WO2006049500A1

WO2006049500A1 - Gear pump with variable capacity

Info

Publication number: WO2006049500A1
Application number: PCT/NL2005/000784
Authority: WO
Inventors: Tjerk Kingma; Richard De Roos
Original assignee: Tjerk Kingma; Richard De Roos
Priority date: 2004-11-08
Filing date: 2005-11-08
Publication date: 2006-05-11
Also published as: NL1027440C2

Abstract

Gear pump with variable capacity with a first liquid chamber and a second liquid chamber, a first gear wheel (11, 111) and a second gear wheel (10, 110) which separate the liquid chambers from each other, wherein the gear wheels are axially displaceable relative to each other so that the second gear wheel can be brought into engagement with the first gear wheel along a length 11 with a volume flow proportional to the length 11 from the first liquid chamber to the second liquid chamber, and wherein a third gear wheel (12, 112) which also separates the two liquid chambers from each other and which can be placed into engagement over a length 12 with the first gear wheel or a gear wheel which is connected fixedly thereto in non-rotatable and axial manner and which also separates the liquid chambers from each other, such that a volume flow which is proportional to the length 12 is brought about from the second liquid chamber to the first liquid chamber.

Description

GEAR PUMP WITH VARIABLE CAPACITY

The invention relates to a liquid pump comprising a housing with a first liquid chamber having a first external port and a second liquid chamber having a second external port, a first gear wheel and a second gear wheel which separate the first liquid chamber and the second liquid chamber from each other, wherein the gear wheels are axially displaceable relative to each other so that the second gear wheel can be brought into engagement with the first gear wheel along a length 11, such that by rotating these gear wheels a volume flow which is proportional to the length 11 is brought about from the first liquid chamber to the second liquid chamber.

Such a pump is described in US-A-2001/0024618. The output (Q) of such a pump is determined by the area of the gear cavity (A), the length of the gear cavity (1), the number of gear cavities (s) on the driven gear wheel and the rotation speed (h) of the driven gear wheel. This times two because there are two gear wheels. Q = A x l x s x h x 2. The gear cavity length (1) is varied in order to enable adjustment of the output. The operative gear cavity length (1) is changed by displacing the gear wheels relative to each other.

The output can hereby vary, but not from zero to the maximum since if the output were zero the gear wheels would no longer engage each other. Nor can the flow direction of the liquid between the external ports be reversed.

The invention has for its object, among others, to obviate these drawbacks. For this purpose the housing comprises a third gear wheel which also separates the first liquid chamber and the second liquid chamber from each other and which can be placed into engagement over a length 12 with the first gear wheel or a gear wheel which is connected fixedly thereto in non- rotatable and axial manner and which also separates the first liquid chamber and the second liquid chamber from each other, such that owing to said rotation of these gear wheels a volume flow which is proportional to the length 12 is brought about from the second liquid chamber to the first liquid chamber.

The output and flow direction of the pump can hereby be adjusted by mutually displacing the gear wheels in axial direction while the gear wheels are rotated substantially at a constant speed and in only one direction. The total output, the volume flow from the first port to the second port, is proportional to the length 11 minus the length 12. A continuously adjustable output from zero to the maximum and a reversible flow can thus be achieved in the pump using a single rotation direction.

The pump is preferably manufactured such that the total of the lengths 11 and 12 is the same in different axial positions of the first gear wheel.

The first liquid chamber preferably comprises an orifice which extends between the liquid inlet side of the first and second gear wheel and the liquid outlet side of the first and third gear wheel, and the second liquid chamber comprises an orifice which extends between the liquid inlet side of the first and third gear wheel and the liquid outlet side of the first and second gear wheel. The parts of the end surface of the gear wheels which are not in engagement with another gear wheel are preferably sealed by end walls which lie thereagainst.

The second and the third gear wheel are preferably mounted at a fixed mutual distance as seen in axial direction.

In a particular preferred embodiment the second and the third gear wheel extend co-axially to each other. The first gear wheel is here preferably movable axially in a gear ring with complementary internal gearing, which internal gearing forms a separating wall extending between the first and the second liquid chamber.

The invention also relates to a method for displacing a liquid, wherein the liquid is displaced between a first external port in a first liquid chamber and a second external port in a second liquid chamber, wherein a first gear wheel and a second gear wheel which separate the first liquid chamber and the second liquid chamber from each other are displaced axially relative to each other so that the second gear wheel is brought into engagement with the first gear wheel over a length 11, wherein these gear wheels are rotated such that a volume flow which is proportional to the length 11 is brought about from the first liquid chamber to the second liquid chamber, and wherein a third gear wheel is brought into engagement over a length 12 with the first gear wheel or a gear wheel fixedly connected thereto in non- rotatable and axial manner, such that a volume flow which is proportional to the length 12 is brought about from the second liquid chamber to the first liquid chamber.

The invention is further elucidated on the basis of exemplary embodiments shown in the figures, wherein like components are designated with the same reference numerals, and in which:

Figure 1 shows a perspective view of a first exemplary embodiment of a pump according to the invention;

Figure 2 shows an exploded view of the pump according to figure 1;

Figure 3 shows a cross-section of the pump as according to arrows III in figure 1;

Figure 4 shows a cross-section of the pump as according to arrows IV in figure 1;

Figures 5A, 5B and 5C show schematically the operation of the pump of figures 1-4;

Figure 6 shows a graph of the output of the pump in relation to the position of the displaceable gear wheel in the pump of figure 1;

Figure 7 is a perspective view of a second exemplary embodiment of a pump according to the invention;

Figure 8 shows a partially exploded view of the pump of figure 7;

Figure 9 is a perspective view of connecting blocks with orifices of the pump as according to arrow IX in figure 7;

Figure 10 shows a cross-section of the pump as according to arrows X in figure 7; Figure 11 is a perspective view of an internal gear ring as according to arrow XI in figure 10; and

Figures 12A, 12B and 12C show schematically the operation of the pump of figures 7-11.

The pump according to figures 1-4 comprises a housing 1 with a recess 2 formed substantially by three parallel cylindrical bores which partially overlap each other. Substantially cylindrical bearing blocks 3, 4, 5, 6, 7, 8 are arranged in the respective bores, in which bearing blocks are suspended gear wheels 10, 11, 12. Bearing blocks 3, 4, 5, 6, 7, 8 also close off the parts of the end surfaces of gear wheels 10, 11, 12 which are not in engagement with an opposite gear wheel. The housing is closed on both sides by a cover 13, 14.

In the pump according to figures 1-4 the upper gear wheel 10 and the lower gear wheel 12 are arranged fixedly but mutually offset in housing 1. The middle gear wheel 11 can slide back and forth in axial direction between upper gear wheel 10 and lower gear wheel 12. For this purpose the hollow shaft 15 of the middle gear wheel 11 is mounted in two bearing blocks 5, 6 which can move like pistons in cylinders 16, 17. Hollow shaft 15 is provided with a key way and slides over a central shaft 18 which is provided with a key and which extends outside cover 13, where it can be driven.

Housing 1 is provided at the front and rear with bores 19, 20, 21, 22 which extend from the engaging zones of gear wheels 10, 11, 12, and which form ports to which liquid conduits can be connected. Figure 4 shows schematically by means of broken lines 23, 24 how these conduits can extend according to the invention. Bores 19, 20 and conduit 24 together form a first liquid chamber, bores 21, 22 and conduit 25 together form a second liquid chamber.

Due to this arrangement the pump can be considered as two gear pumps which are coupled to each other and which each have their own output. The dimensions of the gear wheels are chosen such that there is no pulsation action, so that there is a uniform output.

The operation of the pump will be illustrated with reference to figures 5A, 5B and 5C. In figure 5A the middle gear wheel 11 is situated in the middle position. The hatched portions represent the operative gear cavity lengths 11 and 12, and these are here both the same length. The output of the upper two gear wheels 10, 11 is thereby equal to the output of the lower two gear wheels 11, 12.

The outlet side of the upper two gear wheels 10, 11 is coupled to the inlet side of the lower two gear wheels 11, 12 by means of a first channel 23, and the outlet side of the lower two gear wheels 11, 12 is coupled to the inlet side of the upper two gear wheels 10, 11 by means of a second channel 24. The oil hereby circulates and there is no output.

In figure 5B the middle gear wheel 11 is displaced to the left. The operative gear cavity length 11 of the upper two gear wheels 10, 11 is thereby greater than the operative gear cavity length 12 of the lower two gear wheels 11, 12. This creates a flow to the left. The magnitude of the flow depends on the position of the middle gear wheel 11 and is continuously adjustable between zero and the maximum. In figure 5C the middle gear wheel 11 is displaced to the right. The operative gear cavity length 11 of the upper two gear wheels 10, 11 is thereby smaller than the operative gear cavity length 12 of the lower two gear wheels 11, 12. This creates a flow to the right. The magnitude of the flow is continuously adjustable between zero and the maximum, but in the opposite direction to figure 5. The flow direction of the oil in the pump itself is always the same. Figure 6 shows the relation between the position of the middle gear wheel 11 and the output of the pump.

In an alternative embodiment the channels 23, 24 can be absent or closed, whereby the pump can be used to generate two different complementary outputs. Such a pump is very suitable as control pump or as hydraulic barrier for wheeled vehicles.

The figures 7-11 show a second exemplary embodiment of the pump in which the lower gear wheel 111 is displaceable and the upper gear wheels 110, 112 are not displaceable. The pump has four ports 119, 120, 121, 122. Port 119 and port 122 are mutually connected by means of an orifice 123 and together form a first liquid chamber, port 120 and port 121 are mutually connected by means of an orifice 124 and together form a second liquid chamber. In figure 10 the lower gear wheel 111 is displaced into the extreme left-hand position.

The operative gear cavity lengths 11, 12 are varied with the lower long gear wheel 111 which is placed through a gear ring 125 with internal gearing, as shown in figure 11, and can be moved reciprocally therein. Gear ring 125 precisely encloses the lower gear wheel 111. According to figure 10 the pump has to the right of the lower gear wheel 111 a cylinder 117 in which there is a piston 106. The piston presses against the lower gear wheel 111 in order to obtain a good sealing on the side of gear wheel 111. Also to the left of lower gear wheel 111 there is a cylinder 116 having therein a piston 105 which presses against gear wheel 111. These two pistons 105, 106 can slide the long lower gear wheel 111 back and forth in the same manner in which the piston of a hydraulic cylinder is moved back and forth, for instance with an external control valve block.

In addition to this hydraulic method of displacement, the lower gear wheel 111 can also be moved reciprocally in mechanical, electrical or pneumatic manner. Shaft 115 of lower gear wheel 111 is connected with a slide coupling 136 to drive shaft 118 which is mounted in clearance-free manner in two conical roller bearings 126, 127, and cannot displace. By means of a cover 128 and thin filler plates 129, 130, 131, 132 the conical roller bearings 126, 127 are enclosed in the bearing housing. An oil sealing ring 133 provides for oil sealing of the bearing housing which is connected in every situation to the suction side of the pomp.

The upper gear wheels 110, 112 cannot slide and are sealed on the side by a piston 103 on the left and a piston 104 on the right. These pistons have the same diameter as gear wheels 110, 112. The upper bore 102 in housing 101 serves here as cylinder. Between the two upper gear wheels 110, 112 is a spacer 109 which provides the correct distance between the upper gear wheels 110, 112 and the seal on the side of these upper gear wheels 110, 112. The width of spacer 109 is the same as the width of gear ring 125. The pressure side of the left-hand section is connected to the suction side of the right-hand section with an orifice 123 which runs underneath. The pressure side of the right- hand section is connected to the suction side of the left- hand section with an orifice 124 which runs over the top. Mounted on the outer side of the housing are two connecting blocks 134, 135 to which the orifices 123, 124 are connected. On these connecting blocks 134, 135 are external connecting options to which conduits or hoses can be connected. The ports to which no external conduit or hose is connected is closed. On the pump there are also two further connections (not shown) for hydraulic conduits with which pistons 105, 106 can be actuated.

The operation of the pump is illustrated with reference to figures 12A, 12B and 12C. According to figure 12A pressure port 212 produces for instance 50 cc oil per rotation. Because port 121 is connected to port 120, all oil flows to port 120 because port 120 also draws in 50 cc per rotation. Port 122 also produces 50 cc per rotation. Because port 122 is connected to port 119, all oil flows to port 119 because port 119 also draws in 50 cc per rotation. The output of the pump in this position (middle position) of lower gear wheel 111 is zero.

If lower gear wheel 111 is displaced to the left as shown in figure 12B, the operative gear cavity length 11 on the left is greater and port 121 will produce more per rotation. For instance 80 cc per rotation, which is 30 cc more than in figure 12A. Because the operative gear cavity length 12 on the right has become smaller, port 122 now produces 30 cc per rotation less. This is 20 cc per rotation. Port 119 demands 80 cc per rotation. This creates a shortfall of 60 cc per rotation in the connecting conduit 123 between port 122 and port 119. At port 122, which is connected to the outside world, a suction of 60 cc per rotation hereby occurs. Port

120 demands 20 cc per rotation. This creates a surplus of 60 cc per rotation in the connecting conduit 124 between port

121 and port 120. An output of 60 cc per rotation is hereby created at port 121.

A hydraulic user, for instance a hydraulic motor, can be connected between port 122 (or port 119) and port 121 (or port 120) . Because lower gear wheel 111 can be displaced from the middle position (the zero position) , the output can be regulated from zero to the maximum in continuously variable manner.

In order to reverse the flow, lower gear wheel 111 is first carried back again to the middle position, whereby the output once again becomes zero. By sliding the middle gear wheel 111 through to the right the output becomes greater again, but in reverse direction as shown in figure 12C.

Port 122 hereby becomes a pressure port and port 121 a suction port. The flow direction in the pump is always the same in all cases and does not change.

It is important to take into account the pressure- lubricated slide bearings present in the pump. When the flow reverses, pressure on these bearings must still continue. This is also the case when the flow is zero. This is achieved with a hydraulic non-return valve which consists of four ball valves. Although the invention is illustrated with reference to two exemplary embodiments, many variations hereof are possible within the scope of the invention as defined by the claims.

Claims

1. Liquid pump comprising a housing (1, 101) with a first liquid chamber (19, 20, 24; 119, 122, 123) having a first external port (19, 20; 119, 122) and a second liquid chamber (21, 22, 23; 120, 121, 124) having a second external port (21, 22; 120, 121), a first gear wheel (11; 111) and a second gear wheel (10; 110) which separate the first liquid chamber and the second liquid chamber from each other, wherein the gear wheels (10, 11; 110, 111) are axially displaceable relative to each other so that the second gear wheel (10, 110) can be brought into engagement with the first gear wheel (11, 111) along a length 11, such that by rotating these gear wheels (10, 11; 110, 111) a volume flow which is proportional to the length 11 is brought about from the first liquid chamber to the second liquid chamber, characterized in that the housing (1, 101) comprises a third gear wheel (12, 112) which also separates the first liquid chamber and the second liquid chamber from each other and which can be placed into engagement over a length 12 with the first gear wheel (11, 111) or a gear wheel which is connected fixedly thereto in non-rotatable and axial manner and which also separates the first liquid chamber and the second liquid chamber from each other, such that owing to said rotation of these gear wheels (11, 12; 111, 112) a volume flow which is proportional to the length 12 is brought about from the second liquid chamber to the first liquid chamber.

2. Liquid pump as claimed in claim 1, wherein the volume flow from the first port (19, 20; 119, 122) to the second port (21, 22; 120, 121) is proportional to the length 11 minus the length 12.

3. Liquid pump as claimed in claim 1 or 2, wherein the total of the lengths 11 and 12 is the same in different axial positions of the first gear wheel (11; 111) .

4. Liquid pump as claimed in any of the foregoing claims 1-

3, wherein the second gear wheel (10; 110) and the third gear wheel (12; 112) are mounted at a fixed mutual distance as seen in axial direction.

5. Liquid pump as claimed in any of the foregoing claims 1-

4, wherein the parts of the end surfaces of the gear wheels (10, 11, 12; 110, 111, 112) which are not in engagement with another gear wheel are sealed by end walls which lie thereagainst.

6. Liquid pump as claimed in any of the foregoing claims 1-

5, wherein the second gear wheel (110) and the third gear wheel (112) extend co-axially to each other.

7. Liquid pump as claimed in any of the foregoing claims 1-

6, wherein the first gear wheel (111) is movable axially in a gear ring (125) with complementary internal gearing, which internal gearing forms a separating wall extending between the first and the second liquid chamber.

8. Liquid pump as claimed in any of the foregoing claims 1-

7, wherein the first liquid chamber comprises an orifice (24; 124) which extends between the liquid inlet side of the first gear wheel (11; 111) and the second gear wheel (10; 110) and the liquid outlet side of the first gear wheel (11; 111) and the third gear wheel (12; 112), and wherein the second liquid chamber comprises an orifice

(23; 123) which extends between the liquid inlet side of the first gear wheel (11; 111) and the third gear wheel (12; 112) and the liquid outlet side of the first gear wheel (11; 111) and third gear wheel (12; 112) .

9. Method for displacing a liquid, wherein the liquid is displaced between a first external port (19, 20; 119,

122) in a first liquid chamber (19, 20, 24; 119, 122,

123) and a second external port (21, 22; 120, 121) in a second liquid chamber (21, 22, 23; 120, 121, 124), wherein a first gear wheel (11; 111) and a second gear wheel (10; 110) which separate the first liquid chamber and the second liquid chamber from each other are displaced axially relative to each other so that the second gear wheel (10; 110) is brought into engagement with the first gear wheel (11; 111) over a length 11, and wherein these gear wheels (10, 11; 110, 111) are rotated such that a volume flow which is proportional to the length 11 is brought about from the first liquid chamber to the second liquid chamber, characterized in that a third gear wheel (12; 112) is brought into engagement over a length 12 with the first gear wheel (11; 111) or a gear wheel fixedly connected thereto in non-rotatable and axial manner, such that a volume flow which is proportional to the length 12 is brought about from the second liquid chamber to the first liquid chamber.

10. Method as claimed in claim 9, wherein the gear wheels

(10, 11, 12; 110, 111, 112) are rotated substantially at a constant speed and in only one direction.