristic. (Threshold signal N) is generated every threshold signal generation time. Then, the comparison circuit 19 compares the amplified reception signal M and the comparison portion of the threshold signal N for each threshold signal generation time. At this time, the magnitude of the amplified reception signal M is small (for noise) and the ultrasonic detection signal P is not output until the ultrasonic receiver 11 is reached after the ultrasonic wave is transmitted by the ultrasonic transmitter 10. When the ultrasonic wave reaches the ultrasonic receiver 11, the amplified received signal M and the threshold signal N (comparison part) are substantially compared. The threshold signal N (comparison portion) having a smaller magnitude than the reception level at the distance (stroke) to be measured is used as the magnitude of the threshold signal N at this stage. For this reason, even if the reception level at the distance (stroke) to be measured is, for example, the A part or B part of FIG. 4, the detection point is not changed, and it is detected that the ultrasonic wave has been properly received. Therefore, the ultrasonic reception signal J can be output at a highly accurate timing, and the measurement accuracy can be improved.
[0014]
Although there is a device that feeds back the received signal J to stabilize the measurement in the prior art, the time required for feedback is unnecessary, and the measurement can be speeded up by that amount, and the feedback Accordingly, the circuit configuration is simplified, and accordingly, the failure rate is lowered and the cost of the apparatus can be reduced.
[0015]
In the above-described embodiment, the reflection surface separately provided with the reflection plate 13 fixed to the shell case 3 is provided. However, the present invention is not limited thereto, and the end portion of the shell case 3 may be formed flat as the reflection surface. good.
[0016]
【The invention's effect】
Since the present invention is a vehicle height sensor configured as described above, it is based on the ultrasonic transmission / reception time required from the transmission time of the transmitter to the time when the reception signal of the receiver becomes a predetermined threshold value or more. While the vehicle height is detected, the threshold value generating means is a signal indicating the threshold value based on the reception level characteristic of the ultrasonic wave according to the distance between the transmitter / receiver and the ultrasonic reflection surface due to the resonance phenomenon in the internal space of the surrounding member. Therefore, the threshold value to be compared with the reception signal corresponds to the reception level in the portion to be measured , that is, the resonance phenomenon generated in the internal space of the surrounding member. For this reason, it is possible to appropriately and reliably detect the reception signal by appropriately dealing with the resonance phenomenon occurring in the internal space of the surrounding member, and to improve the measurement accuracy.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a vehicle height sensor according to an embodiment of the present invention.
FIG. 2 is a view 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;
4 is a diagram showing a relationship between a reception level of the vehicle height sensor of FIG. 1 and a threshold signal. FIG.
FIG. 5 is a diagram schematically showing a relationship between a change in vehicle height level and a measurement cycle.
6 is a timing waveform diagram for illustrating the operation of the vehicle height sensor of FIG. 1; FIG.
FIG. 7 is a diagram illustrating a relationship between a reception level and a threshold in an example of a conventional vehicle height sensor.
FIG. 8 is a diagram showing a decrease in received signal in a stroke region where the reception level is low.
[Explanation of symbols]
10 ultrasonic transmitter 11 ultrasonic receiver 13 reflector
17 threshold signal generation circuit (threshold generation means)

Claims (1)

An ultrasonic transmitter / receiver provided on one of the vehicle body side and axle side of the vehicle, and an ultrasonic wave from the transmitter provided on the other side of the vehicle body side and axle side of the vehicle is reflected to the receiver. And a surrounding member provided so as to surround the ultrasonic wave propagation path from the radial direction, from a transmission time of the transmitter to a time when a reception signal of the receiver becomes a predetermined threshold value or more. A vehicle height sensor for detecting a vehicle height based on an ultrasonic transmission / reception time required for an ultrasonic wave according to a distance between the transmitter / receiver and an ultrasonic reflection surface due to a resonance phenomenon in an internal space of the surrounding member . A vehicle height sensor comprising threshold value generating means for generating a signal indicating the threshold value based on reception level characteristics .

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