CN115789185A

CN115789185A - Four-speed power gear shifting transmission of tractor

Info

Publication number: CN115789185A
Application number: CN202211518460.4A
Authority: CN
Inventors: 王子龙; 邱辉鹏; 王梦梦; 严鉴铂; 刘义
Original assignee: Xian Fast Auto Drive Co Ltd
Current assignee: Xian Fast Auto Drive Co Ltd
Priority date: 2022-11-29
Filing date: 2022-11-29
Publication date: 2023-03-14

Abstract

The invention discloses a four-speed power gear-shifting transmission of a tractor, wherein a first clutch and a second clutch share an outer hub, the inner hub of the first clutch transmits power to a first intermediate shaft through a first gear set, and the first intermediate shaft transmits the power to a gear-shifting element; the transmission can realize four-speed power shifting and power reversing functions, has compact structure, high integration and low cost, and can meet the use requirements of market customers.

Description

Four-speed power gear shifting transmission of tractor

Technical Field

The invention belongs to the technical field of transmissions, and particularly belongs to a four-speed power gear shifting transmission of a tractor.

Background

The transmission system matched with the tractor on the market mainly comprises a plurality of forms of meshing sleeve gear shifting, synchronizer gear shifting and power gear shifting. The engagement sleeve shifts gears, a driver operates a gear shift lever to drive a transmission shifting fork to move so that the engagement sleeve is combined with a gear, the operation during shifting is complex, a series of operations such as clutch treading, gear shifting, clutch treading again, gear engaging and the like need to be completed, the driving operation performance is not improved, and power interruption exists in the gear shifting process; the synchronizer is a device which enables the rotating speed of the gear to be meshed to be synchronized through the synchronizer and then meshed with the gear, and when the synchronizer is used for shifting, the gear can be directly engaged after the clutch is stepped to disengage, so that the gear shifting operation is simplified to a certain extent, but power interruption still exists in the gear shifting process.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a four-speed power gear shifting transmission of a tractor, wherein power gear shifting is realized by controlling the combination and the separation of a clutch or a brake through an electro-hydraulic control system so as to realize gear shifting or reversing under the condition of uninterrupted power, the transmission can realize the functions of four-speed power gear shifting and power reversing, has compact structure, high integration and low cost, and can meet the use requirements of market customers.

In order to achieve the purpose, the invention provides the following technical scheme: a four-speed power shift transmission of a tractor comprises a first clutch, a second clutch, a high-gear clutch and a low-gear brake, wherein the first clutch and the second clutch share an outer hub, the inner hub of the first clutch transmits power to a first intermediate shaft through a first gear set, and the first intermediate shaft transmits the power to a shift element; the second clutch inner hub transmits power to a second intermediate shaft through a second gear set, the second intermediate shaft transmits the power to a gear shifting element, the gear shifting element is arranged on a second shaft, the second shaft transmits the power to a sun gear shaft, the sun gear shaft is connected with an outer hub of a high-gear clutch and a planetary gear train, the inner hub of the high-gear clutch is connected with the planetary gear train, the planetary gear train is sleeved on a planet carrier in an empty mode, the inner hub of a low-gear brake is connected with the planet carrier, the outer hub of the low-gear brake is fixedly connected with a transmission shell, and two ends of an output shaft are respectively connected with the planetary gear train and an output connecting piece.

Further, the first clutch and the second clutch are connected to the output of the engine through a common outer hub and a clutch shaft.

Further, the shifting elements comprise two to three sets of synchronizers, and the gear gears on the first countershaft and the second countershaft are correspondingly meshed with the shifting gears combined by the synchronizers.

Further, the shifting element includes a second-gear synchronizer, a third-fourth-gear synchronizer, a first-gear second-shaft gear and a second-gear second-shaft gear which are combined with the second-gear synchronizer, and a third-gear second-shaft gear and a fourth-gear second-shaft gear which are combined with the third-fourth-gear synchronizer.

Further, be provided with first jackshaft drive gear on the first jackshaft S, first jackshaft first fender gear, first jackshaft second fender gear, first jackshaft third fender gear and first jackshaft fourth fender gear, first gear train includes first jackshaft drive gear and first jackshaft drive gear, the inner hub and the first jackshaft drive gear fixed connection of first clutch, first jackshaft drive gear and the meshing of first jackshaft drive gear, second jackshaft first fender gear and the meshing of first jackshaft first fender gear, second jackshaft second fender gear and the meshing of first jackshaft second fender gear, second jackshaft third fender gear and the meshing of first jackshaft third fender gear, second jackshaft fourth fender gear and the meshing of first jackshaft fourth fender gear.

Furthermore, a second intermediate shaft transmission gear, a first intermediate shaft blocking gear, a second intermediate shaft second blocking gear, a second intermediate shaft third blocking gear and a second intermediate shaft fourth blocking gear are arranged on the second intermediate shaft, the second gear set comprises a second intermediate shaft driving gear and a second intermediate shaft transmission gear, an inner hub of the second clutch is fixedly connected with the second intermediate shaft driving gear, the second intermediate shaft transmission gear is meshed with the second intermediate shaft driving gear, the second intermediate shaft first blocking gear is meshed with the second intermediate shaft first blocking gear, the second intermediate shaft second blocking gear is meshed with the second intermediate shaft second blocking gear, the second intermediate shaft third blocking gear is meshed with the second intermediate shaft third blocking gear, and the second intermediate shaft fourth blocking gear is meshed with the second intermediate shaft fourth blocking gear.

Furthermore, the clutch and the reverse gear clutch are further included, the clutch and the reverse gear clutch share the outer hub, the two shafts are fixedly connected with the shared outer hub of the double clutches, the inner hub of the clutch and the forward gear driving gear are fixedly connected, the inner hub of the clutch and the reverse gear driving gear are fixedly connected, the forward gear driving gear and the reverse gear driving gear are sleeved on the two shafts in an empty mode, the forward gear driving gear is meshed with the forward gear driving gear, the reverse gear driving gear is meshed with the reverse gear driving gear, and the forward gear driving gear and the reverse gear driving gear are fixed at one end of the sun gear shaft.

Furthermore, the planetary gear train comprises a first sun gear, a second sun gear and a third sun gear, the first sun gear is sleeved on the sun gear shaft in an empty manner, the other end of the sun gear shaft is connected with the second sun gear and an outer hub of the high-gear clutch, an inner hub of the high-gear clutch is connected with the first sun gear, the third sun gear is fixedly connected with the output shaft, the three sun gears are meshed with the first planet gear, the second planet gear and the third planet gear in the circumferential direction, and the first planet gear, the second planet gear and the third planet gear are fixedly connected and sleeved on the planet carrier in an empty manner.

Furthermore, two ends of the output shaft are respectively and fixedly connected with the third sun gear and the output connecting piece.

Further, the shift schedule of the range gear of the shift transmission is specifically as follows:

1, gear: the inner hub and the outer hub of the first clutch are combined, and the inner hub and the outer hub of the low-gear brake are combined;

and 2, gear: the inner hub and the outer hub of the second clutch are combined, and the inner hub and the outer hub of the low-gear brake are combined;

and 3, gear shifting: the inner hub and the outer hub of the first clutch are combined, and the inner hub and the outer hub of the high-gear clutch are combined;

4, gear: the inner hub and the outer hub of the second clutch are combined, and the inner hub and the outer hub of the high-gear clutch are combined.

Compared with the prior art, the invention at least has the following beneficial effects:

the invention provides a four-speed power gear shifting transmission of a tractor, which can realize four-speed power gear shifting and power reversing functions by utilizing the cooperative work of a first clutch, a second clutch, a high-gear clutch and a low-gear brake, has compact structure, high integration and low cost, and can meet the use requirements of domestic market customers.

The dual-clutch transmission adopts the dual clutches to simultaneously input and share the outer hub, has compact structure and low cost, and can reduce the axial length of the transmission.

The section gear shifting is realized by utilizing the cooperative work of the first-gear synchronizer, the second-shaft first-gear and the second-shaft second-gear and the cooperative work of the third-fourth synchronizer, the second-shaft third-gear and the second-shaft fourth-gear; and the power reversing is realized by utilizing the cooperative work of the forward gear clutch and the reverse gear clutch.

Drawings

FIG. 1 is a diagram of a delivery route according to the present invention;

in the drawings: 1-engine, 2-first countershaft drive gear, 3-first countershaft drive gear, 4-second countershaft drive gear, 5-second countershaft drive gear, 6-second countershaft first gear, 7-second countershaft second gear, 8-second countershaft third gear, 9-second countershaft fourth gear, 10-first countershaft first gear, 11-first countershaft second gear, 12-first countershaft third gear, 13-first countershaft fourth gear, 14-second countershaft first gear, 15-second countershaft second gear, 16-second countershaft third gear, 17-second countershaft fourth gear, 18-forward gear drive gear, 19-forward gear drive gear 20-reverse drive gear, 21-reverse idler gear, 22-reverse drive gear, 23-first sun gear, 24-second sun gear, 25-third sun gear, 26-first planet gear, 27-second planet gear, 28-third planet gear, 29-planet carrier, 30-transmission housing, 31 output connection, C1-first clutch, C2-second clutch, CF-forward clutch, CR-reverse clutch, C3-high clutch, B1-low brake, T1-second synchronizer, T2-third-fourth synchronizer, S1-clutch shaft, S2-first countershaft, S3-second countershaft, S4-countershaft, S5-sun gear shaft, S6-output shaft.

Detailed Description

The invention is further described with reference to the following figures and detailed description.

The invention provides a four-speed power gear shifting transmission of a tractor, which can realize four-speed power gear shifting and power reversing functions, has compact structure, high integration and low cost, can meet the use requirements of domestic market customers, and consists of a double-clutch transmission device, a double-intermediate shaft transmission device, a double-clutch reversing device and a multi-planet-row transmission device.

As shown in fig. 1, in the dual clutch transmission, the dual clutch is composed of a first clutch C1 and a second clutch C2, and the dual clutches share an outer hub. The clutch shaft S1 is fixedly connected to the engine 1 and the common outer hub of the dual clutch, the inner hub of the first clutch C1 is fixedly connected to the first intermediate shaft drive gear 2, and the inner hub of the second clutch C2 is fixedly connected to the second intermediate shaft drive gear 4.

Friction components are arranged between a common outer hub of the double clutches and the first countershaft driving gear 2 and the second countershaft driving gear 4, when the clutches work, the friction components are combined, and when the clutches are separated, the friction components are separated. The engagement and disengagement of the friction assembly may effect the transmission and disconnection of power.

In a dual countershaft transmission: the first intermediate shaft S2 is fixedly connected with a first intermediate shaft transmission gear 3, a first intermediate shaft first-gear 10, a first intermediate shaft second-gear 11, a first intermediate shaft third-gear 12 and a first intermediate shaft fourth-gear 13.

The first intermediate shaft transmission gear 3 is meshed with the first intermediate shaft driving gear 2, when the first clutch C1 is combined, power is transmitted to the first intermediate shaft S2 through the first intermediate shaft driving gear 2 and the first intermediate shaft transmission gear 3, and then is transmitted to a gear shifting gear combined with a synchronizer through the first intermediate shaft S2;

the second intermediate shaft S3 is fixedly connected with a second intermediate shaft transmission gear 5, a second intermediate shaft first-gear 14, a second intermediate shaft second-gear 15, a second intermediate shaft third-gear 16 and a second intermediate shaft fourth-gear 17;

the second intermediate shaft transmission gear 5 is meshed with the second intermediate shaft driving gear 4, when the second clutch C2 is combined, the second intermediate shaft driving gear 4 and the second intermediate shaft transmission gear 5 are utilized to transmit power to the second intermediate shaft S3, and the power is transmitted to a shifting gear combined with a synchronizer through the second intermediate shaft S3;

the second shaft S4 is fixedly connected with a first-gear synchronizer T1 and a second-gear synchronizer T2, a second-shaft first-gear 6, a second-shaft second-gear 7, a second-shaft third-gear 8 and a second-shaft fourth-gear 9 are sleeved on the second shaft S4 in an empty way, the second countershaft first gear 6 meshes with a first countershaft first gear 10 and a second countershaft first gear 14, the second-shaft second gear 7 is meshed with a first intermediate shaft second gear 11 and a second intermediate shaft second gear 15, the second-shaft third gear 8 is meshed with a first intermediate shaft third gear 12 and a second intermediate shaft third gear 16, and the second-shaft fourth gear 9 is meshed with a first intermediate shaft fourth gear 13 and a second intermediate shaft fourth gear 17.

Preferably, in consideration of the compactness and the engineering feasibility of the transmission assembly, the synchronizer can select two or three groups, namely 4-6 range gears, the more the range gears are, the wider the speed ratio range is, and the whole vehicle dynamic property, the fuel economy and the shifting comfort can be considered.

In a dual clutch reversing device: the twin clutch consists of a forward clutch CF and a reverse clutch CR, the twin clutches sharing an outer hub. The second shaft S4 is fixedly connected to a common outer hub of the dual clutch, the forward drive gear 18 is fixedly connected to an inner hub of the forward clutch CF, and the reverse drive gear 20 is fixedly connected to an inner hub of the reverse clutch CR. The forward drive gear 18 and the reverse drive gear 20 are freely mounted on the second shaft S4. The forward drive gear 19 and the reverse drive gear 22 are fixed to one end of the sun gear shaft S5, and the reverse idler gear 21 is interposed between the reverse drive gear 20 and the reverse drive gear 22.

The multi-planet-row transmission device comprises a planetary gear train, a low-gear brake B1 and a high-gear clutch C3, wherein the planetary gear train comprises a first sun gear 23, a second sun gear 24 and a third sun gear 25, the first sun gear 23 is sleeved on a sun gear shaft S5 in a non-slip mode, the other end of the sun gear shaft S5 is fixedly connected with the second sun gear 24 and an outer hub of the high-gear clutch C3, the first sun gear 23 is fixedly connected with an inner hub of the high-gear clutch C3, and the third sun gear 25 is fixedly connected with an output shaft S6.

Still include respectively with three sun gear peripheral mesh's first planet wheel 26, second planet wheel 27 and third planet wheel 28, first planet wheel 26, second planet wheel 27 and third planet wheel 28 fixed connection and the empty cover of three are on planet frame 29, planet wheel quantity according to overall structure and intensity demand design, general more than or equal to 3.

An inner hub of the low-gear brake B1 is fixedly connected with the planet carrier 29, an outer hub of the low-gear brake B1 is fixedly connected with the transmission shell 30, and two ends of the output shaft S6 are fixedly connected with the third sun gear 25 and the output connecting piece 31 respectively.

The invention realizes the power gear shifting of the power gear in 4 section gears by utilizing the cooperative work of the first clutch C1, the second clutch C2, the high-gear clutch C3 and the low-gear brake B1; the section gear shifting is realized by utilizing the cooperative work of a first-gear synchronizer T1, a second-shaft first-gear 6 and a second-shaft second-gear 7 and the cooperative work of a third-gear synchronizer T2, a second-shaft third-gear 8 and a second-shaft fourth-gear 9; the power reversing is realized by utilizing the cooperative work of the forward clutch CF and the reverse clutch CR;

before the whole vehicle starts, all clutches and brakes of the transmission are disengaged, and all synchronizers are set to be neutral gears. A section gear is selected according to the actual working condition, when the section first gear starts, a first-gear synchronizer T1 and a second-shaft first-gear 6 are combined firstly, then a first clutch C1 and a low-gear brake B1 are combined, and finally a forward-gear clutch CF is combined to drive the whole vehicle forwards; if the reverse clutch CR is engaged, the entire vehicle travels backward.

As shown in Table 1, when a vehicle advances in a first gear of a transmission section, a forward gear clutch CF is combined, and the power transmission route of the transmission is as follows (note: the clutch combination is the combination of an inner hub and an outer hub of the clutch, the combination of the inner hub and the outer hub of a brake, a planet carrier is fixed with a transmission shell, and a planetary gear train transmits power according to the meshing relation of parallel shafts):

a first gear: the first clutch C1 is engaged, the low brake B1 is engaged, the second synchronizer T1 is engaged with the second shaft first gear 6, and the power of the engine 1 is transmitted from the input shaft S1 → the first counter drive gear 2 → the first counter drive gear 3 → the first counter shaft S2 → the first counter shaft first gear 10 → the second shaft first gear 6 → the second shaft S4 → the forward drive gear 18 → the forward drive gear 19 → the sun gear shaft S5 → the second sun gear 24 → the second planetary gear 27 → the third planetary gear 28 → the third sun gear 25 → the output shaft S6 → the output connecting member 31;

and a second stage: the second clutch C2 is coupled to the low brake B1, the second-speed synchronizer T1 is coupled to the second-shaft first-speed gear 6, and the power of the engine 1 is transmitted from the input shaft S1 → the second counter drive gear 4 → the second counter drive gear 5 → the second counter shaft S3 → the second counter shaft first-speed gear 14 → the second counter shaft first-speed gear 6 → the second shaft S4 → the forward drive gear 18 → the forward drive gear 19 → the sun gear shaft S5 → the second sun gear 24 → the second planetary gear 27 → the third planetary gear 28 → the third sun gear 25 → the output shaft S6 → the output connecting member 31;

and a third gear: the first clutch C1 is coupled to the high-range brake C3, the second synchronizer T1 is coupled to the second shaft first gear 6, and the power of the engine 1 is transmitted from the input shaft S1 → the first counter drive gear 2 → the first counter drive gear 3 → the first counter shaft S2 → the first counter shaft first gear 10 → the second shaft first gear 6 → the second shaft S4 → the forward drive gear 18 → the forward drive gear 19 → the sun gear shaft S5 → the first sun gear 23+ the second sun gear 24 → the first planet gear 26+ the second planet gear 27 → the third planet gear 28 → the third sun gear 25 → the output shaft S6 → the output coupling member 31;

and a fourth gear: the second clutch C2 is coupled to the high-range brake C3, the second-speed synchronizer T1 is coupled to the second-shaft first-speed gear 6, and the power of the engine 1 is transmitted from the input shaft S1 → the second counter drive gear 4 → the second counter drive gear 5 → the second counter shaft S3 → the second counter first-speed gear 14 → the second counter first-speed gear 6 → the second shaft S4 → the forward drive gear 18 → the forward drive gear 19 → the sun gear shaft S5 → the first sun gear 23+ the second sun gear 24 → the first planet gear 26+ the second planet gear 27 → the third planet gear 28 → the third sun gear 25 → the output shaft S6 → the output coupling member 31;

the power transmission route of the first gear of the section is as above, and the power transmission routes of different section gears are only reflected on the meshing state of the gears of the synchronizer: the section second gear synchronizer T1 is combined with the second shaft second gear 7, the section third gear synchronizer T2 is combined with the second shaft third gear 8, the section fourth gear synchronizer T2 is combined with the second shaft fourth gear 9.

When the transmission is shifted up in the range gear, for example, the 1 gear is shifted up and the 2 gear is shifted in the range gear, the combination state of the range gear and the power gear is maintained, namely, the first gear synchronizer T1 and the second gear synchronizer T1 are combined with the second shaft gear 6, the first clutch C1 and the low gear brake B1 are combined, then the first clutch C1 is simultaneously separated and the second clutch C2 is combined, and after the double clutches are switched, the whole shifting-up process is completed, and the power is not interrupted. The process of the in-range downshift is similar.

When the whole vehicle needs power reversing in a working project, taking forward gear reversing as an example, the combined state of a forward gear clutch CF is kept, when the vehicle speed reaches a certain condition, the forward gear clutch CF is separated from the combined reverse gear clutch CR, and after the double clutches are switched, the whole power reversing process is finished, and the power is not interrupted.

When the transmission reaches the highest gear of the range gear and the range gear needs to be switched, taking the forward case that the range gear is shifted to the second gear of the range gear-up range as an example, two gear shifting strategies are available:

the first scheme is as follows: and keeping a 4-gear combination state, namely a first-gear synchronizer T1 is combined with a second-shaft first-gear 6, a second clutch C2 is combined with a high-gear brake C3, a forward gear clutch CF is firstly separated, a first-second synchronizer T1 and the second-shaft first-gear 6 are separated, then the first-second synchronizer T1 and a second-shaft second-gear 7 are combined, and then the forward gear clutch CF is combined, so that the gear of the transmission is shifted from 4 to 8.

The second scheme is as follows: and (3) keeping a 4-gear combination state, namely combining a first-gear synchronizer T1 with a second-shaft first-gear 6, combining a second clutch C2 with a high-gear brake C3, firstly separating a forward gear clutch CF, then separating a first-gear synchronizer T1 with the second-shaft first-gear 6, then simultaneously separating the second clutch C2 and the high-gear clutch C3, combining the first clutch C1 with a low-gear brake B1, then combining the first-gear synchronizer T1 with a second-shaft second-gear 7, and then combining the forward gear clutch CF, so that the gear of the transmission is shifted from 4 to 5. The sector downshift process is similar.

TABLE 1 Shift schedule of the present invention

Claims

1. A four-speed power shift transmission of a tractor is characterized by comprising a first clutch (C1), a second clutch (C2), a high-gear clutch (C3) and a low-gear brake (B1), wherein the first clutch (C1) and the second clutch (C2) share an outer hub, the inner hub of the first clutch (C1) transmits power to a first intermediate shaft (S2) through a first gear set, and the first intermediate shaft (S2) transmits the power to a shift element; the power of the inner hub of the second clutch (C2) is transmitted to a second intermediate shaft (S3) through a second gear set, the power of the second intermediate shaft (S3) is transmitted to a gear shifting element, the gear shifting element is arranged on a second shaft (S4), the power of the second shaft (S4) is transmitted to a sun wheel shaft (S5), the sun wheel shaft (S5) is connected with the outer hub and the planetary gear train of the high-gear clutch (C3), the inner hub of the high-gear clutch (C3) is connected with the planetary gear train, the planetary gear train is sleeved on a planet carrier (29) in an empty mode, the inner hub of the low-gear brake (B1) is connected with the planet carrier (29), the outer hub of the low-gear brake (B1) is fixedly connected with a transmission shell (30), and two ends of an output shaft (S6) are respectively connected with the planetary gear train and an output connecting piece (31).

2. A tractor four-speed powershift transmission according to claim 1, characterised in that the first clutch (C1) and the second clutch (C2) are connected to the output of the engine (1) by means of a common outer hub and clutch shaft (S1).

3. A tractor four-speed powershift transmission according to claim 1, characterized in that the shifting elements comprise two to three sets of synchronizers, the gear wheels on the first (S2) and second (S3) countershafts being in corresponding engagement with the shifting gears associated with the synchronizers.

4. A tractor four-speed powershift transmission according to claim 1, characterised in that the shifting elements comprise a two-gear synchronizer (T1) and a three-four-gear synchronizer (T2), a two-shaft one-gear (6) and a two-shaft two-gear (7) coupled to the two-gear synchronizer (T1), a two-shaft three-gear (8) and a two-shaft four-gear (9) coupled to the three-four-gear synchronizer (T2).

5. The tractor four-speed power shift transmission according to claim 4, characterized in that a first countershaft transmission gear (3), a first countershaft first gear (10), a first countershaft second gear (11), a first countershaft third gear (12) and a first countershaft fourth gear (13) are disposed on the first countershaft (S2), the first gear set includes a first countershaft drive gear (2) and a first countershaft transmission gear (3), an inner hub of the first clutch (C1) is fixedly connected with the first countershaft drive gear (2), the first countershaft transmission gear (3) is engaged with the first countershaft drive gear (2), the second countershaft first gear (6) is engaged with the first countershaft first gear (10), the second countershaft second gear (7) is engaged with the first countershaft second gear (11), the second countershaft third gear (8) is engaged with the first countershaft third gear (12), and the second countershaft fourth gear (9) is engaged with the first countershaft fourth gear (13).

6. A four-speed power shift transmission of a tractor according to claim 4, characterized in that the second intermediate shaft (S3) is provided with a second intermediate shaft drive gear (5), a second intermediate shaft first gear (14), a second intermediate shaft second gear (15), a second intermediate shaft third gear (16) and a second intermediate shaft fourth gear (17), the second gear set comprises a second intermediate shaft drive gear (4) and a second intermediate shaft drive gear (5), the inner hub of the second clutch (C2) is fixedly connected with the second intermediate shaft drive gear (4), the second intermediate shaft drive gear (5) is engaged with the second intermediate shaft drive gear (4), the second intermediate shaft first gear (6) is engaged with the second intermediate shaft first gear (14), the second intermediate shaft second gear (7) is engaged with the second intermediate shaft second gear (15), the second intermediate shaft third gear (8) is engaged with the second intermediate shaft third gear (16), and the second intermediate shaft fourth gear (9) is engaged with the second intermediate shaft fourth gear (17).

7. The tractor four-speed power shift transmission according to claim 1, further comprising a forward Clutch (CF) and a reverse Clutch (CR), wherein the forward Clutch (CF) and the reverse Clutch (CR) share an outer hub, a second shaft (S4) is fixedly connected with the shared outer hub of the dual clutches, an inner hub of the forward Clutch (CF) is fixedly connected with a forward drive gear (18), an inner hub of the reverse Clutch (CR) is fixedly connected with a reverse drive gear (20), the forward drive gear (18) and the reverse drive gear (20) are sleeved on the second shaft (S4) in a free manner, the forward drive gear (18) is meshed with the forward drive gear (19), the reverse drive gear (20) is meshed with the reverse drive gear (22), and the forward drive gear (19) and the reverse drive gear (22) are fixed at one end of a sun gear shaft (S5).

8. A tractor four-speed powershift transmission according to claim 1, characterized in that the planetary gear train comprises a first sun gear (23), a second sun gear (24) and a third sun gear (25), the first sun gear (23) is freely sleeved on a sun gear shaft (S5), the other end of the sun gear shaft (S5) is connected with the second sun gear (24) and an outer hub of a high-gear clutch (C3), an inner hub of the high-gear clutch (C3) is connected with the first sun gear (23), the third sun gear (25) is fixedly connected with an output shaft (S6), the three sun gears are circumferentially engaged with a first planetary gear (26), a second planetary gear (27) and a third planetary gear (28), the first planetary gear (26), the second planetary gear (27) and the third planetary gear (28) are fixedly connected and the three are freely sleeved on a planet carrier (29).

9. The four-speed power shift transmission of a tractor according to claim 8, characterized in that both ends of the output shaft (S6) are fixedly connected with the third sun gear (25) and the output connecting piece (31), respectively.

10. The tractor four-speed powershift transmission according to claim 1, wherein the shift schedule of the range gears of the transmission is specifically:

1, gear 1: the inner hub and the outer hub of the first clutch (C1) are combined, and the inner hub and the outer hub of the low-gear brake (B1) are combined;

and 2, gear: the inner and outer hubs of the second clutch (C2) are combined, and the inner and outer hubs of the low-gear brake (B1) are combined;

3, gear shifting: the inner hub and the outer hub of the first clutch (C1) are combined, and the inner hub and the outer hub of the high-gear clutch (C3) are combined;

4, gear 4: the inner and outer hubs of the second clutch (C2) are combined, and the inner and outer hubs of the high-gear clutch (C3) are combined.