Claims:We Claim:

1. A pressure-limiting apparatus (100) mounted on to fuel rail (202) of a common rail fuel injection system, comprising:
a casing (102), comprising;
a spring element (105) positioned between a top plate (103) and a bottom plate (104), and adapted to compress on application of fuel pressure in the fuel rail;
a valve member (106) set up with the bottom plate (104) and adapted to provide axial movement to the spring element (105) via the bottom plate (104);
characterized that pressure-limiting apparatus (100) further comprising a piezo element (107) positioned inside the casing (102) and placed on to the top plate (103), wherein the piezo element (107) adapted to generate an electrical voltage signal based on a compression load on the spring element (105), which is lifted by the bottom plate (104) and the valve member (106) set up.

2. The pressure-limiting apparatus (100) as claimed in claim 1, wherein the electrical voltage signal generated by the piezo element (107) can be read by engine control unit (110) of the common rail fuel injection system.

3. The pressure-limiting apparatus (100) is adapted to provide real-time count of pressure-limiting valve openings for the common rail fuel injection system.

4. The pressure-limiting apparatus (100) as claimed in claim 1, wherein the compression load on the spring element (105) is subject to increase in fuel rail pressure and a sudden drop thereafter.

5. The pressure-limiting apparatus (100) as claimed in claim 1, wherein the casing (102) further comprising a number of non-metallic spacers positioned such that to stop any movement of the piezo element (107).
, Description:Complete Specification:

The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed.

Field of the invention
[0001] Present invention relates to the field of common rail fuel injection system of a vehicle. The invention relates in specific to a pressure-limiting apparatus for providing real-time count of pressure-limiting valve openings, monitored by ECU.

Background of the invention
[0002] In a common rail fuel injection system, the high-pressure circuit features an integrated mechanical pressure-limiting valve (PLV) for safety reasons, this valve is mounted on the fuel rail of the common rail fuel injection system. When, the pressure exceed the permissible level, fuel is returned via the pressure-limiting valve to the low pressure circuit.

[0003] Pressure-limiting valve (PLV) prevents the fuel pressure from reaching unacceptably high levels when the fuel-supply control valve is non-operational. The PLV limits the fuel pressure in the high-pressure system to a value below the burst pressure. On the other hand, the PLV ensures the operation of the high-pressure fuel injectors through the flat pressure curve over the volumetric flow even in normal operation at operating points without fuel-supply control intervention such as overrun and shutdown. To be exact, no fuel is injected at these operating points such that the stored quantity is heated up by the heat from the engine. Each degree of temperature rise results in a pressure increase of roughly 1MPa. If the pressure is too high, the fuel injector is no longer able to open against the high fuel pressure. This means that reuse after overrun fuel cutoff or short-term restarting of the engine after a hot shutdown would not be possible without pressure limitation. Thus, the pressure limiting valve (PLV) reduces the system pressure in case of overload and thus protects the other injection components from damage.

[0004] The prior art US8511275 discloses a common rail fuel system for an engine of a vehicle, such as a locomotive, comprises a higher-pressure fuel sub-system and a lower-pressure fuel sub-system, wherein a pressure limiting valve, is in fluid communication with to the higher-pressure fuel sub-system to relieve excess pressure. In a condition where pressure of the higher-pressure fuel sub-system is below a desired and expected threshold, it is possible that the pressure limiting valve is open. An example method is provided to close the pressure limiting valve and determine if opening of the pressure limiting valve is the cause of the pressure being below the threshold or if a leak is present in the common rail fuel system. In this manner, unnecessary disabling of the engine is avoided and, if a leak is present, the leaking sub-system is identified.

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 pressure-limiting apparatus for a common rail fuel injection system, according to one embodiment of the invention.

Detailed description of the embodiments
[0007] FIG. 1 illustrates a pressure-limiting apparatus 100 for a common rail fuel injection system. The pressure-limiting apparatus 100 is mounted on to a fuel rail 202 of the common rail fuel injection system. The pressure-limiting apparatus 100 is provided for protection, from an inadmissibly high pressure level in the fuel rail 202, and it opens at an increased pressure level. When the pressure-limiting apparatus 100 opens, fuel is released from the fuel rail 202 via return fuel line to the fuel tank in a controlled manner. As a result, the pressure level in the fuel rail 202 drops to a lower value below a desired upper limit.

[0008] The pressure-limiting apparatus 100 comprises a casing 102, a spring element 105, a valve member 106 and a piezo element 107. The pressure-limiting function is integrated by way of the valve member 106 and the spring element 105, to protect the components against unacceptably high rail pressures, for example, in the event of actuation failure. Each component is described in further detail below.

[0009] The operation of the common rail fuel injection system is controlled by an electronic control unit (ECU) 110. The ECU 110 includes the usual components of a microcomputer system, such as for example, a microprocessor, I/O components, buffer and storage components (e.g. EEPROM, RAM). In the storage components, the operational data relevant for the operation of the internal combustion engine are deposited in the form of performance graphs or characteristic curves.

[0010] The casing 102 comprising a top plate 103, a spring element 105 and bottom plate 104. The spring element 105 is positioned between the top plate 103 and the bottom plate 104 and adapted to compress on application of fuel pressure. The spring element 105 is adapted to compress on application of fuel pressure in the fuel rail. The valve member 106 positioned set up with the bottom plate 104 and adapted to provide axial movement to the spring element 105 via the bottom plate 104. In one embodiment, the top plate 103 is adapted to provide a separation for piezo element 107 and spring element 105.

[0011] The piezo element 107 positioned inside the casing 102 and placed on to the top plate 103. The piezo element 107 adapted to generate an electrical voltage signal based on a compression load on the spring element 105, which is lifted by the bottom plate 104 and the valve member 106 set up. In one embodiment, the piezo element 107 is positioned at the top plate 103 by means of connectors.

[0012] In operation a high-pressure fuel pump pressurizes fuel and delivers fuel to the fuel rail 202 through a conduit. The working of the pressure-limiting apparatus 100 for controlling the fuel pressure from reaching unacceptably high levels, is described as an example. The pressure-limiting apparatus 100 limits the fuel rail 202’s pressure to a maximum value and keep it in the desired range. Primarily, the pressure-limiting apparatus 100 is closed and only in case of the fuel rail pressure increase it opens and starts to control the pressure in the high pressure circuit.

[0013] When pressure increase in the fuel rail 202, the increased pressure causes the valve member 106 to push the bottom plate 104. Therein, that push will cause the axial movement to the spring element 105, which is positioned in between the top plate 103 and the bottom plate 104. This axial movement will create mechanical pressure, which is then applied to the piezo element 107, thereby forces the electric charges within the piezo element 107. In general, the piezo element 107 convert mechanical stress applied onto it, to electrical energy. In one embodiment, the piezo element 107 made up of crystals which are polar in nature without electrical field being applied.

[0014] When no force is applied on the piezo element 107, the charges are exactly balanced and the net dipole moment is zero producing zero electrical voltage across its terminals. In one embodiment, a bridge rectifier 108 is connected to the piezo element 107 in the casing 102, and adapted to stabilize the output of the piezo element 107. In this embodiment, the bridge rectifier 108 helps in converting the possible AC output from the piezo element to DC, hence avoiding any negative voltage from the piezo element.

[0015] In one embodiment, the piezo element 107 is fixed to its position in order to arrest accurate movement of the spring element 105. The piezo element 107 is not movable with the movement of the spring element 105. In one embodiment, the casing 102 further comprising a number of non-metallic spacers positioned such that to stop any movement of the piezo element 107. In an exemplary embodiment, the non-metallic spacers may be used in any number depending on the spring element 105’s setting required.

[0016] Further, the electrical voltage signal generated by the piezo element 107 can be read by ECU 110 of the common rail fuel injection system. In one embodiment, the piezo element 107 is connected to the ECU 110 via the bridge rectifier 108. The output from the piezo element 107 is directly proportional to the mechanical stress induced by the spring element 105. As the spring element 105, starts compressing on application of fuel pressure in the fuel rail 202, the output of the piezo element 107, is increases. In one embodiment the compression in the spring element 105 is directly proportional to increase in fuel pressure in the fuel rail 202 and a sudden drop thereafter.

[0017] Furthermore, after receiving the electrical voltage signal from the piezo element 107, the ECU 110 will calculate the real-time counting of opening of the pressure-limiting apparatus 100. Further, ECU will recognize the increase in the output of the piezo element 107, and based on received electrical voltage signal, ECU will consider as a PLV opening and will keep count of number of openings.

[0018] By using the pressure-limiting apparatus 100, the life and performance of a common rail fuel injection system is increased. As the output of piezo element 107 correlates with the accurate time and count of pressure-limiting apparatus 100 openings. Thereby avoiding the pseudo opening counts and eliminate pseudo errors in the system.

[0019] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. 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 claim.