GB2199382A - Speed-change and steering gear system for an endless track vehicle - Google Patents

Abstract

A switchable clutch (86) is provided for selective functional connection of two zero shaft parts (82, 84) of a zero shaft (60) for a "travel mode" operational state, and for the functional separation of the two zero shaft parts (82, 84) for a "working mode" operational state. In the "travel mode" a travel drive force flow passes from a power distribution means (14) by way of a control gear mechanism (22), and a steering drive force-flow passes through two separate controllable hydrostatic pump motor units (94, 96), the two force flows being directed to summing differential gears (46, 48) and from there to take-off shafts (70, 72) for the caterpillar tracks of the full-track vehicle. In the "working mode" the travel drive force flow does not pass through the control gear mechanism (22), but, additionally to the steering drive force flow, passes through the hydrostatic units (94, 96) to the summing differential gears (46, 48) and from there to the take-off shafts (70, 72). <IMAGE>

Description

SPEED-CHANGE AND STEERING GEAR SYSTEM FOR A FULL TRACK VEHICLE SPECIFICATION This invention relates to a speed-change and steering gear system for a full-track vehicle which carries at least one work unit, the system comprising: a) travel drive means which includes a hydrodynamic torque converter and a control gear mechanism through which the travel drive force flow passes in a "travel mode" operational state, b) steering drive means which includes a steplessly adjustable hydrostatic torque transmission device through which the steering drive force flow passes in the "travel mode" operational state, c) power distribution means arranged to distribute power from a driving element drivable by a vehicle motor to the input of the control gear mechanism and to the input of the hydrostatic torque trans mission device, d) two summing differential gears, each of which has a first element drivable from the output of the control gear mechanism, a second element drivable from the output of the steering drive means, and also a take-off element, the speeds of rotation of the take-off elements being dependent upon the speeds of rotation of the two drivable elements of the differential gears, e) a zero shaft connecting the two said second elements during the "travel mode" operational state by way of gear means.

The work unit or units can be a mine-sweeping device, a trench-digging device or some other apparatus. The speed-change and steering gear system makes it possible for the full-track vehicle to have a high travel speed in the "travel mode" operational state and a low travel speed in the "working mode" operational state.

One speed-change and steering gear system of the type referred to above is known from DE-PS 1480725.

By means of the present invention one can achieve the object of providing a speed-change and steering gear system such that a full-track vehicle can have a relatively high speed (of the order of 60 km/hour) and at the same time good steering properties for the "travel mode", and also a relatively low, steplessly adjustable travel speed (0.2 to 5.0 km/hour) in the "working mode". The steering of the full-track vehicle in "travel mode" and in "working mode" is possible purely mechanically using the same steering member and using a mechanical actuating chain. Furthermore, it is possible steplessly to regulate the travel speed in the "working mode" by means of electrical signals.

This is achieved in accordance with the invention in a system of the type first referred to above, in which: f) the zero shaft is divided and a switchable connecting device is provided for the selective functional connection of the two zero shaft parts for "travel mode" or for functional separation of the two zero shaft parts for a "working mode" operational state, g) the hydrostatic torque transmission device comprises two steplessly adjustable hydrostatic units having inputs which are drivable from the driving element by way of the power distribution means, with the output of one of said hydrostatic units being arranged to drive said second element of one of said differential gears and with the output of the other hydrostatic unit being arranged to drive said second element of the other differen tial gear, and h) means are provided by which the travel drive force flow coming from the driving element can be interrupted at the input side of the control gear mechanism and the said first elements of the differential gears which are drivable from the output of the control gear mechanism can be blocked, so that then, with a functionally divided zero shaft, in the "working mode" both the steering drive force flow and also the travel drive force flow flow through the two hydrostatic units.

In order that the invention may be fully understood, a number of embodiments in accordance with the invention will now be described in detail by way of example and with reference to the accompanying drawings, in which; Fig. 1 is a schematic illustration of a speedchange and steering gear system in accordance with the invention for a full-track vehicle; Fig. 2 shows the speed-change and steering gear system of Fig. 1 in the "travel mode" operational state, in which a zero shaft is functionally in one piece; Fig. 3 shows the speed-change and steering gear system of Fig. 1 in the "working mode" operational state, in which the zero shaft is functionally divided and is split into two zero shaft parts, so that each of two sprocket wheels for the driving of caterpillar tracks of a tracked vehicle can be driven in a steplessly controllable manner by separate respective hydrostatic units;; Fig. 4 is a schematic representation of a further embodiment of speed-change and steering gear system according to the invention for a full-track vehicle, with a couplable differential reversing gear between two zero shaft parts of a functionally divisible zero shaft, in which the zero shaft parts are rotationally coupled to one another in the same rotational sense selectively for the "travel mode" by two clutches, or, for the "working mode" operational state, are functionally divided from each other, with the zero shaft parts being arranged to be coupled to each other rotationally in opposite senses by way of a reversing gear in order to provide a third operational state "special working mode" with "stabilised linear travel"; Fig.5 is a schematic representation of a control device for the gear systems shown in Figs. 1 to 4; and, Fig. 6 shows a preferred embodiment of a setting device for the control device shown in Fig. 5 and for the gear systems shown in Figs. 1 to 4, for mechanical transmission of control movements and simultaneous automatic regulation of the travel speed in dependence upon electrical signals.

Fig. 1 is a schematic representation of the gearing of a control gear and steering gear system according to the invention. A vehicle motor 10 of a full-track vehicle (which is not otherwise shown) can be coupled by means of a clutch 12 to a driving element 14. The driving element 14 can be selectively connected to a drive shaft 20 either by way of a hydrodynamic torque converter 16 or by way of a by-pass clutch 18, bypassing the torque converter. A control gear mechanism 22 which is switchable under load is connected at its input 24 to the drive shaft 20 by way of a bevel gearing 26 and is connected at its output 28 to a takeoff shaft 32 by way of a planet wheel carrier 30. The ex-pression "switchable under load" means that the control gear mechanism 22 can be switched while it is coupled to the vehicle motor 10.The bevel gearing 26 makes it possible to carry out a reverse switching of the control gear mechanism 22 from forward travel, in which a switching clutch V is engaged, to rearward travel by opening the switching clutch V and closing a switching clutch R. The take-off shaft 32 drives a secondary pump 34 and a tachometer 36. The two ends 38 and 40 of the take-off shaft 32 are-respectively connected to outer hollow wheels 42 and 44 of two summing differential gear systems 46 and 48. Positioned on the take-off shaft 32 between the control gear mechanism 22 and the differential gear 48 is a current brake (retarder) 50 for braking the take-off shaft 32 and thereby also braking the tracked vehicle.

The inner sunwheels 52 and 54 of the two differential gears 46 and 48 are-connected to each other by way of a zero shaft 60 and respective intermediately connected gear stages 62 and 64. The one gear stage 62 has one gearwheel more than the other gear stage 64, so that a rotation of the zero shaft 60 is transmitted with different directions of rotation. The planet wheel carriers 66 and 68 respectively form the take-off elements of the differential gears 46 and 48 and drive sprocket wheels 78 and 80 for the tracks of the tracked vehicle by way of respective shafts 70 and 72, on which are located mechanical vehicle brakes 74 and 76 respectively.

As alternative embodiments, the hollow wheels 42,44 planet carriers 66,68 and inner sunwheels 52,54 can be transposed with regard to their respective functions as driving elements, take-off elements and reaction elements.

The zero shaft 60 is divided into two zero shaft parts 82 and 84, which can be connected to one another selectively by a switchable clutch 86 or which can be separate from each other, so that in one case the zero shaft 60 acts as a functionally one-piece zero shaft, while in the other case it acts as a functionally divided zero shaft. The zero shaft parts 82 and 84 are provided each with a speed of rotation sensor 90 and 92 of a control device 93 for the purpose of measuring their speeds of rotation and their directions of rotation.

A hydrostatic torque transmission device comprises two steplessly adjustable hydrostatic units 94 and 96, whose inputs 98 and 100 are connected by way of respective gear stages 102 and 104 to the driving element 14. The driving element 14 serves to distribute the power, whereby the power from the clutch 12 is transmitted on the one hand to the drive shaft 20 and on the other hand, by way of the gear stages 102 and 104, to the inputs 98 and 100 of the two hydrostatic units 94 and 96. Moreover, the driving force flow from the driving element 14 goes directly to oil pumps 108 positioned on the primary side of the control gear mechanism 22, and, by way of a hydrodynamic clutch 109, to a fan 111.The output 110 of the one hydrostatic unit 94 is connected by way of a gear mechanism 114 to the one zero shaft part 82; the output 112 of the other hydrostatic unit 96 is connected by way of a gear mechanism 116 to the other zero shaft part 84. Each hydrostatic unit comprises a controllable oil pump 95 and an oil motor 97 driven by the oil from the pump. The oil motors 97 are preferably controllable in like manner.

The control gear mechanism 22 has a switching clutch 1 for the first gear, a switching clutch 2 for the second gear, a switching clutch 3 for the third gear, a switching clutch 4 for the fourth gear, a switching clutch V for forward travel, and a switching clutch R for rearward travel. By opening both switching clutches V and R for forward and rearward travel the control gear mechanism 22 can be separated from the drive shaft 20, and by closing the two switching clutches 1 and 4 for the first and fourth gears the driving elements, namely the hollow wheels 42 and 44, of the two summing differential gears 46 and 48, can be blocked.

Fig. 2 shows the speed-change and steering gear system of Fig.l in the "travel mode" operational state.

Here, the clutch 86 of the zero shaft 60 is closed, so that the two zero shaft parts 82 and 84 are connected to each other and the zero shaft 60 is functionally a one-piece shaft. The driving force which is available at the clutch 12 from -the vehicle motor 10 divides itself at the driving element 14, which constitutes a power divider, into a travel driving force and a steering ariving force. The travel driving force flow is indicated by arrows 120, which are shown as solid line arrows, and the steering driving force flow 122 is represented by broken line arrows. From this it is apparent that in the "travel mode" shown in Fig.2 the travel driving force flow 120 is from the driving element 14 via the torque converter 16 to the control gear mechanism 22, and from there is by way of the summing differential gears 46 and 48 to the sprocket wheels 78 and 80.The steering driving force flow 122 is from the driving element 14 to the two hydrostatic units 94 and 96, in which the flow is transmitted from the respective oil pumps 95 to the oil motors 97 and from these to the zero shaft 60. The functionally onepiece zero shaft 60 is stationary for linear travel of the tracked vehicle, i.e. it does not rotate. For curved path travel, the two zero shaft parts 82 and 84, and thereby the whole functionally one-piece zero shaft 60, are driven by the two hydrostatic units 94 and 96 in the same direction of rotation, with the direction of rotation being dependent upon the direction of the turning movement of the tracked vehicle.

The steering driving force flow 122, in the case of curved path travel, passes from the zero shaft 60 by way of the gear stages 62 and 64 in opposite directions of rotation to the two summing differential gears 46 and 48. In this "travel mode" operational state, in normal conditions, the dominant part 120 of the driving force is used by way of the control gear mechanism 22 for the travel drive, and only a smaller part 122 is necessary for the steering, so that the travel speed can be very high.

Fig. 3 shows the speed-change gear system and steering gear system of Fig. 1 in the "working mode" operational state. In this state the clutch 86 on the zero shaft 60 is open, so that the zero shaft 60 is functionally divided and its zero shaft parts 82 and 84 can rotate independently of each other. The steering drive force flow 122 of the one hydrostatic unit 94 is transmitted only to the zero shaft part 82, while another part of the steering drive force flow 122 is transmitted by the other hydrostatic unit 96 to the other zero shaft part 84. Moreover, in this "working mode" operational state, one element, namely the outer hollow wheel 42 and 44, of the two summing differential gear systems 46 and 48 is blocked, which is represented by an arrow 130 on the take-off shaft 32.The blocking of the hollow wheels 42 and 44 arises from closure of the two switching clutches 1 and 2 of the first and fourth gears, with the result that the take-off shaft 32 is blocked. In an alternative arrangement, the take-off shaft 32 could alternatively be blocked by other means, for example by a brake acting on it.

Moreover, the travel driving force flow 120 is interrupted at the input side 24 of the control gear mechanism 22. For this the two switching clutches V and R for forward and rearward travel respectively are opened. Additionally, or instead of opening the two switching clutches V and R, the travel driving force flow 120 could be interrupted in such a way that for this operational state the hydrodynamic torque converter 16 is discharged and the bypass clutch 18 is opened, so that no driving force can pass from the clutch 12 of the vehicle motor by way of the driving element 14 to the input 24 of the control gear mechanism 22.This means that no driving force flow 120 passes through the control gear mechanism 22, but that the driving force flow 120 passes instead, in the same manner as does the steering drive force flow 122, from the driving element 14 by way of the one hydrostatic unit 94 to the one zero shaft part 82 and by way of the other hydrostatic unit 96 to the other zero shaft part 84. By this means it is possible for the two hydrostatic units 94 and 96 to cause the tracked vehicle to travel very slowly during the "working mode". The travel driving force and the steering force can be split between the two sprocket wheels 78 and 80 by way of the two hydrostatic units 94 and 96 in a steplessly variable manner. Thus, for extreme travel situations, it is possible that the whole of the travel driving force and steering force produced by the vehicle motor can be transmitted to only one sprocket wheel 78 or 80. By this means it is possible for a tracked vehicle which has become bogged down to "break free" and to be made mobile again. Furthermore, it is possible to match the vehicle working speed to the working speed of work units which are mounted on the tracked vehicle, even right down to zero speed. Such work units could be mine-sweeping units, trench-digging machines or any other equipment and apparatus.

Furthermore, it is possible to make both the travel speed and also the direction of travel of the tracked vehicle dependent on the working speed and type of work of the work units, by arranging that these work units send signals dependent on their work to the hydrostatic units 94 and 96, in which case the tachometers 90,92 function as real-value transducers.

According to the special embodiment of speed-change gear system and steering gear system shown in Fig. 4, instead of a simple switchable clutch 86, there is a switchable, blockable differential reversing gear mechanism 140 comprising a reversing gear 141, a switchable first clutch 142 for blocking the reversing gear 141 and thus rigidly connecting the two zero shaft parts 82 and 84 into a functionally one-piece zero shaft 60, and a switchable second clutch 144. By closing the second clutch 144 one likewise creates a functionally one-piece zero shaft 60, but with shaft parts 82 and 84 rotating in mutually opposite directions. With the second clutch 144 opened, one can switch selectively between the two operational states.

With. the first clutch 142 closed one is in the "travel mode" operational state and the force flows 120 and 122 are as shown in Fig. 2 and as have been described already above. With the first clutch 142 opened, one is in the "working mode" operational state and the force flows 120 and 122 are as shown in Fig.3 and as described above. In the "working mode" each hydrostatic unit 94 and 96 separately drives only one zero shaft part 82 or 84. The hydrostatic units 94 and 96 drive the zero shaft parts 82 and 84 in mutually opposite directions of rotation in the case of linear travel of the tracked vehicle, since a reversal of the direction of rotation occurs by virtue of the difference in the gear stages 62 and 64.

Moreover, one has a third operational state "special working mode" which can be brought into effect if one opens the first clutch 142 and closes the second clutch 144. As a result, the two zero shaft parts 82 and 84 are connected functionally to each other by way of the reversing gear mechanism 140, but the zero shaft parts nevertheless rotate in opposite directions of rotation relative to each other. In the "special working mode" state the power flows 120 and 122 are the same as for the "working mode" state illustrated in Fig.3, and additionally one achieves the effect that these power flows "support" each other by way of the differential reversing gear 140.This support arises in the case of the "special working mode" in the way that although only linear travel of the tracked vehicle is possible, one does nevertheless have the following advantages: a) the linear travel is stabilised, since in the case of unequal resistance to movement at the two caterpillar tracks of the tracked vehicle the force flows from the two hydrostatic units 94 and 96 to the two sprocket wheels 78 and 80 divide themselves in a manner which is unequally inversely proportional by way of the reversing gear 141, as is necessary in order to drive the two caterpillar tracks with the same travel speed. In the extreme case, both hydrostatic units 94 and 96 operate jointly on only one caterpillar track.Thereby, in the "special working mode" operational state, linear travel is guaranteed even if the tracked vehicle travels in an inclined attitude on a slope or if it travels wit one caterpillar track on ground covered with ice. The take-off shafts 70 and 72 always have exactly the same speed of rotation.

b) small errors in the setting and in the output characteristics (absorption behaviour) of the hydrostatic units 94 and 96 are automatically compensated.

Fig. 5 shows further details of the control device 93. The fluid pumps 95, in order to be able to adjust their delivery volumes, each have a setting lever 202.

The one setting lever is adjustable by an actuating lever 208 of a setting device 210 via a rod 206, and the other setting lever is adjustable by an actuating lever 209 of the setting device 210 via a further rod 206. The fluid motors 97 of the two hydrostatic units 94 and 96 have setting devices 212 which serve to adjust their take-off speed and which are hydraulically actuated from the setting device 210 by way of hydraulic connections 214. The setting device 210 is supplied with oil from the control gear mechanism 22 by way of a supply pipe 216 and a return pipe 218. The control gear mechanism 22 can be switched, in the "travel mode" operational state shown in Fig.2, to different gears by a gear-selector switch 220 via an electronic gear control circuit 222.For steerage of the tracked vehicle, steering movements of a steering wheel 224 are transmitted mechanically by way of a linkage 226 to a control lever 228 which transmits the steering movements of the steering wheel 224 mechanically into the setting device 210 and thus to the actuating levers 208 and 209 which themselves transmit the movements to the setting levers 202 of the fluid pumps 95 of the two hydrostatic units 94 and 96.

In the "working mode" operational state, the zero shaft parts 82 and 84 of the zero shaft 60 are functionally divided one from the other corresponding to the illustration of Fig. 3, and the travel driving force flow goes not by way of the control gear mechanism 22, but the travel drive force flow and the steering drive force flow go by way of the hydrostatic units 94 and 96 to the zero shaft parts 82 and 84 and from these to the differential gears 46 and 48. Thus, the travel speed can no longer be set by the control gear mechanism 22, but only by setting the hydrostatic units 94 and 96. This means that the setting levers 202 of the fluid pumps 95 of the two hydrostatic units 94 and 96 must be adjusted not only in dependence on steering movements of the steering wheel 224, but, in combination, also in dependence on the desired travel speed.The two functions are combined together in the setting device 210 by a setting unit 230 which is described in more detail with reference to Fig. 6. By the use of an operational mode selector switch 232 one can choose selectively between "travel mode" or "working mode". The "special working mode" operational state, in which the clutch 144 is automatically closed and the clutch 142 remains open, is always automatically switched in when the steering wheel is set to "linear travel" in the "travel mode" operational state. The operational state selector switch 232 is connected to a work unit 234 carried by the tracked vehicle and which in the "working mode" and "special working mode" operational states supplies signals indicative of desired vehicle speed to the electronic gear control circuit 222 by way of an electrical connector system 236. The electronic gear control circuit 222 compares the desired signals from the electrical leads 236 with the actual value speed signals from the tachometers 90 and 92, to which it is connected by way of leads 238 and 239, and produces, in dependence upon this comparison, electrical signals indicative of desired vehicle speed for the setting device 210 by way of an electrical lead 242. In this setting device 210 the electrical desired signals are converted into mechanical magnitudes and these are superimposed on the mechanical steering adjustment movements of the control lever 228. In dependence upon this superimposition, the setting levers 202 are moved into a position corresponding both to the desired speed of the vehicle and also to the steering direction set by the steering wheel 224.The work unit 234 can be for example a mine-sweeping unit or a ditch-digging unit or some other unit. The desired vehicle speed for "working mode" and "special working mode" can also be set manually in a selective manner by a working speed selector lever 244. The work unit 234 feeds signals to a control device 246 of the vehicle motor 10 by which both in the "working mode" and in the "special working mode" the vehicle motor 10 is held at a driving speed of rotation favourable for the vehicle motor . The magnitude of the desired signals on the electrical lead 236 from the work tool to the electronic gear control circuit 222 thus depends upon to what speed the speed setting lever 244 has been set, and from that what is the most favourable constant driving speed for the vehicle motor 10 for this setting.The operating conditions of the work tool 234 and of the electronic gear control circuit 222, as well as other information, are indicated on an instrument panel 248.

In the "working mode" and "special working mode" operational states, the maximum achievable travel speed is achieved if the setting levers 202 of the fluid pumps 95 and 99 of the hydrostatic units 94 and 96 have reached their end positions. If the vehicle is to travel on a curve at highest speed, then at least one of the two levers 202 must be turned back to a lower speed, so that a speed difference is created between the caterpillar tracks of the tracked vehicle which corresponds to a curved path of that nature.

A sensor 250 shown in Fig. 5 produces signals corresponding to the position of the steering wheel 224. In dependence upon these signals, by way of the electronic gear control circuit 222, the lead 242, the setting device 210 and the setting levers 202 of the two fluid pumps 95 and 99, the speed of movement of one caterpillar track and thereby also the highest speed of the tracked vehicle for a curved path are reduced only as much as is necessary in order to produce the curved path set by the steering wheel 224.

Sensors 251 and 253 in the form of angle sensors or displacement measuring instruments measure the individual positions of the setting levers 202. The signals from the sensors 251 and 253 are compared in the gear control circuit with the signals from the speed-of-rotation sensors 90.92, in order to avoid hunting oscillations.

Fig. 6 shows details of the setting device 210 of Fig. 5. It comprises essentially the setting unit 230 and a proportional valve 262 connected to it by way of a bypass valve 260. The proportional valve 262, a socalled MOOG valve, produces a pressure difference by means of which the setting unit 230 is held in a determined position which corresponds to a predetermined settable travel speed of the tracked vehicle.

The proportional valve produces this pressure difference in dependence on the electrical signals on the lead 242, which in practice is a bundle of several electrical leads, and produces an output in hydraulic pipes 264 and 265 into which the bypass valve 260 is connected.

The setting unit 230 essentially comprises the following components. An entraining tube 268 is mounted rotatably by a bearing 270 in an outer housing 266 with which it is coaxial. On the outer surface of the entraining tube 268 there are a plurality of entraining grooves 272 which extend in the axial direction. The entraining tube 268 can be turned relative to the outer housing 266 by means of the control lever 228 which is secured to the tube. The entraining tube 268 projects coaxially into a connecting tube 274 which has entraining elements 275 which engage in the entraining grooves 272 of the entraining tube 268 and contact against the axial guide surfaces 273 formed by the side walls of the entraining grooves 272, so that the entraining tube 268 is axially displaceable but is nevertheless connected for fixed rotation with the connecting tube 274.Two threaded members 276 and 278 are positioned coaxially within the connecting tube 274 and axially behind the entraining tube 268. Each threaded member has a coarse thread 280 and 282 respectively on its external periphery, which threads are engaged by coarse threads 281 and 283 on entraining elements 284 and 286. These entraining elements 284 and 286 are secured for fixed rotation with the connecting tube 274. In the case of an axial displacement of the connecting tube 274, relative to the entraining tube 268 and the threaded members 276 and 278, the coarse threads 280 to 283 cause a rotation of the threaded members 276 and 278 relative to the connecting tube 274 and to the entraining tube 268.

The coarse threads 280 and 282 of the two threaded members 276 and 278 are oppositely inclined relative to each other, so that these threaded members rotate in mutually opposite directions upon an axial displacement of the connecting tube 274. Thus, the actuating levers 208 and 209 also themselves rotate in opposite directions of rotation. The one actuating lever 208 is connected for fixed rotation by means of a shaft 288 with the threaded member 278, and the other actuating lever 209 is connected for fixed rotation with the threaded member 276 by virtue of a hollow shaft 290 which is coaxial with the shaft 288. The two shafts 288 and 290 extend axially and coaxially through the entraining tube 268, and the shaft 288 also extends axially through the threaded member 276.The number of threaded members 276 and 278 corresponds to the number of setting levers 202 to ne set on the hydrostatic units 94 and 95. Therefore, in alternative embodiments, one could have fewer or more than two threaded members 276, 278. The coarse threads 280 and 282, unlike the drawing, could alternatively both be of the same rotational hand. Their direction of rotation is dependent upon the direction of rotation in which the actuating levers 208 and 209 are to be pivoted.

The connecting tube 274 consequently serves for fixed rotation connection of the entraining tube 268 with the threaded members 276 and 278, so that all four components 268, 274, 276 and 278 are turned jointly when the entraining tube 268 is turned by the control lever 228. This rotational movement of the entraining tube 268 can have superimposed on it an axial movement of the connecting tube 274, because the connecting tube 274 in the "working mode" and "special working mode" operational states is displaced axially into a defined position for the setting of a desired travel speed.An axial displacement of the connecting tube 274 has the effect, by virtue of the entraining elements 284 and 286, of producing a rotation corresponding to the axial displacement~, in mutually opposite directions of rotation, of the threaded members 276 and 278 and thus also of the actuating levers 208 and 209. This axial displacement of the connecting tube 274 does not however change the rotational position and the axial position of the entraining tube 268, and thus does not change the rotational speed difference between the outputs 110 and 112 of the hydrostatic units 94 and 96 set for a defined curved travel path.

The coarse threads 280 to 283 are self-locking in the direction of rotation. This means that with a rotation of the connecting tube 274 by means of the entraining tube 268 the two threaded members 276 and 278 do not rotate relative to the connecting tube 274, but only together with the connecting tube 274, and thus their rotational positions relative to the connecting tube 274 remain the same. Only in the case of an axial displacement of the connecting tube 274 do the two threaded members 276 and 278 rotate in the manner described above relative to this connecting tube 274. The shaft 288 is mounted rotatably in the hollow shaft 290 and in the threaded member 276 by bearings 291. The hollow shaft 290 is mounted rotatably in the entraining tube 268 by bearings 292.

The entraining elements 275, 284 and 286 each consist of two entraining parts divided transversely to their longitudinal axes, with each pair of parts having its parts rotatable relative to each other, in order to eliminate contact play between them and the entraining surfaces of the entraining grooves 272 and of the coarse threads 280 and 282. By this means the whole unit is free from play and the aforementioned rotational movements and axial movements can be transmitted between the individual components without play.

A mechanical, hydraulic, pneumatic or electrical device, or a combination of these, can be used for the axial displacement of the connecting tube 274 relative to the entraining tube 268 and the threaded members 276 and 278. In the illustrated embodiment the axial setting of the connecting tube 274 is effected hydraulically in dependence upon electrical signals. On the connecting tube 274, at its end 296 remote from the entraining tube 268, a cylinder 300 is mounted by means of a bearing 298 so as to be axially fixed to the connecting tube but rotatable relative thereto. The connecting tube 274 can rotate relative to the cylinder 300, but can only be displaced together with the cylinder 300. Within the cylinder 300 there is positioned a piston 302 which is spatially fixed to a base 304 of the outer housing 266 by a piston rod 306.

The cylinder 300 and piston 302 are arranged axially in relation to the connecting tube 274. On both axial sides of the piston 302 there is a pressure chamber 310 and 312 respectively, between the piston and a cylinder base 308. A pipe section 264/2 of the hydraulic pipe 264 and leading away from the bypass valve 260 extends through the piston rod 306 and up into the one pressure chamber 310. A pipe section 265/2 of the hydraulic pipe 265 and which also leads away from the bypass valve 260 also extends through the piston rod 306 and up into the other pressure chamber 312. The switched state shown in Fig. 6 corresponds to the "travel mode" operational state. In this state the bypass valve 260 is in a setting in which the pipes 264 and 265 are closed off and their pipe sections 264/2 and 265/2 are connected to a sump 316.Thus, the two pressure chambers 310 and 312 are empty and two oppositely acting springs 320 and 322 hold the cylinder 300, and consequently also the connecting tube 274, in the middle position which is shown in Fig. 6. Rotational movements of the control lever 228 are transmitted directly to the actuating levers 208 and 209. A superimposition of other movements therefore does not take place.

In order to be able to superimpose on the rotary movement of the control lever 228 a further influencing factor, namely an electrical speed signal at the proportional valve 262, the bypass valve 260, in the "working mode" and "special working mode" operational states is switched over to a setting in which the hydraulic pipes 264 and 265 of the proportional valve 262 are not interrupted, and where pressurised fluid can flow through the pipe sections 264/2 and 265/2 to and from the pressure chambers 310 and 312, in order to bring the axially displaceable cylinder 300 into an axial position relative to the stationary piston 302 which corresponds to the electrical signal applied to the proportional valve 262, and to hold the cylinder in this axial position. The connecting tube 274 follows the axial movements of the cylinder 300.With this displacement, the connecting tube 274 turns the threaded members 2V6 and 278 and consequently also turns the actuating levers 208 and 209 into a rotary position in which the hydrostatic units 94 and 96 produce a travel speed corresponding to the electrical signal. By rotating the steering lever 228 by means of the steering wheel 224 the take-off speed of rotation at the outputs 110 and 112 of the hydrostatic units 94 and 96 can be delayed or accelerated, departing from the speed set by the aforesaid axial displacement, in order to establish a curved path for the tracked vehicle.

A position sensor 330 produces for the electronic gear control circuit 222 of Fig. 5 electrical signals in dependence upon predetermined axial positions of the connecting tube 274 and thus also in dependence upon the set travel speed of the tracked vehicle. By this means the electronic gear control circuit 222, upon rotation of the steering wheel 224, can allow for when for the curved path of travel no acceleration of the take-off speed of rotation of the two hydrostatic units 94 and 96 is any longer possible, since these have already reached their maximum speed of rotation, but for the curved path only the take-off speed of rotation of one of the hydrostatic units can be throttled back.

A pressure source 334, which in the arrangement described here is constituted by the oil pumps 34 and 108 of the control gear mechanism 22, supplies oil under pressure by way of the supply pipe 216 to the proportional valve 262 and to a pressure-reducing valve 336. The output 340 of the pressure-reducing valve 336 is connected by way of a pipe 342 and the hydraulic pipes 214 to setting cylinders 344 and 346 of the setting devices 212 of the adjustable fluid motors 97 of the two hydrostatic units 94 and 96. In the lower and middle speed ranges of the tracked vehicle the pressure in the setting cylinders 344 and 346, and thus the setting of the fluid motors, is kept at a constant value. If in the "working mode" and "special working mode" operational states in the upper speed range of the vehicle an entraining lug 346 on the cylinder 300 strikes against an actuating element 348, then with further increasing displacement of the cylinder 300 the supply of pressurised fluid to the setting cylinders 334 and 336 is changed. Thereby, the travel speed in the upper speed range of the tracked vehicle is no longer determined solely by the setting of the fluid pumps 95, but is also determined by the setting of the fluid motors 97.

Changes which can be made to the setting unit 230 can include inter alia an arrangement in which the cylinder/piston unit 300, 302 is replaced by an electrical, hydraulic or pneumatic setting motor or by some other corresponding setting device. An important advantage is that electrical signal values are converted and can be superimposed as mechanical values on another mechanical value, namely the rotary movement of the control lever 228. A further advantage is that from the movement of the control lever 228 one can produce not only a single mechanical output movement, but several different output movements, which can be variable and also can have different directions of movement, according to just how many threaded members 276 and 278 are used and in dependence upon the slope and direction of the coarse threads 280 and 282 on these threaded members. The use of the setting device 210 with the setting unit 230 is not limited to the setting of hydrostatic units, but can also serve for the setting of any other devices which are to be actuated in dependence upon at least two control values. A particular advantage of the setting unit 230 is that the setting movements of the control lever 228 are transmitted purely mechanically and consequently one has very good functional reliability, in contrast to electrical, pneumatic or hydraulic transmission chains.

Claims (10)

CLAIMS:

1. A speed-change and steering gear system for a full-track vehicle which carries at least one work unit, the system comprising: a) travel drive means which includes a hydrodynamic torque converter and a control gear mechanism through which the travel drive force flow passes in a "travel mode" operational state, b) steering drive means which includes a steplessly adjustable hydrostatic torque transmission device through which the steering drive force flow passes in the "travel mode" operational state, c) power distribution means arranged to distribute power from a driving element drivable by a vehicle motor to the input of the control gear mechanism and to the input of the hydrostatic torque trans mission device, d) two summing differential gears, each of which has a first element drivable from the output of the control gear mechanism, a second element drivable from the output of the steering drive means, and also a take-off element, the speeds of rotation of the take-off elements being dependent upon the speeds of rotation of the two drivable elements of the differential gears, e) a zero shaft connecting the two said second ele ments during the "travel mode" operational state by way of gear means, f) wherein the zero shaft is divided and a switch able connecting device is provided for the selec tive functional connection of the two zero shaft parts for "travel mode" or for functional separa tion of the two zero shaft parts for a "working mode" operational state, g) wherein the hydrostatic torque transmission device comprises two steplessly adjustable hydros tatic units having inputs which are drivable from the driving element by way of the power distribu tion means, with the output of one of said hydros tatic units being arranged to drive said second element of one of said differential gears and with the output of the other hydrostatic unit being arranged to drive said second element of the other differential gear, h) and in which means are provided by which the travel drive force flow coming from the driving element can be interrupted at the input side of the control gear mechanism and the said first elements of the differential gears which are drivable from the output of the control gear mechanism can be blocked, so that then, with a functionally divided zero shaft, in the "working mode" both the steering drive force flow and also the travel drive force flow flow through the two hydrostatic units.

2. A gear system in accordance with claim 1, in which for combined control of the steering and regulation of the travel speed in the "working mode" operational state a combined setting device is provided which causes setting movements to be imparted to setting members of the two hydrostatic units in dependence upon electrical control signals for the regulation of the travel speed of the tracked vehicle, and which simultaneously transmits setting movements necessary for the steering in a purely mechanical manner from a vehicle steering member to said setting members of the hydrostatic units, superimposing these latter setting movements on the setting movements for travel speed regulation.

3. A gear system in accordance with claim 2, in which the same vehicle steering member and the same components of the combined setting device serve for the control of the steering both in the "travel mode" operational state and also in the "working mode" operational state.

4. A gear system in accordance with any preceding claim, in which speed-of-rotation sensors for measuring the speed of rotation of the take-off elements of the summing differential gears or the speed of rotation of a tachometer corresponding thereto are provided for the automatic regulation of travel speed in the "working mode" operational state.

5. A gear system in accordance with claim 4, in which angle sensors and/or displacement sensors are provided for the measurement of the respective positions of the setting members of the hydrostatic units, the signals from which sensors are compared with the signals from the speed of rotation sensors in order to avoid hunting oscillations.

6. A gear system in accordance with any preceding claim, in which in the "working mode" operational state the setting of the hydrostatic units for the steering movement takes place with priority over the setting of the hydrostatic units for the travel speed, in such a way that, if necessitated by steering movements, the travel speed signal is reduced automatically in order to produce the necessary steering speed of rotation.

7. A gear system in accordance with any preceding claim, in which for the "working mode" operational state the travel drive force transmission path at the input side of the control gear mechanism is functionally broken by the opening of switching clutch means, and said first elements of the summing differential gears drivable by the output of the control gear mechanism are blocked by simultaneously switching in at least two gear stages of the control gear mechanism.

8. A gear system in accordance with any preceding claim, in which the two zero shaft parts of the zero shaft can be functionally connected or separated selectively by means of a clutch in order to be able to switch between the "travel mode" operational state and the "working mode" operational state.

9. A gear system in accordance with any of claims 1 to 7, in which, for switching between the "travel mode" and "working mode" operational states, the zero shaft is provided, as a connecting device, with a differential reversing gear mechanism comprising a reversing gear and two clutches, the arrangement being such that the following switching states are possible:: a) both clutches are open, with the result that the two zero shaft parts are functionally separate, for curved path travel in the "working mode", b) one of said clutches is closed and the other clutch is open, with the result that said one clutch functionally connects the two zero shaft parts to each other, for the "travel mode", c) said one clutch is open and said other clutch is closed, with the result that the two zero shaft parts are connected functionally to each other by way of the reversing gear, for a "stabilised linear travel" in the "working mode" operational state, as a special operating mode"special working mode", in which in dependence upon different resistance to motion at the take-off shafts of the summing differential gears the driving forces of the two hydrostatic units are divided correspondingly in a variable manner between the two zero shaft parts by way of the differential reversing gear mechanism.

10. A gear system in accordance with claim 2 or any of claims 3 to 9 when dependent on claim 2, in which the setting device comprises a combination setting unit with the following components for combining the regulation of the travel speed with the mechanical control of the steering process: a) an entraining member rotatable by the vehicle steering member, b) at least one rotatable setting element which includes at least one thread and which is mechani cally connected to the setting elements of the hydrostatic units, c) a connecting member which is rotatably fixed with the entraining member but which is coupled displaceably with it for relative axial movement, and which has at least one thread which is engage able with the thread of the setting element, a a cylinder with a piston therein which is ar- ranged to be actuated on both sides by pressurised fluid, one of said piston and said cylinder being spatially fixed and the other being axially dis placeable relative thereto, with the axially displaceable part being axially fixed to the connecting member but coupled rotationally thereto for relative movement, and in which an electrically actuatable valve means is provided which supplies pressurised fluid to or withdraws pressurised fluid from the cylinder in dependence upon electrical signals corresponding to a presettable travel speed.