1. Field of the Invention
The present invention relates generally to a self-sealing coupling for use in connection and disconnection of a hydraulic sub-circuit to a midway portion of a main circuit of a hydraulic device in tandem, and more specifically to a self-sealing coupling with a bypass for a hydraulic circuit in which a flow of pressurized oil is detoured to the sub-circuit by closing of the bypass for blocking off of the midway portion of the main circuit under the connected condition or, optionally, the flow being directly supplied to the main circuit by opening of the bypass in a disconnected condition.
2. Background of the Prior Art
For example, when an operator mounts or dismounts an agricultural loader onto an agricultural tractor, a hydraulic sub-circuit provided on the side of the loader is adapted to be connected in tandem to a midway portion of a main circuit of a hydraulic device provided on the side of the tractor. Thereupon, a self-sealing coupling with a bypass for a hydraulic circuit is interposed in the tandem connection portion between the main circuit and the sub-circuit.
When the agricultural tractor is used for the cultivation of land, usually the agricultural loader is removed from the tractor. For removing the loader, the bypass within the self-sealing coupling is opened by the operator so that a link hitch of a three-point support type can be hydraulically actuated.
When the operator uses the tractor equipped with external hydraulic implement and machinery such as the agricultural loader and the like, the bypass is blocked off so that the oil to be supplied to the main circuit is detoured to the sub-circuit.
Generally, a conventional self-sealing coupling with a bypass for a hydraulic circuit having relation to the present invention is constituted as follows.
A coupling body is provided with an input passage and an output passage separately from each other. In the outlet portion of the input passage and in the inlet portion of the output passage, there are provided respective valves on the main circuit.
Each self-closing valve is adapted to close a valve port thereof with a self-closing valve element urged outward by a valve closing force exerting means, and each valve element is adapted to be pushed back inwardly by an external force so as to open the valve port.
The input passage and the output passage are adapted to be interconnected through a bypass opened and closed by means of a bypass valve.
A first example of prior art is the embodiment shown in FIGS. 1 and 2 of Japanese Laid Open Utility Model Publication No. 1987-163688.
In the accompanying drawings of FIGS. 8 and 9 showing the first conventional embodiment, a block-like coupling body 101 is provided on its upper side with a pair of self-closing valves 106, 106 secured to body 101 side by side. Within each self-closing valve 106, there is provided a self-closing valve element 107 which is urged toward the valve closing position by means of a valve closing spring 108. The coupling body 101 is further provided with an input passage 102 opened in one side and with an output passages 103 opened in the other side thereof. These input passage 102 and output passage 103 are disposed horizontally and are spaced apart vertically, and are interconnected by a vertical bypass 110 formed in the middle portion of the coupling body 101.
A cylindrical bypass valve 111 is disposed through the vertical middle portion of the coupling body 101 and is passed vertically and slidably through the bypass 110. The bypass valve 111 is adapted to be urged upward by means of a valve opening spring 113 provided in the lower portion of the coupling body 101 so as to open the bypass 110.
However, there are the following problems associated with the first example:
(a) Since the coupling body 101 is provided separately with the self-closing valves 106 and the bypass valve 111 and further provided separately with the valve closing spring 108 as the urging means for the self-closing valve 107 and the valve opening spring 113 as the urging means for the bypass valve 111, the general constitution has to be larger and more complicated.
(b) Since the coupling connection portion on the main circuit side is provided with the similar self-closing valves 106, 106 for the input side as well as for the output side, operator tends to make the connection mistakes for the input sides and the output sides respectively on the side of the sub-circuit as well as on the side of the main circuit when connecting the self-closing valves on the side of the sub-circuit to the self-closing valves 106, 106 on the side of the main circuit. It is therefore possible that a loader and the like provided in the output portion of the sub-circuit could be driven in a reverse direction, which might cause an accident, due to such connection mistakes.
A second example of known art is obtained by simplifying the constitution provided in the first conventional embodiment, as shown in FIGS. 5 and 6 of the above-mentioned Publication.
In the related accompanying drawings of FIGS. 10 and 11, a coupling body 201 is provided with an input passage 202 and an output passage 203 which are disposed vertically therethroughout 201. A pair of self-closing valves 206, 206 are fitted side by side into the input passage 202 and into the output passage 203 from above respectively. One of them is fitted vertically and slidably into the input passage 202 with its cylindrical lower portion 200 facing a holizontal bypass 210. The other one, for the output passage 203, is threadably secured to the coupling body 201.
In such structure, under the "disconnected" and "self-closed" condition of the coupling for using only the main condition of the coupling for using only the main circuit of the hydraulic device, the self-closing valve 206 is adapted to be pushed up by means of an oil pressure within the "input passage 202 so as to open the bypass 210. Under the "connected" and "self-open" condition of the coupling for using the sub-circuit, a duplex coupling provided in the leading end of the sub-circuit is adapted to be pushed into the paired self-closing valves 206, 206 provided in the coupling body 201 and the self-closing valve 206 on the input passage side is lowered so as to close the bypass 210.
In this second example, the cylindrical lower portion 200 of the self-closing valve 206 on the input passage side serves as a bypass valve element 212 also, and an oil pressure within the input passage 202 acts as a valve opening force exerting means. Accordingly, the self-closing valve 206 serves as the bypass valve 211 also so that a valve for the exclusive use of the bypass can be omitted and the general constitution of the hydraulic device can be simplified.
However there are the following associated with the second example:
(a) Since the self-closing valve 206 on the input passage side is adapted to be raised and lowered vertically, a duplex connection coupling 280 on the sub-circuit side is secured only to the self-closing valve 206 on the output passage side of the coupling body 201 in an unstable cantilevered state when the sub-circuit is used.
Accordingly, when the self-closing valve 206 on the input passage side is extended or retracted by means of an external force such as a tension force or a pushing force transmitted through an oil supply hose, the force exerted to the self-closing valve 206 on the input passage side acts so as to bend the self-closing valve 206 on the output passage side. As a result, it is possible that the self-closing valve 206 on the output passage side could be deformed by a stress concentration, so that an oil leak is caused or the valve 206 is damaged during a long term use.
(b) The input side and the output side may be distinguished readily because the self-closing valve 206 on the input passage side is projected outward farther than that on the output passage side before being connected.
However, since similar self-closing valves 206, 206 are used for both the input passage side and the output passage side, one of the self-closing valves 206, 206 provided on the main circuit side is connectable to either of self-closing valves on the input side and on the output side provided on the sub-circuit side. Therefore, it is still possible that an operator could make a connection mistake similar to that possible in the above-mentioned first example.