Claims:I claim:
1. A method of operating a fuel injection system (10) for a single cylinder engine comprising:
- operating a mechanically controlled high pressure pump (12) to define the delivery end pressure of said mechanically controlled high pressure pump (12);
- receiving in an electronic control unit (18) engine parameter or fuel pressure information from at least one sensor;
- actuating a solenoid of said common rail injector (14) to start injection based on said received information and said defined delivery end pressure; and
- de-actuating said solenoid of said common rail injector (14) to end injection based on of said received information and said defined delivery end pressure.
2. The method as claimed in claim 1, wherein said at least one sensor may be at least one selected from a group of sensors such as a pressure sensor, an accelerator pedal sensor, an engine speed sensor and the like.
3. The method as claimed in claim 1 and 2, wherein said electronic control unit (18) receives fuel pressure information from a pressure sensor.
4. The method as claimed in claim 1 and 2, wherein said electronic control unit (18) receives information from an accelerator pedal sensor and engine speed sensor and determines the actuating and de-actuating time of said solenoid of said common rail injector (14).
5. The method as claimed in claim 1, wherein said electronic control unit (18) determines the actuating and de-actuating time of said solenoid based on the constant speed operation of the single cylinder engine.
6. A fuel injection system (10) for a single cylinder engine comprising:
- a mechanically controlled high pressure pump (12);
- a common rail injector (14); and
- an electronic control unit (18) adapted to control operation of said common rail injector (14) based on the information received from at least one sensor, said electronic control unit (18) adapted to vary start of injection and end of injection in a manner such that said common rail injector (14) is operated at varying opening pressure and varying closing pressure.
7. A fuel injection system (10) as claimed in claim 6, wherein said at least one sensor may be at least one selected from a group of sensors such as a pressure sensor, an accelerator pedal sensor, an engine speed sensor and the like.
8. A fuel injection system (10) as claimed in claim 6, wherein said pressure sensor (16) is a pressure sensor integrated into said common rail fuel injector (14).
9. A fuel injection system (10) as claimed in claim 6, wherein injector characteristic map is stored in the memory of said electronic control unit (18).
10. A fuel injection system (10) as claimed in claim 6 and 9, wherein said electronic control unit (18) receives information from an accelerator pedal sensor and engine speed sensor and determines the actuating and de-actuating time of said solenoid of said common rail injector (14) based on the characteristic map stored in the memory of said electronic control unit (18).
, Description:Field of the invention
[0001] This disclosure relates to a fuel injection system and a method of operating the fuel injection system.
Background of the invention:
[0002] Common rail fuel injection system known for single cylinder engines may have two configurations in terms of the components that are used in the fuel injection system. A fuel pump is used in the fuel tank to pump fuel from the fuel tank to high pressure pump. The high pressure pump is an electronically controlled pump from the point of view that the high pressure pump is provided with a metering unit which ensures that only metered quantity of fuel is sent to the high pressure pump. The fuel injection system known in the state of the art are able to provide fuel at the delivery end which may be at a constant pressure and the hence it will not be possible to have varying pressure during start of injection and end of injection.

Brief description of the accompanying drawings:
[0003] An embodiment of the disclosure is described with reference to the following accompanying drawings;
[0004] Figure 1 illustrates a fuel injection system in accordance with this disclosure;
[0005] Figure 2 illustrates another embodiment of the fuel injection system in accordance with this disclosure; and
[0006] Figure 3 illustrates a graph wherein fuel pressure is plotted against position of plunger of the fuel pump.
Detailed description of the embodiments:
[0007] Figure 1 illustrates a fuel injection system in accordance with this disclosure. The fuel injection system 10 for a single cylinder engine comprises a mechanically controlled high pressure pump 12, a common rail injector 14 and an electronic control unit 18 adapted to control operation of the common rail injector 14 based on of the information received from at least one sensor. The electronic control unit 18 adapted to vary start of injection and end of injection in a manner such that the common rail injector 14 is operated at varying opening pressure and varying closing pressure.
[0008] In the fuel injection system the at least one sensor which sends the information to the electronic control unit 18 may be at least one selected from a group of sensors such as a pressure sensor, an accelerator pedal sensor, an engine speed sensor and the like.
[0009] For the purposes of easier understanding we consider one embodiment of the fuel injection system wherein the pressure sensor 16 is integrated into the common rail fuel injector 14. The construction of the fuel injection system for a single cylinder engine in accordance with this embodiment can be described as follows. The fuel injection system comprises a fuel tank 20 which stored fuel. Fuel from the fuel tank 20 flows through a filter 22, where any particulate matter that may be present in the fuel is filtered. From the fuel filter 22 the fuel flow to the mechanically controlled high pressure pump 12. The mechanically controlled high pressure pump 12 is driven by a cam. The cam shaft connected to the cam of the mechanically controlled high pressure pump 12 may be driven by the engine. The mechanically controlled high pressure pump 12 does not have any means of metering the fuel that it receives neither is a metering unit provided upstream of the mechanically controlled high pressure pump 12. The mechanically controlled high pressure pump 12 has a plunger with a helix, the helix on the plunger can be displaced in a manner such as to ensure that fuel pressure at the delivery end of the mechanically controlled high pressure pump can be controlled. The displacement of the helix is controlled by a control rod which may be connected to the accelerator pedal. The fuel from the mechanically controlled high pressure pump 12 is then sent direct to a common rail fuel injector 14. Since the fuel injection system 10 is for a single cylinder engine on only one injector is shown and hence a common rail is not required in this fuel injection system 10. However, it is important that there should be some means which would ensure that even for the fuel injection system 10 as disclosed there is a possibility of metering the amount of fuel that is injected into the engine. The common rail fuel injector 14 is a fuel injector which has an connector to which a connector is fitted from an electronic control unit 18. The electronic control unit 18 controls the actuation of the common rail fuel injector 14 by control the solenoid of the common rail fuel injector 14. The common rail fuel injector 14 also has a pressure sensor which is integrated into it. The pressure sensor 16 is adapted to check the pressure of fuel that exist in the fuel injector 14 and this pressure information is communicated to the electronic control unit 18. There also exist a fuel flow path from the common rail injector 14 back to the fuel tank 20 to carry an excess quantity of fuel which may be present in the injector back to the fuel tank 20.
[00010] In accordance with another embodiment of the fuel injection system 10, the fuel injection system comprises a mechanically controlled high pressure pump 12, a common rail fuel injector 14a. However, in this embodiment the pressure sensor is not integrated with the common rail fuel injector 14a or the pressure sensor is not present in the fuel injection system at all. In this embodiment of the fuel injection system, the electronic control unit 18 still controls operation of the common rail fuel injector 14a and injector characteristic map is stored in the memory of said electronic control unit 18. The electronic control unit 18 receives information from an accelerator pedal sensor 24 and an engine speed sensor 26, as seen in figure 2. Based on the information received from the accelerator pedal sensor and the engine speed sensor, the pressure of fuel in the fuel injection system 10 is determined based on an injector characteristic map that is stored in the electronic control unit. The electronic control unit 18 determines the actuating and de-actuating time of said solenoid of said common rail injector 14 based on the characteristic map stored in the memory of electronic control unit 18 and the start and end of injection can be decided and varied.
[00011] In accordance with another embodiment the fuel injection system 10 may be used in a constant speed application of the single cylinder engine such a genset or the like. In such a case the mechanically controlled high pressure pump 12 delivery characteristics are already known and an injector characteristic map with reference to the delivery characteristics is stored in the electronic control unit 18. Based on the constant speed characteristics of the high pressure pump 12, the electronic control unit 18 determines the actuating and de-actuating time of said solenoid of said common rail injector 14 based on the characteristic map stored in the memory of electronic control unit 18 and the start and end of injection can be decided and varied.
[00012] A method of operating the fuel injection system 10 for a single cylinder engine is also disclosed. The method comprises the following steps operating the mechanically controlled high pressure pump 12 to define the delivery end pressure of the mechanically controlled high pressure pump 12; receiving in an electronic control unit 18 pressure information from at least one sensor; actuating a solenoid of the common rail injector 14 to start injection based on the received information and defined delivery end pressure and de-actuating the solenoid of the common rail injector 14 to end injection based on the received information and the defined delivery end pressure.
[00013] With reference to the embodiments of the fuel injection system mentioned earlier, the at least one sensor may be at least one selected from a group of sensors such as a pressure sensor, an accelerator pedal sensor, an engine speed sensor and the like. Where the embodiment has a pressure sensor, in the method of operating the fuel injection system 10 the electronic control unit 18 receives fuel pressure information from a pressure sensor. Where the embodiment of the fuel injection system 10 does not have a pressure sensor, but instead the electronic control unit receives information from an accelerator pedal sensor and an engine speed sensor, the electronic control unit 18 determines the actuating and de-actuating time of said solenoid of the common rail injector 14. Wherein the embodiment of the fuel injection system is operated in a constant speed operation, the electronic control unit 18 determines the actuating and de-actuating time of the solenoid based on the constant speed operation of the single cylinder engine.
[00014] The method of operation of the fuel injection system 10 can further be explained as follows with reference to figure 3, however for this explanation we consider only the first embodiment of the fuel injection system. As mentioned earlier figure 3 illustrates a graph wherein fuel pressure is plotted against position of plunger of the fuel pump and is representative of the pressure curves for pump end pressure and injection end pressure. In figure 3, the points marked as 1 and 2 are possible points wherein the solenoid is actuated to open the injector in order to inject fuel and points marked as 3 and 4 are possible wherein the solenoid is de-actuated to close the injector so that no fuel is injected. The mechanically controlled fuel high pressure pump 12 is operated in a manner such that the helix on the plunger of the pump is oriented such that the delivery end pressure of the mechanically controlled high pressure pump 12 is defined. The pressure at the delivery end of the mechanically controlled high pressure pump 12 is the same as the pressure of fuel which is present in the common rail fuel injector 14. The pressure sensor 16 senses the pressure of fuel and this information is communicated to the electronic control unit 18 and hence the pressure of fuel during injection is now available in the electronic control unit 18. The electronic control unit 18 then decides based on the pressure sensor 16 information when the solenoid of the common rail fuel injector should be actuated such as to start the injection of fuel. The common rail fuel injector 14 along with the mechanically controlled high pressure pump 12 is able to define at fuel pressure at which the start of injection should be done. This is indicated in figure 3 by points 1 and 2, wherein point 1 represents a point where the start of fuel injection can happen at a fuel pressure of approximately 600bar when the engine cylinder is approximately 10 degree before TDC. Similarly point 2 represents a point where the start of fuel injection can happen at a fuel pressure of approximately 800bar when the engine cylinder is approximately between 0 and 5 degrees before TDC. Thus the it is possible ensure phasing of the start of fuel injection over different speed range of the engine, also that camshaft of the mechanically controlled high pressure fuel pump 12 has to be operated to ensure that enough fuel pressure is available for early opening or start of fuel injection. This is particularly important for the noise sensitive regions of the pressure curve wherein sometimes enough fuel pressure for certain opening timing may not be otherwise available. Further since the injector in the fuel injection system 10 is a common rail fuel injector 14, wherein it is possible to de-actuate the solenoid to ensure the end of injection, it is possible that the end of injection can happen early or late. An example of early end of the injection is represented by point 3 wherein there is a possibility that the fuel pressure is enough for injection, however, the electronic control unit 18 de-actuates the solenoid and the end of injection happens approximately 10-12 degrees after the engine cylinder has passed TDC. An example of late end of injection is represented by point 4, wherein the electronic control unit 18 de-actuates the solenoid to end the injection event approximately 12-15 degrees after the engine cylinder has passed TDC. However, during the early end of injection as mentioned the fuel pressure may still be enough for injection, this fuel in the mechanically controlled high pressure pump 12 can be stopped from pressurizing further by controlling the movement of the helix in the plunger of the fuel injection pump 12.
[00015] Thus the fuel injection system 10 and the method of operating the fuel injection system as disclosed above provides the possibility that the point of opening and closing the injector can be chosen to a certain extent. For example at higher injection end pressures, opening the injector slightly later is possible. This can be an advantage in full load performance for the single cylinder engine. Due to the additional degree of freedom by actuating the injector, various injection timings and injection pressures can be calibrated. Additionally the integrated pressure sensor gives an electrical control functionality as well as safety functionality which is important functionality of single cylinder engine applications. Even in the case that the pressure sensor fails the common rail fuel injector 14 has a ball type throttle to ensure that the pressure in the system will not increase beyond a safe limit for example say 2000bar. This not only avoids breakage of high pressure parts but also high pressure leakage.

[00016] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention in terms of the pressure values and degree of cylinder movement nearing TDC as mentioned in figure 2. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.