U.S. patent application number 16/866714 was filed with the patent office on 2021-02-11 for electric displacement control for an open circuit variable displacement pump.
The applicant listed for this patent is DANFOSS POWER SOLUTIONS INC.. Invention is credited to Stanislav Smolka.
Application Number | 20210040944 16/866714 |
Document ID | / |
Family ID | 1000004844075 |
Filed Date | 2021-02-11 |
United States Patent
Application |
20210040944 |
Kind Code |
A1 |
Smolka; Stanislav |
February 11, 2021 |
ELECTRIC DISPLACEMENT CONTROL FOR AN OPEN CIRCUIT VARIABLE
DISPLACEMENT PUMP
Abstract
An electric displacement control system has a hydraulic variable
displacement pump that operates in an open hydraulic circuit. A
servo piston is disposed within a servo bore that is connected to
the hydraulic variable displacement pump. Located in the servo bore
is a control spool valve having an orifice that vents fluid
pressure from the servo bore to a pump case. The flow rate of the
system depends upon a fluid force between a feedback spring on a
first side of the control spool valve and a solenoid actuator force
on a second side of the control spool valve.
Inventors: |
Smolka; Stanislav;
(Nordborg, DK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DANFOSS POWER SOLUTIONS INC. |
Ames |
IA |
US |
|
|
Family ID: |
1000004844075 |
Appl. No.: |
16/866714 |
Filed: |
May 5, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62884380 |
Aug 8, 2019 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04B 17/00 20130101;
F04B 49/002 20130101; F04B 49/22 20130101 |
International
Class: |
F04B 49/00 20060101
F04B049/00; F04B 17/00 20060101 F04B017/00; F04B 49/22 20060101
F04B049/22 |
Claims
1. An electric displacement control system, comprising: a hydraulic
variable displacement pump operated in an open hydraulic circuit; a
servo piston disposed within a servo bore connected to the
hydraulic variable displacement pump; a control spool valve located
in the servo bore and having an orifice that vents fluid pressure
from the servo bore to a pump case.
2. The control system of claim 1 wherein flow rate depends upon a
fluid force between a feedback spring on a first side of the
control spool valve and a solenoid actuator force on a second side
of the control spool valve.
3. The control system of claim 1 wherein the control spool valve is
located in a housing and has a plug with a system pressure access
to a porting hole, a moveable control spool, a feedback compression
spring at a first side and a solenoid actuator at a second
side.
4. The control system of claim 1 wherein the control spool valve is
a two-way two-position spool type valve.
5. The control system of claim 1 wherein the control spool valve is
a two-way three-position spool type valve.
6. The control system of claim 1 wherein the control spool valve
has a groove where fluid in the groove is connected with fluid in
the servo bore and fluid volume at a solenoid actuator.
7. The system of claim 1 wherein an axis of the control spool valve
is aligned with an axis of the servo bore.
8. The system of claim 1 wherein a feedback spring is positioned
between the servo piston and a first side of the control spool
valve.
9. A method of controlling the displacement of a variable
displacement pump, comprising the steps of: providing a hydraulic
control system that includes a spool type valve having an axis
aligned with an axis of a servo bore, wherein the spool type valve
has a solenoid actuator on one end and a feedback spring on an
opposite end; communicating system pressure through the spool type
valve with servo pressure when there is no solenoid force acting
upon the spool type valve sending a variable displacement pump to
minimum displacement.
10. The method of claim 9 further comprising the step of increasing
solenoid force to move the spool type valve against feedback spring
force reducing flow to a servo control to send pump displacement to
maximum until the feedback spring force and solenoid force are
balanced.
11. The method of claim 10 further comprising the step of
decreasing solenoid force so that the spool type valve is pushed by
the feedback spring force against the solenoid force.
12. The method of claim 9 wherein the spool type valve is a
two-direction three position spool valve that blocks system
pressure when solenoid force drops below a preset minimum.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of the priority of U.S.
Provisional Application No. 62/884,380 filed on Aug. 8, 2019, the
contents of this application is hereby incorporated by reference in
its entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention is directed to a control system for a
hydraulic variable displacement pump, and more particularly a
control system for an open circuit variable displacement pump which
is adjustable by means of a servo piston that shifts inside of a
servo cylinder.
[0003] Control systems for an open circuit variable displacement
pump are known in the art. In one example, as disclosed in U.S.
Publication No. 2015/0050165 by Zavadinka, a control device is used
to set various power levels for the variable displacement pump that
are reliably maintained by automatically regulating the control
device without requiring any external control intervention.
Electric displacement controls (EDC) for a pump regulate the speed
of a machine function such as speed of a conveyor belt or drilling
speed on a drill rig. EDCs typically replace PVG-like valves
allowing cost reductions as well as lowering the hydraulic losses
across the valve for better system efficiency. While useful,
problems still exist with respect to cost and space while still
meeting application requirements.
[0004] A solution to these problems involves an EDC concept that
includes use of a two-way, two or three position, spool type valve
located in the pump servo bore and having an orifice to vent fluid
from the servo bore to the pump case. The spool type valve meters
fluid from system pressure to the servo bore and the flow rate
across the valve depends on a force balanced between a feedback
spring force on one side of the spool and a solenoid actuator force
on another side of the spool.
[0005] An objective of the present invention is to provide an
electric displacement system that reduces the cost of manufacturing
and still meets application requirements.
[0006] Another objective of the present invention is to provide an
electric displacement system that reduces the space needed and
still meets application requirements.
[0007] These and other objectives will be apparent to those having
skill in the art based upon the following written description,
drawings, and claims.
SUMMARY OF THE INVENTION
[0008] An electric displacement control system has a hydraulic
variable displacement pump that operates in an open hydraulic
circuit. A servo piston is disposed within a servo bore that is
connected to the hydraulic variable displacement pump. Located in
the servo bore is a control spool valve having an orifice that
vents fluid pressure from the servo bore to a pump case. The flow
rate of the system depends upon a fluid force between a feedback
spring on a first side of the control spool valve and a solenoid
actuator force on a second side of the control spool valve.
[0009] The control spool valve is located in a housing and has a
plug with a system pressure access to a porting hole, a moveable
control spool, a feedback compression spring at a first side and a
solenoid actuator at a second side. Preferably the control spool
valve is a two-way, two-position spool type valve or a two-way,
three-position spool type valve. The control spool valve has a
groove where fluid in the groove is connected with a fluid in the
servo bore and fluid volume at a solenoid actuator. An axis of the
of the control spool valve is aligned with an axis of the servo
bore. Positioned between the servo piston and a first side of the
control spool valve is a feedback spring.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic view of an electric displacement
control system; and
[0011] FIG. 2 is a schematic view of an electric displacement
control system.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0012] Referring to the figures, an electric displacement control
system 10 includes a variable displacement pump 12. The variable
displacement pump 12 has an inlet 14 and an outlet 16. The outlet
16 is connected to a control device 18 via a pressure line 20.
[0013] Control device 18 has a control piston 22 mounted within a
housing 24 and is adapted to shift or move longitudinally. A first
end 26 of the control piston 22 has an actuator 27 that is exposed
to high pressure fluid that exerts hydraulic force toward a second
end 28 having an adjustable spring 30.
[0014] The housing 24 has a first port 32, a second port 34, and a
third port 36. The first port 32 is positioned to selectively align
with pressure line 20. The second port 34 is positioned to
selectively align with drain line 37 that extends between the
control device 18 and a tank 38. The third port 36 is positioned to
selectively align with pressure line 40. The control device 18 has
a first position that permits flow through the control device 18
between drain line 36 and pressure line 40. The control device 18
has a second position where fluid flows from pressure line 20 to
pressure line 40.
[0015] The pressure line 40 extends from the control device 18 and
a spool type valve 42. The spool type valve 42 is of any type and
preferably is a two-way two position spool valve 42A for a zero
flow and minimum fail-safe control design, or a two-way three
position spool valve 42B for a full flow and maximum pressure
fail-safe control design.
[0016] The spool valve 42 is located in a pump servo bore 44 and
the axis of the spool valve 42 is aligned with the axis of the
servo bore 44. The spool valve 42 includes a plug 46 with a system
pressure access to a porting hole 48, a moveable control spool 50,
a feedback compression spring 52 on one end, and a solenoid
actuator 54 on the opposite end. A groove 56 on the control spool
50 selectively permits flow from the outlet 16, through the control
spool 50 to pressure line 40. The two-way three position spool
valve 42B has a pair of plugs 46A and 46B on each side of the
groove 56.
[0017] The servo bore 44 has an orifice 58 to maintain a pressure
differential between servo pressure and case pressure. Fluid
pressure from the spool valve 42 acts upon a servo piston 60 moving
the piston 60 against the force of a return spring 62. Movement of
the servo piston 60 adjusts the variable displacement pump 12 as
required via an activation link 64. This adjustment results in a
change in the deflection angle of a swashplate.
[0018] In operation, using the two-way two position spool valve
42A, with no or minimum solenoid force, fluid pressure flows from
outlet 16, through control spool 50 to pressure line 40. This
results in sending the pump 12 to minimum displacement.
[0019] As solenoid force increases, the spool valve 42A moves
toward and against feedback spring 52 reducing flow to the servo.
As a result, the pump bias system returns pump 12 displacement to
maximum while compressing the feedback spring 52 until the spring
force and the actuator force are balanced.
[0020] When the actuator force is decreased, moveable control 50 is
pushed by feedback spring 56 against the solenoid actuator 54 and
system pressure is communicated to the servo piston 60. The servo
piston 60 moves out of the servo bore 44 and force from the
feedback spring 56 is lowered until spring force and solenoid
actuator force are balanced again. With maximum solenoid force,
system pressure is blocked at porting hole 48 and fluid in servo
bore is all vented to case as the pump bias system returns the pump
12 to maximum displacement.
[0021] The two-way three-position spool valve 42B operates in a
similar manner to move the control member 50 between maximum and
minimum displacement, but also provides an emergency or fail safe
when electrical power to the solenoid actuator 54 is lost. More
specifically, when solenoid force drops below a preset minimum
force from the feedback spring 52 moves the control member 50 all
the way against the solenoid actuator which blocks system pressure.
Pump displacement would be returned to maximum as all fluid would
be vented to the pump case through the orifice.
* * * * *