Split path power shift transmission

A transmission for a vehicle includes an input shaft, a carrier sun shaft, and an output shaft. A planetary gear set includes a sun gear coupled with the carrier sun shaft, a ring gear coupled with the output shaft, and a plurality of planetary gears enmeshed between the sun gear and the ring gear. A plurality of shift elements each include a first gear coupled with the input shaft, and a second gear coupled with the carrier sun shaft and enmeshed with the first gear. A plurality of shift clutches are each selectively coupled between a corresponding shift element and the input shaft or carrier sun shaft. A low range clutch is selectively coupled between the input shaft and the plurality of planetary gears. A high range clutch is selectively coupled between the carrier sun shaft and the output shaft. A reverse range clutch is selectively coupled between an immovable feature and the plurality of planetary gears.

FIELD OF THE INVENTION

The present invention relates to work machines, and, more particularly, to transmissions used in such work machines.

BACKGROUND OF THE INVENTION

A work machine such as an agricultural tractor may include an internal combustion (IC) engine which provides input power to a transmission, which in turn is coupled with and drives the rear axles through a rear end differential. The transmission, rear end differential and rear axles are sometimes referred to as the “rear end” of the work machine. The transmission typically is attached to the front of and provides input power to the rear end differential. The rear end differential provides ground power to the two rear axles, and also usually includes at least one power take-off (PTO) shaft extending rearwardly within the three point hitch arrangement at the rear of the tractor.

With a work machine as described above, it is common to provide a transmission with multiple shift ranges. Typically one shift lever is used to shift between multiple gear ranges (e.g., A, B, C and D gear ranges), and a second shift lever is used to shift between discrete gear pairs within each range (e.g., 1, 2, 3 or 4). The assignee of the present invention also markets a “PowerShift” series transmission in which at least one shift lever need not be foot clutched to shift “on-the-fly” during use. Variants of the PowerShift transmission go back to the 4020 series tractors manufactured in the 1960's.

Many transmissions used with work machines as described above include multiple shift elements (two or more gear pairs) which are shifted to place the transmission in a selected gear range and gear. Shifting multiple shift elements can be complex and difficult.

What is needed in the art is a transmission which is easier and simpler to shift during operation.

SUMMARY OF THE INVENTION

The invention in one form is directed to a transmission for a vehicle, including an input shaft, a carrier sun shaft, and an output shaft. A planetary gear set includes a sun gear coupled with the carrier sun shaft, a ring gear coupled with the output shaft, and a plurality of planetary gears enmeshed between the sun gear and the ring gear. A plurality of shift elements each include a first gear coupled with the input shaft, and a second gear coupled with the carrier sun shaft and enmeshed with the first gear. A plurality of shift clutches are each selectively coupled between a corresponding shift element and the input shaft or carrier sun shaft. A low range clutch is selectively coupled between the input shaft and the plurality of planetary gears. A high range clutch is selectively coupled between the carrier sun shaft and the output shaft. A reverse range clutch is selectively coupled between an immovable feature and the plurality of planetary gears.

The invention in another form is directed to a transmission for use in a work machine, including a power input shaft, a carrier sun shaft, and a power output shaft. A plurality of shift elements each include a first gear carried by the input shaft, a second gear carried by the carrier sun shaft and enmeshed with the first gear, and a shift clutch selectively coupling the first gear or second gear with the input shaft or carrier sun shaft, respectively. A planetary gear set includes a sun gear mounted to the carrier sun shaft, at least one planetary gear engaged with and positioned radially outside of the sun gear, and a ring gear positioned radially outside of the at least one planetary gear. The ring gear interconnects the at least one planetary gear with the output shaft. A low range clutch selectively interconnects the input shaft with the at least one planetary gear. A high range clutch selectively and directly interconnects the carrier sun shaft with the output shaft.

The invention in yet another form is directed to a work machine including an engine and a rear end coupled with the engine. The rear end includes a transmission having an input shaft, a carrier sun shaft, and an output shaft. A planetary gear set includes a sun gear coupled with the carrier sun shaft, a ring gear coupled with the output shaft, and a plurality of planetary gears enmeshed between the sun gear and the ring gear. A plurality of shift elements each include a first gear coupled with the input shaft, and a second gear coupled with the carrier sun shaft and enmeshed with the first gear. A plurality of shift clutches are each selectively coupled between a corresponding shift element and the input shaft or carrier sun shaft. A low range clutch is selectively coupled between the input shaft and the plurality of planetary gears. A high range clutch is selectively coupled between the carrier sun shaft and the output shaft. A reverse range clutch is selectively coupled between an immovable feature and the plurality of planetary gears.

The invention in all the above forms has only single elements shifts from one gear to the next. In the first five gears, only the input clutches are changing, between gear5and6only the output clutches are changing, and in the higher fives gears only the input clutches are changing. This can be summarized in the following table, which is given only as an example.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly toFIG. 1, there is shown a portion of a vehicle or work machine10in the form of an agricultural tractor, particularly the rear end drive train of the tractor. Although shown as an agricultural tractor, it is possible that vehicle or work machine10could be in the form of a different type of vehicle or work machine, such as a construction tractor or forestry machine.

Tractor10includes a rear end with a transmission12which is coupled with a rear end differential14, which in turn drives a pair of rear axles16. Each rear axle16includes an outboard hub18to which a respective rear drive wheel (not shown) is mounted. Although rear axles16are shown configured for carrying respective drive wheels, it is also possible that rear end differential14can be configured for driving a pair of ground engaging tracks.

Transmission12includes a driven shaft20which is mechanically coupled with and receives rotational input power from IC engine22, shown schematically inFIG. 1. Driven shaft20extends through and is rotatably carried by housing24, which likewise houses and rotatably carries a number of other components. For example, housing24carries a mechanical front wheel drive (MFWD) module (not specifically shown) which selectively transfers output power to an output shaft26providing rotational output power to the MFWD at the front axle of tractor10. A clutch arrangement (not shown) selectively interconnects with output shaft26so that the MFWD is engaged by actuation of a switch (not shown) in the operator's station.

Driven shaft20also transfers rotational power to a shifting arrangement28positioned within transmission housing24. Shifting arrangement28transfers the rotational power, according to a selected gear ratio, to rear end differential14(seeFIG. 2).

According to an aspect of the present invention, shifting arrangement28generally includes an input shaft30, a carrier sun shaft32, an output shaft34, a planetary gear set36, a plurality of shift elements38, a plurality of shift clutches40, a low range clutch42, a high range clutch44, and a reverse range clutch46.

Input shaft30of shifting arrangement28receives rotational input power either directly or indirectly from driven shaft20, which is the power input to transmission12. Input shaft30has an output end which is coupled either directly or indirectly with a PTO drive, as indicated.

Carrier sun shaft32has a longitudinal axis which is arranged generally parallel to the longitudinal axis of input shaft30. Carrier sun shaft32and input shaft30together carry a number of shift elements38which are arranged sequentially adjacent to each other along a length of input shaft30and carrier sun shaft32. Each shift element38generally corresponds to an operator selected gear, and includes a first gear48coupled with input shaft30, and a second gear50coupled with carrier sun shaft32. Shifting arrangement28is shown as including five discrete shift elements38. When viewed from left to right, it is apparent that each first gear48becomes smaller in diameter, with the fastest shift element38being on the left side and the slowest shift element38being on the right side. Conversely, when viewed from left to right, each shift element38has a second gear50carried by carrier sun shaft32which becomes increasingly larger corresponding to the same shift elements. (The gears do not necessarily have to be ordered from largest to smallest)

Each shift element38also has a shift clutch40associated therewith. The shift clutch40selectively couples a gear on the input shaft20to the corresponding gear on the carrier sun shaft. Each shift clutch40is preferably electronically engaged, such as through a transmission control unit (TCU). Since each shift clutch40takes additional axial space along the length of the corresponding input shaft30or carrier sun shaft32, shifting arrangement28shown inFIG. 2includes a plurality of shift clutches40which alternate between adjacent shift elements38for selective interconnection with either input shaft30or carrier sun shaft32. This reduces the axial spread of shifting elements38along the length of input shaft30and carrier sun shaft32. It is to be understood, however, that shift clutches40need not necessarily alternate for selective connection with input shaft30or carrier sun shaft32, and could possibly all be configured to couple with input shaft30or carrier sun shaft32.

Planetary gear set36includes a sun gear52which is coupled with carrier sun shaft32. One or more planetary gears54are engaged with and positioned radially outside of sun gear52. A ring gear56is positioned radially outside of the one or more planetary gears54. Ring gear56is rigidly coupled with an end of output shaft34, thereby interconnecting the one or more planetary gears54with output shaft34.

In the embodiment shown inFIG. 2, planetary gear set36includes a plurality of planetary gears54which are enmeshed between sun gear52and ring gear56. The plurality of planetary gears54are mounted in a planetary carrier. The carrier gear58is also coupled to the planetary carrier and rotates at the same speed as the planetary carrier. Carrier gear58has outboard teeth which enmesh with the gear of the low range clutch42and the gear of the reverse range clutch46, as will be described in more detail below.

High range clutch44is configured to lock the planetary action of planetary gear set36, and concurrently directly couple an end of carrier sun shaft32with an adjacent end of the coaxially arranged output shaft34. Other ways of locking the planetary carrier for direct drive are also possible.

Reverse range clutch46is selectively coupled between an immovable feature and the plurality of planetary gears54by a carrier gear58. For example, reverse range clutch46can be coupled with an immovable feature such as housing24of transmission12.

During operation, if an operator selects one of the five lower gears, low range clutch42is engaged and power flows directly from input shaft30to the combining planetary gear set36through carrier gear58. Power also flows from input shaft30through a selected shift clutch40marked C1-C5to carrier sun shaft32, and sun gear52carried thereby. The output to output shaft34is effected through ring gear56when low range clutch42is engaged.

In the upper five gears, the combining planetary gear set36is locked by engaging high range clutch44so that there is no planetary action. Input shaft30is coupled to output shaft34through one of the shift clutches40marked C1-C5.

In reverse, reverse range clutch46is engaged and rotation of carrier gear58is stopped, which reverses the rotational direction of ring gear56coupled with output shaft34. The particular reverse speed is selected using one of the shift clutches40marked C1-C5.

From the foregoing description of operation, it is apparent that only two clutches at any given time are engaged, one shift clutch40marked C1-C5, and either the low range clutch42, high range clutch44or reverse range clutch46. This results in an effective and yet more simple shifting arrangement for transmission12.

Although the description of mechanical components and method of operation for shifting arrangement28are described above with respect to a ten-speed transmission, it will also be apparent that the same inventive concepts can be applied to other transmissions, such as an eight-speed transmission, etc.