JPH02236451A - Detector for frictional coefficient of road surface - Google Patents

Abstract

PURPOSE:To perform the control in consideration of the braking condition and to inexpensively detect the frictional coefficient of the road surface by emitting an ultrasonic wave and measuring the pulse width of the reflected wave from the road surface. CONSTITUTION:A short pulse electric signal having an ultrasonic frequency is generated by a transmitter 1. This electric signal is sent to a transmitter- receiver 3 through a transmission/reception switch 2 and is radiated to air from the transmitter-receiver 3 as an ultrasonic pulse. This ultrasonic pulse is propagated in air and reaches the road surface and is reflected on the road surface and is received as the reflected wave by the transmitter-receiver 3. Since the frictional coefficient of the road surface is related to the hardness of the road surface and this hardness is related to the reflection coefficient of the ultrasonic wave, the pulse width of the reflected wave is measured by a pulse width measuring part 5 to detect the frictional coefficient of the road surface.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a road surface palm 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 the road surface while driving. It is related to.

``Prior art'' A method of electronically controlling the degree of braking in order to prevent the wheels from locking due to road surface conditions and causing a skid when sudden braking is applied while the vehicle is in motion.
A skid prevention device called LB (anti-lock 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 the system works, the tires will slip on the road surface, making it difficult to control the vehicle's speed. Furthermore, if the tires start to skid in this way, the braking force of each tire is different, causing the car 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 brake application 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] The 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 this electric signal into an ultrasonic wave and transmits it onto the road surface. Send it towards
It is equipped with a transducer that receives reflected waves reflected from the road surface and converts them into electrical signals, and a pulse width measuring device that measures the pulse width of the received reflected waves, and is installed in a car.

[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.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1st
The figure 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 receiver amplifier, and (5) is a pulse width measuring device. Next, the operation will be explained. A transmitter (1) generates a short pulsed electrical signal having an ultrasonic frequency. This electrical signal is sent to the transducer (3) via the transceiver switch (2), and is emitted into the air as an ultrasonic pulse from there. 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 ultrasonic pulses emitted from the transducer (3). In the figure, (D) shows the directivity of the ultrasonic waves at each point (PO). (Pi) and (P2) indicate each position on the road surface that the ultrasonic waves reach, and (R) indicates the road. As shown in Figure 2, the ultrasonic pulses emitted from the transducer (3) have the shape of a searchlight or fan beam, and have a wide range of directivity (D), but the characteristics of the transducer (3) from,
Ultrasonic pulses with the maximum energy are emitted to the point (PO) facing each other on the vertical line, and the ultrasonic pulses are emitted as they deviate from this vertical line toward points (PL) and (P2) having angles θ1 and θ2. The energy of ultrasonic waves is low. Furthermore, the ultrasonic waves that arrive become weaker as the distance they reach becomes longer. In other words, as the distance increases from OPO to OPI to OP2, the energy that arrives becomes weaker. Next, the ultrasonic waves that reached the road (R) in this way are
The waves reflected at each point on the road surface are received by the transducer (3), but in this case as well, the angle of incidence on the transducer (3) decreases according to each point, that is, (PO) → (P1 )→(
P2) becomes weaker in this order.

Furthermore, the intensity of the reflected wave reflected on the road surface depends on the condition of the road surface. In other words, when the road surface is hard, the reflection intensity is strong,
When the road surface is soft, the reflection intensity also becomes weaker.

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

As shown in Fig. 2, when the transducer (3) deviates from the position of the point (PO) facing each other on the vertical line in the direction of the points (Pi) and (P2) where the emission angle is θ1θ2, the third As shown in the figure, the intensity of the reflected wave from the soft road surface (R1) is at the point (
P1), that is, θ1 is below the threshold value, but on a hard road surface (R
The intensity of the reflected wave from 2) up to point (P2), that is, θ2, is:
Indicates a value above the threshold.

Next, we will explain the arrival time of the reflected waves from each point (PO), (PL), (P2>.The ultrasonic wave emitted from the transducer (3) reaches each point (PO), (PI) on the road surface. , (P2)
The respective times tpo, tpl, 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 if the road surface is hard, even a reflected wave 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 different from the pulse width (W2) from the soft road surface (Rl).
W1) compared to {2×oP2/■}-{2×○P 1
/v).

Therefore, by measuring the pulse width (W) of the reflected wave that exceeds a predetermined threshold value (RO) using the pulse width measuring device (5) shown in Figure 1, information regarding the friction coefficient of the road surface can be obtained in advance. It can be provided as information to the stability control device.

Please note that this is caused by the vibration of the car body while the car is running.
In order to avoid the influence of changes in the distance between the transducer (3) and the road (R), more precise measurements can be made by providing STC (ffi degree time control).

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 vehicle after taking into account the degree of brake application. This has the effect of making it possible.

[Brief explanation of drawings]

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. lit diagram m2 diagram

Claims (1)

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