FR2828843A1 - Control apparatus for internal combustion engine, has throttle valve switched to closed state based on negative pressure in brake booster, so as to change idle revolution number of engine to target revolution number - Google Patents

Abstract

A throttle valve (11) is switched to a closed state, when the negative pressure in a brake booster (12) is less than the setting value, during idle condition. The ignition timing or fuel injection quantity is controlled and the idle revolution number of engine is changed to target revolution number after closing the throttle valve.

Description

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CONTROL APPARATUS FOR INTERNAL COMBUSTION ENGINE
The invention relates to a control device for an internal combustion engine.

 It has been proposed to equip a vehicle with a braking assistance device in order to reduce the pressure force applied to the brake pedal by a driver during the braking operation. A brake assist device generally used uses negative pressure in an intake manifold. Such a braking assistance device comprises a first and a second chamber which are connected to each other by means of a diaphragm or a similar device. A negative pressure generated in an intake manifold is introduced into the first chamber. If there is no pressure on the brake pedal, the negative pressure in the first chamber is introduced into the second chamber. If the driver presses the brake pedal, atmospheric pressure is introduced into the second chamber so that a differential pressure is generated between the first and second chambers. This differential pressure assists the driver in applying pressure to the brake pedal.

 If the driver then releases the brake pedal, negative pressure in the first chamber is introduced into the second chamber as preparation for the next braking operation.

Thus, each time the driver releases the brake pedal, the negative pressure, that is to say the absolute value of the negative pressure in the first chamber, drops and approaches atmospheric pressure. However, if negative pressure is generated in the intake manifold due to a decrease in

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 opening the butterfly valve, the negative pressure in the first chamber can be increased.

 It should be noted here that the instant of ignition or the quantity of fuel injected is subjected to a command by reaction while the engine is idling, so as to guarantee that the engine speed at idle becomes equal to the desired speed. of the motor. While the engine is idling as in this case, the driver can step on the brake pedal even if the vehicle has been stopped. If it is pressed repeatedly on the brake pedal, the negative pressure in the first chamber of the brake assist device drops considerably. For this reason, the differential pressure generated when the second chamber is at atmospheric pressure introduced into the second chamber is insufficient.

It becomes impossible to assist the driver in applying pressure to the brake pedal. As a result, the driver feels a sense of abnormality, that is, he feels that the brake pedal is weighing heavily on his foot.

 Japanese Patent Application No. 2000-257474 describes that if the negative pressure in a brake assist device falls so as to become equal to or less than a predetermined value, the butterfly valve is shifted in the closing direction so as to generate negative pressure in the intake manifold.

 However, if such a control of the butterfly shutter is carried out only when the engine is idling, the flow rate of the air flowing in the cylinders suddenly drops. Thus, even if the instant of ignition or the quantity of fuel injected is subjected as usual to a command by reaction, the engine idling speed drops

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 well below the desired engine speed.

As a result, the driver feels a sense of abnormality, including a suspicion that the engine is out of order;
The objective of the invention is therefore to improve a control device intended for an internal combustion engine to which is connected a braking assistance device using negative pressures in an intake manifold of the engine, in a way such that the driver feels neither a feeling of abnormality relating to the brake pedal, nor a feeling of abnormality relating to idling speed despite repetitive pressure on the brake pedal while the engine is idling.

 A control device is provided for an internal combustion engine to which a brake assist device is connected. The brake assist device uses negative pressure downstream of the butterfly valve in the intake system of the internal combustion engine. The control unit is equipped with a controller which executes the control by reaction of at least either the instant of ignition, or the quantity of fuel injected, during idling operation by means of at least one coefficient so that the engine idling speed is controlled in accordance with the desired idling speed. When it is determined that the negative pressure in the brake assist device becomes less than a fixed value, the controller increases the negative pressure in the engine intake system by reducing the opening angle of the throttle valve so as to deliver the increased negative pressure to the brake assist device, and increases at least one reaction coefficient used for

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 control by reaction in order to advance the ignition instant or increase it even more.

 A control device is provided for an internal combustion engine to which a brake assist device is connected. The brake assist device uses negative pressure downstream of the butterfly valve in the intake system of the internal combustion engine. The control unit is equipped with a controller which executes the control by reaction of at least either the instant of ignition, or the quantity of fuel injected, during idling operation by means of at least one coefficient so that the engine idling speed is controlled in accordance with the desired idling speed. When it is determined that the negative pressure in the brake assist device becomes less than a fixed value, the controller increases the negative pressure in the engine intake system by reducing the opening angle of the throttle valve so as to deliver the increased negative pressure to the brake assist device and when the idle speed, obtained by determining that the negative pressure in the brake assist device becomes less than the value set during idling operation , is greater than the desired idle speed, sets the idle speed to an updated desired value used for the reaction control.

 The controller gradually reduces the opening angle of the butterfly shutter to a predetermined speed.

 The controller gradually reduces the opening angle of the butterfly shutter to a predetermined speed, and the predetermined speed is set by

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 so that increasing the reaction coefficient does not cause pumping in the idle speed.

 Figure 1 is a schematic longitudinal sectional view of an internal combustion engine with spark plug ignition type in the cylinders, equipped with a control device according to the invention.

 FIG. 2 represents a main program intended for controlling the opening of the butterfly shutter and the instant of ignition.

 FIG. 3 represents a first subroutine used in the main program represented by FIG. 2.

 FIG. 4 represents a second subroutine used in the main program represented by FIG. 2.

 FIG. 5 represents a third subprogram used in the main program represented by FIG. 2.

 FIG. 6 represents a fourth subprogram used in the main program represented by FIG. 2.

 FIG. 7 represents a fifth subprogram used in the main program represented by FIG. 2.

 Figure 8 shows a time diagram explaining how the subroutines work.

 Figure 9 shows a sixth routine which can be executed in place of the first routine.

 Figure 10 shows a seventh subroutine which can be executed in place of the fifth subroutine.

 Figure 1 is a schematic view of an internal combustion engine with spark plug type

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 injection into the cylinders, equipped with a control device according to the invention. An intake lumen 1 and an exhaust lumen 2 are shown in Figure 1. The intake lumen 1 and the exhaust lumen 2 communicate with a space in a cylinder through a respective valve d intake 3 and an exhaust valve 4. A cavity 8 is formed in the upper surface of a piston 5. A spark plug 6 is arranged in the vicinity of the center of the upper part of the cylinder. A fuel injection valve 7 is arranged on the side of the intake port, which is subjected to relatively low temperatures in a region near the top of the cylinder. An intake manifold 10a is connected to the intake port 1. The intake manifold 10a of each cylinder is connected to an equilibrium chamber 10b. A butterfly valve 11 is disposed in an intake pipe 10c located upstream of the balance chamber 10b. The intake port 1, the intake manifold 10a, the balance chamber 10b, the intake pipeline 10c and the like are the engine intake system.

 The fuel injection valve 7 has a slit-shaped injection orifice and is designed to inject the fuel in the form of a generally fan-shaped mist, of relatively small thickness. A generally fan-shaped fuel mist, of relatively small thickness, comes into direct contact with the high-temperature intake air in the cylinder during engine operation, receives sufficient heat, and is atomized.

During stratified combustion, valve 7

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 fuel injection injects fuel in the second half of the engine compression time. The fog generally in the form of a fan of fuel thus injected enters the cavity 8 formed in the upper surface of the piston, disperses again in the form of a fan on the lower wall of the cavity, receives a sufficient amount of heat from the piston, is deflected in an easily gasifiable state towards the vicinity of the spark plug depending on the shape of the cavity, and forms a good combustible mixture with possibility of ignition in the vicinity of the spark plug 6 to the instant of ignition. By igniting and burning this combustible mixture, stratified combustion is achieved. Because of the stratified combustion, a lean mixture can be burned in the cylinder as a whole, thereby setting the aperture of the butterfly valve to a relatively large value and reducing the loss by pumping. As a result, a high efficiency in fuel consumption can be obtained.

 The internal combustion engine with spark plug ignition type injection into the cylinders allows both homogeneous combustion and stratified combustion. In homogeneous combustion, the fuel is injected in a compression time, and a homogeneous air-fuel mixture is formed in the cylinder at the time of ignition. Homogeneous combustion requires control of the air-fuel ratio in order to achieve the air-fuel ratios determined in advance according to the operating state of the engine. In other words, when homogeneous combustion occurs, the amount of fuel injected and the flow rate of the intake air must be controlled. In general, we choose combustion

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 stratified and conducted when injecting a relatively small amount of fuel while choosing homogeneous combustion and conducting it when injecting a relatively large amount of fuel. One reason for such a choice is that the fuel injection cannot be performed for only a compression time if a relatively large amount of fuel has to be injected. Another reason is that homogeneous combustion has the advantage of obtaining high output power from the engine.

 To control the flow rate of the intake air depending on whether homogeneous combustion or stratified combustion is carried out, the internal combustion engine with spark ignition of the injection type in the cylinders is designed such so that the butterfly valve 11 is not locked with the accelerator pedal and that the opening of the butterfly valve 11 cannot be freely adjusted by a control unit 11a such as a stepping motor. When the butterfly valve 11 is opened in a relatively narrow manner, negative pressure is generated downstream of the butterfly valve 11 in the engine intake system. A brake assist device 12 is provided to use this negative pressure.

 The braking assistance device 12 has first and second chambers which are connected to each other by means of a diaphragm. The balance chamber 10b, which is located downstream of the butterfly valve in the engine intake system, communicates with the first chamber via a communication passage 15. A check valve allowing the air to flow only in one direction, from the

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 first chamber to the balance chamber, is disposed in the communication passage 15, so that a negative pressure generated in the balance chamber 10b is introduced into the first chamber. Thus, the negative pressure, i.e. the absolute value of the negative pressure in the first chamber does not fall (i.e. does not shift towards atmospheric pressure) below the pressure negative in the balance chamber.

 If a driver stops pressing the brake pedal 13, negative pressure in the first chamber of the brake assist device 12 is introduced into the second chamber of the brake assist device 12. If the driver then presses the brake pedal 13, atmospheric pressure is introduced into the second chamber. As a result, a differential pressure is generated between the first and second chambers. This differential pressure assists the driver in pressing the accelerator pedal. Thus, the negative pressure in the first chamber of the braking assistance device 12 drops each time that the brake pedal 13 is pressed and that it is released. However, as soon as a negative pressure is generated in the equilibrium chamber 10b, it is introduced into the first chamber. As shown in FIG. 1, a brake switch 14 is arranged adjacent to the brake pedal 13, in order to detect whether the brake pedal has been pressed or if it has been released.

 It should be noted here that while the combustion engine is idling immediately after it has been started, a reheat command is executed in order to heat and activate in the preliminary stages a catalytic converter (not shown) arranged

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 in the engine exhaust system. In the reheat control, the ignition time is delayed so that the combustion is long lasting in an expansion time and the temperature of the exhaust gas is increased. In this embodiment, stratified combustion is chosen at this time, and the combustible mixture in the vicinity of the spark plug guarantees the possibility of ignition. It is therefore possible to substantially delay the ignition time and to raise the temperature of the exhaust gases sufficiently.

On the other hand, however, a substantial delay in the ignition time leads to a substantial drop in the output power generated by the engine. Thus, the quantity of fuel injected and the flow rate of the intake air are increased in order to avoid the fall in the output power generated by the engine and to maintain a desired speed when the engine is idling.

 If the driver presses the brake pedal repeatedly while the engine is idling as in this case, the negative pressure in the first chamber of the brake assist device 12 drops considerably. However, since stratified combustion occurs during the reheat command, the butterfly valve 11 is opened relatively large as described above, and the negative pressure generated in the equilibrium chamber 10b is not high. For this reason, the negative pressure in the first chamber is not increased. Therefore, if this state is left as such, the differential pressure generated between the first and second chambers is very low, even after the pressure in the second chamber has become equal to atmospheric pressure in response to

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 press the brake pedal. It is therefore impossible to effectively assist the driver in applying pressure to the brake pedal. As a result, the brake pedal weighs heavily on his foot.

 The feeling of abnormality felt by the driver can be resolved by closing the butterfly valve 11 so as to generate a high negative pressure in the balance chamber 10b. However, generating the high negative pressure can cause the idle speed to drop substantially below the desired speed when the engine output decreases. As a result, the driver feels a sense of abnormality, that is, thinks that the engine may be out of order.

 The control device according to this embodiment prevents the driver from experiencing two types of abnormal feelings by controlling the opening of the butterfly shutter and the instant of ignition according to a main program represented on FIG. 2. First of all, a first subroutine 100 shown in FIG. 3 is executed. In the first subroutine 100, it is determined whether or not the command intended to increase the negative pressure in the brake assist device executed. A second sub-program 200 shown in FIG. 4 is then executed. In the second sub-program, the flow rate of the intake air is modified.

 A third subroutine 300 shown in FIG. 5 is then executed. In the third subroutine, a desired speed of the motor is fixed. A fourth subroutine 400 shown in FIG. 6 is then executed. In the fourth subroutine, a reaction coefficient used is fixed

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 for the execution of the command by reaction of the ignition instant. Finally, a fifth routine 500 shown in FIG. 7 is executed. In the fifth subroutine 500, the ignition time is modified.

 In the first subroutine 100 shown in FIG. 3, in step 101, a flag F1 indicating the approval for the current execution of the command is stored in memory as flag FO indicating the last approval for the execution of the command.

Next, in step 102, it is determined whether the negative pressure P in the first chamber of the braking assistance device 12 is less than or not than a first fixed negative pressure Pi. That is to say that it is determined whether the absolute value of the negative pressure P is lower or not than the absolute value of the first fixed negative pressure PI. If a YES is obtained in step 102, that is to say if the brake assist device 12 does not succeed in operating sufficiently as described above, the process advances to step 103 In step 103, the flag F1 is set to 1, and the process returns to the main program represented in FIG. 2. If a NO is obtained in step 102, the process advances to step 104 in which one determines whether the negative pressure P in the first chamber is higher or not than a second fixed negative pressure P2. That is to say that it is determined whether the absolute value of the negative pressure P is greater than or not the absolute value of the second fixed negative pressure P2. If a NO is obtained in step 104, the process returns to the main program without modification of the flag F1.

If a YES is obtained in step 104, the flag F1 is set to 0 in step 105, and the process returns to the main program shown in FIG. 2.

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 Thus, the flag F1 is kept at 0 until the negative pressure in the first chamber of the brake assist device 12 drops below the first fixed negative pressure PI. If the negative pressure in the first chamber drops below the first negative pressure PI, the flag F1 is set to 1. The flag F1 is held at 1 until the negative pressure in the first chamber exceeds a second set negative pressure P2. In this subroutine, the negative pressure P in the brake assist device 12 is detected by a pressure sensor or the like.

 In the second subroutine shown in FIG. 4, it is first determined in step 201 if the current flag F1 has been set or not to 1. If it is determined in the first subroutine that the device d braking assistance 12 does not succeed in functioning sufficiently, a YES is obtained in step 201 and the process advances to step 202. It is determined in step 202 whether the flag FO has been set or not at 0, that is, the F1 flag has now set to 1 for the first time. The process advances to step 203 if a YES was obtained in step 202. In step 203, a current desired flow rate of the intake air Gt is stored in memory as the flow rate d initial flow of intake air Gto.

 A flag F2 indicating approval for execution is then set to 1 in step 204, and a new desired flow rate of the intake air Gt is calculated in step 205 by subtracting a predetermined value a of the desired flow rate of the intake air Gt. It is then determined in step 206 whether the desired flow rate of the intake air Gt has fallen below a value or not Gtm limit. If a NO is obtained in step 206, the

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 process returns to the main program. If a YES is obtained in step 206, the desired flow rate of the intake air Gt is set as the limit value Gtm in step 207, and the process returns to the main program. Thus, while the flag F1 is kept at 1, the desired flow rate of the intake air Gt is reduced by the predetermined value each time the second subroutine is executed until the flow rate desired flow Gt of the intake air reaches the lower limit value Gtm. On the other hand, if the flag F1 has been set to 0, a NO is obtained in step 201. It is then determined in step 208 whether or not the flag F2 has been set to 1.

 When a fuel injection pump fails to operate sufficiently when the engine is started, it is difficult to inject fuel at high pressures. As a result, homogeneous combustion is carried out based on injection in the intake time instead of stratified combustion, which requires that the fuel is injected into the cylinders at high pressures, for example in a compression time. . Thus, when the engine is started, the butterfly shutter 11 throttles the intake air flowing in the cylinders. A high negative pressure is therefore generated in the balance chamber 10b and it is delivered to the braking assistance device 12. At this time, a NO is obtained in step 102 of the first sub-program. A YES is then obtained in step 104, and the flag F1 has been set to 0. In this case, the flag F2 has been set to 0, and a NO is obtained in step 208. Thus, the process returns to the main program without modifying the desired flow rate of the intake air Gt.

 So, if the F1 flag is set to 1 and the

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 process goes through step 204, the flag F2 is set to 1 even after the flag F1 has been set to 0.

That is, if it is determined that the negative pressure in the brake assist device 12 is insufficient in the first routine and that the insufficiency of the negative pressure is overcome, a YES is obtained. in step 208. The desired flow rate of the intake air Gt is then increased by a predetermined value b and it is fixed as the new desired flow rate of the intake air Gt at l step 209. It is then determined in step 210 if the desired flow rate of the intake air has exceeded or not the initial desired flow rate of the intake air Gto. If a NO is obtained in step 210, the process returns immediately to the main program. If, on the other hand, a YES is obtained in step 210, the desired flow rate of the intake air Gt is fixed as the initial desired flow rate Gto of the intake air. The flag F2 is then set to 0 in step 212, after which the process returns to the main program. Thus, if the flag F2 has been set to 1 while the flag has been set to 0, that is to say if a negative pressure deficiency in the brake assist device 12 has been overcome, it is gradually increased the desired flow rate of the intake air Gt each time the second subroutine is executed, until the desired flow rate of the intake air Gt reaches the flow rate desired initial intake air Gto. If the main program is resumed after the desired flow rate of the intake air Gt has been modified in the second subprogram, the control unit 11a acts on the butterfly shutter 11 so as to obtain the flow rate d desired flow of intake air thus modified.

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 In the third subroutine shown in FIG. 5, it is first determined in step 301 whether or not the flag F2 has been set to 1. If a YES is obtained in step 301, it is that is, if the desired flow rate Gt of the intake air has been modified in the second subroutine, it is determined in step 302 whether or not the last flag FO has been set to 0. If a NO is obtained in step 302, the process returns to the main program. If, on the other hand, a YES is obtained in step 302, that is to say if the negative pressure P in the braking assistance device has just become lower than the first fixed negative pressure PI, it is determined in step 303 whether or not the current speed N of the motor is greater than a current desired speed Nt of the motor. If a NO is obtained in step 303, this subroutine is immediately terminated. If, on the other hand, a YES is obtained in step 303, the current desired speed Nt of the motor is stored in memory as the new desired speed of the motor Nto in step 304.

The current speed N of the motor is fixed as Nto of the motor in step 305, after which the process returns to the main program.

 On the other hand, if the flag F2 has been set to 0, a NO is obtained in step 301. Thus, the desired speed Nt of the engine is set as the initial desired speed Nto of the engine in step 306, and the process returns to the main program.

proportionnel Kp est fixé comme valeur usuelle Kpl à l'étape 402. Le coefficient de terme proportionnel Kpl est un coefficient de réaction utilisé dans l'exécution In the fourth subroutine shown in FIG. 6, it is first determined in step 401 whether or not the flag F2 has been set to 1. If a NO is obtained in step 401, a coefficient of term

proportional Kp is set as the usual value Kpl in step 402. The proportional term coefficient Kpl is a reaction coefficient used in the execution

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 control by reaction of the ignition instant according to the fifth sub-program, which will be described later. An integral term coefficient Ki is set as the reaction coefficient as a usual value Kil in step 403, and the main program is then resumed.

 However, if the execution flag F2 has been set to 1, that is to say if the desired flow rate Gt of the intake air has been modified in the second subroutine, the proportional term coefficient Kp is fixed in step 404 as Kp2, which is greater than the usual value. The integral term coefficient Ki is fixed in step 405 as Ki2, which is greater than the usual value.

 In the fifth sub-program represented in FIG. 7, a difference dN is first calculated in step 501 between the current speed N of the motor and the desired speed Nt fixed in the third sub-program. A product of the proportional term coefficient Kp fixed in the fourth subroutine and the difference dN as a proportional term Ap is then calculated in step 502. A total value dNi of the difference dN is calculated in step 503 . A product of the integral term coefficient Ki fixed in the fourth subroutine and the total value dNi as the integral term Ai is calculated in step 504. Then, in step 505, a reference ignition instant Ab in a current operating state is determined using a card or the like. The reference ignition instant Ab is corrected in step 506 based on the proportional term Ap and the integral term Ai. The reference ignition time thus corrected is used as the desired ignition time Ax. The process returns to the main program, and the ignition is executed at the ignition time Ax.

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 We will now describe in a time-sequential manner how the opening of the butterfly shutter 11 and the instant of ignition are controlled, with reference to a timing diagram shown in FIG. 8. Above all, if it is determined that the braking assistance device 12 does not succeed in operating sufficiently due to the fall of the negative pressure P in the first chamber of the braking assistance device below the first fixed negative pressure PI at an instant tl, we do pass the two flags F1 and F2 from 0 to 1. If the actual speed N of the engine before time tl is greater than the desired speed Nt for one reason or another, it is used as the desired speed Nt of the engine after instant tl.

 Since the execution approval flag has been set to 1, the flow rate Gt of the intake air is gradually reduced, which results in a gradual closing of the butterfly shutter 11. When the butterfly valve 11 is closed, the negative pressure in the balance chamber 10b gradually increases. This means that the negative pressure in the brake assist device 12 gradually increases. If the negative pressure in the brake assist device 12 exceeds the first negative pressure Pi and reaches the second negative pressure P2 at an instant t2, the flag F1 is set to 0. Therefore, the desired flow rate Gt intake air gradually increases until the initial desired flow rate is reached, and the butterfly valve 11 opens gradually. When the butterfly shutter 11 is open, the negative pressure in the balance chamber 10b gradually drops. On the other hand, however, the negative pressure in the device

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 brake assist 12 is maintained at the second negative pressure P2. If the desired flow rate Gt of the intake air reaches the initial desired flow rate of the intake air at an instant t3, the execution flag F2 is set to 0, and the desired speed Nt of the motor is fixed as the initial desired speed of the motor.

 While the butterfly valve 11 is forcibly moved in the closing direction from its current opening (from time tl to time t3) so as to increase the negative pressure in the brake assist device 12 , the ignition instant Ax is progressively advanced, proportional to a decrease in the flow rate of the intake air (from instant tl to instant t2), and is delayed progressively, proportionally to an increase the flow rate of the intake air (from time t2 to time t3). If the throttle valve 11 is shifted in the opening direction, the current speed of the motor drops due to a fall in the output power of the motor resulting from a decrease in the air flow rate of admission. Because the current engine speed is used as the desired engine speed Nt in this embodiment, the ignition time is advanced immediately after the butterfly valve 11 has been shifted in the closing direction. Thus, it is possible to prevent the output power of the engine from falling substantially due to the decrease in the flow rate of the intake air. If the desired engine speed remains the same instead of being changed as in the case of this embodiment, the ignition time is not advanced until the current engine speed drops to the speed desired engine

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 due to the decrease in the flow rate of the intake air. In addition, even if the ignition time is slightly advanced at that time, a substantial drop in engine speed is inevitable. As a result, the driver may feel that the engine is out of service.

 As described above, this embodiment is designed so that the ignition instant is advanced immediately after the butterfly shutter 11 has been shifted in the closing direction, thanks to the increase in the coefficients of Kp and Ki reaction for controlling the ignition time. Thus, as indicated by a dashed line in Figure 8, such a substantial drop in engine speed which should cause the driver to feel abnormal does not cause it. As described above, the internal combustion spark ignition engine of the type injected into the cylinders of this embodiment is configured so that homogeneous combustion is carried out when the engine is started and that the stratified combustion with delay in the ignition time in order to warm up the catalyst in the first stages immediately after starting the engine. Compared with homogeneous combustion, more intake air is delivered to the cylinders during stratified combustion. The butterfly shutter 11 is relatively wide open when conducting stratified combustion. In particular, the quantity of fuel injected and the flow rate of the intake air are increased so as to increase the output power of the engine in accordance with a delay in the ignition time, whereby the the butterfly shutter 11 is again shifted in the opening direction. Because of this, especially when

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 the catalyst is warming up while the engine is idling, the butterfly shutter 11 is wide open. It is therefore highly likely in this case that the above-mentioned command is executed as a measure against a tendency towards a drop in negative pressure in the brake assist device. However, the above-mentioned command is accompanied by an advance of the ignition instant and therefore constitutes a drawback for the reheating of the catalyst in the first stages. It is therefore preferable to close the butterfly valve 11 at a relatively high speed so as to increase the negative pressure in the brake assist device in the first stages and to complete the above-mentioned command in the preliminary stages.

 If the butterfly shutter 11 is closed at a relatively high speed, it is necessary to advance the ignition instant to a corresponding high speed. Otherwise, you cause a substantial drop in engine speed. It is necessary to increase the reaction coefficients in order to avoid such a substantial drop in engine speed. However, if the reaction coefficients are increased too much, the motor speed may in turn increase to an extent likely to cause pumping. It is therefore necessary to fix the closing speed of the butterfly shutter 11 and the reaction coefficients so as to avoid pumping of the motor speed.

 The throttle valve opening control or the ignition timing control executed to increase the negative pressure in the brake assist device, as described above, are not exclusively designed for engines in which stratified combustion is carried out

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 to warm up a catalyst in the preliminary stages.

For example, even if homogeneous combustion is conducted while the engine is idling, the amount of fuel injected and the flow rate of the intake air can be increased immediately after the engine is started due to '' a desired high engine speed which has been set for the purpose of heating a catalyst or the engine. In this case, the throttle valve is opened relatively wide and, as expected, the negative pressure generated in the engine intake system is not high.

If a driver repeatedly presses a brake pedal, it becomes necessary to execute a command in order to increase the negative pressure in the brake assist device.

 Figure 9 shows the sixth routine which can be executed in place of the first routine shown in Figure 3. The sixth routine will be described below. First of all, as in the case of step 101 of the first subroutine, the current execution approval flag F1 is stored in step 601 as the last execution approval flag FO. It is then determined in step 602 whether or not a current signal BS1 delivered by the brake switch 14 indicates 0, that is to say whether or not the brake pedal 13 has been released.

If a NO is obtained in step 602, that is to say if the brake pedal 13 is pressed, the flag F1 is set to 0 in step 603. The current signal BS1 of the brake switch 14 is stored in step 604 as the last BSO signal, and the process returns to the main program.

On the other hand, if the current signal BS1 of the brake switch indicates 0, that is to say if the brake pedal 13 has been released, it is determined to

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 step 605 if the last BSO signal indicates 1 or not.

If a NO is obtained in step 605, i.e. if the brake pedal 13 was pressed this time as well as the last time, the treatments in steps 603 and 604 are executed as it is described above, and the process returns to the main program.

 However, if the brake pedal 13 was pressed the last time and was released this time, a YES is obtained in step 605, and the flag FI is set to 1 in step 606. As described more top, the brake assist using negative pressure is designed so that negative pressure is introduced from the first chamber into the second chamber when the brake pedal is released and the pressure drops as a result negative in the first room. Therefore, in many cases, the negative pressure in the brake assist device falls at this time below the first fixed negative pressure PI.

 Therefore, the execution approval flag FI is set to 1. It is then determined in step 607 whether the current opening TH of the butterfly shutter is or not smaller than a fixed opening TH1. If a YES is obtained in step 607, it is concluded that a relatively high negative pressure has been generated in the balance chamber and that the negative pressure in the brake assist device has not fallen below the first set negative pressure PI. The flag FI is therefore reset to 0 in step 603. However, if a NO is obtained in step 607, it is concluded that the negative pressure generated in the equilibrium chamber is not high and that the negative pressure in the brake assist device may fall below the first fixed negative pressure PI due to the release of the brake pedal.

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Thus, the flag F1 is set to 1, and the process advances to the main program in order to initiate the command to open the throttle valve or the command for the ignition time mentioned above.

 As a result, the determinations made in the sixth subroutine lack more or less precision compared to the case in which the pressure in the first chamber of the brake assist device is controlled as in the case of the first subroutine . However, the function for detecting a drop in negative pressure in the brake assist device can be additionally assigned to the brake switch which is originally designed to light a brake light, while the sensor braking is eliminated.

 Figure 10 shows the seventh subroutine which can be executed in place of the fifth subroutine shown in Figure 7. The seventh subroutine is used to set a desired injected quantity Qx of fuel. The seventh subprogramme will be described below. First of all, in step 701 a difference dN is calculated between the current speed N of the motor and the desired speed Nt of the motor fixed in the second subroutine. Then, in step 702, a product of the difference dN and of a proportional term coefficient Kp'fixed in a subroutine which is designed to increase the coefficients of proportional term and of integral term is calculated as in the case of the fourth subroutine, as a proportional term Qp. A total value dNi of the difference dN is then calculated in step 703. A product of the total value dNi and of an integral term coefficient Ki 'fixed in the above-mentioned subroutine, as integral term Qi, is calculated in step 704. We then determine at

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 step 705 a reference quantity Qb of fuel injected for the current operating state of the engine, using a card or the like. The reference quantity Qb of fuel injected is corrected in step 706 based on the proportional term Qp and the integral term Qi. The reference quantity Qb of fuel injected thus corrected is used as the desired quantity Qx of fuel injected. The process returns to the main program, and the fuel injection is carried out according to the quantity of fuel injected Qx.

 The fifth subroutine is designed to avoid a substantial drop in engine speed by advancing the ignition time when the throttle valve opening is reduced, so as to overcome the insufficient pressure negative in the brake assist device. However, as in the case of the seventh sub-program, it is also appropriate to increase the quantity of fuel injected based on the same concept as for the advance of the ignition instant, so as to avoid a fall substantial engine speed.

Of course, it is also appropriate to simultaneously execute the control of the ignition time in the fifth sub-program and the control of the quantity of fuel injected in the seventh sub-program.

 Thus, in accordance with the apparatus intended for an internal combustion engine according to the invention, if it is determined that the negative pressure in the brake assist device has fallen below the fixed value, we shift l '' butterfly valve in''closing direction to increase the negative pressure in the engine intake system and deliver it to the brake assist device. The

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 driver therefore does not feel an abnormality relating to the heaviness of the brake pedal, resulting from insufficient pressure in the brake assist device. When the engine is idling, the ignition instant or the quantity of fuel injected are controlled by reaction using the predetermined reaction coefficients so that the engine idling speed becomes equal to the desired speed of the engine. engine. If it is determined during reaction control that the negative pressure in the brake assist device has fallen below the set value, the butterfly valve is shifted in the closing direction, and the coefficients of reaction used in reaction control. As a result, the engine speed drops when the throttle valve is closed. However, since the fall in engine speed is compensated by a relatively large fluctuation in the ignition time or the amount of fuel injected by reaction control in which the increased reaction coefficients are used, the speed of the motor is protected from a substantial fall. As a result, the driver does not feel a sense of abnormality relating to idling, even when the butterfly valve is closed to overcome a lack of negative pressure in the brake assist device.

 In addition, in accordance with the control unit for the internal combustion engine, if it is determined that the negative pressure in the brake assist device has fallen below the set value, the butterfly valve is shifted into the closing direction to increase the negative pressure in the system

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 engine intake and deliver it to the brake assist device. The driver therefore does not feel any abnormality relating to the heaviness of the brake pedal, resulting from an insufficient negative pressure in the brake pedal. When the engine is idling, the ignition instant or the quantity of fuel injected are subjected to a reaction control so that the engine idling speed becomes equal to the desired engine speed. If it is determined during reaction control that the negative pressure in the brake assist device has dropped below the set value, the butterfly valve is shifted in the closing direction. If the engine idling speed at the time of this determination is greater than the desired engine speed, a reaction control is executed by setting the engine idling speed at the time of the determination as the desired engine speed. As a result, the engine speed drops when the throttle valve is closed.

However, the fact that the ignition instant or the quantity of fuel injected are subject to a reaction control to compensate for the fall in engine speed, not after the engine speed has fallen below speed desired speed of the motor before the time of determination, but as soon as the speed of the motor begins to drop in response to the shift of the butterfly shutter in the closing direction, the speed of the motor is protected against a substantial fall. As a result, the driver does not feel an abnormality relating to idling, even when the butterfly valve is closed to overcome an insufficiency of negative pressure in the brake assist device.

Claims (16)

CLAIMS: 1. Control apparatus for an internal combustion engine to which a brake assist device (12) is connected, the brake assist device (12) using negative pressure downstream of a butterfly valve ( 11) in the intake system of the internal combustion engine; the control apparatus comprising a controller which executes a control by reaction of at least either an instant of ignition, or a quantity of fuel injected during idling, by means of at least a reaction coefficient, so that the engine idling speed be controlled according to a desired idling speed, wherein when it is determined that the negative pressure in the brake assist device (12) becomes less than a fixed value, the controller increases the negative pressure in the engine intake system by reducing the opening angle of the butterfly valve (11) so as to deliver the increased negative pressure to the brake assist device, and to increase at least one reaction coefficient used for reaction control in order to advance the ignition instant or to increase it even more. 2. Control apparatus for an internal combustion engine to which a brake assist device (12) is connected, the brake assist device (12) using negative pressure downstream of a butterfly valve (11) in the intake system of the internal combustion engine; the control unit comprising a controller which <Desc / Clms Page number 29>  performs a reaction control of at least either an instant of ignition or an amount of fuel injected during idling, using at least one reaction coefficient, so that the engine idle speed is controlled at a desired idle speed, wherein when it is determined that the negative pressure in the brake assist device (12) becomes less than a fixed value, the controller increases the negative pressure in the engine intake system by reducing the opening angle of the butterfly shutter (11) so as to deliver the increased negative pressure to the brake assist device (12), and when the idle speed obtained, when it is determined that the negative pressure in the brake assist device (12) becomes less than the value set during idling, is greater than the desired idling speed, fixes the idling speed an updated desired idle speed used for feedback control. 3. Control device according to claim 1 or 2, wherein the controller gradually reduces the opening angle of the butterfly shutter (11) at a predetermined speed. 4. The control device as claimed in claim 1, in which the controller progressively reduces the opening angle of the butterfly shutter (11) at a predetermined speed, and in which the predetermined speed is fixed so that the increase reaction coefficients does not cause pumping in idle speed. <Desc / Clms Page number 30> 5. The control device as claimed in claim 1 or 2, in which a brake switch (14) is used to turn on and off a brake light to determine a decrease in the negative pressure of the brake assist device (12 ). 6. Control device according to claim 1, in which the desired quantity of intake air (Gt) is progressively reduced when the opening angle of the butterfly shutter (11) is reduced to a limit value lower, and is gradually increased from the lower limit value. 7. Control device according to claim 1, in which the ignition instant is corrected on the basis of a proportional term coefficient and an integral term coefficient, each of the coefficients being obtained by a difference between the current speed. of the motor and a desired speed of the motor and by a reaction coefficient (Kp, Ki). 8. Control device according to claim 1, in which the quantity of fuel injected is corrected on the basis of a proportional term coefficient and an integral term coefficient, each of the coefficients being obtained by a difference between the current speed of the motor and a desired speed of the motor and by a reaction coefficient (Kp, Ki). 9. A method of controlling an internal combustion engine to which a braking assistance device (12) is connected, the braking assistance device (12) using negative pressure downstream of a butterfly valve (11) in the admission system of the <Desc / Clms Page number 31>  internal combustion engine, the method comprising the steps of carrying out a reaction control of at least either an instant of ignition, or a quantity of fuel injected during idling, by means of at least one reaction coefficient , so that the engine idle speed is controlled at a desired idle speed, when it is determined that the negative pressure in the brake assist device (12) becomes less than a fixed value, increase the negative pressure in the engine intake system by reducing the opening angle of the butterfly valve (11) so as to deliver the increased negative pressure to the brake assist device, and increase at least one reaction coefficient used for the control by reaction in order to advance the ignition instant or increase even more. 10. A method of controlling an internal combustion engine to which a braking assistance device (12) is connected, the braking assistance device (12) using negative pressure downstream of a butterfly valve (11) in the intake system of the internal combustion engine, the method comprising the steps consisting in carrying out a control by reaction of at least either an instant of ignition or a quantity of fuel injected during idling operation, by means of at least one reaction coefficient, so that the engine idle speed is controlled at a desired idle speed, when it is determined that the negative pressure in the brake assist device (12) <Desc / Clms Page number 32>  becomes less than a fixed value, increase the negative pressure in the engine intake system by reducing the opening angle of the butterfly valve (11) so as to deliver the increased negative pressure to the brake assist device (12), and when the idle speed obtained, when it is determined that the negative pressure in the brake assist device (12) becomes less than the value set during idling operation, is greater than the desired idle speed , sets the idle speed to a desired updated idle speed used for feedback control. 11. The method of claim 9 or 10, wherein the opening angle of the butterfly shutter (11) is gradually reduced at a predetermined speed. Control device according to claim 9, in which the opening angle of the butterfly shutter (11) is progressively reduced to a predetermined speed, and in which the predetermined speed is fixed so that the increase of the reaction coefficient does not cause the idling speed to pump. 13. The method of claim 9 or 10, wherein wherein a brake switch (14) is used to turn on and off a brake light to determine a decrease in the negative pressure of the brake assist device (12 ). 14. The method of claim 9, wherein the <Desc / Clms Page number 33>  desired quantity of intake air (Gt) is gradually reduced when the opening angle of the butterfly valve (11) is reduced to a lower limit value, and is gradually increased from the lower limit value . 15. The method of claim 9, wherein the ignition instant is corrected based on a proportional term coefficient and an integral term coefficient, each of them being obtained by a difference between the current speed of the engine. and a desired engine speed and by a reaction coefficient (Kp, Ki). 16. The method as claimed in claim 9, in which the quantity of fuel injected is corrected on the basis of a proportional term coefficient and an integral term coefficient, each of them being obtained by a difference between the current speed of the engine and a desired engine speed and a reaction coefficient (Kp, Ki).