PERSSON MIKAEL (SE)
JENNISCHE MATS (SE)
PERSSON MIKAEL (SE)
| EP1323927A1 | 2003-07-02 | |||
| EP1323912A1 | 2003-07-02 | |||
| EP1621746A2 | 2006-02-01 | |||
| EP1323907A1 | 2003-07-02 | |||
| US20030216856A1 | 2003-11-20 |
CLAIMS
1. A method of controlling a combustion engine (100) adapted to power a motor vehicle (10), the engine comprising a turbocharger, the turbocharger comprising a compressor (102) and a turbine (103), the speed of the turbine being controllable by a control unit (106) with the object of preventing a reverse gas mass flow through the compressor of the turbocharger, characterized by the steps of:
- receiving current values for gas mass flow and pressure difference across the compressor,
- comparing (203) current values for gas mass flow and the pressure difference across the compressor with limit values stored in a map,
- in a first control mode, applying a first rapid filter when the combustion engine (101) is operating in a state which is not close to a situation which might cause a reverse gas mass flow, which is determined by comparison of current values for gas mass flow and the pressure difference across the compressor with corresponding values stored in the map, - in a second control mode (205), applying, when the combustion engine (101) is operating close to a state which might cause backflow through the compressor, a second filter which gives a more uniform low-frequency signal with a smaller bandwidth and a relatively long time constant, and
- controlling (205) the turbine speed so that a reverse gas mass flow through the compressor (102) is prevented.
2. The method according to claim 1, characterized by the step of:
- replacing the pressure difference value across the compressor by the speed of the turbine.
3. The method according to claim 1 or 2, characterized by the step of:
- adjusting gas mass flow and/or turbine speed values received for ambient pressure and ambient temperature.
4. The method according to claim 3, characterized by the steps of: - comparing (203) current values of the parameters represented in the limit value map with corresponding values recorded in the limit value map, and - switching (205) to a second control mode when the difference between the current values of the parameters represented in the limit value map and the corresponding values recorded in the limit value map is less than a certain predefined threshold value.
5. The method according to any of claims 1 - 4, characterized by the step of:
- controlling the speed of a turbine with Variable Turbine Geometry by controlling the position of the Variable Turbine Geometry.
6. A system for controlling a combustion engine (100) adapted to power a motor vehicle (10), the engine comprising a turbocharger, the turbocharger comprising a compressor (102) and a turbine (103), the speed of the turbine being controllable by a control unit (106), characterized by:
- means for receiving the current gas mass flow and pressure difference across the compressor, - means for comparing (203) current values for gas mass flow and the pressure difference across the compressor with limit values stored in a map,
- means for applying in a first control mode a first rapid filter when the combustion engine
(101) is operating in a state which is not close to a situation which might cause a reverse gas mass flow, which is determined by comparison of current values for gas mass flow and the pressure difference across the compressor with corresponding values stored in the map,
- means for applying in a second control mode (205), when the combustion engine (101) is operating close to a state which might cause backflow through the compressor, a second filter which gives a more uniform low- frequency signal with a smaller bandwidth and a relatively long time constant, and - controlling (205) the turbine speed so that a reverse gas mass flow through the compressor
(102) is prevented.
7. The system according to claim 6, characterized by - means for replacement of the pressure difference across the compressor by the speed of the turbine.
8. The system according to claim 7, characterized by:
- means for adjusting gas mass flow and/or turbine speed values received for ambient pressure and ambient temperature.
9. The system according to any of claims 6 - 8, characterized by:
- means for comparing current values of the parameters represented in the limit value map with corresponding values recorded in the limit value map, and
- means for switching to a second control mode when the difference between the current values of the parameters represented in the limit value map and the corresponding values recorded in the limit value map is less than a certain predefined threshold value.
10. The system according to claim 9, characterized by:
- means for applying a filter having low pass characteristics to the signal indicative of the current gas mass flow as compared with the filter characteristics of the filter used to filter the signal indicative of the current gas mass flow when not in the second control mode.
11. The system according to any of claims 6 - 10, characterized by:
- means for controlling the speed of a turbine with Variable Turbine Geometry by controlling the position of the Variable Turbine Geometry.
12. A computer program product (110) for controlling a combustion engine (100) adapted to power a motor vehicle (10), the engine comprising a turbocharger, the turbocharger comprising a compressor (102) and a turbine (103), the speed of the turbine being controllable by a control unit (106), characterized in that the computer program product comprises program segments which when executed on a computer for controlling the combustion engine cause the computer to perform the steps of:
- receiving current values for gas mass flow and pressure difference across the compressor,
- comparing (203) current values for gas mass flow and the pressure difference across the compressor with limit values stored in a map, - in a first control mode, applying a first rapid filter when the combustion engine (101) is operating in a state which is not close to a situation which might cause a reverse gas mass flow, which is determined by comparison of current values for gas mass flow and the pressure difference across the compressor with corresponding values stored in the map,
- in a second control mode (205), applying, when the combustion engine (101) is operating close to a state which might cause backflow through the compressor, a second filter which gives a more uniform low-frequency signal with a smaller bandwidth and a relatively long time constant, and
- controlling (205) the turbine speed so that a reverse gas mass flow through the compressor (102) is prevented.
13. The computer program product according to claim 12, characterized by program segments for:
- replacing the pressure difference across the compressor by the speed of the turbine.
14. The computer program product method according to claim 13, characterized by program segments for:
- adjusting gas mass flow and/or turbine speed values received for ambient pressure and ambient temperature.
15. The computer program product according to any of claims 12 - 14, characterized by: program segments for:
- comparing current values of the parameters represented in the limit value map with corresponding values recorded in the limit value map
- switching to a second control mode when the difference between the current values of the parameters represented in the limit value map and the corresponding values recorded in the limit value map is less than a certain predefined threshold value.
16. The computer program product according to claim 15, characterized by program segments for:
- applying a filter having low pass characteristics to the signal indicative of the current gas mass flow as compared with the filter characteristics of the filter used to filter the signal indicative of the current gas mass flow when not in the second control mode.
17. The computer program product according to any of claims 12 - 16, characterized by program segments for:
- controlling the speed of a turbine with Variable Turbine Geometry by controlling the position of the Variable Turbine Geometry.
18. A digital storage medium (108) on which the computer program product according to any of claims 12 - 17 is stored. |
A TURBO CHARGER CONTROL METHOD
TECHNICAL FIELD
The present invention relates to a method and a system for controlling an engine having a turbo charger driven by a controllable turbine such as a Variable Turbine Geometry (VTG) turbo charger.
BACKGROUND
Diesel engines for use in heavy vehicles such as trucks and buses are sometimes provided with a Variable Turbine Geometry (VTG) also termed Variable Geometry Turbocharger or Variable Geometry Turbine (VGT). Such an engine can typically be provided with an EGR (Exhaust Gas Recirculation) valve. Other engines for other uses may also be provided with a VTG or other types of turbochargers. One reason for employing VTG technology and EGR technology is that it facilitates fulfillment of emission requirements for i.a. diesel engines.
A VTG turbo charger comprises a turbine with a variable geometry powering a compressor for feeding the air intake of the combustion engine with compressed air. If the difference in pressure upstream and downstream the compressor, i.e. the pressure difference over the compressor exceeds some value, the compressor will be unable to maintain the pressure difference and there will be a reverse gas mass flow through the compressor. This is also known as surging.
A reverse gas mass flow through the compressor is highly unwanted for a number of different reasons. Firstly, such an event will generate a bang having a fairly loud volume, which of course is disturbing for a driver of a vehicle propelled by the engine and people in the vicinity of the vehicle. Secondly, the compressor of the turbo charger will experience an abnormal operation condition that may shorten the life time of the compressor or even directly damage the compressor. Thirdly, there will be a drop in charge gas pressure, which
may result in an instant drop in torque generated by the engine, which will be felt by the driver of the motor vehicle.
It is therefore desirable to avoid a reverse gas mass flow through the compressor of a turbo charged engine powering a motor vehicle. Hence there exists a need for a method of controlling a turbo charged combustion engine which prevents a reverse mass flow through the compressor of the turbo charger.
SUMMARY It is an object of the present invention to provide a method and a system that is able to reduce the risk of or even prevent a reverse gas mass flow through the compressor of a turbo charged combustion engine for powering a motor vehicle such as a truck or a bus.
This object and others are obtained by the method, system and computer program product as set out in the appended claims. Thus, in order to prevent a reverse gas mass flow through a compressor of a turbo charged combustion engine, the maximum allowed pressure drop over the compressor for each gas mass flow is mapped in a pressure difference/ gas mass flow map stored in the control system of the engine. When the readings of current pressure difference and current gas mass flow indicates that engine operation is close to a value pair resulting in a reverse gas mass flow through the compressor, the control unit, in particular the electronic control unit (ECU), controlling the engine controls the turbine speed of the turbo charger to a reduced speed resulting in a lower pressure difference over the compressor thereby avoiding a reverse gas mass flow through the compressor of the turbo charger. Because the pressure difference can be derived from the turbine speed it is possible to directly control the turbine speed using the current gas mass flow as input signal in addition to the turbine speed signal.
In accordance with one embodiment of the present invention the control unit used to control the engine is adapted to receive the current gas mass flow for example given by a sensor located in conjunction with the compressor, as input signal. The gas mass flow can for calibration reasons be adjusted for ambient pressure and ambient temperature. The control unit controls the turbine speed, which may also be adjusted for ambient pressure and
ambient temperature, in response to the current gas mass flow. Depending on the type of turbine the turbine speed is controlled differently. For example in the case of a VTG type of turbine the VTG position is controlled to control the turbine speed.
In accordance with another embodiment, two different filtering modes are employed when controlling the turbine speed to avoid a reverse gas mass flow through the compressor of the turbocharger. Thus, in a first mode when the engine is operated in a state not close to generate a reverse gas mass flow as determined by comparing the current gas mass flow and turbine speed to the corresponding values of the map comprising limit values, a first fast filter is employed.
A fast signal response is used to enable accurate control of the turbine speed and to enable fast detection of when the operating conditions are such that the values of gas mass flow through the compressor of the turbo charger and the turbine speed are close to values of the map comprising limit values.
When the values of gas mass flow through the compressor of the turbo charger and the turbine speed are close to values of the map comprising limit values, another filter with low pass filter characteristics, as compared to the filter used in the first mode, is used to provide a smooth signal. By applying a filter providing a smooth signal, the risk for oscillation in the control system, resulting in surging is reduced.
Thus, by applying a filter with lower bandwidth in case the regular VTG controller requests a more closed VTG than acceptable as given by the mapped pair of turbine speed and gas mass flow values, the risk of oscillation of the VTG is reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described in more detail by way of non-limiting examples and with reference to the accompanying drawings, in which:
- Fig. 1 is a general partial view of an engine including a turbo charger with VTG and EGR, and
- Fig. 2 is a flow chart illustrating steps performed in a control procedure when controlling a combustion engine preventing a reverse gas mass flow.
DETAILED DESCRIPTION In Fig.l selected parts of an engine 100 of a motor vehicle 10 is schematically depicted. The engine depicted in Fig. 1 can for example be designed to be part of a truck or any other heavy vehicle such as a bus or the like. The exemplary engine 100 in Fig. 1 is a diesel engine provided with a turbocharger and having five cylinders 105. The turbo charger can be of any type with a variable turbo charger for example a turbo charger having a Variable Turbine Geometry (VTG) or another turbo charger having a controllable turbine, such as a turbo charger with a waste gate. The turbo charger comprises a compressor 102 driven by a turbine 103. Furthermore the engine comprises an EGR valve 107. The EGR valve 107 controls the amount of exhaust gas that is re-circulated to the gas inlet of the engine 100.
The engine is controlled by an electronic control unit (ECU) 106. The ECU 106 is connected to the engine to control the engine. In addition sensors provided in the vehicle provide sensor signals to the ECU 106. Using the sensor signals and other signals, the ECU 106 exercises control of the engine using some programmed computer instructions or similar means. Typically, the programmed computer instructions are provided in the form of a computer program product 110 stored on a readable digital storage medium 108, such as memory card, a Read Only Memory (ROM) a Random Access Memory (RAM), an EPROM, an EEPROM or a flash memory.
In Fig. 2, a flow chart illustrating steps performed in a control procedure when controlling turbine speed in order to prevent a reverse gas mass flow through a compressor of a turbo charged combustion engine is shown. In a first step 201, the maximum allowed turbine speed / pressure drop over the compressor for each gas mass flow is mapped in a pressure difference or turbine speed/ gas mass flow map and stored in the control system of the engine. In particular the map is made available to the electronic control unit adapted to control the engine and the speed of the turbine of a turbocharger of the engine.
Next, the ECU begins to monitor the gas mass flow and the turbine speed and compare the values to the limit values of the map in a second step 203. If the readings of current pressure difference (or turbine speed) and current gas mass flow indicates that engine operation are close to values resulting in a reverse gas mass flow through the compressor, the control system used to control the engine switches to another control mode in a third step 205. hi the second control mode the control unit, in particular the electronic control unit (ECU) controlling the engine controls the turbine speed of the turbo charger to a reduced speed resulting in a lower pressure difference over the compressor thereby avoiding a reverse gas mass flow through the compressor of the turbo charger.
In accordance with one embodiment of the present invention the control unit used to control the engine is adapted to receive the current gas mass flow as input signal. The gas mass flow can be adjusted for ambient pressure and ambient temperature. The control unit controls the turbine speed in response to the current gas mass flow. The turbine speed may also by be adjusted for ambient pressure and ambient temperature.
In accordance with another embodiment, two different filtering modes are employed when controlling the turbine speed to avoid a reverse gas mass flow through the compressor of the turbo charger. Thus, in the first mode when the engine is operated in a state not close to generate a reverse gas mass flow as determined by comparing the current gas mass flow and turbine speed to the map comprising limit values, the filter used for filtering the gas mass flow can be a fast filter providing quick response.
In the second mode, where the engine is operated in a state close to conditions that can generate surging through the compressor, the control system applies a different filter providing a smoother, low frequency, signal in a fourth step 207. Hence, when the values of gas mass flow through the compressor of the turbo charger and the turbine speed are close to values of the map comprising limit values another filter providing smooth signal response with a relatively long time constant is used in order to ensure that the turbine speed does not exceed the maximum value as given by the limit value map and the current gas mass flow. Finally, in a fifth step 209 it is checked if the gas mass flow value and turbine speed value are still close to the limit values as given by the map. If the values are still close to the limit
values the control system stays in the second mode and the procedure returns to step 205. If on the other hand the values have changed so that there is no longer a need to stay in the second mode because the values are no longer close to the limit values of the map, the procedure returns to step 201.
Using the method and system as described herein will reduce the risk of surging occurring in a compressor powered by a turbine having a controllable speed, such as a VTG or a turbo with a waste gate.