CLIAMS:We claim:
1. A fuel metering unit (10) in a fuel injection system (12), said fuel metering unit (10) adapted to receive fuel from a feed pump (14) and supply fuel to a high pressure pump (16), said fuel metering unit (10) comprising:
an inlet (18) adapted to receive fuel from said feed pump (14);
an outlet (20) adapted to supply fuel to said high pressure pump (16); and
a plunger (22);
characterized in that
said plunger (22) having a flow passage (24) such that on detection of fuel metering unit error said fuel metering unit (10) supplies fuel to said high pressure pump (16) at a constant flow rate though said outlet (20).
2. The fuel metering unit (10) as claimed in claim 1, wherein said constant flow rate of fuel supplied by the fuel metering unit (10) is less than the maximum flow rate of said fuel metering unit (10) on detection of said fuel metering unit error.
3. The fuel metering unit (10) as claimed in claim 1, wherein on detection of fuel metering unit error the fuel metering unit (10) is operated in a limited but controlled functionality mode.
4. The fuel metering unit as claimed in claim 1, wherein said fuel metering unit error is due to electrical contact disconnection to the fuel metering unit (10) or any electrical error.
5. A method of operating a fuel injection system (12), said fuel injection system (12) comprises a fuel metering unit (10) comprising the following steps:
- detecting fuel metering unit error;
- operating said fuel metering unit (10) such that said fuel metering unit (10) supplies fuel to a high pressure pump (16) at a constant flow rate.
6. The method as claimed in claim 5, wherein on detection of fuel metering unit error the fuel metering unit is operated in a limited but controlled functionality mode.
7. The method as claimed in claim 5, wherein said fuel metering unit error is due to electrical contact disconnection to the fuel metering unit.
8. The method as claimed in claim 5, wherein said fuel metering unit (10) supplies fuel at a constant flow rate in absence of a pressure limiting valve. ,TagSPECI:Field of the invention:
[001] This invention relates to a fuel metering unit in a fuel injection system and a method thereof
Background of the invention:
[002] In a common rail fuel injection system 100 known in the state of the art as seen in figure 1 the fuel is drawn from a fuel tank 102 by feed pump 104. The feed pump 104 supplies the fuel from the fuel tank to a high pressure pump 106. The high pressure pump 106 pressurizes the fuel that it receives from the feed pump 104 and sends the fuel to a common rail/accumulator 108. The common rail/accumulator 108 stores and maintains the fuel at a particular pressure. Pressure of the fuel in the common rail/accumulator 108 depends not only on the system design but also on the size of the common rail/accumulator 108. The fuel from the common rail/accumulator 108 is then sent to the injectors 110 and further to the engine (not shown in figure 1). The high pressure pump 106 may also be provided with a fuel metering unit 112 which performs the function of inlet fuel metering. The concept of inlet fuel metering is that the fuel metering unit 112 allows only particular amount of fuel into the high pressure pump 106. The concept of inlet fuel metering allows for pressurization of a limited amount of fuel based on the need/demand, thereby reducing the amount of work done by the high pressure pump 106 as well as keep a check on the pressure of the fuel in the common rail/accumulator108. The common rail/accumulator 108 is also provided with a pressure limiting valve 114 to ensure release of fuel from the common rail 108 to the fuel tank 102. The fuel injection system 100 is controlled by an electronic control unit 116.
[003] The focus of this disclosure is the fuel metering unit and the method of operation of the fuel injection system which uses the fuel metering unit in accordance with this disclosure.
[004] The fuel metering unit 112 is an electronically controlled device. The working principle of the fuel metering unit 112 is that based on the need of the providing the fuel to the engine or pressure of fuel in the common rail/accumulator 108, the fuel metering unit can be actuated to allow only certain amount of fuel to be sent to the high pressure pump 106. One embodiment of the fuel metering unit 112 known in the state of the art is one which allows all fuel received by the fuel metering unit 112 to pass to the high pressure pump 106 in case a fuel metering unit error is detected. Another embodiment of the fuel metering unit 112 known in the state of the art is one which does not allow any fuel to pass to the high pressure pump 106 in case a fuel unit error is detected.
[005] One such embodiment known in the state of the art is discussed in patent publication numbered DE-102011005592. A method of controlling combustion engine is disclosed. the method involves supplying fuel to a high pressure storage unit i.e. common rail, from a fuel tank via a feed pump, a metering unit and a high pressure pump. A pressure signal of pressure in the storage unit is determined. A defect of the metering unit is detected, and the metering unit is opened when defect is detected. The time duration is determined as a function of the determined pressure signal, and the feed pump is switched on for the time duration, where the time duration is increased, if the determined pressure signal does not exceed a pressure value.
[006] The method allows controlling the fuel pressure in the high pressure storage unit based on the detected fault of the metering unit, so that controlled fuel injections can be performed, and a precise injection quantity is achieved, thus enabling a problem-free driving of the engine even with the malfunctioning metering unit. The method allows for opening the malfunctioning metering unit, so that the fuel pressure in a high pressure storage unit is maintained high within a certain limit, thus preventing switching off of the combustion engine when the metering unit is malfunctioning, and hence increasing the availability of the combustion engine and the associated motor car.

Brief description of the accompanying drawings:
[007] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:
[008] Figure 1 illustrates a schematic of a common rail fuel injection system;
[009] Figure 2 illustrates a schematic of the common rail fuel injection system incorporating the fuel metering unit in accordance with this disclosure;
[0010] Figure 3 illustrates a fuel metering unit in accordance with this disclosure;
[0011] Figure 4a illustrates the system pressure behavior during normal and limp home mode and the transition between the two known in the state of art;
[0012] Figure 4b illustrates the system/metering unit flow behavior during normal and limp home mode and the transition between the two known in the state of art;
[0013] Figure 4c illustrates a graph representing flow characteristics of a metering unit known in the state of the art;
[0014] Figure 5a illustrates the system pressure behavior during normal and limp home mode and the transition between the two, in accordance with this disclosure;
[0015] Figure 5b illustrates the system/metering unit flow behavior during normal and limp home mode and the transition between the two, in accordance with this disclosure;
[0016] Figures 5c and 5d illustrates a graph representing flow characteristics of a metering unit in accordance with this disclosure; and
[0017] Figure 6 illustrates various embodiment of the flow passage in the fuel metering unit in accordance with this disclosure.

Detailed description of the embodiments:
[0018] The fuel metering unit 10 in accordance with this disclosure is represented in figure 2 and figure 3. The fuel metering unit 10 is provided in a fuel injection system 12. The fuel metering unit 10 is adapted to receive fuel from a feed pump 14 and supply fuel to a high pressure pump 16. The fuel metering unit 10 comprises an inlet 18 adapted to receive fuel from the feed pump 1, an outlet 20 adapted to supply fuel to the high pressure pump 16 and a plunger 22. The fuel metering unit 10 is characterized such that the plunger 22 has a flow passage 24 such that on detection of fuel metering unit error the fuel metering unit 10 supplies fuel to the high pressure pump 16 at a constant flow rate though the outlet 20.

[0019] For better understanding of the fuel metering unit 10 in accordance with this disclosure a fuel injection system as seen in figure 2 is describer further. The fuel injection system 12 comprises a fuel tank 11 from where fuel is drawn by the feed pump 14 and sent to the high pressure pump 16 through the fuel metering unit 10. The fuel metering unit 10 provides an inlet metering functionality and supplies fuel to the pressurizing chamber of the high pressure pump 16. The high pressure pump 16 pressurizes the fuel received from the metering unit and supplies the fuel to the common rail/accumulator 26. From the common rail 26 the fuel is sent to the injectors 28 to inject fuel into the engine (not shown in the figure). The common rail is also provided with a pressure limiting valve (PLV). The PLV is a valve which operates on the pressure of the fuel in the common rail 26. If the pressure in the common rail exceeds beyond a pressure limit of the PLV defined as (Pplv) then the PLV opens and the fuel is sent back to the tank thus the pressure in the common rail is kept under check and any damage to the common rail 26 can be avoided. An electronic control unit 30 controls the operation of the various components of the fuel injection system 12 including the operation of the fuel metering unit 10.

[0020] As mentioned earlier the focus of this disclosure is the fuel metering unit 10 and the method of operating a fuel injection system employing the fuel metering unit 10 of this disclosure. For better understanding of the method of operation of the fuel injection system 12 in accordance with this disclosure the method of operation of a fuel injection system known in the state of the art is necessary.
[0021] The method of operating of the fuel injection system known in the state of the art can be explained with the help of figure 4a, 4b and 4c. The fuel metering unit being explained is one which allows all fuel received by the fuel metering unit 112 to pass to the high pressure pump 106 in case a fuel metering unit error is detected. Figure 4a illustrates a graph representing the fuel pressure (P) in the system of high pressure rail. Figure 4b illustrates a graph representing flow characteristics (Q) of the metering unit for the system pressure behavior as seen in figure 4a. Figure 4c illustrates a graph representing flow characteristics of the metering unit with reference to quantity (Q) and current supplied I(A) for actuating the metering unit. In figure 4a, Pplv is the pressure exceeding which the PLV opens to relieve the pressure from the common rail. Pmax is the maximum operating pressure of the common rail fuel injection system. P_op1 and P_op2 is the operating pressure range after PLV is open. Pset (set pressure) is the demanded pressure during normal operation. Part A of the graph represents the operation of the fuel metering unit before a fuel metering unit error is detected. Part B of the graph represents the operation of the fuel metering unit after the fuel metering unit error is detected. Part C of the graph represents the operation of the fuel metering unit after the PLV is opened. During operation of the fuel metering unit in part A, the fuel metering unit allows small quantity of fuel to pass to the high pressure pump at lower values of current supplied of the fuel metering unit. Towards the end of the operation in part A, a fuel metering unit error occurs. The error is such that the electrical connection to the fuel metering unit is broken. Due to the error the fuel metering unit now does not control the quantity of fuel sent to the high pressure pump and hence quantity increase such that flow is max. Thus at current value of I=0; Q=max. When quantity increases the quantity of fuel sent to the common rail increases thus increasing the pressure beyond the Pmax value. When the pressure exceeds the Pplv value the PLV opens and the fuel is sent from the common rail to the tank, thereby reducing pressure. The PLV is designed such that the pressure in the common rail is reduced and is now operated within a pressure range which allows limited functionality of the fuel injection system and the engine. The limited functionality of the fuel injection system is defined as the limp home mode of operation of the fuel injection system.
[0022] The fuel metering unit 10 in accordance with this disclosure is provided with a flow passage 24 in the plunger 22, which is also defined a flow cross-section geometry. The flow cross-section geometry 24 is such that the when the fuel metering unit error is detected the flow of fuel from the fuel metering unit 10 to the high pressure pump 16 is constant. The constant flow rate of fuel supplied by the fuel metering unit 10 is less than the maximum flow rate of the fuel metering unit 10 on detection of the fuel metering unit error. The error occurring in the fuel metering unit 10 is due to electrical contact disconnection to the fuel metering unit 10. As known from the state of the art, due to disconnection of the electrical contact control of quantity of fuel from the fuel metering unit 10 to the high pressure pump 16 is not possible. However, the fuel metering unit 10 in accordance with this invention allows constant flow of fuel to the high pressure pump 16.
[0023] The method of operation of the fuel injection system 12 in accordance with this disclosure can be briefly explained as follows. The method of operating a fuel injection system 12 comprises the following steps: detecting fuel metering unit error and operating said fuel metering unit 10 such that the fuel metering unit 10 supplies fuel to a high pressure pump 16 at a constant flow rate, lesser than the maximum flow, based on system pressure requirement in limp home mode of operation.
[0024] The working of the fuel metering unit 10 will be explained in detail with respect to the working of the fuel injection system 12 in accordance with this disclosure as follows. During normal working of the fuel injection system and the fuel metering unit 10, depending of the pressure of fuel in the common rail 26 and operating parameters of the fuel injection system 12, the electronic control unit 30 controls the amount of current to be supplied to the fuel metering unit 10. Based on the amount of current supplied to the fuel metering unit 10, the fuel metering unit 10 opens and allows controlled amount of fuel to enter the pressurizing chamber of the high pressure pump16. When an error occurs in the fuel metering unit 10, the electronic control unit 30 detects the error. The error occurring is one where there is disconnection of the electrical connection from the electronic control unit or any other component providing electrical connection to the fuel metering unit 10. When the error is detected by the electronic control unit 30, the functionality of the fuel injection system is changed to a limited functionality. The limited functionality operating mode of the fuel injection system 12 and the limited functionality operating mode of the fuel metering unit 10 is defined as a limp home mode. Thus in the limp home mode, the fuel metering unit 10 in accordance with this aligns the plunger 22 of the fuel metering unit 10 to be in flow communication between the inlet 18, outlet 20 and the flow passage 22 of the plunger 24. The flow communication between the inlet 18, outlet 20 and the flow passage 22 is established and the flow passage or flow cross-section geometry is such that a constant flow of fuel flows from the fuel metering unit 10 to the high pressure pump 16. The flow rate of the fuel during the constant flow is less than the maximum flow rate of the fuel metering unit 10.
[0025] The method of operating of the fuel injection system known in accordance with this disclosure can be explained with the help of figure 5a, 5b, 5c and 5d. Figure 5a illustrates a graph representing the fuel pressure (Pr) in the system o or high pressure rail. Figure 5b illustrates a graph representing flow characteristics (Q) of the metering unit for the system pressure behavior as seen in figure 5a. Figure 5c illustrates a graph representing flow characteristics of the metering unit with reference to quantity (Q) and current supplied I(A) for actuating the metering unit and figure 5d illustrates a graph representing an alternative manner of operating the metering unit in accordance with this disclosure which provides a flow characteristics as shown in figure 5d. Similar to figure 4a, Pplv is the pressure exceeding which the PLV opens to relieve the pressure from the common rail. Pmax is the maximum operating pressure of the common rail fuel injection system. P_op1 and P_op2 is the operating pressure range after PLV is open. Pset (set pressure) is the demanded pressure during normal operation. Part A of the graph represents the operation of the fuel metering unit before a fuel metering unit error is detected. Part B of the graph represents the operation of the fuel metering unit after the fuel metering unit error is detected, and represents transition between Part A and Part C. Part C of the graph represents the operation of the fuel metering unit in limp home mode. In this case limp home is possible without the component Pressure Limiter Valve (PLV). During operation of the fuel metering unit in part A, the fuel metering unit allows small quantity of fuel to pass to the high pressure pump at lower values of current supplied of the fuel metering unit. Towards the end of the operation in part A, a fuel metering unit error occurs. The error is such that the electrical connection to the fuel metering unit is broken. During Part B of the operating stage, in accordance with the fuel metering unit 10 of this disclosure fuel metering unit 10 aligns the plunger 22 with the inlet 18 and the outlet 20 such that the flow passage 24 on the plunger 22 of the fuel metering unit 10 allows a constant flow of fuel from the fuel metering unit 10 to the high pressure pump 16. Thus the fuel metering unit 10 is able to control the quantity of fuel sent to the high pressure pump and hence quantity increase such that flow is less than max flow based on the system pressure requirement during limp home operation.. Thus at current value of I=0; Q=constant. In this case the pressure in the fuel injection system 12 does not continue to rise and is maintained within a specified limit as seen in Part C of the operating characteristics of the fuel metering unit 10 in accordance with this invention. During the Part C of the operating characteristics the pressure of the fuel in the common rail 26 is maintained such that it allows for limited functionality of the fuel injection system 12 and limited but controlled functionality of the fuel metering unit 10. This limited but controlled functionality of the fuel metering unit 10 is defined as the limp home mode of operation.
[0026] The advantages of fuel metering unit 10 in accordance with this disclosure and the method of operating the fuel injection system as described above ensures that the increase of pressure of in the fuel injection system is avoided. Avoiding of pressure increase also ensures that any damage to the components of the fuel injection system is reduced. Further as seen in figure 5a, the limited but controlled operation of the fuel metering unit 10 ensures that during the limp home mode of operation the pressure does not increase till the Pmax or Pplv level. Thus implementation of the fuel flow passage 24 in the plunger 22 of the fuel metering unit 10 in accordance with this invention also allows for not requiring the PLV in the fuel injection system. Thus one component from the fuel injection system is reduced. This also decreases the overall cost and maintenance of the fuel injection system 12 in accordance with this disclosure.
[0027] Figure 6 illustrates various embodiment of the flow passage 24 of the plunger 22 in the fuel metering unit in accordance with this disclosure. Based on the type of the fuel injection system and the quantity of fuel required to be supplied from fuel metering unit 10 to the high pressure pump 16 the geometry of the flow passages will be different.
[0028] 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 geometry of the flow passages 24 provided on the plunger 22 of the fuel metering unit 10. The flow cross section 24 can also be realized on the inlet 18 as an alternate embodiment, instead of on the plunger 22. The scope of the invention is also not limited to the type of error occurring in the fuel metering unit 10. For any error which leads to the limited functionality of the fuel injection system 12, the method of providing constant flow from the fuel metering unit 10 to the high pressure pump 16 as described above, this disclosure is applicable. 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.