CLIAMS:We claim:
1. A method for implementing limp home mode in a vehicle, comprising:
determining (100) if conditions for implementing a limp home mode are met by an electronic control unit;
detecting (101) if a pressure relief valve is in closed condition based on said determination result; and
controlling (102) energization of an injector upon detecting closed condition of said pressure relief valve so as to implement limp home mode.
2. The method of claim 1, wherein said controlling step comprises activating the injector for a specific energization time.
3. The method of claim 1, further comprising calculating the energizing time of an injector based on rail pressure and injection quantity by said electronic control unit.
4. The method of claim 1, further comprising calculating the energization time of an injector based on engine speed by said electronic control unit.
5. The method of claim 1, further comprising calculating the energization time of an injector based on fuel temperature by said electronic control unit.
6. The method of claim 3, wherein magnitude of said rail pressure is obtained from a data map stored in said electronic control unit.
7. The method of claim 1, further comprises
comparing said energizing time of said injector calculated based on engine speed with said energizing time of said injector calculated based on said rail pressure and said injection quantity to determine a minimum value of energization time by said electronic control unit; and
energizing said injector for said minimum value of energization time.
8. An electronic control (200) unit for implementing limp home mode in a vehicle, said electronic control unit adapted to:
determine if conditions for implementing a limp home mode are met;
detect if a pressure relief valve (202) is in closed condition based on said determination result; and
control energization of an injector (204) upon detecting closed condition of said pressure relief valve so as to implement limp home mode.
9. The electronic control unit of claim 8, wherein the injector (204) is activated for an energization time.
,TagSPECI:Field of the invention
[0001] This invention relates to implementing field limp home function in a vehicle.
Background of the invention
[0002] Limp home function in engine management system ensures that a vehicle operates under minimum working parameters whenever there is a fault or problem in the components of the engine or failure of the software that controls the engine management system. When a vehicle is under limp home the engine may operate under restricted speed, the entire functionality of the vehicle may not be available to the user, or the user may be able to drive the vehicle in a manner such that only the basic functions that are needed for the vehicle to be in operable state are available.
[0003] For low geometric volume pumps, generally the pump is not able to deliver high flow rate into rail, to kick of the pressure relief valve in order to avail limp home. High geometric volume pumps are able to kick off the pressure relief valve to implement limp home without blocking injector. But these systems are generally expensive. One of the alternate methods to implement limp home, is to increase the engine rpm to the maximum in order to force open the pressure relief valve. But, increasing engine rpm for implementing limp home might not be fully robust as there are chances of re-closing of pressure relief valve. Hence there is a need to develop a system for low cost pumps that can implement limp home function.
[0004] Prior art patent application US 6578555 discloses a method of controlling the operation of an engine fuel system including at least one fuel injector, a high pressure fuel pump for delivering fuel to the injector and a pressure sensor arranged to provide an output signal indicative of the pressure of fuel delivered to the injector, comprises the steps of controlling the rate of flow of fuel delivered from the pump to the injector by means of a metering valve arrangement supplied with a control current, measuring the speed of the engine and monitoring the status of the pressure sensor so as to determine whether a fault condition has occurred within the sensor. In the event that a fault condition has occurred in the pressure sensor, the control current supplied to the metering valve arrangement is varied in response to the measured engine speed signal so as to maintain operation of the engine at a substantially constant, predetermined engine speed. The invention also relates a fuel system for implementing the control method.
Brief description of the accompanying drawing
[0005] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:
[0006] FIG. 1 illustrates a method for implementing limp home in a vehicle; and
[0007] FIG. 2 illustrates an electronic control unit (ECU) adapted to implement limp home mode.
Detailed description of the embodiments
[0008] FIG. 1 illustrates a method for implementing limp home in a vehicle. The method comprises determining 100 if conditions for implementing a limp home mode are met by an electronic control unit, detecting 101 if a pressure relief valve is in closed condition based on the determined result, and controlling 102 energization of an injector upon detecting closed condition of the pressure relief valve so as to implement limp home mode. The controlling step comprises activating the injector for a specific energizing time. In an embodiment the energizing time of the injector is calculated based on rail pressure and injection quantity. In another embodiment the energizing time of the injector is also calculated based on engine speed. A comparison is made between the energizing time of the injector calculated based on engine speed with the energizing time of the injector calculated based on the rail pressure and the injection quantity to determine a minimum value of energizing time. Based on the comparison the injector is energized with the minimum value of the energizing time.
[0009] For the purpose of better understanding the above mentioned method is explained by considering a limp home condition in a vehicle. A limp home mode is activated when certain conditions are met. for e.g. the conditions can be, malfunction of components of engine, errors generated in the fuel injection system, metering unit errors, malfunction of the rail pressure sensor, or errors in the software that controls the overall engine management, etc. As mentioned earlier, when a vehicle is under limp home, the engine management system in the vehicle ensures that only minimum operation parameters of the vehicle are active in order to ensure that the vehicle can be taken to a nearest service station for implementing corrective measures. In the proposed method upon determining that the conditions for implementing limp home are met, the electronic control unit detects if the pressure relief valve is closed condition. A closed condition of the pressure relief valve implies that the high pressure pump of the fuel injection system is not able to generate sufficient pressure in order to force open the pressure relief valve. By opening the pressure relief valve, the fuel is sent back to the tank. By sending the fuel back to the tank, the pressure of fuel in the rail can be reduced, thereby preventing damage to the components of the rail and/ or injector. There may also be a case, wherein the user of the vehicle may press the accelerator in a way so as to increase the engine speed correspondingly increasing the pressure of fuel in the rail and force open the pressure relief valve. Increasing engine rpm for implementing limp home is not fully robust as there are chances of re-closing of pressure relief valve. At this stage, the proposed method makes use of additional system parameters to bring about limp home. The same shall now be described in further detail.
[00010] In the proposed method, the energization of injector is sought to be controlled to control the engine speed during limp home mode. The fuel injection system may be a common rail system, a unit injector system, or a system combination that uses a high pressure pump and a fuel injector. In one embodiment, the injector is activated only for an energization time. The energization time of the injector is calculated based on rail pressure and injection quantity. In another embodiment the energization time of the injector is calculated based on engine speed. The energizing time of the injector is calculated from two different stand points. Firstly, from rail pressure and injection quantity and secondly based on engine speed.
[00011] In case there is an error in rail pressure sensor (RPS), then RPS may not be able to give the exact value of rail pressure. If the value of rail pressure with error is taken as an input, then it may lead to erroneous calculation of energization of injector and this may lead to overfilling and/ or under-filling of fuel in the rail. In such a case for arriving at the correct value of rail pressure, a rail pressure substitution map may be used for calculating the energizing time. The rail pressure substitution map is a data map stored in said electronic control unit and stores information about rail pressure at different operating ranges of the injector. The rail pressure substitution map is calibrated based on test bench measurements. The electronic control unit monitors the data received from RPS to determine any abnormal variation in pressure in order to check if there is an RPS error or not.
[00012] In case of RPS errors, the data from the substitution map is used as an input for calculating energizing time.
[00013] In another embodiment along with engine speed the fuel temperature can also be taken as an input for calculating the energizing time.
[00014] In yet another embodiment, an energization time calculated based on rail pressure and fuel quantity, and an energization time calculated based on engine speed are considered. A minimum value of the two energizing time values is computed to obtain a minimum energizing time. The injector is activated only for the minimum energizing time. As a result it is now possible to limit the pressure of fuel in the fuel injection system. By making use of the above mentioned method it is possible to drive the vehicle without the risk of over fuelling during limp home, even when the pressure relief valve is under closed condition. The damage to components of the engine and fuel injection system are avoided as the vehicle will not be working under maximum operating condition during limp home. In addition to this the engine speed will also be limited so as to ensure that the fuel pressure in the rail is limited to the minimum operating condition, thereby preventing damage to the components of the rail.
[00015] FIG. 2 illustrates an electronic control unit (ECU) 200 adapted to implement limp home mode. The electronic control unit 200 disclosed herein determines if conditions for implementing a limp home mode are met. This is done by taking input from different sources comprising but not limited to, rail pressure sensor (201), temperature sensor (203), and engine speed sensor (205). Based on the inputs, the ECU (200) determines if the vehicle is operating normally. In case of any deviation, the ECU (200) determines if a limp home needs to be implemented or not. In case of a demand for limp home, the ECU (200) then detects if a pressure relief valve is in closed condition. If the pressure relief valve is in closed condition, then the ECU (200) controls the energization of the injector (204) for an energization time so as to implement limp home mode. The energization time is calculated such that the rail pressure is reduced and the engine speed is limited to activate the limp home mode.
[00016] In one embodiment energization time of the injector (204) is calculated based on rail pressure and injection quantity. In another embodiment the energization time of the injector (204) is calculated based on engine speed. In yet another embodiment, the energization time of the injector (204) is calculated based on fuel temperature. A comparison is made between the energization time arrived at from the above mentioned parameters. Based on the comparison the minimum value of energization time is chosen and given as an input to the injector (204) during limp home. Thus, the injector (204) operates under minimum value of energization time. This helps in preventing damage to the components of the fuel injection system during limp home as the pressure in the rail is drastically reduced compared to the pressure during normal working of the vehicle. After the vehicle has been serviced for faults that led to creation of limp home, the ECU (200) will reset the working of the fuel injection system to normal operating condition.
[00017] 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 type of fuel injection system used. 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.