JPH059747B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is designed to be attached to a moving object such as a car, and to be used for various control purposes by detecting the state of acceleration acting on the car. The present invention relates to an acceleration detection device equipped with a semiconductor acceleration sensor.

[Prior Art] For example, when attempting to perform brake anti-skid control or automatic suspension control in a car, it is necessary to detect the acceleration acting on the body of the car in the longitudinal direction as well as in the lateral direction. be. Various structures have been considered as such acceleration detection means, but a semiconductor-based acceleration detection sensor is one that is compact and can perform highly accurate acceleration detection operations. It is becoming more and more used.

Semiconductor acceleration detection sensors form a single-crystal silicon vibrating piece from a semiconductor substrate made of a single crystal such as silicon, and when an acceleration acts on this vibrating piece, it responds to the magnitude of this acceleration. It is constructed in such a way that it bends. A piezoresistive element is attached to this vibrating element, and an electrical signal corresponding to the degree of bending of the vibrating element is detected from the piezoresistive element.

That is, from this semiconductor acceleration detection device,
It is possible to obtain an electrical signal corresponding to the magnitude of applied acceleration, and this detection signal can be used effectively when attempting to electronically control antiskid or suspension. be.

However, when such semiconductor acceleration detection sensors are used for long periods of time, especially in automobiles that are used in harsh natural conditions, changes in the resistance value of the piezoresistive element over time, temperature changes, etc. DC drift due to changes etc. may become impossible to ignore. For this reason, low frequency components of the signal are removed using, for example, an AC coupling circuit using a capacitor.

Figure 6 shows the configuration of an acceleration detection device using this capacitor coupling.
An output signal from a bridge circuit in which semiconductor acceleration sensors _S1 and _S2 are set on one side is amplified and detected by a differential amplifier A1. The output signal from the differential amplifier A1 is supplied to the amplifier A2 via a coupling circuit constituted by a filter circuit consisting of a capacitor C and a resistor R, and the output signal from the amplifier A2 is used as an acceleration detection signal. It came to be used as a.

In a device configured in this way, the amount of low frequency cut in the output signal is determined by the respective values of capacitor C and resistor R, and the value of capacitor C or resistor R can be infinitely increased. In this case, the value of the cut-off frequency becomes infinitely low, but there is a limit to the values of the capacitor C and the resistor R, and the limit of the cut-off frequency is usually about 0.1 to 0.5 Hz.

However, when performing electronic control such as anti-skid control and suspension control of automobiles, it is now required to measure acceleration changes close to direct current, which were previously removed by AC coupling circuits and the like. However, as mentioned above, the coupling circuit using a capacitor has a limit in its range, so it cannot be configured to meet the demand conditions such as detecting changes in acceleration close to the DC component. be.

[Problems to be Solved by the Invention] This invention has been made in view of the above points, and can be configured to be sufficiently small and lightweight, and can be effectively installed in, for example, a car, etc. for electronic control. acceleration detection, which also ensures that sufficient low-frequency changes in acceleration can be detected, such that it can be used effectively as a detection element for e.g. electronic antiskid control, suspension control, etc. The aim is to provide equipment.

[Means for Solving the Problems] That is, in the acceleration detection device according to the present invention, the reference operating point of the amplification means for amplifying the detection signal from the sensor circuit including the semiconductor detection sensor is variably controlled. This reference operating point is corrected and controlled in a direction that eliminates drift.

[Operation] In the acceleration detection device configured as described above, the reference operating point of the amplification means for amplifying the output signal from the sensor circuit is corrected in accordance with the state of occurrence of drift. ing. Therefore, the signal output from this amplification means is used as it is as an acceleration detection signal, and moreover, the drift component has been removed from this output signal. In other words, it is possible to reliably output a signal corresponding to changes in acceleration in a state close to a DC component. This allows a detection signal to be obtained.

[Embodiment of the Invention] An embodiment of the invention will be described below with reference to the drawings. Figure 1 shows its configuration.
Resistors 111 and 112 made of semiconductors are resistors 1
21 and 122 to form a bridge circuit. In this case, the resistor 111,
Reference numeral 112 is constituted by a piezoresistance element that is attached to a vibrating piece made of a semiconductor, for example, and is set to a resistance value corresponding to the bending of the vibrating piece. The output signal from this bridge circuit is supplied to a differential amplifier 13, and a detection signal corresponding to the acceleration is output from the differential amplifier 13. The output signal from the differential amplifier 13 is amplified by an output amplifier 14, and all frequency components including drift are amplified and taken out as output.

Here, the reference operating point of the output amplifier 14 is corrected and changed by an operating point correction circuit 15. The operating point correction circuit 15 is supplied with an output signal from the output amplifier 14, and a correction point is set in accordance with the state of the output signal from the amplifier 14. Further, this operating point correction circuit 15 is supplied with a stop state determination signal from a vehicle stop determination circuit 16, so that the above-mentioned correction operation is executed only when determining the stopped state of the vehicle. ing.

This acceleration detection device is installed in a car and detects the acceleration that acts on the car body when the car starts and stops, as well as the acceleration that acts in the lateral direction when driving around a curve. When the vehicle is stopped, the output signal from the amplifier 14 is detected, and the amount of deviation of this output signal is detected. Then, the operating point of the amplifier 14 is corrected in accordance with this amount of deviation. That is, the feedback system using the operating point correction circuit 15 cancels output errors due to DC drift when the vehicle is stopped, where measurement of acceleration is not necessary. Therefore, the output signal from the amplifier 14 is corrected so that it accurately corresponds to the acceleration acting on the vehicle body.

FIG. 2 shows the above device in more detail, and the output signal from the sensor circuit 21 section consisting of the bridge circuit and the differential amplifier 13 is as follows.
It is supplied to an operational amplifier 22 that forms part of the amplifier 14, and the output signal from this operational amplifier 22 is used as an amplifier output signal whose operating point is controlled.

The output signal from operational amplifier 22 is further supplied to comparators 23 and 24, respectively.
The comparators 23 and 24 are further supplied with reference voltages of +ΔV and −ΔV, respectively, with respect to the reference value set by a voltage setting circuit including resistors R1 to R3. Here, the reference value is, for example, a voltage value corresponding to a state of acceleration "0", and when the acceleration is detected from the sensor circuit 21, the outputs from the comparators 23 and 24 are turned on and off quite frequently. is becoming repeated.

The output signals from the comparators 23 and 24 are supplied to an exclusive OR 25, and the output signal from the exclusive OR 25 is supplied to a monostable multivibrator 26 as a set command.

Here, this monostable multivibrator 26 is set with a retrigger function, and each new trigger is triggered by the latest trigger (set command) that comes within the time constant set by this multivibrator 26. The rising edge of the output is set to .

Therefore, this monostable multivibrator 2
If the time constant of 6 is set to be longer than the maximum period of acceleration that occurs while the car is moving, the output signal from the multivibrator 26 will be within the period of "time range of the car moving + time constant". It will be set to high level.

The output signal from this monostable multivibrator 26 is inverted by an inverter 27 and sent to an AND circuit 2.
8. This AND circuit 28 is supplied with a clock signal from a clock generator 29, and while the output signal from the multivibrator 26 is at a high level, the clock signal is output from this AND circuit 28. never be done.

The output signals from the comparators 23 and 24 are supplied to the flip-flop circuit 30 as set and reset commands, and each time the outputs from the comparators 23 and 24 are repeated,
Flip-flop circuit 30 will now be repeatedly set and reset. Then, in the set state of the flip-flop circuit 30, that is, in the state in which the output is generated from the comparator 23, the up/down
A count-down command is given to the down counter 31, and a count-up command is given to the counter 31 in a state in which an output is generated from the comparator 24 and the flip-flop circuit 30 is reset.

The up/down counter 31 is set to an enabled state by the output of the inverter 32 which is supplied with the output signal from the exclusive OR 25, and uses the clock signal from the AND circuit 28 as the up-count or down-count command. Count accordingly. The count value data of the counter 31 is converted into a voltage value by the resistor ladder circuit 33, that is, D/A converted, and is appropriately amplified and supplied to the operational amplifier 22.

In the device configured as described above, when the vehicle equipped with this acceleration detection device is running and acceleration is frequently applied to the vehicle body, the output signal from the operational amplifier 22 fluctuates frequently. However, due to this fluctuation, the comparators 23 and 2
The output from 4 is frequently inverted. The monostable multivibrator 26 is held in the set state by the output from the exclusive OR 25, and the AND circuit 28 is brought into a state in which output of the clock signal is blocked. Therefore, the output from the resistance ladder circuit 33 does not change either.
No correction operation of the operating point of amplifier 14 is performed.

On the other hand, when the car is stopped and there is no acceleration acting on the car body, the operational amplifier 2
The output signal from 2 becomes stable. In this state, if there is a deviation due to drift in the output from the operational amplifier 22, an output signal will be generated from either the comparator 23 or 24, and the output from the exclusive OR 25 will become a low level, causing the up/down counter 31 to be output. Enabled. Furthermore, since the output of the exclusive OR 26 is set to a stable state, the monostable multivibrator 26 takes a time corresponding to the set time constant after the output from the operational amplifier 22 becomes stable. After the time has elapsed, that is, when it is confirmed that the vehicle has stopped, the reset state is entered, and a gate signal is given to the AND circuit 28, so that the clock signal generated by the clock generator 29 is given to the counter 31. Become.

In this state, the counter 31 is set to an up-count state or a down-count state in response to the output signal from the comparator 23 or 24, and the counter 31 counts the input clock according to this setting state. become,
A voltage signal from the resistance ladder circuit 33 corresponding to the count value of the counter 31 is supplied to the operational amplifier 22. That is, the operating point is corrected in a direction corresponding to the deviation of the output from the operational amplifier 22 from the reference value, and when the correction is completed, both the output signals from the comparators 23 and 24 are set to a low level. .

When the outputs from comparators 23 and 24 both become low level, exclusive OR 25
The output from the inverter 32 becomes high level, the output signal from the inverter 32 becomes low level, the up/down counter 31 is set to a non-operating state, and the operating point correction operation is stopped. is now in a completed state. Therefore, the sensor output subsequently obtained from the operational amplifier 22 in response to the output from the sensor circuit 21 is an acceleration detection signal that does not include a drift component.

With the acceleration detecting device configured in this way, when the car is moving, there is no need to perform any sudden braking or sudden steering operations.
Taking advantage of the fact that some kind of acceleration is always acting, when a state in which the change in acceleration is less than a certain value continues for a specified time range, it is determined that the vehicle has stopped. and,
When it is determined that this vehicle has stopped, the system corrects the DC drift component included in the output signal so that the DC drift component is cut out, and it is determined that other vehicles are moving. When this occurs, the DC component is also included in the output.

Therefore, although it is not possible to eliminate DC drift when the vehicle is not judged to be stopped, the drift that occurs at this time is sufficiently slight and within a range that is sufficiently practical. be. Here, it is thought that the state in which it is determined that the vehicle is substantially in motion continues for about one day at most, and the amount of drift that occurs during this period is substantially extremely small.

The acceleration frequency range required for anti-skid control, automatic suspension control, etc. in automobiles ranges from the DC level, which corresponds to the state in which the lateral acceleration that acts during steady turning continues as long as the steering wheel is turned, to the range in which the suspension operates. The upper limit is approximately 100Hz. Therefore, the drift of the detection mechanism and signal processing circuit is
If it can be completely separated from low-frequency acceleration and cancel drift, it will theoretically be possible to detect even DC component acceleration.

Therefore, as shown in the embodiment, by performing an operating point correction operation that cancels the signal component corresponding to the drift, the drift can be canceled, and the effect on the automobile may be reduced. This makes it possible to reliably detect even accelerations at sufficiently low frequencies, making it possible to electronically control various vehicles.

FIG. 3 shows another embodiment, in which resistors 111, 112 and 121, 12 each have a piezoelectric term as in the previous embodiment.
The differential amplifier 13 is configured to detect the output of the bridge circuit configured by 2.
The output signal from the differential amplifier 13 is supplied to an output amplifier 14, from which an acceleration detection output signal is obtained. The output signal from this output amplifier 14 is supplied to an operating point correction circuit 15.
Feedback control is performed so that the operating point of the output amplifier 14 is corrected by the signal from the output amplifier 14.

In this embodiment, the operating point correction circuit 15 executes the correction operation in response to a timing signal from the timing circuit 17.
That is, the output signal from the output amplifier 14 is monitored at each specified timing, and the operating point of the output amplifier 14 is corrected in accordance with the state of the output signal.

FIG. 4 shows a configuration embodying the above embodiment, in which the output signal from the output amplifier 14, which is supplied with the output signal from the sensor circuit 21 consisting of the bridge circuit and the differential amplifier 13, is The signal is supplied to comparators 41 and 42 of. This comparator 41 and 42
are supplied with reference voltages V _A and V _B set by resistor voltage divider circuits each consisting of resistors R4 to R6 as comparison voltages, so that the output signal from the output amplifier 14 reaches a positive level. When the output signal of the comparator 41 is at a high level, when the output signal is at a negative level, the output of the comparator 42 is set at a high level.
The output signal is set to high level. And these comparators 41 and 42
The output signals from each are supplied to the up/down counter 31 as a down count command and an up count command.

The counter 31 is supplied with a clock signal from a clock generator 29, and is counted down or up in response to a command supplied from a comparator 41 or 42. The count value information of this counter 31 is converted into an analog voltage signal by the resistance ladder circuit 33, and
The signal is appropriately amplified by the amplifier 43 and fed back to the output amplifier 14, and the operating point of the amplifier 14 is set based on the fed back signal.

Here, assuming that the acceleration waveform that normally occurs is as shown in A in Figure 5, and further assuming that the operating point fluctuation waveform due to DC drift is as shown in B in Figure 5, the sensor The waveform of the output signal from the circuit 21 is as shown in A and B in FIG.
The waveform obtained by adding the waveforms shown in FIG. 5 by the broken line C is obtained.

In this device, the output signal from output amplifier 14 is compared with reference voltages V _A and V _B set in comparators 41 and 42, respectively. When the output signal has a positive polarity higher than V _A , the output of the comparator 41 is at a high level, and when the output signal has a negative polarity, the output from the comparator 42 is at a high level _.
In a higher state, the count value of the up/down counter 31 is set to “-1” at the timing of the clock signal.
However, when the output signal is lower than V _B , the counter 31 is set to "+1" at the timing of the clock signal.
do. Then, the output signal is “V _A ” close to 0 volts.
≦Output signal voltage≦V _B ”, counter 3
A counting operation of 1 is not performed, and the state up to that point is maintained.

That is, as shown by the solid line in C in FIG. 5, at each correction timing corresponding to the clock signal from the clock generator 29, the level of this signal is corrected to be lower by 1 bit while the output signal is in the positive polarity state, and the output signal is in the negative polarity state. When the value is negative, the value is corrected to be one bit higher.

This type of correction is performed by changing the time it takes for the output waveform to return to the "0" point (the cutoff frequency of the capacitor coupling) by the timing time interval (frequency of the clock generator 29) of the timing circuit 17 corresponding to the clock generator 29. (corresponding to) can now be changed, making it practically possible to realize a circuit with an extremely low cutoff frequency, which has been difficult to realize in the past.

Here, the correction width is, for example, about 10 mV, and the timing frequency may be set to about 1 Hz.

The drift canceling operation in this embodiment is based on the clock signal frequency and the number of bits (voltage correction width that can be changed in one operation) of the D/A conversion circuit consisting of the counter 31 and the resistance ladder circuit 33.
A pseudo time constant can be freely set by .
Depending on the setting conditions, a sufficiently low cutoff frequency can be achieved.

[Effects of the Invention] As described above, according to the acceleration detection device according to the present invention, the DC drift that occurs in response to, for example, changes in temperature over time is effectively canceled, and the Changes in acceleration can also be detected reliably. Therefore, when installed in a car, for example, it is possible to reliably detect the acceleration that acts on the car body in response to acceleration, brake operation, and steering wheel operation when the car is running, and is useful for anti-skid control of the car.
Electronic control such as automatic suspension control can be executed reliably.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating an acceleration detection device according to an embodiment of the present invention, FIG. 2 is a block diagram showing the above embodiment in more detail, and FIG. 3 is a block diagram illustrating another embodiment of the present invention. FIG. 4 is a block diagram showing the above embodiment in more detail, FIG. 5 is a diagram showing the form of a signal waveform for explaining the above embodiment, and FIG. 6 is a diagram showing a conventional acceleration detection device. FIG. 111, 112, 121, 122...Resistor (for acceleration detection), 13...Differential amplifier, 14...Output amplifier, 15...Operating point correction circuit, 16...Car stop determination circuit, 17...Timing circuit ,2
1...Sensor circuit, 23, 24, 41, 42...
Comparator, 31...up/down counter, 33...resistance ladder circuit.

Claims (1)

[Scope of Claims] 1. A semiconductor acceleration detection sensor that detects the magnitude of applied acceleration, an amplification means to which a detection signal from a sensor circuit including this acceleration detection sensor is supplied, and a reference operation of this amplification means. and correction command means for detecting a change in the output signal level from the amplifying means and instructing the operating point correcting means to a correction value corresponding to the detection result, An acceleration detection device characterized in that the correction means sets the operation reference point of the amplification means to an operation point that eliminates DC drift. 2. The correction command means is constituted by a stop determination means for detecting a stop state where no acceleration is applied;
The reference operating point correction means includes means for determining the deviation direction of the output signal from the amplification means in a state in which stoppage has been determined by the stoppage determination means, and means for setting a correction value corresponding to the determined deviation direction. Claim 1 consisting of
Acceleration detection device described in Section 2. 3. The reference point correction means comprises a polarity determination means for determining the polarity of the output signal from the amplification means, and means for modifying a correction value corresponding to the polarity determination result, and the correction command means is configured by a clock. Acceleration detection according to claim 1, wherein the acceleration detection device is constituted by signal generation means, and the correction value is corrected in response to a clock signal from the clock signal generation means. Device.