JPH09210823A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rectangular wave signal free from fluctuation by detecting a lower limit of a pressure detection signal by a bottom hold circuit, setting a threshold with the lower limit as a reference, and comparing the threshold with the pressure detection signal for outputting constant rectangular wave signals. SOLUTION: A pressure signal from a pressure-sensitive element 7 is input to a sensing circuit 9, and pressure is detected by a pressure detecting circuit 21. A bottom hold circuit 22 detects a lower limit of the pressure signal, a threshold setting means 23 sets a predetermined threshold with an output signal from the circuit 22 as a reference, and a comparison circuit 24 compares the threshold as the reference with the pressure signal for outputting constant rectangular wave signals. Since a reference value applied to the circuit 24 is the predetermined threshold set with the lower limit of the pressure value as the reference, correlation with the pressure signal is always constant so that rectangular wave signals free from fluctuation can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor for detecting a fuel injection pump pressure in a diesel engine, for example.

[0002]

2. Description of the Related Art Regulations on harmful exhaust gas from diesel engines are becoming stricter year by year. As a countermeasure against this, electronic control of fuel injection is required to appropriately control the fuel injection timing represented by the crank angle during rotation of the engine to reduce harmful exhaust gas. Therefore, it is first necessary to accurately determine the injection timing. In the conventional fuel injection timing determination method generally well known in the art, the position of the timer piston of the fuel injection pump is detected by a timer position sensor, and the injection timing is determined based on the detection value of the timer position sensor. Was there.

The injection timing obtained on the basis of the detection value of the timer position sensor and the actual injection timing do not exactly coincide with each other, so that it is impossible to accurately determine the fuel injection timing. In order to reduce sulfur oxides in exhaust gas, the sulfur content in fuel tends to be reduced year by year. Since sulfur acts as a lubricant for the fuel injection pump, when the sulfur content decreases, each sliding part of the fuel injection pump deteriorates, causing an error between the injection timing detected by the timer position sensor and the actual injection timing. However, there was a problem that the

In another conventional fuel injection pump for a diesel engine, a valve of a fuel injection nozzle for injecting fuel into a cylinder operates by a pressure responsive valve to raise fuel discharged from the fuel injection pump to a predetermined pressure. Is opened and fuel is injected into the cylinder. In this conventional example, the fuel injection timing is determined by measuring the pressure of the fuel in the fuel injection pump. This detection method has a more accurate relationship with the engine rotation phase than the former, and can always determine the actually required injection timing. In the fuel injection timing determination device according to this determination method, the pressure of the fuel pressurized by the fuel injection pump is compared with a predetermined reference value, and when the reference value is reached, a rectangular wave signal is output. Therefore, the injection start timing and the injection end timing are determined by detecting the rising or falling edge of this rectangular wave signal with the controller of the fuel injection pump.

In the pressure sensor for detecting the injection pressure which outputs the rectangular wave signal by comparing the pressure of the fuel in the fuel injection pump with the reference value like the above-mentioned other conventional example, a slight fluctuation of the pressure is generated. As a result, the output timing of the rectangular wave signal fluctuates, causing an error in the determination of the injection timing. The fuel in the fuel injection pump is compressed by the plunger and its pressure rises, but when the fuel injection nozzle starts injection, the pressure temporarily drops and then rises again, and the pressure rises near the injection start timing of the fuel injection nozzle. There is a step in the change and it does not rise smoothly. Therefore, it is desirable to set the pressure at the time when the pressure does not change much and is stable as the reference value.

Further, since the pressure value for determining the injection timing is a low pressure of about 1/6 to 1/10 of the maximum pressure in the fuel injection pump, the detection output is relatively low, and the error in the injection timing detection varies. In order to reduce, the detection circuit as a pressure sensor needs to have a very high S / N ratio and the reference value must be set with high accuracy.

FIG. 8 shows a conventional pressure sensor. Reference numeral 101 denotes a pressure sensitive element made of a pressure sensitive resistor.
The output from 1 is a pressure detecting means 102 comprising a differential amplifier.
And a predetermined pressure signal a is output. The pressure signal from the pressure detecting means 102 is input to the comparing means 103 and compared with a predetermined reference signal b to obtain a rectangular wave signal c. Here, the reference signal b is set so that the pressure at the time when the pressure does not change so much and is stable is used as the reference value, and on the other hand, in order to increase the S / N ratio, a filter is provided in front of the comparison means 103. Things were being done.

[0008]

However, in the conventional pressure sensor, the pressure signal changes in response to the fluctuation of the pump pressure of the fuel injection pump, and the offset of the input signal to the comparison means 103 cannot be determined. There is a problem that the duty ratio of the rectangular wave signal c that is output changes even if b is constant.

[0009]

In order to solve the above-mentioned problems, the pressure sensor of the present invention has a pressure detecting means for detecting the pressure applied to the pressure sensitive element and a lower limit value of the pressure signal from the pressure detecting means. Bottom hold means for detecting, threshold setting means for setting a predetermined threshold value based on the signal output from the bottom hold means, and threshold value set by the threshold setting means And a comparison means for outputting a constant rectangular wave signal for comparison with the pressure signal from the pressure detection means.

With this configuration, since the reference value applied to the comparison means is a predetermined threshold value based on the lower limit value of the pressure signal, even if the offset of the pressure signal applied to the comparison means cannot be determined. The relative relationship between the pressure signal and the threshold value is always constant, and a rectangular wave signal without fluctuation can be obtained.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention comprises pressure detection means for detecting the pressure applied to the pressure-sensitive element,
Bottom holding means for detecting the lower limit value of the pressure signal from the pressure detecting means, threshold setting means for setting a predetermined threshold value based on the signal output from the bottom holding means, and this threshold value. A pressure sensor having a threshold value set by the value setting means as a reference signal, and comparing means for outputting a constant rectangular wave signal in comparison with the pressure signal from the pressure detecting means, which is a highly accurate reference. It has the effect that the value can be determined.

The invention according to claim 2 of the present invention is a pressure sensor in which the threshold value setting means is a constant voltage drop circuit utilizing a constant voltage drop due to a constant current circuit and a resistor, and the pressure signal and the threshold value are always provided. Has the effect that a square wave signal with no fluctuation can be obtained.

According to a third aspect of the present invention, the pressure detecting means for detecting the pressure applied to the pressure sensitive element and the threshold value for setting the threshold value relative to the pressure signal from the pressure detecting means. A value setting means and a comparing means for outputting a constant rectangular wave signal by comparing the pressure signal from the pressure detecting means with the threshold value set by the threshold setting means as a reference signal; The threshold value setting means detects a constant current circuit receiving the pressure signal from the pressure detecting means and a constant voltage drop circuit utilizing a constant voltage drop due to a resistance, and a lower limit value of the pressure signal from the constant voltage drop circuit. Is a pressure sensor including a bottom hold circuit, which is configured to use the output signal from the bottom hold circuit as a reference signal,
This has the effect that the relative relationship between the threshold value and the pressure signal can be kept constant to obtain a rectangular wave signal with no fluctuation.

According to a fourth aspect of the present invention, the pressure detecting means for detecting the pressure applied to the pressure sensitive element, and the threshold value for setting the threshold value relative to the pressure signal from the pressure detecting means. A value setting means, a constant voltage circuit using a constant current circuit that receives a pressure signal from the pressure detecting means and a constant voltage drop by a resistor, and a threshold value set by the threshold value setting means. A threshold value setting means for detecting a lower limit value of the pressure signal from the pressure detecting means, and a comparing means for outputting a constant rectangular wave signal as a signal in comparison with the pressure signal from the constant voltage lowering means. It is a pressure sensor that includes a bottom hold circuit and uses the output from this bottom hold circuit as a reference signal to obtain a square wave signal that does not fluctuate by keeping the relative relationship between the threshold value and the pressure signal constant. It has the effect that it is possible.

(Embodiment 1) FIGS. 1 to 5 show a case where a pressure sensor in a first embodiment of the present invention is used as an injection pressure sensor of a fuel injection pump. 1 to 5, reference numeral 7 denotes a pressure sensitive resistor as a pressure sensitive element, and a pressure signal from the pressure sensitive element 7 is input to the detection circuit 9.
Here, the detection circuit 9 detects a pressure applied to the pressure signal from the pressure sensitive element 7, a bottom hold circuit 22 that detects a lower limit value of the pressure signal from the pressure detection circuit 21, and a bottom hold circuit 22. The threshold value setting means 23 for setting a predetermined threshold value based on the signal output from the hold circuit 22, and the threshold value set by the threshold value setting means 23 as a reference signal are used to detect the pressure. Circuit 2
It is composed of a comparison circuit 24 which outputs a constant rectangular wave signal in comparison with the pressure signal from 1.

The pressure signal output from the pressure detection circuit 21 has no fixed offset as shown in FIG. 2 (a). When this pressure signal is passed through the bottom hold circuit 22, a bottom hold signal which is the lower limit value of the pressure signal can be obtained as shown in FIG. Next, when the threshold value signal shown in FIG. 2C set by the threshold value setting means 23 from the bottom hold signal is input to the comparison circuit 24, the comparison circuit 24 outputs the pressure signal shown in FIG. And the rectangular wave signal shown in FIG. 2D is output. Here, the threshold signal shown in FIG. 2C is calculated from the bottom hold signal, which is the lower limit value of the pressure signal, by Δ.
Since the value of V is constant, the comparison circuit 24 in FIG.
In comparison with the pressure signal shown in (a), the comparison is made between the pressure signal on which the same offset is superimposed and the threshold value, and the comparison is always made with a constant value of ΔV from the lower limit value of the pressure signal being secured as the threshold value. Therefore, the crank angle information obtained as the rectangular wave signal is always constant.

By the way, when an Ac-type operational amplifier is used in each means constituting the detection circuit 9, it is necessary to couple each means with a capacitor, which is affected by offset fluctuation (drift) due to Ac coupling. It will be. In this case, the influence of offset fluctuation can be eliminated by using a constant current circuit and a constant voltage drop circuit utilizing a constant voltage drop due to a resistor as the threshold value setting means 23. That is, when a resistance voltage dividing circuit is used as the threshold value setting means 23, the absolute value of the threshold value is different due to the influence of offset variation even if the ratio between the power supply voltage _Vcc and the bottom hold signal is the same. However, the influence of offset fluctuation can be canceled by using a constant voltage drop circuit.

3 and 4 show the case where the same pressure sensor is used as an injection pressure sensor. In FIG. 3 and FIG. 4, the injection pressure sensor 1 is attached by screwing a screw 4 into an injection pressure sensor attachment portion 3 of a conventionally known combustion injection pump 2. The injection pressure sensor 1 has a pressure guide hole 5 in its lower portion, and this pressure guide hole 5 communicates with a plunger chamber 15 of the fuel injection pump 2 for applying pressure to the fuel. The upper end of the pressure guiding hole 5 is sealed by the diaphragm 6. On the upper surface of the diaphragm 6, two conventionally known pressure-sensitive resistors 7 are provided. The pressure sensitive resistor 7 is connected to a pressure detection circuit of a detection circuit 9 provided in the upper housing 8.

When the fuel pressure is applied to the diaphragm 6, the diaphragm 6 is distorted and the pressure sensitive resistor 7 is also distorted. The resistance value changes due to the strain of the pressure-sensitive resistor 7, and the pressure detection circuit of the detection circuit 9 causes the plunger chamber 1 to move.
The fuel pressure of 5 is measured.

The fuel injection pump 2 is connected to a crankshaft (not shown) of the engine and is adapted to rotate at half the rotational speed thereof. The discharge port 10 of the fuel injection pump 2 for discharging the pressurized fuel is connected to an injection nozzle 13 attached to a cylinder 12 of the engine by an injection pipe 11. Valve 1 according to the injection nozzle 13
Fuel is injected into the cylinder 12 by opening 4.

FIG. 5 is a waveform diagram showing changes in the pressure in the plunger chamber 15 of the fuel injection pump 2 detected by the pressure detection circuit. The fuel is compressed by the plunger 17 in the plunger chamber 15 when the crank angle of the crankshaft exceeds θ1. When the pressure in the plunger chamber 15 exceeds the residual pressure Pa, which is the pressure after fuel injection in the injection pipe 11, the discharge valve 18 of the fuel injection pump 2 opens. When the pressure further increases and reaches the valve opening pressure Pn at which the valve 14 of the injection nozzle 13 opens at the crank angle θ11, the valve 14 opens and the fuel is injected into the cylinder 12.
When the valve 14 is opened, the pressure increase temporarily becomes slow due to the fuel injection, but since the compression by the plunger 17 is further continued, the pressure increase starts again with pulsation. The injection ends by bypassing the fuel in the plunger chamber 15 and reducing the pressure at the crank angle θ3, for example. As a result, the discharge valve 14 closes at the crank angle θ13. After that, a sudden pressure change occurs and pressure pulsation occurs in the plunger chamber 15 (crank angle θ
5). This pulsation decays over time.

The detection output of the pressure detection circuit 21 is the comparison circuit 2
4 is input to one of the input terminals. In the threshold value setting circuit 23, a predetermined reference pressure Pr is set in advance. As the reference pressure value Pr, the pressure at the time when the pressure in the plunger chamber 15 is monotonously increasing, such as a constant increase rate, as will be described later, is selected. The output indicating the reference pressure value Pr is input to the other input terminal of the comparison circuit 24. In the comparison circuit 24, the detection output of the pressure detection circuit 21 is compared with the output representing the reference pressure value Pr. The output of the comparison result is used to determine the injection start timing.

Here, the reference pressure value Pr is the injection nozzle 13
Is set to a value lower than the valve opening pressure Pn at which the valve 14 is opened.

When the pressure of the fuel in the plunger chamber 15 rises due to the operation of the combustion injection pump 2 and exceeds the reference pressure value Pr at the crank angle θ10, the output is reversed and goes from the high level to the low level. The timing of the crank angle θ10 is referred to as “injection start timing”, but at this injection start timing, fuel has not yet been injected into the cylinder 12. After that, the fuel pressure further increases, and at the crank angle θ11, the valve opening pressure P
When n is reached, fuel is injected into the cylinder 12 of the engine. The fuel pressure further increases and reaches the maximum value at the crank angle θ12. After that, by bypassing the fuel in the plunger chamber 15, the pressure is reduced and the crank angle θ13
Thus, the value becomes lower than the reference pressure value Pr. As a result, the output goes high again. The timing from the crank angle θ10 to θ13 is called the “injection period”. The injection period has a constant time width as long as the shapes of the waveform diagrams showing changes in the reference pressure value Pr and the pressure are unchanged, and a rectangular wave having this time width is output. Therefore, the angle between the crank angles θ10 and θ11 is always constant, and the crank angle θ1 at which the valve 14 of the injection nozzle 13 opens based on the timing of the crank angle θ10.
The time of 1 can be accurately determined. By applying such a rectangular wave output to the controller (not shown) of the electronically controlled fuel injection pump and performing the same processing as in the past, it is possible to determine the crank angle of the injection start and the injection period, and control the injection timing. Is possible.

(Second Embodiment) FIG. 6 shows a pressure sensor according to a second embodiment of the present invention. In FIG. 6, a pressure detection circuit 21 for detecting the pressure applied to the pressure sensitive resistor 7.
Is applied to one input terminal of the comparison circuit 24. The pressure signal from the pressure detection circuit 21 is applied to threshold value setting means for setting a threshold value relative to the pressure signal. This threshold setting means is a constant voltage drop circuit 2 utilizing a constant voltage drop due to a constant current circuit and a resistor.
5 and a bottom hold circuit 26 for detecting the lower limit value of the pressure signal from the constant voltage drop circuit 25. The output from the bottom hold circuit 26 is used as a reference signal to the other input terminal of the comparison circuit 24. Is applied.

In this example, when the pressure signal passed through the constant voltage drop circuit 25 is passed through the bottom hold circuit 26, the bottom hold signal which is the lower limit value of the pressure signal converted into the constant voltage can be obtained, and the comparison circuit 24 By comparing with the pressure signal from the pressure detection circuit 21, the bottom hold signal applied to the comparison circuit 24 becomes a threshold value relative to the pressure signal, and a highly accurate threshold value can be determined. .

(Third Embodiment) FIG. 7 shows a pressure sensor according to a third embodiment of the present invention. In FIG. 7, a pressure detection circuit 21 for detecting the pressure applied to the pressure sensitive resistor 7.
The pressure signal from is applied to one input terminal of the comparison circuit 24 through a constant current circuit and a constant voltage drop circuit 27 utilizing a voltage drop due to resistance. On the other hand, the pressure detection circuit 21
Is applied to the other input terminal of the comparison circuit 24 through a threshold value setting means for setting a threshold value relative to the pressure signal. Here, the threshold setting means is a bottom hold circuit 2 for detecting the lower limit value of the pressure signal.
8.

In this example, the bottom hold signal is obtained by comparing the pressure signal, which has been converted to a constant voltage through the constant voltage drop circuit 27, and the bottom hold signal, which is the lower limit value of the pressure signal, by the comparison circuit 24. It becomes a threshold value relative to the pressure signal converted into a constant voltage, and a highly accurate threshold value can be determined.

[0029]

As described above, according to the present invention, the reference value applied to the comparing means is set to the predetermined threshold value based on the lower limit value of the pressure signal, so that the pressure signal applied to the comparing means is determined as the threshold value. It is possible to obtain a square wave signal with no fluctuation by keeping the relative relationship with the value always constant.

The reference signal applied to the comparison means is
Since the threshold value is set relative to the pressure signal, a square wave signal that does not fluctuate can be obtained as a highly accurate threshold value.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a pressure sensor according to a first embodiment of the present invention.

FIG. 2 is a signal waveform diagram of essential parts of the pressure sensor.

FIG. 3 is a sectional view of an injection pressure sensor showing an application example of the pressure sensor.

FIG. 4 is a side view of a fuel injection pump to which the injection pressure sensor is attached.

FIG. 5 is a waveform chart showing the relationship between the fuel pressure pressurized in the fuel injection pump and the crank angle of the engine.

FIG. 6 is a circuit diagram of a pressure sensor according to a second embodiment of the present invention.

FIG. 7 is a circuit diagram of a pressure sensor according to a third embodiment of the present invention.

FIG. 8 is a circuit diagram of a conventional pressure sensor.

[Explanation of symbols]

 7 Pressure Sensing Element 21 Pressure Detection Circuit 22, 26, 28 Bottom Hold Circuit 23 Threshold Setting Means 24 Comparison Circuit 25, 27 Constant Voltage Drop Circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Rito Tokaibayashi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. In-house (72) Inventor Shinjiro Ueda 1006 Kadoma, Kadoma-shi, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A pressure detection means for detecting a pressure applied to a pressure sensitive element, a bottom hold means for detecting a lower limit value of a pressure signal from the pressure detection means, and a signal output from the bottom hold means as a reference. Threshold value setting means for setting a predetermined threshold value, and a threshold value set by the threshold value setting means as a reference signal, and a constant rectangular wave compared with the pressure signal from the pressure detecting means. A pressure sensor having a comparison means for outputting a signal. 2. The pressure sensor according to claim 1, wherein the threshold value setting means is a constant voltage drop circuit utilizing a constant voltage drop due to a constant current circuit and a resistor. 3. A pressure detecting means for detecting the pressure applied to the pressure-sensitive element, a threshold setting means for setting a threshold value relative to a pressure signal from the pressure detecting means, and this threshold setting. Comparing the pressure signal from the pressure detecting means with a threshold signal set by the means and outputting a constant rectangular wave signal, the threshold setting means includes the pressure detecting means. The bottom hold circuit includes a constant current circuit that receives a pressure signal from the input terminal, a constant voltage drop circuit that uses a constant voltage drop due to a resistor, and a bottom hold circuit that detects the lower limit value of the pressure signal from the constant voltage drop circuit. A pressure sensor configured to use an output signal from a circuit as a reference signal. 4. A pressure detecting means for detecting a pressure applied to the pressure sensitive element, a threshold setting means for setting a threshold value relative to a pressure signal from the pressure detecting means, and the pressure detecting means. The constant voltage circuit using the constant current circuit that receives the pressure signal of the above, and the constant voltage drop means that uses the constant voltage drop due to the resistance, and the threshold value set by the threshold value setting means as the reference signal. The threshold value setting means includes a bottom hold circuit for detecting a lower limit value of the pressure signal from the pressure detection means, and a bottom hold circuit for comparing the pressure signal and a constant rectangular wave signal. A pressure sensor configured to use the output from the circuit as a reference signal.