Hydraulic circuit and control system therefor

• US 5,138,838 A
• Filed: 02/15/1991
• Issued: 08/18/1992
• Est. Priority Date: 02/15/1991
• Status: Expired due to Term

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Crosser, Jeffrey A.
• Primary Examiner(s): Look, Edward K.
• Assistant Examiner(s): Mattingly, Todd
• Application Number:
  US07/655,703
• Time in Patent Office: 550 Days
• Field of Search: 91/461, 91/463, 91/465, 91/420, 91/421, 91/529, 60/393, 60/433, 60/426, 60/427, 60/445, 60/452, 60/461, 60/462
• US Class Current: 60/433
• CPC Class Codes: F15B 11/0423 by controlling pump output or bypass, other than to maintain constant speed
• CPC Class Codes: F15B 11/044 by means in the return line , i.e. "meter out"F15B11/046, F15B11/05 take precedence
• CPC Class Codes: F15B 21/087 Control strategy, e.g. with block diagram
• CPC Class Codes: F15B 2211/30565 having multiple valves for a single output member, e.g. for creating higher valve function by use of multiple valves like two 2/2-valves replacing a 5/3-valve
• CPC Class Codes: F15B 2211/327 electrically or electronically
• CPC Class Codes: F15B 2211/329 actuated by fluid pressure
• CPC Class Codes: F15B 2211/35 Directional control combined with flow control
• CPC Class Codes: F15B 2211/355 Pilot pressure control
• CPC Class Codes: F15B 2211/6309 the pressure being a pressure source supply pressure
• CPC Class Codes: F15B 2211/6313 the pressure being a load pressure

Abstract

Hydraulic control of reversible hydraulic motors typically requires several different valves to provide for the various operating parameters. The subject hydraulic control circuit has only a pair of electrohydraulic control valves to provide all the typical operating parameters. Operation of the control valves is controlled by a microprocessor in response to receiving command signals from a manually controlled command signal outputting device which establishes a desired fluid flow rate and direction of flow through the control valves.

Claims

1. A control system for a hydraulic circuit having a tank, a pump connected to the tank, a supply conduit connected to the pump, a reversible hydraulic motor, and a pair of motor conduits connected to the motor, comprising:

first and second independently operable electrohydraulic control valves with each being disposed between an associated one of the motor conduits and the supply conduit and the tank, each of the control valves having a neutral position at which the associated motor conduit is blocked from the supply conduit and the tank and being movable in a first direction in response to receiving a first control signal for establishing communication between the associated motor conduit and the supply conduit and in a second direction in response to receiving a second control signal for establishing communication between the associated motor conduit and the tank, the extent of movement in either direction being dependent upon the magnitude of the control signal received thereby;

pressure sensing means connected to the conduits for outputting a plurality of discrete pressure signals to the control means corresponding to the fluid pressures in the conduits;

means for outputting a command signal to establish a desired fluid flow rate and direction of fluid flow through both of the control valves; and

control means for processing the command signal, for producing the first and second control signals in response to the command signal, and for outputting the first control signal to one of the control valves and the second control signal to the other of the control valves, said control means being operative for processing the pressure signals and modifying the first control signal to maintain the desired flow rate through the control valve receiving the first control signal regardless of the pressure differential thereacross.

5. The control system of claim 1 wherein each of the control valves includes a pilot operated valve member having opposite ends, and electrohydraulic proportional valve means for controlling the position of the valve member in response to receiving the control signals.

6. The control system of claim 5 wherein the proportional valve means includes a pair of electrohydraulic proportional valves electrically connected to the control means to receive the first an second control signals and individually hydraulically connected to the opposite ends of the valve member, and including a source of pressurized fluid connected to the proportional valves.

7. The control system of claim 6 wherein each of the proportional valves has a first position at which the associated end of the valve member is communicated to the tank and is movable in a first direction for communicating the source of pressurized fluid with the associated end of the valve member, wherein the level of the pressurized fluid being directed to the associated end corresponds to the magnitude of the control signal directed to the proportional valve.

8. The control system of claim 7 wherein the source of pressurized fluid is the pump and the supply conduit.

11. The control system of claim 1 wherein the command signal outputting means includes a manually controlled lever and a position sensor for sensing an operating position of the lever and outputting the command signal to the control means representative of the direction and the degree of movement of the lever.

2. A control system for a hydraulic circuit having a tank, a pump connected to the tank, a supply conduit connected to the pump, a reversible hydraulic motor, and a pair of motor conduits connected to the motor, comprising:

first and second independently operable electrohydraulic control valves with each being disposed between an associated one of the motor conduits and the supply conduit and the tank, each of the control valves having a neutral position at which the associated motor conduit is blocked from the supply conduit and the tank and being movable in a first direction in response to receiving a first control signal for establishing communication between the associated motor conduit and the supply conduit and in a second direction in response to receiving a second control signal for establishing communication between the associated motor conduit an the tank, the extent of movement in either direction being dependent upon the magnitude of the control signal received thereby;

means for outputting a command signal to establish a desired fluid flow rate and direction of fluid flow through both of the control valves; and

control means for processing the command signal, for producing the first and second control signals in response to the command signal, and for outputting the first control signal to one of the control valves and the second control signal to the other of the control valves,

pressure sensing means connected to the conduits for outputting a plurality of discrete pressure signals to the control means corresponding to the fluid pressures in the conduits, the pressure sensing means including first and second pressure sensors connected to the motor conduits to output at least two of the pressure signals to the control means, the control means being operative for processing the pressure signals and modifying the second control signal to achieve the desired flow rates through the control valves when the fluid pressure in the motor conduit connected to the control valve receiving the second control signal is the higher of the fluid pressures in the motor conduits.

3. A control system for a hydraulic circuit having a tank, a pump connected to the tank, a supply conduit connected to the pump, a reversible hydraulic motor, and a pair of motor conduits connected to the motor, comprising:

first and second independently operable electrohydraulic control valves with each being disposed between an associated one of the motor conduits and the supply conduit and the tank, each of the control valves having a neutral position at which the associated motor conduit is blocked from the supply conduit and the tank and being movable in a first direction in response to receiving a first control signal for establishing communication between the associated motor conduit and the supply conduit and in a second direction in response to receiving a second control signal for establishing communication between the associated motor conduit and the tank, the extent of movement in either direction being dependent upon the magnitude of the control signal received thereby;

means for outputting a command signal to establish a desired fluid flow rate and direction of fluid flow through both of the control valves;

control means for processing the command signal, for producing the first and second control signals in response to the command signal, and for outputting the first control signal to one of the control valves and the second control signal to the other of the control valves, and

pressure sensing means connected to the conduits for outputting a plurality of discrete pressure signals to the control means corresponding to the fluid pressures in the conduits, the control means being operative to determine which of the fluid pressures in the motor conduits is higher and to select which of the control valves will be controlled to achieve the desired flow rate therethrough based on that determination.

9. The control system of claim 3 wherein each of the control valves includes a pilot operated valve member having opposite ends, and a pair of electrohydraulic proportional valves electrically connected to the control means to receive the first and second control signals and individually hydraulically connected to the opposite ends, each of the proportional valves being connected to the pump and the tank.

10. The control system of claim 9 wherein each of the proportional valves has a first position at which the associated end of the valve member is communicated to the tank and is movable in a first direction for communicating the pump with the associated end of the valve member, wherein the level of the pressurized fluid being directed to the associated end corresponds to the magnitude of the control signal directed to the proportional valve.

4. A control system for a hydraulic circuit having a tank, a pump connected to the tank, a supply conduit connected to the pump, a reversible hydraulic motor, and a pair of motor conduits connected to the motor, comprising:

first and second independently operable electrohydraulic control valves with each being disposed between an associated one of the motor conduits and the supply conduit and the tank, each of the control valves having a neutral position at which the associated motor conduit is blocked from the supply conduit and the tank and being movable in a first direction in response to receiving a first control signal for establishing communication between the associated motor conduit and the supply conduit and in a second direction in response to receiving a second control signal for establishing communication between the associated motor conduit and the tank, the extent of movement in either direction being dependent upon the magnitude of the control signal received thereby;

means for outputting a command signal to establish a desired fluid flow rate and direction of fluid flow through both of the control valves;

control means for processing the command signal, for producing the first and second control signals in response to the command signal, and for outputting the first control signal to one of the control valves and the second control signal to the other of the control valves; and

pressure sensing means connected to the conduits for outputting a plurality of discrete pressure signals to the control means corresponding to the fluid pressures in the conduits, and wherein said pump is a variable displacement pump having a displacement controller for controlling the displacement thereof in response to the magnitude of a pump control signal directed thereto, said control means being operative to process the pressure signals and to direct a pump control signal to the displacement controller at a magnitude sufficient to establish a predetermined pressure differential between the supply conduit and one of the motor conduits.

12. A control system for a hydraulic circuit having a tank, a pump connected to the tank, a supply conduit connected to the pump, a reversible hydraulic motor, and a pair of motor conduits connected to the motor, comprising:

first and second independently operable electrohydraulic control valves with each being disposed between an associated one of the motor conduits and the supply conduit and the tank, each of the control valves having a neutral position at which the associated motor conduit is blocked from the supply conduit and the tank and being movable in a first direction in response to receiving a first control signal for establishing communication between the associated motor conduit and the supply conduit and in a second direction in response to receiving a second control signal for establishing communication between the associated motor conduit and the tank, the extent of movement in either direction being dependent upon the magnitude of the control signal received thereby;

means for outputting a command signal to establish a desired fluid flow rate and direction of fluid flow through both of the control valves; and

control means for processing the command signal, for producing the first and second control signals in response to the command signal, and for outputting the first control signal to one of the control valves and the second control signal to the other of the control valves, wherein the command signal outputting means is operative to interrupt the outputting of the command signal and the control means is operative for determining when the fluid pressure in one of the motor conduits exceeds a predetermined level and for outputting the second signal to the control valve connected to the one motor conduit.

13. A control system for a hydraulic circuit having a tank, a pump connected to the tank, a supply conduit connected to the pump, a reversible hydraulic motor, and a pair of motor conduits connected to the motor, comprising:

first and second independently operable electrohydraulic control valves with each being disposed between an associated one of the motor conduits and the supply conduit and the tank, each of the control valves having a neutral position at which the associated motor conduit is blocked from the supply conduit and the tank and being movable in a first direction in response to receiving a first control signal for establishing communication between the associated motor conduit and the supply conduit and in a second direction in response to receiving a second control signal for establishing communication between the associated motor conduit and the tank, the extent of movement in either direction being dependent upon the magnitude of the control signal received thereby;

means for outputting a command signal to establish a desired fluid flow rate and direction of fluid flow through both of the control valves;

means for sensing the fluid pressure in the supply conduit and at least one of the motor conduits and outputting at least two discrete pressure signals; and

control means for processing the command signal and the pressure signals, producing the first control signal with the magnitude thereof based on a combination of the command and pressure signals, and outputting the first control signal to one of the control valves to move the one control valve to a position providing the desired flow rate.

14. A control system for a hydraulic circuit having a tank, a variable displacement pump connected to the tank, a supply conduit connected to the pump, a reversible hydraulic motor, and a pair of motor conduits connected to the motor, comprising:

an electronic displacement controller connected to the pump to control the displacement of the pump in response to the magnitude of a pump control signal directed thereto;

first and second electrohydraulic control valves with each being disposed between an associated one of the motor conduits and the supply conduit and the tank, each of the control valves having a neutral position at which the associated motor conduit is blocked from the supply conduit and the tank and being movable in a first direction in response to receiving a first control signal for establishing communication between the associated motor conduit and the supply conduit and in a second direction in response to receiving a second control signal for establishing communication between the associated motor conduit and the tank, the extent of movement in either direction being dependent upon the magnitude of the control signal received thereby;

means for outputting a command signal to establish a desired fluid flow rate and direction of fluid flow through both of the control valves;

means for sensing the fluid pressure in the supply conduit and the motor conduits and outputting a plurality of discrete pressure signals; and

control means for processing the command and pressure signals, determining whether the desired fluid flow rate is to be established by controlling the position of the control valves only or by moving one of the control valves to a position based on the magnitude of the command signal and controlling the pump displacement to establish a predetermined pressure drop across the one control valve, and outputting the appropriate signals to the control valves and the displacement controller.

15. The control system of claim 14 wherein the determination is based on the difference between the fluid pressure in the supply conduit and the higher of the fluid pressures in the motor conduits.

16. The control system of claim 14 wherein the control means is operative to determine which of the fluid pressures in the motor conduits is higher and to select which one of the control valves will be controlled to achieve the desired fluid flow rate therethrough based on that determination.

17. The control system of claim 16 wherein the control means is operative to output the first control signal to the selected one of the control valves, the second control signal to the other control valve, and a pump control signal to the displacement controller when the pressure in the supply conduit is a predetermined amount higher than the highest of the pressures in the motor conduits.

18. A control system for a hydraulic circuit having a tank, a variable displacement pump connected to the tank and having an electronic displacement controller, a supply conduit connected to the pump, a reversible hydraulic motor, and a pair of motor conduits connected to the motor, comprising:

first and second electrohydraulic control valves with each being disposed between an associated one of the motor conduits and the supply conduit and the tank, each of the control valves having a neutral position at which the associated motor conduit is blocked from the supply conduit and the tank and being movable in a first direction in response to receiving a first control signal for establishing communication between the associated motor conduit and the supply conduit and in a second direction in response to receiving a second control signal for establishing communication between the associated motor conduit and the tank, the extent of movement in either direction being dependent upon the magnitude of the control signal received thereby;

means for outputting a command signal to establish a desired fluid flow rate and direction of fluid flow through both of the control valves;

means for sensing the fluid pressure in the supply conduit and at least one of the motor conduits and outputting at least two discrete pressure signals; and

control means for processing the command and the pressure signals, determining the relative fluid pressures in the supply conduit and the one motor conduit on the basis of the pressure signals, producing the first control signal with the magnitude thereof based solely on the command signal when the pressure in the one motor conduit is higher than the pressure in the supply conduit, and outputting the first control signal to one of the control valves so that the one control valve moves to a position providing the desired fluid flow rate.

19. The control system of claim 18 wherein the control means is operative to output a pump control signal to the displacement controller at a magnitude sufficient to establish a predetermined pressure differential between the supply conduit and the one motor conduit when the pressure in the one motor conduit is higher than the pressure in the supply conduit.

20. A control system for a hydraulic circuit having a tank, a variable displacement pump connected to the tank and having an electronic displacement controller, a supply conduit connected to the pump, a reversible hydraulic motor, and a pair of motor conduits connected to the motor, comprising:

first and second electrohydraulic control valves with each being disposed between an associated one of the motor conduits and the supply conduit and the tank, each of the control valves having a neutral position at which the associated motor conduit is blocked from the supply conduit and the tank and being movable in a first direction in response to receiving a first control signal for establishing communication between the associated motor conduit and the supply conduit and in a second direction in response to receiving a second control signal for establishing communication between the associated motor conduit and the tank, the extent of movement in either direction being dependent upon the magnitude of the control signal received thereby;

means for outputting a command signal to establish a desired fluid flow rate and direction of fluid flow through both of the control valves;

means for sensing the fluid pressure in the supply conduit and at least one of the motor conduits and outputting at least two discrete pressure signals; and

control means for processing the command and the pressure signals, determining the relative pressures in the supply conduit and the one motor conduit on the basis of the pressure signals, producing the first control signal with the magnitude thereof based on a combination of the command and pressure signals when the pressure in the supply conduit is higher than the pressure in the one motor conduit by a predetermined amount, and outputting the first control signal to one of the control valves so that the one control valve moves to a position providing the desired fluid flow rate.