Abstract:
An agricultural-implement hydraulic circuit includes a pump supplying pressurized fluid to a first service line and a second service line via a feed line and a device for varying the flow rate of the pump. A distributor valve is disposed between the first service line and the second service line, with the first service line and the second service line being connected and disconnected according to a position of the distributor valve. A hydraulic motor is coupled to the first service line through the valve and discharges fluid to a return line. A hydraulic actuator is coupled to the second service line. An indicator-valve assembly is coupled to the feed line, with the indicator-valve assembly including an indicator sensitive to pressure in the feed line such that the indicator indicates a predetermined pressure in the feed line to an operator.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to means for providing hydraulic power to an agricultural implement, in particular to a hydraulic power system for an implement including a flow-rate indicator. 
   2. Description of Background Art 
   It is well known in the art to provide towed or carried agricultural implements with a hydraulic pump, e.g. a gear pump, for supplying power to one or more hydraulic actuators. Such gear pump can be driven by the Power-Take-Off (PTO) shaft of the agricultural tractor which tows or carries the implement. For each apparatus it is possible to find an appropriate pump which provides the required flow rate and/or pressure. However, the hydraulic pump on each implement adds to the cost thereof. 
   Meanwhile it is also conventional to equip medium- or top-range tractors with a hydraulic pump for providing auxiliary power to an implement. One or more pairs of standard connectors allow for a direct connection of the implement circuitry to the hydraulic system on the tractor. The operator can control the hydraulic components on the implement through handles and/or knobs inside the tractor cab. The use of such tractor-mounted pumps solves the problem of providing a distinct pump on each implement. The pump on the vehicle may be selected to provide a maximum flow rate suitable for the largest implements. However, such design will result in poor overall efficiency because most implements require a considerably smaller amount of oil and most oil would flow back to the tank via a pressure-relief valve. 
   It is possible to use a variable-flow-rate pump and to adapt the pump output to the needs of the implement. However, the required minimum flow rate may vary substantially per implement and, frequently, the operator only notices that the flow rate is too low when the implement is not working adequately. When he adapts the flow rate, he may very well exceed the needed minimum value, such that hydraulic power may be lost unnecessarily. 
   SUMMARY OF THE INVENTION 
   Hence, there is a need for an apparatus and method that ensures a proper setting of the hydraulic flow rate without excess losses of hydraulic energy. According to a first aspect of the present invention, an agricultural-implement hydraulic circuit includes a pump supplying pressurized fluid to a first service line and a second service line via a feed line and a device for varying the flow rate of the pump. A distributor valve is disposed between the first service line and the second service line, with the first service line and the second service line being connected and disconnected according to a position of the distributor valve. A hydraulic motor is coupled to the first service line through the valve and discharges fluid to a return line. A hydraulic actuator is coupled to the second service line. An indicator-valve assembly is coupled to the feed line, with the indicator-valve assembly including an indicator sensitive to pressure in the feed line such that the indicator indicates a predetermined pressure in the feed line to an operator. 
   The preferred embodiment ensures that the available flow rate at the inlet of the circuitry is sufficient for the adequate operation of the hydraulic actuators of the implement. 
   In a preferred embodiment, the circuitry comprises a flow divider having an inlet port connected to the connection means, preferably quick-acting couplings, a first outlet port connected directly or indirectly to an hydraulic actuator and a second outlet port connected to the indicator means. The flow divider may prevent oil flow to the second port as long as a predetermined flow rate, equal to the minimum flow rate for adequate operation, has not been reached. It may also limit the oil flow to the first port to this predetermined flow rate, while deriving the excess oil flow to the second port. 
   The indicator means may comprise a pressure-sensitive element connected to a by-pass line which is connected to the second outlet port of the divider, the by-pass line being provided with a flow restrictor. The pressure-sensitive element may comprise a spring-loaded piston, which may be provided with a visual indicator, e.g. a colored tab. Alternatively, the piston may be provided with means for generating an electrical signal, e.g. an electrical switch. The implement may then be provided with an electrical connector for transmitting the signal to flow rate control means on the tractor for automatic adjustment of the source of pressurized hydraulic fluid. The flow rate signal may also be converted into a digital message which is sent to the tractor via a serial bus, e.g. a CAN-bus. 
   A spring-loaded check valve may be arranged in parallel to the flow restrictor for limiting the maximum pressure on the indicator. 
   Advantageously, the flow divider, flow restrictor and piston may be combined into a single valve assembly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in further detail, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is a side view of a baler-wrapper combination; 
       FIG. 2  is a schematic of part of the hydraulic circuitry of the baler-wrapper combination of  FIG. 1 ; and 
       FIG. 3  is a schematic of an indicator valve assembly used in the circuitry of  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The agricultural implement shown in  FIG. 1  is a baler-wrapper combination  10 , comprising a round baler  11  for picking up crop material, such as hay or straw, from a field and compressing it into a cylindrical bale, and a bale wrapper  12  for wrapping sheet material, such as plastic film, around the finished bale. 
   The baler  11  has a support frame provided with a set of wheels  14  and a tow bar  15  for attachment to a tractor or other towing vehicle. The bale wrapper  12  comprises a subframe  17  which is removably attached to and supported by the support frame of the baler. The baler has a baling chamber  19  wherein the crop material lifted up from the field by a pick-up  20 , is rotated and compressed by appropriate conveyor means. The conveyor means may comprise transverse rollers and/or juxtaposed belts disposed along the periphery of the baling chamber. 
   When the material inside the bale chamber  19  has reached its full diameter or its full density, a mechanism (not shown) is operated to tie the crop material into a stable bale. Thereafter, a tailgate  22  at the rear of the baling chamber is opened and the bale  24  is deposited onto a transfer mechanism  26  of the wrapper  12 . This mechanism comprises a fork  27  which receives the bale  24  and tilts rearwardly in order to deposit the bale upon a wrapping table  30 . 
   The bale wrapper  12  comprises a boom  31  which rotatably carries a pair of dispensers  32  which each hold a supply of wrapping material. The wrapping table  30  below the dispensers  32  comprises a conveyor  34  for rotating the bale  24 . During the wrapping operation the dispensers  32  are rotated around the bale  24  on the wrapping table, while table conveyor  34  is rotating the bale about its horizontal axis. The sheet of wrapping material is wrapped around the bale until it forms two or more layers around the complete bale surface. Thereafter two knives (not shown) are raised to intercept the wrapping material and then lowered to cut the same and to hold a tail of the wrapping material in a start position until the next wrapping cycle. Meanwhile the wrapping table  30  is tilted rearwardly to deposit the finished bale onto the field. 
     FIG. 2  shows the hydraulic circuitry  36  used to control the wrapping operation. The tailgate  22  is opened and closed by a single-acting hydraulic cylinder  38 . The fork  27  of the transfer mechanism  26  is tilted by a double-acting hydraulic cylinder  39 . The knives are raised and lowered by double-acting cylinders  40  and the wrapping table  30  is tilted by a pair of double-acting cylinders  41 . The conveyor  34  of the wrapping table  30  is driven by a hydraulic motor  42  and the dispensers  32  are rotated around the bale  24  by a further hydraulic motor  43 . 
   The circuitry  36  comprises a pair of connectors  45  for connecting the circuitry to an adjustable hydraulic power source on the towing vehicle, e.g. a tractor. Hydraulic power may be provided by a variable displacement pump  47 , e.g. a pump having a movable swash plate, drawing oil from an oil tank  48 . The pump may be driven either directly or indirectly by the engine of the vehicle. Alternatively, the pump may be a fixed-flow-rate pump which supplies pressurized oil via an adjustable flow divider, such that it is possible to vary the output rate of the tractor circuitry to the implement circuitry  36 . 
   Oil from the pump  47  is fed to a valve assembly  49  and therefrom to the hydraulic actuators  38 – 41  via an indicator valve assembly  50  which will be described in further detail hereinafter. The valve assembly  49  comprises a pilot-controlled distributor valve  52  which receives the pressurized oil and splits the oil flow between a first service line  53  and a second service line  54 . The first service line is provided with an electrically controlled, proportional control valve  56  which determines the oil flow rate to the conveyor motor  42  and therefrom to the dispenser motor  43 . The serial connection between the two motors  42 ,  43  ensures a fixed relationship between the rotational speeds of the conveyor  34  and the dispensers  32 , such that the wrapping material is disposed adequately over the full surface of the bale  24 . The solenoid of the proportional valve  56  is connected to electrical control means which provide for a low speed at the start and at the end of the wrapping cycle and for a full speed in-between. 
   The action of the proportional valve  56  influences the pressure in the first service line  53  which, through a pilot, affects the position of the distributor valve  52  such that, at any time, the required oil flow is fed to the motors  42 ,  43 . The remainder of the incoming oil flow is deviated to the second service line  54  to which are connected the electrically controlled valves  59 ,  60 ,  61  and  62  of the tailgate cylinder  38 , the fork cylinder  39 , the knife cylinders  40  and the table cylinders  41 , respectively. 
   When no pressurized oil is needed for any of the cylinders  38 – 41 , the control means opens a by-pass valve  64  which branches the second service line  54  directly onto a return line  65 . 
   It is clear from the description above that the setting of the proportional valve  56  fully determines the amount of oil fed to the first service line  53 . Hence, when the oil flow rate from the pump  47  is too low and the motors  42 ,  43  are turning, all available oil will be directed to this first line  53  and the second service line  54  will receive no or only an insufficient amount of oil. Such situation may occur at the end of the wrapping cycle, when the conveyor  34  and the dispensers  32  are driven and the knives have to be raised for cutting the tail of the wrapping material. If no sufficient oil flow is available, the cylinders  40  will not, or only too slowly raise the knifes into the path of the wrapping material. 
   The oil flow rate is even more critical shortly after the start of the wrapping cycle, when the dispensers  32  and the conveyor  34  are already working at full speed. At this stage the first wraps of sheet material are already secured against the bale by the following wraps, but the knives are still seizing the starting tails against the subframe  17 . The knives have to be raised and lowered in order to release the tails of wrapping material before they start hampering the rotation of the bale. Initially, the revolution of the bale  24  stretches the tail only on one side of the wrapper  12 . The knives have to be raised to release this stretched tail. Meanwhile the other tail keeps dangling between the bale  24  and the subframe  17 . Only after half a revolution of the bale  24 , also the other tail is stretched and then the knives have to be raised once more to release also the starting tail on this side. As the raised knives extend into the path of the dispensers  32 , which are now rotated at full speed, there remains only a very short time interval for raising and lowering the knives. The knife cycle must take less time than half a revolution of the dispensers. A slow operation of the knife cylinders  40  because of insufficient oil flow will cause interference between the raised or half-raised knives and the dispensers  32 . 
   Hence it is preferable for the operator to be able to verify that the tractor pump  47  is set to provide the adequate amount of oil to the implement  10 . To this end, the circuitry  36  of the implement is provided with the indicator valve assembly  50 . Herein, a flow divider  67  directs the full oil flow from the tractor pump  47  to the inlet port of valve assembly  49  as long as the oil flow rate remains below a predetermined value. When this value is exceeded, the divider  67  will limit the oil flow to the valve assembly  49  to this predetermined value and direct the remainder of the oil flow via a by-pass line  68  to the return line  65 . The by-pass line  68  is provided with a restrictor  69 , such that a pressure differential is created between the by-pass line and the return line. This differential is sensed at one side of a spring-loaded piston  70  which has at its outer end an indicator tab. The pressure pushes the piston outwardly such that the indicator tab becomes visible to an operator standing between the implement  10  and the tractor. 
   In order to limit the maximum pressure on the piston  70 , the by-pass line  68  has, parallel to the orifice  69 , a spring-loaded check valve. As a further safety measure, a pressure relief valve  72  is provided between the feed line, upstream the inlet port of the flow divider  67 , and the return line  65 . The flow divider  67 , the restrictor  69 , the piston  70 , the check valve  71  and the pressure relief valve  72  may all be combined into a single valve assembly  50 , which may be mounted to the control valve assembly  49 . 
   When the operator connects the hydraulic circuitry  36  of the baler-wrapper combination  10  to the tractor, he now has the means of verifying whether the pump  47  is set to an adequate oil flow rate. After coupling the connectors  45 , he engages the pump  47  and sets the flow rate to a low value. Meanwhile, no cylinders  38 – 41  or motors  42 ,  43  are activated. Consequently, the flow divider  67  will direct the full oil flow to the distributor valve  52  and therefrom to the second service line  54  and, via the by-pass valve  64  to the return line  65 . Then the operator gradually increases the flow rate of the pump  47  while monitoring the flow indicator. When the flow rate reaches the predetermined value which corresponds to the minimum flow rate for adequate implement operation, the flow divider  67  will deviate part of the oil flow to the by-pass line  68  and the piston will be pushed outwardly. The indicator tab shows to the operator, who is thereby informed that he no longer needs to increase the flow rate. This setting provides for a proper operation of the hydraulic components, without an excess of oil flow which never would be used and which hence would be circulated needlessly through the system. 
   Although the apparatus and the method have been described with reference to a baler-wrapper combination, other embodiments of the invention can be thought of without departing from the scope of the invention as defined by the claims. For instance, the invention can be used for adjusting the oil flow to other towed or carried agricultural machinery, such as balers, wrappers, hay tedders, mowers, etc. In particular, the invention may prove useful where a single source of hydraulic power is used for a more or less continuously driven component and an intermittently used actuator. The constant flow to the driven component should not hamper the action of the actuator. For instance, there should be no interference between the rotation of a hay tedder rotor and the lifting action of the support arm of the rotor where repositioning is needed in order to adapt to changing field gradients. 
   The pressure indicator may also comprise an electrical switch which is actuated by the movement of the piston. The signal from the switch may then be used for lighting a warning light, e.g. in the vicinity of the flow rate controls, where the operator can readily see it. The signal may also be used as a feedback signal for adjusting the flow rate of the vehicle in an automatic control procedure.