SE531169C2 - A method for preventing reverse flow I - Google Patents

Description

531 169 A reverse mass fl fate of gas through the compressor is extremely unfavorable for fl your reasons.

First, an acoustic bang occurs with a relatively high sound pressure, which is disturbing to the driver of the vehicle driven by the engine and to persons in the vicinity of the vehicle. Secondly, an abnormal operating situation occurs in the turbocharger, which can shorten the life of the compressor and even damage it. Third, the charging pressure, which causes an instantaneous loss of torque from the engine, is clearly noticeable to the driver of the motor vehicle.

It is therefore desirable to avoid a reverse mass flow of gas through the compressor in a pre-charged engine that drives a motor vehicle. Consequently, there is a need for a method of controlling a turbocharged internal combustion engine so that a reverse direction of mass through the turbocharger compressor is avoided.

DESCRIPTION An object of the present invention is to describe a method and system which can prevent a reverse mass fate of gas through the compressor of a turbocharged internal combustion engine which drives a motor vehicle such as a truck or a bus.

This object, and others, are achieved by the method, system and computer software product as claimed in the claims. Therefore, in order to avoid a reverse mass fate of gas through a compressor on a turbocharged internal combustion engine, the engine control unit of the engine driving a motor vehicle such as a truck or a bus is equipped with a detector which reveals a rapid reduction of the fuel supply. If the reduction rate of the fuel supply exceeds a certain predetermined threshold value, the control unit activates an operating mode that prevents backflow through the turbocharger.

In a realization, where the turbocharger is equipped with VTG (Variable Turbine Geometry), the control system begins to control the VTG to generate high power in the drive mode to prevent backflow through the compressor. The high power from the turbine prevents a rapid power reduction that could lead to reverse flow. 531 'IBS In another embodiment, the control unit begins to steer an EGR valve to a more open position to allow gas to flow in the opposite direction in the EGR branch in the drive position to prevent backflow through the compressor. Thereby, the charging pressure is reduced so that reverse flow through the turbocharger can be prevented.

In one implementation, the control system stores a table with optimal EGR valve positions and optimally closed Variable T urbine Geometry positions for different engine operating conditions, and controls Variable Turbine Geometry and / or the EGR valve position to positions corresponding to current engine operating conditions according to the table. This further reduces the risk of backflow.

With the aid of the control method in accordance with the invention, it is possible to gently reduce the charging pressure and thereby prevent the backflow through the turbocharger which may otherwise occur in the event of a rapid reduction of the fuel supply.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described in more detail by way of non-limiting example and with reference to the accompanying drawings, in which: - Fig. 1 is a general partial view of one of the engine, including a turbocharger with VTG and EGR.

Fig. 2 is a fate diagram illustrating the steps of a control procedure in controlling an internal combustion engine in order to prevent a reverse mass fate of gas in accordance with a realization.

Fig. 3 is a fate diagram illustrating the steps of a control procedure in controlling an internal combustion engine in order to prevent a reverse mass fate of gas in accordance with another embodiment.

DETAILED DESCRIPTION I fi g. 1, selected parts of an engine 100 in a motor vehicle 10 are schematically depicted. The motor depicted in fi g. 1 may, for example, be intended to be included in a truck or other heavy vehicle, such as a bus or the like. Example engine 100 in fi g. l is a diesel engine equipped with a turbocharger and has five cylinders 105. The turbocharger can be of any type, for example a turbocharger of type VTG (Variable Turbine Geometry, or 531 'H39 another turbocharger with steerable turbine or without steerable turbine. The turbocharger has a compressor 102 driven by a turbine 103. In addition, the engine is equipped with an EGR valve 107. The EGR valve 107 controls the amount of exhaust gas returned to the air intake of the engine 100.

The motor is controlled by an electronic control unit (ECU) 106. The ECU 106 is connected to the motor to control the motor. For example, the ECU can be adjusted to control the EGR valve and the position of the VTG, as well as other parameters used to control the engine. In addition, sensors deliver sensor mains to the ECU 106. Based on the sensor signals, the ECU 106 controls the motor using memory-stored computer instructions or the like. Typically, memory stored computer instructions are in the form of a computer program product 10 stored on a readable digital storage medium 108, such as a memory card, a read only memory (ROM), a working memory (RAM), an EPROM, an EEPROM or an fl memory.

I fi g. 2a illustrates a fate diagram of the steps involved in a control procedure performed by an ECU in controlling an engine equipped with a VTG to prevent a reverse mass fate of gas via the turbocharger to the engine. In the first step 201, the ECU detects a rapid decrease in the fuel supply, i.e. the rate of change of the fuel supply exceeds a certain advanced level. After determining that the fuel supply decreases faster than a certain depleted value, the ECU changes operating mode and proceeds to the second stage 203. In the second stage 203, the VTG is controlled to generate maximum turbine speed to help the compressor maintain the charge pressure. Consequently, by controlling the VTG position so that the turbine speed is maximized when the fuel supply is reduced, the risk of a rapid reduction in the fuel supply which could lead to a reverse mass flow of gas through the compressor is reduced, a condition which in most cases can be prevented.

The VTG position that the control system is adapted to control to maximize turbine power / turbine speed can e.g. prescribed via a table which stores an optimal closed VTG position and which ensures the maximum turbine speed for each operating condition that may become relevant for IIIOÉOIII. 534 'ISS Since reverse flow usually occurs at high engine load and within a relatively narrow engine speed band, the control system can be adapted to steer the VTG to a position corresponding to maximum power under these conditions. In other words, the control system can be simplified to adjust the VTG position to provide maximum turbine power / maximum turbine speed for a specific mass fate of gas, ie. the mass gas fate of gas corresponding to the operating state where reverse flow is likely. In a third step 205, the ECU checks whether the conditions are met for exiting the operating condition which prevents reverse mass destruction of gas through the turbocharger. In that case, the process returns to step 201, via a fourth step 207 where the control system is restored to its original normal mode of operation. Otherwise, it remains in operation to prevent reverse mass fl gas depletion through the turbocharger and the procedure returns to step 203.

I fi g. 3a illustrates a fate diagram of the steps involved in a control procedure performed by an ECU in controlling an engine equipped with an EGR system to prevent a reverse mass fl fate of gas via the turbocharger to the engine, in accordance with another embodiment of the present invention. recovery. In the first step 301, the ECU detects a rapid decrease in the fuel supply, i.e. the rate of change in the fuel supply exceeds a certain predefined level. After determining that the fuel supply decreases faster than a certain torque value, the ECU changes operating mode and proceeds to the second stage 303. In the second stage 303, the EGR valve opens to a more open position in order to reduce the charge pressure by creating another gas path, which allows a reverse mass fl fate of gas via the EGR path. Consequently, by directing the EGR valve to a more open position, the risk of a rapid reduction in the fuel supply which could lead to a reverse mass fl waste of gas through the compressor is reduced, because the high pressure gas in the turbocharger can be evacuated through the EGR valve instead of through the turbocharger compressor.

In a third step 305, the ECU checks whether the conditions are met for exiting the operating condition which prevents reverse mass destruction of gas through the turbocharger. In that case, the process returns to step 301, via a fourth step 307 where the control system is restored to its original normal mode of operation. Otherwise, it remains in the mode of operation to prevent reverse mass fl fate of gas through the turbocharger and the procedure returns to step 203. 531 'H59 a certain maintained level. This level may, but does not have to, be the same level as the one at which the mode of operation to prevent an opposite mass fl of gas through the turbocharger is activated.

In accordance with a third embodiment of the present invention, the control systems described above are combined in conjunction with Figures 2 and 3. This means that if a rapid decrease in fuel supply is detected in an engine with both VTG and an EGR system, the ECU will control VTG to a position that provides maximum turbine speed to help the compressor maintain charge pressure, and steer the EGR valve to a more open position to reduce turbocharging pressure by creating a different gas outlet path and allowing a reverse mass flow of gas through the EGR valve.

In such a realization, where both VTG and EGR are controlled, the control system can be adapted to take into account the higher exhaust pressure that results from a more closed VTG position. Consequently, if the exhaust gas pressure rises above the gas pressure of the turbocharger, no gas fl fate can occur in the reverse direction through the EGR valve. By storing a table in the control system that gives the control system combined positions for VTG and EGR for different operating conditions of the engine, it can be ensured that the charging pressure is always higher than the exhaust pressure. This is achieved by storing VTG positions that are more open when a VTG position that provides maximum turbine power would otherwise result in the exhaust pressure exceeding the charge pressure.

Claims (10)

531 '169 i * PATENT REQUIREMENTS A method of controlling an internal combustion engine (100) for driving a motor vehicle (10), wherein the engine is equipped with a turbocharger, which contains a compressor (I02) and wherein the engine is further equipped with a duct for returning exhaust gases. to the engine, where the amount of recirculated exhaust gases is controlled by an EGR valve (107), which in turn is controlled by a control unit (106), characterized by the steps of: - detecting (301) whether the fuel supply decreases faster than a certain fed och threshold and if this is the case, switch (303) to a drive position where the EGR valve is controlled to a more open position and Variable Turbine Geometry is controlled to a position that gives a substantially maximum turbine speed. The method according to claim 1, characterized by the steps: - storing a table indicating optimal EGR valve positions and / or optimally closed Variable Turbine Geometry positions for different drive states of the engine - determination of the current drive condition of the engine - control of Variable Turbine Geometry and / or the EGR valve position to position (s) corresponding to the current operating state of the engine according to the table. The method according to one of claims 1 and 2, characterized by the step: - termination of the operating mode to prevent a reverse mass fl waste of gas through the compressor when the fuel supply no longer decreases faster than a certain fi maintained nivå level. A system for controlling an internal combustion engine (100) for driving a motor vehicle (10), wherein the engine is equipped with a turbocharger, which contains a compressor (102) and wherein the engine is further equipped with a channel for returning exhaust gases to the engine, where the amount of exhaust gas recirculated is controlled by an EGR valve (107), which in turn is controlled by a control unit (106), characterized by: a device (106) for detecting whether the fuel supply decreases faster than a certain l fi threshold threshold and if this is the case, switch (303) to an operating mode where partly the EGR valve is controlled to a more open position and partly Variable Turbine Geometry is controlled to a position that gives a substantially maximum turbine speed. The system according to claim 4, characterized by the steps: - a device for storing a table indicating optimal EGR valve positions and / or optimally closed Variable Turbine Geometry positions for different operating conditions of the engine - determining the current operating condition of the engine - controlling Variable Turbine Geometry and / or the EGR valve position to position (s) corresponding to the current operating state of the engine according to the table. The system according to claim 4 or 5, characterized by: - a device for exiting the operating mode to prevent a reverse mass fl fate of gas through the compressor when the fuel supply no longer decreases faster than a certain advanced level. A computer program product (110) for controlling an internal combustion engine (100) for driving a motor vehicle (10), wherein the engine is equipped with a turbocharger, which contains a compressor (102) and wherein the engine is further equipped with a channel for return exhaust gases to the engine, where the amount of recycled exhaust gases is controlled by an EGR valve (107), which in turn is controlled by a control unit (106), characterized in that the computer program product contains program sections which, when executed on a computer, e.g. the control unit (106) for controlling the internal combustion engine with internal combustion, causes the computer to perform the step: - detecting (301) whether the fuel supply decreases faster than a certain specified threshold value and if so switch (303) to a driven position where the EGR valve is controlled to a more open position and partly Variable Turbine Geometry is controlled to a position that gives a substantially maximum turbine speed. 531 169 .í \ Computer program product according to claim 7, characterized by program segments for: - storage of a table indicating optimal EGR valve positions and / or optimally closed Variable Turbine Geometry positions for different operating states of the engine - determination of current operating state of the engine - control of Variable Turbine Geometry and / or EGR valve position to position (s) corresponding to the current operating state of the engine according to the table. Computer program product according to claim 7 or 8, characterized by program segments for: - termination of the operating mode to prevent a reverse mass fl waste of gas through the compressor when the fuel supply no longer decreases faster than a certain level of fuel. A digital storage medium (108) on which the computer program product of any of claims 7-9 is stored.