Claims:We claim
1. An actuation mechanism (10) for a fuel pre-supply pump (12), said fuel pre-supply pump (12) comprising at least a plunger (14) driven by a roller tappet (16), said actuation mechanism (10) comprising:
- a movable cam-sleeve (18) mounted on a cam shaft (20) in a manner such that at least a part of said movable cam-sleeve (18) is in contact with said roller tappet (16) of said fuel pre-supply pump (12);
- a first roller (22) fitted on said movable cam-sleeve (18) and a second roller (24) positioned away from first roller (22);
- a handle (26) having a cable (28) extending therefrom, said cable (28) adapted to be wound around said first roller (22) and said second roller (24) in a manner such that rotation of said handle (26) causes said cable (28) to be pulled thereby displacing the movable cam sleeve (18).
2. The actuation mechanism (10) as claimed in claim 1, said actuation mechanism (10) comprising two end plates (30, 32) located at either end of said movable cam sleeve (18), said end plates (30, 32) adapted to support and restrict movement of said movable cam sleeve (18).
3. The actuation mechanism (10) as claimed in claim 2, wherein one end of said movable cam sleeve (18) abuts said end plate (30).
4. The actuation mechanism (10) as claimed in claim 2, wherein second end of said movable cam sleeve (18) is spring (34) supported against said end plate (32).
5. The actuation mechanism (10) as claimed in claim 1, wherein said cam shaft (20) has external gear teeth (36) and said movable cam-sleeve (18) has internal gear teeth (38) such that during mounting of said movable cam-sleeve (18) onto said cam shaft (20) said external gear teeth (36) and said internal gear teeth (38) mesh with each other.
6. The actuation mechanism (10) as claimed in claim 1, wherein said cam shaft (20) comprises a radial bore (40).
7. The actuation mechanism (10) as claimed in claim 1 and 6, wherein said movable cam-sleeve (18) has at least two grooves (42,44), at least one groove of said at least two grooves (42, 44) adapted to align with said radial bore (40) in said cam shaft (20).
8. The actuation mechanism (10) as claimed in claim 1, 6 and 7, said actuation mechanism (10) comprising a ball (46) and a spring (48) arrangement located in said radial bore (40) in a manner such that in a first position of said movable cam-sleeve (18) said ball (46) engages said one groove (40) and in a second position of said movable cam sleeve (18) said ball (42) engages said second groove (42) in said movable cam-sleeve (18)
9. The actuation mechanism (10) as claimed in claim 1, wherein at least a part said movable cam-sleeve (18) which is in contact with said roller tappet (16) of said fuel pre-supply pump (12) has a first feature (50) which provides a first lift to said roller tappet (16).
10. The actuation mechanism (10) as claimed in claim 1, wherein at least a part of said movable cam-sleeve (18) which is in contact with said roller tappet (16) of said fuel pre-supply pump (12) has a second feature (52) which provides a second lift to said roller tappet (16). , Description:Field of the invention
[0001] This disclosure relates to an actuation mechanism for a fuel pre-supply pump.

Background of the invention:
[0002] The invention relates to a process for generating and delivering high-pressure fuel to a high-pressure storage chamber of a fuel injection system, in particular a common rail injection system, of an internal combustion engine, wherein by means of a low-pressure pump as a pre-feed pump, fuel is supplied from a tank and is delivered to the intake side of a high-pressure pump and wherein a part of the fuel delivered by the low-pressure pump is used to lubricate the high-pressure pump.
[0003] The delivery volume or the delivery capacity of the low-pressure pump and high-pressure pump must be designed so that a sufficient quantity of high-pressure fuel is always available. However, since the high-pressure pump is usually driven as a function of the motor speed, the available fuel quantity is usually too high in comparison with the required fuel quantity, for example when the driver of a vehicle "lets up on the gas" at a high speed and the vehicle is coasting. The fuel quantity delivered by the high-pressure pump is still very high, but it is not required by the injection system of the internal combustion engine. When a threshold pressure is reached under such circumstances, a pressure regulating valve provided on the high-pressure side is normally opened and a connection to the tank is produced. The fuel is therefore fed in the circuit and is very intensely heated with this high-pressure-side, so-called rail pressure regulation, which is accompanied by dangers. In addition, the use of return lines made of plastic is critical and the overall motor efficiency decreases with high power consumption by the high-pressure pump.
[0004] The fuel lubricated high pressure pumps known in the state of the art can be described as follows. The fuel lubricated high pressure pumps comprises three main parts from the point of view of the flow of fuel within the fuel lubricated high pressure pump viz a low pressure circuit, the pump chamber or pump room and a high pressure circuit. The low pressure circuit of the pump include all flow paths within the high pressure pump which carries fuel before it is sent to the pumping chamber for pressurizing. The pump chamber or pump room is the part of the high pressure fuel pump which houses a polygonal ring which rotates within the pump chamber in a manner such that the rotation of the polygonal ring causes the plunger within the pump to pressurize the fuel. Once the fuel is pressurized it is sent from the pumping chamber to the common rail through the high pressure circuit. The high pressure circuit of the high pressure fuel pump includes all the flow paths within the high pressure pump which are downstream from the pumping chamber.
[0005] The high pressure pumps also have an overflow valve. The overflow valve regulates the low pressure in the pump and the quantity of fuel that flows back into the tank. The fuel which flow out of the overflow valve is also used for cooling the pump. In one embodiment of the fuel lubricated high pressure pump, the cooling flow of the pump comprises at least a part of the high pressure fuel quantity, at least a part of the backflow fuel quantity and at least a part of the low pressure fuel quantity flowing through the overflow valve. In another embodiment of the fuel lubricated high pressure pump, the cooling flow of the pump comprises at least a part of the backflow fuel quantity and at least a part of the low pressure fuel quantity and an additional low pressure metering unit is implemented to regulate the quantity of fuel that is delivered from the high pressure pump.

Brief description of the accompanying drawings:
[0006] An embodiment of the disclosure is described with reference to the following accompanying drawings;
[0007] Figure 1 illustrates the actuation mechanism for a fuel pre-supply pump.
Detailed description of the embodiments:
[0008] Figure 1 illustrates an actuation mechanism 10 for a fuel pre-supply pump 12. The fuel pre-supply pump 12 comprises at least a plunger 14 driven by a roller tappet 16. The actuation mechanism 10 comprises: a movable cam-sleeve 18 mounted on a cam shaft 20 in a manner such that at least a part of the movable cam-sleeve 18 is in contact with the roller tappet 16 of the fuel pre-supply pump 12, a first roller 22 is fitted on the movable cam-sleeve 18 and a second roller 24 is positioned away from the first roller 22, a handle 26 having a cable 28 extends therefrom. The cable 28 is adapted to be wound around the first roller 22 and the second roller 24 in a manner such that rotation of the handle 26 causes the cable 28 to be pulled thereby displacing the movable cam sleeve 18. In accordance with one embodiment of this disclosure the cable 28 used is a Bowden cable.
[0009] Further constructional details of the actuation mechanism can be explained as follows with reference to figure 1. The actuation mechanism 10 comprises two end plates 30, 32 located at either end of the movable cam sleeve 18. The end plates 30, 32 are adapted to support and restrict movement of the movable cam sleeve 18. The movable cam-sleeve is located in between the two end plates 30 and 32 in a manner such that one end of said movable cam-sleeve 18 abuts the end plate 30. The movable cam-sleeve is located in between the two end plates 30 and 32 in manner such that the second end of the movable cam sleeve 18 is spring 34 supported against the end plate 32. The spring 34 restricts the movement of the movable cam-sleeve 18 and also pushes the movable cam-sleeve 18 to a position wherein it abuts the end plate 30.
[00010] As mentioned earlier the movable cam-sleeve is mounted on a cam shaft 20. The cam shaft 20 has external gear teeth 36 and the movable cam-sleeve 18 has internal gear teeth 38 such that during mounting of the movable cam-sleeve 18 onto the cam shaft 20 the external gear teeth 36 and the internal gear teeth 38 mesh with each other. The cam shaft 20 comprises a radial bore 40. The radial bore 40 is located in proximity of the first roller 22. The movable cam-sleeve 18 has at least two grooves 42 and 44, at least one groove of the at least two grooves 42, 44 are adapted to align with the radial bore 40 in the cam shaft 20. The actuation mechanism 10 comprises a ball 46 and a spring 48 arrangement which is located in the radial bore 40 in a manner such that in a first position of the movable cam-sleeve 18, the ball 42 engages one groove 40 and in a second position of the movable cam-sleeve 18 the ball 42 engages the second groove 42 in the movable cam-sleeve 18.
[00011] As described in the earlier paragraph, at least a part of the movable cam-sleeve 18 is in contact with the roller tappet 16 of the fuel pre-supply pump 12. The part of the movable cam-sleeve 18 which is in contact with the roller tappet 16 of the fuel pre-supply pump 12 has a first feature 46 which provides a first lift to the roller tappet 16. Further, the part of the movable cam-sleeve 18 which is in contact with the roller tappet 16 of the fuel pre-supply pump 12 has a second feature 46 which provides a second lift to the roller tappet 16.
[00012] From the overall system perspective the actuation mechanism 10 can be explained as follows. The actuation mechanism 10 forms a part of the overall fuel injection system. The components of the fuel injection system described below are only those which are important for the functioning of the actuation mechanism 10. A person skilled in the art will be aware of the other components of the fuel injection system known in the state of the art. The fuel injection system normally comprises a tank where fuel is stored. A fuel pre-supply pump or a feed pump which may be either located inside the tank or may be external to the tank. The function of the fuel pre-supply pump is to supply fuel from the fuel tank to the high pressure pump. For the purposes of this disclosure the main part of the fuel pre-supply pump 12 is the roller tappet 16. The roller tappet 16 is the part of the fuel pre-supply pump 12 which displaces the plunger of the fuel pre-supply pump 12. In fuel pre-supply pumps known in the state of the art the lift that is provided by the roller tappet 16 to the plunger of the fuel pre-supply pump is constant. Also the fuel pre-supply pumps known in the state of the art are directly driven by the cam shaft 20. The cam shaft 20 is driven by the engine (not shown in figures). In accordance with this disclosure there is provided an actuation mechanism 10 for a fuel pre-supply pump 12 which is mounted on the cam shaft 20 and has the possibility of varying the lift of the plunger of the fuel pre-supply pump 12 such that the final quantity of fuel that is delivered to the high pressure pump can be varied. The actuation mechanism 10 of this disclosure also provides the flexibility to the user to vary the lift of the plunger.
[00013] The working principle of the actuation mechanism 10 and the subsequent working of the fuel injection system can be explained as follows. The actuation mechanism 10 is operated such that the variable filling of the high pressure pump is possible by varying the stroke of the fuel pre-supply pump 12. Thus, varying the stroke of the fuel pre-supply pump 12 also provides the flexibility for high pressure shaping of the high pressure pump in the fuel injection system.
[00014] The detailed working of the actuation mechanism 10 can be explained as follows. For the ease of understanding we assume that engine operation is in high engine speed range for example 3000rpm or more. While the vehicle is being operated in the high speed range, the actuation mechanism 10 of the fuel pre-supply pump 12 is in a position such that the ball 46 engages the groove 42. When the ball 46 engages in the groove 42, the first feature 50 of the movable cam-sleeve 18 is in contact with the roller tappet 16 of the fuel pre-supply pump 12. During the engine operation due to the conditions that may or may not be in the control of the vehicle driver, the speed of the vehicle is reduced consequently the engine speed also reduces. As the engine speed reduces to value for example 1500rpm, the vehicle driver turns the handle 26 of the actuation mechanism 10. As the handle is turned, the Bowden cable 28 which is attached to the handle 26 is pulled in a manner such that the cable 28 pulls the movable cam-sleeve 18 in a manner such that the ball 46 is displaced from the groove 42 and engages the groove 44. While moving from groove 42 to groove 44, the spring 48 is compressed. When the ball 46 engages the groove 44, the spring ensures that the ball 46 remains locked in that position. When the movable cam-sleeve 18 is pulled and the ball 46 engages the groove 44, the second feature 52 of the movable cam-sleeve 18 comes in contact with the roller tappet 16 of the fuel pre-supply pump 12. Thus when the feature 52 comes in contact with the movable cam-sleeve 18, the lift of the plunger 14 of the fuel pre-supply pump 12, is varied. The lift of the plunger 14 is increased. The increase in the lift of the plunger ensures that the amount of fuel that is getting delivered to the high pressure pump from the fuel pre-supply pump 12 increases. This also ensures the pressure of the fuel that is being sent from the fuel pre-supply pump 12 to the high pressure pump is higher, when the feature 50 of the movable cam-sleeve 18 is in the contact with the roller tappet 16. Thus, at lower engine speeds, the actuation mechanism 10 of the fuel pre-supply pump is operated in a manner such that fuel is delivered at high pressure to the fuel injection pump increasing the pump filing efficiency and thereby injection pressure at lower speeds.
[00015] Further, while the engine is being operated, when the engine speed increases, the vehicle driver turns the handle of the actuation mechanism 10. The Bowden cable 28 which is attached to the handle 26 is pulled in a manner such that the cable pulls the movable cam-sleeve 18 in a manner such that the ball 46 is displaced from the groove 44 and engages the groove 42. While moving from groove 44 to groove 42, the spring 48 is compressed. When the ball 46 engages the groove 42, the spring ensures that the ball 46 remains locked in that position. When the movable cam-sleeve 18 is pulled and the ball 46 engages the groove 42, the first feature 50 of the movable cam-sleeve 18 comes in contact with the roller tappet 16 of the fuel pre-supply pump 12. Thus when the feature 50 comes in contact with the movable cam-sleeve 18, the lift of the plunger 14 of the fuel pre-supply pump 12, is varied. The lift of the plunger 14 is reduced. The reduction in the lift of the plunger ensures that the amount of fuel that is getting delivered to the high pressure pump from the fuel pre-supply pump 12 reduces. Thus, at higher engine speeds, the actuation mechanism 10 of the fuel pre-supply pump is operated in a manner such that the fuel pre-supply pump pressure will be set such that the fuel supply to the fuel injection pump is just able to pump the fuel at required injection pressure.
[00016] Thus in accordance with this disclosure there is provided an actuation mechanism 10 for a fuel pre-supply pump 12, which can be used in fuel injection system which comprises at least a high pressure fuel pump which receives fuel from the fuel pre-supply pump 12. The actuation mechanism 10 is a simple system without any electrical actuation and provides the flexibility of variable filling of the high pressure pump by stroke variation of the fuel pre-supply pump 12. The stroke variation of the fuel pre-supply pump 12 also allows the flexibility of high pressure shaping of the high pressure pump. The actuation mechanism 10 allows operation of the fuel pre-supply pump 12 in a manner such that even at lower rpm and low load of the engine due to the increased lift the high pressure output can be maintained. This also provides an improved soot/NOx trade off due to improved filing of the high pressure pump due to the variable lift of the fuel pre-supply pump 12.
[00017] It must be understood that the embodiments and the working of the actuation mechanism explained in the above detailed description is only illustrative and does not limit the scope of this invention from the point of view type of the cable, types of rollers used, type of the handle used or how high engine speed or low engine speed is defined. 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.