JPS61210226A - Engine with supercharger - Google Patents

Abstract

PURPOSE:To prevent the drop of engine output by providing a means for forcibly closing a waste gate valve in a bypass passage detouring a supercharger turbine, for raising engine output at the trough of output characteristic curves as appearing in a medium speed range. CONSTITUTION:In a supercharged engine 1, the turbine 9 of a supercharger 4 is provided in way of an exhaust pipe 8 and a waste gate valve 11 is provided at a bypass passage 10 detouring the said turbine 9. The said waste gate valve 11 is controlled for opening and closing by an actuator 13 working on supercharged pressure at the down-stream of a compressor 5. The pressure of a pressure signal passage 12 is regulated by a supercharged pressure control valve 16 as controlled by a control part 14. In this case, the control part 14 makes comparison between a predetermined fuel injection pulse band corresponding to an engine speed and an actual fuel injection pulse band. If there is any difference between both bands, the control part 14 makes judgement that the output torque of the engine 1 has dropped, and then controls the waste gate valve 11 for its closing.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a supercharged engine, which prevents a decrease in output by increasing supercharging pressure in a medium speed rotation range where the output decreases. Regarding.

(Prior art) In an engine equipped with a supercharger that supercharges intake air with a compressor rotationally driven by a turbine driven by engine exhaust gas, when the supercharging pressure exceeds a predetermined value,
The wastegate valve is opened to bypass the exhaust gas to the above turbine, preventing knocking in the engine's low speed range, while maintaining the durability of the supercharger and engine body in the high speed range. There are known devices that do this (for example, Japanese Utility Model Application Publication No. 18027/1983).
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However, in such a supercharged engine, a phenomenon has occurred in which the engine output torque decreases when the engine speed is in a medium speed rotation range.

This is because the intake pipe length of an engine's intake system is generally designed to match the high-speed operation flj range, so the intake inertia effect cannot be sufficiently achieved in the mid-speed range as the engine speed increases. There is also a savings.

In other words, to explain this using Fig. 2, as the engine speed increases, the boost pressure becomes like curve A, and in the middle speed rotation range where the boost pressure is suppressed to the set value, inertia supercharging Since the effect is not sufficiently obtained, the intake air filling efficiency is insufficient, and therefore, the curve B of the fuel pulse width of the fuel injector, which is determined from the intake air amount based on the air 70-meter and the engine speed, is as shown by the broken line B2. temporarily decreased, resulting in
The engine output torque curve C is a broken line C in the medium speed rotation range.
As shown in 2, a trough appears and the output torque temporarily decreases.

(Object of the Invention) The present invention has been made in view of the above-mentioned conventional problems, and includes controlling the supercharging pressure so as to increase the supercharging pressure in the middle speed rotation range where the output torque of the engine decreases. It is an object of the present invention to provide a supercharged engine that can prevent a decrease in output in this rotation range.

(Structure of the Invention) The present invention relates to a supercharger that supercharges intake air using a compressor rotationally driven by a turbine driven by engine exhaust gas, and an exhaust gas to the turbine when the boost pressure exceeds a predetermined value. A wastegate valve that opens to bypass gas is used in a supercharged engine where the engine's output torque characteristic reaches a valley in the middle speed range when the boost pressure is constant. A supercharging pressure control means is provided for forcibly closing the waste gate valve and increasing the supercharging pressure so that the output torque at the trough of the output torque characteristic that occurs in the rotation range increases.

With this configuration, when the throttle valve is fully open or close to fully open, if the output is about to decrease in the middle speed rotation range, the supercharging pressure is forcibly increased and the output torque is increased.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, an intake pipe 2 is connected to an engine 1,
An air flow meter 3 is provided at the upstream end of the intake pipe 2, and a compressor 5 of a supercharger 4 is provided downstream of the air flow meter 3. Further, a throttle valve 6 is provided downstream of the compressor 5, and a fuel injection valve 7 for injecting fuel is further provided. An exhaust pipe 8 is connected as an exhaust system of the engine 1, and a turbine 9 of a supercharger 4 is interposed in the middle of the exhaust pipe 8. A bypass passage 10 that bypasses the turbine 9 is provided with a wastegate valve 11 that is opened and closed based on boost pressure. This wastegate valve 11 introduces supercharging pressure at a downstream position of the compressor 5 from a pressure signal passage 12,
Actuator 13 operated by this introduced supercharging pressure
When the supercharging pressure exceeds a predetermined value, the valve is opened to bypass the exhaust gas to the turbine 9.

The control unit 14 is composed of a microcomputer, etc., and receives output signals from the air flow meter 3, the throttle valve 6, and the engine speed sensor 15 as input, and determines a predetermined engine speed corresponding to the engine speed when the throttle valve 6 is fully open. The fuel injection pulse width corresponding to the output is stored as a map, and the actual fuel injection pulse width of the engine calculated based on the input when the throttle valve 6 is fully open or close to it and the predetermined pulse width are stored. When the actual pulse width becomes smaller than the predetermined pulse width in the medium speed rotation range of N1 to N2, it is determined and an output signal is generated.

The supercharging pressure control valve 16 is interposed in the pressure signal passage 12, and operates to forcibly close the wastegate valve 11 based on the output from the control section 14. That is, by operating the supercharging pressure control valve 16 based on the output signal from the control section 14, the supercharging pressure in the pressure signal passage 12 is released. This allows the actuator 13 to keep the wastegate valve 11 fully open or half open, that is, to prevent it from fully opening unless the boost pressure is higher.

In this embodiment, the control unit 14 maps a predetermined injection pulse width of the fuel injector 7 to the engine speed when the throttle valve 6 is fully open, as shown by the solid line B1 in FIG. The calculated pulse width and the actual pulse width are compared, and if there is a difference, it is determined that the output torque of the engine is lower than a predetermined output torque,
An output signal is generated so that the portion of the boost pressure indicated by the broken line A2 is raised as shown by the solid line A1. In other words, the boost pressure is
When the engine speed rises above a predetermined value, the wastegate valve 11 opens and is kept at a constant value from that point on, but by forcibly closing the wastegate valve 11 in the region where there is a difference in the pulse width. , increase boost pressure.

Through such control, the injection pulse width of the fuel injection valve 7 is increased, and as a result, the trough of the engine output torque characteristic indicated by the broken line C2 rises as indicated by the solid line C1, and a predetermined output is obtained. .

The operation of the control section 14 will be explained using the flowchart shown in FIG.

In step S1, it is determined whether the throttle valve 6 is fully open or not. If it is not fully open, it returns to the original state, and if it is fully open, the basic injection pulse width TS mapped in step S2 and the injection pulse width T at time t (t ), and if the actual injection pulse width T(t) at time t is larger than the basic injection pulse width TS, it returns to the original state. If the injection pulse width T (t) is smaller, the process proceeds to step S3, where the boost pressure control valve 16 is energized to relieve the boost pressure in the boost pressure signal path 12. In step S4, n is set to 1, and in step S5, the injection pulse width T (t+nto) at time (t+ntQ) of each sampling period to is compared with the basic injection pulse width TS, and if the basic injection pulse width TS is larger, In step S6, n is set to n+1. When a certain sampling period has elapsed and the actual injection pulse width becomes larger than the basic injection pulse width Ts, the power supply to the supercharging pressure control valve 16 is turned off in step S7.

After that, the process returns to step S1 again. Through these steps, when the actual injection pulse width is smaller than the mapped basic injection pulse width when the throttle valve 6 is fully open, the supercharging pressure control valve 16 is energized and the wastegate valve 11 is forcibly closed. I'm trying to be talked about.

In the above embodiment, the control unit 14 operates by detecting the mapped injection pulse width and the actual pulse width. This is not limited to the method of detecting the injection pulse width, but may also be performed by detecting the combustion pressure at the engine rotation speed when the throttle valve is fully open or close to it, or by directly detecting the output torque.

Furthermore, the present invention is not limited to the one using the fuel injection valve 7, but is equally applicable to the one using a carburetor.

(Effects of the Invention) As described above, the present invention forcibly closes the wastegate valve so that the output torque at the trough of the above output torque characteristic that occurs in the medium speed rotation range increases, and increases the supercharging pressure. This system is equipped with supercharging pressure control means to control the boost pressure.

Therefore, in addition to preventing knocking in the low speed range, the boost pressure is forcibly increased in the middle speed range where the output decreases, without impairing the durability of the engine in the high speed range. Output torque in the medium speed rotation range is increased. Thus, in a supercharged engine where the intake pipe length is set so that the intake inertia effect can be obtained in the high-speed rotation range, when the throttle valve is fully open or close to the throttle valve, the intake inertia effect will be reduced in the medium-speed rotation range. This eliminates the problem of a decrease in engine output torque due to unobtainable torque.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a supercharging pressure control means for a supercharged engine according to an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the fuel injection valve and the engine speed of a supercharged engine according to the present invention and a conventional example. A characteristic diagram of injection pulse width, engine output torque, and supercharging pressure, and FIG. 3 is a flowchart showing the operation of the control section in the supercharging pressure control means of the present invention. DESCRIPTION OF SYMBOLS 1... Engine, 4... Supercharger, 5... Compressor, 6... Throttle valve, 9... Turbine, 11
...Wastegate valve, 12...Pressure signal passage, 1
3...Actuator, 14...Control unit, 16...
・Supercharging pressure control valve (supercharging pressure control means).

Claims (1)

[Claims] 1. A supercharger that supercharges intake air with a compressor rotationally driven by a turbine driven by engine exhaust gas;
Equipped with a wastegate valve that opens to bypass exhaust gas to the turbine when boost pressure exceeds a predetermined value, the output torque characteristics of the engine are at a valley in the medium speed rotation range when boost pressure is constant. In a supercharged engine where A supercharged engine characterized by being provided with supercharging pressure control means.