Patent Grant
6974312
The present disclosure is directed towards hydraulic pumps and, more particularly, to a pumping element for a hydraulic pump.
Hydraulic pumps are commonly used for many purposes and in many different applications. Vehicles, such as, for example, highway trucks and off-highway work machines, commonly include hydraulic pumps that are driven by an engine in the vehicle to generate a flow of pressurized fluid. The pressurized fluid may be used for any of a number of purposes during the operation of the vehicle. A highway truck, for example, may use pressurized fluid to operate a fuel injection system or a braking system. A work machine, for example, may use pressurized fluid to propel the machine around a work site or to move a work implement.
A hydraulic pump typically includes a pumping element that applies work to an operating fluid to increase the pressure of the fluid. In one type of hydraulic pump, the pumping element includes a series of piston that are disposed in cylinders. The pistons are driven through a reciprocal movement within the cylinders to compress the operating fluid. The pumping element may be fixed displacement, where the stroke length of the pistons is constant. Alternatively, the pumping element may be variable displacement, where the stroke length of the pistons may be varied.
As shown in U.S. Pat. No. 6,035,828 to Anderson et al., a fixed displacement pump may include a metering device that allows the output flow rate of the pump to be varied. In the described system, the metering device includes a series of metering sleeves that are disposed around a series of pistons. The metering sleeves are configured to selectively block a passageway that provides a fluid connection with a compression chamber in the cylinder. When the passageway is open, operating fluid may flow from the compression chamber through the passageway to thereby prevent pressurization of the operating fluid during the compression stroke of the piston. The rate at which the pump generates pressurized fluid may be controlled by varying the position of the metering sleeves. The rate of pressurized fluid generation may be increased by covering the passageway for a greater portion of the compression stroke. The rate of pressurized fluid generation may be decreased by leaving the passageway open for a greater portion of the compression stroke.
The metering sleeves have a close tolerance relative to the outer surface of the pistons to minimize the amount of fluid that leaks from the passageway. It is expected that some operating fluid will leak from the passageway through the clearance between the metering sleeve and the piston surface. This fluid may be used to lubricate the surfaces of the metering sleeve and piston, which may facilitate movement between the metering sleeve and piston. Under some operating conditions, such as when the engine is cold, the viscosity of the operating fluid may be relatively high. The high viscosity of the fluid results in a greater drag between the metering sleeve and the piston. This increases the force required to move the metering sleeve relative to the piston. Accordingly, accurately controlling the position of the metering sleeve relative to the piston may be more difficult when the engine is cold.
In addition, when the metering sleeves are covering the spill ports, an inner surface of the metering sleeves will be exposed to the pressurized fluid within the compression chamber. Particularly in high pressure systems, the pressurized fluid exerts a significant force on the inner surface of the metering sleeve. Over time, this force may cause the metering sleeve to swell or deform. The swelling or deformation of the metering sleeve may increase the clearance between the metering sleeve and the piston. The increased clearance may lead to an increase in the amount of fluid that leaks from the passageway, which may decrease the volumetric efficiency of the pump.
The pumping element of the present disclosure solves one or more of the problems set forth above.
According to one aspect, the present disclosure is directed to a pumping element for a hydraulic pump. The pumping element includes a cylinder that forms a compression chamber and has a discharge port. A piston having a pressure surface, a spill port, and a passageway connecting the pressure surface with the spill port is disposed in the cylinder for reciprocal movement between a first position and a second position. The pressure surface of the piston is adapted to increase the pressure of a fluid disposed in the compression chamber as the piston moves between the first position and the second position. The pressurized fluid flows through the discharge port of the cylinder. A metering sleeve is disposed around the piston and is configured to selectively cover the spill port as the piston reciprocates between the first and second positions. The metering sleeve has a groove that is adapted for fluid communication with the spill port as the piston reciprocates between the first and second positions.
In another aspect, the present disclosure is directed to a method of operating a metering sleeve in a hydraulic pump. A piston is driven through a reciprocal movement in a cylinder to pressurize an operating fluid. The operating fluid is released from the cylinder through a discharge port when the pressure of the operating fluid reaches a predetermined limit. The position of a metering sleeve is adjusted to selectively cover a spill port to vary the amount of operating fluid pressurized by the piston. Pressurized operating fluid is allowed to flow from the spill port to a groove in the metering sleeve as the piston reciprocates within the cylinder.
a and 2b are schematic and diagrammatic representations of a metering sleeve and piston in accordance with an exemplary embodiment of the present invention; and
An exemplary embodiment of a pump 20 is diagrammatically and schematically illustrated in
A supply pump 14 may draw operating fluid from tank 12 and direct the operating fluid through an inlet line 16 to inlet 22 of pump 20. Supply pump 14 may be a relatively low pressure pump, such as, for example, a sump pump as is commonly used in a vehicle lubrication system to distribute lubricating oil within an engine and/or vehicle. Supply pump 14 may increase the pressure of the fluid to a relatively low pressure, such as, for example, about 70 kPa (10.2 psi).
As also illustrated in
Pumping element 26 also includes a series of pistons 32. One piston 32 is slidably disposed within each cylinder 46. As shown in
As also shown in
Referring to
As further shown in
Pump 20 may further include a swashplate 28 that is rotatably disposed in housing 21. Swashplate 28 may include an angled driving surface 29. Input shaft 52 may be connected to swashplate 28 so that a rotation of input shaft 52 causes a corresponding rotation of swashplate 28 and driving surface 29.
Driving surface 29 of swashplate 28 is operatively engaged with each piston 32. Driving surface 29 is angled so that rotation of swashplate 28 sequentially moves each piston 32 from the first position to the second position. After each piston 32 has reached the second position and as swashplate 28 continues to rotate, springs 50 will move each piston 32 from the second position towards the first position.
A device, such as, for example, a pivoting shoe 30, may be disposed between each piston 32 and driving surface 29. Pivoting shoe 30 is configured to pivot relative to piston 32. The pivoting motion ensures that the respective piston 32 will remain operatively engaged with driving surface 29 as swashplate 28 rotates.
In the illustrated embodiment, driving surface 29 of swashplate 28 has a fixed angle. It should be noted, however, that pump 20 may include a mechanism configured to vary the angle of driving surface 29. By varying the angle of driving surface 29, the amount of motion, or the length of the compression stroke, of each piston 32 may be changed.
As further illustrated in
Hydraulic pump 20 may include a collector 38. Pressurized operating fluid that is released from each compression chamber 48 through check valve 36 may be directed to collector 38. Collector 38 may be configured to store a desired quantity of pressurized operating fluid.
Collector 38 is connected to an outlet 24, which may be further connected to an outlet line 18. Outlet line 18 may be connected to a fluid rail 19. Fluid rail 19 may be configured to distribute pressurized operating fluid to a system, such as, for example, a fuel injection system, associated with a vehicle and/or engine.
As also schematically shown in
As illustrated in
As also shown in
As shown in
The position of metering sleeve 34 relative to piston 32 determines the portion of the compression stroke 80 in which metering sleeve 34 covers spill port 74 in piston 32. In the first position, metering sleeve 34 covers spill port 74 for the entire compression stroke 80 of piston 32. In the second position, metering sleeve 34 leaves spill port 74 uncovered for the entire compression stroke 80 of piston 32. Metering sleeve 34 may also be positioned between the first and second positions so that spill port 72 is covered for a portion of the compression stroke of piston 32.
With reference to
The operation of an exemplary embodiment of the described pumping element will now be described with reference to the figures. The described pump 20 may be included as part of a vehicle to provide pressurized fluid to a system in the vehicle. The vehicle may be, for example, a highway truck or an off-highway work machine.
Operation of the engine of the vehicle results in a rotation of input shaft 52. Rotation of input shaft 52 causes a corresponding rotation of swashplate 28 and driving surface 29. Rotation of driving surface 29 acts to move each piston 32 through a compression stroke, i.e. from the first position towards the second position.
When metering sleeve 34 is in the first position, spill port 72 is covered for the entire compression stroke of piston 32. When piston 32 is moving towards the second position, pressure surface 70 of piston 32 will exert a force on operating fluid disposed in compression chamber 48. The force exerted on the operating fluid will increase the pressure of the fluid. When the pressure of the operating fluid within compression chamber 48 reaches a predetermined limit, check valve 36 will open to allow the pressurized fluid to flow into collector 38.
To reduce the rate at which pressurized fluid is generated, metering sleeve 34 may be moved towards the second position, which will leave spill port 72 uncovered for a greater portion of the compression stroke of piston 32. When spill port 72 is uncovered and piston 32 moves towards its second position, pressure surface 70 will force operating fluid from compression chamber 48 through passageway 74 and spill port 72. Accordingly, when piston 32 is moving towards the second position, pressure surface 70 will not pressurize the operating fluid.
If metering sleeve 34 is positioned between the first and second positions, spill port 72 will move under metering sleeve 34 at some point during the compression stroke of piston 32. When metering sleeve 34 covers, or blocks, spill port 72, operating fluid is not allowed to escape from compression chamber 48. At this point, pressure surface 70 will act to pressurize the operating fluid remaining in compression chamber 48. When the fluid reaches the predetermined pressure, check valve 36 will open to allow the pressurized fluid to flow to collector 38. However, as some operating fluid escaped from compression chamber 48 when spill port 72 was uncovered, the quantity of pressurized fluid released to collector 38 will be less than would have been released had spill port 72 been covered for the entire compression stroke.
As piston 32 slides within metering sleeve 34, spill port 72 will move into fluid communication with grooves 82 in inner surface 84 of metering sleeve 34. In certain situations, such as when the operating fluid in compression chamber 48 is approaching the predetermined limit, the operating fluid may exert a significant force on inner surface 84 of metering sleeve 34. Grooves 82 allow the pressurized fluid to flow around metering sleeve 34. This will distribute the force exerted by the pressurized fluid around the entire metering sleeve 34.
The distribution of the fluid force may reduce or prevent swelling or deformation of metering sleeve 34 that could result from repeated exposure to highly pressurized fluid. Reducing or preventing swelling and/or deformation of metering sleeve 34 may allow a close tolerance to be maintained between metering sleeve 34 and piston 32. This will prevent or reduce an increase in leakage from compression chamber 48 as is typically experienced over an extended operation of pump 20. By maintaining a constant amount of leakage, metering sleeve 34 may prevent a decrease in the volumetric efficiency of pump 20 over time.
In addition, grooves 82 may reduce the force required to move metering sleeve 34 relative to piston 32 or to move piston 32 relative to metering sleeve 34. The presence of grooves 82 in inner surface 84 will reduce the shear area between metering sleeve 34 and outer surface 76 of piston 32. The reduction in shear area translates to a reduction in the drag force experienced when the surfaces of metering sleeve 34 and piston 32 are moved relative to each other. The reduction in force may be particularly apparent when the viscosity of the operating fluid is high, such as when pump 20 is operating in cold conditions. Thus, grooves 82 in metering sleeve 34 may effectively improve the lubrication characteristics between metering sleeve 34 and piston 32.
It will be apparent to those skilled in the art that various modifications and variations can be made in the described pump and pumping element without departing from the scope of the invention. Other embodiments may be apparent to those skilled in the art from consideration of the specification and practice of the pumping element disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the present disclosure being indicated by the following claims and their equivalents.
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|---|---|---|---|
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| Number | Date | Country |
|---|---|---|
| 2568944 | Feb 1986 | FR |
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| WO 0161193 | Aug 2001 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20040115066 A1 | Jun 2004 | US |
