U.S. patent number 3,732,036 [Application Number 05/127,738] was granted by the patent office on 1973-05-08 for summing valve arrangement.
This patent grant is currently assigned to Caterpiller Tractor Co.. Invention is credited to William F. Busbey, Donald L. Hopkins.
United States Patent |
3,732,036 |
Busbey , et al. |
May 8, 1973 |
SUMMING VALVE ARRANGEMENT
Abstract
There is disclosed control means that is operative to vary the
horsepower output of a plurality of variable displacement pumps in
response to the sum of the outputs of the pumps.
Inventors: |
Busbey; William F. (Pekin,
IL), Hopkins; Donald L. (Joliet, IL) |
Assignee: |
Caterpiller Tractor Co.
(Peoria, IL)
|
Family
ID: |
22431685 |
Appl.
No.: |
05/127,738 |
Filed: |
March 24, 1971 |
Current U.S.
Class: |
417/216;
417/222.1 |
Current CPC
Class: |
F04B
49/002 (20130101); F04B 49/007 (20130101) |
Current International
Class: |
F04B
49/00 (20060101); F04b 049/00 () |
Field of
Search: |
;417/212,213,216,217,426,429,199,201,202,218,222 ;91/506 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,528,476 |
|
Sep 1969 |
|
DT |
|
1,922,269 |
|
Nov 1970 |
|
DT |
|
Primary Examiner: Freeh; William L.
Assistant Examiner: Smith; Leonard E.
Claims
What is claimed is:
1. A horsepower controlling system, said system comprising in
combination:
a plurality of variable displacement pumps driven by a common prime
mover and including pressure responsive means for varying the
displacement of said pump,
a source of actuating pressure comprising a fixed displacement pump
driven by said common prime mover for actuating said pressure
responsive means;
a valve having a bore in communication with said source of
actuating pressure and with said pressure responsive means;
a spool disposed in said bore and operative to control said
communication;
means comprising a plurality of individual pistons communicating
with and responsive to the sum of the outputs of said variable
displacement pumps to actuate said valve to thereby communicate
said actuating pressure with said actuating means to alter the
displacement of said pumps; and,
a piston selectively communicating with said source of actuating
pressure and operatively connected to said valve to oppose said
plurality of individual pistons.
2. The invention of claim 1 wherein said source of actuating
pressure is a fixed displacement pump driven by said common prime
mover.
3. The combination of claim 1 comprising a pressure reducing valve
operatively connected between said valve actuating means and the
output of said variable displacement pump.
4. The horsepower controlling system of claim 1 wherein said source
is the one of said variable displacement pumps having the highest
pressure output.
5. A horsepower controlling system for controlling the horsepower
output of a plurality of variable displacement pumps driven by a
single prime mover, said system comprising:
a source of control pressure comprising a fixed displacement pump
driven by said prime mover for controlling the displacement of said
pumps;
a valve having a pre-determined bias to a cut-off position for
controlling the communication of said control pressure with said
pump displacement means;
means responsive to the sum of the output pressure of said pumps
for moving said valve to control said control pressure;
pressure responsive means responsive to the output of said variable
displacement pumps to bias said valve in a direction to provide
open communication between said source of control pressure and said
pump displacement controlling means, said pressure responsive means
comprising a plurality of pistons disposed in cylinders,
said cylinders being in communication with the output of said pumps
at one end of said piston; and,
the other end of said piston in operative engagement with said
valve means.
6. The system of claim 5 comprising:
a piston disposed at the opposite end of said valve from said
plurality of pistons; and,
said piston being responsive to communicate one end of said piston
with said source of control pressure when said valve is positioned
for open communication, whereby said piston urges said valve toward
a non-communicating position.
7. The system of claim 6 wherein said spool includes means to
provide communication between said pump displacement controlling
means and a sump.
Description
BACKGROUND OF THE INVENTION
The present invention relates to horsepower controlling means and
pertains more particularly to a summing valve arrangement that is
operable to control the horsepower output from a plurality of
hydraulic pumps.
Many hydraulic machines are designed to perform a plurality of
functions either independently or simultaneously. These machines
normally employ two or more variable displacement pumps, driven by
a single internal combustion engine for supplying fluid to motors
for performing the functions. Each pump is normally capable of
delivering the entire horsepower output of the engine to the motor
or motors which it is arranged to supply. Thus, when several
functions are being performed simultaneously be motors that are
supplied by separate pumps, the horsepower demand of the load may
exceed the horsepower capability of the engine and cause it to
stall.
Numerous prior art devices have been proposed for controlling the
horsepower output of a variable delivery pump. These devices,
however, have proven to be unsatisfactory because they tend to be
expensive, unduly complicated and unreliable. Such devices normally
employ complicated arrangements of cam and linkages.
One proposed system for controlling horsepower is disclosed in U.S.
Pat. No. 2,932,948. This system, however, employs a complex
arrangement of interconnected cams, levers, and pistons. This type
of complex mechanism is subject to substantial frictional losses
and tends to be insensitive to pressure changes.
A more simplified system is disclosed in British Pat. specification
No. 1,128,657 filed Sept. 30, 1965. This more simplified system has
the disadvantage of being responsive only to pump output pressure.
This results in a lack of sensitivity to engine speed and
consequently a lack of sensitivity to engine horsepower.
Other proposed solutions to the problem of horsepower control are
disclosed in U.S. Pat. Nos. 2,080,810, 2,009,608 and 2,179,071.
These systems also suffer from undue complexity and lack of
sensitivity to actual engine horsepower.
SUMMARY OF THE INVENTION
It is, therefore, the primary object of the present invention to
provide a simple and inexpensive control system for controlling the
horsepower output of a plurality of pumps.
A further object of the present invention is to provide simple
horsepower controlling means for a plurality of variable
displacement pumps that eliminates the need for complicated
arrangements of cams and linkages.
In accordance with the present invention, the output pressures from
a plurality of variable displacements are summated and utilized to
operate a valve to control fluid from a source for varying the
displacement of said pumps.
BRIEF DESCRIPTION OF THE DRAWINGS
The aforementioned and other objects and advantages of the present
invention will become apparent from the following description when
read in conjunction with the accompanying drawings wherein:
FIG. 1 is a schematic illustration, partially in section of a pump
control circuit embodying a preferred embodiment of the present
invention;
FIG. 2 is a view taken generally along lines II--II of FIG. 1;
FIG. 3 is an elevational view in section of a modification of the
summing valve of the present invention;
FIG. 4 is a schematic layout of an alternate embodiment of the
present invention; and,
FIG. 5 is an end view, in section, of the summing valve of FIG.
4.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to the drawings, and in particular to FIG. 1, there
is illustrated a horsepower controlling means comprising a pair of
variable displacement pumps 10 and 12 driven by a common prime
mover such as an internal combustion engine and each having a servo
control motor and valve 14 and 16 interconnected by means of
conduits 18 and 19. The servo motors 14 and 16 may be of
conventional design.
The output from the pumps 10 and 12 is supplied by means of
suitable conduits 20 and 22 for operation of the implements for a
hydraulic machine such as an excavator or loader (not shown). It
should be emphasized that this system is not limited to two pumps
10 and 12 but may include any number of variable displacement
pumps. The pumps are arranged such that they are normally in the
maximum flow position with the control means of the present
invention operative to reduce the pump output in response to
overload conditions in the operation control circuit.
A source of fluid pressure comprising in this embodiment a fixed
displacement pump 24, preferably driven by the same prime mover or
engine 25 which drives the variable displacement pumps,
communicates by way of a conduit 26 and a summing valve 28 with the
conduit 18 and 19 for supplying control fluid or pressure to the
servo control systems 14 and 16 for varying the displacement of the
pumps 10 and 12. The pump 24 is preferably driven by the same prime
mover means as the variable displacement pumps 10 and 12, so that
the source of control pressure will be related to the horsepower
output of the prime mover.
The valve 28 comprises a housing 30 having a bore 32 communicating
with inlet conduit 26 by means of an inlet passageway 33. The bore
32 is also in communication with conduits 18 and 19 by means of an
annular passageway 68 and an outlet passageway 34. A spool 36 is
slidably disposed in the bore 32 and biased by means of the spring
38 to a leftwardmost position to block communication between inlet
passageway 33 and outlet passageway 34.
The position of the valve member 36 for controlling the flow of
fluid between inlet 33 and outlet 34 is controlled by pressure
responsive means comprising a plurality of pistons 40, 42, 44 and
46 received in suitable bores in the housing 30 and operative to
apply a force against the spool member 36 in response to pressure
output from the pumps 10 and 12. Chambers 48, 50, 52 and 54 at the
head of each of the pistons 40, 42, 44 and 46 are in communication
by way of conduits 56 and 58 with the outputs of the variable
displacement pumps 10 and 12. In particular, the chambers 48 and 52
are in communication by means of conduit 56 with the output of pump
10. Likewise chambers 50 and 54 are in communication by way of
conduit 58 with the output of variable displacement pump 12. The
valve spool 36 is also provided with further pressure responsive
means which comprises a piston 60 disposed in a bore 62 formed in
the spool 36 and having a pressure chamber 64 in communication by
way of the passageway 66 with an annular passageway 68 in
communication with bore 32 and outlet passageway 34. A metering
slot 70 is formed on spool 36 to meter the flow of fluid from the
inlet 33 to the entering of passageway 68. Thus, it is seen that
with this arrangement pressure exerted in chamber 64 will be
substantially the pressure acting in the passageway 34 and conduit
18 whether in communication with the inlet 33 or not.
When the spool 36 is moved to the right as a result of pressure
from the pumps 10 and 12, a flow path is established between the
inlet 33 from pump 24 and the outlet 34. The fluid is then directed
from passage 34 by way of conduits 18 and 19 to the servo valves 14
and 16 of the variable displacement pumps 10 and 12.
The summing valve arrangement operates to control the horsepower
output of the variable displacement fluid pumps 10 and 12. When
both of the pumps 10 and 12 are operating, fluid is delivered along
lines 20 and 22 of the various control valves controlling the
implements. Since these pumps are variable in displacement, the
flow rate delivered by the pumps can vary according to the demand
from the working implements of the machine. So long as the flow
rate and pressure of the system plus pump losses does not exceed
the maximum horsepower of the prime mover or engine 25, the summing
valve assembly will remain inactive. However, when the pressure in
the output lines 20 and 22 exceeds a predetermined value, the flow
delivery rate of the two variable pumps must then be decreased in
order to prevent the pumps from stalling the engine 25 of the
machine. Such stalling will occur when the pump demands more
horsepower than the machine prime mover is capable of
producing.
A portion of the output from pump 10 passes through a pressure
reducing valve 55 along conduit 56 and into chambers 48 and 52. The
portion of the fluid from pump 12 passes through pressure reducing
valve 57 along conduit 58 and into the chambers 50 and 54. The
purpose of the reducing valves 55 and 57 is to reduce the pressure
output from the pumps by a factor of approximately 10 to 1. The
pressure in the chambers 48, 50, 52 and 54 exert a force on pistons
40, 42, 44 and 46 and consequently on the valve 36. When the sum of
these pressures exceeds a certain predetermined maximum pressure,
the force of the pistons begin to move the spool 36 to the right
against a force of spring 38. Communication is then established
between annular inlet 33 and the outlet passage 34 by way of
metering slot 70. This causes the output from pump 24 to be
delivered along the conduits to servo valves 14 and 16 of the pumps
10 and 12. This pressurized fluid activates the servo valves and
swivels the two pumps to a lower position of volumetric
delivery.
The amount that the delivery rate of the two variable pumps is
reduced is dependent on the distance that the spool 36 moves to the
right which is dependent on the pressure in lines 56 and 58 working
on the four pistons 40, 42, 44 and 46. Since the horsepower output
of the pump is a function of the pressure and the volume, a
reduction of the volume output permits the pressure to remain
substantially the same or to even increase without an increase in
horsepower requirement. When the pressure has dropped off
sufficiently to permit the spool 36 to move back to the left and
cut off communications between the inlet 33 and outlet 34, the
pressure applied to the servo valves 14 and 16 will begin to relax
due to a drain orifice 72 which permits the fluid from lines 18 and
19 to drain back to the sump. Thus, the stroke of the pumps begins
to increase again until an equilibrium position is maintained.
Referring now to the embodiment of FIG. 3, the spool has been
modified in a manner that it eliminates the drain orifice or
restriction 72 and the spring 38 of the previous embodiment. In
this embodiment, the spool 80 is nearly identical to the spool 36
of the previous embodiment. However, it has been provided with a
slot 82 which provides communication between the passage 34 and the
bore at the right hand end of the spool and consequently the drain
passage 74 back to drain. In this manner, the orifice 72, a
restriction of the previous embodiment is eliminated and replaced
by a plug 84. In this manner, the lines 18 and 19 are drained only
when required, that is, only when the spool 80 is in such a
position as to cut off communication between inlet 33 and outlet
34. Another modification of spool 80 over the previous embodiment
was to increase the diameter of bore 61 and piston 63 in order to
provide the required force balance to position the spool 80 without
the use of a spring such as 38 in FIG. 1.
Turning now to FIG. 4, there is illustrated a modified arrangement
of the control system. Identical components, as in the previous
embodiment, are identified by the same numerals. In this
embodiment, all the major pumps in the system, whether fixed or
variable displacement, contribute in supplying fluid for actuation
of the summing valve 28. Thus, a portion of the fluid for
controlling the summing valve is from a pump whose output is in
proportion to engine speed. In this embodiment, the output is
supplied to pressure sensitive cylinder arrangements 81, 82, 85, 87
and 89 similar to those in the previous embodiment. The size and/or
number of the pressure response chambers 81, 83, 85, 87 and 89 may
vary in accordance with the ratio of the load from each pump to
that of the total pump load. In other words, the actuating force
contributed from each pump is in proportion to the total system.
For example, a pump supplying only half the horsepower of a second
pump in the system would also be arranged to have, for example, one
sensing element as compared to two for the second pump, if the
diameters of the sensing elements are the same.
The source of fluid for activating the servo control valves 14 and
16, in this embodiment, comes from the pumps being controlled
rather than from a totally independent source, as in the previous
embodiment. For example, the supply line 56 is tapped by a branch
conduit 86 and supplies through a check valve 88 to the inlet
conduit 90 of the control valve 28. The supply line 91 from pump 24
is tapped by branch conduit 92 having a check valve 94 and supplies
to the inlet conduit 90. A branch conduit 96 taps the supply from
conduit 58 and supplies it by way of the check valve 98 to the
inlet 90. With this arrangement, the supply into or across the
control valve 28 from inlet 90 will be from the pump having the
greatest outlet pressure. Again, it should be emphasized that the
present control system is not to be limited to a specific number of
variable displacement pumps but may be used in conjunction with any
number of variable pumps either alone or in combination with a
number of fixed displacement pumps.
While the present invention has been described with respect to
particular embodiments, it is to be understood that many changes
may be made in arrangement in parts without departing from the
spirit and scope of the appended claims.
* * * * *