Planet transmission, drive device comprising the planet transmission and vehicle comprising the drive device

A planetary transmission includes a sun gear, which constitutes an input drive to the planetary transmission, a ring gear arranged around the sun gear, and a planet carrier which is designed to rotate and which carries at least one planet wheel, which planet wheel meshes with the sun gear and the ring gear. The planet carrier constitutes an output drive from the planetary transmission. The planetary transmission further includes a wet disk brake, a first set of brake disks in the brake being rotationally locked to the planet carrier and thereby in operation rotating at the rotational speed of the planet carrier. The planetary transmission further comprises an arrangement for circulation of a cooling fluid through the brake which is rotationally locked to the sun gear and thereby in operation rotates at the rotational speed of the sun gear.

BACKGROUND AND SUMMARY

The present invention relates to a planetary-transmission comprising a sun gear, which constitutes an input drive means to the planetary transmission, a ring gear arranged around the sun gear, a planet carrier which is designed to rotate and which carries at least one planet wheel, which planet wheel meshes with the sun gear and the ring gear. The planet carrier constitutes an output drive means from the planetary transmission. The planetary transmission further comprises a wet disk brake, a first set of brake disks in the brake being rotationally locked to the planet carrier and thereby in operation rotating at the rotational speed of the planet carrier. The invention further relates to a drive device comprising such a planetary transmission.

The invention relates primarily to the field of work machinery or work vehicles, such as wheel loaders and dumpers (frame-steered vehicles). The invention could also be utilized for other types of work vehicle, such as backhoes (excavator loaders), and excavators. The invention also has applications in other types of heavy, non-commercial vehicles, such as trucks.

The drive device therefore comprises the planetary transmission and forms a so-called final drive, or hub-mounted reduction gear. The wheel is then arranged rotationally locked on a hub and the planetary transmission is connected between a drive shaft and the hub. The drive shaft is driven by an angular gear, or center gear, which is in turn driven by the vehicle engine by way of a transmission system.

Arranging a planetary transmission on each drive wheel in this way produces a reduction in rotational speed from the drive shaft to the hub and an increase in torque from the drive shaft to the hub.

Since the planet carrier is rotationally locked to the wheel hub the first set of brake disks will in operation rotate at the speed of the wheel. Such a brake affords a high degree of precision and sensitivity in braking.

Rotationally locking a first set of brake disks to a planet carrier in such a planetary transmission, as disclosed by WO 99/03699, for example, is already known. The brake disks are then connected via splines on a radially outer surface of the planet carrier.

WO 04/104436 describes a planetary transmission in which multiple planet wheel journals are joined by a bolted connection to a common, annular carrier, which has radially outer splines for the first set of brake disks.

It is desirable to provide a planetary transmission with an integral brake, which affords a good circulation of cooling fluid to the brake. The invention is also intended to minimize the number of parts and/or to provide a design construction that is as simple and hence as cost-effective as possible. A further intention is to achieve the most compact solution possible in an axial direction.

According to an aspect of the invention, a planetary transmission comprises a sun gear, which constitutes an input drive means to the planetary transmission, a ring gear arranged around the sun gear, a planet carrier which is designed to rotate and which carries at least one planet wheel, which planet wheel meshes with the sun gear and the ring gear, the planet carrier constituting an output drive means from the planetary transmission. The planetary transmission further comprises a wet disk brake, a first set of brake disks in the brake being rotationally locked to the planet carrier and thereby in operation rotating at the rotational speed of the planet carrier. The brake further comprises a means for circulation of a cooling fluid through the brake, the brake circulation means being rotationally locked to the sun gear and thereby in operation rotating at the rotational speed of the sun gear. The fact that the sun gear rotates substantially faster than the planet carrier means that an efficient cooling of the brake is achieved. The cooling fluid is forced radially outwards by the brake circulation means.

According to a preferred embodiment said means for circulation of the cooling fluid is arranged, at least substantially, radially directly inside the brake in order to force the cooling fluid outwards to the brake as the cooling fluid rotates under the effect of the centrifugal force. In other words, viewed in a radial direction there is an overlap between the position of said means for circulation of the cooling fluid and the actual brake.

According to a further development of the preceding embodiment said means for circulation of the cooling fluid comprises a plurality of elements for forcing the cooling fluid, and the cooling fluid forcing elements and the brake disks in the first set are arranged so that they alternate in an axial direction. In this way the cooling fluid is forced in between the opposing brake surfaces of the brake designed for engagement with one another. Said means for circulation of the cooling fluid is preferably disk-shaped.

According to a further development of the preceding embodiment said means for circulation of the cooling fluid comprises a third set of brake disks. This creates the prerequisites for a further braking effect. The third set of brake disks is arranged radially inside the engagement surfaces between the first set and a second set of brake disks in the brake. The third set of brake disks is preferably designed to interact with the first set of brake disks.

According to a further development of the preceding embodiment the opposing surfaces of the first and third set of brake disks, which are designed to interact with one another, form a part of a parking brake. The service brake function has thereby been combined with a parking brake function in a compact, space-saving manner. The parking brake preferably comprises a separate brake piston that is suitably spring-loaded.

According to a further preferred embodiment the brake disks in the first set comprise means for rotationally locking the brake disks directly to the planet wheel journal. This creates the prerequisites for a brake having a smaller overall outside diameter than when the brake disks are seated radially outside the planet carrier. In order to be able to carry not only the planet wheel but also a plurality of brake disks, the planet wheel journals have been lengthened in comparison to hitherto known planet wheel journals.

According to a further development of the preceding embodiment each of the brake disks in the first set comprises at least one hole, in which said planet wheel journal is received. This connection entails less machining than when a splined connection is used.

DETAILED DESCRIPTION

FIG. 1shows a wheel loader1. The body of the wheel loader1comprises a front section2and a rear section3, which each have a pair of drive shafts12,13with wheels16,17. The rear vehicle section3comprises a cab14. The vehicle sections2,3are designed to rotate in relation to one another about a vertical axis with the aid of two first actuators in the form of hydraulic cylinders4,5arranged between the two sections. The hydraulic cylinders4,5are arranged on either side of a horizontal center line through the vehicle for the purpose of steering the vehicle.

The wheel loader1comprises a device11for moving objects or material. The device11comprises a lifting arm unit6and an implement7in the form of a shovel, which is arranged on the load arm unit6. A first end of the load arm unit6is rotatably connected to the front vehicle section2. The implement7is rotatably connected to a second end of the load arm unit6.

The load arm unit6can be raised and lowered in relation to the front section2of the vehicle by means of two other actuators in the form of two hydraulic cylinders8,9, which are each connected by one end to the front vehicle section2and by the other end to the load arm unit6. The shovel7can be tilted in relation to the load arm unit6by means of a third actuator in the form of a hydraulic cylinder10, which is connected by a first end to the front vehicle section2and by its other end to the shovel7via a linkage arm system15.

FIG. 2shows a drive device18for driving one of the wheels16,17of the wheel loader. The drive device18comprises a planetary transmission19with an integral brake20. The drive device18forms a so-called final drive, or hub-mounted reduction gear. The wheel16,17is intended to be arranged rotationally locked on a hub21by means of wheel bolts22. The planetary transmission19is connected between a drive shaft12and the hub21. The drive shaft12is driven by an angular gear, or center gear, which is in turn driven by the vehicle engine by way of a transmission system (not shown).

The planetary transmission19comprises a sun gear23which is rotationally locked to the drive shaft12and which is designed to drive the planetary transmission.

The planetary transmission19further comprises a fixed ring gear24and multiple planet wheels25which are arranged between the sun gear23and the ring gear24and mesh with them.

The planetary transmission19further comprises a planet carrier26having multiple projecting journals27, each for supporting one of said planet wheels25. The planet carrier26comprises a rotationally symmetrical body, which is rotationally locked to the hub21. The planet wheel journals27are here integrally formed with the body. The planet wheel journals27are arranged equidistant from one another in the circumferential direction of the planet carrier. In the exemplary embodiment shown the planet carrier26comprises four journals27, but the number of journals may also be fewer or more than four. Each of the journals27has a circular cross-sectional shape and an indentation47, or beveling, at its free end38, which faces radially inwards. The indentations47are of such a shape that a circular inner space is defined between the journals27.

The disk brake20of the planetary transmission19is a wet brake. The brake20comprises a set of brake disks, which comprises a first set of brake disks in the form of rotor disks28and a second set of brake disks in the form of stator disks29, seeFIG. 4. The term “rotor disks” relates to the disks which rotate in operation and the term “stator disks” relates to the disks which are fixed, that is to say non-rotating in operation. Every other brake disk comprises a stator disk and every second disk comprises a rotor disk. The brake disks are furthermore displaceable in relation to one another along a central axis34for engagement and disengagement with one another.

The stator and rotor disks28,29are preferably of a metallic material, such as steel, preferably a normalized, low-alloy carbon steel. Alternatively the stator disks and the rotor disks28,29may be of some other material, such as plastics or carbon fibers.

Each of the rotor disks28comprises at least one hole31for receiving said journal27of the planet carrier26for rotationally locked connection to the planet carrier. These holes31for the planet carrier journals27are arranged at a radial distance from the intended axis of rotation34of the rotor disk28, which is defined by the geometric center of the brake disk. According to the preferred embodiment multiple holes31are arranged equidistant from one another in the circumferential direction of the rotor disk, each hole being intended to receive a planet carrier journal. Said holes31for the planet carrier journal27extend through the rotor disk.

Said holes31have a shape corresponding to the cross-sectional shape of the planet carrier journal27. Said holes31in this case have a lunate shape in order to match the cross-sectional shape of the free end38of the journal27.

Each of the rotor disks28comprises a central through-opening32for receiving the drive shaft12. The central hole32has an inside diameter larger than the outside diameter of the drive shaft12, so that the drive shaft can rotate at a greater speed than the rotor disks.

The rotor disks28are furthermore displaceable along the planet wheel journals27in the axial direction34of the planetary transmission. The stator disks29are arranged rotationally locked in a fixed housing33, in the form of an axle casing. The stator disks29are arranged so that they are displaceable in the same direction in the housing33, that is to say in a direction parallel to the axis of rotation34of the planetary transmission. The housing33accordingly comprises radially inner means35for engagement with the stator disks29, so that the rotation of the disks is counteracted and so that the brake disks can be displaced parallel to their central axis34. This means of engagement35may comprise, for example, a toothed structure in the internal surface of the housing33and of a correspondingly shaped toothed structure on the radially outer surface of the brake disks29.

There is a layer30of coating material on at least one of the sides of the stator disk for engagement with the adjacent rotor disk28. There are preferably layers30of coating material on both sides of each of the stator disks29. The rotor disks28on the other hand are devoid of layers of coating material on their sides. The coating material here is of paper, but it may alternatively be of some other material, such as plastics. The layer30of coating material preferably has a pattern, seeFIG. 4, in order to permit a cooling flow between the stator disks and the rotor disks28,29when the brake is activated.

The surface of the rotor disks28that is intended to come into contact with the layer of coating material30on the stator disks29when braking is preferably treated and has a certain surface fineness.

The brake2comprises a brake piston36, designed on activation to compress the brake disks28,29against a counter-pressure plate37. The counter-pressure plate37in this case forms part of the fixed housing33.

The transmission of rotation and torque between the planet carrier26and the rotor disk28therefore occurs between the relatively long planet wheel journals27and the holes31in the rotor disks28.

The fact that the planet carrier26is rotationally locked to the wheel hub21by a bolted connection37means that they rotate with the planet wheel journals27rotationally locked to the rotor disks28at the same speed as the wheel.

The brake disks28,29are arranged closer to the free end38of the planet wheel journal than is the planet wheel25.

The planetary transmission further comprises a means40for circulation of a cooling fluid through the brake20. This means40for circulation of the cooling fluid is rotationally locked to the sun gear23and thereby in operation rotates at the rotational speed of the sun gear.

Said means40for circulation of the cooling fluid is arranged, at least substantially, radially directly inside the brake20in order to force the cooling fluid outwards to the brake as the cooling fluid rotates under the effect of the centrifugal force.

Said means40for circulation of the cooling fluid comprises a plurality of disk-shaped elements41for forcing the cooling fluid. The elements41and the brake disks28in the first set are arranged so that they alternate in an axial direction. The radial extent of the brake disks28in the first set is such that they overlap the elements41viewed in an axial direction34.

The cooling fluid forcing elements41are furthermore displaceable along the drive shaft12in the axial direction34of the planetary transmission. Radially inside, therefore, the elements41comprise a toothed structure for engagement with the sun gear23so that the elements41are rotationally locked to the sun gear.

Said means40for circulation of the cooling fluid further comprises a structure for influencing the cooling fluid in order to promote the circulation. This structure may be represented, for example, by a pattern in form of a perforated surface, a grooved structure or the like on the lateral surfaces of the cooling fluid forcing elements41.

More specifically, said means40for circulation of the cooling fluid comprises a third set of brake disks41. The brake disks41in the third set are arranged radially inside the engagement surfaces for the first and second set of brake disks28,29. The third set of brake disks41is designed to interact with a radially inner surface42of the first set of brake disks28.

There is a layer48of coating material on at least one of the sides of the brake disk41for engagement with the adjacent brake disk28. There are preferably layers48of coating material on both sides of each of the rotor disks41. The coating material here is of paper, but it may alternatively be of some other material, such as plastics. The layer48of coating material preferably has a pattern, seeFIG. 4, in order to improve the circulation of a cooling flow through the brake and to permit a cooling flow between the disks28,41when the brake is activated.

The surface of the rotor disks28in the first set that is intended to come into contact with the layer of coating material48on the rotor disks41when braking is preferably treated and has a certain surface fineness.

The opposing surfaces of the first and third set of brake disks28,41which are designed to interact with one another, furthermore form a part of a parking brake43. The parking brake43comprises a separate brake piston44. The brake piston44is spring-loaded, see spring45. A line46for a brake fluid opens out opposite a surface47of the piston in such away that the spring45is compressed when the piston is pressurized. The parking brake43is therefore in a passive state when the piston is pressurized. When the pressurization is cancelled the spring45will compress the set of brake disks in the parking brake43, thereby applying the parking brake.

FIG. 5shows an alternative embodiment of said element41for circulation of the cooling fluid. The element41comprises a structure for influencing the cooling fluid with the object of promoting the circulation. This structure comprises a plurality of blades49, which are defined by grooves50in the circumferential direction of the elements41. The structure also comprises a pattern on its flat sides. In this case the pattern is formed by a layer of brake lining.

The invention must not be regarded as being limited to the exemplary embodiments described above, a number of further variants and modifications being feasible without departing from the scope of the following patent claims.

It is feasible, for example, to eliminate the parking brake43and to utilize the available braking effect between the first and third set of brake disks28,41in order to enhance the braking effect of the brake20, that is to say to boost the service brake. In such a

case the brake piston44is designed in a corresponding way to the piston36for application of the brake.

Said element41for circulation of the cooling fluid, for example, could have just blades according to the embodiment as shown inFIG. 5(that is to say without any layer of a brake lining).