JPH0549943B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a road surface friction coefficient detection device that is mounted on a vehicle such as an automobile (hereinafter collectively referred to as a vehicle) and detects the friction coefficient of a road surface while driving. It is something.

[Prior art] In order to prevent the risk of the wheels locking up and skidding due to road surface conditions when sudden braking is applied while the vehicle is running, anti-lock brakes (ALB) are used to electronically control the degree of brake application. A skid prevention device called ``break'' is widely used.

A car's brakes apply braking force to the wheels according to the pressure applied to the brake pedal, controlling the speed of the car and stopping the car. However, if the road surface is slippery, the braking force is applied to the wheels. Even if it works, the tires will slip on the road and the car's speed will not be controlled properly. Furthermore, when the tires start to slip, the braking force of each tire is different, causing the vehicle to skid and causing an accident. In order to prevent this skid, a skid prevention device detects when a tire actually begins to skid on the road surface and applies braking force to the wheel until the tire stops skidding, regardless of the pressure applied to the brake pedal. Forced control is used to prevent the vehicle from skidding in such cases.

[Problems to be Solved by the Invention] Conventional skid prevention devices are configured as described above, so they can only be controlled after the tires actually begin to skid on the road surface, thereby preventing the vehicle from skidding. There is a problem in that the original and sufficient performance of prevention cannot be obtained.

However, by detecting the friction coefficient of the road surface in advance and using this as data to control the degree of application of the brakes from the beginning, it becomes possible to develop a skid prevention device that can effectively prevent skids.

This invention was made in order to solve this problem, and the object is to obtain a road surface friction coefficient detection device that can detect the friction coefficient of the road surface at any time while the vehicle is running and provide it as data to the stability control device. It is said that

[Means for Solving the Problems] A road surface friction coefficient detection device according to the present invention includes a transmitter that generates a pulsed electric signal having an ultrasonic frequency, and a transmitter that converts the electric signal into an ultrasonic wave and sends it onto the road surface. The device is equipped with a transducer that transmits the reflected wave toward the road surface, receives the reflected wave reflected on the road surface, and converts it into an electrical signal, and a pulse width measuring device that measures the pulse width of the received reflected wave. did.

[Effect] The coefficient of friction of the road surface is related to the hardness of the road surface, and the hardness of the road surface is related to the reflection coefficient of ultrasonic waves, so it is possible to detect the coefficient of friction of the road surface by measuring the pulse width of the reflected waves. Become.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a road surface friction coefficient detection device which is an embodiment of the present invention. In the figure, 1 is a transmitter, 2 is a transmitter/receiver switch, 3 is a transducer, 4 is a receiving amplifier, is a pulse width measuring instrument.

Next, the operation will be explained. A transmitter 1 generates a short pulse-like electrical signal having an ultrasonic frequency. This electrical signal is sent via the transmitter/receiver switch 2 to the transducer 3, from which it is emitted into the air as an ultrasonic pulse. The emitted ultrasonic pulse propagates through the air, reaches the road surface, is reflected on the road surface, and is received by the transducer 3 as a reflected wave.

Fig. 2 is a diagram showing an example of the directivity of the ultrasonic pulse emitted from the transducer 3. In the figure, (D) shows the directivity of the ultrasonic wave, and each point (P0), (P1), (P2) are each position on the road surface that the ultrasonic waves reach, and (R) indicates the road. As shown in Figure 2, the ultrasonic pulse emitted from the transducer 3 has a shape such as a searchlight or a fan beam, and has a wide directivity (D), but due to the characteristics of the transducer 3, its vertical Ultrasonic pulses with the maximum energy are emitted to the point (P0) facing each other on the line, and as they deviate from this vertical line toward points (P1) and (P2) having angles θ1 and θ2, they are emitted. The energy of ultrasonic waves is low.

Furthermore, the arriving ultrasonic waves become weaker as the distance they reach becomes longer. In other words, as the distance increases from 0 to 1 to 2, the energy that arrives becomes weaker.

Next, the ultrasonic waves that have reached the road (R) in this way are reflected at various points on the road surface, and the reflected waves are received by the transducer 3. In this case as well, the transducer 3
The angle of incidence becomes smaller at each point, that is, in the order of (P0) → (P1) → (P2).

Furthermore, the intensity of the reflected wave reflected on the road surface depends on the condition of the road surface. That is, when the road surface is hard, the reflection intensity is strong, and when the road surface is soft, the reflection intensity is weak.

Under such conditions, the reflected wave received from the transducer 3, converted into an electrical signal, and amplified by the reception amplifier 4 becomes as shown in FIG. Here, (R1) is the intensity of the reflected wave from the soft road surface,
(R2) indicates the intensity of reflected waves from a hard road surface, and (R0) indicates a predetermined threshold value.

As shown in Figure 2, from the position of the point (P0) where the transducer 3 faces on the vertical line, the emission angles θ1, θ2
When shifted in the direction of points (P1) and (P2) where , the intensity of the reflected wave from the hard road surface (R2) shows a value above the threshold value up to point (P2), that is, θ2.

Next, the arrival time of reflected waves from each point (P0), (P1), and (P2) will be explained. The ultrasonic waves emitted from the transducer 3 are transmitted to each point (P0), (P1), (P2) on the road surface.
The respective times tp0, tp1, tp2 at which the reflected waves are received by the transducer 3 are as follows:
If the propagation speed of ultrasonic waves in the air is v, then 2×0/v, 2×1/v, 2×2/
It becomes v. Furthermore, when the road surface is hard, even reflected waves reflected from a relatively far point (P2) on the road surface can be received relatively strongly.

Therefore, as shown in Fig. 4, the pulse width (W2) from the hard road surface (R2) is {2×2/v}− compared to the pulse width (W1) from the soft road surface (R1).
It has a spread of {2×1/v}.

Therefore, by measuring the pulse width (W) of the reflected wave exceeding a predetermined threshold value (R0) using the pulse width measuring device 5 shown in FIG. It can be provided as information to the prevention device.

In addition, in order to avoid the influence of changes in the distance between the transducer 3 and the road (R) caused by vibrations of the car body while the car is running, the STC (impression time control)
By providing this, more precise measurements can be made.

Furthermore, by attaching the transducer 3 at a predetermined angle to the road surface, it becomes possible to appropriately adjust the detection sensitivity depending on the road surface condition.

[Effects of the Invention] As explained above, this invention enables the road surface friction coefficient to be detected at low cost by a simple method of emitting ultrasonic waves and measuring the pulse width of the reflected waves reflected from the road surface, and is useful for automobiles. The system can be installed on a vehicle and provide the road surface friction coefficient as data to the electronic stability control system at any time while driving, so the electronic stability control system can detect the friction coefficient of the road surface in advance and control the brakes after carefully considering the degree of application. This has the effect of making it possible.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing an embodiment of the present invention, Figure 2 is a diagram showing an example of the directivity of emitted ultrasonic waves, Figure 3 is a diagram showing the intensity of reflected waves, and Figure 4 is a diagram showing the road surface. A diagram showing differences in reflected waves due to differences in situations. 1 is a transmitter, 2 is a transmitter/receiver switch, 3 is a transducer,
4 is a receiving amplifier, 5 is a pulse width measuring device, R1 is a reflected wave from a soft road surface, and R2 is a reflected wave from a hard road surface. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A transmitter mounted on a vehicle that generates a pulsed electric signal with an ultrasonic frequency, converts this electric signal into an ultrasonic wave, sends it out onto the road surface, and receives the reflected waves reflected on the road surface. A road surface friction coefficient detection device comprising: a transducer that converts into an electrical signal; and a pulse width measuring device that measures the pulse width of a reflected wave received by the transducer.