JP2744880B2 - Pulse width measurement device and rotation speed measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse width measuring apparatus for detecting the input pulse signal, determining the start and end of counting of a measuring clock, and measuring the period of the pulse signal.

[0002]

2. Description of the Related Art An input pulse signal (including an AC signal) is detected to determine the start and end of counting of a measurement clock, and the cycle (time related to the cycle, such as a half cycle) of the input pulse signal is determined. A pulse width measuring device for measuring has been put to practical use. The pulse width measurement device is applied, for example, to a vehicle wheel speed measurement device.

The wheel speed measuring device is an ABS (Anti-Lock Br).
eaking System) is an important component of the equipment,
A vehicle speed sensor inputs an AC signal formed for each rotation angle of a unit of a wheel, measures a cycle of the AC signal, and converts it into an instantaneous wheel speed.

FIG. 4 is an explanatory diagram of an ABS device. FIG.
In the figure, (a) shows the configuration, and (b) shows the operation. Here, an arithmetic unit for controlling a vehicle (hereinafter referred to as an ECU: Electronic)
Control Unit) as an interrupt program
An ABS device is configured.

In FIG. 4, an ECU mounted on an automobile
Reference numeral 45 denotes a microcomputer circuit that is controlled by a program, and includes a CPU (not shown), a memory, an A / D converter,
Built-in D / A converter, power supply circuit, etc. ECU45
Executes arithmetic processing such as various engine control, constant speed running, suspension control, and the like, by allocating the arithmetic capacity in a time-division manner. However, when the driver strongly operates the brake, the ABS control program is started to execute the interrupt processing.

The vehicle speed sensor 43 connected to the wheels 41
Detecting the magnetic flux of each tooth of the permanent magnet molded into a gear mold,
An AC signal for inverting the polarity for each rotation angle of the unit of the wheel 41 is formed. The ECU 45 determines the cycle of the AC signal and converts it into wheel speed.

The wheel speed calculator 47 of the ECU 45 rectifies the input AC signal, performs waveform processing on the rectified AC signal, and converts it into a square wave pulse signal. The wheel speed calculation unit 47 outputs the number of measurement clocks integrated during one cycle of the pulse signal as a cycle of the pulse signal.

A calculation unit 49 of the ECU 45 periodically takes in the cycle of the AC signal measured by the wheel speed calculation unit 47,
An instantaneous brake control signal is formed in comparison with a predetermined braking condition 48. The output unit 46 operates the actuator 44 based on the brake control signal every moment. Through such a series of processes, the hydraulic pressure applied to the brake 42 is increased or decreased, and the wheel speed is attenuated stepwise.

In FIG. 4 (b), the vehicle speed v ₀ is equal to the wheel speed V _0.
When the brake is depressed strongly from the constant speed running state that matches the vehicle speed, the wheel speed V is reduced prior to the vehicle speed v, and a slip occurs between the wheel contact surface and the road surface. Then, at time t ₁
In after the brake is depressed strongly, and reaches the wheel speed V _C corresponding to the slip ratio of 10% at time t _2, ABS control is started automatically, ABS control is continued as long as the brake is continuously depressed.

In the ABS control, an instantaneous vehicle speed v is calculated from instantaneous wheel speeds obtained for four wheels. And
Target wheel speed V at which a slip ratio of 10% with respect to vehicle speed v
Calculate ₁ . Then, the acceleration and the moment by moment of the effect depth of the brake, to asymptotic while vibrating the wheel speed V with respect to the target wheel speed V _1.

By the way, in the ECU 45 shown in FIG. 4 (a), as described above, a plurality of arithmetic processes are performed in a time-division manner. In recent years, with the multifunctionalization of vehicles, automatic driving, automatic control of equipment, and the like, the types of calculations to be processed by the ECU 45 are increasing and tend to be complicated.

Therefore, the old CPU in the ECU 45
An attempt has been made to increase the computational capacity per unit time in the ECU 45 by replacing the CPU with a new CPU having a high computation bit number and high-speed computation. However, in this case, the basic clock frequency used by the ECU 45 increases. Therefore, in order to prevent an increase in the number of processing bits required to measure the same time, it is necessary to adjust the measurement clock in the timer, counter, and the like of the ECU 45.

For example, with the increase in the speed of the CPU of the ECU 45, the basic clock frequency is changed from 0.5 msec to 62.5 ns.
If the speed is increased to ec (0.0625 msec), the time that can be measured using the same 8-bit counter decreases from 0.13 seconds to 0.016 seconds. And the same 0.
To measure 13 seconds, it is necessary to use an 11-bit counter instead of an 8-bit counter.

Accordingly, the wheel speed calculating section 47 of the ECU 45 shown in FIG. 4A forms a low-frequency measuring clock by dividing the basic clock, and determines the period of the AC signal output from the vehicle speed sensor 43. The measurement clock is counted and measured.

[0015]

The ECU 45 shown in FIG.
When the cycle of the AC signal is measured by using the low-frequency measurement clock formed from the basic clock in the wheel speed calculation unit 47, the measurement error of the wheel speed increases at high speed.

When the wheel speed is high, the cycle of the AC signal is shortened, and the number of measurement clocks counted in one cycle of the AC signal is reduced. Then, the length of the measurement clock that is truncated without being involved in counting at the end of one cycle cannot be ignored.

That is, in single-shot measurement in which one cycle (half cycle) of an AC signal is measured only once, the error increases as the cycle becomes shorter. For example, when the vehicle speed exceeds 100 km / h, the accurate wheel speed is obtained. Measurement becomes impossible. Although the ABS device should operate accurately only at such a high speed, the operation of the ABS device becomes unstable due to an error in the wheel speed.

In the ECU 45 shown in FIG. 4 (a), the calculation unit 49 sets the wheel speed calculation unit 4 at regular intervals (for example, 5 msec).
The count value is taken from 7. Then, the wheel speed calculator 47
Effectively uses this fixed time to improve the accuracy of the cycle measurement. That is, the measuring clocks are counted for all the half cycles of the AC signal input within the fixed time, and the cycle of the AC signal is obtained as an average value of the count value of each cycle. This eliminates the influence of variations in each cycle in the AC signal output from the vehicle speed sensor 43.

However, in this case, since the formation of the measurement clock is reset for all the half periods of the input AC signal, the above-mentioned error caused by the resolution of the measurement clock is not affected by any single measurement. It doesn't change. Therefore, at higher speeds, the measurement error of the wheel speed increases significantly.

For example, when the output is inverted every time four basic clocks are counted to form a measuring clock with a period corresponding to eight basic clocks, the borrow signal for every eight basic clocks is the edge of the measuring clock. Is counted as
Then, in the measurement of the first half cycle of the AC signal,
At most, a time corresponding to seven basic clocks may be truncated, resulting in a measurement error.

The time corresponding to the seven basic clocks can be ignored when the cycle of the AC signal is long, but cannot be ignored when the wheel speed exceeds 100 km / h and the cycle of the AC signal is short. . Then, the error of the wheel speed calculated from the count value of the measurement clock is increased, the brake operation process is erroneously performed, the ABS device is malfunctioned, and the
Lock or increase the braking distance.

An object of the present invention is to provide a pulse width measuring apparatus capable of accurately measuring the period of a short pulse signal even with a low-frequency measuring clock.

[0023]

FIG. 1 is an explanatory diagram for explaining the operation principle of the present invention. The pulse width measurement device according to the present invention detects an edge of an input pulse signal, determines start and end of counting of a measurement clock, and outputs a cycle of the pulse signal as a measurement number of the measurement clock. A frequency dividing means (12) for counting input basic clocks and forming the measuring clock for each predetermined number, and a period of the pulse signal. Controlling the frequency dividing means (12) according to the distinction between single-shot measurement and continuous measurement of
(1) In the single-shot measurement, the counting operation in the frequency dividing means (12) is reset every time the counting of the measurement clock is started. (2) In the continuous measurement, the counting in the frequency dividing means (12) is performed. Frequency dividing control means (13) which does not reset the operation at least during the continuous measurement.

Further, the rotation speed measuring device according to the present invention measures a rotation speed sensor for forming a sensor signal which is a one-cycle pulse signal for each predetermined number of rotations of the rotating body, and measures a period of the sensor signal. Calculating means for calculating the instantaneous rotational speed, wherein the calculating means detects an edge of the input sensor signal, determines start and end of counting of a measurement clock, and The period of the signal
A measuring unit that outputs the measured clock as a measured number, a frequency dividing unit that counts the input basic clock and forms the measuring clock for each predetermined number, and a single-shot measurement of the cycle of the sensor signal. The frequency dividing means is controlled in accordance with the distinction of continuous measurement. (1) In the single-shot measurement, the counting operation in the frequency dividing means is reset every time the counting of the measurement clock is started. In the measurement, the frequency dividing control means that does not reset the counting operation in the frequency dividing means at least during the continuation of the continuous measurement, and, in the case of the continuous measurement, an average value of a plurality of count values of the measurement clock in a predetermined measurement period And a conversion means for calculating the rotation speed based on

[0025]

In FIG. 1, in the pulse width measuring apparatus according to the first aspect, a continuous cycle (half cycle or the like) of the input pulse signal is used.
When measuring the frequency, the frequency dividing means 1 is used for each cycle (half cycle, etc.).
2 is not reset, and is counted every cycle (half cycle or the like) using a measurement clock generated continuously without interruption. That is, in the continuous measurement mode, the measuring unit 11 is reset for each cycle (half cycle or the like), but the frequency dividing unit 12 is not reset.

Therefore, the basic clock discarded without being involved in the counting in one cycle (half cycle, etc.) reduces the time until the first counting in the next cycle (half cycle, etc.), The count value in the next cycle (half cycle or the like) is increased by one, thereby canceling the error.

As described above, when measuring all the cycles (half cycle, etc.) during a certain period of time, the measurement error that increases as the pulse signal becomes shorter becomes less than the measurement error of the continuously measured cycle (half cycle, etc.). Can be offset by number. This is because the larger the number of continuously measured cycles (half cycle or the like), the more effectively the surplus time of the measurement clock is used. As a result, as the number of measured cycles increases, the resolution of the measuring clock increases, and accurate measurement can be performed even in a short cycle.

The average value need not be a count value for one cycle, but may be calculated as a count value corresponding to, for example, a half cycle, 2.3 cycles, 7 cycles, or the like.

On the other hand, in the single measurement mode in which only one cycle (half cycle or the like) is measured, the frequency dividing means 12 is reset every time the measuring means 11 is reset. As a result, the phases of the measurement clocks in each measurement are matched.

In the wheel speed measuring device according to the second aspect, for example,
4A fetches a plurality of count values stored in the wheel speed calculator 47 at regular intervals. The plurality of count values are obtained by counting the measurement clocks for all the cycles (half cycle or the like) during the predetermined time.

During this fixed time, the measuring clock is continuously generated without being interrupted (reset). Therefore, the error of the measurement clock is canceled out for a plurality of cycles (half cycle, etc.) measured continuously, and the cycle (half cycle, etc.) as an average value is accurately obtained.

That is, when the wheel speed is low, since one cycle of the AC signal is long, the measuring clock itself exhibits a sufficient resolution. On the other hand, when the wheel speed increases, the resolution of the measurement clock itself becomes insufficient, but since the number of cycles within a certain time increases, the remainder of the basic clock after the last measured clock is counted. Utilizing serially in a cycle, the resolution of the measurement clock is substantially improved.

[0033]

FIG. 2 is an explanatory diagram of a wheel speed calculating device according to an embodiment, and FIG. 3 is an explanatory diagram of pulse width measurement. 2A shows the configuration, and FIG. 2B shows the operation. Here, the base clock of the CPU in the ABS device of FIG.
A description will be given of a wheel speed calculation device employed when increasing the processing capacity of the vehicle.

In FIG. 2A, the frequency dividing circuit 22 has an EC
Dividing the high frequency base clock used in U,
Form a low frequency measurement clock. Dividing circuit 22
Generates a measurement clock by counting the number of basic clocks and inverting the output every time the count reaches a certain number. When the clock reset signal is input from the control circuit 23, the frequency divider 22 returns the count value of the basic clock to 0 without inverting the output, and starts counting the basic clock again from the beginning.

The control circuit 23 resets the count of the measurement clock in the counter 21 every time the edge of the measurement signal is detected. When the reset signal is input from the control circuit 23, the counter 21 returns the count value to 0 and starts counting the measurement clock again from the beginning. At the same time,
The previous counting result is stored in the memory 24.

The memory 24 sends a plurality of count values continuously measured during the fixed time (5 msec) to the arithmetic unit 49 in FIG. 4 (a) every fixed time (5 msec).
The calculation unit 49 recalculates the brake control signal every predetermined time (5 msec) and rewrites the output state.

In the wheel speed calculating device of the embodiment, the continuous measurement mode is set, and the counter reset signal is not input to the frequency dividing circuit 22. That is, the length of the 1 level and the length of the 0 level of the square wave pulse of the measurement signal are continuously measured as the count value of the measurement clock, but at this time, the frequency dividing circuit 22 is never reset.

Accordingly, the count value of the basic clock that did not reach the borrow signal in one half cycle measurement shortens the time until the first borrow signal in the next half cycle.

Thus, when an average value is obtained for a plurality of half cycles continuously measured within a certain time,
The counting error of the measurement signal due to the large period of the measurement clock is completely canceled. In other words, the increase in the number of samples taken within a certain time offsets the increase in the error of each sample value.

Therefore, if the cycle of the measurement clock almost coincides with the cycle of the measurement signal corresponding to the wheel speed of several hundred km / h, it is impossible at all to measure the exact cycle with single shot measurement. The measurement error of the wheel speed obtained from the average value of the sample is not so different from the case of the wheel speed of several tens km / h.

In FIG. 2B, the dividing process A shows a case where the dividing circuit 22 is reset every time an edge of the measurement signal is detected. At this time, the half cycle is the basic clock 15
The measurement signal corresponding to the individual signal is erroneously determined to have a half cycle corresponding to 12 basic clocks.

That is, since the measurement clocks (borrow signals) for every four basic clocks are counted, the last three basic clocks are discarded in each half cycle to increase the error.

On the other hand, in the frequency dividing processes B and C, a measurement clock (borrow signal) continues to be generated for every four basic clocks regardless of the edge of the measurement signal, and the counting error in one half cycle is reduced. It is completely canceled in the subsequent half cycles. The frequency dividing processes B and C show that the phases of the measurement clocks when they enter the first half cycle happen to be slightly shifted.

For example, if the output of the vehicle speed sensor shown in FIG.
In the case where 700 km at 00 km / h, the basic clock of the ECU 45 is 125 nsec, and the basic clock is divided by 4 to form the measurement clock, at 200 km / h, the period is 7 pulses.

At this time, if the frequency dividing process A is adopted and the frequency dividing circuit is reset every measurement, at worst,
(4-1) × 125 nsec × 6 = 2250 nsec error occurs. This is the case of the cycle calculation between edges of the same polarity (every cycle), but the case of the cycle calculation between edges (every half cycle) is (4-1) × 62.5 nsec × 13 = 48.
An error of 75 nsec will occur.

This error is 0.22 when converted to wheel speed.
This corresponds to a measurement error of 1 km / h, which is 1.27 G when converted to a change in G (acceleration). Since the control reference G value of the ABS device is 1.5 G, there is almost no margin, and there is a risk of malfunction.

That is, at the oscillating wheel speed V shown in FIG.
The timing is selected when the absolute value of (deceleration) exceeds 1.5 G and the difference between the vehicle speed v and the wheel speed V reaches 10 to 15% of the vehicle speed v. Therefore, when the error reaches 1.27G, 1.5G is changed from 0.23G to 2.77G.
The former results in an increase in the braking distance and the latter results in locking of the wheels.

However, actually, as a result of the wheel speed being evaluated unduly lower than the actual speed, when the slip ratio reaches 10 to 15%, the wheel speed often already reaches 1.5 G,
A 1.5G cap becomes meaningless.

On the other hand, in the frequency dividing processes B and C, the errors are offset by a plurality of continuous counts, so that the measurement error of the wheel speed is at a negligible level.

In FIG. 3, in the wheel speed measuring apparatus of the embodiment, the measurement error of the wheel speed is compressed by effectively utilizing the interval of 5 msec at which a plurality of count values are read from the memory 24 of FIG. That is, the measurement clock is counted for each of a plurality of continuous half cycles included in 5 msec, and the measurement clock that is continuously formed without being reset is used in the measurement.

For example, at 200 km / h, one cycle is 0.7 msec, and counting is performed for seven pulses.
At 00 km / h, one cycle is 1.4 msec, 3.5
A count is made of the pulses. In this way, the relative error of the wheel speed measurement is kept almost constant in a wide range from high speed to medium speed to constant speed. The wheel speed V is calculated as V = KN / T as a constant K, a cycle T, and a pulse number N.

[0052]

According to the pulse width measuring apparatus of the first aspect,
While pulse width measurement as in the past can be performed in the single-shot measurement mode, pulse width measurement with a small measurement error in the continuous measurement mode can be performed.

According to the continuous measurement mode, the measurement error caused by the lack of the resolution of the measurement clock is almost completely canceled out for a plurality of continuous pulse signals (period, half period, etc.) included within a fixed time. Is done. Accordingly, the pulse width can be measured with a substantially constant error regardless of the length of the cycle.

Even when a low-frequency measurement clock is used, the pulse width can be measured with high accuracy.
It is also possible to further reduce the frequency of the measurement clock to save the number of bits of the counter and the timer. As a result, the CPU and the communication interface are simplified, and the processing speed is increased.

According to the wheel speed measuring device of the second aspect, the measurement error of the wheel speed can be kept substantially constant low irrespective of the level of the high-speed to low-speed wheel speed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic configuration of the present invention.

FIG. 2 is an explanatory diagram of a wheel speed calculation device according to the embodiment.

FIG. 3 is an explanatory diagram of pulse width measurement.

FIG. 4 is an explanatory diagram of an ABS device.

[Explanation of symbols]

 11 measuring means 12 frequency dividing means 13 frequency dividing controlling means

 ────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-54-32371 (JP, A) JP-A-64-15666 (JP, A) JP-A-3-191874 (JP, A)

Claims (2)

(57) [Claims] A measuring means (11) for detecting an edge of an input pulse signal to determine start and end of counting of a measuring clock, and outputting a cycle of the pulse signal as a measured number of the measuring clock. ), A frequency dividing means (12) for counting the input basic clocks and forming the measuring clock for every predetermined number of the basic clocks; The frequency dividing means (12) is controlled according to the distinction of the measurement. (1) In the single-shot measurement, the counting operation in the frequency dividing means (12) is reset every time the counting of the measurement clock is started. (2) In the continuous measurement, there is provided a frequency division control means (13) which does not reset the counting operation in the frequency division means (12) at least during the continuous measurement. Pulse width measurement device. 2. A rotation speed sensor for forming a sensor signal, which is a pulse signal of one period for each predetermined number of rotations of the rotating body, and a calculating means for measuring a period of the sensor signal and calculating an instantaneous rotation speed. In the rotational speed measuring device, the calculating means detects the edge of the input sensor signal, determines the start and end of the counting of the measuring clock, and determines the cycle of the sensor signal, Measuring means for outputting as a measured number; frequency dividing means for counting the input basic clocks and forming the measuring clock for each predetermined number; and distinguishing between single-shot measurement and continuous measurement of the cycle of the sensor signal. (1) In the single-shot measurement, the counting operation in the frequency dividing unit is reset each time the counting of the measurement clock is started. (2) In the continuous measurement, A frequency division control unit that does not reset the counting operation in the frequency division unit at least during the continuation of the continuous measurement; and, in the case of the continuous measurement, based on an average value of a plurality of count values of the measurement clock in a predetermined measurement period. And a conversion means for calculating the rotation speed by using a rotation speed measuring device.