GB2543519A

GB2543519A - High pressure fuel pump with torque limiter device

Info

Publication number: GB2543519A
Application number: GB1518517.6A
Authority: GB
Inventors: D Wilson Neil; Rajaram Kartik; Voigt Peter; John Mccrindle Christopher
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2015-10-20
Filing date: 2015-10-20
Publication date: 2017-04-26
Also published as: GB201518517D0

Abstract

A high pressure fuel pump, eg of engine fuel injection equipment, is provided with a pumping unit 30 having a first spring 38 biassing with a first force a first cam follower 36, eg a roller shoe, against a cam 28, the cam rotating about a cam axis Z to reciprocally actuate a first plunger 34 along a pumping axis Y. The first force generates on the cam 28 and about the cam axis Z a first torque which varies as a function of the angular position of the cam 28. The high pressure pump 22 is further provided with a torque limiter device 40 generating on the cam 28, and about the cam axis Z, a second torque compensating at least partially the first torque. The torque limiter device 40 may comprise a second spring 46 biassing a second cam follower 42, eg a second roller shoe, against the cam 28 with a second force along a second axis X eg at 90o to the first axis Y. Peak drive torque is thereby reduced and timing belt life extended.

Description

High pressure fuel pump with torque limiter device

TECHNICAL FIELD

The present invention is about the fuel pump of an engine fuel injection equipment. It more particularly relates to a torque limiter device arranged to cooperate with the pumping device in order to minimize a torque induced on the engine.

BACKGROUND OF THE INVENTION

The durability of timing drive belts on common rail diesel engines is largely influenced by the peak drive torque applied to the belt. This comes from a number of sources, but one of the primary contributors is the high pressure Common Rail fuel pump.

Peak drive torque is a function of fuel pressure and delivery and hence increases with injection pressure, as new requirements drive pump pressures higher, then the drive torque is also increasing. To maintain timing belt durability, then the peak drive torque needs to be limited.

Currently, high pressure pumps feature a ‘Roller-Shoe’ driven by a camshaft, where the drive torque is primarily a function of pump pressure and delivery. Typically, there is no apparatus to limit the peak drive torque.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a high pressure pump provided with a pumping unit having a first plunger, a first spring and a first cam follower arranged so that, in use, the first spring biases with a first force the first cam follower against a cam. The cam is adapted to rotate about a cam axis in order to reciprocally actuate the first plunger along a pumping axis between a Top Dead Centre position TDC and a Bottom Dead Centre position BDC. The pumping axis is perpendicular to the cam axis and, the first force generates on the cam and about the cam axis a first torque Ml which varies as a function of the angular position of the cam,

Advantageously, the high pressure pump is further provided with a torque limiter device generating on the cam, and about the cam axis a second torque compensating at least partially the first torque. To compensate the first torque, the second torque has to be in the opposite direction.

More precisely, the torque limiter device comprises a second spring and a second cam follower arranged so that, in use, the second spring biases the second cam follower against the cam with a second force, said second force generating the second torque M2.

The second force is generated along a second axis that is angled with the pumping axis and comprised in a plan perpendicular to the cam axis. The second cam follower reciprocally translates along said second axis between a Top Dead Centre TDC position and a Bottom Dead Centre BDC position.

In a specific embodiment, the first spring and the second spring have same stiffness.

In another embodiment the first spring and the second spring have different stiffness.

Hence, the angle between the pumping axis and the second axis is arranged so that when the first cam follower translates along the pumping axis toward TDC, the second cam follower translates along the second axis toward BDC.

More particularly, the angle between the pumping axis and the second axis is arranged so that when the first cam follower translates along the pumping axis toward BDC, the second cam follower translates along the second axis toward TDC and, the angle between the pumping axis and the second axis is arranged so that when the first cam follower is at TDC, the second cam follower is at BDC.

In a specific embodiment, the angle between the pumping axis Y and the second axis X is substantially 90°.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is a general isometric view of an engine equipped with a high pressure pump as per the invention.

Figure 2 is a view of the high pressure pump of figure 1.

Figure 3 is a schematic representation of figure 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In reference to the figures is represented the internal structure of a known internal combustion engine 10 where the rotations of the crankshaft 12 are transmitted to a camshaft 14 via a timing belt 16 tensioned between a driving pulley 18, fixed to the crankshaft 12, and a driven pulley 20, fixed at an extremity of the camshaft 14. The engine 10 further comprises fuel injection equipment which representation is limited to a high pressure pump 22 driven in rotation by the camshaft 14 via a gear train 24 that is arranged opposite the driven pulley 20. In the context of the present application the fuel flowing through said pump 22 may be pressurized to 2500 bars or more.

The high pressure pump 22 comprises a housing defining an internal volume and being provided with aligned bearings enabling a pump camshaft 26 to rotate around a rotation axis Z, the pump camshaft 26 being driven by the gear train 24. The pump camshaft 26 is provided with at least one cam 28 cooperating with at least one pumping unit 30. A known pumping unit 30 includes a pump head 32 provided with a blind bore defining at one end a fuel compression chamber whose volume varies under the influence of the motion of a first plunger 34 sliding in the blind bore.

The first plunger motions are induced by a first roller shoe 36 fixed to an end of the first plunger 34 and which cooperates with the cam 28. As the cam 28 rotates, the first plunger 34 axially translates along a pumping axis Y, or first axis Y, between a top dead center (TDC) position and a bottom dead center position (BDC).

In alternative embodiments instead of roller shoe having a roller rolling on the cam and following its profile, high pressure pumps are provided with cam followers ensuring similar function. Although the illustrated example shows roller shoe, the teachings of the present invention are applicable to any type of cam followers

The first roller shoe 36 is forced in contact against the cam 28 by a first spring 38 arranged around the first plunger 34 and compressed between the pumping head 32 and the first roller shoe 36. The axial force FI, or first force FI, imparted by the first spring 38 to the first roller shoe 36 is transmitted to the cam 28 perpendicularly to the tangent T to the contact point C between the first roller and the cam.

In the simplified illustration of figure 3, the pumping axis Y intersects the rotation axis Z and therefore, in any intermediate position between BDC and TDC, such as on figure 3, the contact point C is not on the pumping axis Y, from which it is offset, and the tangent T is not perpendicular to the pumping axis Y, from which it is angled as a function of the cam profile. Therefore the first force FI is transmitted to the cam in a first transmitted force FT1 angled relative to the pumping axis Y and it generates on the cam 28 a pumping torque Ml, or first torque Ml, along the rotation axis Z.

When moving from BDC to TDC, as in figure 3 considering the counter clockwise rotational direction R of the cam 28, the first plunger 34 enters the pumping head 32 and the volume of the compression chamber diminishes so the fuel therein pressurizes. In this phase of the rotation, the pumping torque Ml increases and resists the rotation of the cam since, in addition to the compression of the first spring 38, the first plunger has to pressurize the fuel.

Once passed TDC, and moving toward BDC, the first plunger 34 exits the pumping head 32, the first spring extends and the volume of the compression chamber increases for non-pressurized fuel to enter. In this phase, the pumping torque Ml has changed direction and is driving the rotation.

The present invention consists in providing a torque limiter device 40 generating on the cam 28 a second torque M2 substantially compensating the pumping torque Ml.

On the illustrated example, the torque limiter device 40 is similar to the pumping unit 30 and is offset relative to it by 90°. The torque limiter device 40 comprises a second roller shoe 42 fixed at the end of a second plunger 44, the second roller shoe 42 being pressed against the cam 28 by a second compression spring 46 so that the second roller shoe 42 generates on the cam 28 a second spring force F2 along a second axis X. Similarly to the first spring force FI, the second force F2 generates on the cam 28 a second transmitted force FT2 creating a second torque M2 and, in order for said second torque M2 to provide compensation to the first torque Ml, the second axis X is angularly offset relative to the pumping axis Y.

In the illustration of figure 3, said offset angle is a right angle of 90° so that, when the pumping unit 30 is at TDC, the torque limiter device 40 is at BDC and, when the pumping unit 30 is at BDC, the torque limiter device 40 is at TDC. The torque limiter device 40 and the pumping unit 30 operate in phase opposition so, when one generates a driving torque, the other one generates a resisting torque.

Conclusive results have been obtained where the first torque Ml gets compensated by a second torque M2 resulting in a 20% decrease of the peak torque and therefore a timing belt life duration extension. Other tests have been performed varying the angular offset of the pumping axis Y and of the second axis X as well as the relative spring stiffness’s, the first 38 and second 46 springs having the same stiffness or different stiffness’s.

The person skilled in the art of high pressure pumps will easily derive from the above example and teachings a torque limiter device adapted to alternative embodiments of high pressure pumps. In particular, whatever is the cam profile, number of lobes on the cam, two, or three or more, the angular offset between a pumping unit 30 and a torque limiter device 40 is to be selected so the pumping unit 30 and the torque limiter device 40 operates in phase opposition.

LIST OF REFERENCES X compensating axis Y pumping axis Z rotation axis TDC top dead center BDC bottom dead center T tangent C contact point R rotational direction of the cam FI spring force - first force FT1 first transmitted force

Ml pumping torque - first torque M2 second torque F2 second force FT2 second transmitted force 10 engine 12 crankshaft 14 camshaft 16 timing belt 18 driving pulley 20 driven pulley 22 high pressure pump 24 gear train 26 pump camshaft 28 cam 30 pumping unit 32 pumping head 34 first plunger 36 first roller shoe - first cam follower 38 first spring 40 torque limiter device 42 second roller shoe - second cam follower 44 second plunger 46 second spring

Claims

1. High pressure fuel pump (22) provided with a pumping unit (30) having a first plunger (34), a first spring (38) and a first cam follower (36) arranged so that, in use, the first spring (38) biases with a first force (FI) the first cam follower (36) against a cam (28), the cam being adapted to rotate about a cam axis (Z) in order to reciprocally actuate the first plunger (34) along a pumping axis (Y) between a Top Dead Centre position (TDC) and a Bottom Dead Centre position (BDC), the pumping axis (Y) being perpendicular to the cam axis (Z) and, the first force (FI) generating on the cam (28) and about the cam axis (Z) a first torque (Ml) which varies as a function of the angular position of the cam (28), characterized in that the high pressure pump (22) is further provided with a torque limiter device (40) generating on the cam (28), and about the cam axis (Z), a second torque (M2) compensating at least partially the first torque (Ml).

2. High pressure fuel pump (22) as claimed in the preceding claim wherein the torque limiter device (40) comprises a second spring (46) and a second cam follower (42) arranged so that, in use, the second spring (46) biases the second cam follower (42) against the cam (28) with a second force (F2), said second force generating the second torque (M2).

3. High pressure fuel pump (22) as claimed in claim 2 wherein the second force (F2) is generated along a second axis (X) that is angled with the pumping axis (Y) and comprised in a plan perpendicular to the cam axis (Z), the second cam follower (42) reciprocally translating along said second axis (X) between a Top Dead Centre position (TDC) and a Bottom Dead Centre position (BDC).

4. High pressure fuel pump (22) as claimed in any one of the claims 2 or 3 wherein the first spring (38) and the second spring (46) have same stiffness.

5. High pressure fuel pump (22) as claimed in any one of the claims 2 or 3 wherein the first spring (38) and the second spring (46) have different stiffness.

6. High pressure fuel pump (22) as claimed in any one of the claims 4 or 5 wherein the angle between the pumping axis (Y) and the second axis (X) is arranged so that when the first cam follower (36) translates along the pumping axis (Y) toward TDC, the second cam follower (42) translates along the second axis (X) toward BDC.

7. High pressure fuel pump (22) as claimed in any one of the claims 4 to 6 wherein the angle between the pumping axis (Y) and the second axis (X) is arranged so that when the first cam follower (36) translates along the pumping axis (Y) toward BDC, the second cam follower (42) translates along the second axis (X) toward TDC.

8. High pressure fuel pump (22) as claimed in any one of the claims 4 to 7 wherein the angle between the pumping axis (Y) and the second axis (X) is arranged so that when the first cam follower (36) is at TDC, the second cam follower (42) is at BDC.

9. High pressure fuel pump (22) as claimed in any one of the claims 3 to 8 wherein the angle between the pumping axis (Y) and the second axis (X) is substantially 90°.