GB2228768A

GB2228768A - Supercharging pressure control system for an engine with a turbocharger

Info

Publication number: GB2228768A
Application number: GB9003245A
Authority: GB
Inventors: Tetsuya Okazaki
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1989-02-28
Filing date: 1990-02-13
Publication date: 1990-09-05
Also published as: GB9003245D0; JPH02227522A; DE4005046A1

Description

f 1 SYSTEM FOR CONTROLLING SUPERCHARGING PRESSURE OF ENGINE WITH

TURBOCHARGER The present invention relates generally to a motor vehicle engine provided with a turbocharger and, more particularly, to a system for controlling the supercharging pressure of the vehicle engine. More specifically, the invention relates to a system for compensating for acceleration in a feed-forward control of the opening degree of a waste gate valve of the engine.

in general, in an engine with a turbocharger, there is provided a bypass passage having a waste gate valve for a turbine of the turbocharger. In the turbo region of operation, the waste-gate valve opens to bypass a portion of the exhaust gas from the turbine. By this measure, the supercharging pressure is controlled at a substantially constant value. Thus knocking is suppressed. In this case, one method is to control opening and closing of the waste gate valve responsive to the supercharging pressure at the delivery side of a compressor of the turbocharger. This method is not desirable since the supercharging pressure overshoots to a much extent in a transient state, such as acceleration, whereby overcorrecting causes hunting in the control. For this reason, there has been proposed an electronic control system for controlling supercharging pressure by the opening degree of the waste gate valve in accordance.

with various operational conditions.

An example of the electronic control of the supercharging pressure is disclosed in Japanese Patent Laid-Open Publn. (Kokal) No. In the method disclosed in this publication, the actual supercharging pressure is detected by a pressure sensor. Then the differences or deviations between the actual supercharging pressures and a predetermined pressure are 1 2 determined. A signal proportional to the difference and a signal corresponding to an integrated value of the differences are then delivered to a correction unit of the control system for a feedback control of the 5 supercharging pressure.

In the feedback control, however, the following problem arises. That is, overshooting may occur when the control quantity is determined responsive to the supercharging pressure deviation. For this reason, in a transient state, the supercharging pressure is delayed in - rising and then rises abruptly. As a consequence the - overshooting becomes excessive. Thus the supercharging pressure peak cannot be sufficiently suppressed. For this reason, the supercharging pressure overshoots by a relatively large quantity, whereby knocking may occur readily.

As one possible method of reducing the overshooting of the supercharging pressure, a map of a basic duty ratio may be provided to set the predetermined supercharging pressure at each operational condition. Then the feed- forward control is suitably carried out by means of the map. By such feed- forward control, however, a mechanical problem may arise such as a response delay in the rotational speed of the turbine wheel at the time of acceleration. In such a case, correction of the problem cannot be carried out. For this-reason, a state of insufficient supercharging pressure occurs during the rotational speed delay of the turbine immediately after the accelerator pedal is depressed. Therefore, there is a need for a measure for compensative correction with respect to this problem.

It is an object of the present invention to provide a control system for a feed-forward control of engine supercharging pressurer which is capable of appropriately compensatively correcting insufficient supercharging -pressure at the beginning of acceleration.

3 According to the present invention, the above stated object and other objects thereof have been achieved by providing a system for controlling supercharging pressure of an engine, having a turbocharger including a compressor and a turbine driven by exhaust gas from the engine, detecting means for detecting operational conditions of the engine, a bypass passage for bypassing the turbine, a waste gate valve provided in the bypass passage, an actuator for actuating the waste gate valve, a control valve for controlling to actuate the waste gate valve and to regulate flow of the exhaust gas through the turbine thereby to control the supercharging pressure, and control means responsive to signals from said detecting means for producing a control signal to regulate the control valve, said control means comprising:

basic duty retrieving means responsive to said signals for calculating a basic duty ratio corresponding to various operational conditions of the engine and for producing a supercharging pressure signal; acceleration duty retrieving means responsive to said signals for calculating and for outputting an acceleration duty ratio signal; and duty 'ratio determining means responsive to said basic duty-ratio and the acceleration duty ratio signals for adding the acceleration duty ratio signal to the basic duty ratio signal and for producing a corrected duty ratio signal upon acceleration.

In the supercharging pressure control system of the above described features, the degree of opening of the waste gate valve is controlled by feed-forward control based on a basic duty ratio map in a steady-state. The supercharging pressure is theriby constantly controlled by the predetermined supercharging pressure. Then, at acceleration, the supercharging pressure is corrected according to the corrected duty ratio signal so as to prevent -the delay in increase of the turbine rotational4 speed. Thus, insufficiency of the supercharging pressure is eliminated.

A preferred embodiment of the present invention will become understood from the following detailed description referring to the accompanying drawings.

FIG. 1 is a schematic (iagram showing a supercharging pressure control system, according to the present invention, in an engine with a turbocharger; FIG. 2 is a block diagram of a controller in the control system; FIG. 3A is a graph showing a basic duty ratio map; FIG. 3B is a graph showing a corrected duty ratio map; FIG. 4 is a flow chart indicating supercharging pressure-control procedures; and FIG. 5 is a time chart indicating variations of the duty ratios with time. .

In FIG. 1, an embodiment of the supercharging pressure control system applied to an engine 1 with a turbocharger 4 according to the present invention is shown. An air cleaner 2 is provided in an engine intake system. The air cleaner 2 is communicatively connected via an intake pipe 3 to a compressor 4a of the turbocharger 4. A delivery side of the compressor 4a is connected through a throttle valve 5, a chamber 6, and an intake manifold 7 to an intake port of the engine 1. An exhaust port of the engine 1 is connected through an exhaust manifold 8 to a turbine 4b of the turbocharger 4. An exit side of the turbine 4b is connected to an exhaust pipe 9.

The supercharging pressure of the engine 1 is controlled by a supercharging pressure control system 10 having the following essential components. A bypass passage 12 having a waste gate valve 11 is connected between the upstream and downstream sides of the turbine 1 4b. A regulating -vane 4c is installed in the inlet opening of the turbine 4b. The waste gate valve 11 and the vane 4c are actuatable by diaphragm type actuators 13 and 14 respectively coupled thereto. The actuators 13 and 14 are operable by variable pressure applied thereto through a control passage 17 from a three-way solenoid valve 16 constituting a control valve.

A supercharging pressure passage 15 is connected between a downstream side of the compressor 4a and a supercharging pressure port 16c of the solenoid valve 16. A leak port 16d of the solenoid valve 16 is connected by way of a leak passage 18 having an orif ice 19 to the upstream side of the compressor 4a. The three-way solenoid valve 16 is provided with an electromagnetic solenoid 16a and valves 16b. The valves 16b are actuatable by the solenoid 16a to open and close the supercharging pressure port 16c and the leak port 16d, respectively. The solenoid 16a is energized by signals from the controller 30 and the solenoid 16a operates in response to"duty signals as described hereinafter. Thus, the time period of opening and closing the supercharging pressure port 16c and the leak port 16d are adjusted beforehand. The pressure for driving the actuators 13 and 14 and the degrees of opening of the waste gate valve 11 and the- vane 4c are thereby controlled.

The function of the controller. 30 will now be described with reference to FIG. 2..

The general function of the controller 30 is to operate, in response to signals from at least one of four sensors, to transmit duty signals to the solenoid 16a of the solenoid valve 16 thereby to operate the valve 16. An air flow meter 21 detects the air flow rate flowing through the intake pipe 3 and produces an air quantity signal. An engine speed sensor 22 detects the engine rotational speed Ne and produces an engine speed signal. A throttle valve opening sensor 23 detects the degree of 6 opening 8 of the throttle valve 5. A pressure sensor 24 detects the supercharging pressure.

The controller 30 performs a feed-forward control as indicated in FIG. 2. A basic duty retrieving unit 31 receives air quantity signal Q from the air flow meter 21 and the engine speed signal Ne from the engine speed sensor 22. The basic duty retrieving unit 31 is provided with a map setting unit 32. The basic duty retrieving unit 31 delivers a basic duty ratio signal DB- A function of the basic duty ratio signal D,, the engine speed signal Ne and the air quantity signal Q is as indicated in FIG. 3A. The map of the basic duty ratio signal D. is set so that a predetermined supercharging pressure Pt can be constantly obtained under various steady-state operational conditions.

More specifically, in a low load region in which the engine speed signal Ne and the air quantity signal Q are low, the basic duty ratio signal D. is large, and the leaking time through the leak port 16d of the solenoid valve 16 is lengthened to reduce the actuator pressure applied to the actuators 13 and 14. Then, as the engine speed signal Ne and the air quantity signal Q increase, the basic duty ratio signal D. decreases. The actuator pressure is thereupon increased. The basic duty retrieving - unit 31 then derives the basic duty ratio signal DB according to the map and transmits the ratio signal DB to a duty ratio determining unit 33.

The controller 30 also has a calculating unit 34 for determining throttle opening degree variation. The unit 34 receives the throttle opening degree signal 0 from the throttle opening degree sensor 23. Responsive to the throttle opening degree signal the unit 34 determines the throttle opening degree variation de/dt with respectto time. The engine speed signal Ne, the throttle opening degree e and the throttle opening degree variation dO/dt are transmitted to an acceleration detecting unit 35.

71 i A set value NI (for ex"ample,. 4.000 7 rpm) of the engine speed signal Ne, a set value el (f or example 80 degrees) of the throttle opening degree signal e, and a set value T of the throttle opening degree variation de/dt are predetermined. In a partial region of Ne < NI, 0 < 01, and de/dt > T, if the variation of the throttle opening degree is large, the acceleration detecting unit 35 determines that the operational state is acceleration.

The supercharging pressure as detected by the pressure sensor 24 is fed into a supercharging state determining unit 36. The unit 36 thereupon determines the supercharging state from the supercharging pressure variation dP/dt and produces a correction signal after elapse of a predetermined time T from a state of dP/dt:S 0, as will be described in more detail later. An acceleration signal' from the unit 35, the correction signal from the unit 36, and the engine speed signal Ne are fed into an acceleration duty retrieving unit 37. The acceleration duty retrieving unit 37 thereupon derives an accleration correction duty ratio Da from a setting unit 38 and transmits the ratio Da as output to the duty ratio determining unit 33. The acceleration correction duty ratio Da is set by a function which reduces as the engine speed signal Ne increases, as indicated ún FIG. 3B.

The duty ratio determining unit 33 calculates and determines an output duty ratio signal D according to the equation D = Da + Da. The output duty ratio signal D is transmitted by way of a driver unit 39 to the solenoid valve 16.

The operation of the supercharging pressure control system described above will now be described with reference to the flow chart of FIG. 4.

First, when the engine is operating, the energy of its exhaust gas drives the turbine 4b of the turbocharger 4- The compressor 4a therefore rotates. Thus the air drawn into the intake pipe 3 is compressed and is 1 8 supercharged into the engine 1. At this time, the air quantity signal Q and the engine speed signal Ne are fed to the basic duty retrieving unit 31 of the controller 30. The unit 31 thereupon derives the basic duty ratio D. in conformance with the air quantity signal Q and the engine speed signal Ne according. to the map set by the setting unit 32. When the engine is operating in a steady state, the duty signal of the basic duty ratio D. is outputted through the driver unit 39 to the solenoid valve 16. Thus the pressure supplied to the actuators 13 and 14 is controlled.

Then, when the air quantity signal Q and the engine speed signal Ne are low, the basic duty ratio D. becomes large and the actuator pressure becomes low. As a consequence, the waste gate valve 11 is closed. Also, the vane 4c at the turbine inlet is opened to increase the supercharging rate. When the air quantity signal Q and the engine speed si.gnal.Ne increase, the value of the basic duty ratio D. decreases. The actuator pressure then increases. As a consequence.. the waste gate valve 11 is opened by a specific degree to permit a portion of the exhaust gas energy to escape, and the exhaust gas quantity is reduced by the vane 4c. Thus the power for the turbocharger 4 is reduced. Then, feed-forward control depending on the basic duty ratio D. is carried out so that the supercharging pressure-coincides with the predetermined supercharging pressure Pt.

At the time of acceleration when the throttle opening degree increases abruptly, the engine speed signal Ne increases. Thus the supercharging pressure P rises as indicated in FIG. 5. Elowever, the basic duty ratio D. takes a low value. as determined by the map. Also, as mentioned hereinabover-the feed-forward control is carried out. Therefore, the supercharging pressure rises without overshooting. When abrupt acceleration occurs with a large variation in the throttle opening degree signal er resulting in a delay in the response of is 1 - 9 1 the turbine 4, the acceleration detecting unit 35 detects the acceleration. Thus an acceleration correction duty ratio Da is derived from the map setting unit 38 according to the engine speed signal Ne.

The state of supercharging is monitored by the supercharging state determining unit 36. After elapse of a specif ic time T (FIG. 5) f rom the-instant of a drop in the supercharging pressure under the condition of dP/dt < 0, the risk of overshooting disappears. Thus, after the elapse of the predetermined time Tr the acceleration correction duty ratio Da is outputted from the unit 37. Then the duty ratio D is increasingly corrected in the duty ratio determining unit 33 by adding the acceleration correction duty ratio Da to the basic duty ratio D.. For this reason, the waste gate valve 11 slightly closes from the previous open. state. The turbocharger 4 thereby increases the supercharging. As a result, the supercharging pressure recovers from the deficiency in supercharging pressure due to the delay in response of the turbine 4b (the state- of deficiency is indicated by single-dot chain line P' in FIG. 5) to the state of the solid line. Thus the supercharging pressure is brought into coincidence with the predetermined pressure value P.

The acceleration correction duty ratio Da decreases with increa---se in the engine speed signal Ne as indicated in FIG. 3B. After a specific time, it becomes zero and the acceleration correction comes to an end. However. during this time, the turbine speed delay is corrected. For this reason, the control mode Zeturns to that of steady-state operation depending on only the basic duty ratio D.. Thus control of the supercharging pressure coincides with the predetermined supercharging pressure Pt.

The supercharging pressure control system according to the present invention has a number of advantageous and useful features, which are summarized below.

1 The control system is based on the feed-forward control according to a basic duty ratio map. Therefore stable supercharging pressure control with little overshooting is accomplished.

Furthermore, at the time of acceleration, the basic duty ratio is corrected according to an acceleration correction duty ratio. For this reason, deficiency in the supercharging pressure due to a mechanical cause such as delay of rotational response of the turbine is corrected.

Still another feature is that the correction for acceleration is carried out after a drop in the supercharging pressure. Therefore, there is little possibility of overshooting due to correcting.

A further feature is that the acceleration correction duty ratio is set in accordance with the engine speed. Therefore, there is no possibility of correcting excessively. beyond that necessary during a rise in the engine speed at the time of acceleration.

While the presently preferred embodiment of the present invention has been shown and described, it is to be understood that the disclosure is for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.

is c 11

Claims

CLAIMS:

1. A system for controlling supercharging pressure of an engine, having a turbocharger including a compressor and a turbine driven by exhaust gas from the engine,,, detecting means for detecting operating conditions of the engine, a bypass passage bypassing the turbine,. a waste gate valve provided in the bypass passager an actuator for operating the waste gate valve, a control valve for controlling the waste gate valve, and control means responsive to said operating condition signal for producing a control signal to regulate the control valve, characterized by:

basic duty retrieving means responsive to signal for calculating a basic duty ratio (D B) corresponding to various operational conditions of the engine and for producing a predetermined supercharging pressure signal (Pt); acceleration duty retrieving means responsive to said operating condition signal for calculating an acceleration duty ratio (Da) and for generating an acceleration duty ratio signal; and duty ratio determining means responsive to said supercharging pressure signal and the acceleration duty ratio-signal for adding the acceleration duty ratio signal to the basic duty ratio signal and for producing a corrected output duty ratio (D) to the control valve upon occurrence of an engine acceleration condition.

2. The system as claimed in claim 1, wherein said detecting means comprises an air flow meter for detecting intake air quantity to the engine and an engine speed sensor for detecting engine speed, and wherein the basic duty retrieving means is responsive to signals from the air flow meter and the engine speed sensor.

1 W 12

3. The system as claimed in claim 2, wherein said acceleration duty retrieving means has means to calculate the acceleration duty ratio (Da) depending upon the output (Ne) from the engine speed sensor.

4. The system as claimed in claim 2, wherein said detecting means further comprises.. a throttle opening degree sensor for detecting the degree of opening of a throttle valve of the engine, and wherein said system further comprises throttle opening degree variation calculating means responsive to an output signal (e) from the throttle opening degree sensor to calculate variation (de/dt) of the degree of opening of the throttle valve, and acceleration detecting means responsive to output signals (Ne, de/dt, e) from the engine speed sensor., the throttle opening degree variation calculating means and the throttle opening degree sensor for. determining said engine acceleration condition to transmit an output signal to said acceleration duty retrieving means.

5. The system as claimed in claim 4, wherein said detecting means further comprises a pressure sensor for detecting intake pressure (P) of the engine, and wherein th-! system further comprises supercharging state determining means responsive to output signals (P) of the pressure sensor for determining a supercharging state on the basis of variations of the intake pressure to deliver an output correction signal to the acceleration duty retrieving means,

6. The system as claimed in claim 5, wherein said acceleration duty retrieving -means has means responsive to a drop in the intake pressure (P) from an overshooting supercharging pressure for outputting the acceleration duty ratio (Da) with a time delay (T).

k_ 3

7. A system for controlling supercharging pressure of an engine substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

PublIshed 1990 at The Patent Office. State House. 6671 High RjIbnrn.1, ondonWC1R4TP.Purther copies Tnay be obtamedfrom The Patent =ice