JPH05157832A - Doppler type vehicle speed sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] In a Doppler type vehicle speed sensor that has a transmission unit, a reception unit and a signal processing unit and detects the vehicle speed by utilizing the Doppler effect of the wave, enhances the intensity of the wave received by the reception unit. As a result, the variation width of the vehicle speed detection value output by the signal processing unit is reduced. A transmitter 10 and a receiver 12 are attached to a rear end portion of a bottom surface of a vehicle body so as to face rearward of a vehicle and have a relative positional relationship in which the receiver 12 is separated from the transmitter 10 rearward of the vehicle by a predetermined distance. Among the waves in which the transmission wave from the transmission unit 10 is diffusely reflected on the road surface, the one having a high intensity close to the wave in which the transmission wave is regularly reflected on the road surface is received by the reception unit 12, and the reception intensity is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Doppler type vehicle speed sensor for detecting a vehicle speed, which is a moving speed of a vehicle body, by utilizing the Doppler effect of waves, and particularly, to suppress the variation width of the detected value of the vehicle speed to be small. It is about technology.

[0002]

2. Description of the Related Art A Doppler type vehicle speed sensor is generally (a) mounted on a vehicle body to direct a transmitted wave to a road surface, as described in, for example, Japanese Patent Application No. 2-245679 of the present applicant. And a receiving unit that receives the received wave that is transmitted irregularly on the road surface (b)
And a signal processing unit that outputs the vehicle speed that is the moving speed of the vehicle body based on the frequencies of the transmitted wave and the received wave.

The term "vehicle speed" used herein means not only the longitudinal speed of the vehicle body but also the lateral speed, for example. In addition, in this Doppler type vehicle speed sensor system, both the transmitting unit and the receiving unit face forward in both forward and reverse directions of vehicle body movement (equal to both forward and reverse directions of vehicle speed to be detected by the Doppler type vehicle speed sensor). There is a formula and a backward formula that faces in the opposite direction. For example, when the Doppler type vehicle speed sensor detects the front-rear direction speed of the vehicle body, normally, both the transmitting unit and the receiving unit face the front side of the vehicle body (forward direction) and the rearward direction (reverse direction) of the vehicle body.
The one that faces is said to be the backward type. The vehicle speed detected by the Doppler type vehicle speed sensor is used in a vehicle motion control device such as an antilock control device and a traction control device. An example of such an antilock control device is described in the above-mentioned application specification, Japanese Patent Laid-Open No. 63-64861, and the like.

In the Doppler type vehicle speed sensor (hereinafter, simply referred to as a preceding device) described as an example in the specification of the application, the transmitting unit and the receiving unit have the following relative positional relationship with the vehicle body. Was installed.
That is, when the vehicle body is viewed horizontally from a direction perpendicular to the direction of movement of the vehicle body, the transmitter portion and the receiver portion are mounted in such a relative positional relationship that they overlap each other.

[0005]

In the Doppler type vehicle speed sensor, the transmitted wave generally propagates from the transmitting section toward the road surface using air between the transmitting section and the road surface as a medium. There is a flow of air, which is usually faster at high vehicle speeds than at low vehicle speeds. This air flow tends to scatter the waves propagating through it, and this tendency is generally stronger the faster the flow is, so generally for Doppler type vehicle speed sensors,
When the vehicle speed is high, the strength of the received wave received by the receiving unit, that is, the reception strength tends to be lower than when the vehicle speed is low.

Further, in the Doppler type vehicle speed sensor, generally, the body moves in the positive direction between the time when the wave is emitted from the transmitting portion and the time when the wave is irregularly reflected on the road surface and reaches the receiving portion. Move in the direction. Therefore, when the Doppler type vehicle speed sensor is of the forward type, the diffuse reflection wave received by the receiving unit is closer to the regular reflection wave of the transmission wave on the road surface than when the vehicle speed is high and when it is low. (Hereinafter, the receiver simply approaches the regular reflection wave)
On the other hand, in the case of the backward type, the diffuse reflection wave received by the receiving unit is farther from the specular reflection wave in which the transmission wave is specularly reflected on the road surface (hereinafter, simply the reception unit is the specular reflection wave. Away from). On the other hand, the intensity distribution of diffusely reflected waves is usually
It decreases as the distance from the regular reflection wave increases. Therefore, when the Doppler type vehicle speed sensor is a backward type,
The movement of the receiving unit also tends to reduce the reception intensity.

Therefore, in order for the Doppler type vehicle speed sensor to accurately detect the vehicle speed, it is necessary that the variation width of the output signal from the receiving unit does not become small even if the reception intensity decreases, that is, the reception intensity decreases. Even so, it is important that the receiving section receives a sufficiently strong diffuse reflection wave.

However, when the transmitting unit and the receiving unit overlap each other as in the prior art device, the receiving unit cannot receive a sufficiently strong diffuse reflection wave. This is because the receiving unit can receive only the diffusely reflected wave that is far from the specularly reflected wave. Therefore, in the preceding device, when the vehicle speed is high, the variation width of the signal output by the receiving unit according to the received wave is larger than when the vehicle speed is low, and the signal processing unit outputs the signal based on the output signal. There is a problem that there is a strong tendency that the variation range of the detected values of the vehicle speed becomes large. This problem becomes particularly noticeable when the Doppler type vehicle speed sensor is of the backward type.

In view of these circumstances, an object of the present invention is to reduce the variation width of the detected value of the vehicle speed due to the reduction of the reception intensity.

[0010]

In order to solve this problem, the gist of the present invention is to: (a) A transmitter that is attached to a vehicle body and that transmits a transmitted wave obliquely to the road surface; A receiving unit that receives the received wave that is diffusely reflected by
(b) In a Doppler-type vehicle speed sensor including a signal processing unit that outputs a vehicle speed that is the moving speed of the vehicle body based on the frequencies of the transmitted wave and the received wave, the transmitting unit and the receiving unit are placed on the vehicle body, and the receiving unit is This is because the transmitter is mounted so as to have a relative positional relationship that deviates in a direction close to the traveling direction of the transmitted wave from both the forward and reverse directions of the vehicle body movement from the transmitting unit.

[0011]

In the Doppler type vehicle speed sensor according to the present invention, the transmitter and the receiver are separated from the vehicle body, and the receiver is separated from the transmitter in a direction close to the traveling direction of the transmitted wave in both the forward and reverse directions of the vehicle movement. It is attached with a positional relationship. Explaining using a specific example, when the Doppler type vehicle speed sensor is a forward-looking type, the receiving unit has a relative positional relationship in which the receiving unit deviates from the transmitting unit to the front of the vehicle, and when the Doppler-type vehicle speed sensor is a backward-facing type, the receiving unit transmits They are attached so that they have a relative positional relationship in which they are dislocated from the rear portion to the rear of the vehicle.

Therefore, it becomes possible to mount the receiving unit at a position closer to the regular reflection wave from the road surface than in the prior device in which the receiving unit is mounted so as to overlap with the transmitting unit in the direction perpendicular to the direction of movement of the vehicle body. The stronger diffuse reflection wave in the preceding device can be received, and the reception intensity is increased. If the reception strength is increased, the signal output by the reception unit according to the reception wave will reflect the true frequency of the reception wave more faithfully, and the influence of the decrease in reception strength due to the increase in vehicle speed from the reception unit It becomes difficult to receive the output signal, and the variation width of the output signal becomes small. When the variation width of the output signal from the receiving unit becomes smaller, the variation width of the frequency of the received wave acquired by the signal processing unit based on the output signal also becomes smaller, and thus the variation width of the detected value of the vehicle speed also becomes smaller. ..

[0013]

As described above, according to the present invention, since the reception intensity is higher than that of the preceding device, the output signal from the receiving section is less likely to be affected by the decrease in reception intensity due to the increase in vehicle speed, and the vehicle speed is reduced. It is possible to obtain the effect of reducing the variation width of the detected value of.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An ultrasonic vehicle speed sensor which is an embodiment of the present invention will be described in detail below with reference to the drawings. As shown in FIG. 1, this ultrasonic type vehicle speed sensor (hereinafter, simply referred to as vehicle speed sensor) detects the longitudinal speed (hereinafter, simply referred to as vehicle speed) of a vehicle body by utilizing the Doppler effect of ultrasonic waves as waves. It includes a transmitter 10, a receiver 12, and a signal processor 14. The transmission unit 10 transmits ultrasonic waves toward the road surface. The receiving unit 12 receives a wave in which the ultrasonic waves are diffusely reflected on the road surface, and outputs a signal representing a sine wave in which peaks and valleys alternate with each other as the sound pressure of the received wave changes with the passage of time. To do.

The transmitter 10 and the receiver 12 both have a relative positional relationship at the rear end of the bottom surface of the vehicle body and as shown in FIG. Then installed. Further, as shown in the figure, both the transmission unit 10 and the reception unit 12 face the rear of the vehicle and are inclined at the same angle θ with respect to the road surface.

The signal processing section 14 calculates the frequency of the received wave based on the output signal from the receiving section 12. Specifically, the sine wave represented by the output signal from the receiver 12 is converted into a pulse wave by validating only those peaks of which the signal level exceeds the threshold level, and the sine wave is converted into a pulse wave according to the number of pulses. To calculate the frequency of the received wave. The signal processing unit 14 further determines that the actual incident angle of the ultrasonic wave incident on the road surface while the vehicle is running and the actual output angle of the ultrasonic wave received by the receiving unit 12 and the road surface are both close to the mounting angle θ. Under the assumption, the vehicle speed V is calculated using the following equation.

V = C (Ft-Fr) / ((Ft + Fr) COS θ) where C: sound velocity of ultrasonic wave Ft: frequency of transmitted wave (hereinafter, simply referred to as transmission frequency) Fr: frequency of received wave (Hereinafter, simply referred to as reception frequency)

By the way, in the preceding device, as shown by the solid line graph in FIG. 3, when the vehicle speed exceeds about 100 km / h, the variation width of the vehicle speed detection value (hereinafter, simply referred to as the detection variation width) increases rapidly. There was a problem that it would end up.
The cause of this problem is considered as follows. That is, when the vehicle speed is high, the reception intensity becomes lower than when the vehicle speed is low, and the sine wave represented by the output signal from the receiving unit 12 has a threshold level even though it should normally exceed the threshold level. This is because the tendency that a peak that cannot be exceeded is increased, the number of pulses of the pulse wave decreases, and the reception frequency Fr calculated in the signal processing unit 14 becomes lower than the true value.

Therefore, in order to solve this problem, in the present embodiment, the transmission unit 10 and the reception unit 12 are arranged so that the reception unit 12 is separated from the transmission unit 10 by the distance L toward the rear of the vehicle.
The relative positional relationship of is determined. The receiving unit 12 is designed to be closer to the regular reflection wave from the road surface than in the preceding device.

As a result, as shown by the broken line graph in the figure, the increase in the detection variation width after the vehicle speed exceeds about 100 km / h is suppressed in the present embodiment to be smaller than that in the preceding device. The effect that the detection variation width can be suppressed to a small value as a whole vehicle speed that can be detected by the vehicle speed sensor is obtained.

The broken line graph is obtained when the following values are given to the respective parameters. Mounting angle θ: 40 ° Distance H between each of the transmitter 10 and the receiver 12 and the road surface:
300mm Sound velocity C: 350m / s Distance L: 80mm

In this embodiment, the distance L is 80
Although the ultrasonic wave is selected as mm, the ultrasonic wave is transmitted by 1 mm.
It is approximately equal to the distance that the vehicle body moves forward, that is, the distance that the receiving unit 12 moves from the time when it goes out of 0 and is reflected on the road surface to reach the receiving unit 12. In this way, the distance L is selected to be 80 mm because when the vehicle speed is about 100 km / h, the receiving unit 12 has substantially the same diffused reflection wave received by the preceding device when the vehicle is stopped, and the emission angle from the road surface. That is, the irregular reflected waves having almost the same intensity are received, and thereby the increase in the detection variation width due to the increase in the vehicle speed is suppressed to be small.

As is apparent from the above description, in the present embodiment, the effect that the detection variation width when the vehicle speed is high can be suppressed to be smaller than that in the preceding device, the effect is as follows. You can also get the effect.

The vehicle speed detected by the vehicle speed sensor is used, for example, in a vehicle motion control device such as an antilock control device or a traction control device. However, the detected vehicle speed is not used as it is, but within a certain time. It is usual to use the obtained vehicle speeds by averaging them. Therefore, as in the present embodiment, if the vehicle speed detection variation width is reduced, it is possible to shorten the time required for the averaging, it is possible to sensitively detect the change in the true value of the vehicle speed, and eventually the vehicle motion control. This also has the effect of improving the control response of the device.

Although one embodiment of the present invention has been described in detail with reference to the drawings, the present invention can be implemented in other modes.

For example, in the above embodiment, the actual incident angle at which ultrasonic waves are incident on the road surface while the vehicle is running, and the receiving section 1
The vehicle speed V is calculated under the assumption that the actual output angles formed by the ultrasonic waves received by the vehicle and the road surface are approximated to the mounting angle θ which is one aspect common to the reference incident angle and the reference output angle. However, it is also possible to obtain the actual incident angle and the actual outgoing angle and calculate the vehicle speed V based on them.

In addition to the above, the present invention can be implemented in various modified and improved modes based on the knowledge of those skilled in the art without departing from the scope of the claims.

[Brief description of drawings]

FIG. 1 is a side view conceptually showing the structure of an ultrasonic vehicle speed sensor which is an embodiment of the present invention.

FIG. 2 is a side view for explaining a relative positional relationship between a transmitter and a receiver in the above embodiment.

FIG. 3 is a graph showing an example of the variation width of the detected value of the vehicle speed and an example of the variation width of the preceding device in the above embodiment.

[Explanation of symbols]

 10 transmitter 12 receiver 14 signal processor

Claims (1)

[Claims] 1. A transmission unit both mounted on a vehicle body for transmitting a transmission wave obliquely toward a road surface, a reception unit for receiving a reception wave in which the transmission wave is diffusely reflected on the road surface, and each of the transmission wave and the reception wave. A Doppler type vehicle speed sensor including a signal processing unit that outputs a vehicle speed that is the moving speed of the vehicle body based on the frequency of the vehicle body, wherein the transmitting unit and the receiving unit are the vehicle body, and the receiving unit is the forward / reverse movement of the vehicle body from the transmitting unit. A Doppler type vehicle speed sensor, wherein the Doppler type vehicle speed sensor is mounted so as to have a relative positional relationship that deviates in a direction close to a traveling direction of the transmitted wave in both directions.