Claims:We Claim:
1 A method of operating a fuel metering unit (10) in a fuel injection system, said fuel metering unit (10) comprising a plunger (24) movable based on current supplied by a controller, said plunger (24) having a secondary-opening, and movement of said plunger (24) closing a secondary-flowpath when said fuel metering unit (10) is operated at a zero-delivery-state for preventing flow of fuel into a common rail in said fuel injection system;
said method comprising:
receiving real-time pressure from a pressure sensor in said common rail, by said controller, when said fuel metering unit (10) is operated at said zero-delivery-state (105);
determining pressure variation by comparing said real-time pressure with a pre-defined pressure, said pressure variation occurring due to flow of fuel into said common rail through said secondary-flowpath when said fuel metering unit (10) is operated at said zero-delivery-state (110); and
altering said current supplied to said fuel metering unit (10), by said controller, for closing said secondary-flowpath, until said pressure variation is within a threshold range (115).

2 The method as claimed in claim 1, wherein said plunger (24) is movable using a solenoid actuator (22).

3 The method as claimed in claim 1, wherein said current is altered based on pre-defined steps of current values.

4 The method as claimed in claim 1, wherein said current is altered in one of a positive direction and a negative direction.

5 A controller for operating a fuel metering unit (10) in a fuel injection system, said fuel metering unit (10) comprising a plunger (24) movable based on current supplied and said plunger (24) having a secondary-opening, movement of said plunger (24) closing a secondary-flowpath when said fuel metering unit (10) is operated at a zero-delivery-state for preventing flow of fuel into a common rail in said fuel injection system;
said controller adapted to:
receive real-time pressure from a pressure sensor in said common rail when said fuel metering unit (10) is operated at said zero-delivery-state;
determine pressure variation by comparing said real-time pressure with a pre-defined pressure, said pressure variation occurring due to flow of fuel into said common rail through said secondary-flowpath when said fuel metering unit (10) is operated at said zero-delivery-state; and
alter said current supplied to said fuel metering unit (10) for closing said secondary-flowpath, until said pressure variation is within a threshold range.

6 The controller as claimed in claim 5, wherein said current is altered based on in one of a positive direction and a negative direction.

7 The controller as claimed in claim 5, wherein comparing said real-time pressure with said pre-defined pressure is performed using a comparator. , Description:Field of the invention:
[0001] The invention relates to a method of operating a fuel metering unit in a fuel injection system.
Background of the invention:
[0002] A fuel metering unit in the fuel supply system is used for supplying metered quantity of fuel to a high pressure pump. The fuel metering unit comprises an inlet for receiving fuel from a feed pump, an outlet for supplying fuel to the high pressure pump. The fuel metering unit also has a plunger that is movable within a chamber defined in the fuel metering unit. The plunger has a primary opening for enabling fuel to flow into the high pressure pump through the outlet. Primary opening is an opening made on the plunger through which the fuel from the inlet of the fuel metering unit flows into the outlet of the fuel metering unit.
[0003] In case of fuel metering unit error, the current supply to the fuel metering unit is cut-off. When no current is supplied to the fuel metering unit, components in the fuel metering unit are arranged such that a primary-opening is completely opened. That is, the working of the fuel metering unit is such that, during the error state, the primary-opening is completely inline with the inlet. Hence, during such an error state, fuel from the inlet flows through the primary opening and reaches the outlet of the fuel metering unit thus supplying fuel to the high pressure pump.
[0004] The fuel thus supplied, is pressurized by the high pressure pump and delivered to the common rail. However, the quantity of fuel flowing, when the primary-opening is completely open is high. Hence excess fuel is delivered to the common rail. Supply of excess fuel to the common rail causes increased pressure in the common rail. When the pressure in the common rail reaches above a threshold limit, a pressure limiting valve (PLV) provided in the common rail is opened so that excess fuel from the common rail flows back into the fuel tank. Hence, to avoid such excess pressure in common rail, a flow passage is made on the plunger for allowing constant quantity of fuel to flow into the high pressure pump.
[0005] According to an Indian patent application numbered 168-CHE-2015, the fuel metering unit is adapted to receive fuel from a feed pump and supply fuel to a high pressure pump. The fuel metering unit comprises an inlet adapted to receive fuel from the feed pump, an outlet adapted to supply fuel to the high pressure pump and a plunger. The fuel metering unit is characterized such that the plunger has a flow passage such that on detection of fuel metering unit error the fuel metering unit supplies fuel to the high pressure pump at a constant flow rate though the outlet.
Brief description of the accompanying drawings:
[0006] Figure 1 illustrates a fuel metering unit in accordance with a prior art; and
[0007] Figure 2 is a flowchart describing a method of operating a fuel metering unit, in accordance with an embodiment of the invention.
Detailed description of the embodiments:
[0008] A fuel metering unit (10), in the fuel injection system, is used for delivering metered quantity of fuel to the high pressure pump. The concept of supplying metered quantity of fuel to the high pressure pump is called as inlet (16) fuel metering.
[0009] The fuel metering unit (10) comprises an inlet (16) for receiving fuel from a feed pump, an outlet (18) for supplying fuel to the high pressure pump. The inlet (16) is in fluid communication with the feed pump. Fuel from the feed pump flows into the fuel metering unit (10) through the inlet (16). The outlet (18) is in fluid communication with the high pressure pump. The metered quantity of fuel is supplied to the high pressure pump through the outlet (18). The fuel metering unit (10) also has a plunger (24) that is movable within a chamber defined in the fuel metering unit (10). A solenoid actuator (22) is used for movement of the plunger (24).

[0010] When current is supplied to the solenoid actuator (22), electromagnets in the solenoid actuator (22) are magnetized and causes movement of the plunger (24). Similarly, when supply of the current to the solenoid actuator (22) is cut-off, the solenoid actuator (22) is de-magnetized. Such de-magnetization also imparts movement to the plunger (24).

[0011] The plunger (24) is a hollow cylinder and comprises a primary-opening (12). As the plunger (24) moves, the primary-opening also moves. When a part of the primary-opening (12) or the whole of the primary-opening (12) is inline with the inlet (16), then a fuel-flowpath is formed enabling flow of fuel from the fuel metering unit (10) to the high pressure pump.

[0012] When a part the primary-opening (12) is inline with the inlet (16) then the fuel-flowpath is considered to be partially open. When the whole of the primary-opening (12) is inline with the inlet (16), then the fuel-flowpath is considered to be completely open. When the primary-opening (12) is not inline with the inlet (16) then the fuel-flowpath is considered to be closed.

[0013] During metering, the plunger (24) is moved such that a part of the primary-opening (12) is inline with the inlet (16) so that fuel from the inlet (16) flows through that part of the primary- opening and reaches the outlet (18) thus supplying fuel to the high pressure pump. That is, the fuel-flowpath is opened and closed based on the position of the primary-opening (12) with respect to the inlet (16). Therefore, by adjusting position of the primary-opening (12) with respect to the inlet (16), inlet (16) fuel metering is achieved.

[0014] A secondary-opening (14) is provided in addition to the primary-opening (12) and is located proximal to the primary-opening (12). The secondary-opening (14), in one example, is a circular cross-section of a fixed diameter that is perpendicular to the axis of the plunger (24). However, it should be noted that shape of the secondary opening is not limited to being circular and that the secondary-opening (14) can be in various other shapes.

[0015] During an error state (when no current is supplied to the solenoid actuator (22)) of the fuel metering unit (10), the working of the fuel metering unit (10) is such that the secondary-opening (14) is inline with the inlet (16) thereby opening a secondary-flowpath. Hence, fuel from the inlet (16) now flows through the secondary-opening (14). Fuel flowing through the secondary-opening (14) supplies constant quantity of fuel to the high pressure pump. This constant quantity of fuel is pressurized by the high pressure pump and is delivered to the common rail so that the vehicle operates in limp home mode.

[0016] In certain operating conditions of the vehicle, the fuel metering unit (10) is operated at the zero-delivery-state. The zero-delivery-state is defined as a state when the fuel metering unit (10) is not required to supply fuel to the high pressure pump. One exemplary scenario where the fuel metering unit (10) is operated at zero-delivery-state is, when the vehicle is operating at overrun condition. When the vehicle is operating at such overrun condition, no fuel is required to be supplied to the high pressure pump and thus to the common rail. In such a condition, the fuel metering unit (10) is operated at zero-delivery-state so that no fuel is supplied to the high pressure pump. That is, the plunger (24) in the fuel metering unit (10) is moved such that the primary-opening (12) and the secondary-opening (14) are not inline with the inlet (16). That is, the fuel-flowpath and the secondary-flowpath are closed. Therefore supply of fuel to the high pressure pump is prevented.

[0017] The current supplied to the fuel metering unit (10) for operating the fuel metering unit (10) at the zero-delivery-state is referred to as zero-delivery-current for purpose of explanation of the disclosure. The zero-delivery-current may be of particular value which is stored in memory of the controller and when the controller supplies this zero-delivery-current to the fuel metering unit (10), the plunger (24) moves to a position such that both the fuel-flowpath and the secondary-flowpath is closed.

[0018] However, one drawback of providing the secondary-opening (14) is that, although the controller supplies zero-delivery-current, due to the manufacturing tolerances in the secondary-opening (14), a part of the secondary-opening (14) may be inline with the inlet (16) thereby partially opening the secondary-flowpath. Thus allowing flow of fuel through the partially opened secondary-flowpath to the common rail. As a result, the pressure in the common rail increases when the metering unit is operated at the zero-delivery-state causing unnecessary pressure fluctuations in the common rail thereby reducing shelf-life of the common rail.

[0019] In order to overcome this drawback, the present disclosure discloses a method of operating the fuel metering unit (10) to ensure that no fuel is supplied by the fuel metering unit (10) to the high pressure pump when the fuel metering unit (10) is operated at the zero-delivery-state. Step by step method of operating the fuel metering unit (10) is explained in the following paragraphs. The method is performed by a controller embedded in the vehicle.

[0020] It should be noted that the disclosure discloses the method of operating the fuel metering unit (10) in a fuel injection system that do not have any pressure control mechanism such as a pressure limiting valve (PLV) or a pressure control valve (PCV), thereby providing a cost efficient solution.

[0021] At step 105, real-time pressure is received from a pressure sensor when the fuel metering unit (10) is operated at the zero-delivery-state. The pressure sensor is fitted to the common rail and is used for indicating pressure of fuel existing in the common rail in real-time. It should be noted that, according to this disclosure, the real-time pressure is received when the fuel metering unit (10) is being operated in the zero-delivery-state to ensure no fuel is supplied to the high pressure pump at the zero-delivery-state. The pressure sensor is electrically connected to the controller and therefore transmitting the pressure existing in the common rail to the controller.
[0022] At step 110, pressure variation is determined by comparing the real-time pressure with a pre-defined pressure. The pre-defined pressure is stored in the memory of the controller. A comparator embedded in the controller is used for comparing the real-time pressure with the pre-defined pressure. The controller reads the pre-defined pressure stored in the memory and further compares the real-time pressure received from the pressure sensor with the pre-defined pressure value using the comparator. Upon comparing, a pressure variation is determined.
[0023] The pressure variation is determined by the controller to check if the real-time pressure, received from the pressure sensor, is greater than the pre-defined pressure stored in the memory.
[0024] The real-time pressure will be greater than the pre-defined pressure when fuel flows into the common rail during the zero-delivery-state. One reason for the flow of fuel during the zero-delivery-state is due to the manufacturing tolerance in the secondary-opening (14) as already explained above. Although the controller supplies the zero-delivery current to the fuel metering unit (10) to prevent fuel flow when the fuel metering unit (10) is operating at zero-delivery-state, fuel still flows into the common rail through the secondary-opening (14) due to such manufacturing tolerance in the secondary-opening (14). Due to such flow of fuel, the real-time pressure is greater than the pre-defined pressure when the fuel metering unit (10) is operated at the zero-delivery state. Therefore, pressure variation occurs and such pressure variation is determined in step 110
[0025] At step 115, the controller alters the current until the pressure variation is within the threshold range. The current is altered with respect to the zero-delivery current that is supplied to the fuel metering unit (10) for moving the plunger (24) so that the secondary-opening (14) is not inline with the inlet (16) (closing the secondary-flowpath) to prevent fuel flow into the high pressure pump when the fuel metering unit (10) is operated at the zero-delivery-state.

[0026] It should be noted that the current supplied may be altered positively or negatively with respect to the zero-delivery current until the secondary-opening (14) is not inline with the inlet (16) of the fuel metering unit (10). The current is altered in terms of pre-defined steps of smaller current values. The positive and negative alteration of current is obtained by changing the direction of the current supplied to the fuel metering unit (10). The altered current supplied to the controller actuates the solenoid actuator (22) to move the plunger (24) to an extent such that the secondary-opening (14) is not inline with the inlet (16) of the fuel metering unit (10). Thereby flow of fuel into the common rail is prevented when the fuel metering unit (10) is operated at the zero-delivery-state.

[0027] It should be noted that the current is altered until the pressure variation is within a pre-defined threshold range. This threshold range is stored in the memory of the controller. It should also be noted that when the pressure variation is determined to be within the threshold range, the secondary-opening (14) is not inline with the inlet (16) (secondary-flowpath is closed completely) and hence no fuel is supplied to the common rail when the fuel metering unit (10) is operated at the zero-delivery-state.
[0028] It should also be noted that the controller performs the above mentioned methods in various operating conditions such as in over-run condition and during transition from high load to low load.
[0029] Therefore by performing the methods described in this disclosure, flow of fuel into the common rail due to manufacturing tolerances in the secondary-opening (14) can be avoided. Also it should be noted, according to this disclosure, that there is no need for a Pressure Limiting Valve or a Pressure Control Valve due to the secondary-opening (14) through which constant quantity of fuel is supplied during any error in the fuel metering unit (10) and yet ensures that no unnecessary fuel flows into the common rail during such error state. Hence, the disclosure provides for a cost effective solution.

[0030] The method of operating the fuel metering unit (10) is explained with an example for clear understanding of the disclosure. It should be noted that the dimensions and numbers used in the below paragraphs are for the purpose of exemplary description only and that the components mentioned in the disclosure is not limited to those numbers or dimensions only.
[0031] The fuel injection system comprises a fuel metering unit (10), a high pressure pump and a common rail. It should be noted that the example describes the method of operating the fuel metering unit (10) in a fuel injection system that do not have any pressure control mechanism such as a pressure limiting valve (PLV) or a pressure control valve (PCV), thereby providing a cost efficient solution.
[0032] In this example, it is considered that the secondary-opening (14) has a circular cross-section with diameter 5mm. Also, it is considered that the zero-delivery-current is 500mA. That is when the fuel metering unit (10) is operated at the zero-delivery-state, the controller supplies 500mA so that the secondary-flowpath is closed (the secondary-opening (14) is not inline with the inlet (16) of the fuel metering unit (10)).
[0033] In this example, it is considered that the fuel metering unit (10) is operated at zero-delivery-state. Also it is considered that the secondary opening has a manufacturing tolerance of diameter 5.15mm.
[0034] Since the fuel metering unit (10) is operated at the zero-delivery-state, the controller supplies 500mA current (zero-delivery-current). However, due to the manufacturing tolerance in the secondary opening, although the controller supplies 500mA, some quantity of fuel is supplied to the high pressure pump and thus to the common rail because of the 0.15mm difference in the secondary opening.
[0035] That is, due to manufacturing tolerance, 0.15mm (small portion) of the secondary opening is inline with the inlet (16) and hence opening the secondary-flowpath partially. Therefore, some quantity of fuel flows into the high pressure pump through the partially opened secondary-flowpath. The high pressure pump pressurizes this fuel and delivers it to the common rail.
[0036] When the pressurized fuel is delivered to the common rail, the real-time pressure (pressure existing) in the common rail increases with respect to an expected pressure in the common rail. In this example, the expected pressure is also referred to as the pre-defined pressure and is considered to be 400 bar.
[0037] However, due to supply of fuel to the common rail due to the manufacturing tolerance in the secondary opening, the pressure existing in the common rail increases to 450 bar which is the real-time pressure existing in the common rail. This is due to flow of fuel through the partial opening of the secondary-flowpath which is a consequence of manufacturing tolerances existing in the secondary-opening (14).
[0038] The controller then receives this real-time pressure of 450 bar from a pressure sensor in the common rail as shown in step 105 of Figure 2.
[0039] Upon receiving the real-time pressure, the controller compares the real-time pressure of 450 bar with the pre-defined pressure of 400 bar for determining if there is a pressure variation shown in step 110 of Figure 2. The pre-defined pressure of 400 bar is stored in the memory of the controller. A comparator embedded in the controller is used for comparing the real-time pressure with the pre-defined pressure.
[0040] It should also be noted that, the pressure in the common rail can vary within a range with respect to the pre-defined pressure of 400 bar, when the fuel metering unit (10) is operated in the zero-delivery-state. In this example, the range is considered to be 390 bar - 410 bar. That is, the pressure in the common rail can vary anywhere between the range of 390 bar-410 bar when the fuel metering unit (10) is operated in the zero-delivery-state.
[0041] Upon comparing the real-time pressure with the pre-defined pressure, the controller determines a pressure variation of 50 bars. Further, the controller determines that the pressure variation of 50 bar is above a threshold range. In this example the threshold range of the pressure variation is considered to be between -10 bar to +10bar. However, in this case, since the pressure variation is 50 bar which is higher than the threshold range. Hence, the controller alters the current supplied to the fuel metering unit (10).
[0042] The controller alters current of 500mA to 495mA. This alteration of current moves the plunger (24) by a certain distance for closing the secondary-flowpath. Movement of the plunger (24) based on altering the current value from 500mA to 495mA closes the secondary-flowpath by a certain degree. Further, upon closing the secondary-flowpath to a certain degree, the pressure in the common rail is measured in real time. It is considered that the pressure existing in the common rail is now measured to be 425 bar by the pressure sensor. Hence, now the real-time pressure is 425 bar.
[0043] The controller now repeats steps 105-115 in second iteration. That is, the controller receives the real-time pressure of 425 bar from the pressure sensor. The controller then compares the real-time pressure of 425 bar with the pre-defined pressure of 400 bar and determines a pressure variation of 25 bar in the second iteration. Since the pressure variation of 25 bar is still above the threshold range, the controller is required to alter the current further.
[0044] The controller now alters the current from 495mA to 490mA. Altering of the current from 495mA to 490mA moves the plunger (24) further such that the secondary-flowpath is closed completely. Hence, no fuel is supplied to the high pressure pump and thus no fuel is delivered to the common rail. Further, the pressure sensor in the common rail measures the pressure existing in the common rail and determines the real-time pressure now to be 400 bar. Hence, now the real-time pressure is said to be 400 bar.

[0045] Now the steps 105-115 is repeated in yet another iteration. The controller receives the real-time pressure of 400 bar for the pressure sensor. The controller compares the real-time pressure of 400 bar with the pre-defined pressure which is also 400 bar. Hence, in this case, the pressure variation is zero which is within the threshold range of (-10bar to +10bar). Therefore, the controller learns that 490mA current is required to be supplied instead of 500mA, when the fuel metering unit (10) is operated in the zero-delivery-state due to the manufacturing tolerances (0.15mm) existing in the secondary opening of this particular fuel metering unit (10). In this manner, the controller will adjust the current supplied to the fuel metering unit (10) based on the manufacturing tolerances in the secondary-opening (14) so that when the fuel metering unit (10) is being operated at the zero-delivery-state, both, the fuel-flowpath and the secondary-flowpath are closed and hence no fuel is delivered to the high pressure pump.
[0046] In the above example, the current is negatively altered with respect to the zero-delivery-current specified. That is current is altered in a decreasing manner with respect to the zero-delivery-current (500mA) that is supplied initially by the controller considering the secondary opening is exactly 5mm in diameter. However, it should also be noted that the current can be positively altered in certain cases based on the type of solenoid actuator (22) used for moving the plunger (24). That is, the current is altered in an increasing manner with respect to the zero-delivery-current (500mA) that is supplied initially by the controller considering the secondary opening is exactly 5mm in diameter. The alteration of the current in a decreasing manner or an increasing manner with respect to the zero-delivery-current depends on the type of solenoid actuator (22) used and also on the direction of movement of the plunger (24) with respect to the primary-opening and the secondary-opening.
[0047] Thus using the method of operating a fuel injection system as disclosed hereinabove allows for a cost effective solution to ensure that the pressure in the common rail does not increase beyond the threshold value in a fuel injection system having a common rail which does not have any pressure controlling mechanism such as a pressure limiting valve (PLV) or a pressure control valve (PCV) in place.
[0048] It must be understood that the embodiments explained in the above detailed description is only illustrative and does not limit the scope of this invention. Any modification in the embodiments with regard to the type of the pressure sensor, shape of the secondary opening, type of solenoid actuator are envisaged and form a part of this invention. The scope of this invention is limited only by the claims.