RELATED APPLICATIONS

This claims priority to EP Application No. 20185266.2, titled Switching Device and a Transmission having such a Switching Device, filed Jul. 10, 2020, which is hereby incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to a switching device for a transmission.

BACKGROUND OF THE DISCLOSURE

A transmission may have a first and a second transmission housing portions and a switching device. The switching device comprises a shift collar, a shift fork which engages in the shift collar, a control actuator which is arranged in the first transmission housing portion and an actuator rod which is connected at one end to the control actuator and at the other end to the shift fork. The actuator rod is supported in a first guiding hole which is formed in the first transmission (gear) housing portion.

Such switching devices are known and are used, for example, in agricultural vehicles, in particular in tractors or harvesting machines, such as combine harvesters or field choppers. Particularly in the combine harvesters, the transmissions are provided with the switching device in order to be able to switch the output rotation direction of the transmission from a first rotation direction into a reversed second rotation direction. The reversed rotation direction, that is to say, a reversal of the driving, is in principle only intended to be adjusted when specifically required, for example, in the event of blockages in the harvesting header and/or on the harvested material conveyor in the conveyor channel of the combine harvester. The switching devices generally make provision for a shift collar to be connected to a shift fork which can be displaced by means of a hydraulically controllable actuation cylinder. The shift fork is to this end secured to an actuator rod which is connected to the actuation cylinder and which is supported so as to be able to be axially displaced in guiding holes arranged in opposing housing halves of the switching device. In order to minimize a switching torque acting on the actuator rod when the shift collar is displaced, the shift fork is arranged between the guiding holes. This type of arrangement of the shift fork, actuator rod and guiding holes in both housing halves is at the expense of the compactness of the switching device and requires a relatively large structural space. In addition, the shift fork is generally connected to the actuator rod only at an outer location on the shift fork, whereby a relatively large bending torque acts on the shift fork and the actuator rod when the required actuation force for displacing the shift collar is intended to be applied. Furthermore, as a result of the only localized connection, the shift fork may also have a degree of rotational play with respect to the actuator rod, whereby the fork members of the shift fork can radially apply a load to the shift collar in a disadvantageous manner which, inter alia, leads to friction losses.

SUMMARY OF THE DISCLOSURE

The object forming the basis of the disclosure is considered to be to provide a switching device of the type mentioned in the introduction and a transmission by means of which the above-mentioned disadvantages are overcome.

It is proposed to construct a switching device of the type mentioned in the introduction in such a manner that a second guiding hole which is formed in the first transmission housing portion parallel with the first guiding hole is arranged and a guide rod which is orientated parallel with the actuator rod is provided and is connected at one end to the shift fork and at the other end is supported in the second guiding hole. This arrangement is particularly suitable for a transmission device having a small structural space, in which an arrangement of the second guiding hole for the actuator rod in the second transmission housing portion opposite the first guiding hole in the first transmission housing portion would be at the expense of the compactness of the transmission. As a result of the arrangement of the second guiding hole for the actuator rod parallel with the first guiding hole and the arrangement of a guide rod which is supported in the second guiding hole, the arrangement of a guiding hole for the actuator rod in the second transmission housing portion is prevented. The first transmission housing portion remains almost unchanged in terms of its structural depth, but in contrast the second transmission housing portion can be constructed with a smaller structural depth, whereby on the whole a smaller structural space can be achieved. In addition, the shift fork is thereby supported both by the actuator rod and by the guide rod so that the shift fork is retained concentrically relative to the shift collar and a rotational play of the shift fork with respect to the actuator rod and resultant friction losses between the shift fork and the shift collar are prevented. The wear on the shift fork and the shift collar is thereby reduced. Furthermore, as a result of an additional connection location of the shift fork and guide rod, which represents a support location for the shift fork with respect to the actuator rod, the bending torque acting on the shift fork and the actuator rod when the shift collar is displaced is minimized and the switching operation is thereby facilitated.

The first guiding hole is preferably formed between the control actuator and the shift fork. The guiding hole can thereby be constructed in a structurally technically advantageous manner as an integral component of the first transmission housing portion.

In order to ensure a switching position in a preferred direction, at least a first resilient element may be provided and urges the shift fork in the corresponding preferred direction. Should an actuation force which is applied to the actuator rod by the control actuator fail, for example, as a result of failure or as a result of a defect on the control actuator, the shift fork is urged by the actuation force applied by the resilient element in the preferred direction and retained in the corresponding switching position which is produced in the preferred direction provided. The control actuator may, for example, be constructed as a hydraulically activated actuation cylinder, having an actuation piston which is connected to the actuator rod. In the event of a failure of the hydraulics, the actuation force which is intended to be applied by the control actuator would fail so that the force applied by the resilient element acts as the only actuation force in the preferred direction. Alternatively, the control actuator could also be operated electrically, wherein, in the event of a failure of the electrical system, no actuation force is applied to the actuator rod by the control actuator and also in this instance the force applied by the resilient element acts as the only actuation force in the preferred direction. The preferred direction may, for example, be the switching direction in which the shift collar has to be moved in order to operate a harvesting header to receive harvested material. The switching direction which is opposite the preferred direction may then, for example, be a switching direction in which the shift collar has to be moved in order to achieve a reverse of the drive with a reversed rotation direction, for example, in the event of a clogging or blockage of the harvesting header and/or harvested material conveyor in the conveyor channel of the combine harvester.

The resilient element is preferably arranged between the first transmission housing portion and the shift fork. Alternatively, however, the resilient element could also be arranged in the control actuator and, for example, apply an actuation force to the actuation piston. In the event of a failure of the hydraulic or electrical system, an actuation force in the preferred direction originating from the resilient element would be maintained on the actuation piston.

Preferably, the resilient element is constructed as a pressure spring and extends at least partially in a spring guiding hole which is formed in the first transmission housing portion parallel with the first and second guiding holes. The pressure springs apply an actuation force to the shift fork by means of which the shift fork is moved or urged in the direction of the second transmission housing portion. The spring guiding hole acts, on the one hand, as a bending protection for a pressure spring which is, for example, constructed as a helical spring, but, on the other hand, also as an auxiliary assembly member since the insertion and assembly of the resilient element are facilitated.

In addition to the one or first resilient element, a second or additional resilient element may also be provided. Depending on the structural space and required actuation force, the number and dimensions of the resilient elements may vary, wherein the structural space between the shift fork and the first transmission housing portion advantageously enables the arrangement of a plurality of resilient elements. This has the advantage that the actuation force originating from the resilient elements can be configured in a very variable manner. The otherwise conventional arrangement of resilient elements in order to produce an actuation force in a preferred direction is carried out in the control actuator itself, for example, by a pressure spring which is arranged in a hydraulic chamber of the actuation piston. This type of arrangement is, however, limited by the construction type and construction size of the control actuator. Preferably, the same number of resilient elements are provided at both sides of the guide rod in order to prevent an action of torque on the guide rod and on the actuator rod. In a preferred embodiment, there are arranged two pressure springs which are constructed as helical springs and which are arranged at both sides of the guide rod. The spring guiding holes extend in the first transmission housing portion parallel with the second guiding hole. The pressure springs and the spring guiding holes are arranged in such a manner that the pressure springs engage at both sides of the shift fork. The pressure springs are in this instance sized in such a manner that, when an actuation force is not present or is deactivated from the hydraulically operated control actuator, a sufficiently large actuation force is generally applied by the pressure springs to the shift fork so that the shift fork and the shift collar can be moved in the preferred direction and the shift collar can be retained in the preferred switching position. It is thereby ensured that the drive connection to the harvesting header is maintained and the user also does not have to interrupt or can continue the harvesting work in the event of a failure of the hydraulic system.

A transmission which is provided with the above-described switching device preferably has a second transmission housing portion which is connected to the first transmission housing portion. An output shaft extends through the first and second transmission housing portions. A first drive element for the transmission can be connected to the output shaft by means of a planetary gear set. Furthermore, a second drive element can be connected to the output shaft. The transmission further has a gear which is connected to the output shaft in a rotationally secure manner and which is in engagement with a shift collar. In a first switching position, the shift collar is brought into engagement with the planetary gear set and the gear and, in a second switching position, the shift collar is brought into engagement with the second drive element and the gear.

Preferably, the first switching position, in which the shift collar is brought into engagement with the planetary gear set, is the switching position in the preferred direction or the switching position for the normal operation of the combine harvester.

The planetary gear set comprises a ring gear which is arranged on the second transmission housing portion, a planetary set which rolls in the ring gear, a planetary carrier which can be brought into engagement with the shift collar in the first switching position and a sun gear which is connected to the first drive element and which rolls with the planetary gears. Starting from the first drive element, in the first switching position the drive flow is consequently carried out via the sun gear and via the planet wheels which are rolling in the ring gear onto the planetary carrier and from there via the shift collar onto the gear of the output shaft. Starting from the second drive element, in a second switching position the drive flow is carried out via the shift collar onto the gear of the output shaft. The rotation direction of the drive shaft in the first switching position is counter to the rotation direction of the drive shaft in the second switching position in which the transmission is operated in reverse mode if, for example, the harvesting header and/or the harvested material conveyor is clogged or blocked in the conveyor channel of the combine harvester.

The first drive element is used for normal operation of the harvesting machine with a first rotation direction in which the harvesting header and the harvested material conveyor are operated to collect the harvested material. The first drive element may in this instance be constructed as a belt drive drum which is connected to the sun gear by means of a flange connection. Preferably, the belt drive drum is sized and constructed in such a manner that the transmission per se is substantially located in a hollow space surrounded by the belt drive disk.

The second drive element is used for reversal operation of the harvesting machine with a second, opposing rotation direction, in which the harvesting header and the harvested material conveyor are operated in the opposite direction in order, for example, to eliminate a blockage or clogging in the harvesting header and/or at the harvested material conveyor. The second drive element is constructed as a worm gear and is connected to a gear worm. Alternatively, another type of drive which is used in reverse mode could also be selected in this instance, for example, also a spur gear, hypoid gear, bevel gear and the like.

With reference to the drawings, which show an embodiment of the disclosure, the disclosure and other advantages and advantageous developments and configurations of the disclosure will be described below in greater detail and explained.

