WO2014185827A1

WO2014185827A1 - Transmission assembly

Info

Publication number: WO2014185827A1
Application number: PCT/SE2013/000073
Authority: WO
Inventors: Jan Dersjö; Per Mattsson; Mathias LEHIKOINEN; Mats ÅKERBLOM; Mirko Leesch; Jörg Müller; Rico Resch
Original assignee: Volvo Construction Equipment Ab
Priority date: 2013-05-15
Filing date: 2013-05-15
Publication date: 2014-11-20

Abstract

The present disclosure relates to a transmission assembly (10) comprising a first (12), a second (14) and a third (16) planetary gear set, each one of said planetary gear sets (12, 14, 16) comprising a ring gear, a planet carrier and a sun gear, said transmission assembly (10) further comprising a transmission housing (20).

Description

TRANSMISSION ASSEMBLY

TECHNICAL FIELD

The present disclosure relates to a transmission assembly according to the preamble of claim 1. Moreover, the present disclosure relates to a working machine.

BACKGROUND

A working machine, such as a wheel loader, an articulated hauler or any other type of construction equipment, is generally provided with a transmission assembly in order to control the propulsion of the working machine. A transmission assembly may comprise a plurality of planetary gear sets. Different gears of such a transmission assembly may be obtained by engaging selected components of the planetary gear sets with other components or a transmission housing.

An example of such a transmission assembly is disclosed in US 2010/0184554 A1.

However, the US 2010/0184554 A1 transmission assembly comprises five planetary gear sets and seven connecting or locking mechanisms. The plurality of planetary gear sets and shifting mechanisms results in a relatively complex and expensive transmission assembly.

SUMMARY

One object of the present disclosure is to provide a transmission assembly that is capable of providing an appropriate number of positive and negative gears using an appropriately small number of planetary gear sets and shifting mechanisms. This object is achieved by a transmission assembly according to claim 1.

As such, the present disclosure relates to a transmission assembly comprising a first, a second and a third planetary gear set. Each one of the planetary gear sets comprises a ring gear, a planet carrier and a sun gear. The transmission assembly further comprises a transmission housing. The transmission assembly is configured such that:

- the planet carrier of the first planetary gear set and the ring gear of the second planetary gear set are operatively connected to each other; - the sun gear of the second planetary gear set and the ring gear of the third planetary gear set are operatively connected to each other;

- the planet carrier of the third planetary gear set and the ring gear of the first

planetary gear set are operatively connected to each other;

- the sun gear of the first planetary gear set is selectively connectable to the planet carrier of the first planetary gear set and the ring gear of the second planetary gear set;

planetary gear set are selectively connectable to the planet carrier of the second planetary gear set;

- the planet carrier of the first planetary gear set and the ring gear of the second planetary gear set are selectively lockable to the transmission housing;

- the sun gear of the second planetary gear set and the ring gear of the third

planetary gear set are selectively lockable to the transmission housing;

- the sun gear of the third planetary gear set is selectively lockable to the

transmission housing;

- the sun gear of the first planetary gear set being adapted to be connected to a first power transmitting member, and

- the planet carrier of the second planetary gear set being adapted to be connected to a second power transmitting member.

A transmission assembly according to the present disclosure implies that a plurality of gears may be obtained by using only a few planetary gear sets and only a few shift mechanisms, i.e. connecting or locking mechanisms.

For instance, the transmission assembly according to the present disclosure may be suitable for being connected to a further planetary gear set, either before or after the three planetary gear sets presented hereinabove, and two additional shift elements in order to arrive at a transmission assembly that is capable of producing a plurality of gears, such as ten gears in one direction and four gears in the opposite direction, by using only four planetary gear sets and only a few, e.g. seven, shift mechanisms, i.e. connecting or locking mechanisms. Moreover, by virtue of the configuration of the transmission assembly according to the present disclosure, it is possible to obtain appropriate ratios and steps for at least a plurality of the gears of the transmission assembly even if the stationary gear ratio of each one of the planetary gear sets is negative. Planetary gear sets with negative stationary gear ratios are generally cheaper than gear sets with positive stationary gear ratios.

DEFINITIONS

The relationship between the rotational speeds of the different members in a planetary gear set is defined according to the following: ω$-<ύρ

= R (Eq. 1) wherein ω₅ is the speed of rotation of the sun gear;

ω_Ρ is the speed of rotation of the planet carrier;

o)_R is the speed of rotation of the ring gear, and

R is the stationary gear ratio of the planetary gear set.

As used herein, the expression "stationary gear ratio" R for a planetary gear set is defined as the ratio of the speed of rotation of the sun gear to the speed of rotation of the ring gear in a situation in which the planet carrier is stationary, i.e.: for single planet gear wheels (Eq. 2) and

for double planet gear wheels (Eq. 3)

wherein z_R is the number of teeth of the ring gear, and

z_s is the number of teeth of the sun gear. In a similar vein, as used herein, the expression "ratio" for a transmission assembly relates to the number of revolutions of the transmission input shaft of the transmission assembly divided by the number of revolutions of the transmission output shaft of the transmission assembly. Moreover, as used herein, the expression "step" relates to the quotient of the ratio of a gear divided by the ratio of an adjacent gear of a transmission assembly.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

In the drawings: Fig. 1 illustrates a vehicle;

Fig. 2 schematically illustrates a transmission assembly according to an embodiment of the present disclosure; Fig. 3 schematically illustrates a transmission assembly according to another embodiment of the present disclosure, and

Fig. 4 schematically illustrates a transmission assembly according to a further embodiment of the present disclosure.

It should be noted that the appended drawings are not necessarily drawn to scale and that the dimensions of some features of the present invention may have been exaggerated for the sake of clarity. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will below be described for a vehicle in the form of an articulated hauler 1 such as the one illustrated in Fig. 1. The articulated hauler 1 should be seen as an example of a vehicle which could comprise a transmission assembly 10 according to the present invention. However, the transmission assembly of the present invention may be implemented in a plurality of different types of objects, e.g. other types of vehicles. Purely by way of example, the transmission assembly could be implemented in a truck, a lorry, a tractor, a car, a bus, a working machine such as a wheel loader or an articulated hauler or any other type of construction equipment.

Fig. 2 illustrates an embodiment of a transmission assembly 10. The Fig. 2 embodiment of the transmission assembly 10 comprises a first 12, a second 14 and a third 16 planetary gear set. Each one of the planetary gear sets comprises a ring gear R, a planet carrier P and a sun gear S. The transmission assembly further comprises a transmission housing 20. The transmission housing 20 is only schematically depicted in Fig. 2 but the transmission housing 20 is generally adapted to enclose at least a portion of the planetary gear sets. In the Fig. 2 embodiment of the transmission assembly 10, the planetary gear sets are arranged in the transmission housing 20 in the following order: the first 12, the second 14 and the third 16 planetary gear sets. The order illustrated in Fig. 2 implies that a relatively compact transmission assembly 10 may be obtained. The transmission assembly 10 illustrated in Fig. 2 is configured according to the following.

The planet carrier 12P of the first planetary gear set 12 and the ring gear 14R of the second planetary gear set 14 are operatively connected to each other, for instance via a first connector 26.

The sun gear 14S of the second planetary gear set 14 and the ring gear 16R of the third planetary gear set 16 are operatively connected to each other, for instance via a second connector 28. The planet carrier 16P of the third planetary gear set 16 and the ring gear 12R of the first planetary gear set 12 are operatively connected to each other, for instance via a third connector 30. The sun gear 12S of the first planetary gear set 12 is selectively connectable to the planet carrier 12P of the first planetary gear set 12 and the ring gear 14R of the second planetary gear set 14. The planet carrier 16P of the third planetary gear set 16 and the ring gear 12R of the first planetary gear set 12 are selectively connectable to the planet carrier 14P of the second planetary gear set 14.

The planet carrier 12P of the first planetary gear set 12 and the ring gear 14R of the second planetary gear set 14 are selectively lockable to the transmission housing 20.

The sun gear 14S of the second planetary gear set 14 and the ring gear 16R of the third planetary gear set 16 are selectively lockable to the transmission housing 20. The sun gear 16S of the third planetary gear set 16 is selectively lockable to the transmission housing 20.

The sun gear 12S of the first planetary gear set 12 is adapted to be connected to a first power transmitting member, such as a transmission shaft or a member of an additional adjacent planetary gear set (not shown in Fig. 2). In a similar vein, the planet carrier 14P of the second planetary gear set 14 is adapted to be connected to a second power transmitting member, such as a transmission shaft or a member of an adjacent additional planetary gear set. Such an additional planetary gear set is not one of the first three planetary gear sets that have been discussed hereinabove.

Purely by way of example, each one of the above discussed connectors 26, 28, 30 may comprise a shaft. As a non-limiting example, one or more of the connectors 26, 28, 30 may comprise a hollow shaft. For instance, such a hollow shaft may accommodate another member, e.g. another shaft and/or another connector.

Purely by way of example, the stationary gear ratio of each one of said first 12, second 14 and third 16 planetary gear set may be negative.

The Fig. 2 embodiment of the transmission assembly 10 further comprises a gear selection arrangement 36 that enables selection of different operating modes with different gear ratios.

The implementation of the gear selection arrangement 36 illustrated in Fig. 2 comprises shift mechanisms that are presented hereinbelow.

The gear selection arrangement 36 comprises a first connecting mechanism 38 that is adapted to assume an engaged condition in which the sun gear 12S of the first planetary gear set 12 is operatively connected to the planet carrier 12P of the first planetary gear set 12 and the ring gear 14R of the second planetary gear set 14. Moreover, the first connecting mechanism 38 is also adapted to assume a disengaged condition in which the sun gear 12S of the first planetary gear set 12 is not operatively connected to the planet carrier 12P of the first planetary gear set 12 and the ring gear 14R of the second planetary gear set 14.

Additionally, the gear selection arrangement 36 comprises a second connecting mechanism 40 adapted to assume an engaged condition in which the planet carrier 16P of the third planetary gear set 16 and the ring gear 12R of the first planetary gear set 12 are operatively connected to the planet carrier 14P of the second planetary gear set 14. Moreover, the second connecting mechanism 40 is adapted to assume a disengaged condition in which the planet carrier 16P of the third planetary gear set 6 and the ring gear 12R of the first planetary gear set 2 are not operatively connected to the planet carrier 14P of the second planetary gear set 14. Purely by way of example, each one of the first and second connecting mechanisms 38, 40 may comprise a clutch, such as a friction clutch, a dog clutch or a one-way clutch.

Moreover, the gear selection arrangement 36 comprises a first locking mechanism 44 adapted to assume an engaged condition in which the planet carrier 12P of the first planetary gear set 12 and the ring gear 4R of the second planetary gear set 14 are locked to the transmission housing 20. Furthermore, the first locking mechanism 44 further being adapted to assume a disengaged condition in which the planet carrier 12P of the first planetary gear set 12 and the ring gear 14R of the second planetary gear set 14 are not locked to the transmission housing 20. Furthermore, the gear selection arrangement 36 comprises a second locking mechanism 46 adapted to assume an engaged condition in which the sun gear 14S of the second planetary gear set 14 and the ring gear 16R of the third planetary gear set 16 are locked to the transmission housing 20. Further, the second locking mechanism 46 is adapted to assume a disengaged condition in which the sun gear 14S of the second planetary gear set 14 and the ring gear 16R of the third planetary gear set 16 are not locked to the transmission housing 20.

Additionally, the gear selection arrangement 36 comprises a third locking mechanism 48 adapted to assume an engaged condition in which the sun gear 16S of the third planetary gear set 16 is locked to the transmission housing 20. Moreover, the third locking mechanism 48 is adapted to assume a disengaged condition in which the sun gear 16S of the third planetary gear set 16 is not locked to the transmission housing 20. Purely by way of example, each one of the first 44, second 46 and third 48 locking mechanisms may comprise a brake, such as a friction brake, a dog clutch type brake or a one-way clutch type brake.

In addition to the planetary gear sets and shifting mechanisms illustrated in the Fig. 2 embodiment of the transmission assembly 10, the transmission assembly according to the present invention may also comprise a fourth planetary gear set.

Fig. 3 illustrates an embodiment of a transmission assembly 10 that also comprises a fourth planetary gear set 18. As for the three previous planetary gear sets, the fourth planetary gear set 18 comprises the following three members: a ring gear R, a planet carrier P and a sun gear S.

Preferably, the sun gear 18S of the fourth planetary gear set 8 is selectively lockable to the transmission housing 20. Moreover, a first member of the fourth planetary gear set 18 is selectively connectable to a second member of the fourth planetary gear set 18.

In the Fig. 3 implementation of the fourth planetary gear set 18, the first member of the fourth planetary gear set 18 is the sun gear 18S and the second member of the fourth planetary gear set 18 is the planet carrier 18P. Purely by way of example, the stationary gear ratio of the fourth planetary gear set 18 may be negative.

The Fig. 3 implementation of the gear selection arrangement 36 comprises a third connecting mechanism 42 that is adapted to assume an engaged condition in which the first member, exemplified as the sun gear 18S in Fig. 3, of the fourth planetary gear set 18 is operatively connected to the second member, exemplified as the planet carrier 8P, of the fourth planetary gear set 18. The above implementation may have the advantage that the third connecting mechanism 42 is subjected to moderate loads during use.

Moreover, the third connecting mechanism 42 is adapted to assume a disengaged condition in which the first member of the fourth planetary gear set 18 is not operatively connected to the second member of the fourth planetary gear set 18. Purely by way of example, the third connecting mechanism 42 may comprise a clutch, such as a friction clutch, a dog clutch or a one-way clutch.

Moreover, the Fig. 3 implementation of the gear selection arrangement 36 comprises a fourth locking mechanism 50 that is adapted to assume an engaged condition in which the sun gear 18S of the fourth planetary gear set 18 is locked to the transmission housing 20. Further, the fourth locking mechanism 50 is adapted to assume a disengaged condition in which the sun gear 18S of the fourth planetary gear set 18 is not locked to the

transmission housing 20. Purely by way of example, the fourth locking mechanisms 50 may comprise a brake, such as a friction brake, a dog clutch type brake or a one-way clutch type brake.

The Fig. 3 embodiment of the transmission assembly 10 comprises a first transmission shaft 22 and a second transmission shaft 24.

Purely by way of example, the ring gear 18R of the fourth planetary gear set 18 and the planet carrier 14P of the second planetary gear set 14 are operatively connected to each other, for instance via a fourth connector 32. The sun gear 12S of the first planetary gear set 12 is operatively connected to the first transmission shaft 22 and the planet carrier 18P of the fourth planetary gear set 18 is operatively connected to the second transmission shaft 24.

As another non-limiting option, the ring gear 18R of the fourth planetary gear set 18 may be operatively connected to the second transmission shaft 24. In such an embodiment of the transmission assembly, the planet carrier 18P of the fourth planetary gear set 18 and the planet carrier 14P of the second planetary gear set 14 are operatively connected to each other. Fig. 3 further illustrates an embodiment of the transmission assembly in which the planetary gear sets are arranged in the transmission housing in the following order: the first 12, the second 14, the third 16 and the fourth 18 planetary gear set.

Purely by way of example, the first transmission shaft 22 may be a transmission input shaft and the second transmission shaft 24 may be a transmission output shaft.

Alternatively, the first transmission shaft 22 may be a transmission output shaft and the second transmission shaft 24 may be a transmission input shaft.

As has been intimated hereinabove, the stationary gear ratio of each one of the first 2, second 14, third 16 and fourth 18 planetary gear sets may be negative.

As a non-limiting example, the stationary gear ratios of the planetary gear sets may be within the ranges that are presented in Table 1 hereinbelow.

Table 1 - Stationary gear ratio ranges

Purely by way of example, the stationary gear ratios of the planetary gear sets may be selected in accordance with the values presented in Table 2. Table 2 - Stationary gear ratios

The above discussed implementation of the gear selection arrangement 36 is adapted to assume the gears as presented in Table 3 with absolute values of gear ratios in descending order. Moreover, the gear selection arrangement 36 may also be adapted to assume the gears as presented in Table 4 with absolute values of gear ratios in descending order. The gears as presented in Table 4 are in the opposite driving direction as compared to the driving direction of the gears presented in Table 3.

In each one of Table 3 and Table 4, a cell marked with an x indicates an engaged condition whereas a blank cell indicates a disengaged condition. Moreover, each one of Table 3 and Table 4 presents the gear ratios and steps obtainable if the planetary gear sets have the stationary gear ratios that are presented in Table 2.

Furthermore, Table 3 as well as Table 4 presents values for a transmission assembly 10 in which the first transmission shaft 22 is a transmission input shaft and the second transmission shaft 24 is a transmission output shaft. Table 3 - Gears obtainable by the Fig. 3 gear selection arrangement 36

Table 4 - Gears obtainable by the Fig. 3 gear selection arrangement 36

Fig. 4 illustrates another embodiment of the transmission assembly 10. As may be gleaned from Fig. 4, in the embodiment illustrated therein, a fourth planetary gear set 18 is located before the other three planetary gear sets 2, 14, 16. Moreover, in the Fig. 4 embodiment of the transmission assembly 10, the planet carrier 18P of the fourth planetary gear set 18 and the sun gear 12S of the first planetary gear set 12 are operatively connected to each other, for instance via a fourth connector 32. Moreover, in the Fig. 4 embodiment, the ring gear 18R of the fourth planetary gear set 18 is operatively connected to the first transmission shaft 22 and the planet carrier 14P of the second planetary gear set 14 is operatively connected to the second transmission shaft 24. It is also envisaged that in embodiments of the transmission assembly 10, the fourth planetary gear set 18 may be reversely arranged to the other three planetary gear sets such that the ring gear 18R of the fourth planetary gear set 18 and the sun gear 12S of the first planetary gear set 12 are operatively connected to each other. In such an embodiment, the planet carrier 18P of the fourth planetary gear set 18 may be operatively connected to the first transmission shaft 22 and the planet carrier 14P of the second planetary gear set 14 may be operatively connected to the second transmission shaft 24.

The stationary gear ratio of each one of the first 12, second 14, third 16 and fourth 18 planetary gear sets may be negative for the Fig. 4 embodiment of the transmission assembly 10. Moreover, it is envisaged that the stationary gear ratios of the planetary gear sets may be within the ranges that are presented in Table 1 hereinabove. Purely by way of example, the stationary gear ratios of the planetary gear sets of the Fig. 4 embodiment may be selected in accordance with the values presented in Table 2. If the stationary gear ratios are selected in accordance with the values presented in Table 2, the gear ratios and steps that are presented in Tables 3 and 4 are also obtainable for the Fig. 4 embodiment of the transmission assembly 10.

As for the Fig. 3 embodiment, the implementation of the fourth planetary gear set 18 illustrated in Fig. 4 is configured such that a first member thereof is selectively

connectable to a second member of the fourth planetary gear set 18.

In fact, Fig. 4 illustrates an implementation of the fourth planetary gear set 18 in which the first member of the fourth planetary gear set 18 is the ring gear 18R and the second member of the fourth planetary gear set 18 is the planet carrier 18P. The above implementation may have the advantage that the gear wheels of the fourth planetary gear set 18 do not transfer any load when the third connecting mechanism 42 is engaged.

However, in another embodiment of the transmission assembly, the first member of the fourth planetary gear set 18 may be the ring gear 18R and the second member of the fourth planetary gear set 18 may be the sun gear 18S. In yet another embodiment of the transmission assembly, the first member of the fourth planetary gear set 18 may be the sun gear 18S and the second member of the fourth planetary gear set 18 may be the planet carrier 18P. Both these implementations may have the advantage that the third connecting mechanism 42 is subjected to moderate loads during use. Finally, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

A transmission assembly (10) comprising a first (12), a second (14) and a third (16) planetary gear set, each one of said planetary gear sets (12, 14, 16) comprising a ring gear, a planet carrier and a sun gear, said transmission assembly (10) further comprising a transmission housing (20), said transmission assembly (10) being configured such that:

- said planet carrier (12P) of said first planetary gear set (12) and said ring gear (14R) of said second planetary gear set (14) are operatively connected to each other;

- said sun gear (14S) of said second planetary gear set (14) and said ring gear (16R) of said third planetary gear set (16) are operatively connected to each other;

- said planet carrier (16P) of said third planetary gear set (16) and said ring gear (12R) of said first planetary gear set (12) are operatively connected to each other;

- said sun gear (12S) of said first planetary gear set (12) is selectively

connectable to said planet carrier (12P) of said first planetary gear set (12) and said ring gear (14R) of said second planetary gear set (14);

- said planet carrier (16P) of said third planetary gear set (16) and said ring gear ( 2R) of said first planetary gear set ( 2) are selectively connectable to said planet carrier (14P) of said second planetary gear set (14);

- said planet carrier (12P) of said first planetary gear set (12) and said ring gear ( 4R) of said second planetary gear set ( 4) are selectively lockable to said transmission housing (20);

- said sun gear (14S) of said second planetary gear set (14) and said ring gear (16R) of said third planetary gear set (16) are selectively lockable to said transmission housing (20);

- said sun gear (16S) of said third planetary gear set (16) is selectively

lockable to said transmission housing (20);

- said sun gear (12S) of said first planetary gear set (12) being adapted to be connected to a first power transmitting member, and

- said planet carrier (14P) of said second planetary gear set (14) being

adapted to be connected to a second power transmitting member.

2. The transmission assembly ( 0) according to claim , wherein the stationary gear ratio of each one of said first, second and third planetary gear sets (12, 14, 16) is negative.

The transmission assembly (10) according to claim 1 or claim 2, wherein said planetary gear sets are arranged in said transmission housing in the following order: said first (12), said second (14) and said third (16) planetary gear set.

4. The transmission assembly (10) according to any one of the preceding claims, wherein said transmission assembly (10) comprises a gear selection arrangement (36) that enables selection of different operating modes with different gear ratios, said gear selection arrangement (36) comprising:

- a first connecting mechanism (38), said first connecting mechanism (38) being adapted to assume an engaged condition in which said sun gear (12S) of said first planetary gear set (12) is operatively connected to said planet carrier (12P) of said first planetary gear set (12) and said ring gear (14R) of said second planetary gear set (14), said first connecting mechanism (38) also being adapted to assume a disengaged condition in which said sun gear (12S) of said first planetary gear set (12) is not operatively connected to said planet carrier (12P) of said first planetary gear set (12) and said ring gear (14R) of said second planetary gear set (14);

- a second connecting mechanism (40), said second connecting mechanism (40) being adapted to assume an engaged condition in which said planet carrier (16P) of said third planetary gear set (16) and said ring gear (12R) of said first planetary gear set (12) are operatively connected to said planet carrier (14P) of said second planetary gear set (14), said second connecting mechanism (40) being adapted to assume a disengaged condition in which said planet carrier (16P) of said third planetary gear set (16) and said ring gear (12R) of said first planetary gear set (12) are not operatively connected to said planet carrier (14P) of said second planetary gear set (14);

- a first locking mechanism (44) adapted to assume an engaged condition in which said planet carrier (12P) of said first planetary gear set (12) and said ring gear (14R) of said second planetary gear set (14) are locked to said transmission housing (20), said first locking mechanism (44) further being adapted to assume a disengaged condition in which said planet carrier (12P) of said first planetary gear set (12) and said ring gear (14R) of said second planetary gear set (14) are not locked to said transmission housing (20);

- a second locking mechanism (46) adapted to assume an engaged

condition in which said sun gear (14S) of said second planetary gear set (14) and said ring gear (16R) of said third planetary gear set (16) are locked to said transmission housing (20), said second locking mechanism (46) further being adapted to assume a disengaged condition in which said sun gear (14S) of said second planetary gear set (14) and said ring gear (16R) of said third planetary gear set (16) are not locked to said transmission housing (20);

- a third locking mechanism (48) adapted to assume an engaged condition in which said sun gear (16S) of said third planetary gear set (16) is locked to said transmission housing (20), said third locking mechanism (48) further being adapted to assume a disengaged condition in which said sun gear (16S) of said third planetary gear set (16) is not locked to said transmission housing (20).

The transmission assembly (10) according to any one of the preceding claims, wherein said transmission assembly (10) further comprises a fourth planetary gear set (18) comprising the following members: a ring gear, a planet carrier and a sun gear, said transmission assembly (10) being configured such that:

- said sun gear (18S) of said fourth planetary gear set (18) is selectively lockable to said transmission housing (20), and

- a first member of said fourth planetary gear set (18) is selectively

connectable to a second member of said fourth planetary gear set (18).

6. The transmission assembly (10) according to claim 5, wherein said first member of said fourth planetary gear set (18) is said ring gear (18R) and said second member of said fourth planetary gear set (18) is said planet carrier (18P).

7. The transmission assembly (10) according to claim 5, wherein said first member of said fourth planetary gear set (18) is said ring gear (18R) and said second member of said fourth planetary gear set (18) is said sun gear (18S).

8. The transmission assembly (10) according to claim 5, wherein said first member of said fourth planetary gear set (18) is said sun gear (18S) and said second member of said fourth planetary gear set (18) is said planet carrier (18P).

9. The transmission assembly (10) according to any one of claims 5 to 8, wherein the stationary gear ratio of said fourth planetary gear set (18) is negative.

10. The transmission assembly (10) according to any one of claims 5 to 9, when

dependent on claim 4, wherein said gear selection arrangement (36) further comprises:

- a third connecting mechanism (42), said third connecting mechanism (42) being adapted to assume an engaged condition in which said first member of said fourth planetary gear set (18) is operatively connected to said second member of said fourth planetary gear set (18), said third connecting mechanism (42) being adapted to assume a disengaged condition in which said first member of said fourth planetary gear set (18) is not operatively connected to said second member of said fourth planetary gear set (18);

- a fourth locking mechanism (50) adapted to assume an engaged condition in which said sun gear (18S) of said fourth planetary gear set (18) is locked to said transmission housing (20), said fourth locking mechanism (50) further being adapted to assume a disengaged condition in which said sun gear (18S) of said fourth planetary gear set (18) is not locked to said transmission housing (20).

11. The transmission assembly (10) according to any one of claims 5 to 10, wherein said transmission assembly (10) further comprises a first (22) and a second (24) transmission shaft and wherein:

- said ring gear (18R) of said fourth planetary gear set (18) and said planet carrier (14P) of said second planetary gear set (14) are operatively connected to each other; - said sun gear ( 2S) of said first planetary gear set (12) is operatively connected to said first transmission shaft (22), and

- said planet carrier (18P) of said fourth planetary gear set (18) is operatively connected to said second transmission shaft (24).

12. The transmission assembly (10) according to claim 11 , wherein said planetary gear sets are arranged in said transmission housing in the following order: said first (12), said second (14), said third (16) and said fourth (18) planetary gear set.

13. The transmission assembly (10) according to any one of claims 5 to 10, wherein said transmission assembly (10) further comprises a first (22) and a second (24) transmission shaft and wherein:

- said planet carrier (18P) of said fourth planetary gear set (18) and said sun gear (12S) of said first planetary gear set (12) are operatively connected to each other;

- said ring gear (18R) of said fourth planetary gear set (18) is operatively connected to said first transmission shaft (22), and

- said planet carrier (14P) of said second planetary gear set (14) is

operatively connected to said second transmission shaft (24).

14. The transmission assembly (10) according to claim 13, wherein said planetary gear sets are arranged in said transmission housing in the following order: said fourth (18), said first (12), said second (14) and said third (16) planetary gear set.

15. The transmission assembly (10) according to any one of claims 11 to 14, wherein said first transmission shaft (22) is a transmission input shaft and said second transmission shaft (24) is a transmission output shaft.

16. The transmission assembly (10) according to any one of claims 10 to 15, wherein said gear selection arrangement (36) is adapted to assume the following gears with absolute values of gear ratios in descending order: Locking Mechanism # Connecting Mechanism #

Gear # (x=engaged condition) (x=engaged condition) first (44) second (46) third (48) fourth (50) first (38) second (40) third (42)

1 X X X

2 X X X

3 X X X

4 X X X

5 X X x

6 X x X

7 X X X

8 X X X

9 X X X

10 X X X

17. The transmission assembly (10) according to claim 16, wherein said gear selection

arrangement (36) is adapted to assume the following gears, in the opposite driving direction as compared to the driving direction of the gears of claim 16, with

absolute values of gear ratios in descending order:

18. A working machine (1) comprising a transmission assembly (10) according to any

one of the preceding claims.