JPH035521B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vehicle tread measurement device that can be applied to a vehicle type discrimination device used, for example, at a toll booth on an automobile road or at a place where traffic volume surveys are carried out.

It has been proposed in the past to measure the tread of a vehicle and use the measured value as a means of identifying the vehicle type. The tread of a vehicle refers to the distance L _n between the centers of the tires 2 of the vehicle (automobile) 1 in FIG. An example of the above-mentioned proposal is one described in, for example, Japanese Patent Laid-Open No. 19051/1983. In this known example, as shown in FIG. 2, two length measuring converters 3a and 3b are buried in the road, and a vehicle 1
The left and right tire positions and tire tread widths are measured separately, and the results are used to calculate the tread by an arithmetic circuit.

FIG. 3 is an explanatory diagram of the configuration of such a length measuring converter. In the figure, 4 is a flexible conductor, 5 is a pressure-sensitive conductive rubber, 6 is a resistor, and 7 is a tire.

When the tire 7 presses the pressure-sensitive conductive rubber 5 via the flexible conductor 4, only the pressed portion of the rubber becomes conductive, and the other portions remain insulated. Therefore, let a constant current flow between A and B,
When measuring the voltage between A and B, when there is pedal pressure from the tire 7, the resistor 6 is short-circuited over a length corresponding to the pedal pressure part by the conductive rubber 5. , B changes, and a voltage also appears between A and C. Tire 7 from the voltage change between A and B and the voltage between A and C
The tread width WL and tread pressure position PL can be determined.

Now, in the length measuring converter as described above, when there is no pedal pressure from the tire 7, it is necessary to check whether there is any insulation failure or short circuit between the flexible conductor 4 and the resistor 6. There are times when you want to check for any malfunctions. In such a case,
As shown in FIG. 4A, the test is carried out by measuring the potential V _D between one end C of the flexible conductor 4 and the ground with a current flowing through the resistor 6 from the constant current source 8.

However, when measuring the potential V _D when there is no pedal pressure from the tires, the resistance value due to the pressure-sensitive conductive rubber is several tens of MΩ or more, and the resistance value due to the pressure-sensitive conductive rubber is over several tens of MΩ.
Since a capacitance is formed between the two, the measured value is affected by noise, causing a situation where the measured value is not constant. Therefore, as shown in FIG. 4B, if a high resistance R ₃ is connected between the terminal C and the ground to clamp the potential, it will be less susceptible to noise, but this time, when the pedal pressure from the tire 7 is applied,
The resistance R ₃ (hereinafter sometimes referred to as failure detection resistance) has a negative effect on the measurement accuracy of tire tread width (tire width) and tread pressure position. This will be considered below.

When the tire 7 presses the resistor 4 with a constant current i ₀ flowing through the resistor 6 having a resistance value R,
Pressure-sensitive conductive rubber only on the treading area (i.e. tire width) 5
conducts and short-circuits the resistor 6, so ΔR
The resistance value decreases from R by . At this time, the current i ₂ is also shunted to the resistor R ₃ inserted between the flexible conductor 4 and the ground due to the above-mentioned circumstances.

Here, the voltage ΔV representing the tire width is calculated when the failure detection resistor R ₃ is not connected and when it is present. It is expressed as equation (2).

ΔV=i ₀ (R-R ₁ -R ₂ )...(1) ΔV=i ₀ (R-R ₁ )-i ₀ R ₂・R ₃ /R ₂ +R ₃ ...(2) However, in the resistor 6 , the resistance value on the right side of the resistance value ΔR portion is R ₁ , and that on the left side is R ₂ .

Since the error voltage can be obtained as the difference between the above equations (1) and (2), it becomes as shown in the following equation.

Error voltage of ΔV=−i ₀ R ² ₂ /(R ₂ +R ₃ ) (3) That is, due to this error voltage, the measured tire width becomes larger than the actual width. Similarly, errors occur in the measurement of the tire tread pressure position. Moreover, as is clear from equation (3) above, the tire width measurement error varies depending on the pedal pressure position.
Accurate measurement of tire width and tread pressure position becomes difficult.

The present invention has been made in order to solve the problems in the prior art as described above, and an object of the present invention is to eliminate the negative influence of failure detection resistance and accurately determine tire width and pedal pressure position. An object of the present invention is to provide a tread measuring device capable of performing measurements.

The main point of the configuration of the present invention is that in the tread measuring device, when a vehicle does not approach, a failure detection resistor is connected and the length measuring converter operates in failure detection mode, and when a vehicle approaches. The point is that the resistance is separated and it is possible to accurately measure the width of the tire and the position of the pedal pressure.

Next, one embodiment of the present invention will be described with reference to the drawings, but before that, the principle of measuring the tread will be explained with reference to FIGS. 4A to 4C.

First, tire width measurement will be explained. The pressure of the tire 7 is applied to the pressure-sensitive rubber 5 by the pressure of the wheel, and the pressure-sensitive rubber in the area where the pressure is applied becomes electrically conductive, so that the voltage between terminals A and B of the resistor 6 placed under the pressure-sensitive rubber The pressure-sensitive rubber short-circuits the resistance by an amount corresponding to the width of the tire. Therefore, by measuring the resistance change ΔR between terminals A and B of this resistor 6, the tire width can be obtained. However, the second axis of buses etc.
When the tire (wheel) is pressed, the flexible conductor 4 becomes the width of the tire including the space SP between the tires, as shown in FIG. 4C.

Next, a method for measuring the tire pressure position will be explained. The pressure position of the tire is obtained by measuring the change in resistance between one end A of the resistor 6 and the flexible conductor 4 as a reference. That is, the total resistance R of the resistor 6
(between terminals A and B) is designed to be proportional to its length, so if the resistance value between terminal A and conductor 4 is known, the distance to the pressing position can be determined. For example, when the tire is not under pressure, the resistance between the upper and lower surfaces of the pressure-sensitive rubber is several tens of MΩ, so the flexible conductor 4 and the resistor 6
The resistance between the terminal A and the terminal A is several tens of MΩ. Next, when the tire is pressed, the resistance value between the flexible conductor 4 (terminal C) and the terminal A will show the value of resistance R2, as shown in Fig. 4A, and from this resistance value, the resistance value of the tire The pedal pressure position can be obtained. From the tire widths (right side tire width WR, left side tire width WL in Figure 3) and tread pressure positions (right side tread pressure position PR, left side tread pressure position PL, seam length (constant) LC) obtained in the above manner, The tread T can be found using the formula.

T=LC+PL+PR+1/2WL+1/2WR (4) FIG. 5 is a block diagram showing an embodiment of the present invention. In the same figure, 11 is the terminal A, B of the resistor.
a constant current source for supplying a constant current _i0 between 12
is a tire width measurement amplifier that extracts the voltage generated in the resistor by supplying a constant current i ₀ ,
13 is an amplifier for measuring tire pressure position; 14, 1
4A is a changeover switch, and when operating in a failure detection mode such as detecting insulation failure or short circuit in the length measuring converter, the switch 14 is closed and the switch 14A is opened. To perform normal tread measurement operation, open switch 14 and switch 1.
Close 4A. 15 is an A/R converting the analog voltage output from the amplifiers 12 and 13 into a digital signal;
A D converter 16 is an I/port for inputting the digital output from the A/D converter 15 to the microcomputer 17, and 17 is an I/port for processing the digital signal input from the I/port 16.
A microcomputer that judges the results, 18
1 is a memory and control memory for storing data resulting from arithmetic processing in the computer 17;
9 is a vehicle detection device that detects whether or not a vehicle is entering;
It is.

Next, the operation will be explained. First, the operation when no vehicle approaches, that is, the operation in the failure detection mode in the length measuring converter will be explained.

There is “no” vehicle entry from the vehicle detection device 19
When an L-level vehicle detection signal indicating that
It is learned through the O port 16 and issues a command to close the switch 14 and open the switch 14A. Then,
The constant current source 11 loses its constant current characteristic, and the voltage at terminal B of the resistor becomes an open circuit voltage V ₀ . Further, the switch 14 becomes conductive, and the failure detection resistor R ₃ and the insulation resistor R _Z of the length measuring converter are connected in series. Therefore, the voltage V _R3 generated across the failure detection resistor R ₃ is expressed by the following equation.

V _R3 = R ₃ · V ₀ / (R ₃ + R _Z ) Insulation resistance R _Z is determined from this voltage V _R3 and known resistance R ₃ using the following formula.

R _Z = (R ₃ · V ₀ − R ₃ V _R3 ) / V _R3 ...(5) However, at what value of insulation resistance R _Z should we judge that the length measuring converter is defective?
This is determined based on the measurement accuracy M. When the measurement accuracy is M, if the insulation resistance R _Z is less than or equal to the value expressed by the following formula, it is determined to be defective.

R _Z =(R-R・M)/M...(6) Therefore, the voltage generated in the failure detection resistor _R3 is amplified by the amplifier 13, converted to a digital signal by the A/D converter 15, and then The data is read into the microcomputer 17 via the O port 16. Then, the microcomputer 17 compares the voltage generated across the failure detection resistor R ₃ with the reference voltage value obtained by back calculating from the equation (6) above to determine whether or not the length measuring converter is in failure.

Next, the operation when a vehicle approaches, that is, when performing the original tread measurement, will be explained.

When the vehicle detection device 19 outputs an H-level vehicle detection signal indicating the presence of a vehicle entering, the microcomputer 17 becomes aware of this and issues a command to open the switch 14 to make it non-conductive, and the switch 14A is turned off. Close this to conduct electricity. That is, when a vehicle is present, the failure detection resistor _R3 is disconnected so that the tire width and tread pressure position can be measured with high accuracy. When the switch 14A becomes conductive, the current source 11
restores constant current characteristics, and a constant current i ₀ flows from terminal B to A of the resistor. Further, since the switch 14 is non-conductive, no leakage current flows through the flexible conductor. First, before the tire steps on the length measuring converter, the microcomputer 17 first converts the output voltage of the tire width measuring amplifier 12 into a digital signal using the A/D converter 15, and sends the obtained digital data to the I/port. 16 and stored in memory 18.

FIG. 6 is a time chart showing the waveforms of the vehicle detection signal output from the vehicle detection device 19, the output voltage of the tire width detection amplifier 12, and the output voltage of the pedal pressure position detection amplifier 13.

In FIG. 6, waveform ○a is the waveform obtained when the tire on the first axis of the vehicle presses against the length measuring converter, and waveform ○b is the waveform obtained when the tire on the second axis of the vehicle presses the length measuring converter. The voltage VF is determined by the tire width detection amplifier 1 at the initial stage when there is no pressure from the tire.
This is the voltage output from 2.

The process of tire width measurement will now be described with reference to FIGS. 5 and 6.

The microcomputer 17 monitors the output voltage of the tire width measurement amplifier 12, and when it drops below the initial voltage VF and reaches the pedal pressure level,
It is determined that the tire pressure has started, and thereafter the data is stored in another area of the memory 18. As the vehicle tire presses the length measuring converter, the output voltage of the tire width amplifier 12 decreases by a voltage corresponding to the tire width, so the microcomputer 17 determines that the output voltage of the tire width amplifier 12 is the lowest. The measurement is performed so that the value (data obtained from the voltage VD by the A/D converter) is stored in the memory 18. And after the tire passes, memory 18
The first data stored in (VF when no pressure is applied)
The tire width voltage VW is obtained by subtracting the lowest value data VD of the output of the tire width amplifier 12 from the tire width amplifier 12.

Next, the process of measuring the pedal pressure position will be explained. The microcomputer 17 monitors the output voltage of the tire width measuring amplifier 12, and only when it determines that the tire has sufficiently pressed the length measuring converter, changes the output voltage VP of the pedaling position measuring amplifier 13 to A. /D converter 15 and I/port 16 as digital data to the microcomputer 17.
Load into. This data is the tread pressure position data,
It is stored in the memory 18.

As shown in Figure 5, two sets of length measuring converters are provided to detect the left and right tires of the vehicle, so both the tire width and the pedal pressure position are on the L (left) side and the R (right) side. The computer 17 uses the above-mentioned equation (4) to calculate the tread based on the measurement result.

According to this invention, a switch is inserted between the flexible conductor included in the length measuring converter and the failure detection resistor _R3 , and between one end of the resistor in the length measuring converter and the ground. By controlling the switch from a microcomputer to change between measuring the vehicle tire width and pedal pressure position and detecting a failure in the length measuring converter, failures in the length measuring converter can also be detected. This method has the advantage that accurate tire width and tread pressure position can be measured without being adversely affected by the failure detection resistor.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram showing the back of a car, Fig. 2 is a top view showing an example of the arrangement of a length measuring converter with respect to a moving vehicle, Fig. 3 is an explanatory diagram of the configuration of the length measuring converter,
Figures 4A to 4C are diagrams explaining the operating principle of the length measuring converter;
FIG. 5 is a block diagram showing one embodiment of the present invention, and FIG. 6 is a time chart showing waveforms of main signals in FIG. Description of symbols, 1...Vehicle, 2...Tire, 3a,
3b... Length measurement converter, 4... Flexible conductor, 5...
Pressure-sensitive conductive rubber, 6... Resistor, 7... Tire, 8
... constant current source, 11 ... constant current source, 12 ... tire width detection amplifier, 13 ... pedal pressure position detection amplifier, 14, 14A ... changeover switch, 15 ...
A/D converter, 16...I/port, 17...
Microcomputer, 18...Memory, 19...
...Vehicle detection device.

Claims (1)

[Claims] 1 A flexible conductor, a resistor placed parallel to the conductor, and a resistor inserted between the two and in contact with each other, so that the pressure-applied part is turned on and off according to the pressure applied through the flexible conductor. a length measuring transducer comprising an inclusion exhibiting an electrical switch effect, the voltage detected across the resistor and the voltage appearing on the flexible conductor when a vehicle steps on the transducer; A device for measuring the tread of a vehicle is provided with a first switch that opens one end of the resistor, and a second switch that connects the flexible conductor to ground through a high resistance, When no vehicle is approaching, the first switch opens one end of the resistor, and the second switch leads the flexible conductor to ground through a high resistance, thereby measuring the length. When the converter is operating in failure detection mode and a vehicle is approaching, the first and second switches are switched, one end of the resistor is not opened, and the flexible conductor is lifted from the ground. A vehicle tread measuring device characterized by measuring tread.