GB2259333A

GB2259333A - Gear pump with a delivery rate depending non-linearly on pump speed

Info

Publication number: GB2259333A
Application number: GB9218193A
Authority: GB
Inventors: Manfred Kahrs
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1991-09-07
Filing date: 1992-08-27
Publication date: 1993-03-10
Also published as: GB9218193D0; FR2681105A1; ITMI921884A1; DE4129854A1; ITMI921884A0

Abstract

A gear pump, such as a lubricating oil pump for internal combustion engines, comprises a restrictor provided on the suction side of the pump which limits the delivery rate of a delivery cell of the pump depending on the rate of revolution of the pump gears (3, 4, Fig 3) so that the delivery rate of the pump is non-linearly dependent on the pump speed. The restrictor may be provided by an inlet opening 5 of small cross-sectional area. A valve 27 may be provided to control the size of the inlet opening in response to the discharge pressure and a non-return valve may be provided in the outlet of the pump. To reduce noise generation two outlets (19, 20, Fig 7) may be provided. <IMAGE>

Description

1 GEAR PUMP WITH A DELIVERY RATE DEPENDING NON-LINEARLY ON THE RATE OF

REVOLUTIONS This invention relates to gear pumps.

In the case of conventional gear pumps, in particular for the delivery of lubricating oil, the delivery rate increases in direct proportion to the rate of revolution of the pump drive means (e.g. combustion engine). Therefore, the following equation holds good: V' [volume per minute] = q (volume per revolution). n (rate of revolutions per minute).

However, a constant or slightly increasing delivery rate from gear pumps is demanded in many cases (as for example the oil flow demanded for the lubrication of engine bearing points and for the heat dissipation through the lubricating oil cycle) in spite of increase in the rate of revolution of the pump gear means. The consequence of an excess between the pump delivery rate (existing flow of lubricating oil) and the effective demand is that as the rate of revolution of the engine increases a multiple of the required delivery rate (oil flow) is discharged through an over-pressure valve and is uselessly transformed into thermal energy. As a result of this, the energy consumption of the pump is, unduly excessive.

Along with the multitude of individual provisions which have already been realised in internal combustion engines the adaptation of the delivery rate of an engine lubricant pump to the actual demand is another provision 2 offering considerable potential in energy saving.

It is, therefore, an object of the invention to make provision in a gear pump for the delivery rate of the delivered fluid to increase nonlinearly with the rate of revolution by low-cost means for limiting the value of the delivery rate as the rate of revolution rises.

In accordance with the present invention there is provided a gear pump, characterised in that for the generation of a delivery rate which is dependent non- linearly on the rate of revolution of the pump gear means a restrictor is provided on the suction side of the pump which limits the delivery rate of a delivery cell depending on the rate of revolution (n) of the pump gear.

The invention provides a low-cost means for the application of so-called suction throttling to customary types of oil pumps, such as external gear, internal gear and annular gear pumps. The invention presents a suitable design for gear pumps, in particular for those being applied in lubricating oil systems, which results in an adaptation of the delivery rate to the demand. In this connection, assuming an equal starting pressure of approximately 5 bar, the energy consumption of the pump is proportional to the delivery characteristics, so that a reduction by 0.5 kW and more of the energy consumed may be achieved with the suction-throttled pump.

In carrying out the invention the filling of the pump cells may be achieved during the suction stroke through the throttling point only during a relatively short interval, so that at more elevated rates of revolutions of the pump an increasingly shorter time period will be available for the filling which will result in the partial filling gnly of the pump cells. The reason for this is that on account of the reduced filling time and on account of the resistance to flow of the inlet opening only a reduced volume of fluid (e.g. lubricating oil) to be delivered by the pump will be allowed to flow into the delivery cells.

Preferably, this partial filling of the cell is done 3 in such a way that filling of the cell is commenced only at a later moment than customary. In this context, the inflow of fluid may take place both radially and laterally, depending on the particular configuration of pump. 5 The pump according to the invention may be an external gear pump in which the restrictor is provided by a narrow suction slot. In order to avoid refluxes from the discharge duct of the pump and consequential pressure rises and undesirable noises within the operating range of the suction throttling at the inlet of the cells being partly filled with fluid (oil) non-return valve means may be provided in the pressure circuit of the pump. A non-return valve may, in the case of an external gear pump, be positioned in the discharge duct of the pump as near as possible to the point of inlet of the cells.

The nonreturn valve means may be moulded into the housing of the gear pump.

The non-return valve controls the pressure buildup within the partly filled cells before the inlet into the discharge duct and thereby prevents refluxes and inherent capacity losses and noises. The non-return valves required for this purpose need to operate at a high frequency (product of rate of revolutions and number of cells) which can however/ be realised with conventional valves due to the small volumes conveyed and to the low pressure levels involved.

In the case of an annular gear pump, two or more pressurised cells may be temporarily connected to the conventionally designed discharge slot in the course of the rotation of the rotor. However, in applying the invention to such pumps the discharge slot may be connected to the delivery line with one non-return valve. A pressure balance and a corresponding reflux could take place between the cells simultaneously connected through the discharge slot but this can be avoided by adequately reducing the size of the outlet slot so that the two cells are not simultaneously 4 connected to the outlet slot. Another possibility resides in. subdividing the outlet-side discharge slot into two positions having a smaller crosssectional area in the inlet position and being disposed at a determined distance from each other. In such a configuration a non-return valve may be inserted between the outlet opening in the precompression position and the discharge duct.

The result of the latter measure is that at the inlet of the partly filled cell and first of all into the smaller slot in the pre-compression range (which is connected to the discharge duct through the non-return valve) a pressure buildup takes place by compression as a result of a reduction of the cell volume and not by a reflux from the discharge duct or from a previous cell. Only after the cell has reached a higher pressure level will passage into the larger outlet slot and the last adaptation to the operating pressure will take place.

The geometric dimensioning of the two discharge slots and their distance result as a compromise between the optimum rate of revolution, the operating pressure and the size and dimensioning of the pump.

If it is desired to keep the initial pressure of the pump with suction throttling as constant as possible, then the suction throttling may be controlled. Especially with regard to lubricating oil pumps with suction throttling, this will enable the lubricating pressure of the engine to be kept constant within narrower limits than has customarily been provided. It is generally known that on account of an elevated temperature of a low-viscosity oil, as well due to wear of the pump and of the engine the delivery rate will decrease and the lubricating pressure will be reduced. This effect can be counteracted by designing the pump inlet-side restrictor with a variable cross- sectional area which is influenced by the outletside pressure. The mode of functioning of the adjustable restrictor is such that the cross- sectional area of the restrictor is automatically increased as the lubricating pressure decreases so that above a point on the characteristic curve of the pump a larger delivery rate and, thus, a higher lubricating pre ssure will come about within certain limits.

A control slide valve may be disposed transversely to the axis of the suction duct of the pump which is maintained by a spring in a limit position such that the suction duct is completely opened. On the front face opposite the spring the control slide valve is subject to the pressure existing in the outlet of the pump. By an adequate dimensioning of the components the slide valve will, above a pressure threshold and as the pressure rises, be moved in such a way contrasting the spring force that the suction-side cross-sectional area is reduced in size. The size reduction continues until a stop which is predetermined by the configuration of the component parts and which corresponds to an associated minimum cross-sectional area is reached. In the event of a decrease of the pump pressure the slide valve will be moved by the spring force again in the direction of opening of the suction-side crosssectional area. A maximum opening may correspond to the inlet opening of a nonthrottled type of pump. With the foregoing simpledesign features which can be integrated in the pump the lubricating pressure of a system including the pump can be maintained constant within certain limits, independently of the rate of revolution of the engine, the oil temperature and viscosity, as well as of the conditions of wear. By way of example embodiments of the invention will now be described with reference to the accompanying drawings in which: 30 Figure 1 shows a graph which illustrates the mode of operation of a conventional pump and a gear pump according to the present invention; Figure 2 shows a sectional view of an external gear pump with a conventional suction opening; 35 Figure 3 shows a gear pump according to Figure 2 but provided with suction throttling; Figure 4 illustrates the construction and operation 6 of an annular gear pump with a conventional suction slot; Figure 5 illustrates a pump construction and operation according to Figure 4 but with reduced suction opening being provided for suction throttling according to the invention; Figure 6 shows a pump according to Figure 3 but provided with a nonreturn valve in the discharge duct; Figure 7 shows an annular gear pump according to Figure 5 but provided with a divided discharge slot in lo substitution for the discharge slot in Figure 5; and Figure 8 shows a gear pump according to Figure 6 with controlled suction throttling.

The graph of Figure 1 shows the dependence of the delivery rate V (litres per minute) of the pump on the rate of revolution n of the engine in revolutions per minute both for a conventional lubricating oil pump (see curve K) and for a lubricating oil pump in accordance with the invention (see curve S). In the case of the conventional lubricating oil pump a directly proportional relationship is evident between the delivery rate and the rate of revolution of the pump, whereas in the case of the pump having suction throttling in accordance with the invention the delivery rate only increases slightly or, may remain constant at elevated rates of revolution.

Figure 2 shows a conventional external gear pump whose mode of operation is amply explained in lloelhydraulik" (Oil Hydraulics) by Findeisen, 3rd edition, published by Springer-verlag, pages 49 et seq. This known gear pump comprises an inlet opening 1 and an outlet opening 2 which are so dimensioned as to ensure that the individual delivery cells of the pump will be filled with fluid to be delivered even when the gears 3 and 4 are running at the maximum rate of revolution n.

In Figure 3 the conventional external gear pump 35 of Figure 2 is modified according to the present invention in such a manner that the inlet opening 5 is considerably restricted with respect to the inlet opening 1 of Figure 2.

z z 7 The restriction is such that one pump cell only which is to be filled is being supplied at a time. The invention is based on the realisation that at the more elevated rates of revolution of the pump gears 3 and 4 the relevant pump cell can no longer be completely filled during the filling time available on account of the resistance to flow through the restricted inlet opening 5 as a consequence of which the delivery rate will no longer rise steeply but only slightly when the rate of revolution increases still further.

Figure 4 shows an annular gear pump with a conventional suction slot. The mode of operation of such a pump is described, for example, in the pocket book by Krauskopf entitled 11Bauelemente der OelhydraulikI, (Structural Elements of oil Hydraulics), part I, pages 61 et seq. The known annular gear pump of Figure 4 comprises an internally- toothed stator 6 and an externally-toothed rotor 7 which is driven by a shaft (not shown). In this construction, the stator has one tooth more than the rotor by which it is driven in a manner comparable to step-down gearing. The pump has a comparably large inlet slot 8 which is inserted in the lateral wall of the pump and which is outlined in a dashed line in Figure 4. The size of the slot 8 is again sufficient to fill the pump cells even at the maximum rate of revolution and, thus, to let the delivery rate increase linearly with the rate of revolution of the rotor 7.

As can be seen from Figure 5, the inlet slot 9 of the pump according to the invention has been consideraly reduced in size as compared to the design of Figure 4. This means in practice that the filling of the relevant cell is delayed. Whereas, the cell filling time which is available very well suffices for the filling of the cell at low rates of revolution n, the resistance to flow in the inlet opening will prevent such a complete filling at elevated rates of revolution since the filling time available becomes so short that the flow is no longer sufficient for the complete filling. As a result of this, the delivery rate of the pump 8 will no longer increase linearly in proportion to the rate of revolution at elevated rates of revolutions but rather only slightly. Whilst it is true that an inlet slot 9 which is reduced in size will in any event bring about a limitation of the delivery rate, the reduced inlet slot 9 will, however, preferably be disposed such that it permits only as late as possible a filling of the relevant cell.

By means of the individual cells a determined amount of the f luid to be delivered by the pump will be conveyed to the pump outlet. Now, if the relevant cell is no longer completely filled on account of the elevated rate of revolution n, then the delivered volume of fluid will anyway be sufficient on account of the rate of revolution. The comparatively low pressure and the partial filling of the cell may, however, bring about a brief reflux of fluid from the outlet duct 10 (Figure 6) to the cell chamber 11, which makes itself noticeable by unpleasant noises. In order to prevent this reflux, a non-return valve 12 is employed in which a spring 13 pre-stresses, for example, a valve ball 14 in such a manner that the path to the outlet duct 10 is opened only if and when the pressure in the delivery chamber 15 is higher than that in the discharge duct 13.

As will be seen from Figure 6, the non-return valve 12 may be integrated in the housing 16 of the gear pump.

Figure 7 illustrates several possibilities for reducing the generation of noise in an annular gear pump according to the invention. The annular gear pump corresponds to Figure 5 and is accordingly furnished with a restricted inlet slot 9. However, the outlet slot corresponding to slot 18 in Figure 5 is sub-divided into two outlets 19, 20, namely into a precompression outlet 20 and into a discharge outlet 19. Both the discharge outlet 19 and the pre-compression outlet 20 are connected to a delivery line 21. The purpose of the sizereduction in the discharge outlet 19 is that the latter is not simultaneously connected by two delivery cells due to which a noisegenerating reflux could occur from the cell with higher Z 9 pressure towards the cell less compressed. This may occur in particular when the discharge outlet 19 only is sealed of f with respect to the delivery line 21 by a first nonreturn valve 22. While both the cell 23 and the cell 24 would normally be unloaded through the outlet slot 18 in the known pump construction (Figure 5), this is no longer the case in the construction according to the invention shown in Figure 7 since here the pre- compression cell 23 is unloaded through the pre-compression outlet 20 and the pressure cell 24 is unloaded through the discharge outlet 19. A short circuit of these two cells 23 and 24 is, thus, no longer possible. Moreover, the two non-return valves 22 and 25 prevent it that a pressure balance takes place between the delivery line 21 and the cells 23,24 which are partly filled.

Circumstances permitting, the first non-return valve 22 may be dispensed with since realising a certain optimisation the pressure in the cell 24 is already precompressed to the pressure in the delivery line 21.

Figure 8 shows a modification of the external gear pump shown in Figures 6 and 3. In this modified pump, a slide valve 27 which is subject to the action of a spring 26 is inserted in the inlet opening 5. This slide valve is capable of varying the resistance to flow of fluid through the inlet opening 5. As is indicated by a fluid coupling line 28 in dashed outline it is possible to vary the position of the slide valve 27 by means of the discharge pressure in the outlet duct 10, and in such a way that the slide valve closes progressively as the pressure in the discharge duct increases. The return coupling line 28 can, thus, be regarded as a discharge pressure duct which acts on a corresponding piston of the slide valve 27. In this way it will be possible to control the throttling in the inlet opening 5 depending on the pressure in the outlet duct 10, so that the throttling is increased at a more elevated pressure and consequently the filling volume in the cells is reduced.

Pumps according to the invention may also be used for lubricating and cooling systems of automatic gear change equipment, power transmissions and gears of commercial vehicles.

Claims

CLAIMS:

A gear pump, characterised in that for the generation of a delivery rate which is dependent nonlinearly on the rate of revolution of the pump gear means a restrictor is provided on the suction side of the pump which limits the delivery rate of a delivery cell depending on the rate of revolution (n) of the pump gear.
2. A gear pump as claimed in claim 1, characterised in that in the limitation of the delivery rate is effected by a reduced loading time of the delivery cell.
3. A gear pump as claimed in claim 2, characterised in that the presence of a radial and/or lateral inflow a restricted inlet slot serving as a suction-side control slot is shifted toward a later moment as regards its opening moment.
4. A gear pump as claimed in claim 1 or claim 2, characterised in that the pump is an external gear pump and in that the restrictor is constituted by a narrow suction duct.
5. A gear pump as claimed in any one of claims 1 to 4, characterised in that nonreturn valve means is provided in the pressure circuit of the pump.
6. A gear pump as claimed in claim 5, characterised in that a non-return valve is provided between an outlet opening in the pre-compression position and the pressure circuit and in that a nonreturn valve is provided in a connecting path between a discharge outlet and a delivery line (21) or the connecting path is direct without such nonreturn valve. 30
7. A gear pump as claimed in claim 6, characterised in that the pump is an annular gear pump and that a small, additional pre-compression slot is arranged in the precompression position of the delivery cell (23).
8. A gear pump as claimed in claim 7, characterised in that the additional slot has an area of passage which is smaller than that of the discharge outlet slot.
9. A gear pump as claimed in claim 5, characterised 12 in that the non-return valve means is moulded into the housing of the gear pump.
10. A gear pump as claimed in claim 1, character34ised in that a suction throttling is provided which is controlled by the delivery pressure.
11. A gear pump as claimed in claim 10, characterised in that the suction throttling is provided by a slide valve which is controlled by the outletside pressure and which is inserted in an inlet opening.
12. A gear pump as claimed in any one of claims 1 to 11 connected as a lubricating oil pump for internal combustion engines and/or for vehicle gears.
13. A gear pump substantially as hereinbefore described and as illustrated in Figures 3, 5, 6, 7 and 8.