阅读说明：本技术 一种动力换挡变速器及车辆 (Power shift transmission and vehicle ) 是由 王松林 杨浩 蒋仁科 鄢万斌 曾垂远 于 2020-06-18 设计创作，主要内容包括：本发明涉及变速器领域,公开了一种动力换挡变速器及车辆,其中,动力换挡变速器包括输入轴、第一轴、第二轴和第三轴,第一轴上设有第一活动齿轮、第二活动齿轮、第一离合器和第二离合器,第二轴上设有第一固定齿轮和第二固定齿轮,第三轴上设有第三固定齿轮。本发明将第三固定齿轮与第一固定齿轮啮合的同时与第一活动齿轮啮合,实现前进挡和后退挡时第三轴转动方向变换,取消了现有的惰轮设计,减少了动力换挡变速器中轴的个数,减小了动力换挡变速器的体积,减小了动力换挡变速器的占用空间及生产成本。(The invention relates to the field of transmissions and discloses a power shifting transmission and a vehicle. According to the invention, the third fixed gear is meshed with the first fixed gear and simultaneously meshed with the first movable gear, so that the rotation direction of the third shaft is changed when the third shaft is in forward gear and backward gear, the existing idle gear design is cancelled, the number of middle shafts of the power gear-shifting transmission is reduced, the size of the power gear-shifting transmission is reduced, and the occupied space and the production cost of the power gear-shifting transmission are reduced.)

1. A powershift transmission, comprising, arranged in parallel with one another:

the clutch comprises an input shaft, a clutch body and a clutch body, wherein a first movable gear, a second movable gear, a first clutch and a second clutch are sleeved on the input shaft, the first clutch enables the first movable gear to be fixed or rotate relative to the input shaft, and the second clutch enables the second movable gear to be fixed or rotate relative to the input shaft;

a first shaft on which a first fixed gear and a second fixed gear are sleeved and fixed relative to the first shaft, the second fixed gear being meshed with the second movable gear;

a second shaft on which a third fixed gear is provided, fixed with respect to it, said third fixed gear meshing with said first fixed gear and simultaneously with said first movable gear;

and the second shaft drives the third shaft to rotate through a gear transmission assembly.

2. The powershift transmission of claim 1, wherein the gear assembly comprises:

a third loose gear, a fourth loose gear, a third clutch and a fourth clutch, wherein the third loose gear and the fourth loose gear are arranged on the second shaft, the third clutch enables the third loose gear to be fixed or rotate relative to the second shaft, and the fourth clutch enables the fourth loose gear to be fixed or rotate relative to the second shaft;

a fourth shaft parallel to the second shaft, on which a fourth fixed gear meshing with the third fixed gear, a fifth loose gear meshing with the third loose gear, a sixth loose gear meshing with the fourth loose gear, a fifth clutch enabling the fifth loose gear to be fixed or rotated with respect to the fourth shaft, and a sixth clutch enabling the sixth loose gear to be fixed or rotated with respect to the fourth shaft are fitted, the fourth fixed gear being fixed with respect to the fourth shaft;

and the fifth fixed gear and the sixth fixed gear are arranged on the third shaft and are fixed relative to the third shaft, the fifth fixed gear is meshed with the fifth movable gear, and the sixth movable gear can drive the sixth fixed gear to rotate.

3. The powershift transmission of claim 2, wherein the first movable gear, the first fixed gear, the third fixed gear, and the fourth fixed gear are located on a same end of a shaft.

4. The powershift transmission of claim 2 or 3, having four forward gears and four reverse gears;

the second clutch and the fourth clutch are both closed to be a forward first gear; the second clutch and the sixth clutch are both closed to be in forward two-gear; the second clutch and the third clutch are both closed to be a forward third gear; the second clutch and the fifth clutch are both closed to be a forward fourth gear;

the first clutch and the fourth clutch are both closed to be a reverse first gear; the first clutch and the sixth clutch are both closed to be a reverse second gear; the first clutch and the third clutch are both closed to be a reverse third gear; and the first clutch and the fourth clutch are both closed to be a reverse fourth gear.

5. The powershift transmission of claim 4, wherein the gear ratios of the forward first gear and the reverse first gear are equal; and/or the transmission ratio of the forward second gear and the backward second gear is equal; and/or the transmission ratio of the forward third gear and the reverse third gear is equal; and/or the gear ratios of the forward fourth gear and the reverse fourth gear are equal.

6. The powershift transmission of claim 5, wherein a ratio of the number of teeth of the first movable gear to the number of teeth of the first fixed gear is equal to a ratio of the number of teeth of the second movable gear to the number of teeth of the second fixed gear.

7. The powershift transmission of claim 6, wherein the first fixed gear has a greater number of teeth than the second fixed gear, the first movable gear and the first fixed gear being axially offset;

or the number of teeth of the first fixed gear is smaller than that of the second fixed gear, and the first movable gear and the first fixed gear are axially arranged in a staggered mode or are arranged in the same plane with the third fixed gear.

8. The powershift transmission of claim 4, further comprising a fifth shaft parallel to said third shaft, said fifth shaft having a seventh fixed gear fixed relative thereto;

the seventh fixed gear is meshed with the fifth fixed gear or the sixth fixed gear; or, an eighth fixed gear which is fixed relative to the third shaft and meshed with the seventh fixed gear is arranged on the third shaft.

9. A vehicle characterized by a powershift transmission according to any one of claims 1 to 8.

10. The vehicle of claim 9, further comprising a contingency axis parallel to the third axis;

the emergency shaft is provided with an emergency gear, and the emergency gear is meshed with a gear which is arranged on the third shaft and can be fixed relative to the third shaft;

the emergency gear is fixed relative to the emergency shaft, and the emergency shaft can be selectively connected with or disconnected from a steering system of a vehicle; alternatively, the emergency gear may be fixed or rotatable relative to the emergency shaft by an emergency clutch.

Technical Field

The invention relates to the field of transmissions, in particular to a power shifting transmission and a vehicle.

Background

For a power shift transmission with more gears, such as four forward gears and four reverse gears, in order to meet the shift requirement, there are two main ways, one is to adopt a plurality of gear shafts arranged in parallel, but the number of the gear shafts is more; the other is to use fewer gear shafts, but more gears per gear shaft. The power gear shifting transmission adopting the two structures has the defects of high cost and large volume, and is not suitable for mechanical equipment with limited installation space.

Disclosure of Invention

The invention aims to provide a power shift transmission and a vehicle, which can reduce the volume of the transmission and reduce the cost of the transmission.

In order to achieve the purpose, the invention adopts the following technical scheme:

a powershift transmission comprising, arranged parallel to each other:

the clutch comprises an input shaft, a clutch body and a clutch body, wherein a first movable gear, a second movable gear, a first clutch and a second clutch are sleeved on the input shaft, the first clutch enables the first movable gear to be fixed or rotate relative to the input shaft, and the second clutch enables the second movable gear to be fixed or rotate relative to the input shaft;

a first shaft on which a first fixed gear and a second fixed gear are sleeved and fixed relative to the first shaft, the second fixed gear being meshed with the second movable gear;

a second shaft on which a third fixed gear is provided, fixed with respect to it, said third fixed gear meshing with said first fixed gear and simultaneously with said first movable gear;

and the second shaft drives the third shaft to rotate through a gear transmission assembly.

According to the invention, the third fixed gear is meshed with the first fixed gear and simultaneously meshed with the first movable gear, so that the rotation direction of the third shaft is changed when the third shaft moves forward and backward, the existing idle gear design is cancelled, the number of the middle shafts of the power gear-shifting transmission is reduced, the size of the power gear-shifting transmission is reduced, and the occupied space and the production cost of the power gear-shifting transmission are reduced.

As a preferable aspect of the powershift transmission described above, the first fixed gear and the second fixed gear are provided at both ends of the first shaft.

Preferably, the first fixed gear and the second fixed gear are symmetrically arranged about the first axis. When the second clutch is closed, both the first fixed gear and the second fixed gear transmit torque; when the first clutch is closed, neither the first fixed gear nor the second fixed gear transmits torque; therefore, the bearings which are arranged at the two ends of the first shaft and used for supporting the first shaft are stressed uniformly, and the bearings which are arranged at the two ends of the first shaft adopt the bearings with the same type, so that the design and the installation of the first shaft are facilitated.

As a preferable aspect of the above powershift transmission, the gear transmission assembly includes:

a third loose gear, a fourth loose gear, a third clutch and a fourth clutch, wherein the third loose gear and the fourth loose gear are arranged on the second shaft, the third clutch enables the third loose gear to be fixed or rotate relative to the second shaft, and the fourth clutch enables the fourth loose gear to be fixed or rotate relative to the second shaft;

a fourth shaft parallel to the second shaft, on which a fourth fixed gear meshing with the third fixed gear, a fifth loose gear meshing with the third loose gear, a sixth loose gear meshing with the fourth loose gear, a fifth clutch enabling the fifth loose gear to be fixed or rotated with respect to the fourth shaft, and a sixth clutch enabling the sixth loose gear to be fixed or rotated with respect to the fourth shaft are fitted, the fourth fixed gear being fixed with respect to the fourth shaft;

and the fifth fixed gear and the sixth fixed gear are arranged on the third shaft and are fixed relative to the third shaft, the fifth fixed gear is meshed with the fifth movable gear, and the sixth movable gear can drive the sixth fixed gear to rotate.

The gear transmission assembly provided by the invention has a simple structure, the number of shafts and the number of gears are not increased while the design of an idler gear is cancelled, and the cost of the power gear shifting transmission is reduced.

As a preferable aspect of the above powershift transmission, the first movable gear, the first fixed gear, the third fixed gear and the fourth fixed gear are located at the same end of a shaft to facilitate arrangement and installation of the respective gears.

As a preferable aspect of the above powershift transmission, the powershift transmission has four forward gears and four reverse gears;

the second clutch and the fourth clutch are both closed to be a forward first gear; the second clutch and the sixth clutch are both closed to be in forward two-gear; the second clutch and the third clutch are both closed to be a forward third gear; the second clutch and the fifth clutch are both closed to be a forward fourth gear;

the first clutch and the fourth clutch are both closed to be a reverse first gear; the first clutch and the sixth clutch are both closed to be a reverse second gear; the first clutch and the third clutch are both closed to be a reverse third gear; and the first clutch and the fourth clutch are both closed to be a reverse fourth gear.

By adopting the power shifting transmission provided by the invention, four forward gears and four backward gears can be realized so as to meet the shifting requirement.

As a preferable technical solution of the above powershift transmission, the gear ratios of the forward first gear and the reverse first gear are equal; and/or the transmission ratio of the forward second gear and the backward second gear is equal; and/or the transmission ratio of the forward third gear and the reverse third gear is equal; and/or the gear ratios of the forward fourth gear and the reverse fourth gear are equal. By adopting the power shifting transmission provided by the invention, the transmission ratios of corresponding gears of a forward gear and a backward gear can be equal by limiting the number of gear teeth, so that the shifting requirement can be met.

As a preferable aspect of the above powershift transmission, a ratio of the number of teeth of the first loose gear to the number of teeth of the first fixed gear is equal to a ratio of the number of teeth of the second loose gear to the number of teeth of the second fixed gear. The arrangement is adopted to ensure that the transmission ratio of the forward gear and the corresponding reverse gear from the input shaft to the second shaft is the same.

As a preferable mode of the power shift transmission, the number of teeth of the first fixed gear is larger than the number of teeth of the second fixed gear, and the first movable gear and the first fixed gear are axially offset;

or the number of teeth of the first fixed gear is smaller than that of the second fixed gear, and the first movable gear and the first fixed gear are axially arranged in a staggered mode or are arranged in the same plane with the third fixed gear.

When the number of teeth of the first fixed gear is larger than that of the second fixed gear, the first movable gear and the first fixed gear are axially arranged in a staggered mode, and interference between the first movable gear and the first fixed gear can be avoided. When the number of teeth of the first fixed gear is less than that of the second fixed gear, the first movable gear, the first fixed gear and the third fixed gear can be arranged in the same plane, so that the axial width of the transmission is reduced; of course, the first movable gear and the first fixed gear can be axially arranged in a staggered manner according to the limitation of the installation space, so that the installation requirement can be met.

As a preferable technical solution of the above powershift transmission, the powershift transmission further includes a fifth shaft parallel to the third shaft, and the fifth shaft is provided with a seventh fixed gear fixed relative thereto;

the seventh fixed gear is meshed with the fifth fixed gear or the sixth fixed gear; or, an eighth fixed gear which is fixed relative to the third shaft and meshed with the seventh fixed gear is arranged on the third shaft.

The invention can also take the fifth shaft as an output shaft, take the third shaft as a shaft for transmitting power between the input shaft and the fifth shaft, only set a seventh fixed gear on the fifth shaft, and the bearing stress at the two ends of the fifth shaft is more balanced. On the premise that the installation space meets the requirement, the fifth shaft can be used as a power gear shifting transmission of the output shaft.

The invention also provides a vehicle, which further comprises an emergency shaft and the power shifting transmission, wherein the emergency shaft is parallel to the third shaft;

the emergency shaft is provided with an emergency gear which is meshed with one gear which is arranged on the third shaft and can be fixed relative to the third shaft;

the emergency gear is fixed relative to the emergency shaft, and the emergency shaft can be selectively connected with or disconnected from a steering system of a vehicle; alternatively, the emergency gear may be fixed or rotatable relative to the emergency shaft by an emergency clutch.

When a vehicle using the power shift transmission provided by the invention fails and cannot walk, a trailer is usually adopted for dragging, the input shaft does not have power input, the third shaft rotates under the action of external force dragging, the emergency shaft rotates under the drive of the emergency gear meshed with the fifth fixed gear or the sixth fixed gear, and then the power is provided for the steering system through the pump, so that a user can control the steering system to control the steering of the vehicle in an emergency state.

The invention has the beneficial effects that: the third fixed gear is meshed with the first fixed gear and simultaneously meshed with the first movable gear, so that the rotation direction of the third shaft is changed when the third shaft moves forward and moves backward, the existing idle gear design is cancelled, the number of the middle shafts of the power gear-shifting transmission is reduced, the size of the power gear-shifting transmission is reduced, and the occupied space and the production cost of the power gear-shifting transmission are reduced.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the contents of the embodiments of the present invention and the drawings without creative efforts.

FIG. 1 is a transmission schematic of a powershift transmission provided in accordance with an embodiment of the present invention;

FIG. 2 is a side view of a spatial position arrangement of a powershift transmission provided by an embodiment of the present invention.

Detailed Description

In order to make the technical problems solved, the technical solutions adopted and the technical effects achieved by the present invention clearer, the technical solutions of the present invention are further described below by way of specific embodiments with reference to the accompanying drawings. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some but not all of the elements associated with the present invention are shown in the drawings.

As shown in fig. 1 and 2, the present embodiment provides a powershift transmission, which includes an input shaft 1, a first shaft 2, a second shaft 3, and a third shaft 4, wherein the axial end faces of the input shaft 1, the first shaft 2, and the second shaft 3 are projected to be arranged in a triangle, and the input shaft 1, the first shaft 2, the second shaft 3, and the third shaft 4 are arranged in parallel in sequence.

Wherein, the input shaft 1 is sleeved with a first loose gear 11, a second loose gear 12, a first clutch 13 which enables the first loose gear 11 to be fixed or rotated relative to the input shaft 1 and a second clutch 14 which enables the second loose gear 12 to be fixed or rotated relative to the input shaft 1; the first shaft 2 is sleeved with a first fixed gear 21 and a second fixed gear 22 which are fixed relative to the first shaft, and the second fixed gear 22 is meshed with the second movable gear 12; a third fixed gear 31 fixed relative to the second shaft 3 is arranged on the second shaft 3, and the third fixed gear 31 is meshed with the first fixed gear 21 and simultaneously meshed with the first movable gear 11; the second shaft 3 drives the third shaft 4 to rotate through a gear transmission assembly.

In the present embodiment, the third fixed gear 31 meshes with the first fixed gear 21 while meshing with the first movable gear 11. In a forward gear, the second clutch 14 is closed, the input shaft 1 transmits power to the second shaft 3 through the second movable gear 12, the second fixed gear 22, the first fixed gear 21 and the third fixed gear 31 in sequence, and then the power is transmitted to the third shaft 4 through the gear transmission assembly for output; during backward gear shifting, the first clutch 13 is closed, the input shaft 1 transmits power to the second shaft 3 through the first movable gear 11 and the third fixed gear 31 in sequence, and then the power is transmitted to the third shaft 4 through the gear transmission assembly to be output, so that the rotation direction of the third fixed gear 31 is changed, and the rotation direction is changed when the third shaft 4 outputs power.

In the embodiment, the third fixed gear 31 is meshed with the first fixed gear 21 and simultaneously meshed with the first movable gear 11, so that the rotation direction of the third shaft 4 is changed during forward gear shifting and reverse gear shifting; the existing idle wheel design is cancelled, the number of the middle shafts of the power gear shifting transmission is reduced, and the size of the power gear shifting transmission is reduced, so that the occupied space and the production cost of the power gear shifting transmission are reduced, and the power gear shifting transmission is suitable for vehicles with limited installation space of the power gear shifting transmission.

Further, in the present embodiment, the number of teeth of the first fixed gear 21 is greater than that of the second fixed gear 22, and in order to avoid interference between the first movable gear 11 and the first fixed gear 21, the first movable gear 11 and the first fixed gear 21 are axially displaced. Specifically, the first movable gear 11 is half-meshed with the third fixed gear 31, and the first fixed gear 21 is half-meshed with the third fixed gear 31.

The gear transmission assembly includes a third loose gear 32, a fourth loose gear 33, a third clutch 34 for fixing or rotating the third loose gear 32 to or with respect to the second shaft 3, a fourth clutch 35 for fixing or rotating the fourth loose gear 33 to or with respect to the second shaft 3, and a fourth shaft 5 disposed in parallel with the second shaft 3, wherein the fourth shaft 5 is fitted with a fourth fixed gear 51 engaged with the third fixed gear 31, a fifth loose gear 52 engaged with the third loose gear 32, a sixth loose gear 53 engaged with the fourth loose gear 33, a fifth clutch 55 for fixing or rotating the fifth loose gear 52 to or with respect to the fourth shaft 5, and a sixth clutch 56 for fixing or rotating the sixth loose gear 53 to or with respect to the fourth shaft 5, and the fourth fixed gear 51 is fixed to the fourth shaft 5. In this embodiment, the fourth shaft 5 is provided between the second shaft 3 and the third shaft 4.

The gear transmission assembly further comprises a fifth fixed gear 41 and a sixth fixed gear 42 which are arranged on the third shaft 4 and fixed relative to the third shaft 4, wherein the fifth fixed gear 41 is meshed with the fifth loose gear 52, and the sixth loose gear 53 can drive the sixth fixed gear 42 to rotate. In this embodiment, the fourth shaft 5 is provided with a seventh loose gear 54 engaged with the sixth fixed gear 42, and the sixth loose gear 53 and the seventh loose gear 54 are dual gears.

The gear transmission assembly provided by the embodiment has a simple structure, the design of an idler wheel is eliminated, the number of shafts is not increased, the number of gears is not increased, and the cost of the power gear shifting transmission is reduced.

The powershift transmission has four forward gears and four reverse gears; the second clutch 14 and the fourth clutch 35 are both closed to forward first gear, and the power transmission paths include the input shaft 1, the second movable gear 12, the second fixed gear 22, the first shaft 2, the first fixed gear 21, the third fixed gear 31, the second shaft 3, the fourth movable gear 33, the sixth movable gear 53, the seventh movable gear 54, the sixth fixed gear 42 and the third shaft 4.

The second clutch 14 and the sixth clutch 56 are both closed to forward gear, and the power transmission paths are the input shaft 1, the second movable gear 12, the second fixed gear 22, the first shaft 2, the first fixed gear 21, the third fixed gear 31, the fourth fixed gear 51, the fourth shaft 5, the seventh movable gear 54, the sixth fixed gear 42, and the third shaft 4.

The second clutch 14 and the third clutch 34 are both closed to the forward third gear, and the power transmission paths are the input shaft 1, the second loose gear 12, the second fixed gear 22, the first shaft 2, the first fixed gear 21, the third fixed gear 31, the second shaft 3, the third loose gear 32, the fifth loose gear 52, the fifth fixed gear 41, and the third shaft 4.

The second clutch 14 and the fifth clutch 55 are both closed to the fourth forward speed, and the power transmission paths are the input shaft 1, the second movable gear 12, the second fixed gear 22, the first shaft 2, the first fixed gear 21, the third fixed gear 31, the fourth fixed gear 51, the fourth shaft 5, the fifth movable gear 52, the fifth fixed gear 41, and the third shaft 4.

The first clutch 13 and the fourth clutch 35 are both closed to reverse first gear, and the power transmission paths are the input shaft 1, the first loose gear 11, the third fixed gear 31, the second shaft 3, the fourth loose gear 33, the sixth loose gear 53, the seventh loose gear 54, the sixth fixed gear 42, and the third shaft 4.

The first clutch 13 and the sixth clutch 56 are both closed in reverse gear, and the power transmission paths are the input shaft 1, the first movable gear 11, the third fixed gear 31, the fourth fixed gear 51, the fourth shaft 5, the seventh movable gear 54, the sixth fixed gear 42, and the third shaft 4.

The first clutch 13 and the third clutch 34 are both closed in reverse third gear, and the power transmission paths are the input shaft 1, the first loose gear 11, the third fixed gear 31, the second shaft 3, the third loose gear 32, the fifth loose gear 52, the fifth fixed gear 41, and the third shaft 4.

The first clutch 13 and the fourth clutch 35 are both closed in the reverse fourth gear, and the power transmission paths are the input shaft 1, the first loose gear 11, the third fixed gear 31, the second shaft 3, the fourth loose gear 33, the sixth loose gear 53, the seventh loose gear 54, the sixth fixed gear 42, and the third shaft 4.

Further, the transmission ratio of the forward first gear and the reverse first gear is equal; the transmission ratio of the forward second gear and the backward second gear is equal; the transmission ratios of the forward third gear and the reverse third gear are equal; the gear ratios of the forward fourth gear and the reverse fourth gear are equal, so that the gear ratios of the forward gear and the corresponding reverse gear from the input shaft 1 to the second shaft 3 are the same. Specifically, the ratio of the number of teeth of the first movable gear 11 to the number of teeth of the first fixed gear 21 is equal to the ratio of the number of teeth of the second movable gear 12 to the number of teeth of the second fixed gear 22. Preferably, the number of teeth of the first movable gear 11 is equal to the number of teeth of the first fixed gear 21, and the number of teeth of the second movable gear 12 is equal to the number of teeth of the second fixed gear 22.

For example, the tooth number Z1 of the first movable gear 11 is equal to the tooth number Z4 of the first fixed gear 21, the tooth number Z2 of the second movable gear 12 is equal to the tooth number Z3 of the second fixed gear 22, the tooth number Z5 of the third fixed gear 31 is equal to 52, the tooth number Z13 of the third movable gear 32 is equal to 36, the tooth number Z6 of the fourth movable gear 33 is equal to 40, the tooth number Z9 of the fourth fixed gear 51 is equal to 38, the tooth number Z10 of the fifth movable gear 52 is equal to 44, the tooth number Z7 of the sixth movable gear 53 is equal to 50, the tooth number Z8 of the seventh movable gear 54 is equal to 26, the tooth number Z11 of the fifth fixed gear 41 is equal to 31, and the tooth number Z12 of the sixth fixed gear 42 is equal to 49.

The gear ratio of the first forward gear is equal to (Z3/Z2) × (Z5/Z4) × (Z7/Z6) × (Z12/Z8) ═ 3.603, the gear ratio of the second forward gear is equal to (Z3/Z2) × (Z5/Z4) × (Z9/Z5) × (Z12/Z8) ═ 2.106, the gear ratio of the third forward gear is equal to (Z3/Z2) × (Z5/Z4) (Z10/Z13) (Z11/Z10) × 1.317, and the gear ratio of the fourth forward gear is equal to (Z3/Z2) (Z5/Z4) (Z9/Z5) (Z11/Z10) (-0.787).

The transmission ratio of the first reverse gear is equal to (Z5/Z1) (Z7/Z6)) (Z12/Z8) — 3.063, the transmission ratio of the second reverse gear is equal to (Z5/Z1) ((Z9/Z5) ((Z12/Z8)) -2.106, the transmission ratio of the third reverse gear is equal to (Z5/Z1) ((Z10/Z13) ((Z11/Z10) — 1.317, and the transmission ratio of the fourth reverse gear is equal to (Z5/Z1) ((Z9/Z5) ((Z11/Z10) — 0.787. Where "-" indicates that the rotational direction of the third shaft 4 in the reverse gear is opposite to the rotational direction of the third shaft 4 in the forward gear.

Further, the first movable gear 11, the first fixed gear 21, the third fixed gear 31 and the fourth fixed gear 51 are located at the same end of the shaft to facilitate arrangement and installation of the respective gears.

Further, a first fixed gear 21 and a second fixed gear 22 are provided at both ends of the first shaft 2. Preferably, the first fixed gear 21 and the second fixed gear 22 are symmetrically arranged about the first axis. When the second clutch 14 is closed, both the first fixed gear 21 and the second fixed gear 22 transmit torque; when the first clutch 13 is closed, neither the first fixed gear 21 nor the second fixed gear 22 transmits torque; therefore, the bearings installed at both ends of the first shaft 2 for supporting the first shaft 2 are relatively uniformly stressed, and the bearings installed at both ends of the first shaft 2 are bearings of the same type, so as to facilitate the design and installation of the first shaft 2.