ARRANGEMENTAND METHOD FOR CONTROLLING THE BURN IN A

COMBUSTION ENGINE

The present invention relates to an arrangement and a method for a combustion engine according to the preambles of claims 1 and 11.

A known practice is to control combustion processes in certain types of combustion engine, e.g. HCCI engines, on the basis of stored information from one or more previous combustion processes. Control may be exercised individually for each cylinder of the combustion engine, but such control is subject to the limitation that if the injection of fuel is not optimum during a combustion process an adjustment of the fuel injection can only be effected during a subsequent combustion process.

One way of reducing the amounts of particles in the exhaust gases of diesel engines is to inject the fuel at a very high pressure into the cylinders of the diesel engine. A so- called "common rail" system may be used for the purpose. A common rail system comprises a high-pressure pump which pumps fuel at a very high pressure to an accumulator tank (the "common rail"). The pressure in the accumulator tank during operation may be within the range 250 to 2000 bar and, in the future, probably still higher. The fuel in the accumulator tank is intended to be distributed to all the cylinders of the combustion engine. The fuel from the accumulator tank is injected into the respective cylinders by electronic injectors which can open and close very quickly. An electrical control unit calculates substantially continuously the amount of fuel to be supplied to the respective cylinders on the basis of information from various engine parameters such as the load and speed of the engine. The electrical control unit also receives information from a pressure sensor concerning the prevailing pressure in the accumulator tank. On the basis of knowing about the pressure in the accumulator tank, the electrical control unit controls the opening times of the electronic injectors so that the calculated amount of fuel is supplied to the respective cylinders.

Another way of injecting fuel at a high pressure into the cylinders of the combustion engine is to use so-called unit injectors. A unit injector comprises both an injection means and an injection pump. A unit injector is installed close to each of the cylinders of the combustion engine. The unit injectors comprise a solenoid valve controlled by an electrical control unit. On the basis of knowing about the fuel pressure which the pumps of the unit injectors generate, the electrical control unit emits control signals to the solenoid valves for a desired amount of fuel to be injected into the respective cylinders from the respective unit injectors.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an arrangement and a method for a combustion engine whereby the combustion processes can be controlled with very great precision.

This object is achieved with the arrangement of the kind mentioned in the introduction which is characterised by the features indicated in the characterising part of claim 1. The combustion process inevitably begins with a certain delay after the injection of the fuel has begun. The combustion process correspondingly continues for a short period after the injection of the fuel has ceased. The control according to the invention of the fuel injection can therefore only be effected during the time when both an injection process and a combustion process are ongoing. If the information received indicates that an ongoing combustion process is not optimum in a certain respect, the control unit has the possibility of controlling the continued injection of fuel in such a way that any shortcoming is corrected during the remainder of the combustion process. Each combustion process in a combustion engine can therefore be effected in a substantially optimum manner even if shortcomings occur at any stage of the combustion process.

According to a preferred embodiment of the present invention, the control unit is adapted to substantially continuously receiving information concerning the value of said parameter from said sensor and to substantially continuously controlling the injection of fuel by the injection means during the remainder of the ongoing

combustion process on the basis of parameter values received. The injection of the fuel can therefore be controlled with feedback during the remainder of the combustion process. Very accurate control of the combustion pattern is thus made possible. The control unit may be adapted to comparing at least one parameter value received from said sensor with an expected parameter value and, in the event of an undesirable difference between said parameter values, to controlling the injection of fuel by the injection means during the remainder of the combustion process with the object of compensating for that difference. Such expected parameter values may be stored in the control unit or be calculated by the control unit for each comparison.

According to another preferred embodiment of the present invention, said sensor is adapted to detecting a parameter value related to the pressure of the fuel injected into the combustion space. On the basis of information concerning a number of engine parameters, e.g. the load and speed of the engine, the control unit calculates usually in advance the amount of fuel which needs to be supplied during a combustion process. On the basis of the expected injection pressure of the fuel during the injection process, the control unit estimates the amount of time for which the injection means needs to be activated for the desired amount of fuel to be supplied. In this case the control unit thus receives information concerning the actual injection pressure of the fuel during an ongoing combustion process. If that pressure value differs from the expected pressure value, an incorrect amount of fuel will be injected into and burnt in the combustion space. On the basis of this information, the control unit can adjust the continuing injection so that a correct amount of fuel is supplied and burnt during the ongoing combustion process.

According to another preferred embodiment of the present invention, said sensor is adapted to detecting a parameter value which arises from the ongoing combustion process in the combustion space. By detecting one or more parameters during an ongoing combustion process in the combustion space it is possible to decide whether the process is effected in a desired manner. To this end, such a sensor is with advantage situated within or in the immediate vicinity of the combustion space. Such a sensor may be a pressure sensor which detects the pressure prevailing in the

combustion space during a combustion process. According to another alternative, the sensor is a sound sensor which detects the noise which occurs during the combustion process. If an expected pressure or sound does not occur during a combustion process, the injection of the fuel may be adjusted so that the pressure or noise during the remainder of the ongoing combustion process is guided towards desired values.

According to another alternative, the sensor is adapted to detecting an ion stream in the combustion space. When fuel and air are burnt in the combustion space, free electrons and charged ions are formed in the combustion gas. By supplying an electric voltage at a suitable point in the combustion space it is possible to measure the ion stream and hence the concentration of charged particles. Information about the ion stream can be used to assess the ongoing combustion process. According to a further alternative, the sensor is an optical sensor which detects the light generated during the combustion process, which also provides a picture of the ongoing combustion process. A laser beam may also be passed through the combustion space to detect the presence of various substances in the exhaust gases, since each molecule in the combustion space absorbs laser light at a certain wavelength.

According to another preferred embodiment of the present invention, the control unit is adapted to controlling the injection of fuel during the remainder of the ongoing combustion process by varying the length of the period of time during which the injection means injects fuel. If, for example, the actual fuel pressure is lower than the expected fuel pressure or drops more than expected during the injection process, it may be necessary for the injection time to be lengthened to enable the desired amount of fuel to be supplied and burnt during the ongoing combustion process. In a corresponding manner, an expected injection time may be reduced if the actual fuel pressure is higher than an expected fuel pressure value. Alternatively, the control unit may be adapted to controlling the injection of fuel during the remainder of the ongoing combustion process so that the injection of the fuel is effected at least partly intermittently. The injection process may thus be interrupted for a short period and thereafter be resumed.

According to another preferred embodiment of the present invention, the injection means is a piezoelectric injector. A piezoelectric injector has a movable element made of ceramic (piezo) which is widened by electricity. The movable element acts upon one or more fuel injection apertures. Such an injector also makes it possible to adjust the amount of fuel injected per unit time during an ongoing injection process. The amount of injection can thus be varied as desired during the injection time. A piezoelectric injector is also quick and exact and therefore very suitable for use in this context. With advantage, the control unit comprises an FPGA (field programmable gate array) circuit, which is an integrated circuit with hardware which can be reprogrammed directly from a static memory (RAM, ROM or flash memory) at the start of the circuit and be altered to have a different function at each start. This means that necessary calculations and evaluations can be done at a very high speed, which is a prerequisite for the possibility of substantially continuous feedback and control of fuel injection during an ongoing combustion process.

The object of the invention is also achieved with the method of the kind mentioned in the introduction which is characterised by the features indicated in the characterising part of claim 11.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below by way of examples with reference to the attached drawings, in which:

Fig. 1 depicts an arrangement for a combustion engine according to a first embodiment of the invention, Fig. 2 depicts an arrangement for a combustion engine according to a second embodiment of the invention and

Fig. 3 depicts a method for a combustion engine according to an embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 depicts part of a fuel injection system for a combustion engine which may be a diesel engine. The fuel injection system is with advantage fitted in a heavy vehicle. The fuel injection system has a so-called common rail system. The fuel system comprises a fuel line 1 for supplying fuel from an undepicted fuel tank to the respective cylinders of the combustion engine. One of the combustion engine's cylinders 2 is depicted in Fig. 1. A high-pressure pump 3 is arranged in the fuel line 1 to pressurise the fuel so that it is fed at a high pressure into an accumulator tank 4 which takes the form of a so-called common rail. Fuel lines Ia extend between the accumulator tank 4 and the respective cylinders 2 of the combustion engine. Each fuel line Ia leads to an injection means 5 for injection of fuel into a cylinder 2. When the injection means 5 is placed in an open position, it injects fuel from the accumulator tank 4 at a high pressure into a combustion space 6 of the cylinder 2. The injection means 5 is provided with a plurality of apertures for injecting the fuel in the form of a plurality of jets into the combustion space 6. The injection means 5 is with advantage a piezoelectric injector. Very rapid and exact injection of the fuel can be effected with a piezoelectric injector. The injection apertures of a piezoelectric injector are also adjustable, making it possible to vary the amount of fuel injected during an injection process. The combustion space 6 is in a conventional manner bounded downwards by a movable piston 7. The piston 7 is connected to a crankshaft 8 via a connecting rod 9. The movements of the piston 7 in the cylinder 2 are converted to rotary motion by the crankshaft 8. An inlet line 10 is connected to the combustion space 6 via an aperture 11 to make it possible to supply air to the combustion space 6. The air may possibly contain recirculating exhaust gases. The air is with advantage pressurised and cooled before it is led into the combustion space 6. An inlet valve 12 is arranged in the aperture 11 to control the supply of air to the combustion space 6.

An electric control unit 9 is adapted to controlling the operation of the high-pressure pump 3 and the injection means 5 so that an optimum amount of fuel can be injected at desired times into the combustion space 6. A pressure sensor 4a is fitted in the

accumulator tank 4 to detect the pressure prevailing in the accumulator tank 4 and to substantially continuously send signals to the control unit 9 with information about the fuel pressure detected. The control unit 9 comprises an FPGA circuit 9a, which is a programmable circuit enabling very rapid processing of data and control of the injection means 5. An exhaust line 13 is intended to lead the exhaust gases away from the combustion processes in the combustion space 6. The release of exhaust gases from the combustion space 6 is regulated by an exhaust valve 14. The control unit 9 is also adapted to controlling the inlet valve 12 and the exhaust valve 14. A sensor 15, here exemplified as a pressure sensor 15, is arranged in the combustion space 6 to detect the pressure prevailing in the combustion space 6 during an ongoing combustion process. The sensor 15 may alternatively be a sound sensor which detects the noise generated during an ongoing combustion process, a sensor which detects an ion stream in the combustion space 6 or an optical sensor which detects the light generated during an ongoing combustion process. The pressure sensor 15 is adapted to substantially continuously sending signals to the control unit 9 with information about the pressure detected in the combustion space 6.

During operation of the combustion engine, the control unit 9 substantially continuously receives control signals concerning engine parameters, e.g. the load and speed of the engine. On the basis of that information, the control unit 9 calculates the amount of fuel which needs to be supplied to the cylinders 2 of the combustion engine. The control unit 9 receives at the same time information concerning the instantaneous pressure in the accumulator tank 4 from the pressure sensor 4a. From knowing the desired amount of fuel and the prevailing pressure in the accumulator tank 4, the control unit 9 can determine the amount of time for which the injection means 5 needs to be in an open position for the desired amount of fuel to be supplied to the combustion space 6. When the piston 7 moves downwards in the cylinder 2, the inlet valve 12 opens so that air and any recirculating exhaust gases from the inlet line 10 are drawn into the expanding combustion space 6 in an amount which is controlled by the control unit 9. When the piston 7 turns at a lower extreme position, the control unit 9 closes the inlet valve 12. The subsequent upward movement of the piston 7 causes compression of the air and exhaust gases in the combustion space 6. The air and

exhaust gases in the combustion space 6 thereby undergo a temperature rise in proportion to the degree of compression. When the piston 7 approaches an upper extreme position, the control unit 9 places the injection means 5 in an open position so that fuel begins to be injected at a high pressure into the combustion space 6. The fuel ignites and burns during a combustion process in the combustion space 6.

During an ongoing combustion process, the control unit 9 substantially continuously receives information from the pressure sensor 4a concerning the fuel pressure prevailing in the accumulator tank 4. The control unit 9 compares the prevailing fuel pressure with an expected pressure value. If there is a difference, the control unit 9 controls the injection means 5 in such a way that said difference is corrected during the remainder of the combustion process. The control unit 9 may accordingly control the injection process in such a way that the injection time is lengthened or shortened relative to a previously expected injection time. The control unit 9 may control the injection process in such a way that the amount of fuel injected varies during the injection time. In that case the control unit 9 may control the injection process so that fuel is injected intermittently into the combustion space 6. During the ongoing injection process, the control unit 9 also substantially continuously receives information from the pressure sensor 15 concerning the pressure prevailing in the combustion space 6. The control unit 9 compares the pressure prevailing in the combustion space 6 with an expected pressure value. If there is an undesirable difference, the control unit 9 controls the injection means 5 in such a way that said difference is corrected during the remainder of the injection process in at least one of the ways indicated above. Such substantially continuous feedback control of the injection of fuel during an ongoing combustion process makes it possible to achieve very exact control of the fuel injection. The performance and fuel consumption of the combustion engine can thus be optimised with very good accuracy. The discharge of particles and emissions from the combustion engine can be minimised or adjusted with very good accuracy to prevailing legislation. The pressure rise which occurs as a result of the combustion process in the combustion space 6 causes the piston 7 to be pushed downwards. When the piston 7 has passed the lower extreme position, the control unit 9 opens the exhaust valve 14. The subsequent upward movement of the

piston 7 pushes the exhaust gases formed during the combustion process out to the exhaust line 13.

Fig. 2 depicts part of an alternative fuel injection system for a combustion engine. The components of this injection system have been given the same reference notations as corresponding components of the fuel injection system depicted in Fig. 1. In this case, unit injectors 5' are used for injecting fuel at a high pressure into the respective cylinders of the combustion engine. One cylinder 2 is depicted in Fig. 2. A unit injector 5' comprises a combined high-pressure pump and an injection means. A pressure sensor 5a is here applied close to the unit injector 5' to detect the fuel pressure which the pump of the unit injector generates during an injection process. A sensor 15' is here arranged partly within the combustion space 6 of the cylinder 2 to measure the ion stream generated in the combustion space 6 during an ongoing combustion process.

During operation of the combustion engine, fuel is supplied by an undepicted feedpump at a relatively low pressure to the unit injector 5' via a line 1. The control unit 9 calculates the amount of fuel which needs to be supplied to the cylinders 2 of the combustion engine. On the basis of knowing a desired amount of fuel and an expected pressure which the unit injector 5' can generate, the control unit 9 determines the amount of time for which the injection means of the unit injector 5' needs to be in an open position for the desired amount of fuel to be supplied to the combustion space 6. During an ongoing injection process, the control unit 9 substantially continuously receives information from the pressure sensor 5a concerning the prevailing injection pressure. The control unit 9 compares the prevailing injection pressure with an expected pressure value. If there is a difference, the control unit 9 controls the unit injector 5' in such a way that said difference is corrected during the remainder of the injection process. During the ongoing injection process, the control unit 9 also substantially continuously receives information from the sensor 15' concerning the ion stream detected in the combustion space 6. The control unit 9 compares the ion stream detected in the combustion space 6 with an expected ion stream. If there is an undesirable difference, the control unit 9 controls the injection means of the unit

injector 5' so that said difference is corrected during the remainder of the injection process. The result is substantially continuous feedback control of the injection of fuel during an ongoing injection process and the consequent possibility of very exact control of the fuel injection.

Fig. 3 depicts schematically a method for a combustion engine which comprises the components depicted in Fig. 1 or 2. The combustion engine thus comprises a combustion space 6, an injection means 5, 5' adapted to injecting fuel into the combustion space 6 when a combustion process is to be effected, a control unit 9 adapted to controlling the injection means 5, 5' and a sensor 4a, 5a, 15, 15' adapted to detecting a parameter p which has a value related to the combustion processes in the combustion space 6. The method starts at step 16. The control unit 9 here receives information from a sensor 4a, 5a, 15, 15' concerning a detected parameter value p related to an ongoing combustion process in the combustion space 6. At step 17, the control unit 9 compares the parameter value p received from said sensor 4a, 5a, 15, 15' with an expected parameter value p _n . If the parameter value p received corresponds to the expected parameter value p _n , the process starts again at step 16. The injection of the fuel then continues in a predetermined manner. If the parameter value p received does not correspond to the expected parameter value p _n , the process moves on to step 18, where the control unit 9 decides whether the difference is acceptable or not. In certain cases the difference may be acceptable because of being so small that it is better to postpone making an adjustment of the fuel injection. In other cases the parameter p may have a value which indicates a lower content of, for example, particles and emissions in the exhaust gases than is indicated at the expected parameter value p _n . If this difference is acceptable, the process starts again at step 16. If there is an undesirable difference, the control unit decides, at step 19, how the injection of the fuel should be altered with a view to compensating for the difference during the remainder of the combustion process. The injection of the fuel may accordingly be lengthened or shortened relative to a predetermined value. Alternatively or in combination, the injection amount per unit time may be corrected or the injection of the fuel may be effected intermittently. After the adjustment of the fuel injection, the process starts again at step 16.

The process indicated above proceeds with advantage substantially continuously during an ongoing combustion process. The result is continuous monitoring and control so that the actual combustion process will correspond with very good accuracy to an optimum combustion process. With the sensors 4a, 5a, 15, 15' exemplified above, said parameter p may be the pressure at which the fuel is injected into the combustion space, the pressure prevailing in the combustion space, the ion stream in the combustion space, the light from the combustion process etc.

The invention is in no way limited to the embodiment described but may be varied freely within the scopes of the claims. In the embodiments depicted in Figs. 1 and 2, two sensors are used for detecting various parameters during an injection process, but it may be sufficient to detect one such parameter. More than two parameters may of course also be detected in order to control a residual combustion process. In the embodiment examples, the combustion engine is a diesel engine but may also be other types of combustion engine, such as variants of Otto engines and HCCI engines.