FLUID CONTROL SYSTEM

Abstract: A fluid control system (10) has a first fluid pump (12) for supplying pressurized fluid in interrupted series to first and second work elements (14, 16). The first work element (14) in the series has priority which prevents simultaneous full power operation of the first and second work elements (14, 16). A second fluid pump (24) is capable of supplying pressurized fluid to the second work element (16) only upon receiving a signal indicating that pressurized fluid from the first pump (12) is being directed to the first work element (14). The subject fluid control system (10) is especially useful with a tree harvesting machine where it is beneficial to propel the machine and at the same time rotate the upper structure.

Description: FLUID CONTROL SYSTEM This invention relates generally to fluid control systems and more particularly to a system which selectively, controllably supplies pressurized fluid to several work elements. Two separate fluid sources within the fluid control system each controllably, selectively supply pressurized fluid to a preselected single work element under preselected conditions of operation. In fluid control systems having a plurality of work elements, it is common practice to provide the work elements with pressurized fluid from a single fluid source by interconnecting the control valves of the work elements in an interrupted series circuit. Certain ones of the work elements therefore have priority over the other work elements. In such a system, the work elements having less priority are generally not operational when the work elements having the greater priority are functionally operational. In certain fluid control systems using interrupted series circuits, the work elements having less priority may be partially operational by modulation of the control valves which control the higher priority work elements. However, such systems are generally inefficient and require difficult manipulation of the fluid controls by the operator. As it is often desirable to operate several work elements of a work vehicle simultaneously in order to save time and energy and make a work operation more efficient it is known to provide several work elements with separate fluid circuits having individual pumps and controls. However, this increases the costs of the fluid control system, adds weight and bulk to the overall machine, and represents waste. According to the present invention a fluid control system having a first and a second source of pressurized fluid, first, second and third work elements, first control means for controllably delivering pressurized fluid to the first or the second work element and second control means for controllably delivering pressurized fluid from the second source to the third work element is characterized in that means are provided for producing a signal only in response to pressurized fluid being delivered to the first work element; the second control means being arranged to deliver pressurized fluid from the second source to the second work element only in response to receiving the signal. Prior fluid control systems utilized an interrupted series circuit to supply pressurized fluid from a single pump on a priority basis to several work elements. However, a lesser priority work element could not be operated, or could be operated at less than full power, when a higher priority work element was being used. As in many instances, it is advantageous to operate at least two work implements of the priority system simultaneously and at full power, the subject invention provides a solution to these problems by make a second pump available to a lesser priority work element only when fluid from a first pump is being utilized to operate a higher priority work element. One example of a control system according to the invention will now be described with reference to the accompanying diagram of the control system circuit. Referring to the drawing, a fluid control system 10 has a first source of pressurized fluid 12, first and second work elements 14, 16, and a first control means 18 for controllably delivering pressurized fluid to one of the first and second work elements 14, 16. Work element 14 is preferably a fluid motor, such as a track motor, which can be rotated in either direction, for driving the tracks of a track-type machine, such as a tree harvester. Work element 16 is preferably a fluid motor such as a swing motor for rotating the upper portion of the tree harvester. The first control means 18 has first and second pilot operated control valves 20 and 22 for controllably delivering pressurized fluid from the pump 12 to work elements 14 and 16. Valves 20 and 22 are arranged in interrupted series which provides that work element 14 has priority over work element 16. Therefore, work element 16 cannot be operated from pump 12 when work element 14 is functioning. The fluid control system 10 includes a first means 23 for transmitting a signal on line 25 only in response to pressurized fluid being delivered to the first work element 14. The control system 10 has a third work element 28, a second source of pressurized fluid, including a pump 24, and a second means 27 for delivering pressurized fluid from the second fluid source 24 to the second work element 16 only in response to receiving the signal on line 25. The second means 27 includes a second control means 26. The second control means 26 has third and fourth pilot operated control valves 30 and 32 which controllably deliver pressurized fluid from the second source 24 to the work element 28 and the work element 16, as will be hereinafter more fully explained. Control valves 30, 32 are arranged in interruptable series and the control means 26 includes a flow control valve 34 which limits the maximum amount of pressurized fluid being directed from the second source 24 to the third work element 28 so that a controlled portion of the total amount of the pressurized fluid from the second source 24 is simultaneously deliverable to the second and third work elements 16, 28. The first means 23 for transmitting the signal on line 25 includes a pressure actuated travel alarm switch 48, the signal operating a selector valve 50. The fluid control system 10 has a pilot actuating system 36 having a plurality of pilot actuating valves 40, 42, 44 for actuation of the control valves 22 & 32, 20, 30 respectively and a third source of fluid pressure 38. For clarity, the connecting lines between the pilot actuating valves 40, 42, 44, are the associated control valves 20, 22, 30, 32, have been broken. In the drawing, line ends with common letters are in fluid communication with each other. A brake valve 46 and the travel alarm switch 48 are in fluid communication with the track motor 14. When the track motor 14 is activated, the brake valve 46 is shifted to pressurize cylinder 47 which releases the track brakes 49, and at the same time activates the travel alarm switch 48 and its associated alarm. Actuation of the travel alarm switch 48 transmits a signal 25 to a selector valve 50, which shifts the valve 50 to bring lines e and f into communication with the actuating valve 40. With the selector valve 50 in this position, actuating valve 40 is in communication with control valve 32, and in response to shifting valve 40, pressurized fluid is delivered from pump 24 via control valve 32 to the work element 16, the selector valve 50 being actuated only in response to receiving the signal from the travel alarm switch, which indicates that the motor 14 is actuated. When the motor 14 is not being operated the selector switch remains deactivated and lines c and d are brought into communication with the actuating valve 40 to enable fluid to be delivered to the work element 16 from the pump 12 via the control valve 22. With this system it is possible to provide simultaneous power to the track motor 14, the swing motor 16 and the work element 28. To accomplish this, the actuating valve 44 is shifted which provides pilot fluid to lines "g" or "h" to shift control valve 30 to an intermediate position at which a portion of the available flow is conducted to the work element 28 while the remaining flow is directed downstream to the control valve 32. Under these circuit conditions, the flow control valve 34 limits the maximum volume of fluid available to the work element 28, thus forcing the remainder of available flow to the downstream control valve 32, The centering springs in control valve 30 are heavier than those in control valve 32, consequently the pilot pressure being directed to the control valve 30 will shift to control valve 30 only to the intermediate position and never to the fully shifted position that occurs when the same pilot pressure is directed to valve 32. It is to be recognized that the pilot valve 44 could modulate the pilot pressure to the control valve 30 which would only shift the control valve to the intermediate position, thus eliminating the need for heavier centering springs as is noted above. This arrangment as set forth above will automatically allow the control valve 30 to be moved to the intermediate position to supply fluid to the work element 28 and simultaneously allow fluid to be directed downstream to the control valve 32 for operation of the work element 16. It should be understood that the system can be utilized on other machines without departing from the spirit of the invention.

Claims: CLAIMS 1. A fluid control system (10) having a first (12) and a second (24) source of pressurized fluid, first, second and third work elements (14, 16, 28), first control means (18) for controllably delivering pressurized fluid to the first (14) or the second (16) work element and second control means (26) for controllably delivering pressurized fluid from the second source (24) to the third work element (28), characterized in that means (23) are provided for producing a signal only in response to pressurized fluid being delivered to the first work element (14); the second control means (26) being arranged to deliver pressurized fluid from the second source (24) to the second work element (16) only in response to receiving the signal (25). 2. A control system according to claim 1, wherein the means (23) for producing the signal includes a pressure actuated switch (48) and a selector valve (50) actuated by the switch (48). 3. A control system according to claim 1 or claim 2, wherein the second control means (26) includes a flow control valve (34) and limits the maximum amount of pressurized fluid delivered from the second source (24) to the third work element (28), the remainder being available to the second work element (16). 4. A control system according to any of claims 1 to 3, wherein a controlled portion of the total amount of the pressurized fluid from said second source (24) is simultaneously deliverable to said second and third work elements (16, 28). 5. A control system according to any of claims 1 to 4, including a pilot actuating system (36) having a third source of fluid pressure (38) and a plurality of actuating valves (40, 42, 44), the third source of fluid pressure (38) being controllably selectively deliverable to the first and second control means (18, 26) by the actuating valves (40, 42, 44) to actuate the control means (18, 26).

Inventors: MULLER, THOMAS P., WIRT, LEON A.
Applicants: CATERPILLAR TRACTOR CO.
Application year: 1982
Main classification: F15B11
IPC codes: F15B11, A01G23