Patent Application
20080060510
The invention concerns a pump or hydraulic motor in accordance with the preamble of claim 1. Such pumps or hydraulic motors are known as bent axis pumps or motors. The plungers of the known pumps or motors are swivable connected to a flange and are movable in cylinders, which are at one end of a rotor. At the other end of the rotor a port plate is positioned; this end of the rotor forms the valve surface. The port plate is located between the valve surface of the rotor and the housing. In the known pumps or motors, the port plate positioning drive comprises hydraulic actuators, which move a coupling pin in a slot in the housing. The coupling pin is positioned in a hole in the centre of the port plate so coupling the port plate to the hydraulic actuators.
This known construction has the disadvantage that in the centre plane at the location of the slot the housing does not support the port plate sufficiently so that the port plate can deform under influence of the high pressure between the port plate surface and the valve surface. Also between the pressure ports, which is in the area of the centre plane, the pressure between the port plate surface and the valve surface fluctuates with the passage of the cylinder channels and thereby causes fluctuations in the deformations. It is not possible to compensate for these fluctuations in the design of the parts. These fluctuating deformations create gaps, which cause leakage of oil. If the deformations are limited, for instance to a maximum of 3 to 5 micro millimetres, the leakage between the port plate surface and the valve surface remains acceptable. A higher value reduces the efficiency of the pump or motor in an undesirable way. This requirement limits the first radius, as a larger radius reduces the stiffness of the port plate and so increases the deformations.
A further disadvantage of the known construction is that it is not possible to extend the drive axis through an opening in the port plate. Such an extension would make it possible to connect several pumps or motors in-line. An opening in the port plate with a diameter sui-table for letting the drive axis pass through would further reduce the stiffness of the port plate and would interfere with the hydraulic actuators.
In order to overcome these disadvantages the pump or hydraulic motor is in accordance with the characterizing part of claim 1. Supporting the port plate in the centre plane using the hydraulic actuators reduces the deformations caused by the fluctuating high-pressure between the valve surface and the port plate surface, making it possible to overcome the disadvantages of the known design without adding to leakage.
In accordance with an embodiment, the pump or hydraulic motor is according to claim 2. In this way the hydraulic actuators directly support the area with the fluctuating pressure thereby further reducing the fluctuating deformations.
In accordance with an embodiment, the pump or hydraulic motor is according to claim 3. By connecting the second actuator with the high-pressure port, it is necessary that the control unit keeps the first actuator under pressure as well. In this way it is ensured that both actuators support the port plate.
In accordance with an embodiment, the pump or hydraulic motor is according to claim 4. The first actuator and the third actuator work together, whereby the third actuator directly compensates the force that the second actuator exerts on the port plate. This leads to lower forces on the port plate and reduces deformations.
In accordance with an embodiment, the pump or hydraulic motor is according to claim 5 or 6. This reduces the number of separate parts.
In accordance with an embodiment, the pump or hydraulic motor is according to claim 7. This way the torque for positioning or rotating the port plate is more or less independent of the rotational position of the port plate, so making positioning the port plate easier.
In accordance with an embodiment, the pump or hydraulic motor is according to claim 8. In this way, the hydraulic actuators have a simple and cost effective design.
In accordance with an embodiment, the pump or hydraulic motor is according to claim 9. This ensures that the second cylinders do not exert a sideways force on the port plate and that the design can be more compact by having canals in the port plate for supplying oil to the various cylinders.
In accordance with an embodiment, the pump or hydraulic motor is according to claim 10. This ensures that during starting pressure build-up can take place in the high-pressure port and in the connected cylinders by pre-venting leakage through various gaps. After starting, the high pressure ensures that the gaps remain closed.
In accordance with an embodiment, the variable pump or hydraulic motor is according to claim 11. This reduces the number of different parts in the device and eases production or maintenance of the pump or motor.
In accordance with an embodiment, the variable pump or hydraulic motor is according to claim 12. By providing the bearing surfaces with openings connected to the pres-sure ports, there is a simple and direct connection between the pressure lines and the chambers.
In accordance with an embodiment, the variable pump or hydraulic motor is according to claim 13. This further avoids bending forces on and resulting deformations of the port plate.
In accordance with an embodiment, the variable pump or hydraulic motor is according to claim 14. In this way a compact high capacity pump or motor is made.
The invention is explained below with reference to an embodiment and with the aid of a drawing, in which:
The hydraulic device shown in
The pump 12 comprises a housing 22 on which a first cover 10 and a second cover 23 are fastened with bolts 11, the first cover 10 and the second cover 23 have bearings 2 in which a shaft 3 can rotate around a first axis L. The shaft 3 sealingly extends through the second cover 23 and ends as the splined shaft end 24. The shaft 3 has a flange 29 in the centre of the housing 22 and pump plungers 28 extend on both sides of the flange 29, in this embodiment on both sides twelve pump plungers 28. Pump cylinders 26 enclose the pump plungers 28 and rest against a channel plate 25. The pump plungers 28 have a spherical sealing surface that seals against the inside surface of the pump cylinder 26, so that the inside of the pump cylinder 26 forms a pump chamber with the pump plunger 28. During use, the pump cylinders 26 seal against the channel plate 25 under influence of the pressure in the pump chamber. In order to prevent that leakage occurs in situations where the pressure in the pump chamber is too low a spring 27 is provided, this spring 27 presses the pump cylinders 26 against the channel plate 25. In other embodiments in stead or in addition to the spring 27 locking means hold the pump cylinder 26 against the channel plate 25, thereby maintaining the possibility of a sliding movement of the pump cylinder 26 over the channel plate 25.
An opening in the bottom of the pump cylinder 26 connects with a channel 31, which ends at a valve surface 6 of the channel plate 25. The valve surface 6 rotates over a port plate surface 7 of a port plate 8. The channel plate 25 rotates with the shaft 3 and is coupled with the shaft 3 by a sphere shaped coupling 4, so that it can swivel over the coupling 4 and rotate around a second axis M, which intersects the first axis L. The port plate 8 determines the tilt angle of the second axis M. The direction of centre lines M′ of the pump cylinders 26 is parallel to the second axis M, so that the sealing surface between a pump plunger 28 and a pump cylinder 26 is perpendicular to the second axis M. The first cover 10 and the second cover 23 and the housing 22 have canals (not shown) that connect the pressure lines with the port plates 8 and so with the pump chambers.
Due to the angle between the first axis L and the second axis M in a full rotation of the shaft 3 the volume of the pump chamber changes a stroke volume between a maximum volume and a minimum value. The stroke volume determines the pump capacity. By rotating the port plate 8 around a third axis N (see
The second actuator 13 comprises a plunger 1 mounted in the first cover 10 and a cylinder 14 slidable over the slide surface 35. The actuator chamber is connected through the opening in the bottom of the cylinder 14 with a high pressure channel 16 in the port plate 8 that connects the actuator chamber with a high-pressure port 39 (see
When starting the pump 12 a spring 30 presses the port plates 8 in a tilted position, a spring support 32 positions the spring 30 on the port plate 8. In the tilted position, the stroke volume is maximal during starting. In order to prevent leakage between the cylinders 14 and the port plate 8 the cylinders are pressed by a spring (not shown) against the port plate 8. In another embodiment, there are (additional to or instead of the spring) locking means that hold the cylinders 14 slidingly against the port plate 8. After the pump 12 has started the pressure in the actuator chamber presses the cylinders 14 against the port plate 8.
The
During operation the high-pressure port 39 produces a high oil pressure between the port plate surface 7 and the valve surface 6 at the location of the high-pressure port 39 and a diminishing pressure in the surrounding seal land, that is the surrounding area of the high-pressure port 39 that works as a seal between the high pressure and the pressure-less inside of the pump 12. The high oil-pressure causes a force on the port plate 8 that is more or less completely counteracted by force in the direction of the port plate surface 7 caused by the high pressure in the high-pressure canal 38 in the cylindrical bearing surface 37 and the surrounding seal land. This requirement determines the area of the high-pressure canal 38 in the cylindrical bearing surface 37.
The rotating pump cylinders 26 and the rotating channels 31 cause a fluctuating pressure in the crossover area 41 as the pressure changes when a channel 31 changes from the connection with the high-pressure port 39 to the low-pressure port 40 or vice versa. This fluctuating pressure causes a fluctuating force on the port plate 8 and causes fluctuating gaps between the port plate surface 7 and the valve surface 6, which leads to oil leakage that must be as little as possible as it reduces the efficiency of the pump 12. In order to reduce these gaps the first actuator 33 and the second actuator 13 on work the port plate 8 in the direction of the port plate surface 7 and have a direction perpendicular on this surface. In this way, the forces of the actuators help to close the possible gaps and reduce the deformations of the port plate 8. The actuators work at a distance from the third axis on the port plate 8, which is equal or larger than the radius of crossover area 41, which also reduces deformations of the port plate 8. Preferably, the positions of the actuators are such that the stroke of the plungers 1 and 18 in the cylinders 14 is equal or less than the stroke of the pump plungers 28 in the pump cylinders 26, so that the same parts can be used. This means that the distance of the actuators to the first axis L can maximal be twice the radius of the pump plungers 28 around the first axis L.
Placing the actuators at a distance from the third axis N that is greater than the radius of the pressure ports 39 and 40 has the additional advantage that the shaft 3 can extend through a hole in the port plate 8. It is then possible to place several pumps in line with each other whereby the shafts 3 are connected.
The disclosed embodiment shows two sets of pump plungers 28 each working with a port plate 8. This design has the advantage that a small angle between the first axis L and the second axis M obtains a pump of high capacity. It will be clear that the various measures taken to obtain a simple and efficient design are independent from this advantage. In addition, the design of the port plate 8 and the actuators is for instance also suitable for bent axis pumps that have a rotor with cylindrical holes whereby a port plate supports this rotor directly.
| Number | Date | Country | Kind |
|---|---|---|---|
| 05101934.7 | Mar 2005 | EP | regional |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2006/060543 | Mar 2006 | US |
| Child | 11853449 | Sep 2007 | US |
