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|United States Patent Application
Ruffner; Douglas B.
;   et al.
March 8, 2007
IMPROVED DESIGN OF INTEGRATED ELECTRO-HYDRAULIC POWER UNIT
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.
Ruffner; Douglas B.; (Ames, IA)
; Gandrud; Michael D.; (Ames, IA)
; Herrin; Jeff L.; (Ankeny, IA)
ZARLEY LAW FIRM P.L.C.
400 LOCUST, SUITE 200
2800 East 13th Street
September 2, 2005|
|Current U.S. Class:
|Class at Publication:
||F04B 35/04 20060101 F04B035/04|
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
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.
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
 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
 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
 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
 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
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
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
 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
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