SE541433C2

SE541433C2 - A control system for charge control of a combustion engine and a method for carrying out such a control

Info

Publication number: SE541433C2
Application number: SE1650358A
Authority: SE
Inventors: Anton Wetterstrand; Niclas Gunnarsson; Pontus Johansson
Original assignee: Scania Cv Ab
Priority date: 2016-03-17
Filing date: 2016-03-17
Publication date: 2019-10-01
Also published as: SE1650358A1; DE112017000934T5; WO2017160207A1

Abstract

A control system for charge control of a combustion engine (1) comprises a waste gate valve (10) installed in the exhaust pipe (7) from the engine to form a bypass of exhaust gas with respect to a turbine (6) driving a compressor (4). A control unit (18) controls a control valve (11) and by that the waste gate valve (10). The control unit (18) is configured to control the control valve (10) to deliver air of a determined pressure determining the open degree of the waste gate valve by a first use of compressed-air from a compressor-air tank (13) and by a second use of compressed-air from an outlet of the compressor (4) and make a relation of the second use to the first use higher for high loads of the engine than for low engine loads.

Description

A CONTROL SYSTEM FOR CHARGE CONTROL OF A COMBUSTION ENGINE AND A METHOD FOR CARRYING OUT SUCH A CONTROL TECHNICAL FIELD OF THE INVENTION The present invention relates to a control system for charge control of a combustion engine, comprising: a turbo charger with a compressor in an intake pipe to the engine and a turbine in an exhaust pipe from the engine, a waste gate valve installed in the exhaust pipe to form a bypass of exhaust gas with respect to the turbine in the exhaust pipe, a control valve configured to control the waste gate valve by delivering air of a pressure determining the open degree of the waste gate valve, a compressed-air tank connected to the control valve to deliver compressed-air to the control valve, and a control unit configured to control the control valve and by that the waste gate valve, as well as a method for carrying out a charge control of an engine according to the preamble of the appended independent method claim.

The invention is not restricted to any particular type of combustion engine or fuel, and only by means of examples may fuels in the form of diesel, ethanol, biogas and petrol be mentioned. Furthermore, the invention relates to charge control of combustion engines intended for all types of use, such as in industrial applications, in crushing machines and in all types of motor vehicles, although the invention is particularly applicable to wheeled motor vehicles, especially utility vehicles, such as trucks and buses, and it will for that sake mainly be discussed for this use so as to illuminate the invention but not in any way restrict it thereto.

Accurate control of a waste gate valve in a turbo charged combustion engine is of great importance for obtaining proper operation of such an engine in all types of situations, not only for obtaining an optimum performance of the engine but also for addressing emission regulations being more and more strict.

When driving a vehicle with a low engine load the waste gate valve has mostly to be controlled to open to a high degree for making the exhaust gases from the engine to bypass the turbine, whereas for high engine loads the waste gate valve shall be open to a lower degree for making the turbine to drive the compressor of the turbo charger powerfully. It is of great importance that the control of the waste gate valve follows the change of loads and conditions for the engine quickly for instantaneously obtaining the behavior of the engine desired for obtaining an optimum with respect to performance and emissions and also avoiding turbo overspeeding.

BACKGROUND ART A control system according to the introduction is already known through for example US 2009/0301084 A1 in which a control system having a PWM (Pulse Width Modulation) valve as control valve for controlling a waste gate valve by use of compressed-air from a compressed-air tank is described. However, a disadvantage of controlling the waste gate valve by compressed-air from a compressed-air tank is that the feedback of this control to changes in the operation conditions of the engine is rather slow resulting in deviations in the form of considerable “over reactions” when trying to follow operation conditions changing rapidly by regulating the number of revolutions of the turbine. Thus, the charge pressure and turbine speed may in some cases not be regulated as accurate as desired.

EP 2 848 790 A1 discloses a control system for charge control of a combustion engine combining an electrical control of the waste gate valve with use of compressed-air from an outlet of the compressor to control a waste gate valve. The main control is carried out by an electrical motor, but by utilizing compressed-air from the compressor outlet under some conditions the size of the electrical motor may be reduced.

SUMMARY OF THE INVENTION The object of the present invention is to provide a control system and a method of the type defined in the introduction being improved in at least some aspect with respect to such systems and methods already known.

This object is with respect to the control system obtained by providing such a control system with the features listed in the characterizing part of appended claim 1 .

By having a control unit configured to control the control valve to deliver air of a determined pressure by a first use of compressedair from the compressed-air tank and by a second use of compressed-air from the compressor outlet and make a relation of the second use to the first use higher for high loads of the engine than for low engine loads an improved accuracy of a charge control of the combustion engine may be obtained in a cost efficient and reliable way. At low engine loads mostly calling for a high open degree of the waste gate valve compressed-air from the compressed-air tank may be used by the control valve to control the waste gate valve, but when the engine load rises the pressure of the compressed-air from the compressor outlet will also rise making it increasingly able to be used for control of the open degree of the waste gate valve, which will then mostly have to be opened less, although a control of the open degree to achieve an optimum of result with respect to performance, emissions etc. is carried out at each level of the load. The feedback of the control using compressed-air from the compressor outlet with respect to regulation of charge pressure and turbine speed will be excellent and result in a self-regulating control system making it possible to obtain an optimum result with respect to engine performance and creation of emissions. Thus, the waste gate valve may be controlled over the entire operation range of the combustion engine and by a high accuracy at least for loads where this is of greatest importance. “Higher for high loads of said engine than for low engine loads” is in this disclosure to be interpreted broadly and does not mean that the relation has to increase as soon as the load increases, but that the relation is under normal operation conditions of the engine higher for high loads, which are loads of at least 70% of the maximum load, than for low loads, which are loads of less than 30% of the maximum load. But this does not exclude that for e.g. an engine operation point with an engine load of 60% of the maximum load said relation is higher than for another engine operation point with an engine load of 65% of the maximum load.

According to an embodiment of the invention the control unit is configured to control the control valve to make said relation of the second use to the first use increasing with increasing loads of said engine. This means that the participation of compressed-air from the compressor outlet in the control of the waste gate valve will increase with the possibility to use it, so that it may increasingly benefit from the advantages thereof.

According to another embodiment of the invention the control unit is configured to control the control valve to have said first use of compressed-air from the compressed-air tank exceeding the second use of compressed-air from the compressor outlet for loads of said engine at least up to 30% of the maximum load of said engine. For low engine loads for which the pressure of compressed-air from the compressor outlet is low a reliable control of the waste gate valve to open comparatively much when asked for may be reliably ensured by the use of compressed-air from the compressor air tank.

According to another embodiment of the invention the control unit is configured to control said relation by controlling the relation of time intervals of switching in compressed-air from the compressor air tank with respect to compressed-air from the compressor outlet. Said relation may by this type of control easily and accurately be modified to change rapidly for adapting to changing operation conditions of the engine.

According to another embodiment of the invention the control system comprises a further valve arranged in the air flow from the compressed-air tank to the control valve and configured to reduce the pressure of the compressed-air arriving to the control valve from said tank with respect to the pressure of the compressed-air in said tank. A compressed-air tank used by a control system for charge control of a combustion engine has often the task to provide compressed-air to other equipment, especially in a motor vehicle, which require a comparatively high pressure, so that the pressure of the compressed-air in the compressed-air tank is on a level not suitable for a sensitive control of a waste gate valve. Thus, a reduction of the pressure of the compressed-air arriving to the control valve from the tank will result in a more accurate control of the waste gate valve by less expensive parts involved.

According to another embodiment of the invention the compressed-air tank is configured to deliver compressed-air to arrive to the control valve for said first use with a pressure of 2-10 bar, 2-5 bar or 2-4 bar. These are suitable levels of the pressure of compressed-air from the compressed-air tank to be used for proper control of the waste gate valve and will enable to open it fully when needed.

According to another embodiment of the invention the control system comprises a cut-off valve arranged in the air flow from the compressor-air tank to the control valve, and the control unit is configured to control the cut-off valve to be open to provide the control valve with compressed-air from the compressed-air tank or to be closed for preventing compressed-air from the compressedair tank to reach the control valve. The arrangement of such a cut off valve constitutes an option to enable restriction of the control valve to said second use, i.e. use of compressed-air from the compressor outlet, when this is desired.

The object of the present invention is with respect to the method obtained by providing a method according to the appended independent method claim. The advantages of such a method and embodiments thereof defined in dependent claims appear clearly from the above discussion of embodiments of the control system according to the invention.

The invention also relates to a computer program, a computer program product, an electronic control unit and a motor vehicle defined in the corresponding appended claims.

Further advantageous features as well as advantages of the present invention appear from the description following below.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, below follows a specific description of an embodiment of the invention cited as an example.

In the drawings: Fig 1 is a schematic view illustrating a control system for charge control of a combustion engine according to an embodiment of the invention, Fig 2 is a schematic view illustrating the way of operation of the control valve of the control system shown in Fig 1 , Fig 3 is a flow chart illustrating the steps carried out in a method according to an embodiment of the invention, and Fig 4 is a schematic view illustrating an electronic control unit for implementing a method according to the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION Fig 1 illustrates schematically the general structure of a control system for charge control of a combustion engine 1 of a motor vehicle 2 according to an embodiment of the invention comprising a turbo charger 3 with a compressor 4 arranged in an intake pipe 5 to the engine and a turbine 6 in the exhaust pipe 7 from the engine, which is connected to the compressor 4 by a shaft 8 for driving the compressor by the flow of exhaust gases hitting the turbine blades. A charge air cooler 9 is arranged downstream the compressor.

The control system further comprises a waste gate valve 10 installed in the exhaust pipe to form a bypass B of exhaust gas with respect to the turbine 6 in the exhaust pipe. Thus, the open degree of the waste gate valve will decide the influence of the exhaust gas flow in the exhaust pipe upon the turbine and by that upon the operation of the compressor 4. A control valve 11 is configured to control the waste gate valve 10 by delivering air of a pressure determining the open degree of the waste gate valve by influencing an actuator member 12, the position of which will be dependent upon the air pressure delivered thereto and deciding the open degree of the waste gate valve 10.

A compressed-air tank 13, which typically will contain compressedair of a pressure of 7-10 bar and used to deliver compressed-air to different pieces of equipment, such as brakes, of the motor vehicle, is connected to the control valve 1 1 through a further valve 14 configured to reduce the pressure of the compressed-air arriving to the control valve from the tank 13, for instance to be in the order of 3 bar.

The control system also comprises a member 15 diverting compressed-air from an outlet of the compressor 4 to the control valve. Thus, the control valve 11 has two inlets as shown more in detail in Fig 2, one 16 receiving air from the air tank 13 and one 17 receiving air from the member diverting compressed-air from the compressor outlet. A control unit in the form of an electronic control unit 18 is configured to control the control valve, and this control unit may be the same as the electronic control unit controlling other equipment of the motor vehicle. This control unit is configured to control the control valve to alternatively switch in compressed-air from the compressed-air tank 13 and compressedair from the compressor outlet from the member 15 to pass the control valve to create air of a pressure determining the open degree of the waste gate valve by being applied to the actuator member 12. The control unit will do this by considering operation conditions of the combustion engine, such as the level of the load thereof, when determining the relation of air to be taken from the two sources, the compressed-air tank 13 and the outlet of the compressor. The control unit 18 will then preferably control the control valve 1 1 to use compressed-air from the compressor outlet as much as possible for obtaining the open degree of the waste gate valve 10 required for obtaining the performance and emission level asked for.

Fig 3 illustrates a flow chart of a method according to an embodiment of the present invention carried out for a control system for charge control of the type shown in Fig 1 . The method is started with the step S1 of measuring parameters of the existing operation point of the engine, whereupon in a step S2 the engine operation point measured is compared with a table of relations of use of compressed-air from compressed-air tank and compressor outlet for engine operation points. It is then in a step S3 decided which relation is to be used, whereupon in a step S4 the control valve is controlled to switch in compressed-air from the two sources according to this relation.

Computer program code for implementing a method according to the invention is with advantage included in a computer program which can be read into the internal memory of a computer, e.g. the internal memory of an electronic control unit of a motor vehicle. Such a computer program is with advantage provided via a computer program product comprising a data storage medium which can be read by a computer and which has the computer program stored on it. Said data storage medium is for example an optical data storage medium in the form of a CD ROM disc, a DVD disc etc., a magnetic data storage medium in the form of a hard disc etc., or a flash memory or a memory of the ROM, PROM, EPROM or EEPROM type. Fig. 4 illustrates very schematically an electronic control unit 18 comprising an execution means 19, e.g. a central processor unit (CPU), for execution of computer software. The execution means 19 communicates with a memory 20, e.g. of the RAM type, via a data bus 21. The control unit 18 comprises also a non-transitory data storage medium 22, e.g. in the form of a flash memory or a memory of the ROM, PROM, EPROM or EEPROM type. The execution means 19 communicates with the data storage medium 22 via the data bus 21. A computer program comprising computer program code for implementing a method according to the invention, e.g. in accordance with the embodiment illustrated in Fig. 3, is stored on the data storage medium 22.

The invention is of course in no way restricted to the embodiments described above, since many possibilities for modifications thereof are likely to be obvious to one skilled in the art without having to deviate from the scope of invention defined in the appended claims.

The control unit will receive information about the engine load in any conceivable way, directly or indirectly, and it is not necessary that a member measuring this load is present.

The further valve arranged between the compressed-air tank and the control valve may be combined with or replaced by a cut-off valve or both these valves may be omitted.

Claims

1. A control system for charge control of a combustion engine, comprising: • a turbo charger (3) with a compressor (4) in an intake pipe (5) to the engine (1) and a turbine (6) in an exhaust pipe (7) from the engine, • a waste gate valve (10) installed in the exhaust pipe to form a bypass (B) of exhaust gas with respect to the turbine (7) in the exhaust pipe, • a control valve (11) configured to control the waste gate valve (10) by delivering air of a pressure determining the open degree of the waste gate valve, • a compressed-air tank (13) connected to the control valve (11) to deliver compressed-air to the control valve, • a control unit (18) configured to control the control valve (11) and by that the waste gate valve (10), and • a member (15) diverting compressed-air from an outlet of the compressor (4) to the control valve (1 1), said control unit (18) being configured to control the control valve (11) to deliver air of a determined pressure by a first use of compressed-air from the compressed-air tank (13) and by a second use of compressed-air from the compressor outlet and make a relation of the second use to the first use higher for high loads of said engine (1) than for low engine loads, characterized in that the control unit (18) is configured to control the control valve (11) to alternatively switch in compressed-air from the compressed-air tank (13) and compressed-air from the compressor (4) outlet to pass the control valve to create air of a pressure determining the open degree of the waste gate valve (10), and that the control unit (18) is configured to control said relation by controlling the relation of time intervals of switching in compressed-air from the compressed-air tank (13) with respect to compressed-air from the compressor (4) outlet.

2. A control system according to claim 1 , characterized in that the control unit (18) is configured to control the control valve (11) to make said relation of the second use to the first use increasing with increasing loads of said engine.

3. A control system according to any of the preceding claims, characterized in that the control unit (18) is configured to control the control valve (11) to have said first use of compressed-air from the compressed-air tank (13) exceeding the second use of compressed-air from the compressor (4) outlet for loads of said engine at least up to 30% of the maximum load of said engine.

4. A control system according to any of the preceding claims, characterized in that it comprises a further valve (14) arranged in the air flow from the compressed-air tank (13) to the control valve (11) and configured to reduce the pressure of the compressed-air arriving to the control valve from said tank with respect to the pressure of the compressed-air in said tank.

5. A control system according to any of the preceding claims, characterized in that the compressed-air tank (13) is configured to deliver compressed-air to arrive to the control valve (11) for said first use with a pressure of 2-10 bar, preferably 2-5 bar, more preferably 2-4 bar.

6. A control system according to any of the preceding claims, characterized in that it comprises a cut-off valve arranged in the air flow from the compressed-air tank (13) to the control valve (11), and that the control unit (18) is configured to control the cut-off valve to be open to provide the control valve with compressed-air from the compressed-air tank (13) or to be closed for preventing compressed-air from the compressed-air tank to reach the control valve.

7. A method for carrying out a charge control of a combustion engine (1) having a charge control system comprising: a turbo charger (3) with a compressor (4) in an intake pipe (5) to the engine and a turbine (6) in an exhaust pipe (7) from the engine, a waste gate valve (10) installed in the exhaust pipe to form a bypass (B) of exhaust gas with respect to the turbine (6) in the exhaust pipe, a control valve (11) configured to control the waste gate valve (10) by delivering air of a pressure determining the open degree of the waste gate valve, and a compressed-air tank (1 3) connected to the control valve (11) to deliver compressed-air to the control valve, in which the method comprises the steps of • controlling the control valve (11) and by that the waste gate valve (10), • diverting compressed-air from an outlet of the compressor (4) to the control valve (1 1), and • carrying out said controlling of the control valve (11) by controlling it to deliver air of a determined pressure by a first use of compressed-air from the compressed-air tank (13) and by a second use of compressed-air from the compressor (4) outlet while making a relation of the second use to the first use higher for high loads of said engine than for low engine loads, characterized by carrying out said controlling of the control valve (11) by controlling it to alternatively switch in compressed-air from the compressed air tank (13) and compressed-air from the compressor (4) outlet to pass the control valve to create air of a pressure determining the open degree of the waste gate valve (10), and that said relation is controlled by controlling the relation of time intervals of switching in compressed air from the compressor air tank (13) with respect to compressed air from the compressor (4) outlet.

8. A computer program comprising a computer program code for causing a computer to implement a method according to claim 7 when the computer program is executed in the computer.

9. A computer program product comprising a data storage medium which can be read by a computer and on which the program code of a computer program according to claim 8 is stored.

10. An electronic control unit comprising an execution means (19), a memory (20) connected to the execution means and a data storage medium (22) which is connected to the execution means and on which the computer program code of a computer program according to claim 8 is stored.

11. A motor vehicle, especially a wheeled motor vehicle, in particular a heavy wheeled motor vehicle (2), such as a truck or a lorry or a bus, characterized in that it is provided with a control system for charge control of an engine (1) of the motor vehicle according to any of claims 1 -6.