Method for controlling vacuum in an internal combustion engine intake manifold

Abstract: The invention relates to a method for controlling vacuum in an intake conduit (4) of a combustion engine in a vehicle, which vehicle is provided with a brake booster (19) and means (16) for actuating the brake booster (19), whereby actuation of the brake booster (19) causes a throttle valve (18) in the intake conduit (4) to close in order to create a vacuum to the brake booster (19).

Description: TECHNICAL FIELD The invention relates to a method for controlling vacuum in an intake conduit in a combustion engine of a vehicle, wherein actuation of the brake booster closes a throttle in the intake conduit in order to provide the brake booster with vacuum. BACKGROUND ART Modern vehicles normally use a brake booster connected to the brake pedal in the brake circuit of the vehicle, in order to amplify the pressure that is required for actuating the brakes. When a driver actuates the brake pedal, the brake booster will supply an hydraulic pressure corresponding to the actuating force applied to the pedal by the driver to the brake circuits of the vehicle, thereby actuating the brake calipers or drums of the vehicle. The brake booster is controlled by a source of vacuum. This source is usually the intake conduit of the engine of the vehicle. The intake conduit is provided with a throttle valve that is controlled by an accelerator pedal via an engine control system. The throttle valve controls the amount of air supplied to the cylinders. It also co-operates with the fuel injection system to control the air/fuel ratio needed for a required power output. The vacuum required for the brake booster is taken from a position downstream of the throttle valve. Under certain running conditions, such as a cold start combined with a high load or during stratified combustion with the throttle wide open, the vacuum downstream of the throttle valve may not be sufficient for proper operation of the brake booster. It is therefore a problem to provide a sufficient vacuum to the brake booster under all operating conditions of the engine. One solution to the problem is shown in EP-A2-0 833 044, in which a sensor is used for monitoring the vacuum in the brake booster. When a pressure level is detected at which the vacuum is insufficient for actuation of the brake booster, the engine will switch from stratified to homogenous combustion. This will cause the throttle to be controlled to create a vacuum in the intake conduit. A drawback with this solution is that the engine will switch between different operating conditions as soon as the pressure in the brake booster passes a set level, whether it is required or not. A further solution is shown in WO-A1-9954613. According to this solution, an actuation of the brake pedal is detected, whereby a counter starts measuring the period of time that the pedal is being actuated. If said period exceeds a set time, the engine is switched from a lean to a rich air/fuel ratio causing the throttle to be controlled so that a vacuum is created in the intake conduit. However, a problem with this solution is that there is a delay between the actuation of the brake pedal and the switching between operating conditions of the engine. This causes a corresponding delay before a vacuum can be supplied to the brake booster. Other known solutions use specially provided air pumps, operated separately from the engine to supply a vacuum for the brake booster. This requires the mounting of an additional pump on the vehicle, which pump must be driven by the engine, requires additional space and is an extra cost to be added to the manufactured product. DISCLOSURE OF INVENTION The purpose of the invention is to solve the above problems by providing a method using direct control by demand. The goal is to switch the engine between different operating conditions only when the brake pedal is actuated. The invention relates to a method for controlling the vacuum in an intake conduit of a combustion engine in a vehicle provided with a brake booster and a pedal for actuating the booster. Actuation of the brake pedal when the engine operated with stratified combustion will control the throttle valve in the intake conduit so that a vacuum is created for the brake booster. The throttle valve is controlled to close instantly, within a few tenths of a second, in order to create a vacuum in the intake conduit as quickly as possible. When the driver actuates the brake pedal, an electrical signal that controls the throttle valve via a control unit is generated. This can be achieved either by closing an electrical contact as soon as the pedal begins to move, or by using the signal that is generated by the actuation of an electrically controlled brake pedal, having no mechanical connection with the brake booster and its associated master brake cylinder. The throttle valve is preferably electrically controlled by an electronic control unit. Said control unit is either connected to or integrated with the engine control system. As soon as the vacuum in the brake booster has reached a predetermined level, or when the electrical signal indicating brake pedal actuation ceases, the throttle valve can be opened. The method may be used under several different operating conditions where the vacuum in the intake conduit is insufficient. One such operating condition is cold starting, when the emissions of for instance HC from the engine reaches their highest level. In order to heat a catalytic converter in the exhaust system quickly, it is desirable to increase the engine load by opening up the throttle and leave it open. The result can be that the vacuum in the intake conduit is too low to give the necessary brake servo effect. If not acted upon, this would cause a loss of a major part of the braking effect during start-up. As a rule the vehicle brakes are not operated immediately after the engine is started. The supply of vacuum to the brake booster may therefore be delayed until the need arises. Hence the warm-up cycle of the engine and the catalytic converter can proceed without interference for a longer period of time. This will help reduce the emissions of hydrocarbons (HC) and other pollutants. By connecting the control unit to a speed sensor and sensors for the brake anti-locking system (ABS), a further embodiment enables the warm-up cycle of the engine and the catalytic converter to continue undisturbed as the procedure is only performed when the vehicle is moving or if the anti-locking system is activated. The latter may occur for instance if the vehicle anti-slip system uses the ABS-system to brake one or more wheels. When the driver actuates the brake pedal and the procedure is started, the engine control unit must make sure that the driveability of the vehicle does not deteriorate, due misfire, variations in engine speed, etc. . As the throttle valve starts to close it is necessary to adjust the ignition timing and/or the amount of injected fuel. BRIEF DESCRIPTION OF DRAWINGS Figure 1 shows a schematic system for generating a vacuum for a brake booster on demand. MODES FOR CARRYING OUT THE INVENTION Figure 1 shows an embodiment of the invention comprising an engine 1 having at least one cylinder 2 with an associated piston 3. Air is supplied through an intake conduit 4 and is mixed with fuel from an injection system comprising a nozzle 5, whereby the mixture passes through an intake valve 6 and into the cylinder 2. After compression the mixture is ignited by an ignition system comprising a spark plug 7, after which the combusted gases are pushed out through an exhaust valve 8. The engine is controlled by a control unit 10 that receives signals from several sensors, such as a sensor 11 connected to the accelerator pedal 12, one or more sensors 13 measuring the rotational speed of one or more vehicle wheels 14 and a contact or sensor 15 sensing the actuation of a brake pedal 16. After having evaluated the signals from these sensors, the control unit 10 sends control signals to the injection system 5, the ignition system 7, and a control unit 17 for a throttle valve 18 in the intake conduit 4. The control unit 17 for the throttle valve preferably comprises an electric motor for manoeuvring the valve 18. The brake pedal 16 is connected to a brake booster 19, which will amplify the force applied to the brake pedal upon actuation by the driver. The amplified pressure acts on a master brake cylinder 20 that supplied hydraulic pressure to the brake circuits (not shown) of the vehicle. The pressure amplifying effect is achieved by means of a membrane in the brake booster, which membrane is acted upon by a vacuum when the brake pedal 16 is actuated. The vacuum is obtained by connecting the brake booster 19 to the intake conduit 4 using a pipe 21. The example shown a brake pedal that is mechanically connected to the brake booster, although a brake pedal using electrical control may be used. The contact 15 in Figure 1 will then be replaced by a sensor, which will indicate both actuation and current position of the pedal to the control unit 10. A signal indicating the position of the brake pedal is transmitted to an electrically controlled and/or actuated brake booster, which will supply the desired pressure to the brake circuits. Under normal operation of the vehicle, vacuum will exist in the intake conduit 4 sufficiently often to supply the brake booster with vacuum for normal use. However, under certain operating conditions, such as cold starting combined with a high load, it may be necessary change the operating parameters of the engine in order to create a vacuum for the brake booster, should the vacuum be missing or insufficient. One such operating condition is a cold start of the engine, when the emission of pollutants such as HC reaches its highest level. In order to achieve rapid warm-up of a catalytic converter in the exhaust system, it is desirable to increase the load on the engine by leaving the throttle valve open. To avoid disturbing the warm-up cycle unnecessarily, the control unit 10 will stand by for a signal from the sensor 15 on the brake pedal 16. Should the driver actuate the pedal 16, the operating condition of the engine is immediately switched by closing the throttle valve. This will take place within a few tenths of a second and the pressure will then drop very quickly. For a 5-cylinder engine, 20% of the swept volume of the engine is sucked from the intake conduit per stroke. An idling speed of 1200 rpm during a cold start will correspond to 600 strokes/minute. The time required to build up a vacuum is directly proportional to the volume of the intake conduit after the throttle valve. A situation of this type may occur when starting the vehicle uphill, or when the driver of a vehicle with automatic transmission actuates the brake before moving the gear selector to the D- or R-position (D- "Drive"; R- "Reverse"). If after a cold start, the vehicle is set in motion without the brakes being actuated, the system may be connected to the ABS-system of the vehicle as well as the brake pedal. Should the vehicle be braked sufficiently hard to activate the ABS-system, the procedure described above will come into operation. However, if the vehicle is provided with an anti-slip system, arranged to prevent one or more of the driving wheels from slipping during start or acceleration, vacuum in the brake booster may be required without the brake pedal being actuated. In such a case the throttle valve 18 may be controlled by the control unit 10 in response to signals from the sensors 13 measuring rotational speed of the wheels. In the same way as described above, the throttle valve 18 is immediately closed as soon as the control unit 10 receives a signal from one or more wheel sensors 13 indicating that one or more wheels must be braked. After a predetermined period of time in a closed or throttled position, the throttle valve 18 will open, wholly or in part, depending on the current parameters from the engine control unit 10 and also on a signal from the sensor 15 indicating that the brake pedal is sill being actuated. In the latter case, the control unit 10 may switch the engine to provide vacuum in the intake conduit 4 until the signal ceases. According to an alternative embodiment, the brake booster may be provided with a pressure sensor that measures the vacuum in the booster. When the vacuum reaches a predetermined limit, the control unit resumes the normal control of the engine. As long as the signal from the brake pedal sensor 15 indicates that the pedal is being actuated it is necessary to ensure that vacuum is available. This can be achieved by controlling the engine so that there is vacuum in the intake conduit until the signal ceases, or by repeating the procedure of closing the throttle valve 18 every time the sensor indicates insufficient vacuum in the brake booster 19. Although the above example is mainly intended for use during a cold start of the engine, it may also be applied to other operating conditions. Such a system can provide a back-up function if the vacuum in the brake booster is insufficient for whatever reason. It can for instance be used if a sudden leak occurs in the accumulator or if the accumulator has lost its vacuum after a long period of stratified combustion. Using a pressure sensor in the brake booster 19, the vacuum can be monitored by the engine control unit 10. When the brake pedal is actuated the throttle valve is instantly closed to create a vacuum, as described above. This could also be used for providing a warning signal to the driver, indicating a malfunction in the brake system. A common feature for all embodiments described above is that the engine control system must compensate for the sudden interruption of mass flow of air when the throttle valve closes. In order to avoid misfire and/or unacceptable variations of engine speed, the engine control system will adjust the ignition timing and the fuel injection to suit the current mass flow in the intake conduit.

Claims: Method for controlling vacuum in an intake conduit (4) of a combustion engine in a vehicle, which vehicle is provided with a brake booster (19) and means (16) for actuating the brake booster (19), characterized in that actuation of the means (16) for actuating the brake booster (19) causes a throttle valve (18) in the intake conduit (4) to close instantaneously in order to create a vacuum for the brake booster. Method according to claim 1, characterized in that actuation of the brake booster (19) occurs by means of a brake pedal (16). Method according to claim 1 or 2, characterized in that actuation of the brake booster (19) occurs by means of an electrical signal generated by a brake pedal (16), which signal control both the brake booster (19) and the throttle valve (18) via a control unit (10). Method according to any of the claims 1-3, characterized in that the throttle valve (18) is electrically controlled. Method according to any of the claims 1-4, characterized in that the throttle valve (18) opens when the vacuum in the brake booster (19) reaches a predetermined level. Method according to any of the claims 1-5, characterized in that the procedure is performed when the engine is running under a high load, e.g. in connection with a cold start. Method according to any of the claims 1-6 characterized in that the procedure is performed when the vehicle is moving Method according to claim 1, characterized in that the brake booster (19) is actuated by an anti-locking system connected to the brakes. Method according to claim 8, characterized in that the procedure is performed continuously as long as the brake anti-locking system is active.

Inventors: ALMKVIST GOERAN, FAST OLLE, GREEN HENRIK, MAXVALL MARCUS, ALMKVIST, GOERAN, FAST, OLLE, GREEN, HENRIK, MAXVALL, MARCUS, ALMKVIST, Göran
Applicants: VOLVO PERSONVAGNAR AB
Application year: 2001
Main classification: B60T13
IPC codes: F02D9, B60T17, B60T13