Arrangement for Controlling the Lifting Mechanism of a Tractor or a Harvester Combine

The present invention relates to an arrangement for controlling the lifting mechanism of tractors or harvester combines for example to control the position of a plough.

Background:

Hydraulic control units have been proposed in which hydraulically operated desired value setting means and actual value transducer means are provided which, like a hydraulic linkage, act on a valve controlling the hydraulic actuator of the tractor. This known arrangement also includes a control valve located between the aforementioned desired value setting and actual value setting means by which signals of two actual valve indicator means may selectively be brought into action. A disadvantage of this known arrangement is that the hydraulic linkage is not adapted for exactly regulating the lifting mechanism especially since in this arrangement columns of pressure fluid have to be shifted in relatively long signal conduits. The volume of the pressure fluid in the long signal conduit will change upon changes in temperature, which will disturb an exact response of the arrangement. Furthermore, this known arrangement is not suitable for mixing different actual value signals.

A hydraulic bridge circuit is also known in which four precontrolled valves are respectively arranged in the four branches of a bridge circuit and in which a servomotor is arranged in the bridge diagonal. Two proportionally working pressure regulating valves are provided for precontrolling the valves in the four bridge branches in which each of the pressure regulating valves acts on two valves located in opposite bridge branches. In this known arrangement the bridge circuit is provided for a working circuit and not for a control circuit and this known arrangement is not used for regulating the lifting mechanism of a tractor or the like.

It is an object of the present invention to provide an arrangement for controlling the lifting mechanism of a tractor or the like comprising a hydraulic working circuit and a hydraulic control circuit for hydraulically transmitting signals of actual force value transducer means and desired force value setting means in the control circuit to a hydraulically operated valve in the working circuit which controls the lifting mechanism. It is a further object of the present invention to provide such a control circuit which will assure quick and exact operation of the hydraulically controlled valve in the working circuit.

A hydraulic working circuit is provided, including a hydraulic actuator, a source of pressure fluid and a control valve between the source and the actuator and having a hydraulically controlled spool movable between a neutral position blocking flow of fluid between the source and the actuator and two working positions in which pressure fluid is fed into, or, respectively discharged or drained from the actuator. A hydraulic control circuit is provided for moving the hydraulically operated spool of the valve between the positions thereof, in which the control circuit is in the form of a bridge circuit having a plurality of bridge branches and a bridge diagonal in which the hydraulically operated valve spool is located and in which desired force value setting means are located in one of the bridge branches to produce hydraulic signal proportional to the desired force while another of the bridge branches is divided in at least two parallel conduits with an actual force value transducer means arranged in each of the two conduits to produce hydraulic signals corresponding to actual forces on the lifting mechanism and means in the other bridge branch upstream of the actual force value transducer means for mixing signals provided by the actual force value transducer means.

The aforementioned mixing means may comprise a control valve, or in a preferred arrangement two adjustable throttles respectively located in the aforementioned two conduits and common adjusting means for the two throttles constructed to reduce during adjustment the open cross-section of one of the two throttles while simultaneously increasing the open cross-section of the other of the two throttles and vice versa, which will assure a very simple mixing of the signals.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

FIG. 1 is a schematic diagram of a first embodiment of an arrangement according to the present invention for controlling a lifting mechanism of an agricultural machine such as a tractor or the like; and

FIGS. 2-4 respectively illustrate the control circuit of a second, a third and fourth embodiment according to the present invention.

FIG. 1 schematically illustrates an arrangement 10 for regulating the movement of the control linkage 11 which is pivotably supported at three points on a tractor. The control linkage 11 comprises a lower guide bar 12 which is movably supported by means of a leaf spring 14 on the housing 13 of the tractor. The linkage 11 comprises further an upper guide bar 15, formed as a multi-arm lever having arms 15a, 15b, 15c pivotably mounted intermediate its ends and as shown at the junctions of the arms, for pivoting movement about a pivot 16 provided on the aforementioned housing and which is connected by a link 11' to the lower guide bar 12 and by a link 11" and to a hydraulic actuator 17 also provided on the housing 13. Actuator 17 has a piston 17a operable in a cylinder 17b. The lower guide bar 12 may carry at its front end for instance a plow P which has to be lifted or lowered in response to the arrangement according to the present invention. The cylinder of the hydraulic actuator 17 is connected to a hydraulic working circuit 18 which includes a pump 21 for feeding pressure fluid from a tank or reservoir 45 into the hydraulic working circuit, and a hydraulically operated three-port, three-position valve 19 having a spool or valve member 19M in the hydraulic working circuit between the pump 21 and the hydraulic actuator. The valve is a spool valve, in which the spool is maintained centered by springs 19a, 19b. The valve 19 is hydraulically operated by pressure fluid in conduits 27 and 27' which feed pressure fluid to respective faces of the spool of the valve 19 from part of a control circuit 22 of the arrangement. The control circuit 22 is constructed as a bridge circuit and has four bridge branches 23, 24, 25 and 26, as well as a bridge diagonal 27 and 27' in which the aforementioned valve 19 is located. An additional source of pressure fluid 28 communicates with the control circuit 22 at the junction of the first bridge branch 23 with the second bridge branch 24 and a constant throttle 29 is located in the first and constant throttle 31 in the second bridge branch. A desired pressure value setting means 32 including, as shown in FIG. 1, a spring biassed valve member, in which the biasing force of the spring may be adjusted by a handle 32a by the operator to the desired value, is located in the third bridge branch 25 of the bridge connected to the junction of the first bridge branch 23 with the bridge diagonal conduit 27'. The fourth bridge branch 26 connected to the junction of the second bridge branch 24 and the bridge diagonal conduit 27 is divided by a four-port, four-position control valve 33 providing for switching and mixing of hydraulic fluid into an upstream section 34 and a downstream section 35. A quick lifting control member 36 is located in the upstream section 34 of the fourth bridge branch 26. This quick lifting control member is constituted by a two-port, two-position valve which in one position, as shown in FIG. 1, permits flow of fluid through the fourth bridge branch 26 and which in the other position prevents such flow. The downstream section 35 of the fourth bridge branch 26 comprises a first conduit 37, a second conduit 38 and a third conduit 39. A first actual force transducer 41, constructed as a displacement-to-pressire converter producing hydraulic signals p depending on the pulling force s applied by the tractor, is located in the first conduit 37. A second actual force transducer 42 transducing the positions s of the element 15 operated by the lifting mechanism into pressure signals p, is located in the second conduit 38. For this purpose, the two actual force transducer means 41 and 42 are each provided with a pin or feeler 43 by means of which they respectively sense movements or displacements s of the leaf spring 14 and the upper guide bar 15, respectively. The third conduit 39 is directly connected with a working fluid conduit 44 which connects the valve 19 with the hydraulic actuator 17 and senses pressure-dependent signals.

Operation:

Assuming the arrangement 10 is in equilibrium and the valve 19 is in the position as shown in FIG. 1 the control chambers 19R and 19L at the end faces of the spool 19M of valve 19 are at equal pressure. The pressure fluid pumped by the pump 21 flows through line 21a to valve 19, and directly back to the tank 45 through line 21b. The hydraulic actuator 17 is blocked. At the same time pressure fluid from the source 28 of control pressure fluid flows over the bridge branches 23, 25 to the tank 45. Control pressure fluid also flows through branch 24, the quick lifting control member 36, which normally is in the position shown in FIG. 1 and branch 26 and through the control valve 33. Valve 33 is in the position c in which only the first actual force transducer 41 responsive to the pulling force applied on the bar 12 is connected into the control circuit 22. The desired value setting means 32, and the first actual force transducer 41, on the other hand, will produce equal pressures, which act equally at both sides of the bridge diagonal 27. The spool of the valve 19 thus will remain in the position shown in FIG. 1, blocking the working conduit 44.

A change in the pulling force acting on the lower guide bar 12 will change the position of the leaf spring 14 causing a corresponding movement on the feeler 43 of the transducer 41, and therewith a change of the pressure in the first conduit 37 of branch 26 which is throttled by the first actual force transducer 41. The thus produced pressure difference at the bridge diagonal conduit 27 will cause shifting of the spool of the valve 19 from its neutral position to a working position producing flow of pressure fluid from the pressure fluid source 21 to the hydraulic actuator 17 or flow of pressure fluid out of the spool of the latter. As a consequence, the plow P on the guide bar 12 is lifted or lowered until the changing pulling force acting on the lower guide bar 12 and detected by the first actual force transducer 41 brings about a condition of equilibrium in the hydraulic bridge of the control circuit 22. It is therefore possible to control the pulling force acting on the lower guide bar 12 according to the desired pessure signal to which the desired value setting means 32 is adjusted.

By moving the spool of control valve 33 to the positions b or d shown in FIG. 1, it is possible to regulate correspondingly the position of the linkage 11 in response to the hydraulic signal from the second actual force indicator 42 or the pressure in the hydraulic actuator 17 in response to the pressure in working conduit 44. By moving the control valve 33 to the position a it is also possible to mix the hydraulic signals generated by the first and second actual force transducer means 41 and 42. By moving the spool of valve 36 from the position shown in FIG. 1 to the other position it is possible to block the fourth bridge branch 26 and to obtain in this way a quick lifting of the lower guide bar 12, for instance to obtain a quick lifting of the plow P connected thereto during turning of the tractor at the edge of a field.

FIG. 2 schematically illustrates the control circuit 51 of a second embodiment 50. The same reference numerals are used for indicating corresponding elements of the control circuit.

In the control circuit 31 shown in FIG. 2 the desired force setting means 32, shown as a controllable throttle is located in the first bridge branch 23. A second desired force setting means 52 likewise shown as a controllable throttle is located in the third bridge branch 25. The throttle of constant cross-section 31 is located in the second bridge branch 24. The first actual force transducer 41 is located in the conduit 37 and the second position depending actual force transducer 42 is located in the conduit 38. Transducers 41, 42 act hydraulically as controlled throttles, as shown. In each of the conduits 37 and 38 which are connected at a point 53 with each other and with the second bridge branch 24 as well as with the bridge diagonal 27, is a mixing throttle unit 53a, namely the variable throttles 54 and 55 located between the junction point 53 and the actual force transducers 41 and 42. Both mixing throttles 54 and 55 of mixing unit 53a are mechanically coupled in such a manner that they will be operated in opposition, or push-pull, that is when the open cross-section of one of the mixing throttles is increased, the open cross-section of the other mixing throttle is simultaneously decreased and vice versa. The first bridge branch 23 and the second bridge branch 24 are connected via a second throttle 56 of constant cross-section with the pressure source 28 which supplies a constant volume of pressure fluid with constant pressure.

The operation of the control circuit 51 corresponds in principle largely to the control circuit 22 shown in FIG. 1. It differs therefrom however that, with the second desired force setting means 52, a second desired force value may be applied. For example, depending on the slip of the wheels of the tractor, the hydraulic actuator 17 may be controlled in such a manner that, during increase of the slip, the hydraulic actuator 17 will, for instance, lift the plow P connected to the lower guide bar 12 so as to prevent overloading of the motor of the tractor. Furthermore, by means of the two mixing throttles 54 and 55 working in opposition to each other it is possible to control the desired relationship of the pulling force, as transduced by the first actual force value transducer 41 or the plow position, as transduced by the second actual force value transducer 42.

FIG. 3: schematically illustrates the control In the control circuit 61 of system 60 a constant throttle 62 is arranged in the first bridge branch 23, whereas the first desired force value setting means, constructed as an adjustable pressure limiting valve 32', is provided in the third bridge branch 25. The second desired force value setting means 52 is located in a control conduit which leads from the point 53 to the tank. The operation of the control circuit 61 is substantially identical to that of the control circuit 51 shown in FIG. 2.

FIG. 4 shows as part of a fourth arrangement 70 a control circuit 71 which is constructed as a half bridge. The valve 19 is only supplied with pressure fluid connected to one chamber 19c from the point 53 over the half bridge diagonal 27 in opposition to the force of a spring 19S. The constant throttle 31 is eliminated and the first bridge branch 23, in which the desired value setting means 32 is located, leads directly to the tank 45. In principle the control circuit 71 shown in FIG. 4 operates in the same manner as the control circuit 51 according to FIG. 2, but its construction is considerably simpler.

While FIGS. 2-4 illustrate only the control circuits of the respective arrangements 50, 60 or 70, it is to be understood that each of these arrangements comprises also a working circuit 18 as shown in FIG. 1, including a pump 21 for feeding fluid under pressure from the tank 45 into the valve 19 and a hydraulic actuator 17 connected by a working conduit 44 to the valve 19.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of arrangements for controlling the lifting mechanism of tractors or the like, differing from the types described above.

While the invention has been illustrated and described as embodied in an arrangement for controlling the lifting mechanism of a tractor or harvester combine comprising a hydraulic actuator connected to the lifting mechanism and controlled by a hydraulically controlled valve arranged in the bridge diagonal of a hydraulic bridge circuit, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Thus, for instance, it is also possible instead of the single first actual value transducer 41 to provide two parallel or series connected actual value transducers which cooperate respectively with two lower guide bars provided on the tractor. Furthermore, it is also possible in order to tune the control circuit to provide further constant throttles. Additional mixing throttles which may work in the same sense or in opposition to each other may also, in special cases, be advantageously used.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.