GB2326677A - Fuel pump - Google Patents

Description

FUEL PUMP This invention relates to a fuel pump for use in supplying fuel under pressure to the cylinders of an associated internal combustion engine, for example a compression ignition internal combustion engine.

In a known fuel pump, a rotatable distributor member is driven at a speed associated with that of an engine, the distributor member including a bore within which a plunger is reciprocable. The plunger and bore together define a pumping chamber to which fuel can be supplied through appropriate ports provided in the distributor member and the sleeve within which the distributor member rotates.

It has been found that such ported filling does not allow sufficient fuel to flow to the pumping chamber in some circumstances. Further, there is a significant risk of seizure of the pump due to thermal expansion of the distributor member, and steps must be taken to avoid such thermal expansion to reduce the risk of seizure. It is an object of the invention to provide a fuel pump in which these disadvantages are reduced or overcome.

According to the present invention there is provided a fuel pump comprising a sleeve rotatable upon a spigot, the sleeve including a radially extending bore within which a plunger is reciprocable under the influence of a cam surface, the plunger and bore defining a pumping chamber, the spigot including a flow passage in constant communication with the pumping chamber, a valve controlling communication between a fuel reservoir and the flow passage, the sleeve including a delivery port communicating with the pumping chamber and registrable, in turn, with a plurality of delivery passages provided in the spigot.

Such an arrangement is advantageous in that filling of the pumping chamber does not occur by way of ports, thus can occur over a relatively long period. It is thus possible to supply a sufficient quantity of fuel to the pumping chamber.

The valve conveniently controls both filling and spill. The valve is conveniently in a part of the body of large dimensions permitting relatively simple and easily achievable cooling of the valve. The heat resulting from spill does not result in significant thermal expansion of the spigot or sleeve.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic sectional view of a fuel pump according to an embodiment of the invention; and Figure 2 is a diagrammatic end view of the pump of Figure 1.

The fuel pump illustrated in the accompanying drawings comprises a valve body 10 having a spigot 12 integral therewith, the spigot 12 being of cylindrical form. A sleeve 14 is rotatably mounted upon the spigot 12, the sleeve 14 having six equiangularly spaced, radially extending bores formed therein, pumping plungers 16 being reciprocable within the bores. The sleeve 14 is provided with an annular groove 18 which interconnects the bores, the interconnected bores defining, with the plungers 16, a pumping chamber.

The edges of the annular groove 18 are deflected towards the outer periphery of the spigot 12, in use, as a result of longitudinal compressive stress in the material forming the sleeve 14. This reduces the dilation of the sleeve 14 occurring where a seal is required between the sleeve 14 and spigot 12, thus leakage is reduced. It is envisaged that a similar annular groove may be provided as denoted by dotted lines 18a in Figure 1 to further reduce leakage.

The radially outer end of each plunger 16 carries a shoe and roller arrangement 20, the roller of which cooperates with the cam surface of a cam ring 22 which is angularly adjustable in a known manner to adjust the timing of fuel delivery. The sleeve 14 is keyed to a drive shaft 24 which is arranged to rotate at a speed associated with engine speed, and it will be appreciated that the rotary motion of the drive shaft 24 and sleeve 14 causes the plungers 16 to reciprocate within the bores under the influence of the cam surface of the cam ring 22. As illustrated in the drawings, appropriate bearings 26 are provided to support the drive shaft 24 for rotary motion, and thrust bearings 28 are provided between the sleeve 14 and the valve body 10.

The valve body 10 is provided with a flow passage 30 which extends along the axis of the spigot 12, and communicates through passages 32 with the annular groove 18. Clearly, therefore, the flow passage 30 communicates with the pumping chamber. The open end of the flow passage 30 is closed by means of a plug 34. The valve body 10 is further provided with a through bore 36 which extends in a direction perpendicular to the flow passage 30, intersecting the passage 30. The bore 36 defines a seating with which a valve member 38 is engageable to control communication between the flow passage 30 and a passage 39 which opens into a chamber 40 defined by the valve body 10 and a nut 42 in screw-threaded engagement with the valve body 10. The valve member 38 is moveable under the influence of an electromagnetic actuator 44 against the action of a spring 46.

The chamber 40 communicates with a fuel inlet 48 which, in use, is arranged to receive fuel at relatively low pressure from a rotary vane feed pump or other type of low pressure pump, conveniently mounted upon the drive shaft 24.

The spigot 12 is further provided with six equiangularly spaced delivery passages 50 which extend parallel to the axis of the spigot 12, the delivery passages 50 communicating through respective angled drillings 52 with respective outlet ports 54 provided in the valve body 10. The ends of the delivery passages 50 are closed by a washer 56 which is secured to the end of the spigot 12 by means of a cap nut 58 which is in screw-threaded engagement with the spigot 12. Each delivery passage 50 communicates with a respective port 60 provided in the spigot 12, the ports 60 being located so as to be registrable with a delivery port 62 provided in the sleeve 14 which communicates with the pumping chamber. Upon rotation of the drive shaft 24 and the sleeve 14, the delivery port 62 communicates with each of the delivery passages 50, in turn.

In order to reduce the volume of the delivery passages 50, the parts of the delivery passages 50 between the ports 60 and the ends of the delivery passages 50 closed by the washer 56 house rod-like members which fill substantially the complete volume of these parts of the delivery passages 50. The rod-like members are secured within the spigot 12 using any appropriate technique, for example by local deformable interfering features such as slight flattening or bends located near the outer end of each rod-like member, or by slight mushrooming.

In use, in the position illustrated in Figure 1 the plungers 16 occupy their radially outermost position and the valve member 38 is in engagement with its seating, the rollers of the shoe and roller arrangements engaging the leading flanks of cam lobes provided on the cam ring 22. As illustrated in Figure 1, in this position the delivery port 62 registers with one of the ports 60, thus one of the delivery passages 50 communicates with the pumping chamber. Rotation of the sleeve 14 causes the plungers 16 to be pushed inwardly thus compressing the fuel within the pumping chamber and causing fuel to be supplied through the delivery port 62 and delivery passage 50 communicating therewith to the corresponding outlet port 54.

When fuel delivery is to be terminated, the electromagnetic actuator 44 is controlled to cause the valve member 38 to move away from its seating. Such movement of the valve member 38 results in fuel being able to flow from the pumping chamber through the flow passage 30 to the chamber 40. The chamber 40 is at relatively low fuel pressure, thus the flow of fuel to the chamber 40 permits the fuel pressure within the pumping chamber to fall. Continued inward movement of the plungers 16 causes further fuel from the pumping chamber to be displaced through the flow passage 30 to the chamber 40. Subsequently, the rollers of the shoe and roller arrangements 20 ride onto the trailing flanks of the cam lobes, and the delivery port 62 moves out of communication with the delivery passage 50. Fuel is then supplied from the inlet 48 through the chamber 40 and flow passage 30 to the pumping chamber, pushing the plungers 16 radially outwardly. Once a sufficient quantity of fuel has been supplied to the pumping chamber, the electromagnetic actuator 44 is operated to move the valve member 38 into engagement with its seating thus breaking the communication between the pumping chamber and the chamber 40. Continued rotation of the drive shaft 24 and sleeve 14 causes the delivery port 62 to register with the next of the ports 60 ready for commencement of the next pumping cycle.

It will be appreciated that the feed pump mounted upon the drive shaft 24 operates substantially continuously thus fuel is supplied through the inlet 48 to the chamber 40 both when fuel is being supplied to the pumping chamber, and when the valve member 38 engages its seating so that such supply of fuel to the pumping chamber is prevented. The volume of the interior of the pump including that of the chamber 40 is conveniently sufficiently high to absorb the fuel supplied by the feed pump during periods when fuel is not being supplied to the pumping chamber. Alternatively, a spring loaded accumulator may be used to increase the volume of fuel which can be stored.

The fuel spilt from the pumping chamber past the valve member 38 to the chamber 40 is at high temperature, and in order to avoid fuel at such a high temperature being returned to the pumping chamber, the chamber 40 communicates through a restricted passage 64 with an end part of the bore 36, and with the interior of a pump housing 66 into which the spigot 12 extends. The remaining hot fuel is mixed with fresh, relatively cool fuel from the inlet 48. In addition to permitting hot fuel to escape from the chamber 40 without being returned to the pumping chamber, the supply of fuel through the restricted passage 64 to the end part of the bore 36 permits cooling of the valve member 38, this part of the pump tending to absorb a significant quantity of the heat of the fuel, in use.

If desired, a non-return valve can be provided to prevent spilt fuel from being returned to the feed pump, protecting the feed pump from high pressure spikes.

As shown in Figure 1, the sleeve 14 is provided with passages 68 which communicate with the ports 60 other than the port 60 which is aligned with the delivery port 62, in use, to permit wiping of the delivery passages 50 communicating with those ports 60 with fuel at relatively low pressure from the interior of the pump housing 66.

The materials of the spigot 12 and sleeve 14 are conveniently selected to expand at substantially the same rate as the temperature thereof increases, or alternatively, the sleeve 14 may be of a material which expands at a greater rate, so that the sleeve 14 becomes a looser fit upon the spigot 12 as the temperature increases. It will be appreciated, therefore, that the risk of seizure of the pump as a result of thermal expansion is reduced. In addition, as the valve member 38 and bore 36 within which the valve member 38 is slidable are located away from the pumping chamber, in a part of the valve body 10 of relatively large dimensions, these parts of the pump tending to absorb a significant amount of heat from the fuel, in use, thermal expansion of the sleeve 14 and spigot 12 is minimised. Further, an annular groove 70 is provided around the spigot 12 adjacent the larger diameter portion of the valve body 10, thus reducing the risk of transfer of heat to the spigot 12, and hence reducing the risk of seizure. The groove 70 doubles as a weak point, such that should the fuel pump become seized, the spigot 12 will tend to fracture from the valve body 10 at the groove 70, thus reducing the risk of damage to other parts of the engine resulting from such seizure.

In a modification, the restricted passage 64 may include a valve controlled by a bimetallic element so as to vary the rate at which fuel can escape from the chamber 40 depending upon the fuel temperature.

In the description hereinbefore, the spigot 12 is integral with the valve body 10. It will be appreciated, however, that the valve body 10 may be separate from the spigot 12, an appropriate clamping arrangement being located to secure the spigot 12 to the valve body 10 and ensure correct alignment of the various passages provided therein.

The location of the spigot 12 between the pumping plungers 16 avoids the requirement to provide an arrangement preventing overshoot or clashing of the plungers 16, thus the design of the pump is simplified compared to current arrangements. In addition, the presence of the spigot 12 removes the disadvantageous feature of some conventional arrangements of including sharp edges at the intersections of the plunger bores.

It will be appreciated that as the spill valve incorporating the valve member 38 does not rotate with the sleeve 14, the valve member and its associated armature can be of any suitable cross-sectional shape. For example, the armature may be of rectangular shape, and may be moveable under the influence of the magnetic field generated by a winding wound around a laminated E-core. Such a core is advantageous in that eddy currents are reduced, resulting in improved performance and a reduction in heat generation. The invention is also advantageous compared to an arrangement in which an actuator pushes a valve member into engagement with a rotary distributor member as the wear which occurs between the valve member and actuator is avoided.

The pump described hereinbefore and illustrated is intended for use with a six cylinder engine. It will be appreciated, that the invention is not restricted to a pump for a six cylinder engine, and that pumps for, for example, four or five cylinder engines incorporating the present invention are envisaged.

Claims (4)

1. A fuel pump comprising a sleeve rotatable upon a spigot, the sleeve including a radially extending bore within which a plunger is reciprocable under the influence of a cam surface, the plunger and bore defining a pumping chamber, the spigot including a flow passage in constant communication with the pumping chamber, a valve controlling communication between a fuel reservoir and the flow passage, the sleeve including a delivery port communicating with the pumping chamber and registrable, in turn, with a plurality of delivery passages provided in the spigot.

2. A fuel pump as claimed in Claim 1, wherein the valve is arranged to control both filling of the pump and spill, in use.

3. A fuel pump as claimed in Claim 1 or Claim 2, wherein the spigot forms part of a body, the valve being located within a part of the body of large dimensions.

4. A fuel pump substantially as hereinbefore described with reference to the accompanying drawings.