CLIAMS:We claim:
1. A device (100) to detect a low rail pressure during starting of an engine in a vehicle, the device comprising:
a determining means (102) to determine the working of a rail pressure sensor (104);
a timer (103) adapted to set a predefined time;
wherein, if the rail pressure sensor (104) is working, the rail pressure sensor (104) measures a rail pressure after the predefined time;
a first comparing means (108) to compare measured rail pressure with a first predefined value set by a first reference means (106);
an ecu (118) adapted to indicate a low rail pressure when the measured rail pressure is less than the first predefined pressure value;
wherein, if the rail pressure sensor (104) is not working,
a replacing means (111) to replace the measured rail pressure with a default pressure value;
a calculating means (110) to calculate a current speed and a previous speed of the engine and to calculate an acceleration of the engine;
a second comparing means (116) adapted to compare the acceleration with a second predefined value set by a second reference means (112);
a checking means (114) to check atleast one shut off requests from atleast one component of the engine;
wherein the ecu (118) indicates a low rail pressure if the acceleration is less than the second predefined value and no shutoff request was found.
2. The device (100) claimed in claim (1), wherein the component of the engine is an injector energizing capacity bank.
3. A method to operate a device (100) to detect a low rail pressure during starting of an engine in a vehicle, the method comprising:
determining the working of a rail pressure sensor (104);
if the rail pressure sensor (104) is working,
measuring the rail pressure by the rail pressure sensor after a predefined time set by a timer (103);
comparing the measured rail pressure with a first predefined value;
indicating a low rail pressure, if the measured rail pressure is less than the first predefined value;
wherein, if the rail pressure sensor (104) is not working,
replacing the measured rail pressure with a default pressure value;
measuring a current speed and a previous speed of the engine to calculate an acceleration of the engine;
comparing the acceleration with a second predefined value;
checking for atleast one shutoff request from atleast one component of the engine;
indicating a low rail pressure, if the acceleration is less than the second predefined value and no shutoff request was found.

4. The method to operate a device (100) claimed in claim (1), wherein the method also comprising a step of, providing a signal from the determining means (102) to the replacing means (111) when the rail pressure sensor (102) is not working.
5. The method to operate a device (100) claimed in claim (1), wherein the method also comprising a step of, indicating a failure in the rail pressure sensor (104) when the voltage of the rail of pressure sensor exceeds a predefined maximum voltage.
6. The method to operate a device (100) claimed in claim (1), wherein the acceleration is calculated from the current speed and the previous speed of the engine.
7. The method to operate a device (100) claimed in claim (1), wherein rail pressure in the common rail is directly proportional to the acceleration of the engine. ,TagSPECI:Field of the invention
[001] This invention relates to a device to detect a low rail pressure during starting of an engine in a vehicle.

Background of the invention
[002] Various sensors are provided in an electronic control device of an automobile internal combustion engine. One among them is a pressure sensor that detects rail pressure in a common rail type fuel injection control apparatus. The pressure sensor is important to achieve appropriate fuel injection. A frequent fault with common rail systems is low fuel pressure, which can cause non-start, difficult starting or loss of power. When the system has detected a loss of pressure, it is important to test the fuel pressure sensor to determine whether the pressure is low, or whether the sensor is misreading. If the sensor is misreading, wiring checks can be carried out before condemning the sensor. If the sensor is reading correctly, it then needs to be established whether sufficient pressure is not being created, or whether pressure is being created but is leaking back to the low pressure side via the injectors or fuel pressure regulator.
[003] Many techniques are known in the state of art to detect a low rail pressure during starting of an engine in a vehicle.
[004] An US patent 7698931 discloses a fuel pressure sensor for detecting pressure in a common rail in which a high-pressure fuel to be supplied to an engine is accumulated, the device detects a stabilized fuel pressure via the fuel pressure sensor subsequent to lapse of the resting and stabilization time, and determining a failure of the fuel pressure sensor when the detected stabilized fuel pressure exceeds a predetermined upper limit threshold value or is less than a predetermined lower limit threshold value.

Advantages of the invention
[005] The invention as claimed in the independent claims has the following advantages. The method disclosed detects the low rail pressure during the starting of an engine and also abnormality in the pressure sensor in a very efficient way and also the pressure sensor can be easily diagnosed without any additional components or separate dedicated circuits. With this invention, it is possible to provide a more highly reliable device in a very economical way. The detection of the low rail pressure can be achieved even during the system errors like sensor failure.

Brief description of the accompanying drawings
[006] An exemplifying embodiment of the invention is disclosed in detail in the description and illustrated in the accompanying drawings:
[007] Figure 1 illustrates a block diagram of a device to detect a low rail pressure in accordance with this invention; and
[008] Figure 2 illustrates a flowchart of a method to operate a device to detect a low rail pressure during starting of an engine in a vehicle in accordance with this invention.

Detailed description of the invention:
[009] Figure 1 illustrates a block diagram of a device 100 to detect a low rail pressure during starting of an engine in a vehicle according to this invention. The device 100 comprises a determining means 102 adapted to determine the working of a rail pressure sensor 104. The rail pressure sensor 104 is adapted to measure a rail pressure in a common rail. The rail pressure sensor 104 measures the pressure of fuel that is to be delivered to a fuel injector in the common rail. The device 100 comprises a timer 103 adapted to set a predefined time for the rail pressure to develop in the common rail. The rail pressure that is developed in the common rail is measured by the rail pressure sensor 104 after the predefined time. The device 100 also comprises a first reference means 106 adapted to set a first predefined value. The first predefined value is a pressure value obtained as a function of a rail pressure value and a coolant temperature of the engine. The first predefined value is a pressure value associated with a coolant temperature of the engine. For instance, if the coolant temperature of the engine is 200 degrees Fahrenheit, the pressure value associated with 200 degrees Fahrenheit is considered as the first predefined value. The device 100 comprises a first comparator means 108 adapted to compare the rail pressure value measured after the predefined time with the first predefined value. The device 100 also comprises a replacing means 111 adapted to replace a default pressure value in the ecu 118 when the rail pressure sensor 104 is not working. The determining means 102 provides a signal to the replacing means 111 if the rail pressure sensor 104 is not working to replace a default pressure value. The replacing means replaces the default pressure value in place of actual pressure value when the rail pressure sensor 104 is not working. The device 100 comprises a calculating means 110 adapted to calculate a current speed and a previous speed of the engine and to calculate acceleration from the current and the previous speeds of the engine. The device also comprises a second reference means 112 adapted to set a second predefined value. The second predefined value is an acceleration value which may be a function of the current speed and the previous speed of the engine. For instance, the acceleration value is a ratio of the current speed and the previous speed of the engine. The device 100 comprises a second comparing means 116 adapted to compare the calculated acceleration with the second predefined value. The device 100 also comprises a checking means 114 adapted to check for atleast one shutoff request from at least one component of the engine. For instance, the component of the engine may be an energizing capacity bank which operates injector solenoid. If there is a short circuit between the energizing capacity bank and a supply from the battery a shutoff requested is given. The device 100 also comprises an electronic control unit (ecu) 118 adapted to monitor the signal from the rail pressure sensor 104 and other components of the engine. If the rail pressure sensor 104 is working, the electronic control unit 118 indicates a low pressure value when the rail pressure measured after the predefined time by the rail pressure sensor 104 is less than the first predefined value. If the rail pressure sensor 104 is not working, the electronic control unit 118 indicates a low rail pressure when the calculated acceleration is less than the second predefined value and if there are no shutoff requests found from atleast one component of the engine.

[0010] A method to operate a device 100 to detect a low rail pressure during the starting of an engine in accordance with this invention, the determining means 102 determines the working of the rail pressure sensor 104 in an operating range. There are different types of errors related to the rail pressure sensor 104.For instance, the determining means 102 will do a sensor signal range check which has an operating range between 0.5V-4.5V.If the rail pressure sensor 104 has no wiring connection, then due to a pull up resistor, a maximum of 5V voltage signal will be detected at the input side .Since, the input voltage signal is more than acceptable maximum voltage, the determining means 102 detects a malfunction in the sensor working. If the rail pressure sensor 104 is working, the rail pressure sensor 104 measures the pressure of rail developing in the common rail after a predefined time set by the timer 103.The first comparing means 108 compares the rail pressure measured after the predefined time with the first predefined value set by the first reference means 106.The ecu 118 indicates a low rail pressure if the measured rail pressure is less than the first predefined value. If the rail pressure sensor 104 is not working, then the determining means 102 provides a signal to the replacing means 111 to replace a default pressure value in place of the actual pressure value. The replacing means 111 replaces the default pressure value as the actual rail pressure in the ecu 118 .Due to the replacement of the default pressure value in the ecu 118, the change in the actual rail pressure is not detected. If the actual rail pressure develops to an acceptable value in the common rail before the predefined time and if all the components of the engine are in operating condition, the engine will start. If the actual rail pressure has not developed to the acceptable value in the common rail before the predefined time and if all the components of the engine are in operating condition, the engine cannot start only due to the low rail pressure. And also, the rail pressure is directly proportional to the acceleration of the engine ,i.e, due to the low rail pressure the engine will have less acceleration .For instance, if the sensor is not working, replaces a default pressure value of 700 Bar in the ecu 118. If the actual rail pressure is more than 120 bar which is a value required to release the injections and if all the components of the engine are in operating condition, the engine will start and will have acceleration. If the actual rail pressure is less than 120 bar and if all the components of the engine are in operating condition, the starting of the engine will not happen only due to the low rail pressure and the engine will have less acceleration. If the rail pressure sensor 104 is not working, in order to check for the variation in the actual rail pressure, the acceleration of the engine is determined. The calculating means 110 calculates the current speed of the engine and the previous speed of the engine and calculates the acceleration from the current and the previous speeds of the engine. The second comparing means 116 compares the calculated acceleration with the second predefined value, set by a second reference means 112. The second predefined value is an acceleration value. For instance, if the acceleration is a ratio of the current speed and the previous speed of the engine, then the second predefined value which is an acceleration value is set in the range of 1.2 - 1. If the calculated acceleration is less than 1.2, then it is interpreted as there is no acceleration in the engine. The checking means 114 checks for at least one shutoff request from at least one component of the engine. There are different types of shut off requests associated with the components of the engine. For instance, the shutoff requests may be due to a short circuit between an injector energizing capacity bank and a supply from a battery or may be due to an error occurring in injector diagnostic chip or may be due to a short circuit between metering unit and ground or may be due to the increase in maximum allowed rail pressure (> 1780 bar). For instance, the ecu 118 has two injector energizing capacity banks which operate injector solenoid. If there is a short circuit occurred between one injector energizing capacity bank and the supply of the battery, then only one energizing capacity bank will operate and via function inhibitors a shutoff requested is given to the ecu 118.The ecu 118 indicates a low rail pressure only if the calculated acceleration is less than the second predefined value and if there are no shutoff requests were found from atleast one component of the engine.

[0011] Fig.3 is a flowchart illustrating the method to detect a low rail pressure during starting of an engine in a vehicle in accordance with this invention. In step S1, a determining means 102 determines the working of a rail pressure sensor 104.If the rail pressure sensor 104 is working then, the rail pressure of the common rail is measured by the rail pressure sensor 104 after a predefined time set by a timer at step s2(a). A first comparing means 108 compares the measured rail pressure with a first predefined value set by a first reference means 106 at step s3 (a). An ecu 118 indicates a low rail pressure if the measure rail pressure is less than the first predefined value at step s4 (a). If the rail pressure sensor 104 is not working, the determining means provides a signal to the replacing means 111 and the replacing means 111 replaces a default rail pressure as actual rail pressure in the ecu 118 in step S2 (b). The ecu 118 checks for atleast one shut off request from atleast one component of the engine in step s3(b) and simultaneously, the calculating means 110 calculates a current speed and a previous speed of the engine and calculates an acceleration of the engine in order to determine the variation in the rail pressure of the common rail in step s3(c). A second comparing means (116) compares the calculated acceleration with a second predefined value set by a second reference means 112 in step s4(b). The ecu 118 indicates a low rail pressure if the acceleration is less than the second predefined value and if there were no shutoff requests found in step s5(b).

[0012] It must be understood that the examples and embodiments of the components explained in the detailed description are only illustrative and do not limit the scope of the invention. The scope of this invention is only limited by the scope of the claims.