ELECTRO-HYDRAULIC PUMP (E-PUMP)
A motor may comprise a stator and a rotor rotatable relative to the stator. A portion of the rotor may house a hydraulic pumping element of a hydraulic pump for effectuating movement of fluid from an inlet to an outlet thereby transforming the rotational power of the shaft into hydraulic power. Specifically, an electro-hydraulic pump may include a piston pump barrel assembly including a plurality of pistons arranged around a central axis for pumping hydraulic fluid and a cam for displacing the plurality of pistons when relative movement between the cam and the plurality of pistons occurs. A plurality of magnets may be fixedly attached to the outside of the piston pump barrel assembly, and electrical windings may radially surround the magnets and be configured to create a magnetic field when energized so as to cause the plurality of magnets and a portion of the piston pump barrel assembly to rotate relative to the windings, thereby actuating the plurality of pistons to pump hydraulic fluid.
This application claims the benefit of U.S. Provisional Application No. 61/613,276 filed Mar. 20, 2012 and U.S. Provisional Application No. 61/791,582 filed Mar. 15, 2013, both of which are hereby incorporated herein by reference.
FIELD OF INVENTIONThe present invention relates generally to hydraulic pumps, and more particularly to an integrated electro-hydraulic pump.
BACKGROUNDA common design in the hydraulics industry is to couple an electric motor to a separate hydraulic pump to perform hydraulic work when electrical or other power is applied to the motor. Common practice in mobile applications has been to use a permanent magnet brushed DC electric motor to drive the hydraulic pump through a coupling between the motor and pump with the pumping element being any of common design (for example, external gear, internal gear, vane, piston, or the like). This design provides for low cost, high power density, and simple design.
The basic design of a brushed DC (BDC) motor consists of magnets glued to the internal housing of motor (stator). The rotating group (rotor) then consists of electrical windings attached to a commutator. When a voltage is applied to the lead wires of the motor, this energy is then transferred to the commutator and motor windings through two contacts called brushes. As this electrical energy is transferred to the rotor, a magnetic field is created through the motor windings that work with the stationary magnets to create rotation. This is a very common design throughout the industry as it is relatively simple and inexpensive to manufacture. Because of problems with BDC motors, brushless DC (BLDG) motors have become an attractive option as they continue to become more prevalent and less expensive. A BLDC motor is essentially a BDC motor turned inside out where the motor windings are mounted to the interior frame of the motor and the magnets are attached to the rotating group.
SUMMARY OF INVENTIONThere are several drawbacks that can be directly related to the fundamental design of the brushed DC motor. Because the motor windings are part of the rotating group, as they heat up during operation it is very difficult to conduct this energy away because they are isolated from the exterior frame of the motor. Also, as the electrical energy must be transferred through the brushes to the rotating element, the brushes wear out over time due to friction and electrical sparking. As such, in hydraulic power units the motor is often the first element to fail thereby greatly limiting the product life of the overall assembly. Finally, the sparking created due to the mechanical contact between the brushes and the rotor causes additional issues included generated electromagnetic interference (EMI), and an increased sensitivity to any flammable elements in or around the motor.
BLDC solves some of these problems. The reversal of components in a BLDC motor as compared to a BDC motor addresses the issues arising from having to transfer the electrical energy to the moving components. Therefore, cooling of the electronics becomes easier and the motor lasts longer as there is no mechanical contact between stationary and rotational components. Finally, because there is no sparking due to this mechanical contact and EMI issues are greatly reduced as are concerns over flammable environments.
Instead of coupling the motor to the pump mechanically, exemplary designs integrate the two by turning the rotating group of the BLDC motor into the hydraulic pumping mechanism. For example, the rotating element of the motor (the rotor) may include an axial piston pump with the magnets attached to the exterior of the barrel. However, essentially any internally driven pump design could be incorporated (bent axis piston, vane, gerotor, or the like) into the motor instead of the axial piston pump described herein (used as an illustrative example for the sake of expediency).
Because there is no electrical conductivity between the rotor and stator of the present design, the internal motor housing 34 can be run “wet” in that it can be safely flooded with hydraulic fluid without concern to the electrical components. An added advantage of this design is that the motor is now able to be liquid cooled while running (in addition to conductive cooling from the outside of the motor housing), which increases duty cycle and efficiency.
Additional advantages include the fact that essentially two components are combined into one. When placed in mobile applications this combination results in substantial benefits in reduction of space and weight of the system as well as minimizing the number of components exposed to environmental elements.
Further, by incorporating the pump element into a BLDC motor, added functionality is now available that would not have been easily accomplished with a BDC motor. Options such as variable speed control, rotor position feedback, revolution counters, and other various input and outputs can be incorporated by integrating a drive mechanism into the design and sensing rotor movement via an encoder or back-EMF signal.
Therefore, according to one aspect of the invention, an electro-hydraulic pump includes a motor having a stator and a rotor rotatable with respect to the stator and including a rotor body housing a hydraulic pumping element driven relative to the rotor body by rotation of the rotor for effectuating movement of fluid from an inlet to an outlet thereby transforming the rotational power of the rotor into hydraulic power.
Optionally, the stator concentrically surrounds the rotor.
Optionally, the motor is flooded with hydraulic fluid.
Optionally, the hydraulic pumping element is an axial piston pump.
Optionally, the hydraulic pumping element is contained within a motor housing.
Optionally, the motor is a brushless DC motor.
Optionally, the stator has electrical windings.
Optionally, the rotor includes permanent magnets.
According to another aspect of the invention, an electro-hydraulic pump includes a piston pump barrel assembly having a plurality of pistons arranged and rotatable around a central axis for pumping hydraulic fluid and a cam for axially displacing the plurality of pistons when relative rotational movement between the cam and the plurality of pistons occurs. The electro-hydraulic pump also includes a plurality of magnets fixedly attached to the outside of the piston pump barrel assembly and electrical windings radially surrounding the magnets and configured to create a magnetic field when energized so as to cause the plurality of magnets and a portion of the piston pump barrel assembly to rotate relative to the windings, thereby actuating the plurality of pistons to pump hydraulic fluid.
Optionally, the cam is stationary with respect to the windings and the plurality of pistons is rotatable about the central axis.
Optionally, the electro-hydraulic pump further includes an outer housing, and the electro-hydraulic pump is flooded with hydraulic fluid.
The foregoing and other features of the invention are hereinafter described in greater detail with reference to the accompanying drawings.
Referring to
The motor may be any type of motor but may preferably be a BLDC motor. If the motor is a BLDC, the motor may include or be connected to an electronic speed controller 15. A BLDC motor is advantageous in some cases for the various advantages it provides. For example, BLDC motors typically have more torque per weight, more torque per watt (increased efficiency), increased reliability, reduced noise, longer lifetime (no brush and commutator erosion), elimination of ionizing sparks from the commutator, and overall reduction of electromagnetic interference (EMI) when compared to BDC motors. BLDC motors are often more efficient at converting electricity into mechanical power than BDC motors. This improvement is largely due to the absence of electrical and friction losses due to brushes. The enhanced efficiency is greatest in the no-load and low-load region of the motor's performance curve. Under high mechanical loads, BLDC motors and high-quality brushed motors are often comparable in efficiency. Further, because the windings are not on the rotor, they are not subjected to centrifugal forces, and because the windings are supported by the housing 34, they can be cooled by conduction, requiring no airflow inside the motor for cooling. This in turn means that the motor's internals can be entirely enclosed and protected from dirt or other foreign matter.
Even more advantageous in the present design, the electro-hydraulic pump (and therefore the BLDC motor) may be flooded with hydraulic fluid, thus allowing efficient convection cooling.
The maximum power that can be applied to a BLDC motor is exceptionally high, limited almost exclusively by heat, which can weaken the magnets. (Magnets demagnetize at high temperatures, the “Curie point,” and for neodymium-iron-boron magnets this temperature is typically lower than for other types.) Thus, an internally convection-cooled BLDC motor can be safely run at higher power than a typical BLDC motor.
The electronic speed controller 15 for the BLDC motors of the present design may be incorporated on the electro-hydraulic pump or may be a separate component. In contrast to the BLDC motor, a BDC motor may be regulated by a comparatively simple controller, such as a rheostat (variable resistor). However, this type of controller may reduce efficiency because power is wasted in the rheostat.
AC induction motors require induction of magnetic field in the rotor by the rotating field of the stator; this results in the magnetic and electric fields being out of phase. The phase difference requires greater current and current losses to achieve power. BLDC motors, in contrast, are microprocessor-controlled to keep the stator current in phase with the permanent magnets of the rotor, requiring less current for the same effect and therefore resulting in greater efficiency.
BLDC motors can be constructed in several different physical configurations, and any of these configurations may be utilized in the present invention. In the ‘conventional’ (also known as inrunner) configuration, the permanent magnets are part of the rotor. Three stator windings may surround the rotor. The inrunner configuration is used herein for conciseness, but the invention is not limited thereto.
In the outrunner (or external-rotor) configuration, the radial-relationship between the coils and magnets is reversed; the stator coils form the center (core) of the motor, while the permanent magnets spin within an overhanging rotor which surrounds the core. The flat or axial flux type, used where there are space or shape limitations, uses stator and rotor plates, mounted face to face. Outrunners typically have more poles, set up in triplets to maintain the three groups of windings, and have a higher torque at low RPMs.
There are also two electrical configurations having to do with how the wires from the windings are electrically connected to each other. The delta configuration connects the three windings to each other (series circuits) in a triangle-like circuit, and power is applied at each of the connections. The wye (Y-shaped) configuration, sometimes called a star winding, connects all of the windings to a central point (parallel circuits) and power is applied to the remaining end of each winding.
A motor with windings in delta configuration gives low torque at low speed, but can give higher top speed. A wye configuration gives high torque at low speed, but also results in a lower top speed.
Although efficiency is greatly affected by the motor's construction, the wye winding is normally more efficient. In delta-connected windings, half voltage may be applied across the windings adjacent to the undriven lead (compared to the winding directly between the driven leads), increasing resistive losses. In addition, windings can allow high-frequency parasitic electrical currents to circulate entirely within the motor. A wye-connected winding, in contrast, may not contain a closed loop in which parasitic currents can flow, preventing such losses.
The hydraulic pump 18 may be any suitable type of hydraulic pump, but may be an axial piston pump 20 in a preferred embodiment.
Referring now to
The cam 26 may be stationary with respect to the windings 32 and the plurality of pistons 22 may be rotatable about the central axis. Alternatively, the opposite configuration is also possible. The cam 26 may be fixed or may be controlled so as to create a variable-displacement axial piston pump.
The electro-hydraulic pump 10 may further include an outer housing 34, and the electro-hydraulic pump may be flooded with hydraulic fluid. The hydraulic fluid may be actively or passively pumped through the system in order to cool the pump 10.
The plurality of pistons 22 (preferably but not necessarily an odd number) may be arranged in a circular array within the rotor 16 in a cylinder block 24, forming the piston pump barrel assembly 27. The rotor 16 may be driven to rotate about its central axis via the magnets 30 and windings 32. The cylinder block 24 creates a face seal with an end plate 35 supported by roller bearings 36 and also rotatable with respect to a central axis.
The plurality of pistons 22 may protrude from one end of the cylinder block 24. There are numerous configurations that may be used for the exposed ends of the pistons 22, but in all cases they bear against a cam 26. In variable displacement units, the cam 26 may be movable and is sometimes referred to as a swash plate, yoke or hanger. For conceptual purposes, the cam 26 can be represented with a plane bearing surface, the orientation of which, in combination with shaft rotation, provides the cam action that leads to piston reciprocation and thus pumping, though the cam may have a more complex shape as is known in the art. The angle between a vector normal to the cam plane and the piston pump barrel assembly axis of rotation, called the cam angle, is one variable that determines the displacement of the pump or the amount of fluid pumped per shaft revolution. Variable displacement units have the ability to vary the cam angle during operation whereas fixed displacement units do not. Either may be used in the present design.
As the piston pump barrel assembly rotates, the exposed ends of the pistons 22 are constrained to follow the surface of the cam 26. Since the cam plane is at an angle to the axis of rotation, the pistons must reciprocate axially as they precess about the piston pump barrel assembly axis. The axial motion of the pistons may be sinusoidal. During the rising portion of the piston's reciprocation cycle, the piston may move toward a valve plate (not shown). Also, during this time, the fluid trapped between the buried end of the piston and the valve plate is vented to the pump's discharge port (not shown) through one of the valve plate's semi-circular ports: the discharge port (not shown). As the piston moves toward the valve plate, fluid is pushed or displaced through the discharge port of the valve plate.
When the piston is at the top of the reciprocation cycle (commonly referred to as top-dead-center or just TDC), the connection between the trapped fluid chamber and the pump's discharge port may be closed. Shortly thereafter, that same chamber may become open to the pump's inlet port. As the piston continues to precess about the piston pump barrel assembly axis, it may move away from the valve plate thereby increasing the volume of the trapped chamber. As this occurs, fluid may enter the chamber from the pump's inlet (not shown) to fill the void. This process may continue until the piston reaches the bottom of the reciprocation cycle—commonly referred to as bottom-dead-center. At bottom-dead-center, the connection between the pumping chamber and inlet port may be closed. Shortly thereafter, the chamber may become open to the discharge port again and the pumping cycle may start over.
In a typical pressure-compensated pump, the swash plate angle is adjusted through the action of a valve which uses pressure feedback so that the instantaneous pump output flow is exactly enough to maintain a designated pressure. If the load flow increases, pressure will momentarily decrease but the pressure-compensation valve will sense the decrease and then increase the cam angle to increase pump output flow so that the desired pressure is restored. As demand increases the cam is moved to a greater angle, piston stroke increases and the volume of fluid increases; if the demand slackens the pressure will rise, and the pumped volume diminishes as the pressure rises. At maximum system pressure the output is once again almost zero. If the fluid demand increases beyond the capacity of the pump to deliver, the system pressure will drop to near zero. The swash plate angle will remain at the maximum allowed, and the pistons will operate at full stroke. This continues until system flow-demand eases and the pump's capacity is greater than demand. As the pressure rises the swash-plate angle modulates to try to not exceed the maximum pressure while meeting the flow demand.
Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.
Claims
1. An electro-hydraulic pump comprising:
- a motor including: a stator; and a rotor rotatable with respect to the stator and including a rotor body housing a hydraulic pumping element driven relative to the rotor body by rotation of the rotor for effectuating movement of fluid from an inlet to an outlet thereby transforming the rotational power of the rotor into hydraulic power.
2. The electro-hydraulic pump of claim 1, wherein the stator concentrically surrounds the rotor.
3. The electro-hydraulic pump of claim 1, wherein the motor is flooded with hydraulic fluid.
4. The electro-hydraulic pump of claim 1 wherein the hydraulic pumping element is an axial piston pump.
5. The electro-hydraulic pump of claim 1 wherein the hydraulic pumping element is contained within a motor housing.
6. The electro-hydraulic pump of claim 1 wherein the motor is a brushless DC motor.
7. The electro-hydraulic pump of claim 1 wherein the stator has electrical windings.
8. The electro-hydraulic pump of claim 1, wherein the rotor includes permanent magnets.
9. An electro-hydraulic pump comprising:
- a piston pump barrel assembly including: a plurality of pistons arranged and rotatable around a central axis for pumping hydraulic fluid, a cam for axially displacing the plurality of pistons when relative rotational movement between the cam and the plurality of pistons occurs;
- a plurality of magnets fixedly attached to the outside of the piston pump barrel assembly; and
- electrical windings radially surrounding the magnets and configured to create a magnetic field when energized so as to cause the plurality of magnets and a portion of the piston pump barrel assembly to rotate relative to the windings, thereby actuating the plurality of pistons to pump hydraulic fluid.
10. The electro-hydraulic pump of claim 9, wherein the cam is stationary with respect to the windings and the plurality of pistons is rotatable about the central axis.
11. The electro-hydraulic pump of claim 9 further comprising an outer housing, and wherein the electro-hydraulic pump is flooded with hydraulic fluid.
Type: Application
Filed: Mar 20, 2013
Publication Date: Nov 28, 2013
Inventor: Parker-Hannifin Corporation
Application Number: 13/847,784
International Classification: F04B 17/03 (20060101);
