JPH07209126A - System for detecting and controlling combustion pressure using piezoelectric sensor - Google Patents

Abstract

PURPOSE:To make it possible to detect the correct combustion pressure by computing a load torque based on the data of the combustion pressure, operating the optimum air-fuel ratio corresponding to the fluctuation of the torque caused by the change in load, and controlling the fuel injection quantity and the feeding quantity of air. CONSTITUTION:The combustion pressure of a combustion chamber 15 is measured by a pressure sensor transmitter 7 based on the ignition timing signal from an ignition plug 12. The torque is computed by an operating unit 16 based on the measured value. When the torque fluctuation is recognized, signals for controlling the actuators for a fuel injection nozzle 13 and an air-quantity regulating valve 14 are outputted. The combustion pressure generated during the operation of an internal combustion engine is measured. The fluctuation of the torque caused by the fluctuation of a load is compared with a reference value, which is stored beforehand. Signals, which control the opening degree of the fuel injection valve and the opening degree of the air-intake valve of a port, are imparted so as to obtain the optimum mixture gas, and the air-fuel ratio is controlled. Thus, the slight change in combustion pressure can be discriminated.

Description

Detailed Description of the Invention

[0001]

[Industrial application] A system for calculating the optimum air-fuel ratio to obtain the required combustion pressure even for torque fluctuations by constantly measuring the combustion pressure of an automobile internal combustion engine, and controlling the air intake and fuel injection actuators. Can be configured. Further, since the speed of the piezoelectric crystal pressure sensor responding to the pressure pulse is 1 μS, and the pressure resolution or the threshold value is 0.01 N, the pressure peak waveform associated with combustion can be detected, so that misfire in the no-load state or engine braking state can be detected. It is possible to configure a system that monitors an abnormal peak waveform associated with the above, compares it with the normal waveform, and self-diagnoses the emission of NOx and the like in the exhaust gas.

[0002]

2. Description of the Related Art In order to avoid knocking due to abnormal combustion of an engine, the following three types of technologies have been used. The first method is to attach an accelerometer type knock sensor to the cylinder block, detect vibration of the engine block caused by abnormal combustion and change ignition timing to avoid knocking. 2 is applied to a lean-burn engine, and a combustion pressure sensor is installed in the combustion chamber to measure the combustion pressure directly with respect to the torque fluctuation due to the fluctuation of the load so as to supply the gas with an appropriate air-fuel ratio. Method. A load washer-type crystal piezoelectric sensor 3 is attached to the cylinder head by a fastening bolt that connects the cylinder head and the cylinder block. Since the cylinder head floats against the tightening force of the tightening bolt due to combustion in the cylinder, a force in the compression direction is applied to the load washer type crystal piezoelectric sensor. The load washer type pressure sensor outputs a charge signal according to the pressure when a compressive force is applied, so this charge can be converted into a voltage signal by a charge amplifier, and the torque can be calculated from that signal, and the torque can be calculated appropriately according to the torque value. It is possible to supply a gas of various air-fuel ratios.

[0003]

A method of detecting the vibration of a cylinder block caused by abnormal combustion by a knock sensor is to attach a sensor to the cylinder block and detect the vibration, so that any vibration generated by the cylinder block is picked up. Will end up. Especially, the vibration caused by the impact when opening and closing the intake and exhaust valves is large. Therefore, it may be difficult to determine the signal whether the vibration itself is due to combustion or due to other factors. In reality, it is necessary to detect the rotation angle of the crankshaft and judge the vibration generated in the compression stroke of the piston, the top dead center, and the combustion stroke as a signal due to combustion. This knock sensor is inferior in detection accuracy because it cannot directly detect combustion pressure due to combustion. The method of installing the combustion pressure sensor in the cylinder to detect the combustion pressure is excellent in accuracy, but since the sensor is directly installed inside the cylinder, the sensor is constantly exposed to a high temperature of about 300 ° C. Since the temperature reaches 3000 ° C, the sensor must have a heat resistant structure. Further, since the pressure due to combustion inside the cylinder is directly measured, it is necessary to increase the number of sensors according to the number of cylinders. In addition, mounting holes for mounting the sensor must be machined. Combustion pressure measurement technology using a load washer-type crystal piezoelectric sensor can measure only the reaction force due to combustion, the ambient temperature where the sensor is used is low, and the number of sensors increases proportionally even if the number of cylinders increases. No need to increase. There is no need for machining for mounting the sensor on the cylinder block or cylinder head. However, the sensor used for this measurement must be of a washer type in order to pass through the tightening bolt, and it takes a lot of cost to process the sensor element and the sensor housing, so that the cost of the sensor itself remains expensive. The combustion pressure sensor and its utilization system according to the present invention can solve the problems related to conventional products, technologies, prices, and the like.

[0004]

Of the three crystallographic axes X, Y and Z of artificial quartz, the two axes X and Y are called electrical axes and Z is called an optical axis. . Quartz generates an electric charge by the piezoelectric effect that it has in response to a given physical force or pressure. Specifically, if a force is applied in the direction of the X axis with respect to the Y axis of the crystal, then both sides of the Y axis will appear. To generate electric charges (vertical axis effect). Similarly, if a force is applied to the X axis in the Y axis direction, electric charges are generated on both sides of the X axis (horizontal axis effect). 1 and 2 are cut (X-
The force or pressure F is applied to the cut quartz piezoelectric element 1.
And the polarity of the electric charge q generated on the quartz crystal piezoelectric element. That is, FIG. 1 shows a case where force or pressure F acts on the piezoelectric crystal element 1 as a compressive force. In Fig. 1, force or pressure is applied in the compression direction, so + F
Indicated by. FIG. 2 shows the electric charge q generated on the quartz crystal piezoelectric element when the force or pressure F acts in the opposite direction in the pulling direction.
Shows the polarity of. In FIG. 2, the force or pressure acts in the pulling direction, and thus is indicated by -F. The dotted line shows the state before the force or pressure is applied to the crystal element, and the solid line shows the state where the element is deformed by the force or pressure. By the way, the mechanical rigidity of the quartz piezoelectric element is extremely high.
N / μm. The nominal sensitivity for the vertical axis effect is 2.31.
pC / N. That is, in the vertical axis effect, an electric charge q appears on the surface of the crystal element on which a load is applied in direct proportion to the total force or pressure applied, and the amount thereof is 2. per 1 Newton regardless of the size or shape of the crystal element. A charge of 31 pico coulombs appears. FIG. 3 shows a basic configuration of a crystal piezoelectric sensor for pressure detection according to the present invention. That is, in FIG. 3, two crystal piezoelectric elements 1, an electrode 2 using a thin and rigid metal plate, and a shape that can be arranged between a cylinder block and a cylinder head of an internal combustion engine are used to assemble the cylinder block and the cylinder head. The housing 3 maintains parallelism so that the applied tightening force is evenly received, and the bush 4 made of a highly insulating material for taking out the generated electric charge q without loss is shown. FIG. 3 shows the structure of the quartz crystal piezoelectric sensor for pressure detection in an easy-to-understand manner. These elements are housed in the housing 3 and then packaged by applying an optimum preload. FIG. 4 shows a state in which a charge amplifier 6 for converting an electric charge (or electric charge signal) q generated in the pressure detecting crystal piezoelectric element 1 into an easily handled electric signal is connected. The quartz crystal piezoelectric sensor for pressure detection is combined with the quartz crystal piezoelectric element 1 so as to output a charge -q which is directly proportional to the total force F applied. Therefore, the charge amplifier 6 is theoretically -T
It is designed as an amplifier that doubles the amplification. FIG. 5 shows the relationship between the force or pressure F acting on the piezoelectric crystal sensor for pressure detection and the signal voltage V output from the charge amplifier 6. That is, if force or pressure acts on the pressure-detecting quartz crystal piezoelectric sensor 1 in -F (pulling direction)-
The charge −q increases in direct proportion to F, and the signal voltage + V from the charge pump 6 conversely increases when the force or pressure acts on + F (compressing direction), the charge + q increases in direct proportion to + F and the charge amplifier 6 increases. Indicates that the signal voltage -V of is output. Next, the application of the proposed system to an internal combustion engine will be described. Capacity 2-3,000
For a small internal combustion engine of about cc, the cylinder block and the cylinder head are generally tightened with a force of about 5 to 7 tons. The reaction force acting on the cylinder head when the air-fuel mixture burns is about 1 ton at maximum. When the combustion pressure sensor according to the present invention is applied to these small-sized internal combustion engines, the sensor is first arranged between the cylinder block and the cylinder head, and the combustion pressure is 3 to 40 regardless of the tightening force of both.
A compressive force + F which is larger by about 10% is given. With this configuration, the reaction force received by the cylinder head during combustion can be applied to the sensor as a tensile force -F. In FIG. 6, a sensor is sandwiched between the cylinder block 9 and the cylinder head 8 and a torque bolt 17 is used to apply force or pressure + F in the compression direction.
7 shows a state in which -F acts on the sensor by the force or pressure in the pulling direction which the cylinder head 8 receives due to the reaction force generated when combustion occurs inside the combustion chamber. Since the force in the compression direction or the pressure + F is always applied to the pressure detecting crystal piezoelectric sensor 1 except during combustion, theoretically the signal voltage -V is output from the charge amplifier 6, so in the system according to the present invention, the internal combustion engine is used. When the engine is started, that is, before combustion occurs in the combustion chamber and the force or pressure in the pulling direction of -F acts on the sensor, the output of the charge amplifier 6 is reset to zero the signal voltage. The crystal piezoelectric sensor element of the present invention has a simple shape as shown in FIG. 3, which is the easiest to process, and the effective surface area of the sensor element is 150 at maximum in consideration of the compression force of about 2 tons.
It may be about mm ² . The housing also has a low-cost shape, so that the entire crystal piezoelectric sensor for pressure detection can be made very compact. Furthermore, the sensor mounting position is only sandwiched between the cylinder block and the cylinder head and not directly installed in the combustion chamber, so the combustion pressure can be measured regardless of the number of combustion chambers (number of cylinders), and no heat countermeasures are required. It is characterized by such things.

[0005]

[Operation] In the piezoelectric crystal sensor, the element is deformed by the force or pressure acting on the piezoelectric crystal element, and the charge energy is charged on the surface of the element according to the deformation amount. Therefore, the force acting by measuring the amount is applied. Alternatively, the principle is to convert it into pressure, but in reality it is difficult to directly handle the charged charge energy, so it must be converted into a voltage signal by a charge amplifier. In order to prevent the discharge of the charged electric charge, it is necessary to keep the insulation resistance of the elements constituting the system such as the sensor element itself, the sensor housing, the connector and the connection cable to the charge amplifier high. Therefore, the crystal piezoelectric sensor for pressure detection according to the present invention is integrated with the charge amplifier to eliminate the connector and the connecting cable, and the charge amplifier circuit is surface-mounted or hybrid IC to be miniaturized as much as possible. It is used as a sensor transmitter with a conversion circuit packaged. This crystal piezoelectric pressure sensor transmitter is calibrated by a force or pressure in the pulling direction, and a preload is applied between the cylinder block and the cylinder head by a built-in torque bolt. The amount of pressurization is + F>-
The force or pressure acting between the cylinder block and the cylinder head during combustion at F must be several tens of percent greater than -F. Since the negative force or pressure acts on the cylinder head due to the combustion in the combustion chamber, the force or pressure in the pulling direction also acts on the quartz crystal voltage sensor transmitter. Since the sensor transmitter is calibrated in advance with the reference pressure (N / m ² ) or the force (N or kgw), the electric signal output in direct proportion to the combustion pressure can be converted into each induction unit. In this proposal, an encoder is attached to the crankshaft to measure whether the signal from the sensor / transmitter is due to combustion in the combustion chamber or noise due to other vibrations, and the rotation angle is measured and used as a reference. The system is configured to determine the measurement signal by linking with the ignition timing of the combustion chamber.

[0006]

FIG. 5 shows the configuration of a system for supplying an optimum air-fuel mixture by a combustion pressure measurement signal from a crystal piezoelectric pressure sensor transmitter according to the present invention. In FIG. 5, 7 is a pressure sensor transmitter, 8 is a cylinder head, 9 is a cylinder block, 10 is a crankshaft rotation angle detection encoder, 11 is an intake port, 12 is a spark plug, 13 is a fuel injection nozzle, and 14 is an air amount. Control valve,
Reference numeral 15 is a combustion chamber, and 16 is an arithmetic unit. The combustion pressure in the combustion chamber 15 is measured by the pressure sensor / transmitter 7 based on the ignition timing signal from the spark plug 12 or the crankshaft rotation angle detection encoder 10. A torque is calculated by the arithmetic unit 16 based on the measured value, and if a torque fluctuation is recognized, a signal for controlling the actuators of the fuel injection nozzle 13 and the air amount adjusting valve 14 is output. The fuel injection valve opening is measured to measure the combustion pressure generated during operation of the internal combustion engine with high accuracy and in real time, and to compare the torque fluctuation due to load fluctuation with a prestored reference value to obtain the optimum mixture. And a signal for controlling the opening degree of the air intake valve of the port to control the air-fuel ratio. The quartz piezoelectric pressure sensor according to the present invention responds to a pressure pulse with a speed of 1 μS and a pressure resolution or threshold value of 0.
Since it is 01N, even a slight change in the combustion pressure can be identified.

[0007]

Since the torque fluctuation due to the load fluctuation can be constantly measured while the internal combustion engine is operating, lean combustion can be performed under normal load conditions, and fuel consumption and NOx amount in exhaust gas can be expected to be reduced. . It is possible to control the air-fuel ratio as the load increases and to respond to torque changes.

[Brief description of drawings]

FIG. 1 shows a charge q and its polarity when a force in a compression direction is applied to a crystal piezoelectric element 1.

FIG. 2 shows a charge q and its polarity when a force in a pulling direction acts on the crystal piezoelectric element 1.

FIG. 3 shows configurations of a piezoelectric crystal element 1 and a sensor housing 3 according to the present invention.

FIG. 4 shows a state of a charge amplifier 6 that converts a charge q generated in a piezoelectric crystal element 1 and a voltage signal corresponding to the charge q.

FIG. 5: Force or pressure applied to a quartz piezoelectric sensor +
F and -F, and signals + V and -V output from the charge amplifier corresponding thereto are shown. The output signal is directly proportional to the applied force or pressure.

FIG. 6 is a torque bolt 17 in which a sensor transmitter 7 is sandwiched between a cylinder block 9 and a cylinder head 8.
Shows a state in which the pressure + F in the compression direction is applied.

FIG. 7 shows a state in which −F acts on the sensor transmitter 7 by the force or pressure in the pulling direction that the cylinder head 8 receives by the reaction force generated when it burns inside the combustion chamber.

FIG. 8 shows a configuration of a torque fluctuation detection and mixture control system of an internal combustion engine according to the present invention.

[Explanation of sign]

 1 Crystal Piezoelectric Element 2 Electrode 3 Housing 4 Insulation Bush 5 Charge Amplifier 6 Pressure Sensor / Transmitter 7 Cylinder Head 8 Cylinder Block 9 Crankshaft Rotation Angle Detection Encoder 10 Intake Port 11 Spark Plug 12 Fuel Injection Nozzle 13 Air Volume Control Valve 14 Combustion chamber 15 Calculation unit 16 Torque bolt 17 Cylinder head tightening bolt + F Force or pressure acting in the compression direction −F Force or pressure acting in the pulling direction q Electric charge q + Positive (+) electric charge q− Polarity − ( Negative) charge

Claims (4)

[Claims] 1. In a crystal piezoelectric pressure detection sensor, a crystal element is arranged so as to output a charge signal -q in direct proportion to the magnitude of the force or pressure applied when the force or pressure is applied in the pulling direction. Structure of a quartz crystal piezoelectric sensor. 2. A quartz piezoelectric pressure detection sensor is arranged between a cylinder block and a cylinder head of an internal combustion engine, and a pressure is applied to the sensor. A structure for mounting a pressure detection sensor in which the combustion pressure generated in the cylinder acts as a reaction force in the pulling direction against the applied pressure. 3. A combustion pressure applied to the cylinder head when the mixed gas burns in the combustion chamber is measured by a crystal pressure voltage pressure detection sensor arranged between the cylinder block and the cylinder head, torque is calculated from the combustion pressure, and load is calculated. A system that controls the actuator by calculating the optimum air-fuel ratio of the mixed gas according to the torque fluctuation due to. 4. A pressure peak waveform associated with combustion applied to a cylinder head when a mixed gas burns in a combustion chamber is detected by a crystal pressure voltage pressure detection sensor arranged between a cylinder block and a cylinder head, and particularly in a no-load state. Or a system that self-diagnoses misfires that occur in engine braking conditions.