US20070053780A1

US20070053780A1 - Improved design of integrated electro-hydraulic power unit

Info

Publication number: US20070053780A1
Application number: US11/162,240
Authority: US
Inventors: Douglas Ruffner; Michael Gandrud; Jeff Herrin
Original assignee: Sauer Danfoss Inc
Current assignee: Danfoss Power Solutions Inc
Priority date: 2005-09-02
Filing date: 2005-09-02
Publication date: 2007-03-08
Also published as: JP2007071201A; CN1924355A

Abstract

An electro-hydraulic power unit with an improved hydraulic fluid flow through the unit. The unit accomplishes the improved fluid flow by having an inlet port in a housing that is fluidly connected to an electric motor that has a rotor with vanes cast thereon and at least one opening within the rotor. A hydraulic pump inlet is fluidly connected to the electric motor such that the vanes of the electric motor will supply hydraulic fluid to the hydraulic pump inlet.

Description

BACKGROUND OF THE INVENTION

The present invention relates to an electrical hydraulic fluid power converter. More specifically, the present invention relates to a device that includes an electrical machine coupled to a hydraulic machine.
In material handling and other related fields, lift trucks are often used for transporting heavy materials. Such trucks often use a large lead acid storage battery or a similar device as a source of electrical power. Lift trucks also typically use a system of hydraulic cylinders for the purpose of raising, lowering, tilting, reaching, shifting, and other load manipulation functions. With conventional trucks, it is common to use a battery powered electric motor to turn a hydraulic pump. With this system, hydraulic pressure and flow are produced by the pump and are modulated through a system of valves that are fluidly connected to a series of hydraulic cylinders for moving the payload.
In the prior art, the use of various direct current electric motors is well known. Recent developments in the art of solid state power electronics have enabled the use of alternating current (AC) motors to perform various functions within industrial trucks. Such AC motors and their solid state controls provide several advantages in industrial trucks which are well known in the art.
Additionally, the use of an electric motor coupled with a hydraulic pump is well known in the art. An example of a prior art electro-hydraulic power converter is disclosed by U.S. Pat. No. 5,591,013 to Kawafune et al. The Kawafune et al. patent, as well as the prior art cited therein discloses a swashplate type axial piston pump disposed within the center of the rotor of an electric motor. Advantages and disadvantages of this design are apparent to persons skilled in the art.
The present invention improves on Kawafune by teaching a device which places a rotary cam type hydraulic machine, such as a hydraulic piston unit or more specifically, a pump, adjacent to and within the same housing as the electric machine. The best known forms of rotary cam type hydraulic power machines are the wobble plate pump and the radial piston pump. Other variations of the rotary cam hydraulic power units could optionally be used in the present invention.
Hydraulic pumps need adequate oil supply to prevent cavitations and to perform properly. They typically require a flooded inlet and minimal negative suction head (positive section head is optimal). In the integrated pump drive, oil is used to cool the electric motor. This is done by drawing oil across the electric motor components. Oil enters the unit at one end and is pulled across the electric motor components where it is available to the pistons at the opposite end. The flow path across the motor is a small air gap between the rotor and stator, which is restrictive and severely limits performance of the pump. Thus, a problem exists in the art in the method of getting oil from one end of the unit to the other with minimal resistance. Thus, the present invention seeks to build upon recent developments in the field of electric motors and related components for battery powered industrial trucks.
The present invention enhances the art of electric fork lift trucks and similar battery powered industrial vehicles. More specifically, the present invention pertains to an improved method of constructing an electro-hydraulic power unit with a rotary cam hydraulic power unit (pump). In particular, the present invention teaches an improved method of communicating hydraulic fluid from the inlet of the assembly to the inlet of the pump contained therein in a manner that it enhances the suction performance of a pump and enhances cooling performance of an electric motor. It is also the intention of the present invention to (1) reduce the cost of the assembly; (2) improve the dynamic characteristics of the electric motor; and (3) improve the method to dynamically balance the mechanical elements in the assembly as a system and not component by component.
It is therefore a primary object of the present invention to provide an electro-hydraulic power converter including a rotary cam hydraulic power unit that has improved efficiency, reduced costs, decrease size, simplified installation, improved suction performance and improved reliability.
Yet another object of the present invention is to provide such a unit where the housing provides for a pathway for oil to get from one end of the unit to another with minimal resistance and with boosted pressure.
Another object of the present invention is to provide openings within the rotor of an electric motor to properly balance with a wobble plate assembly to minimize inertia on the rotor.
Yet another object of the present invention is to use rotor vanes in order to super charge hydraulic pump inlet supply.
Still another object of the present invention is to provide an electro-hydraulic power unit that is capable of operating at increased speed and increased flow rates.
These and other objects, features, or advantages of the present invention will become apparent from the specification and claims.

BRIEF SUMMARY OF THE INVENTION

An electro-hydraulic power unit having a housing that has an inlet port within. Additionally within the housing is an electric motor that is fluidly connected to the inlet port and that has a specially designed rotor having at least one opening therein. Also, the rotor has a shorting ring or similar disk with vanes cast onto the shorting ring that may be used to super charge the hydraulic pump inlet supply. Additionally, the power unit has a hydraulic pump that has an inlet fluidly connected to the electric motor. The power unit is designed so that oil flows into the inlet port of the housing and into the electric motor where the openings within the rotor help cause the oil to move to the inlet of the hydraulic pump.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a shaft rotor, and wobble plate assembly as used in an electro-hydraulic power unit;
FIG. 2 is a sectional view of an electro-hydraulic power unit;
FIG. 3 is a sectional view of an electro-hydraulic power unit; and
FIG. 4 is a sectional view of a stator of an electro-hydraulic power unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

With reference to FIGS. 1 and 2, and electric hydraulic power converter 10 is disclosed with a rotary cam hydraulic power unit 12. This unit 12 includes a housing 14, and an electric machine or motor 16, and a supercharged hydraulic machine or pump 18.
The electric machine, preferably is an alternating current (AC) induction motor, but may be any conventional electric machine, including an alternating current (AC) machine; a direct current (DC) machine; an induction machine; a single phase machine; a three phase machine; a poly phase machine; a switched reluctance machine; a written pole machine; a permanent magnet alternating current (PMAC) machine; a permanent magnet direct current (PMDC) machine; a shunt wound machine; a series wound machine; a compound wound machine; a synchronous machine; a separately excited machine; a brushless machine; a brushed machine; a brushless direct current machine; and a transversal flux machine.
The electric machine 16 is controlled and optionally caused to turn at a desired speed and direction by an electronic controller (not shown). This electronic controller is preferably a three phase alternating current inverter. For simplicity, this inverter may be designed as a variable voltage/variable frequency inverter. For improved accuracy of control, the inverter is preferably a vector type or field oriented control type inverter. The inverter (not shown) preferably contains solid state power switches which are preassembled into a power module. The inverter is preferably integrated with the electro-hydraulic unit described herein. Alternatively, the inverter may optionally be remotely mounted from the device.
FIG. 2 shows one embodiment of an electro-hydraulic power converter wherein the motor of the electric machine is known in the art as a squirrel cage motor. One skilled in the art will understand that other electric motors such as an Internal Permanent Magnet motor may be used. Thus, in FIG. 2 the electric motor 16 includes a stator 20, a stator winding 22 composed of a series of conductive wires, and a rotating assembly 23 having a rotating portion known as a rotor 24 comprising a so called “squirrel cage” assembly 26, and a shaft 28. The stator 20 preferably is pressed fit into the housing 14. The rotating assembly 23 also includes a wobble plate 30 which has an inclined surface. As the rotor 24 rotates, the wobble plate 30 will “wobble” with respect to the hydraulic machine 18. The wobbling motion of the wobble plate will sequentially press each piston 32 into the respective cylinder bore 34, and gives axial piston pump 18 its name of a wobble plate pump.
Additionally, the housing has an inlet port 36 that receives fluid. The rotor 24 has a plurality of axially lined holes, or openings, or porting 38 therein to help push the fluid within the unit directly towards the hydraulic pump inlet 39. Furthermore, in this embodiment, the rotor 24 has centrifugal pumping fins, or vanes 40, that are integrally cast onto the rotor 24 shorting ring 42.
Alternatively, as shown in FIG. 3, an internal permanent magnet (or IPM) motor design is present. In this embodiment a plurality of permanent magnets 44 are disposed within the rotor 24. The stator 20 has a plurality of slots 46 (see FIG. 4) wherein wires 22 are extended therethrough. When the internal permanent magnet motor is used, the centrifugal pump fins 40 are formed integrally with a rotor magnet retainer disk.
In yet another embodiment, the centrifugal pump fins 40 are formed on a separate disk that is attached to the wobble plate 30 or the rotor 24. Thus in these embodiments centrifugal pumps are present. In another embodiment a centrifugal pump is used in conjunction with a hydraulic piston pump to supercharge fluid. In all embodiments the centrifugal pump fins are used to supercharge fluid within the system and cause each embodiment to have a supercharged hydraulic pump 18.
In operation, the electro-hydraulic power unit 10 allows for hydraulic fluid to be drawn into the inlet port 36 and flows along the fluid line shown by numeral 44. The hydraulic fluid is drawn from the inlet port 36 past various components of the motor 16, through the holes or openings 38 within the rotor 24 and is eventually expelled from the rotor 24 on the pump side. The centrifugal pumping fins or vanes 40 throw fluid away from the fins causing the pumping action. Therefore, the centrifugal pumping fins or vanes 40 provide a “boost” in oil pressure prior to the oil entering the reciprocating piston pump thus supercharging the fluid. As the rotor turns, especially at high speed, the vane 40 accelerates the hydraulic fluid radially thus providing a pumping action. Consequently, the fluid is sucked through the rotor 24 and pumped into the piston pump.
Thus, this invention applies to an integrated AC electrical motor and checkball hydraulic pump. The unit is also used in any application requiring integration of a pump and electric prime mover. Additionally, this unit is specifically designed for the fork lift industry. Furthermore, the unit applies to any combination of at least one electrical machine, such as, for example, the integration of a hydraulic motor and an electrical generator. The unit also could be a single electric motor and a plurality of hydraulic units.
Furthermore, by having holes or openings through the motor rotor 24 minimizes the restriction through the unit of hydraulic fluid and thus improves filling of the pistons. Additionally, these openings, or oil ports 38, in one embodiment are to be drilled in a non-symmetrical pattern, such as semi-circular pattern to counteract the inherent mechanical imbalance of the wobble plate 30. Thus, the openings, or porting configuration, will be designed to balance the rotor/wobble plate assembly and minimize inertia (weight) of the rotor 24. Wobble plate 30 may optionally be provided with counter-balancing features thus making the wobble plate internally balanced and removing the need to provide a counter balanced rotor openings pattern. Therefore, the present invention creates a simplified balancing of the mechanical assembly.
One skilled in the art will also appreciate that the vanes 40, or fins, at the end of the rotor 24 nearest the piston group, act as an impeller and tend to super charge the piston inlets with supply fluid. Additionally, this invention provides for improved filling of the hydraulic pump through pre-charging the oil through centrifugal pumping action at the face of the rotor 24. Thus, this causes a cost reduction/simplification of the wobble plate design and an improved dynamic response of the electric motor through reduced weight of the rotor 24. Furthermore, by centrifugally supercharging the piston pump, the piston pump may be operated at increased speeds therefore increasing the flow rates of hydraulic fluid. Therefore, at the very least, all of the stated objectives have been met.
It will be appreciated by those skilled in the art that other various modifications could be made to the device without the parting from the spirit in scope of this invention. All such modifications and changes fall within the scope of the claims and are intended to be covered thereby.

Claims

1. An electro-hydraulic power unit comprising:

a housing;

an inlet port within the housing;

an electric motor within the housing that is fluidly connected to the inlet port and the motor having at least one opening therein;

vanes operatively connected to the electric motor; and

a hydraulic pump fluidly connected to the electric motor.

2. The electro-hydraulic power unit of claim 1 wherein the electric motor is an integrated AC electrical motor.

3. The electro-hydraulic power unit of claim 1 wherein the hydraulic pump is a checkball hydraulic pump.

4. The electro-hydraulic power unit of claim 1 wherein hydraulic pump is a rotary cam hydraulic power unit.

5. The electro-hydraulic power unit of claim 1 wherein the opening within the rotor is semi-circular.

6. The electro-hydraulic power unit of claim 1 wherein the rotor of the electric motor is fluidly connected to the hydraulic pump at a hydraulic pump inlet.

7. The electro-hydraulic power unit of claim 1 wherein the hydraulic pump that increases fluid pressure through centrifugal rotation.

8. The electro-hydraulic power unit of claim 1 wherein the hydraulic pump has a wobble plate.

9. The electro-hydraulic power unit of claim 8 wherein the opening within the rotor balances the rotor and the wobble plate.

10. An electro-hydraulic power unit comprising:

a housing;

an inlet port within the housing;

an electric motor within the housing and fluidly connected to the inlet port;

said electric motor having a rotor with at least one opening therein; and

a hydraulic pump having an inlet port fluidly connected to the electric motor.

11. The electro-hydraulic power unit of claim 10 wherein the rotor supplies oil to the inlet port of the hydraulic pump.

12. The electro-hydraulic power unit of claim 10 wherein the electric motor is an integrated AC electrical motor.

13. The electro-hydraulic power unit of claim 10 wherein the hydraulic pump is a checkball hydraulic pump.

14. The electro-hydraulic power unit of claim 10 wherein hydraulic pump is a rotary cam hydraulic power unit.

15. The electro-hydraulic power unit of claim 10 wherein the opening within the rotor is in a non-symmetric pattern.

16. The electro-hydraulic power unit of claim 10 wherein the hydraulic pump is a piston pump

17. The electro-hydraulic power unit of claim 10 wherein the hydraulic pump has a wobble plate.

18. The electro-hydraulic power unit of claim 17 wherein the openings within the rotor balance, the rotor, and the wobble plate.

19. The electro-hydraulic power unit of claim 10 wherein a centrifugal pump is provided to increase fluid pressure through centrifugal rotation.

20. The electro-hydraulic power unit of claim 18 wherein the electric motor is an internal permanent magnet motor.