GB2057572A - A device for metering fluid flow - Google Patents

Abstract

The device has a plurality of pairs of gears accommodated in chambers, which may be formed in plate-like housings (2). One gear of each pair is secured to a common shaft (40) so that when fluid is supplied under pressure by way of a common inlet manifold the pairs of gears rotate in synchronism with each other. Thus the fluid delivered from the outlet ports is proportioned with respect to the total fluid flow entering the device. The fluid emerging from the outlet ports may be used to drive hydraulic motors at a speed related to the speed of the shaft (40). <IMAGE>

Description

SPECIFICATION A device for metering fluid flow for use in hydraulic systems This invention concerns a device for metering fluid flow for use in hydraulic systems.

Hydraulic systems for use in agricultural equipment comprise a pump, supplying fluid under pressure from a reservoir to one or a number of hydraulic operable units. These units may be hydraulic rams or motors. For example, a crop harvester may have several continuous conveyor surfaces or rotary cutters which are required to be driven by hydraulic motors. The required speed of rotation of each motor is known and the maximum flow rate from the pump driven by a tractor is also known. Thus the individual sizes of the motors may be chosen to take a certain proportion of the available flow from the pump to give the required speed output. Alternatively, a metering device or relief valve is used to divert any unwanted excess flow to the reservoir so that only the required flow is passed to the motor to achieve the required speed of running.Such metering devices are wasteful in energy and cause the fluid to heat up which is undesirable.

It has been found in practice that the speed of the various units or motors varies in dependence upon the loading of the individual conveyors. For example, if one conveyor jams the excess flow may be diverted to the other motor which speeds up. Such fluctuations in speed between the motors are undesirable.

It is the aim of the present invention to avoid speed variations between the motors and to provide a simple means of proportioning the flow in a hydraulic system to simplify the choice of equipment used in a hydraulic system.

According to the present invention there is provided a device for metering fluid flow comprising a plurality of chambers isolated from one another and each chamber having therein a pair of rotatable gears in mating relationship, a fluid inlet port and a fluid outlet port for each chamber, one gear of each pair being secured to a common shaft so that the pairs of gears rotate in synchronism, each pair of gears when the device is in use allowing passage of a predetermined flow of fluid which is a fixed proportion of the fluid flow entering the device via the inlet ports.

Preferably each inlet part is connected to a common inlet manifold and fluid is supplied under pressure to the inlet side of the device, which fluid rotates the gears to drive the common shaft. The capacity of each gear chamber being such that a certain fixed proportion of the inlet flow is discharged from each outlet port.

Conveniently any of the metered outlet flows may be combined to obtain a required outlet flow to operate an auxiliary drive motor or other hydraulic device. In a preferred embodiment of the invention the device is used as a drive motor wherein the output drive is taken from the common shaft.

An advantage of the device according to the invention is that the flow from a pump supplying the hydraulic system may be easily and cheaply porportioned to obtain a number of metered flow paths passing a proportion of the total flow supplied to the device. Advantageously these metered proportions may be used to operate other hydraulic devices, e.g. motors or rams which require a lower flow rate to drive them at the required speed. Such hydraulic devices may have to be inter-related in terms of their speed of operation and this is easily achieved by a device according to the invention which proportions the flow entering the system.

Such a device avoids the need for specially chosen motors since a large capacity motor may be effectively de-rated by reducing the flow supplied to the device.

The invention will now be described further by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of the device according to the invention, Fig. 2 is a sectional view through one chamber of the device, Fig. 3 is a cross-sectional view through the plane of the gears, and Fig. 4 is a schematic arrangement of an hydraulic system incorporating the device.

In a preferred embodiment of the device (1) described with reference to Figs. 1 to 3, a plurality of gear housings (2) (three indicated), conveniently made from cast iron, are assembled in axially spaced relationship. Intermediate plates (4) conveniently constructed from aluminium alloys are positioned adjacent each side of the gear housings.

The gear housings and the intermediate plates are provided with four holes (6) through which clamping bolts (not shown) pass to secure the gear housings and the intermediate plates together to form a housing (7) for the device. A pair of end plates (8, 10) also provided with four holes (6) are positioned at the extreme ends of the housing. As shown with reference to Fig. 2 each gear of housing (2) is substantially rectangular, although any other convenient shape may be employed, and two cylindrical chambers (12, 14) which break into one another are formed in each gear housing. The two cylindrical chambers constitute a gear chamber (20) in each gear housing. An inlet port (16) and an outlet port (18) is machined in each gear housing (2) by means of which hydraulic fluid enters and leaves each gear chamber (20).Each gear chamber (20) accommodates a pair of toothed gears (22, 24) which are in mating relationship.

The gear housing has a certain width which is conveniently the same width as the gear chamber.

The pair of gears occupying a particular chamber have substantially the same width as the gear chamber so that they are a close running fit in the chamber. This is to avoid leakage of fluid past the gears in operation. The construction of the chamber and the associated gears is well known in connection with gear pumps.

As shown with reference to Fig. 3 two shafts (40,42) are journalled for rotation in the housing of the device. Plain bushings (28) are provided in bores (30) in each of the intermediate plates (4).

An antifriction ball bearing (32) is provided in a bore (34) in the end plate (1 0),said ball bearing (32) taking axial float and ail loading on the shaft.

One shaft (40) passes through the end plate (10) and the bearing (32) and acts preferably as an output shaft although it may be used as an input shaft. A seal (36) is provided on the shaft (40) to prevent external leakage of oil. Each chamber is isolated physically from the next and may also conveniently be sealingly isolated. This is not necessary when the inlets to the respective gear chambers are inter-connected as will be described herebelow, but may be necessary when the inlet connections are isolated from one another.

The respective gears (22) are secured by a suitable key (25) to the shaft (40) and the respective gears (24) are similarly secured to the shaft (42).

As shown each pair of gears (22, 24) and the associated gear chambers (20) are of different widths, i.e. the capacity of each gear set is different. Whilst it is not essential that each gear set should have a different capacity it is intended according to the invention that the widths of the gears be specially chosen. The reason for this will be explained further herebelow.

In a preferred mode of operation fluid under pressure is fed via a common manifold and enters each inlet port (16). This causes the gears to rotate and consequently the shaft (40) rotates.

Since the gears are connected via this shaft they all rotate at the same rate. The pump supplying fluid under pressure to the inlet side of the device does so at a certain flow rate. Thus, for example, a flow rate of say 6 galls/min, may be produced by the pump. Each gear set has a certain performance characteristic relating the flow rate to the speed of revolution. This characteristic is particular to each gear set and is related to the size or capacity of the gears. Thus, for example, the capacity of the gears illustrated in Fig. 3 may be related in the proportions 3 :2 :1. Thus, if the pump has a flow rate of 6 galls/min, 3 galls/min will flow through the largest gear, 2 through the intermediate gear and 1 through the smaller gear.

Thus, according to the present invention a device having a plurality of gear chambers (3 in the illustrated example) of different capacities when supplied with fluid under pressure will, as well as acting as a motor driving the output shaft which may conveniently drive a part of a machine to which the device is fitted will also give an output flow from each outlet port which is metered and is a proportion of the total flow to the device.

Thus the metered flow from the device may conveniently be used to operate a further device in the line which requires a lower flow rate than the first motor. Conveniently any combination of outlet flows may be brought together to obtain a flow rate as appropriate to operate another device at the correct speed.

Thus according to one aspect of the invention the device provides a simple method of proportioning the flow from a pump such that the required flow for a particular operation can be achieved.

The invention will now be described with reference to a particular application in which a two gang version of the device is utilised. Referring to Fig. 4, the hydraulic circuit comprises a reservoir 100 containing hydraulic fluid and a pump 102 driven by a suitable motor (not shown) and supplying fluid at a certain pressure and flow rate.

The particular application is to a sprout harvester wherein the pump 102 is driven by the tractor pulling the harvester. The fluid is supplied via a pipeline to a first gear motor (104) which drives the cutting heads of the harvester and the waste or outlet from this motor passes to a two gang version of the device (106). Both inlets to the two gear chambers of the device are interconnected to which the total fluid flow is applied. The device is used to drive a stripping rollers of the harvester and one gear chamber has a larger capacity than the other gear chambers The outlets from the two gear chambers of the device are separate and the flow discharged therefrom is a proportion of the fluid entering the device and is related to the capacity of the individual gear chambers.The outlet from the larger of the two chambers passes to a further gear motor (110) driving an elevator of the harvester. The elevator does not require the same quantity of flow as the first and second motors and thus one of the reduced flow rates discharging from the device is used to supply this further drive. The smaller discharge from the device may as is illustrated be used to drive an hydraulic ram (1 12) or may be returned to the reservoir. The line is selectively controlled by a divertervalve (114).

Since the motors are connected in series the speed of operation of each motor is inter-related and for this type of machine such inter-relation is desirable. If a conventional metering device were used to reduce the flow from the pump to give the required flow for the further motor then this speed inter-relationship would not be achieved and the speed of each motor would be determined by the loading on each motor.

A further advantage of the device is that by varying the flow to a motor, standard motors may be used rather than, as at present, utilising a motor which will give the required performance at the maximum flow from the pump. Thus the present invention provides a relatively simple, effective and cheap means of controlling the flow in a hydraulic circuit and imports considerable flexibility into the use of components not previously possible.

Whilst the invention has been described with reference to a particular embodiment in which all the inlet ports are interconnected and supplied with fluid under pressure it is envisaged that this is not necessarily essential. For example, one inlet port may be supplied with fluid under pressure so as to rotate the device and the other inlet may be used to pump fluid from a reservoir such that the metered outlet quantities may possibly be combined at the outlet stage. For example, this could have applications in the mixing of chemicals for agricultural or other use. The driven output shaft may be used to agitate the chemicals after mixing. Naturally, the material from which the pump is constructed may have to be specially chosen to be resistant to the chemicals employed.

It is further envisaged that the shaft emerging from the device could be coupled directly to a motor so that the device acts solely as a flow proportioning device and not as a motor as previously described.

Whilst the preferred embodiment has been described with reference to a device which has a two or three gear chambers, any number of suitably proportioned gears and chambers may be assembled into one unit. Alternatively, a plurality of separate gear chambers may be coupled to a common shaft rather than combining them in one integral housing.

Claims (8)

1. A device for metering fluid flow comprising a plurality of chambers having therein a respective pair of rotatable gears in mating relationship, a fluid inlet port and a fluid outlet port communicating with each chamber, and a common shaft to which one gear of each pair of gears is secured so that, in use, the pairs of gears rotate in synchronism and the fluid flow from each outlet port is inter-related and is a fixed proportion of the fluid flow entering the device by way of the inlet ports.

2. A device as claimed in claim 1 in which each gear chamber accommodating the pair of gears is formed in a plate-like gear housing which has plate-like closure members disposed on either side thereof.

3. A device as claimed in claim 2 having at least two gear chambers in which adjacent gear chambers are spaced apart by a or a respective intermediate plate which has a bore through which the common shaft passes, and a pair of end plates disposed adjacent the end gear housings, the intermediate plate or plates and the pair of end plates serving as the closure members.

4. A device as claimed in claim 3 in which at least one end of the common shaft passes through one of the end plates.

5. A device as claimed in any preceding claim in which the common shaft is an output drive shaft which is rotatable by fluid pressure applied to one or more pairs of gears.

6. A device as claimed in any preceding claim in which each chamber is interconnected on the inlet side by a common inlet manifold.

7. A device as claimed in any preceding claim in which the pairs of gears have different capacities so that a different fluid flow emerges from the respective outlet ports.

8. A device constructed and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.