JPH07191139A - Doppler type vehicle ground speed detecting device - Google Patents

Abstract

PURPOSE:To provide a Doppler type vehicle ground speed detecting device constituted so that even when an intensity difference between a main beam and a side beam transmitted by an ultrasonic transmitter becomes small only a frequency of the main beam may be detected to accurately find a ground speed. CONSTITUTION:A Doppler type vehicle ground speed detecting device is composed of an ultrasonic sensor unit 4 installed to be positioned between a bottom of a rear luggage compartment 2 and a rear bumper 3 of a vehicle 1 and a control circuit 5. The ultrasonic sensor unit 4 is installed so that orientation of a side beam 11 of a transmission wave may be perpendicular to a ground surface 13. Accordingly, since a Doppler shift of the side beam 11 becomes zero, a ground speed is calculated based on a frequency of a receiving wave of a reflected wave of a main beam 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Doppler type ground vehicle speed detecting device, and more particularly to a Doppler type ground vehicle speed detecting device configured to detect a vehicle ground speed more accurately.

[0002]

2. Description of the Related Art For example, in an automobile, the vehicle speed is obtained from the rotational speed of the wheels and the current vehicle speed is displayed on a speedometer in the driver's seat. However, when traveling on a road surface with low friction (μ) such as a road surface wet with rain, a snowy road, or a frozen road surface, the wheels easily slip, and the vehicle speed obtained from the rotational speed of the slipped wheel is the actual speed. It will be different from the vehicle speed, that is, the ground speed.

On the other hand, as a device for more safely traveling on a road surface with bottom friction, a traction control device for controlling drive torque when the road surface friction is low to prevent wheels from slipping, or when braking on a road surface with low friction. Anti-lock brake devices and the like have been developed that control the braking force so that the wheels do not lock. In these traction control devices or anti-lock brake devices, it is necessary to obtain an accurate vehicle speed when the wheels slip, so a ground vehicle speed detection device that detects the speed of the vehicle body with respect to the ground surface is adopted separately from the speedometer. There is.

As this type of ground speed detecting device, for example, as shown in Japanese Unexamined Patent Publication No. Sho 56-141573, there are a transmitted wave that transmits an ultrasonic wave toward the ground surface and a reflected wave that is reflected by the ground surface. A device for detecting the ground speed of a vehicle body has been developed by utilizing the Doppler effect that a frequency difference is generated depending on the vehicle speed. In this ground vehicle speed detecting device, the ultrasonic waves transmitted from the ultrasonic transmitter provided in the rear part of the vehicle body are reflected on the road surface, and the reflected wave is received by the ultrasonic receiver provided in the rear part of the vehicle body. It has become. Then, in order to effectively obtain the Doppler shift (frequency modulation) of the reflected wave from the road surface, the transmission direction of the ultrasonic wave is about 45 ° to the rear of the vehicle body.
(Transmission angle with respect to the road surface) It is inclined.

[0005]

However, the ultrasonic wave transmitted by the directivity of the ultrasonic transmitter has a main beam traveling at the transmission angle with respect to the road surface and a directivity angle different from the main beam with respect to the road surface. With side beams. That is, the main beam of the transmitted wave travels along the axis of the ultrasonic transmitter, and the side beam travels in a direction inclined at an angle with respect to the axis of the ultrasonic transmitter. Therefore, although the side beam has a weaker transmission intensity than the main beam, the larger the transmission angle with respect to the road surface, the larger the reflectance becomes, and the reception intensity may become stronger than the main beam depending on the traveling conditions of the vehicle.

Further, when the vehicle body travels on a dry road surface, the main beam of ultrasonic waves transmitted from the ultrasonic wave transmitter is reflected by the fine irregularities formed on the surface of the road surface and reaches the ultrasonic wave receiver. In that case, some side beams are also reflected by the road surface and received by the ultrasonic receiver, but since the reception intensity is weak,
It does not exceed the threshold value (threshold level) set in the vehicle speed calculation unit and does not affect the calculation of the vehicle speed.

However, when the road surface is submerged by rain or when the road surface is frozen, the ground surface on which ultrasonic waves are reflected becomes a mirror-like surface with no unevenness, so that the super surface provided at the rear of the vehicle body The main beam of ultrasonic waves transmitted from the ultrasonic wave transmitter is reflected almost at the rear of the vehicle body and is not received by the ultrasonic wave receiver. Therefore, in the reflected wave received by the ultrasonic receiver, the reception intensity of the main beam is weakened and the reception intensity of the side beam is relatively strong, and the difference between the two is small.

Further, when the vehicle is traveling at a high speed, the distance traveled by the vehicle from the transmission of the ultrasonic wave to the reception of the reflected wave is large. You will receive the waves. Also in this case, as in the case of the above-mentioned mirror surface condition of the road surface, in the reflected wave received by the ultrasonic receiver, the received sound wave intensity of the main beam is weakened, and the received sound wave intensity of the side beam is relatively strengthened. The difference between

In the vehicle speed calculating section for calculating the vehicle speed from the frequency difference, the vehicle speed may be calculated based on the reflected wave of the side beam, in which case a speed lower than the actual vehicle speed is calculated. As a result, in the traction control device or the anti-lock brake device, the traction control or the braking control is performed based on the ground speed, so that the control is delayed, and the appropriate control for preventing the wheel slip or the wheel lock is performed. Can not be.

Therefore, in view of the above problems, the present invention does not detect the vehicle speed due to the reflected wave of the side beam even if the reception intensity of the reflected wave of the main beam reflected on the ground surface is weak, and accurately determines only the vehicle speed due to the main beam. The purpose is to calculate.

[0011]

The invention according to claim 1 is
An ultrasonic transmitter that transmits ultrasonic waves toward the ground surface, an ultrasonic receiver that receives the reflected wave reflected by the ground surface, a frequency of the transmitted wave from the ultrasonic transmitter, and a frequency of the reflected wave In a Doppler type ground vehicle speed detection device having a speed calculator that calculates the ground vehicle speed of the vehicle based on the frequency difference of
The ultrasonic transmitter is provided so that the side beam of the transmitted wave is irradiated perpendicularly to the ground surface.

The invention of claim 2 is an ultrasonic transmitter for transmitting ultrasonic waves toward the ground surface, an ultrasonic receiver for receiving reflected waves reflected by the ground surface, and the frequency of the transmitted waves. In the Doppler type ground vehicle speed detecting device having a speed calculator for calculating the ground vehicle speed of the vehicle based on the frequency difference between the frequency of the reflected wave received at a level equal to or higher than a preset threshold value, The speed calculator is provided with threshold value switching means for setting a high threshold value of the reception intensity output from the ultrasonic receiver during traveling and for setting the threshold value to a low value during low speed traveling at a predetermined speed or less. It is characterized by

[0013]

According to the first aspect of the present invention, the Doppler shift of the reflected wave of the side beam is reduced to zero by providing the ultrasonic transmitter so that the side beam of the transmitted wave is irradiated perpendicularly to the ground surface. To do. This eliminates the calculation error of the vehicle speed due to the reflected wave of the side beam.

According to the second aspect of the present invention, the threshold value of the reflected wave is set to a high value when traveling at a high speed above a predetermined speed, and the threshold value is set to a low value when traveling at a low speed below a predetermined speed. When the vehicle is traveling at high speed, the distance traveled by the vehicle from the transmission of the ultrasonic wave to the reception of the reflected wave is large, so the ultrasonic receiver receives the reflected wave reflected from a relatively distant location. Although it will be received, the vehicle speed can be calculated by the main beam of the reflected wave received by the ultrasonic receiver, and an accurate vehicle speed can be obtained.

[0015]

1 to 4 show a first embodiment of a Doppler type ground vehicle speed detecting device according to the present invention. In each of the drawings, the Doppler type vehicle speed detecting device is generally composed of an ultrasonic sensor unit 4 mounted so as to be located between the bottom of the rear trunk 2 of the vehicle 1 and the rear bumper 3, and a control circuit 5. .

In the ultrasonic sensor unit 4, the support members 6a and 6b attached to both sides of the housing 6 are provided in the rear trunk 2.
A cable 9 having a connector 8 that is fixed to the inclined portion 7a of the bracket 7 that is fixed to the bottom portion 2a of the housing 7 and that is connected to the control circuit 5 is pulled out from the rear portion of the housing 6. Both ends 7b and 7c of the bracket 7 are screwed to the bottom 2a of the rear trunk 2.

Accordingly, the ultrasonic sensor unit 4 has the contact surfaces 6c, 6c, which contact the brackets 7 of the support members 6a, 6b.
The inclination angle β in the traveling direction (Y direction) is determined by the inclination angle β of 6d and the inclination angle γ of the inclined portion 7a of the bracket 7.
In the present embodiment, as shown in FIG. 1, the ultrasonic signal transmitted from the ultrasonic sensor unit 4 includes a main beam 10 having different directing directions and a plurality of side beams 11 (11 _1, ... 11).
_n ) and divided into.

That is, the ultrasonic signal of the ultrasonic sensor unit 4 generally travels along the axis 12 of the ultrasonic sensor unit 4 and the main beam 10 in a direction inclined at an angle with respect to the main beam 10. It consists of the next side beam 11 ₁ . In this embodiment, as shown in FIG. 1, for the frequency difference of the first order side beams 11 ₁ to zero, so that the primary side beam 11 ₁ is traveling in a direction perpendicular to the road surface 13, super Attach the sound wave sensor unit 4 to the rear trunk 2
It is fixed to the bottom 2a. In addition, secondary side beam 1
Since 1 _{2 to} 11 _n are weaker than the intensity of the primary side beam 11 ₁ , they can be ignored.

In this case, the transmission angle θ of the main beam 10 with respect to the road surface 13 varies depending on the characteristics of the ultrasonic sensor unit 4, but is about 50 to 70 ° (preferably 55).
~ 65 °). The housing 6 of the ultrasonic sensor unit 4 has an ultrasonic transmitter 14 for transmitting ultrasonic waves (transmission waves).
And an ultrasonic receiver 15 for receiving the reflected wave (received wave) reflected by the road surface 13 are embedded. The ultrasonic transmitter 14 and the ultrasonic receiver 15 have substantially the same structure, and a vibrating body (not shown) for transmitting and receiving ultrasonic waves is housed inside.

The ultrasonic transmitter 14 and the ultrasonic receiver 1
5 is attached at an angle α in the X direction so that the main beam 10 of the transmitted wave transmitted from the ultrasonic transmitter 14 is reflected by the road surface 13 and received by the ultrasonic receiver 15. The angle α is determined by the mounting height of the ultrasonic sensor unit 4 and the distance between the ultrasonic transmitter 14 and the ultrasonic receiver 15 (separation distance in the X direction).

As described above, the main beam 10 of the transmitted wave transmitted from the ultrasonic transmitter 14 is transmitted to the rear of the vehicle 1 at the angle θ because the frequency of the reflected wave reflected on the road surface 13 is the transmitted wave. This is because the Doppler shift is performed, and the ground speed is calculated from the frequency difference between the transmitted wave and the received wave.
This Doppler shift frequency f _d is obtained by the following equation.

F _d = {Vcos θ / (C−Vcos θ)} × 2f ₀ (1) where V is the ground speed, f ₀ is the transmission frequency, θ is the transmission angle with respect to the road surface, and C is the speed of sound. Therefore, when the mounting angle of the ultrasonic sensor unit 4 is set, when the transmission angle θ is small, the frequency difference due to the Doppler shift becomes large, but the intensity of the reflected wave (received wave) from the road surface 13 becomes weak. Therefore, the conventional transmission angle θ is usually about 45 °.
Was set to.

As shown in FIG. 5, the control circuit 5 includes a transmission wave generation circuit 16 for generating a transmission wave and a transmission wave generation circuit 16
An amplifier 17 for amplifying the transmission signal output from the ultrasonic transmitter 14 and supplying it to the ultrasonic transmitter 14, an amplifier 18 for amplifying the reception signal output from the ultrasonic receiver 15, and a main beam with a reception level of the reception signal equal to or higher than a threshold value. 10, a main beam detection circuit 19, a threshold value setter 20 that sets a reception level threshold (threshold level) in the main beam detection circuit 19, a frequency of a reception wave output from the main beam detection circuit 19, and a transmission wave generation circuit Frequency difference detection circuit 21 for detecting the difference between the frequency of the transmission wave output from 16 and frequency difference detection circuit 2
The ground speed calculating circuit 22 calculates the ground speed based on the frequency difference obtained from the above 1.

Therefore, the control circuit 5 detects only the main beam 10 by the main beam detection circuit 19 and calculates the ground speed. However, as described above, the transmission wave transmitted from the ultrasonic transmitter 14 includes not only the main beam 10 traveling in the direction of the axis 12 but also the side beam 11 traveling in a direction deviated from the axis 12 by a different angle. , For example, when the road surface is submerged by rain, or when the road surface is frozen, the surface of the road surface becomes a mirror surface state without unevenness,
The reflected wave of the main beam 10 transmitted from the ultrasonic transmitter 14 almost travels to the rear of the vehicle 1 and the ultrasonic receiver 1
Not received by 5. Therefore, in the reception wave received by the ultrasonic receiver 15, the reception intensity of the main beam 10 is weakened and the reception intensity of the side beam 11 is relatively strong, and the difference between the two is small.

Further, when the vehicle 1 is traveling at a high speed, the distance that the vehicle 1 moves from the transmission of the ultrasonic wave to the reception of the reflected wave is large. The reflected wave reflected will be received. Also in this case, as in the case of the mirror surface state of the road surface 13 described above, the reflected wave received by the ultrasonic receiver 15 has a weakened reception intensity of the main beam 10 and a relatively increased reception intensity of the side beam 11. , The difference between the two becomes smaller.

FIG. 6 shows the experimental results for obtaining the relationship between the reception intensity and the frequency. In the same figure, a graph I shown by a one-dot chain line is an experimental result when the road surface 13 is a mirror surface state, and a graph II shown by a solid line is an experimental result when the vehicle speed is low speed below a predetermined speed (for example, 40 km / h). Yes, graph III shown by dashed line
Is an experimental result when the vehicle is traveling at a high speed of a predetermined speed (for example, 40 km / h) or more.

From the graph I in the figure, when the road surface 13 is a mirror surface, the frequency peaks at -12 dB at about 73 KHz, and becomes -23 dB at the frequency of about 74 KHz. Has a peak of 0 dB at about 72 KHz, and becomes -20 dB at a frequency of about 72 KHz. Therefore, the difference in intensity between the main beam 10 and the side beam 11 is as large as 20 dB during normal traveling, whereas it is as small as 11 dB when the road surface 13 is a mirror surface. From this also, when the road surface 13 is a mirror surface state, the main beam 1
It becomes difficult to distinguish between 0 and the side beam 11, and an error occurs when calculating the vehicle speed.

Therefore, in this embodiment, as shown in FIG. 1, the ultrasonic sensor unit 4 is fixed to the bottom portion 2a of the rear trunk 2 so that the traveling direction of the side beam 11 is perpendicular to the road surface 13. . As a result, the Doppler shift frequency f _d becomes zero according to the above-mentioned formula (1).
Therefore, even if the side beam 11 is received by the ultrasonic receiver 15, a frequency difference does not occur. Therefore, the side beam 11 has no influence when calculating the vehicle speed, and the occurrence of a vehicle speed error by the side beam 11 is prevented.

Therefore, for example, in the traction control device or the antilock brake device, the traction control or the braking control is performed based on the ground speed, so that the control delay is eliminated and the wheel slip or the wheel lock is prevented. Appropriate control can be performed. 8 to 10 show a second embodiment of the present invention.

In FIG. 8, reference numeral 25 is a peak value detection circuit for detecting the peak value received by the ultrasonic receiver 13, and outputs a signal having a magnitude corresponding to the peak value. A threshold switching circuit 26 is supplied with the vehicle speed signal output from the peak value detection circuit 25. For example, when the peak value received by the ultrasonic receiver 15 is equal to or greater than the initial set value L ₀ , the threshold value is set to L ₀ . When the peak value is L ₀ or less and L ₁ or more, the threshold value is set to L ₁ , and when the peak value is L ₁ or less and L ₂ or more, the threshold value is L ₂
Set to. The threshold switching circuit 26 has a vehicle speed of 40 km, for example.
When driving at a low speed of less than / h, the threshold is L
_When the vehicle speed is set to ₀ and the vehicle speed is 40 to 80 km / h, the reception strength is weak, so the threshold value is set to L ₁ and the vehicle speed is 8 km / h.
When the vehicle is traveling at a high speed above, the threshold is set to L because the reception intensity is weak.
Set to ₂ .

As described above, when the vehicle 1 is traveling at a high speed, the distance traveled by the vehicle 1 from the transmission of the ultrasonic wave to the reception of the reflected wave is large. The reflected wave reflected from a far distance will be received. Therefore, the intensity of the received wave received by the ultrasonic receiver 15 is as shown in FIG. 8 when the vehicle speed is 40 km / h or less and the vehicle is traveling at a low speed. As the difference increases and the vehicle speed increases, the reception intensity of the main beam 10 weakens and the reception intensity of the side beam 11 relatively increases. As shown by the broken line, the intensity difference between the main beam 10 and the side beam 11 Becomes smaller.

However, even if the vehicle speed becomes high, it is possible to detect only the frequency of the received wave of the main beam 10 by switching the threshold value from L ₀ to L ₁ or L ₂ , and the vehicle speed calculation circuit 22 with respect to ground can detect the vehicle speed. Side beam 1 when calculating
A vehicle speed error due to 1 is prevented. Further, even when the road surface 13 becomes a mirror surface state, the intensity difference between the main beam 10 and the side beam 11 becomes small, but the threshold value is changed from L ₀ to L _1.
Alternatively, by switching to L ₂ , it is possible to detect only the frequency of the received wave of the main beam 10, and it becomes possible to obtain an accurate ground speed even in the state where the tire is likely to slip.

FIG. 10 is a flowchart of the processing executed by the threshold switching circuit 26. In the figure, in step S1 (hereinafter “step” is omitted), the ultrasonic receiver 15
When the signal strength of the received wave received at is high, the process proceeds to S2, and the threshold value is set to L ₀ . However, in S1, when the signal intensity of the received wave received by the ultrasonic receiver 15 is small, the process proceeds to S3, where it is confirmed that the signal intensity is small, and S
At 4, the threshold is set to L ₁ .

In step S3, the ultrasonic receiver 15 receives the signal.
If the signal strength of the received wave received is weak, proceed to S5.
Confirm that the signal strength is weak and proceed to S6
To L ₂Set to. In the above embodiment, the threshold value is set to 3 levels.
I switched to, but not limited to this, for example
Signal strength of the received wave received by the wave receiver 15
Depending on the threshold, there are 3 or more levels, for example 5 or 6 levels.
You may make it switch to.

In each of the above embodiments, the ultrasonic transmitter 11
Although the integrated ultrasonic sensor unit 4 in which the ultrasonic wave receiver 13 and the ultrasonic wave receiver 13 are housed in the same housing 6 is used, the invention is not limited to this, and the ultrasonic wave transmitter 14 and the ultrasonic wave receiver 15 are respectively provided. Needless to say, a configuration in which they are individually attached may be adopted.

[0036]

As described above, according to the first aspect, since the ultrasonic transmitter is provided so that the side beam of the transmitted wave is irradiated perpendicularly to the ground surface, the Doppler shift of the reflected wave of the side beam is provided. Can be made zero, and thereby, the calculation error of the vehicle speed due to the reflected wave of the side beam is eliminated, and a more accurate ground speed can be obtained.

Further, according to claim 2, the threshold value of the reflected wave is set to a high value when the vehicle is traveling at a high speed above a predetermined speed, and the threshold value is set to a low value when the vehicle is traveling at a low speed below a predetermined speed. When the vehicle is traveling at high speed, the distance traveled by the vehicle from the transmission of ultrasonic waves to the reception of reflected waves is large, so the ultrasonic receiver receives the reflected waves reflected from relatively long distances. However, by setting the threshold value to a low value, the vehicle speed can be calculated only by the received signal of the main beam received by the ultrasonic receiver even when traveling at high speed, and the calculation error of the vehicle speed due to the reflected wave of the side beam is eliminated. , Accurate vehicle speed can be obtained.

[Brief description of drawings]

FIG. 1 is a front view of a first embodiment of a Doppler type ground vehicle speed detecting device according to the present invention.

FIG. 2 is a rear view of the vehicle.

FIG. 3 is a diagram of an ultrasonic sensor unit.

FIG. 4 is a perspective view showing a state in which an ultrasonic sensor unit is attached to a rear portion of a vehicle body.

FIG. 5 is a block diagram of a control circuit.

FIG. 6 is a graph showing an experimental result in which a relationship between reception intensity and frequency is obtained.

FIG. 7 is a block diagram of a control circuit according to a second embodiment of the present invention.

FIG. 8 is a graph showing the difference in received signal strength between low-speed traveling and high-speed traveling.

FIG. 9 is a flowchart of processing executed by a threshold detection circuit.

[Explanation of symbols]

 1 Vehicle 2 Rear Trunk 4 Ultrasonic Sensor Unit 5 Control Circuit 7 Bracket 10 Main Beam 11 Side Beam 14 Ultrasonic Transmitter 15 Ultrasonic Receiver 16 Transmitted Wave Generating Circuit 19 Main Beam Detection Circuit 20 Threshold Setter 21 Frequency Difference Detection Circuit 22 Ground Speed Calculation Circuit 25 Peak Value Detection Circuit 26 Threshold Switching Circuit

Claims (2)

[Claims] 1. An ultrasonic transmitter for transmitting ultrasonic waves toward the ground surface, an ultrasonic receiver for receiving reflected waves reflected by the ground surface, a frequency of a transmitted wave from the ultrasonic transmitter, and In a Doppler type ground vehicle speed detecting device having a speed calculator for calculating the ground vehicle speed of the vehicle based on the frequency difference from the frequency of the reflected wave, the side beam of the transmitted wave is radiated vertically to the ground surface. A Doppler-type ground vehicle speed detecting device, wherein the ultrasonic transmitter is provided as described above. 2. An ultrasonic transmitter for transmitting ultrasonic waves toward the ground surface, an ultrasonic receiver for receiving reflected waves reflected by the ground surface, and the frequency of the transmitted waves and a preset threshold value or more. In a Doppler type ground vehicle speed detecting device having a speed calculator for calculating the ground vehicle speed of the vehicle based on the frequency difference from the frequency of the reflected wave received at the level of A threshold value switching means for setting the threshold value of the reception intensity output from the device to a high value and setting the threshold value to a low value when traveling at a low speed of a predetermined speed or less is provided in the speed calculator. Ground vehicle speed detector.