JPH0445656B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a boost pressure control device for a supercharged internal combustion engine.

[Prior art and problems] Conventionally, in internal combustion engines with a supercharger, in order to prevent the engine from being damaged due to the supercharging pressure becoming too high, a waste gate valve is usually used to reduce the supercharging pressure. It is designed not to exceed a certain value.
Furthermore, by bleeding the supercharging pressure introduced into the actuator of the waste gate valve, the supercharging pressure can be controlled according to the operating state of the engine (for example, see Japanese Patent Laid-Open No. 146023/1983). ). Furthermore, if the waste gate valve continues to close due to the waste gate valve becoming stuck or the hose of the actuator coming off, etc., the supercharging pressure may rise abnormally. Therefore, in such a case, the fuel can be cut to protect the engine.

[Problem that the invention seeks to solve]

The above-mentioned abnormal increase in boost pressure can be basically solved by installing a boost pressure sensor in the intake passage to directly measure the boost pressure, without resorting to cost-increasing measures. By monitoring the amount of intake air detected by the installed air flow meter, we can detect the difference between the amount of intake air and the boost pressure, which means that if the boost pressure becomes excessive, the amount of intake air will become abnormally large. It can be detected using the relationship between In this case, an abnormality in the boost pressure is detected by comparing and determining whether the intake air amount detected by the air flow meter is larger than a predetermined reference value.

However, the gas state equation PV=GRT (however,
P: pressure, V: volume, G: weight, R: gas constant,
As is clear from the equation (T: absolute temperature), even if the volume and pressure of the sucked air are constant, the amount of sucked air in terms of weight changes in inverse proportion to the absolute temperature. Therefore, in order to determine whether abnormal boost pressure is occurring, if the reference value of the intake air amount is set as a constant value for comparison with the actual intake air amount, it is necessary to It is necessary to consider the width and set a relatively high value as the reference value. Otherwise, at low temperatures, the intake air has a constant volume (and pressure) and its weight increases, so the intake air volume (weight) will easily exceed the standard value set as a constant value, and abnormalities will occur each time. This is because an erroneous determination that excessive boost pressure has occurred may be made, leading to a response action such as cutting off the fuel supply.

However, if the reference value is set to a relatively high value, the difference between the reference value and the actual intake air amount becomes large at room temperature, resulting in poor overall response and poor abnormality detection performance. It was a problem.

Yet another problem lies in the temperature characteristics of the wastegate valve's diaphragm and spring-based actuator, which operate to maintain constant boost pressure. In general, a diaphragm becomes stiffer at low temperatures than at room temperature, and the spring constant of the spring that presses the diaphragm tends to increase as the temperature decreases. Due to both of these reasons, the operating pressure of the actuator that opens the wastegate valve increases as the ambient temperature decreases, so it becomes more difficult to open the wastegate valve at low temperatures than at room temperature, and the boost pressure decreases. The height increases accordingly, and the amount of intake air (weight) also becomes relatively large. Therefore, unless some kind of countermeasure is taken, when determining whether there is an abnormal boost pressure based on the amount of intake air, the amount of intake air (weight) may not be set as a constant value even at low temperatures due to this cause. However, if the reference value is set as a high fixed value, the abnormality detection performance will be degraded at room temperature.

The present invention aims to simultaneously solve these two problems that arise when implementing the prior art.

[Means for solving problems]

Both of the above two problems are related to the amount of intake air (weight) used to determine whether there is abnormal boost pressure.
When setting the reference value as a constant value, there is a commonality in that the intake air amount increases at low temperatures and the reference value is easily exceeded. Instead of setting the value as a fixed value, the reference value is changed according to the intake air temperature, and the change is also corrected according to the temperature characteristics of the actuator, so that the reference value of the intake air amount on the low temperature side can be changed to the normal temperature. These problems can be solved at the same time by setting the value to be particularly higher than that at the time.

Based on this idea, the present invention introduces supercharging pressure in the intake passage to an actuator having a diaphragm and a spring that presses the diaphragm, and uses the actuator to open and close a waste gate valve that bypasses the turbine of the turbocharger. In a boost pressure control device for an internal combustion engine that adjusts boost pressure,
Instead of directly detecting the boost pressure in the intake passage,
A supercharging pressure abnormality detection means for detecting an abnormal increase in supercharging pressure by comparing an intake air amount detected by an air flow meter with a predetermined reference value, and an abnormal increase in supercharging pressure. and a means for preparing the predetermined reference value as a function of the engine speed and intake air temperature, The value is set as the amount of intake air that corresponds to a slightly higher boost pressure than the target boost pressure in a specific temperature range, and corresponds to an even higher boost pressure in a lower temperature range. Provided is a supercharging pressure control device characterized in that the amount of intake air is set as the amount of intake air.

〔Example〕

The present invention will be explained below with reference to illustrated embodiments.

FIG. 2 shows an internal combustion engine to which an embodiment of the present invention is applied. In this figure, a piston 12 is slidably supported within a cylinder bore 11 formed in an engine body 10, and a combustion chamber 13 is formed above the piston 12. An intake passage 14 and an exhaust passage 15 communicate with the combustion chamber 13 .

The air cleaner 16 is provided at the most upstream side of the intake passage 14, and the air flow meter 17 is provided at the downstream side thereof. Further downstream, a compressor 19 of the turbocharger 18 is arranged. The throttle valve 20 is provided on the downstream side of the compressor 19, and changes the flow area in the intake passage 14 in conjunction with an accelerator pedal (not shown). On the downstream side of the throttle valve 20, the intake passage 14 is formed as a surge tank 14a and a technical pipe 14b separated for each cylinder. An intake air temperature sensor 21 is attached to the surge tank 14a, and a fuel injection valve 22 is attached to each technical pipe 14b.

A turbocharger 18 is located in the middle of the exhaust passage 15.
A turbine 25 is provided, and this turbine 2
A bypass passage 26 is formed to bypass 5. In the turbocharger 18 , a turbine 25 is rotationally driven by exhaust gas passing through the exhaust passage 15 , which rotates a compressor 19 , and the intake passage 1 is rotated.
The pressure of the air taken in from 4 is increased (supercharged). The waste gate valve 27 opens and closes the bypass passage 26 to shut off the turbine 25.
The rotation of the turbocharger 18 is controlled by adjusting the amount of exhaust gas supplied to the turbocharger 18. Actuator 28 that opens and closes waste gate valve 27
is the diaphragm 3 installed in the shell 29
0 defines a pressure chamber 31 and an atmospheric chamber 32, and a spring 33 is disposed within the atmospheric chamber 32. The boost pressure on the downstream side of the compressor 19 in the intake passage 14 is transmitted into the pressure chamber 31 via a passage 34 . When the pressure within the pressure chamber 31 overcomes the elastic force of the spring 33, the wastegate valve 27 opens the bypass passage 26, reducing the exhaust gas passing through the turbine 25 and exiting the compressor 19 of the turbocharger 18. Control pressure.

A passage 35 branches off from the middle of the passage 34, and this passage 35 is connected to a switching valve 36. Switching valve 3
6 blocks the passage 35 by closing the valve, and opens the passage 35 to the atmosphere by opening the valve. When the switching valve 36 opens the passage 35, the pressure chamber 31 of the actuator 28 communicates with the atmosphere via the passage 35, and when the switching valve 36 closes the passage 35, the pressure chamber 31 communicates only with the passage 34. . Therefore, when the switching valve 36 is opened to lower the pressure in the pressure chamber 31, the waste gate valve 27 becomes difficult to open, thereby controlling the supercharging pressure. An example of controlling the boost pressure according to the engine speed is shown in FIG. 4 by a solid line P.

A control device 50 for controlling the switching valve 36 and the fuel injection valve 22 includes a central processing unit (CPU) 52 having an arithmetic control function, a read-on memory (ROM) 54 that stores programs, and stores data and the like. It consists of a microcomputer equipped with a random access memory (RAM), and each of these is connected by a bus along with an input/output (I/O) port 58. Signals from the air flow meter 17, intake air temperature sensor 21, engine speed sensor 37, and other sensors are input to the control device 50.

The switching valve 36 is controlled by a duty signal determined according to the engine speed to obtain a supercharging pressure as shown by line P in FIG. On the other hand, the fuel injection valve 22 is configured to supply an amount of fuel depending on the operating state, and to cut off the fuel supply when an abnormality in the boost pressure is detected. Third
The figure shows the operation of a control device for controlling such a fuel injection valve 22.

In FIG. 3, the detected intake air amount Q, engine speed N, and intake air temperature T are read (step 60), and the fuel injection amount Fi is calculated in step 61. Calculation of this fuel injection amount Fi can be performed in a conventionally known manner, for example,
The basic injection amount is calculated by multiplying Q/N by a constant, and further corrections are made depending on the warm-up state and acceleration state. Subsequently, in step 62, a reference value _RFC for detecting abnormality in boost pressure is calculated.
This reference value _RFC is provided in a two-dimensional map 5 as a function of the engine speed N and the intake air temperature T, as shown in FIG. 1, and is stored in the ROM 54. The reference value R _FC is determined to correspond to a boost pressure P FC that is slightly higher than the target boost pressure P shown in Figure 4 at a specific temperature, and corresponds to a boost pressure P _FC that is slightly higher than the target boost pressure P shown in Figure 4, and at a temperature lower than the same specific temperature. This is determined to correspond to a boost pressure P _FCL that is even higher than that of the P FCL. This is because when the boost pressure is constant, the amount of intake air in terms of weight increases as the temperature decreases, so basically, the reference value R _FC is set to a boost pressure P _FC that is slightly higher than the target boost pressure P. By setting it to vary accordingly, in order to eliminate dead or sensitive zones in the operation of the fuel cut means, and especially at low temperatures, the diaphragm 30 of the actuator 28 will generally become stiffer and the spring constant of the spring 33 will also increase. This is to prevent the fuel cut means from malfunctioning because the waste gate valve 27 becomes difficult to open and the supercharging pressure tends to increase.

Next, the process proceeds to step 63, where it is determined whether the detected intake air amount Q/N is greater than the reference value _RFC . This routine ends while maintaining the fuel injection amount Fi. This fuel injection amount Fi is used as the opening time of the fuel injection valve 22 at the fuel injection timing determined twice in one cycle of the engine. On the other hand, if the answer in step 63 is YES, it is determined that the boost pressure is abnormal, and the process proceeds to step 64, where the fuel injection amount Fi calculated in step 61 is corrected to zero. Thus, even when the fuel injection timing comes, the fuel injection valve 22 does not open, and the supply of fuel is cut off.

〔Effect of the invention〕

According to the present invention, an abnormal increase in boost pressure is determined by comparing the amount of intake air detected by an air flow meter with a predetermined reference value, and the direct boost pressure in the intake passage is determined. Since there is no need to provide expensive sensors and related equipment for measuring the , it is significantly advantageous in terms of cost.

In addition, the predetermined reference value for the amount of intake air to be compared is changed according to the intake air temperature and engine speed, and at low temperatures, the temperature characteristics of the actuator of the waste gate valve are also taken into account.
Since the reference value is set high, abnormal increases in boost pressure can be detected with high precision, and the fuel cut means is accurately activated only when boost pressure increases abnormally, allowing direct measurement of boost pressure. Even if a sensor is not provided, the engine can be reliably protected from excessive boost pressure without any trouble such as malfunction.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the present invention, Fig. 2 is a block diagram of an embodiment of the present invention, Fig. 3 is a flowchart showing the operation of Fig. 2, and Fig. 4 is a diagram showing supercharging pressure with respect to rotation speed. It is. 10... Engine body, 18... Turbocharger, 2
1... Intake temperature sensor, 22... Fuel injection valve, 27... Waste gate valve, 28... Actuator,
36...Switching valve.

Claims (1)

[Claims] 1. A supercharging system for an internal combustion engine in which supercharging pressure in an intake passage is guided to an actuator having a diaphragm and a spring that presses the diaphragm, and the actuator opens and closes a waste gate valve that bypasses a turbocharger turbine to adjust the supercharging pressure. In the boost pressure control device, instead of directly detecting the boost pressure in the intake passage, abnormalities in boost pressure are detected by comparing the amount of intake air detected by an air flow meter with a predetermined reference value. a supercharging pressure abnormality detection means for detecting an abnormal increase in supercharging pressure; a fuel cut means for cutting off fuel supply when an abnormal increase in supercharging pressure is detected; the predetermined reference value is set as an intake air amount corresponding to a boost pressure slightly higher than a target boost pressure in a specific temperature range. A supercharging pressure control device characterized in that the intake air amount is set to correspond to an even higher supercharging pressure in a temperature range lower than that.