Claims:
We Claim:

1. A cold start timing device (10) for a high pressure fuel pump, said timing device (10) comprising:
a roller ring;
a plurality of rollers coupled to said roller ring;
a pin (16) comprising a first end (18) and a second end (20), said first end (18) coupled to said roller ring, said second end (20) coupled to a piston (22), wherein a bore (24) is defined within said piston (22) to facilitate channeling fuel to a space defined at an end of said bore (24) of said piston (22); characterized in that
a spool (26) positioned proximate to said pin (16) and adapted to permit channeling fuel within said bore (24) of said piston (22) by aligning a bore (28) of said spool (26) with said bore (24) of said piston (22), said spool (26) adapted to be actuated by means of a solenoid valve (30).

2. The cold start timing device (10) for the high pressure fuel pump in accordance with Claim 1 wherein said spool (26) is inserted within said solenoid valve (30) at one end, said solenoid valve (30) adapted to actuate said spool (26) to facilitate aligning the bore (28) of said spool (26) with said bore (24) of said piston (22) to permit channeling fuel within said bore (24) of said piston (22) of said timing device (10).

3. The cold start timing device (10) for the high pressure fuel pump in accordance with Claim 1 further comprising a spring member (32) positioned between said spool (26) and said solenoid valve (30), said spring member (32) adapted to restore said spool (26) to its original position after said spool (26) is deactivated by said solenoid valve (30).

4. The cold start timing device (10) for the high pressure fuel pump in accordance with Claim 1 wherein said solenoid valve (30) is activated by means of a switching mechanism.
, Description:Field of the invention
[0001] This invention relates to a timing device used in combination with a high pressure fuel pump during cold conditions.

Background of the invention
[0002] A timing device is used in a conventional high pressure pump. In order to compensate for injection and ignition lag, the timing device is required to advance the high pressure pump’s injection timing as the engine’s speed increases. In the absence of a timing device, fuel injection occurs at the engine’s top dead centre at all engine speeds. With the use of the timing device, injection of fuel occurs prior to or after the piston approached top dead centre at different engine speeds. At low engine speeds, the roller ring will be in a retracted position. However at higher engine speeds, the timing device is required to be advanced to ensure that the cam disc comes in contact with the timing device before the piston of the engine approaches the top dead centre position. In cold conditions, it is also required to advance the fuel injection prior to the top dead center of engine piston.
[0003] IN Patent Application Number 2208/CHE/2015 describes a cold start timing device for a high pressure pump. The timing device comprises a roller ring and a plurality of rollers coupled to the roller ring. A pin comprising a first end and a second end, the first end coupled to the roller ring, and the second end coupled to a piston. A first end of the piston is coupled to a spring element. An electromechanical actuator is coupled to a second end of the piston, the electromechanical actuator actuates the piston to facilitate advancing the timing device.

Brief description of the accompanying drawing
[0004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:
[0005] Figure 1 illustrates a spool that is positioned within a solenoid valve and a piston of a timing device in one embodiment of the invention.

Detailed description of the embodiments
[0006] A timing device 10 for a high pressure fuel pump is described. The timing device 10 comprises a roller ring and a plurality of rollers coupled to the roller ring. A pin 16 comprising a first end 18 and a second end 20, the first end 18 coupled to the roller ring, the second end 20 coupled to a piston 22, wherein a bore 24 is defined within the piston 22 to facilitate channeling fuel within the bore 24 of the piston 22. A spool 26 is positioned within the timing device 10 and adapted to permit channeling fuel within the bore 24 of the piston 22 by aligning a bore 28 of the spool 26 with the bore 24 of the piston 22. The spool 26 is adapted to be actuated by means of a solenoid valve 30.
[0007] Figure 1 illustrates a spool 26 that is positioned within a solenoid valve 30 and a piston 22 of a timing device 10 in one embodiment of the invention. The timing device 10 includes a roller ring. The roller ring includes an outer ring and an inner ring that is radially inward from the outer ring. The roller ring includes a plurality of rollers coupled between the outer ring and the inner ring of the roller ring. The roller ring is coupled to the piston 22 by means of a pin 16. Specifically, the pin 16 comprises a first end 18 and a second end 20. The first end 18 of the pin 16 is coupled to the roller ring, while the opposite second end 20 of the pin 16 is coupled to the piston 22.
[0008] The piston 22 includes a first end 23 and an opposite second end 25. When the second end 25 of the piston 22 is actuated via fuel that is channelled into a space defined between the second end 25 of the piston 22 and a housing, the piston 22 translates towards the direction of the solenoid valve 30. Therein, the second end 20 of the pin 16 that is coupled to the piston 22 is actuated along with the piston 22 due to the translation of the piston 22. The actuation of the pin 16 causes the roller ring to rotate in a clockwise direction. Thereby, the plurality of rollers that are coupled between the outer ring and the inner ring of the roller ring rotate with the roller ring in the clockwise direction. The rotation of the rollers in the clockwise direction causes the cam disc to advance with respect to the plurality of rollers. The movement of the cam disc with respect to the plurality of rollers causes the advancement of the timing device 10.
[0009] A first end of the spool 26 is positioned within the piston 22. A bore 28 is defined within the spool 26 and proximate to the first end of the spool 26. The bore 28 that is defined within the spool 26 is aligned with the bore 24 that is defined within the piston 22 to facilitate channelling fuel through the bore 24 defined within the piston 22. The second end of the spool 26 is positioned within the solenoid valve 30. When the solenoid valve 30 is energized, the spool 26 is actuated towards the solenoid valve 30. This causes an alignment of the bore 28 of the spool 26 with the bore 24 defined within the piston 22. The alignment of the bore 28 of the spool 26 with the bore 24 defined within the piston 22 causes fuel to flow through the bore 24 to the space defined at an end of the bore 24 of the piston 22. After the roller ring has been restored to its original position, the second end of the spool 26 is de-energized by cutting off the supply of power to the solenoid valve 30. This causes the spring member 32 to apply a restoring force on the spool 26, thereby causing the bore 28 of the spool 26 to misalign with the bore 24 defined within the piston 22. Therefore, fuel cannot flow through the bore 24 defined within the piston 22 to the space defined at an end of the bore 24 of the piston 22.
[0010] The principle of working of the timing device 10 for the high pressure fuel pump is now explained as an example. Fuel is channelled within the piston 22 from the housing of the high pressure fuel pump. The bore 28 of the spool 26 is misaligned with the bore 24 of the piston 22. Therein, fuel from the piston 22 cannot flow through the bore 24 that is defined within the piston 22 to the space defined at an end of the bore 24 of the piston 22. When the solenoid valve 30 is energized in cold conditions, the spool 26 is actuated towards the solenoid valve 30. This causes an alignment of the bore 28 of the spool 26 with the bore 24 that is defined within the piston 22. Therein, the fuel is channelled through the bore 24 of the piston 22 to the space defined at an end of the bore 24 of the piston 22. The pressurized fuel that is channeled to the space defined at the end of the bore 24 of the piston 22 causes the piston 22 to translate towards the direction of the spool 26, thereby causing the roller ring to rotate in a clockwise direction. Thereby, the plurality of rollers that are coupled between the outer ring and the inner ring of the roller ring rotate with the roller ring in the clockwise direction. The rotation of the rollers in the clockwise direction causes the cam disc to advance with respect to the plurality of rollers. The movement of the cam disc with respect to the plurality of rollers causes the advancement of the timing device 10.
[0011] After the advancement of the timing device 10 is complete, the spool 26 is de-energized by shutting off the supply of power to the solenoid valve 30 when the engine warms up. This causes the spring member 32 to apply a restoring force on the spool 26, thereby causing the bore 28 of the spool 26 to misalign with the bore 24 that is defined within the piston 22. Therefore, fuel cannot flow through the bore 24 that is defined within the piston 22 to the space defined at an end of the bore 24 of the piston 22. Therefore, the piston 22 is not translated towards the direction of the spool 26, therefore maintaining the equilibrium position of the roller ring. Energizing / de-energizing of the solenoid 30 is done through a thermal switch which is based on the temperature of coolant in engine.
[0012] 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. The scope of this invention is limited only by the scope of the claims. Many modification and changes in the embodiments aforementioned are envisaged and are within the scope of this invention.