JP2013076362A - Control device for multi-cylinder internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress variations in air-fuel ratio between cylinders resulting from the torsion of a cam shaft.SOLUTION: On the cam shaft 23, a distortion sensor 35 is provided for detecting the torsion of the cam shaft 23. A valve timing for each of the cylinders is calculated on the basis of the torsion of the cam shaft 23, an intake air amount for each of the cylinders is calculated on the basis of the calculated valve timing, and an fuel injection amount is corrected with respect to each of the cylinders to set an air-fuel ratio for each of cylinders to be a target air-fuel ratio, on the basis of the intake air amount. The used distortion sensor 35 is a semiconductor type distortion sensor on the semiconductor substrate of which a wheatstone bridge circuit constituted of a plurality of diffused resistors is formed.

Description

  The present invention relates to a multi-cylinder internal combustion engine in which a fuel injection valve is provided for each cylinder, and more particularly to a technique for suppressing variation in air-fuel ratio between cylinders caused by camshaft torsion.

  In a valve train of an internal combustion engine, generally, rotational power of a crankshaft is transmitted to one end in the longitudinal direction of a camshaft, and a cam provided on the camshaft causes an intake valve or an exhaust valve to react with a valve spring reaction force or It is configured to open and close against the in-cylinder pressure.

  On the other hand, Patent Document 1 describes a technique of attaching a strain sensor to a rotating body and measuring the distortion and torque of the rotating body. This strain sensor is a semiconductor strain sensor in which a Wheatstone bridge circuit composed of a plurality of diffused resistors is formed on a semiconductor substrate, has extremely high sensitivity to strain along a specific direction, and is about 1 to 2 mm square. It is characterized by the following compact and lightweight construction.

JP 2006-220574 A

  A camshaft, which is a rotating body of an internal combustion engine, is driven to rotate at one end in the longitudinal direction via a timing belt or a chain, and therefore, particularly between the one end and the other end in the longitudinal direction on the high rotation and high load side. Causes a twist. If the valve timings of the intake valves of a plurality of cylinders driven by the camshaft differ due to distortion and deformation due to this twisting, the intake air amount varies among the cylinders, and the air-fuel ratio varies among the cylinders. Therefore, there is a risk that the desired exhaust purification performance by the three-way catalyst or the like may be hindered.

  The present invention has been made in view of such circumstances, and uses the strain sensor as described above to suppress variations in air-fuel ratio among cylinders caused by camshaft torsion of a multi-cylinder internal combustion engine. The purpose is that.

  Therefore, in the present invention, a strain sensor is attached to the camshaft to detect the torsion of the camshaft, and based on this torsion, the fuel injection amount is corrected for each cylinder so as to equalize the air-fuel ratio of each cylinder. Configured to do.

  As the strain sensor, a semiconductor strain sensor in which a diffusion resistor and an amplifier circuit are formed on a semiconductor substrate is suitable. Since such a semiconductor strain sensor can obtain very high sensitivity, it is possible to detect a slight distortion and displacement due to torsion of the camshaft with high accuracy. In particular, an integrated amplifier circuit has high noise resistance and is not affected by vibration or noise of the valve train of the internal combustion engine. In addition, since the strain sensor is very small and lightweight with a size of 1 to 2 mm square or less, even when it is attached to the camshaft, the centrifugal force due to its own mass is small, and adhesion and joining to the camshaft is also possible. It can be done easily.

  ADVANTAGE OF THE INVENTION According to this invention, the dispersion | variation in the air fuel ratio between cylinders resulting from the twist of the camshaft of a multicylinder internal combustion engine can be suppressed.

The block diagram which shows the control apparatus of the inline 4 cylinder type internal combustion engine which concerns on one Example of this invention. FIG. 2 is a perspective view showing a valve train of the internal combustion engine of FIG. 1. The perspective view which shows the principal part of the valve operating system of the said internal combustion engine. Explanatory drawing which shows the difference in valve timing of # 1 cylinder and # 4 cylinder resulting from torsion of a camshaft. The functional block diagram which shows the control processing of an engine control unit. Explanatory drawing which shows the input / output system of an engine control unit. The block diagram which shows the correction process of the fuel injection amount for every cylinder using the sensor output of a distortion sensor. The flowchart which shows the flow of correction | amendment control of the fuel injection amount for every cylinder. 6 is a timing chart showing changes in sensor output of a strain sensor in a port injection internal combustion engine, where (A) shows a case where the engine speed is constant and the load changes, and (B) shows a constant load and the engine speed changes. FIG. The characteristic view which shows the relationship between the engine speed and torque of a direct injection type internal combustion engine. 6 is a timing chart showing changes in the sensor output of a strain sensor in a direct injection type internal combustion engine, where (A) shows a case where the engine speed is constant and the load changes, and (B) shows a case where the load is constant and the engine speed is constant. Explanatory drawing in the case of changing.

  A preferred embodiment of a control apparatus for a multi-cylinder internal combustion engine according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing a control device for an in-line four-cylinder spark ignition type internal combustion engine according to an embodiment of the present invention. A cylinder block 1 a of the internal combustion engine 1 is formed with a cylinder (bore) 2 in which a piston 3 is slidably disposed. A combustion chamber 4 is defined above the piston 3. At the center of the ceiling of the pent roof type combustion chamber 4 formed in the cylinder head 1b, an ignition plug 5 is provided as an ignition device for spark-igniting the air-fuel mixture in the combustion chamber 4. In addition, an intake passage 7 is connected to the combustion chamber 4 via an intake valve 6, and an exhaust passage 9 is connected via an exhaust valve 8. The intake passage 7 is provided with a throttle valve 10 for adjusting the amount of intake air, and a fuel injection valve 17 for injecting and supplying fuel toward the intake port for each cylinder. The configuration is not limited to such a port injection type, but may be a direct injection type configuration in which fuel is directly injected into the combustion chamber 4 of each cylinder, as will be described later.

  The exhaust passage 9 is provided with a three-way catalyst 11 for purifying exhaust gas, and an air-fuel ratio sensor 12 such as an oxygen concentration sensor for detecting the air-fuel ratio of the exhaust on each of the upstream side and the downstream side of the catalyst 11. 13 is provided, and air-fuel ratio control is performed according to the detection signals of these air-fuel ratio sensors 12 and 13. For example, depending on the difference between the air-fuel ratio detected by the air-fuel ratio sensors 12 and 13 and the target air-fuel ratio so that the air-fuel ratio of the exhaust is maintained in the vicinity of the target air-fuel ratio (theoretical air-fuel ratio) under specific operating conditions. The well-known air-fuel ratio feedback control for adjusting the fuel injection amount is performed.

  Further, the internal combustion engine 1 includes a water temperature sensor 14 for detecting the cooling water temperature in the water jacket 18, a throttle opening sensor 15 for detecting the opening of the throttle valve 10, and a cam angle based on rotation angles of camshafts 23 and 24 described later. In addition to the cam angle sensor 16 for detecting the crankshaft 21 and the crank angle sensor 196 (see FIG. 2) for detecting the crankshaft 21 and the crank angle, various sensors such as a strain sensor 35 to be described later are provided. An output signal is input to the engine control unit (ECU) 20. Note that the cam angle and the crank angle may be separately detected from the rotation angle of one of the cam angle sensor and the crank angle sensor.

  FIG. 2 is a perspective view showing a valve operating system of the internal combustion engine, and FIG. 3 is a schematic perspective view showing a main part of the valve operating system. This internal combustion engine 1 is of an in-line 4-cylinder type in which four # 1 to # 4 cylinders are arranged in series from the engine front side along the cylinder row direction. The crankshaft 21 is connected to the piston 3 of each cylinder via a connecting rod 22, and the combustion pressure is transmitted to the crankshaft 21 as rotational power via the piston 3 and the connecting rod 22. As an example, the ignition order is # 1 → # 3 → # 4 → # 2, and the crank pins of each cylinder are arranged with a phase difference of 180 degrees in the order of ignition so that the explosion intervals are equal. In FIG. 2, only the configuration of the # 4 cylinder at the rear end of the engine among the four cylinders is illustrated for easy understanding.

  In the valve operating system, a pair of intake valves 6 and a pair of exhaust valves 8 are provided for each cylinder, an intake side camshaft 23 is located above the intake valves 6, and an exhaust side camshaft 24 is cranked above the exhaust valves 8. A so-called DOHC (double overhead cam) mechanism provided in parallel with the shaft 21 is used. The valve operating system is not limited to this and may be a mechanism using a rocker arm or a swing arm, for example.

  In this example, a mechanism including a timing belt 25 which is a toothed belt is used as a mechanism for reducing the rotation of the crankshaft 21 to ½ and transmitting it to the camshafts 23 and 24. The timing belt 25 is wound around a crank pulley 26 provided at the front end of the crankshaft 21 and cam pulleys 27 and 28 provided at the front ends of the camshafts 23 and 24. The timing belt 25 is provided with a tensioner 29A, an idler pulley 29B and the like so as to optimize the trajectory / layout while keeping the belt tension of the timing belt 25 appropriately. The power transmission mechanism to the intake / exhaust valves is not limited to the mechanism using the timing belt 25, but may be a mechanism using gears or chains.

  As shown in FIG. 3, the intake camshaft 23 is provided with a pair of cams 30 for each cylinder, and each cam 30 has a cam nose 31 having a predetermined cam profile corresponding to the valve lift characteristics. Is provided. When the cam nose 31 presses the valve lifter 32 according to the rotation of the camshaft 23, the intake valve 6 is mechanically opened and closed via the valve stem 33 against the valve spring reaction force and the in-cylinder pressure. Yes. The exhaust side camshaft 24 has the same structure as the intake side camshaft 23. The cams 30 of each cylinder are arranged with a phase difference of 90 degrees (a crank angle of 180 degrees) in the order of ignition so that the intake valve and the exhaust valve open and close at an appropriate timing according to the combustion cycle of each cylinder.

  Since the camshafts 23 and 24 are driven on one end side and the engine front end side in the longitudinal direction in which the cam pulleys 27 and 28 are provided, the camshafts 23 and 24 A rotational phase difference occurs between the rear end and so-called twist. The twist angle of the camshaft due to this twist (rotational phase difference with respect to the rotational phase of the cam pulleys 27 and 28 at the front end) becomes larger toward the rear side of the engine. For this reason, as shown in FIG. 4, for example, the valve timing of the # 4 cylinder on the rear side of the engine indicated by the characteristic of the solid line in the figure with respect to the valve timing of the # 1 cylinder on the front side of the engine indicated by the characteristic of the two-dot chain line in the figure. The timing is retarded, and the valve timing becomes uneven among the cylinders. In the illustrated example, the valve timing of the intake valve of the # 4 cylinder is retarded compared to the # 1 cylinder, so that the opening timing of the intake valve is delayed from the exhaust top dead center TDC, and the closing timing of the intake valve is the intake timing. It is further delayed from the bottom dead center BDC. For this reason, the amount of intake air decreases and the combustion stability decreases. When the valve timing varies between the cylinders in this way, the intake air amount varies from cylinder to cylinder, and the air-fuel ratio varies from cylinder to cylinder. Thus, the three-way catalyst 11 is used, deviating from the target air-fuel ratio. The desired exhaust purification performance cannot be obtained.

  Therefore, in this embodiment, a strain sensor 35 that detects torsion of the camshaft 23 is provided. As will be described later, the fuel injection amount is corrected for each cylinder based on the twist of the camshaft 23, so that the air-fuel ratio of each cylinder is made uniform. Although an example in which the strain sensor 35 is provided on the intake side camshaft 23 having a large influence on the intake air amount is described here, the strain sensor 35 is also provided on the exhaust side camshaft 24 in the same manner. May be reflected in the calculation of the intake air amount described later.

  The strain sensor 35 is bonded to, or joined or fitted to, the outer peripheral surface of the camshaft 23 using, for example, an adhesive. Based on the sensor output corresponding to the distortion of the camshaft 23 detected by the distortion sensor 35, the torsion angle (rotational phase difference with respect to the front end position) of the camshaft 23 in each cylinder is obtained. Since the torsion angle of the camshaft 23 increases in a cumulative manner toward the rear end side, the torsion angle of each cylinder is obtained, for example, by integrating the torsion angles for each predetermined section from the front end position of the camshaft 23. It is done.

  In this embodiment, as shown in FIG. 3, the strain sensor 35 has three positions on the outer peripheral surface of the camshaft 23, more specifically, the front end position between the cam pulley 27 provided at the front end and the cam 30 of the # 1 cylinder. 35A, provided at three positions: a central position 35B between the cam 30 of the # 2 cylinder and the cam 30 of the # 3 cylinder, and a rear end position 35C of the rear of the cam 30 of the # 4 cylinder. In this case, the camshaft 23 can be divided into three sections, ie, a front part, a center part, and a rear part, in the longitudinal direction, and the twist angle can be measured for each section. Even when the amount of deformation varies depending on the position, the torsion angle of each cylinder can be detected with high accuracy.

  The installation position and number of strain sensors 35 are not limited to this, and can be appropriately set in consideration of detection accuracy, cost, etc. For example, two positions of the front end position 35A and the rear end position 35C, or the center position It is good also as one place of 35B.

  The specific structure of the strain sensor 35 is publicly known as described in the above Japanese Patent Application Laid-Open No. 2006-220574, and a detailed description thereof will be omitted. And a semiconductor strain sensor in which an amplifier circuit is formed on the same substrate. In principle, when distortion due to torsion occurs in the camshaft 23, shearing stress is generated, and the torsion of the camshaft 23 is measured by detecting this shearing stress using the piezoresistance effect of the silicon substrate. is there.

  Such a semiconductor strain sensor 35 has high sensitivity to strain along a specific direction (generally, two directions orthogonal to each other). Accordingly, the strain sensor 35 is arranged so that the strain detection direction can accurately detect the torsion of the camshaft 23. As an example, as illustrated, the diagonal direction of the rectangular chip, which is the strain detection direction of the strain sensor 35, is arranged along the circumferential direction and the axial direction of the camshaft 23.

  The sensitivity of the semiconductor strain sensor 35 is very high, and the slight distortion and twist of the camshaft 23 can be measured with high accuracy. Moreover, since it is a small and lightweight structure about 1-2 mm square, even if it is a case where it attaches to the camshaft 23, the centrifugal force resulting from own mass is small, and joining is also easy. In particular, the semiconductor strain sensor 35 with an integrated amplifier circuit has high noise resistance and is affected by noise even when applied to the camshaft 23 of a valve train that has many noise sources such as vibration. There is no. The strain sensor 35 is configured to be able to supply power and transmit an output signal to the engine control unit 20 wirelessly.

  As shown in FIG. 5, the engine control unit 20 includes a CPU 101 that calculates and executes various control processes, a ROM 102 as a storage device, a RAM 103, and an EEPROM (external storage unit) 120, as well as an input side. A digital input circuit 104 to which a signal from an IG (ignition) switch 41 is input, a pulse input circuit 105 to which pulse signals from a cam angle sensor 16 and a crank angle sensor 196 are input, an airflow sensor 42 to detect an intake air amount, An analog input circuit 106 to which signals from the water temperature sensor 14, the air-fuel ratio sensors 12 and 13, the strain sensor 35, and the like are input is provided. A digital output circuit 111 for the relay control 43 is provided on the output side, and fuel injection is performed. Timer for valve 17, spark plug 5, and throttle valve 10 Constant output circuit 112 is provided, further, a communication circuit 113 or the like for scanning tool 44 is provided.

  As shown in FIG. 6, the CPU 101 of the engine control unit 20 includes an air flow sensor 42, an intake air temperature sensor 45 that detects intake air temperature, a water temperature sensor 14, a crank angle sensor 16, a throttle opening sensor 15, an air-fuel ratio sensor 12, 13. In addition to the ignition switch 41, an input / output interface 302 for inputting input signals from the three strain sensors 35A to 35C is provided. Control signals are output to the fuel injection valves 17 of the four cylinders and the spark plugs 5 of the four cylinders via the driver 310. In accordance with this control signal, the fuel injection amount, fuel injection timing, and ignition timing are controlled for each cylinder.

  FIG. 7 shows a control process realized by the engine control unit 20 as a functional block diagram. The engine operation state detection means 51 detects the engine operation state such as the intake air amount, the engine speed, and the cooling water temperature based on signals from various sensors such as the air flow sensor 42, the cam angle sensor 16, the crank angle sensor 196, and the water temperature sensor 14. To detect. The valve timing calculation unit 52 calculates the actual valve timing of each cylinder based on the twist angle of the camshaft 23 detected by the strain sensor 35. As described above, since the twist angle of the camshaft 23 increases as the cylinder is closer to the rear end, the actual valve timing is retarded. The intake air amount calculation means 53 calculates the actual intake air amount of each cylinder based on the calculated actual valve timing. The fuel injection amount correction means 54 calculates a fuel injection amount correction amount for each cylinder based on the calculated actual intake air amount so as to obtain the target air-fuel ratio. The fuel injection amount calculating means 55 calculates the final fuel injection amount for each cylinder based on the correction amount of the fuel injection amount for each cylinder and the engine operating state detected by the engine operating state detecting means 51. Calculate every time. The fuel injection valve 17 of each cylinder is driven and controlled in accordance with this final fuel injection amount. In this example, first, the correction amount of the fuel injection amount considering the twist of the crankshaft is obtained, and then the final fuel injection amount is calculated in consideration of the engine operating state. Not limited to this, after obtaining the basic fuel injection amount according to the engine operating state, the fuel injection amount of each cylinder may be corrected in consideration of the twist of the crankshaft.

  FIG. 8 is a flowchart showing a flow of correction control of the fuel injection amount and ignition timing using the strain sensor 35. This routine is repeatedly executed by the engine control unit 20 for each cylinder every predetermined period (for example, every 10 ms), whereby the fuel injection amount and the ignition timing are individually set for each cylinder.

  In step S11, the sensor output of the strain sensor 35 corresponding to the torsion angle of the camshaft is captured. In step S12, the actual valve timing of each cylinder is calculated based on the sensor output of the strain sensor 35. In step S13, based on the actual valve timing, it is determined whether or not correction of the fuel injection amount for suppressing variation in the air-fuel ratio between the cylinders is necessary. For example, when the variation in valve timing between cylinders is large, it is determined that correction is necessary, and the process proceeds to step S14 and subsequent steps. On the other hand, if the variation in the valve timing between the cylinders is small, it is determined that no correction is necessary, and this routine is terminated.

  In step S14, the actual intake air amount of each cylinder is calculated based on the calculated actual valve timing. As an example, the relationship between the valve timing and the intake air amount can be set and stored in advance as a table or map, and the intake air amount can be obtained by referring to this. Although it depends on the engine operating state such as the engine speed and load, basically, as described above, the actual intake air amount decreases as the valve timing is retarded.

  In step S15, the fuel injection amount is set for each cylinder based on the intake air amount calculated for each cylinder so as to equalize the air-fuel ratio of each cylinder to the target air-fuel ratio and suppress variations in the air-fuel ratio among the cylinders. Correct and calculate. That is, the fuel injection amount is calculated for each cylinder in accordance with the intake air amount calculated for each cylinder so that the target air-fuel ratio can be obtained. In step S16, the fuel injection valve 17 of the corresponding cylinder is driven and controlled based on the calculated fuel injection amount, and fuel injection is executed. In this way, by suppressing the variation in the air-fuel ratio between the cylinders and making the air-fuel ratio of each cylinder the target air-fuel ratio, it is possible to stably maintain the desired exhaust purification performance by the three-way catalyst 11. Become.

  On the other hand, when the fuel injection amount is adjusted for each cylinder in this way, the torque generated in each cylinder will be different, causing vibrations due to such variations in torque between the cylinders, and making the vehicle occupant feel uncomfortable. There is a fear. Therefore, when the variation in the generated torque between the cylinders becomes a problem in engine operation, the ignition timing correction control is performed for each cylinder in step S17. That is, the ignition timing is corrected for each cylinder in accordance with the corrected fuel injection amount so that the generated torque of each cylinder is made uniform. As an example, in a cylinder with a large fuel injection amount and a large generated torque, the retard amount of the ignition timing with respect to the optimal ignition timing MBT is increased, and the torque of each cylinder is aligned with the torque of the cylinder with the smallest generated torque. The generated torque can be made uniform. Normally, the cylinder at the rear end of the camshaft (# 4 cylinder in the embodiment) has the greatest effect of torsion and generates the smallest torque, and conversely, the # 1 cylinder at the front end of the camshaft has the least influence of torsion. Therefore, the generated torque is large and the retard amount of the ignition timing is set to be the largest. In this way, by correcting the ignition timing for each cylinder together with correcting the fuel injection amount, the air-fuel ratio of each cylinder is made equal to the target air-fuel ratio, and the generated torque of each cylinder is further made uniform. Can do.

  Referring to FIG. 9, when the engine speed is constant and the load increases as the throttle opening increases (A), the load is constant and the engine speed increases (B). When the engine speed increases (A), the increase R1 in the sensor output of the strain sensor 35 is larger (R1>) due to the influence of an increase in the in-cylinder pressure or the like than when the engine speed increases (B). R2), that is, the torsion of the camshaft is large. Therefore, at the time of acceleration when the load increases, the camshaft torsion tends to increase and the variation of the air-fuel ratio tends to increase, and the application of the present invention is particularly effective.

  Referring to FIGS. 10 and 11, the present invention is applied to an in-cylinder direct injection internal combustion engine in which fuel is directly injected into a cylinder, unlike the port injection internal combustion engine as in the above embodiment. explain. In such an in-cylinder direct injection internal combustion engine, as shown in FIG. 10, since it is necessary to inject fuel directly into a combustion chamber having a high in-cylinder pressure, a high fuel pressure of 20 MPa or more is required, In particular, a very high fuel pressure of about 30 MPa is required on the high load side. For this reason, apart from the feed pump that feeds the fuel in the fuel tank to the low-pressure fuel pipe, a high-pressure fuel pump that boosts the fuel so as to obtain a high fuel pressure is used. As is well known, this high-pressure fuel pump is generally attached to the rear end portion of a camshaft, and a plunger is mechanically reciprocated by a dedicated cam provided at the rear end portion of the camshaft. Boosts fuel.

  In this case, the rotational power is transmitted to the camshaft at the front end provided with the cam pulley, while a large load acts on the rear end provided with the high-pressure fuel pump, so that the camshaft is greatly twisted. There is a tendency. Specifically, as shown in FIG. 11, in the direct injection internal combustion engine, the increase R3 in the sensor output of the strain sensor accompanying the increase in load is greater than in the port injection internal combustion engine as in the above embodiment. Increases (R3> R1), and the increase R4 of the sensor output of the strain sensor accompanying the increase in engine speed also increases (R4> R2). In this way, in a direct injection internal combustion engine, the camshaft torsion is further increased as the load and the rotational speed are increased, and the variation in the air-fuel ratio between the cylinders is also increased. It becomes effective.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... Spark plug 6 ... Intake valve 8 ... Exhaust valve 17 ... Fuel injection valve 20 ... Engine control unit 23, 24 ... Cam shaft 30 ... Cam 35 (35A, 35B, 35C) ... Strain sensor

Claims (5)

A fuel injection valve is provided for each cylinder, and a plurality of cams for opening and closing intake valves or exhaust valves of a plurality of cylinders are provided on a camshaft that is rotationally driven by rotational power transmitted to a part of the longitudinal direction. In the control apparatus for a multi-cylinder internal combustion engine,
A strain sensor that is attached to the camshaft and detects torsion of the camshaft;
Fuel injection amount correction means for correcting the fuel injection amount for each cylinder based on the torsion of the camshaft so as to equalize the air-fuel ratio of each cylinder;
A control device for a multi-cylinder internal combustion engine. The fuel injection amount correcting means includes
Based on the torsion of the camshaft, the valve timing of the intake valve or exhaust valve is calculated for each cylinder,
Based on this valve timing, the intake air amount is calculated for each cylinder,
2. The control apparatus for a multi-cylinder internal combustion engine according to claim 1, wherein the fuel injection amount is corrected for each cylinder based on the intake air amount. An ignition device for spark ignition of the air-fuel mixture in the combustion chamber is provided for each cylinder,
An ignition timing correction unit that corrects the ignition timing for each cylinder in accordance with the fuel injection amount corrected by the fuel injection amount correction unit so as to equalize the generated torque of each cylinder. Item 3. The control device for a multi-cylinder internal combustion engine according to Item 1 or 2.   The multi-cylinder internal combustion engine according to any one of claims 1 to 3, wherein the strain sensors are provided at three positions of a front end position, a rear end position, and a center position in a plurality of positions in the longitudinal direction of the camshaft. Control device.   The control device for a multi-cylinder internal combustion engine according to any one of claims 1 to 4, wherein the strain sensor is a semiconductor strain sensor in which a Wheatstone bridge circuit including a plurality of diffusion resistors is formed on a semiconductor substrate.

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