GB1566385A

GB1566385A - Dual pump flow combining system

Info

Publication number: GB1566385A
Application number: GB1454778A
Authority: GB
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1977-07-11
Filing date: 1978-04-13
Publication date: 1980-04-30
Also published as: FR2397548A1; DE2829551A1; JPS5419071A; FR2397548B1; CA1085267A

Description

(54) DUAL PUMP FLOW COMBINING SYSTEM (71) We, CATERPILLAR TRACTOR CO., a corporation organized and existing under the laws of the State of California, United States of America, of iso() N.E.

Adams Street, Peoria, Illinois, 61629, United States of America do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to dual pump, flow-combining systems.

Many hydraulic systems have a large capacity pump as the primary source of fluid for several control valves, each of which controls fluid flow to one or more fluid motors. In some systems, a smaller capacity pump is provided to supplement the output of the larger pump when the fluid pressure of the system is below a predetermined magnitude. One of the problems encountered with such systems is that although the output of the small pump generally is needed for only the motor or motors controlled by one control valve or for only a small percentage of the time, the output of both pumps passes through the control valves all the time that the fluid pressure is below the predetermined magnitude. This causes additional problems particularly when fluid flow to the motors is being modulated by the control valves since the control valves must then modulate the total output of both pumps.

ne system which solves this problem has a fluid circuit which connects a first pump to a fluid motor and has a control valve for controlling fluid flow from the first pump to the motor. The control valve has an inlet port connected to the pump, a motor port connected to the motor, and a valve spool movable between a first position at which the inlet port is blocked from communication with the motor port, a second position at which fluid flow from the inlet port to the motor port is controllably modulated, and a third position at which substantially the total output of the first pump passes from the inlet to the motor port. The second pump is connected to the fluid circuit through a combining valve in response to the valve spool being moved to the third position.At the third position, the valve spool blocks a flow path from a signal chamber of the combining valve to a drain port so that the fluid pressure equalizes on both ends of a valve member of the combining valve. A spring then moves the valve member to a combining position. However, it has been found in practice that in some instances a combining valve which is shifted to the combining position directly by pressurized fluid is more responsive and is less subject to false pressure signals due to sudden pressure fluctuations in the system than a combining valve having the valve member moved to the combining position solely by the bias of a spring.

According to the present invention a dual pump flow combining system has first and second pumps; a double acting fluid motor; a fluid circuit connecting the first pump to the motor and having a control valve for controlling fluid flow therethrough from the first pump to the motor, the control valve having an inlet port connected to the motor, and a valve spool movable between a first position at which the inlet port is blocked from communication with the motor port, a second position at which fluid flow through the control valve from the inlet port to the motor port is controllably modulated, and a third position at which substantially the total output of the first pump passes through the control valve from the inlet port to the motor port; the control valve having a signal port connected to the inlet port when the valve spool is in the third position; and first means for connecting the second pump to the fluid circuit in response to the valve spool being moved from the second position to the third position, the first means including a valve having a valve member, a chamber at one end of the valve member, and biasing means urging the valve member to a first position at which the second pump is in communication with a tank, and the chamber being connected to the signal port of the control valve, so that when the control valve spool is in the third position the valve member is moved to a second position at which the second pump is blocked from communication with the tank and the output of the second pump is directed to the motor to be combined with the output of the first pum One example of such a system will now be described with reference to the accompanying drawing which is a diagrammatic view of the apparatus of this invention.

A dual pump flow combining system is generally indicated at 10 for selectively combining the fluid output of first and second pumps 11, 12 driven by an engine, not shown. A fluid circuit 13 connects the first pump to a fluid motor 14 and includes conduits 16-18 and a valve 19.

The valve 19 can be, for example as shown, a directional control valve 21 which controls fluid flow from the first pump 11 to and from the fluid motor 14. The control valve has a valve member or spool 22 which is shown at a neutral or centred position indicated by the letter "N". At this position, fluid passing through an inlet port 23 connected to the conduit 16 is returned to a tank 24 through a drain passage 26 and the inlet port is blocked from communication with a pair of motor ports 27, 28 connected to the conduits 17, 18, respectively. The valve spool 22 is movable to the left as viewed in the drawing between the centred position and a fully actuated position indicated by the letter "R".At this position, the inlet port 23 is blocked from communication with the drain passage 26 and is in communication with the motor port 29 sufficient for the total output of the first pump 11 to be directed through the motor port 27 and to the head end of the fluid motor 14. The fluid motor can be connected to an earthworking tool so that directing fluid to the head end raises the tool. The valve spool is movable to a plurality or range of modulating positions intermediate the centered position and the fully actuated position as indicated by the letter "m". At each of these modulating positions, fluid flow from the inlet port 23 to the motor port 27 is controllably modulated with the amount of fluid passing from inlet port 23 to motor port 27 progressively increasing as the valve spool moves from the centered position to the fully actuated position.

The control valve 21 has a signal port 29 which is connected with a drain port 31 through a slot 32 in the valve spool 22 at the centered position and substantially all of the modulating positions of the valve spool.

When the valve spool is moved from the modulating position to the fully actuated position, the signal port 29 is communicated with the inlet port 23 through a passageway 33 in the spool. The signal port is preferably positioned relative to the passageway 33 so that as the valve spool 22 is moved to the left, communication between the passageway and the signal port is established when the spool reaches a position at which substantially the total output of the first pump 11 passes from the inlet port 23 to the motor port 27.

A valve means 36 is connected to the second pump 12 through a conduit 37 and to the motor port 27 through a conduit 38. A valve member 39 is movable between a first position at which the second pump 12 is in communication with the tank 24 and a second position at which the second pump is blocked from communication with the tank and is in communication with the motor port 27 for combining the output of the second pump 12 with the output of the first pump 11 at the motor port 27. A check valve 41 is positioned in the conduit 38 for preventing fluid from passing from the motor port 27 to the valve means 36. A biasing means, for example a spring 42, is positioned within a chamber 40 at one end of the valve member and urges the valve member to the first position. A passageway 45 in the valve member vents the chamber 40 to the tank 24.A signal chamber 43 is positioned at the opposite end of the valve member.

An unloading valve assembly 44 has a chamber 46 connected to the signal port 29.

Another chamber 47 is connected to the chamber 46 through a flow restrictor or orifice 48 and to the signal chamber 43 through a passage 49. A poppet valve 51 is positioned for blocking a passage 52 connected to the chamber 46. The poppet valve is movable between a closed position at which the chamber 47 is blocked from communication with the tank and an opened position at which chamber 47 is in communication with the tank through passage 52. A spring 53 biases the poppet valve to the closed position and is of a size sufficient for allowing the poppet valve to move to its opened position in response to fluid pressure in chamber 47 exceeding a preselected magnitude.

A piston 54 is slidably positioned within a bore 56 having an open end in communication with the chamber 46. An enlarged head portion 57 of the piston is disposed within the chamber 47 adjacent the inner end of the poppet valve 51.

In the operation of this apparatus, the valve member 39 of valve means 36 is moved to the second position in response to pressurized fluid in the signal chamber 43.

With valve spool 22 of control valve 21 in either the centered or modulating positions, the signal port 29 is in communication with the drain port 31 thereby venting signal chamber 43 to the tank. With signal chamber 43 vented, the spring 42 biases the valve member to the first position shown.

Moving the valve spool 22 from the modulating position to its fully open position blocks communication between the signal port 29 and drain port 31 and establishes communication between the signal port 29 and the inlet port 23 through the passageway 33. Pressurized fluid from the inlet port passes through the signal port and into chamber 46, through the orifice 48 and into chamber 47, and through passage 49 and into signal chamber 43 where it moves the valve member 39 to the second position.

The fluid exhausted from the chamber 40 passes through the passageway 45 and into the tank 24. At the second position of the valve member, the output of the second pump 12 is combined with the output of the first pump 11.

Should the fluid pressure in the fluid circuit 13 and thus in inlet port 23, signal port 29 and chambers 46, 47 exceed a preselected magnitude the fluid pressure in the chamber 47 unseats the poppet valve 51 thereby communicating chamber 47 with the tank. The signal chamber 43 is also vented to the tank resulting in the valve member 39 being moved to the first position under the influence of the spring 42.

With chamber 47 opened to the tank, a pressure differential across the orifice 48 between chambers 46, 47 is also created.

The higher fluid pressure in chamber 46 then moves the piston 54 into abutment with the poppet valve 51 holding the poppet valve in the opened position until the fluid pressure in the chamber 46 decreases to a second preselected magnitude at which time the poppet valve will be moved to its closed position by the spring 53.

WHAT WE CLAIM IS: 1. A dual pump, flow-combining system having first and second pumps, a double acting fluid motor; a fluid circuit connecting the first pump to the motor and having a control valve for controlling fluid flow therethrough from the first pump to the motor, the control valve having an inlet port connected to the pump, a motor port connected to the motor, and a valve spool movable between a first position at which the inlet port is blocked from communication with the motor port, a second position at which fluid flow through the control valve from the inlet port to the motor port is controllably modulated, and a third position at which substantially the total output of the first pump passes through the control valve from the inlet port to the motor port, the control valve having a signal port connected to the inlet port when the valve spool is in the third position; and first means for connecting the second pump to the fluid circuit in response to the valve spool being moved from the second position to the third position, the first means including a valve having a valve member, a chamber at one end of the valve member, and biasing means urging the valve member to a first position at which the second pump is in communication with a tank, and the chamber being connected to the signal port of the control valve, so that when the control valve spool is in the third position the valve member is moved to a second position at which the second pump is blocked from communication with the tank and the output of the second pump is directed to the motor to be combined with the output of the first pump.

2. A system according to claim 1, including second means for venting the chamber in response to the fluid pressure in the fluid circuit exceeding a preselected magnitude.

3. A system according to claim 1 or claim 2 including a second chamber at the other end of the valve member and passageway means for venting the second chamber to the tank, the biasing means being positioned within the second chamber.

4. A system according to claim 1, substantially as described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. In the operation of this apparatus, the valve member 39 of valve means 36 is moved to the second position in response to pressurized fluid in the signal chamber 43. With valve spool 22 of control valve 21 in either the centered or modulating positions, the signal port 29 is in communication with the drain port 31 thereby venting signal chamber 43 to the tank. With signal chamber 43 vented, the spring 42 biases the valve member to the first position shown. Moving the valve spool 22 from the modulating position to its fully open position blocks communication between the signal port 29 and drain port 31 and establishes communication between the signal port 29 and the inlet port 23 through the passageway 33. Pressurized fluid from the inlet port passes through the signal port and into chamber 46, through the orifice 48 and into chamber 47, and through passage 49 and into signal chamber 43 where it moves the valve member 39 to the second position. The fluid exhausted from the chamber 40 passes through the passageway 45 and into the tank 24. At the second position of the valve member, the output of the second pump 12 is combined with the output of the first pump 11. Should the fluid pressure in the fluid circuit 13 and thus in inlet port 23, signal port 29 and chambers 46, 47 exceed a preselected magnitude the fluid pressure in the chamber 47 unseats the poppet valve 51 thereby communicating chamber 47 with the tank. The signal chamber 43 is also vented to the tank resulting in the valve member 39 being moved to the first position under the influence of the spring 42. With chamber 47 opened to the tank, a pressure differential across the orifice 48 between chambers 46, 47 is also created. The higher fluid pressure in chamber 46 then moves the piston 54 into abutment with the poppet valve 51 holding the poppet valve in the opened position until the fluid pressure in the chamber 46 decreases to a second preselected magnitude at which time the poppet valve will be moved to its closed position by the spring 53. WHAT WE CLAIM IS:

1. A dual pump, flow-combining system having first and second pumps, a double acting fluid motor; a fluid circuit connecting the first pump to the motor and having a control valve for controlling fluid flow therethrough from the first pump to the motor, the control valve having an inlet port connected to the pump, a motor port connected to the motor, and a valve spool movable between a first position at which the inlet port is blocked from communication with the motor port, a second position at which fluid flow through the control valve from the inlet port to the motor port is controllably modulated, and a third position at which substantially the total output of the first pump passes through the control valve from the inlet port to the motor port, the control valve having a signal port connected to the inlet port when the valve spool is in the third position; and first means for connecting the second pump to the fluid circuit in response to the valve spool being moved from the second position to the third position, the first means including a valve having a valve member, a chamber at one end of the valve member, and biasing means urging the valve member to a first position at which the second pump is in communication with a tank, and the chamber being connected to the signal port of the control valve, so that when the control valve spool is in the third position the valve member is moved to a second position at which the second pump is blocked from communication with the tank and the output of the second pump is directed to the motor to be combined with the output of the first pump.