GB2299689A - Hydraulic governor for a fuel pump - Google Patents

Abstract

A hydraulic governor for a fuel pump comprises a drum 30 attached to a drive shaft of the fuel delivery pump. The drum rotates within a housing 36 which has a step 38 formed by the interconnection of regions 36a, 36b. The region 36a has a relatively large area compared to region 36b. Fuel, due to its viscosity, tends to adhere to the drum 30 as it rotates which results in pressure being developed at step 38, as a consequence of fluid moving from region 36a to region 36b. The pressurized fluid enters passage 42 and acts on piston 44 having connected thereto a linkage 50 which controls a variable valve arrangement (52, fig 1). A governor spring 46 acts against the piston 44, the free end of the spring engages an adjustable stop (48, fig 1). The position of the piston 44 is thus dependent upon the pressure produced at the step and the prestressing of the spring 46. A viscosity compensator 60 is provided to account for viscosity changes in the fuel due to, for example, temperature fluctuations.

Description

GOVERNOR This invention relates to a governor, and in particular to a hydraulic governor suitable for use in the fuel injection system of an internal combustion engine.

Where diesel engines are used in, for example, generator applications, it is desirable to be able to control accurately the amount of fuel delivered by a fuel pump, and it is common to control the flow of fuel by providing an adjustable valve arrangement in the input line to the pump, and controlling the valve so that the rate of flow of fuel therethrough is related to the speed of the engine.

One mechanical type of governor arrangement includes a plurality of weights pivotally mounted upon a shaft which is rotatable at a speed related to engine speed. The pivotal mounting of the weights is such that as the shaft rotates, the weights tend to move radially outwardly, bearing against a lever which is spring biased against the weights so that the position of the lever is dependent upon engine speed. The lever is connected to the valve arrangement so that movement of the lever results in a change in the setting of the valve.

An alternative, hydraulic, arrangement includes a piston acting against a governor spring, the piston being supplied with fuel at a pressure related to engine speed by a rotary vane pump and valve arrangement or the like which is commonly provided in a rotary fuel pump. Movement of the piston is transmitted to the valve arrangement by a suitable linkage.

In both of these arrangements, the sliding parts tend to wear, in use, thus the governor arrangement requires replacing or resetting, in the case of the hydraulic arrangement, the wear often occurring within the rotary vane pump and valve arrangement or the like.

According to the present invention there is provided a governor arrangement comprising a substantially cylindrical body rotatable within a housing, the housing being shaped so as to include a first portion in which the space between the body and the inner wall of the housing is of a first, relatively large area, and a second portion in which the space between the body and the inner wall of the housing is of a second, relatively small area, an inlet permitting fluid to enter the housing, and means for transmitting the fluid pressure developed at the interconnection of the first and second portions on rotation of the body with respect to the housing to an adjustable valve arrangement.

The interconnection of the first and second portions is preferably in the form of a step.

Conveniently, the means for transmitting comprises a piston biassed by a governor spring, the pressure developed at the step acting on the piston against the governor spring. The piston is preferably connected to the valve arrangement by a suitable linkage.

The governor arrangement preferably further comprises a viscosity compensator arranged to substantially compensate for changes in the pressure developed at the step due to viscosity changes.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a rotary distributor pump including a governor mechanism in accordance with an embodiment of the invention; Figure 2 is a diagrammatic perspective view, partially broken away, of part of the governor mechanism of Figure 1; Figures 3 and 4 are diagrammatic views illustrative of the operation of the governor mechanism; Figure 5 is a diagrammatic view of the viscosity compensator used in the governor mechanism of Figures 1 and 2; and Figure 6 is a diagrammatic cross-sectional view of part of a modified embodiment.

The rotary distributor pump illustrated in Figure 1 comprises a body 10 housing a cylindrical sleeve 12. The sleeve 12 has an axially extending through bore within which a cylindrical distributor member 14 is rotatable. The distributor member 14 includes an enlarged head region 16 provided with a pair of perpendicular, diametrically extending through bores each of which houses a pair of plungers 18. The outer end of each of the plungers 18 engages a shoe and roller assembly 20, the roller of which is engagable with the cam surface of a cam ring 22, rotation of the distributor member 14 with respect to the sleeve 12 resulting in the rollers associated with each of the plungers 18 contacting cam lobes provided on the cam ring 22 resulting in inward movement of the plungers 18 within the respective bores.

The distributor member 14 is provided with an axially extending passage 24 which communicates with inlet and outlet passages which are arranged to register with respective ports provided in the sleeve 12 upon rotation of the distributor member 14.

In use, the distributor member 14 is driven at a speed related to engine speed so as to rotate within the sleeve 12. Such movement of the distributor member 14 will result at some stage with the inlet passage registering with the respective inlet port permitting fuel to be delivered through the inlet passage and axially extending passage 24 to the bores which house the plungers 18. The pressure of the fuel so received is sufficient to push the plungers 18 in a radially outward direction.

Further rotation of the distributor member 14 breaks the communication of the inlet passage with the inlet port, continued rotation resulting in the delivery passage registering with a respective delivery port and with the rollers associated with the plungers 18 contacting the cam lobes of the cam ring 22 pushing the plungers 18 in a radially inward direction thus pumping the fuel from the through bores through the passage 24 and delivery passage to the delivery port. From the delivery port, the fuel is carried by a suitable line to the injection nozzle of a cylinder of an associated engine.

This type of delivery pump is well known in the art, and will not be described in further detail.

In order to control the quantity of fuel delivered by the pump, a governor mechanism is associated with the fuel pump. The governor mechanism comprises a substantially cylindrical drum 30 which is keyed to the drive shaft which is arranged to drive the distributor member 14, and is thus arranged to rotate at a speed associated with engine speed.

The drum 30 is rotatable within a housing 32 which is itself located within the body 10. The housing 32 comprises a pair of substantially annular end plates 34 and a substantially cylindrical housing member 36 best shown in Figure 2. As shown in Figure 2, and also diagrammatically in Figure 4, the cylindrical member 36 comprises a first region 36a in which the separation of the inner wall of the member 36 from the outer periphery of the drum 30 is relatively large, and a region 36k in which the separation of the inner wall of the member 36 from the outer periphery of the drum 30 is relatively small. The interconnection of the regions 36a and 36k defines a step 38. As shown in Figure 4, another step similar to the step 38 may be present at the other interconnection of the region 36a and region 36h.

An inlet aperture 40 as shown in Figure 4 is provided in the cylindrical member 36 permitting communication between the interior of the housing 32 and the interior of the body 10. The aperture 40 permits fuel from within the body 10 to enter the housing 32 such that upon rotation of the drum 30 at a speed associated with engine speed, the fuel between the drum 30 and housing 32 tends to rotate with the drum 30 due to the viscosity of the fuel. It will be recognised that where the drum 30 rotates in the direction of arrow A in Figures 2 and 4, a pressure is developed at the step 38 as a result of the fuel moving from region 36a which is of relatively large cross-sectional area to region 36k which is of relatively small area.

As shown in Figures 1 and 2, a passage 42 is provided in the housing 32 extending from the interior of the member 36 adjacent the step 38. The passage 42 communicates with a bore within which is received a piston 44, the fuel within the passage 42 acting against the end of the piston 44. A governor spring 46 acts against the piston 44, the free end of the governor spring 46 engaging an adjustable stop 48 connected to a throttle through a suitable linkage 49 which is used to adjust the prestressing of the governor spring 46. The adjustable stop is conveniently a snap fit onto the end of the governor spring 46. It will thus be recognised that the position of the piston 44 with respect to the housing 32 is dependent upon both the prestressing of the spring 46 and the pressure developed in the fuel at the step 38.Since in use, the position of the stop 48 and hence the prestressing of the governor spring 46 is fixed, the position of the piston is substantially dependent upon the pressure developed at the step 38 alone. A linkage arrangement 50 interconnects the piston 44 and a variable valve arrangement 52 such that movement of the piston 44 is transmitted by the linkage 50 to control the setting of the valve arrangement 52, the valve arrangement 52 being arranged to control the flow of fuel to the inlet port of the rotary fuel pump, and hence to control the rate of fuel delivery by the fuel pump. Such a linkage arrangement 50 is well known and will not be described in detail.

In the embodiment illustrated in Figure 1, the linkage arrangement 50 is arranged to engage with a plate 54 which is attached to the piston 44, the governor spring passing through a relatively large aperture in the plate 54, the linkage arrangement 50 engaging a portion of the plate 54 which extends laterally from the piston 44.

It will be recognised that the number of sliding surfaces in the above described governor arrangement is relatively low, and hence the amount of wear is reduced. The governor arrangement is therefore likely to hold its setting for longer than a conventional arrangement.

The pressure developed at the step 38 is relatively small, for example 0.2 bar greater than that within the body 10, thus it will be recognised that the area of the piston must be relatively large in order for the pressure developed at the step 38 to be able to move the piston 44 against the action of the governor spring 46.

With reference to Figure 3, the principle involved in developing a pressure at the step 38 is the same principle as that employed in a stepped hydrodynamic bearing. Rotation of the drum 30 in the direction A at a rotational speed V is equivalent to moving the lower element 56 shown in Figure 3 in the direction of the arrow at speed V with respect to the upper element 58 which includes the step 38. Where the dimensions are as set out in Figure 3, the pressure developed at the step is equal to:

where ii is the viscosity of the fuel and V is the speed of the element 56 with respect to the element 58.

It is clear that the pressure developed at the step 38 is dependent upon both the rotational speed of the drum 30 and the viscosity of the fuel.

Since the viscosity is dependent upon the temperature of the fuel, it is likely that the viscosity will fluctuate during use of the pump. The viscosity is further dependent upon the choice of fuel, a wide range of suitable fuels being available. It is therefore desirable to be able to compensate for changes in the viscosity of the fuel so that changes in the pressure developed at the step 38 are not transmitted to the valve arrangement 52 and hence do not effect the rate of fuel delivery by the pump.

With reference to Figure 5, a suitable viscosity compensator 60 comprises a passage 62 extending from the step 38, a plunger 64 being slidable within the passage 62. The plunger 64 is biased by a spring 66 so that the spring 66 acts against the pressure of fuel within the passage 62. The plunger 64 is of diameter smaller than the passage 62 so that fuel may pass between the plunger 64 and the inner wall of the passage 62, the passage 62 terminating at an outlet orifice 68 of relatively small diameter. A leakage aperture 70 is also provided in the wall of the passage 62, the plunger 64 being slidable so as to, in a first position, substantially obscure the leakage aperture 70, and in a second position, permit fuel from within the passage 62 to escape through the outlet aperture 70.It will be recognised that when the fuel is of relatively low viscosity, a substantial amount of the fuel will be able to pass between the plunger 64 and the inner wall of the passage 62, and hence the pressure drop across the plunger 64 is relatively low. The plunger 64 will therefore take a position substantially obscuring the leakage aperture 70 and the majority of the fuel flow escaping from the housing 32 will escape through the outlet orifice 68. When the fuel is of a relatively high viscosity, and hence a greater pressure is developed at the step 38, a smaller proportion of the fuel will be able to pass between the plunger 64 and the inner wall of the passage 62, and hence the pressure drop across the plunger 64 will be relatively large.The plunger 64 will therefore be pushed against the spring 66 to a position in which the leakage aperture 70 is exposed, and a proportion of the fuel will be able to leak from the passage 62 via the leakage aperture 70 thus reducing the pressure acting against the plunger 64. It is expected that air entering the system will leave through the outlet orifice 68 provided in the passage 62.

Although in the illustrated and described embodiments the member 36 includes two steps between the region 36a and the region 36b, it may be possible to provide a member 36 having only a single step 38, the other step being replaced by a gradual, continuous increase in the separation of the member 36 from the drum 30.

In addition to providing the step 38, it is desirable for the effective axial width of the space between the drum 30 and the housing 32 to be relatively large at the entrance 40 to facilitate the ingress of fuel into the housing 32, and to be relatively small adjacent the step 38 in order that the peak pressure developed at the step 38 is applied to the piston 44.

Such an arrangement is illustrated in Figure 6, the distance d, representing the effective width of the space at the inlet 40, the distance d2 representing the smaller effective width adjacent the step 38. It is believed that leakage of fuel from the housing 32 is reduced by reducing the effective width of the space, and hence that by reducing the effective width adjacent the step 38, the pressure drop associated with the leakage of fuel from the housing 32 is reduced.

Claims (4)

1. A governor arrangement comprising a substantially cylindrical body rotatable within a housing, the housing being shaped so as to include a first portion in which the space between the body and the inner wall of the housing is of a first, relatively large area, and a second portion in which the space between the body and the inner wall of the housing is of a second, relatively small area, an inlet permitting fluid to enter the housing, and means for transmitting the fluid pressure developed at the interconnection of the first and second portions on rotation of the body with respect to the housing to an adjustable valve arrangement.

2. A governor arrangement as claimed in Claim 1, wherein the interconnection of the first and second portions is in the form of a step.

3. A governor arrangement as claimed in Claim 2, further comprising a viscosity compensator arranged to substantially compensate for changes in the pressure developed at the step due to viscosity changes.

4. A governor arrangement substantially as hereinbefore described with reference to the accompanying drawings.