Field of the invention
[0001]This invention relates to a method of implementing limp home in a
vehicle.
Background of the invention
[0002] Limp home condition in a vehicle is encountered when a fault is recognized in the system of the vehicle by the control unit/ vehicle computer. In the case of diesel fuel injection system, during limp home, a pressure limiting or a pressure control valve (PLV/PCV) that is located on the common rail will open thereby relieving excess pressure in the rail. For the PLV or PCV to open, the fuel injection pump needs to build up pressure. However in cases when the injector leaks fuel and during low speeds of the fuel injection pump, the fuel injection pump may not build up pressure that will cause the PLV or PCV to open. In case of failure of PLV or PCV, there may be a possibility of excess fuel injection during limp which is not desirable from the point of view of vehicle safety.
Brief description of the accompanying drawing
[0003] Different modes of the invention are disclosed in detail in the description
and illustrated in the accompanying drawing:
[0004] FIG. 1 illustrates a method of implementing limp home in a vehicle.
Detailed description of the embodiments
[0005] FIG. 1 illustrates a method of implementing limp home in a vehicle. The method comprises receiving 102, by a control unit at least one magnitude of fuel form any one of a metering unit or a rail pressure sensor. The control unit detects 104 the speed of the engine via a speed sensor. For the detected

engine speed, the control unit calculates 106 the corresponding magnitude of fuel stored in a data map. The control unit compares 108 the calculated magnitude of fuel with said received magnitude of fuel. An energizing time of a fuel injector is modified 110 by the control unit based on the comparison. In an embodiment the magnitude of fuel is anyone of fuel pressure, fuel discharge volume and temperature.
[0006] The method of achieving limp home will now be explained from the point of view of metering unit first followed by rail pressure sensor. Consider the case of achieving limp during failure or error from the metering unit. In such a case the control unit receives 102 the magnitude of fuel from the metering unit. The magnitude may be any one of fuel pressure, fuel discharge volume and fuel temperature. The control unit detects 104 via speed sensor the speed of the engine. The control unit calculates 106 the corresponding magnitude of fuel stored in a data map for the detected engine speed. The control unit compares 108 the calculated magnitude of fuel with the received 102 magnitude of fuel. The energizing time of a fuel injector is modified 110 by the control unit based on the comparison in order to limit the injection quantity as well as speed.
[0007] For the purpose of better understanding, the working of the above mentioned method will be explained for taking into account the speed of the engine and the volume (magnitude) of fuel being controlled by the metering unit of the fuel injection pump. The engine speed is assumed to be 500rpm and volume to be 100 mg/cycle/rpm of the engine. The above mentioned values are the for the purpose of understanding only and does not limit the working of the above mentioned method for the above mentioned speed, volume or pressure. The control unit receives 102 the magnitude of volume

from the control unit. The speed of the engine is detected 104 by the speed sensor. The control unit calculates 106 the corresponding magnitude of fuel stored in the data map for the detected engine speed. The calculated magnitude of fuel is then compared 108 with the received magnitude of fuel. If the magnitude of fuel as stored in the data map is less than or greater than 100 mg/cycle/ rpm, the control unit interprets that the value of 100 mg/cycle/rpm may be due to an error that may be generated during limp home. In order to rectify the same, the control unit modifies 110 the energizing time of the fuel injector. This limits the energizing time during limp home which enables the engine to operate at a speed that is sufficient to take the vehicle to the service station.
[0008]With the use of the above mentioned method the energizing time that is given to the injector may be limited during limp to a time that would enable the vehicle to be taken to the service station. Hence, the above mentioned method may work in the case of failure of PLV/PCV or even in cases where the PLV or PCV is not present in the common rail.
[0009] ‘Adapted’ or ‘arranged’, in the context of the instant disclosure, refers to the technical capability or the technical capacity of a component, in relation to which the term ‘adapted’ or ‘arranged’ is used, to carry out or executed a specified action or actions, upon the requirement of the specified action or actions to be carried out or executed. Moreover, the usage of the term ‘adapted’ or ‘arranged’ here, is in reference with the normal technical capability or technical capacity of the component, imparted by the design or the structure or the composition of the component, and not in reference with any special or extraneous capability or capacity, beyond the scope of the normal technical

capability or technical capacity. Therefore there is a need to address this problem.
[0010]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 solenoid or fuel filter 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.

CLAIMS
We Claim:
1. A method (100) of implementing limp home in a vehicle, said method
comprising:
receiving (102), by a control unit at least one magnitude of fuel form any one of a metering unit or a rail pressure sensor;
detecting (104), by said control unit via a speed sensor, speed of an engine;
calculating (106), by said control unit, corresponding magnitude of fuel stored in a data map for said detected engine speed;
comparing (108), said control unit, said calculated magnitude of fuel with said received magnitude of fuel; and
modifying (110), by said control unit, an energizing time of a fuel injector based on said comparison.
2. The method of claim 1, wherein said magnitude of fuel is anyone of fuel
pressure, fuel discharge volume and fuel temperature.