Winch system having hydraulic transmission including a safety circuit
This application is a continuation of application Ser. No. 397,536, filed July 12, 1982, now abandoned. 
    
    
     The invention relates to a winch system comprising a cable drum coupled with a reversible hydromotor and a reversible hydropump arranged with the hydromotor in a closed circuit by means of two communication conduits, in which a safety circuit connecting the communication conduits with one another at the occurrence of pressure shocks therein is arranged and provided with one relief pressure valve, whose inlet and outlet are connected with each one of the communication conduits through non-return valves allowing supply to and, respectively, drainage from the relief pressure valve. 
     Such a system is known from FR-A-No. 1.508.428. 
     The safety circuit serves to prevent the cable from being exposed to an excessive force likely to cause rupture. The use of such a winch system in which the cable can be wound on and off at a very high rate requires a very sensitive safety circuit. For example, in a wire line unit it may occur that a body connected with the hoisting cable has to be moved up and down with high speed several times in the well (jarring). The switching over of the direction of movement has to be done in such a way, that the cable is not damaged. 
     The invention has for its object to provide a system of the kind set forth in the preamble which can safely operate under such conditions. 
     This is achieved in that the relief valve is controllable. The winch operator can control the relief pressure valve in a manner such that, whilst the hydropump continues supplying pressure in the normal winding-up direction of the hydromotor, the cable nevertheless winds off under the action of a tractive force exerted thereon. By increasing the opening pressure of the relief valve this winding-off movement smoothly goes over into a winding-up movement. In a wire line unit the aforesaid body can be alternately caused to perform a downward movement substantially corresponding to a free fall and an upward movement at a rate of several tens of meters per second. During these movements and the change-over thereof the safety circuit is continuously operative. 
    
    
     The invention will be described more fully hereinafter with reference to the accompanying drawing. 
     FIG. 1 shows an arrangement embodying the invention used as a wire line unit. 
     FIG. 2 schematically shows the winch system of FIG. 1. 
     FIG. 3 schematically shows the hydraulic control of the winch system. 
    
    
     Referring to FIG. 1 the winch system 11 accommodated in a so-called &#34;container&#34; 1 only shows a cable drum 4, along which passes a cable 5, and an oil pump aggregate 2 fed from a Diesel system. The container 1 has a door 3 leading to the control-cabin. The cable 5 passes to the interior of a well 6 via a first cable pulley 7 and a second cable pulley 8 supported at a given distance above the well 6 by a stand 9. With the free end of the cable 5 located inside the well 6 is coupled a body 10, the movements of which inside the well 6 have to be controlled by means of the winch system. Since the well itself, the associated equipment 7, 8, and 9 and the body 10 do not form part of the invention, neither with respect to their construction nor with respect to their modes of operation, the details thereof will not be discussed further. 
     FIG. 2 schematically shows that the winch system 11 comprises an oil pump aggregate 2 having a Diesel engine 15 and a hydropump device 16 mechanically coupled with the former. Through communication conduits 18 and 18&#39; the hydropump 16 is included in a closed circuit with a hydromotor 17. The output shaft of the hydromotor 17 is mechanically coupled with a cable drum 4, on which the cable 5 is wound. Between the communication ducts 18 is arranged a safety circuit 19, which can put the conduits 18 into relative communication in order to mitigate the influence of pressure shocks and to avoid the occurrence of given excessive pressure during operation. The hydropump device 16, the safety circuit 19 and the hydromotor device 17 are controlled by a control-device 20. 
     From FIG. 3 it will be apparent that the hydromotor 17 as well as the hydropump 16 are of the reversible, controllable type. The hydropump device 16 comprises the hydromotor 28 mechanically coupled with the engine 15, an auxiliary pump 29 also coupled with the engine 15, safety members 27 by which the maximum pressure occuring in the hydraulic system is set, and a control-member 31 for controlling the hydropump. 
     The fluid displacement and the direction of operation of the hydropump 28 are controlled with the aid of the pump control 25. This pump control 25 sets in a manner known per se the position of the control-member 31 through a servo-valve 26. 
     The auxiliary pump 29 supplies the pressure for the control-device 20 and ensures supplementing the hydraulic cycle. The auxiliary pump 29 draws oil from the reservoir 30, whereas the outlet oil from the various hydraulic members is fed back to the reservoir 30. 
     The hydromotor device 17 comprises a hydromotor 34 and a control-member 41 for the same. By the control-member 41 the speed of rotation of the motor 34 for a given oil supply is controlled. The control-member 41 is governed in known manner with the aid of a motor control 32 and a servo-valve 33. 
     The safety circuit 19 comprises a relief pressure valve 35. The inlet 36 of the relief valve 35 communicates through non-return valves 37 and 37&#39; with each one of the communication conduits 18. The non-return valves 37 and 37&#39; are arranged so that they pass an effluent from the conduits 18 or 18&#39; to the inlet 36 of the valve 35. The outlet 38 of the valve 35 also communicates through non-return valves 39 and 39&#39; with each one of the communication conduits 18 and 18&#39;. The non-return valves 39 are arranged so that they pass an effluent of oil from the outlet 38 towards the communication ducts 18 or 18&#39;. The relief valve 35 can be controlled in a manner known per se by means of a control valve 40 to be actuated by the operator. 
     In accord with convention, with respect to the operator controlled valve 40 and the controlled relief valve 35, control fluid lines are illustrated in dashed lines whereas controlled fluid lines are illustrated in full lines. Thus, the operator controlled valve 40 controls the bleed of control fluid from the line 62, through the check valve 63 and through the line 60 to the reservoir 30. This controlled bleed causes the pilot valve 61 to bleed fluid from the relief valve 35 over the line 64 to the reservoir 65, thus changing the pressure differential across the relief valve 35 to which it responds. If the pressure in the main line 18 is greater than that in the main line 18&#39; by an amount exceeding the pressure differential to which the relief valve responds, fluid may short circuit from the main line 18, through the check valve 37, the relief valve 35 and the check valve 39&#39; to the other main line 18&#39;. A pressure differential in the opposite direction, again exceeding the pressure differential to which the relief valve 35 responds, short circuits hydraulic fluid between the main lines through the check valve 37&#39; the relief valve 35 and the check valve 39. It will be noted, first of all, that the first bypass path comprising the serial path through the check valve 37, the relief valve 35 and the check valve 39&#39; serves continuously to protect against the condition in which the main line 18 pressure exceeds the main line 18&#39; pressure by an amount exceeding the value to which the relief valve 35 has been set to respond; and, conversely, the second bypass path through the serial connection of the check valve 37&#39;, the relief valve 35 and the check valve 39 protects continuously against the condition in which the pressure in the main line 18&#39; exceeds that in the other main line 18 by such amount as aforesaid. Additionally, the pressure differential across the relief valve to which it responds as set by the operator serves a very important control function heretofore unknown in this art. That is, the adjustable pressure relief valve 35 allows the operator to leave the hydropump in a constant output mode and the hydromotor in a constant setting mode whereby the hydropump will be driven in the cable winding direction at a speed which imparts a maximum upward velocity to the tool suspended by the cable when the relief valve is set to its maximum pressure differential. With the hydropump and hydromotor so set, the operator, merely by controlling the pressure differential to which the relief valve 35 responds, may control the power delivered to the hydromotor at any pressure differential value between a low value corresponding to a low set pressure differential across the relief valve 35 which allows the tool or load to free fall (i.e., as is required in &#34;jarring&#34;) and a high value (less than the value at which destructive tension could be imposed on the cable) corresponding to maximum power delivery to the hydromotor (and consequent maximum winding speed of the hydromotor). In this way, the valve 35 may be switched from the low value to allow the tool to free fall until it is bottomed and then to the high value to impart maximum upward acceleration to the tool until it reaches its maximum upward velocity. During the time when the tool is being subjected to maximum acceleration from bottomed standstill to its maximum upward velocity, the high value at which the relief valve is set by the operator protects the cable from destructive tension while at the same time assuring that acceleration is the maximum possible within that constraint. 
     The invention is not limited to its application to a winch system with the disposition shown in FIG. 2. The invention may be satisfactorily applied to other winch arrangements, for example, an arrangement as described in Dutch Patent Application No. 8100506. The winch arrangement disclosed herein comprises two hydropump devices and hydromotor devices coupled wherewith, the hydromotors being both coupled by means of a planetary gear wheel system with the cable drum. In both cycles a safety circuit embodying the invention can be included. The relief valves 35 can then be controlled by one and the same control-valve.