Claims:We claim:
1. A method for operating a fuel injection system (1) comprising a fuel injector (10), and a pressure sensor (20) integrated with the fuel injector (10), and an engine control unit connected to the pressure sensor (20) and to the fuel injector (10), said method comprising:
determining a first time by the engine control unit that is indicative of a start of energizing in the fuel injector (10) based on information received by the engine control unit from the pressure sensor (20);
determining a second time by the engine control unit that is indicative of a start of injection in the fuel injector (10) based on information received by the engine control unit from the pressure sensor (20);
determining a difference between the second time and the first time by the engine control unit;
comparing the difference between the second time and the first time with a threshold value by the engine control unit; and
activating the fuel injector (10) by supplying current to the fuel injector (10) by the engine control unit based on the comparison.

2. A method for operating a fuel injection system (1) in accordance with Claim 1 further comprising:
determining a third time by the engine control unit that is indicative of an end of injection in the fuel injector (10);
determining a difference between the third time and the first time by the engine control unit;
comparing the difference between the third time and the first time with a threshold value by the engine control unit; and
deactivating the fuel injector (10) by deactivating current to the fuel injector (10) by the engine control unit based on the comparison.
, Description:Field of the invention:
[0001] This disclosure relates to a method of operating a fuel injection system.
Background of the invention:
[0002] U.S. Patent Application Number US20120031376 discloses a fuel injection system. The fuel injection system comprises a high pressure fuel pump and at least two fuel injectors. The fuel injection system has a high-pressure area, which in operation for at least some of the time contains fuel under high injection pressure. The fuel injection system also has a low-pressure area, which in operation contains no fuel and/or is connected to an outlet. Therefore, a high fuel pressure does not build up in the low-pressure area, and a lower pressure prevails than in the high-pressure area. A pressure sensor is located in the low-pressure area and a transmission means is arranged so that for at least some of the time, it exerts a force which corresponds to the pressure of the fuel in the high-pressure area on the sensor. The force exerted on the sensor by the transmission means is proportional to the pressure in the high-pressure area. Since the pressure sensor is located in the low-pressure area of the fuel injector, the sensor does not need to have a special high pressure seal.

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; and
[0005] Figure 2 illustrates a graphical representation of the pressure induced in a pressure sensor that is located in a fuel injector and current induced in the fuel injector of the fuel injection system.

Detailed description of the embodiments:
[0006] Figure 1 illustrates a method for operating a fuel injection system 1 in accordance with this disclosure. The fuel injection system 1 comprises a fuel injector 10, and a pressure sensor 20 integrated with the fuel injector 10. An engine control unit is connected to the pressure sensor 20 and to the fuel injector 10. The method comprises determining a first time by the engine control unit that is indicative of a start of energizing in the fuel injector 10 based on information received by the engine control unit from the pressure sensor 20. The method comprises determining a second time by the engine control unit that is indicative of a start of injection in the fuel injector 10 based on information received by the engine control unit from the pressure sensor 20, determining a difference between the second time and the first time by the engine control unit. The method further comprises comparing the difference between the second time and the first time with a threshold value by the engine control unit, and activating the fuel injector 10 by supplying current to the fuel injector 10 by the engine control unit based on the comparison.

[0007] The method further comprises the following steps: determining a third time by the engine control unit that is indicative of an end of injection in the fuel injector 10; determining a difference between the third time and the first time by the engine control unit; comparing the difference between the third time and the first time with a threshold value by the engine control unit; and deactivating the fuel injector 10 by deactivating current to the fuel injector 10 by the engine control unit based on the comparison.

[0008] The fuel injection system 1 comprises a high pressure fuel pump 32 and a fuel injector 10. The fuel injector 10 is in fluid communication with an outlet 36 of the high pressure fuel pump 32. The fuel injection system 1 includes a pressure sensor 20 that is located in the fuel injector 10 in a manner such that the pressure sensor 20 is adapted to measure pressure of fuel in the fuel injector 10.

[0009] The fuel injector 10 comprises a recess 18 and the pressure sensor 20 that is located in the recess 18 in a manner such that a chamber 22 is formed in the recess 18 between an end wall 24 of the recess 18 and the pressure sensor 20. The fuel injector 10 comprises a flow path extending from the fuel flow path of the fuel injector 10 to the recess 18 such that fuel from the fuel flow path flows into the chamber 22. The fuel injector 10 comprises an inlet 42 and an outlet 38, wherein the inlet 42 is in fluid communication with outlet 36 of the high pressure fuel pump 32. The pressure sensor 20 is located in the recess 18 of the fuel injector 10 in a manner such that time taken to measure pressure by the pressure sensor 20 is lesser than the time between injection events in the fuel injector 10.

[00010] For better understanding of this disclosure, we consider an embodiment of the fuel injection system 1 where the fuel injection system 1 has a single fuel injector 10. Thus for the fuel injection system 1, the fuel injector is marked as 10 in Figure 1. The fuel injection system 1 comprises a high pressure fuel pump 32 and a single fuel injector 10. The fuel injector 10 is in fluid communication with the outlet 36 of the high pressure fuel pump 32. The fuel injection system 1 is characterized such that a pressure sensor 20 is located in the fuel injector 10 in a manner such that the pressure sensor 20 is adapted to measure the pressure of fuel throughout the fuel injection system 1. The pressure sensor 20 is adapted to transmit the pressure of fuel throughout the fuel injection system 1 to an engine control unit.

[00011] The detailed layout of the fuel injection system 1 and the components of the fuel injection system 1 can be explained as follows. The high pressure fuel pump 32 receives fuel from a fuel tank through a low pressure circuit comprising a feed pump and a filter. A person skilled in the art will already be aware of the components involved in the low pressure circuit of the fuel injection system 1. For the purposes of this disclosure, we will focus on the fuel injector 10 and the fuel injection system 1 downstream of the high pressure fuel pump 32. The high pressure fuel pump 32 has an outlet 36 which is connected to the fuel injector 10. The outlet 36 of the high pressure fuel pump 32 is in fluid communication with the inlet 42 of the fuel injector 10. The fuel from the inlet 42 flows into the fuel flow path inside the fuel injector 10.
[00012] The fuel injector 10 comprises a recess 18 and the pressure sensor 20 located in the recess 18 in a manner such that a chamber 22 is formed in the recess 18 between an end wall 24 of the recess 18 and the pressure sensor 20. The fuel injector 10 comprises a flow path extending from the fuel flow path of the fuel injector 10 to the recess 18 such that fuel from the fuel flow path flows into the chamber 22. The fuel injector 10 comprises an inlet 42 and an outlet 38. The inlet 42 is in fluid communication with outlet 36 of the high pressure fuel pump 32. The pressure sensor 20 is located in the recess 18 of the fuel injector 10 in a manner such that the time taken to measure pressure by the pressure sensor 20 is lesser than the time between two injection events of the fuel injector 10. The pressure sensor 20 is located in the recess 18 using internal threads in the recess 18 and mating threads provided on the pressure sensor 20. Upon tightening, the threaded joint between threads on the recess 18 and the pressure sensor 20 produces axial force needed for sealing the high pressure interface between the fuel injector 10 and the pressure sensor 20. The pressure sensor 20 is fitted on the fuel injector 10 along an axis which is perpendicular or inclined to the injector main axis to suit engine/vehicle packaging. An electrical interface of the pressure sensor 20 is used for transmitting the pressure signal to an electronic control unit. The drive current for the injector actuation is received through the electrical interface.

[00013] The working of the fuel injection system 1 and the fuel injector 10 is described in detail in the description below. The fuel which is pressurized in the high pressure fuel pump 32 flows from the outlet 36 towards the inlet 42 of the fuel injector 10. As mentioned earlier, the fuel from the inlet 42 flows into the fuel flow path inside the fuel injector 10 and at least a part of the fuel flows out of the outlet 38 of the fuel injector 10. When the fuel from the fuel flow path enters the flow path, it enters the chamber 22. When the fuel is collected in the chamber 22, it exerts pressure on the pressure sensor 20. The pressure exerted on the components of the pressure sensor 20 is used to provide a signal to an electronic control unit of the fuel injection system 1. The electronic control unit thus receives fuel pressure information from the pressure sensor 20.

[00014] During the working of the fuel injection system 1, the pressure sensor 20 provided in the fuel injector 10 which is able to provide fuel pressure information of the entire fuel injection system 1. When the fuel enters the fuel injector 10, the pressure build up in the fuel injection system 1 is sensed by the pressure sensor 20 provided in the fuel injector 10. When an injection event occurs say in the fuel injector 10, there may be a reduction in the fuel pressure in the overall fuel injection system 1. The pressure sensor 20 is adapted to measure pressure of the fuel throughout the fuel injection system 1 and further control the fuel supplied to the high pressure fuel pump 32 of the fuel injection system 1. The measurement of the fuel pressure using the pressure sensor 20 further allows overall fuel injection system 1 pressure control as fuel pressure information can be used to meter the fuel in the fuel injection system 1.

[00015] Figure 2 illustrates a graphical representation of the pressure induced in the pressure sensor 20 that is located in the fuel injector 10 and current induced in the fuel injector 10. The first plot is an illustration of time vs. current in the fuel injector 10. Specifically, the point at which the current is applied to the fuel injector 10 is depicted as point A on the graph. The point at which the current is deactivated from the fuel injector 10 is depicted as point B on the graph. The second plot is an illustration of pressure vs. time as determined by the pressure sensor 20 in the fuel injector 10. Point C or the first time depicts the start of energizing as determined by the pressure sensor 20 when pressure variations begin to appear in the fuel injector 10. Point D or the second time depicts the start of fuel injection in the fuel injector 10. From point D or the second time, the pressure detected by the pressure sensor 20 decreases rapidly because of fuel injection from an outlet of the fuel injector 10. Point E or a third time depicts the lowest point of pressure that is detected by the pressure sensor 20. Since the pressure detected by the pressure sensor 20 does not vary significantly beyond point E or third time, therefore point E or third time may be considered as the end of fuel injection in the fuel injector 10.

[00016] The difference between the second time or point D, defined as start of fuel injection and the first time or point C, defined as start of injector energizing is received by the engine control unit from the pressure sensor 20 to determine the point at which injection begins in the fuel injector 10. Similarly, the difference between a third time or point E, defined as the end of fuel injection and the first time or point C defined as start of injector energizing is received by the engine control unit from the pressure sensor 20 to determine the point at which the injection ends in the fuel injector 10. Over a period of time, due to gradual erosion of the fuel injector 10, the difference between the start of fuel injection (point D or the second time), and the start of injector energizing (point C or the first time) varies. Moreover, the difference between the end of fuel injection (point E or a third time), and the start of injector energizing (the first time or point C) also varies. Based on the variation of the start of fuel injection (the second time or point D) and the start of injector energizing (the first time or point C), the time at which the injector 10 may be supplied with current is determined based on a comparison with a threshold value by the engine control unit. Similarly, based on the end of fuel injection (the third time or point E) and the start of injector energizing (the first time or point C), the time at which the injector 10 may be deactivated by ceasing the supply of current is determined based on a comparison with a threshold value by the engine control unit. Therefore, it is possible to precisely control the start of fuel injection and the end of fuel injection of the fuel injector 10 over a period of time when the fuel injector 10 gradually wears out over a period of time.

[00017] By using a fuel injector 10 according to the invention having an integral pressure sensor 20, it is possible to dispense directly from the high pressure pump 32. The fuel injection system 1 as disclosed can be designed with few components and is therefore inexpensive. Since the pressure sensor 20 is located in the fuel injector 10 itself, the pressure can easily be measured, even in systems that do not have a central pressure accumulator. It is therefore possible to use simple and inexpensive sensors.

[00018] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. 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.