Gear shifting mechanism of overgear gearbox

Abstract

The utility model relates to the technical field of gearboxes, in particular to a gearshift mechanism of an overgear gearbox, which comprises a shift fork shaft group comprising an R-gear shift fork shaft, a first-second-gear shift fork shaft and a third-fourth-gear shift fork shaft which are arranged in parallel at intervals; the guide block assembly comprises an R-gear guide block, a second-gear guide block and a fourth-gear guide block, the R-gear guide block, the second-gear guide block and the fourth-gear guide block are correspondingly arranged on the R-gear shifting fork shaft, the first-second-gear shifting fork shaft and the third-fourth-gear shifting fork shaft in a sleeving mode respectively, the tops of the guide block assembly extend outwards and are arranged in parallel at equal intervals to form gear engaging groove blocks, rectangular grooves are formed in the surfaces of the gear engaging groove blocks, and gear shifting driving levers are arranged in the rectangular grooves in a matched mode. The problems that in the prior art, due to the fact that a reversing mechanism is additionally arranged, when the reversing mechanism and the gear shifting mechanism are matched in disorder, an upper cover structure of the gear shifting mechanism is prone to mechanical faults, and a gearbox is inconvenient to disassemble, assemble and maintain due to the fact that the upper cover structure is complicated through the reversing mechanism are solved.

Description

Technical Field

[0001] The utility model relates to the technical field of gearboxes, in particular to an overdrive gearbox shifting mechanism. Background Art

[0002] The gearbox, also known as the transmission, is a mechanism used to change the engine speed and torque. Its function is to change the transmission ratio and expand the range of change of the drive wheel torque and speed to adapt to different driving conditions. The gearbox is mainly composed of two parts: the transmission mechanism and the control mechanism; the key function of the transmission mechanism is to change the value and direction of torque and speed. It is generally composed of gears and shafts, and can change speed and torque through different gear combinations; the key role of the control mechanism is to adjust the transmission mechanism to achieve the change of the transmission ratio of the gearbox, that is, to achieve gear shifting to achieve speed change and torque change.

[0003] The transmission reversing mechanism is an important component of the vehicle's transmission system. Its main function is to assist the driver in changing the direction of the vehicle while driving. This mechanism plays different roles in traditional manual transmissions and automatic transmissions, but the basic principles are similar. In a manual transmission, reversing is mainly accomplished by operating the clutch and the shift lever. The driver depresses the clutch to decouple the engine from the transmission, and then moves the shift lever from the current gear position to the target gear position. After releasing the clutch, the engine power can be transferred to the target gear, thereby achieving the vehicle's reversing operation.

[0004] In order to comply with the international gear sorting rules for transmissions, the transmission gears must be designed to satisfy the requirement that one side of the shift lever shift sorting is all odd gears, and the other side is all even gears. In order to meet this requirement, a reversing mechanism needs to be designed on the transmission shift mechanism, and the gear distribution is implemented in accordance with the international gear sorting rules through the reversing mechanism. The installation of the reversing mechanism is generally divided into three ways. The first is to add a reversing lever to the shift top cover (when the top cover and the shell are an integral structure, the fulcrum of the reversing lever is on the top cover), the second is to add a reversing lever to the large cover (the fulcrum of the reversing lever is on the large cover), and the third is to add an insert to the shift lever fork, and the fork uses the two support shafts at the waist as the fulcrum to perform reversing swing. All three methods can solve the problem of complying with the international gear sorting rules, but all of them will cause different degrees of complexity in the parts structure of the transmission.

[0005] A transmission reversing mechanism with announcement number CN216895723U includes a fixed fork shaft, a movable fork shaft, a fork guide block, a shift guide block, a shift fork, a steering head and a support pin fixedly arranged on the transmission, wherein the steering head is rotationally matched with the support pin, the fork guide block is connected with the shift fork, the shift fork is axially slidably matched with the fixed fork shaft, and the shift guide block is connected with the movable fork shaft; the two ends of the steering head are respectively matched with the fork guide block and the shift guide block. The utility model can realize the reversing of the direct gear and the overspeed gear of the shift handle in the cab of the whole vehicle. The technical device adopts the second method mentioned above to add a reversing mechanism. This method connects and matches the reversing head with the movable fork, making the upper cover structure complicated. When the reversing mechanism is working, when the reversing head and the movable fork are disordered, it is easy to cause mechanical failure of the upper cover structure of the shift mechanism, and the gearbox is troublesome to disassemble and assemble, and the shift mechanism is not easy to repair, which is time-consuming and laborious. Utility Model Content

[0006] The utility model provides an overdrive gearbox shift mechanism, which solves the problem in the prior art that, due to the installation of a reversing mechanism, when the reversing mechanism and the shifting mechanism are disordered in coordination, the upper cover structure of the shifting mechanism is prone to mechanical failure, and the reversing mechanism complicates the upper cover structure, which also causes the gearbox to be inconvenient to disassemble and repair.

[0007] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0008] A shift mechanism for an overdrive gearbox comprises a shift fork shaft assembly, comprising an R gear shift fork shaft, first and second gear shift fork shafts, and third and fourth gear shift fork shafts, which are arranged parallel to each other and spaced apart; a guide block assembly, comprising an R gear guide block, a second gear guide block, and a fourth gear guide block, which correspond to and are sleeved on the R gear shift fork shaft, the first and second gear shift fork shafts, and the third and fourth gear shift fork shafts, respectively, the top of the guide block assembly extends outwardly and is arranged parallel to each other and at equal intervals to form a gear-engaging slot block, the surface of the gear-engaging slot block is provided with a rectangular groove, in which a shift lever is fitted.

[0009] Preferably, it also includes a shift control assembly, which includes a shift control assembly, the shift control assembly includes a shift arm, a shift paddle block and a shift shaft, the shift shaft is a cylindrical structure, a shift paddle block and a shift arm are fixed at one end of the shift shaft, the shift paddle block and the shift arm are cooperatively connected, and the shift shaft passes through the shift paddle lever and is fixed to the shift paddle lever.

[0010] Preferably, it also includes a fork assembly, which includes an R gear fork and first and second gear forks and third and fourth gear forks, which respectively correspond to and are slidably mounted on the R gear fork shaft and the first and second gear fork shafts and the third and fourth gear fork shafts, and the first and second gear forks are connected to the second gear guide block and are integrally formed.

[0011] Preferably, the R gear guide block sliding sleeve is arranged on the outer periphery of the middle part of the R gear fork shaft, and the top of the R gear guide block extends upward perpendicular to the R gear fork shaft, and the second gear guide block sliding sleeve is arranged on the outer periphery of the middle part of the second gear fork shaft, and the top of the second gear guide block extends toward the R gear guide block and is parallel to each other and has a gap.

[0012] Preferably, the fourth gear guide block sliding sleeve is arranged on the outer periphery of the middle part of the third and fourth gear fork shaft, and the fourth gear guide block extends to the left side, and is arranged parallel and spaced apart from the R gear guide block and the second gear guide block and extends upward perpendicular to the fork shaft group to form a gear shifting groove block.

[0013] Preferably, the plane where the rectangular groove provided on the surface of the gear shifting groove block is located is parallel to the plane where the shift fork shaft assembly is located.

[0014] Preferably, the shift shaft is located above the gear slot block, and the bottom of the shift lever extends downward to form a gear boss, the width of the gear boss matches the width of the rectangular slot provided in the gear slot block, and the gear boss can slide laterally in the rectangular slot.

[0015] Preferably, it further comprises a gear set, wherein the gear set comprises an input shaft and an output shaft which are coaxially arranged at intervals, and the input shaft is sequentially sleeved with a third gear, an overdrive gear, a first gear and a second gear.

[0016] Preferably, a gear sleeve is provided between the third gear and the overdrive gear and cooperates with the third and fourth gear shift forks, a gear sleeve is provided between the first gear and the second gear and cooperates with the first and second gear shift forks, and a gear sleeve is provided at the end of the input shaft and cooperates with the R gear shift fork.

[0017] Compared with the prior art, the beneficial effects of the utility model are:

[0018] The utility model adopts the method of cooperating the guide block assembly and the shift lever to integrate the function of the reversing mechanism into the sleeve and the fixed pin, which simplifies the shift mechanism while retaining the function of the reversing mechanism. It does not require any form of shift reversing mechanism, which not only retains the function of the reversing mechanism but also does not complicate the shift mechanism. It is therefore easier to disassemble and repair. In addition, since the reversing mechanism is eliminated and the overall structure is simpler, many failure problems caused by the reversing mechanism are reduced, the maintenance rate is greatly reduced, and for the manufacturer, the simplification of the structure also achieves the effect of energy saving, environmental protection, cost reduction and efficiency improvement.

[0019] Furthermore, the utility model also reasonably adjusts the sequence of some shift gears, so that the shift sequence of the shift lever of the utility model conforms to international standards and driver habits, and is convenient for direct production and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1It is a schematic diagram of the overall structure of an embodiment of the utility model.

[0021] Figure 2 The figure is a front view schematic diagram of a shift mechanism according to an embodiment of the utility model.

[0022] Figure 3 The figure is a side view schematic diagram of a shift mechanism according to an embodiment of the utility model.

[0023] Figure 4 It is a front view schematic diagram of the matching structure of the guide block assembly and the shift fork shaft assembly in one embodiment of the utility model.

[0024] Figure 5 The figure is a schematic diagram of the gear arrangement of an embodiment of the utility model.

[0025] In the figure: shift control assembly 1, shift arm 1.1, shift paddle block 1.2, shift shaft 1.3, shift lever 2, gear engagement protrusion 2.1, guide block assembly 3, R gear guide block 3.1, second gear guide block 3.2, fourth gear guide block 3.3, gear engagement groove block 3.4, shift fork assembly 4, R gear shift fork 4.1, first and second gear shift forks 4.2, third and fourth gear shift forks 4.3, shift fork shaft assembly 5, R gear shift fork shaft 5.1, first and second gear shift fork shaft 5.2, third and fourth gear shift fork shaft 5.3, input shaft 6, output shaft 7, third gear gear 8, overdrive gear 9, first gear gear 10, second gear gear 11, gear sleeve 12. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0027] In order to comply with the international gear sorting rules for transmissions, the transmission gears must be designed to satisfy the requirement that one side of the shift lever shift sorting is all odd gears, and the other side is all even gears. In order to meet this requirement, a reversing mechanism needs to be designed on the transmission shift mechanism, and the gear distribution is implemented in accordance with the international gear sorting rules through the reversing mechanism. The installation of the reversing mechanism is generally divided into three ways. The first is to add a reversing lever to the shift top cover (when the top cover and the shell are an integral structure, the fulcrum of the reversing lever is on the top cover), the second is to add a reversing lever to the large cover (the fulcrum of the reversing lever is on the large cover), and the third is to add an insert to the shift lever fork, and the fork uses the two support shafts at the waist as the fulcrum to perform reversing swing. All three methods can solve the problem of complying with the international gear sorting rules, but all of them will cause different degrees of complexity in the parts structure of the transmission.

[0028] A transmission reversing mechanism in the prior art includes a fixed fork shaft, a movable fork shaft, a fork guide block, a shift guide block, a shift fork, a steering head and a support pin fixedly arranged on the transmission, wherein the steering head is rotationally matched with the support pin, the fork guide block is connected with the shift fork, the shift fork is axially slidably matched with the fixed fork shaft, and the shift guide block is connected with the movable fork shaft; the two ends of the steering head are respectively movably matched with the fork guide block and the shift guide block. The utility model can realize the reversing of the direct gear and the overdrive gear of the shift handle in the cab of the whole vehicle. The technical device adopts the second method mentioned above to add a reversing mechanism. This method connects and matches the reversing head with the movable fork, making the upper cover structure complicated. When the reversing mechanism is working, when the reversing head and the movable fork are disordered, it is easy to cause mechanical failure of the upper cover structure of the shift mechanism, and the gearbox is troublesome to disassemble and assemble, and the shift mechanism is not convenient to repair, which is time-consuming and labor-intensive. In order to solve the above problems, this embodiment is provided.

[0029] Reference Figures 1 to 3 For this embodiment, Figure 1 This is a schematic diagram of the overall structure of this embodiment. Figure 2 This is a schematic diagram of the main view of the shift mechanism of the present embodiment. This embodiment is an overdrive gearbox shift mechanism, including a shift fork shaft group, including an R gear shift fork shaft, a first and second gear shift fork shaft, and a third and fourth gear shift fork shaft, the three of which are arranged parallel to each other and spaced apart; a guide block assembly, including an R gear guide block, a second gear guide block, and a fourth gear guide block, which respectively correspond to and are mounted on the R gear shift fork shaft, the first and second gear shift fork shafts, and the third and fourth gear shift fork shafts, the top of the guide block assembly extends outwardly and is arranged parallel to each other and at equal intervals to form a gear shift slot block, the surface of the gear shift slot block is provided with a rectangular groove, in which a shift lever is fitted.

[0030] The shift lever is a bridge between the driver's intention and the gearbox shifting action. It is made of high-strength alloy material and its surface is specially treated to ensure that it is not easy to wear during long-term use, while providing excellent sliding performance. The shape and size of the shift block are precisely calculated to ensure that it can accurately match the rectangular groove for shifting operations.

[0031] When the driver issues a shift command through an operating lever or an electronic signal, the shift lever quickly and accurately slides into the corresponding rectangular slot under the guidance of a sophisticated control system. In this process, the matching accuracy between the shift lever and the gear slot block is crucial. It is worth mentioning that this overdrive gearbox shift mechanism also has an automatic correction function. In extreme cases, such as driver misoperation or system failure, the shift lever can automatically return to a safe position to avoid damage to the gearbox. This function greatly improves the reliability and safety of the gearbox.

[0032] In addition to the above functions, this overdrive gearbox shifting mechanism also has good compatibility and scalability. It can be seamlessly connected with various types of engines and vehicle control systems to meet different vehicle models and driving needs.

[0033] In addition, it also includes a shift control assembly, which is mainly composed of a shift arm, a shift paddle block and a shift shaft. The shift shaft is a cylindrical structure, and a ring-shaped shift paddle block is fixed at the head position of one end of the shift shaft. On one side of the shift paddle block, a shift arm is fixed. The shift shaft passes through the shift paddle block from the middle and is tightly fixed to the shift paddle block. The shift control assembly plays an important role in the overall structure. Through the interaction between the shift arm and the shift paddle block, the gear position is switched, thereby ensuring that the vehicle can be based on different driving needs. When shifting, the driver operates the shift arm, and the shift arm swings forward or backward at a certain angle with the center of the shift shaft, and then the shift shaft drives the shift lever, thereby driving the gear-engaging protrusion to slide in the rectangular groove of the gear-engaging groove block. When sliding to the groove matching the corresponding gear position, the corresponding shift fork can be driven, and the shift fork drives the gear sleeve to move axially, so that the gear sleeve and a certain gear position combination tooth are combined to complete the shift, so as to meet the corresponding driving needs.

[0034] In the vehicle's operating system, the accuracy and reliability of the shift control components are crucial to the driving experience. First, the shift shaft is made of high-strength alloy material, which not only has excellent wear resistance and corrosion resistance, but also maintains stable mechanical properties under extreme conditions. The cylindrical structure of the shift shaft is precisely machined to ensure that the connection with the shift lever is both tight and smooth.

[0035] This embodiment also covers the design of the fork assembly, which is mainly composed of the R gear fork, the first and second gear forks, and the third and fourth gear forks. The above-mentioned forks include the R gear fork, the first and second gear forks, and the third and fourth gear forks. Both ends of the forks cooperate with the fixing holes at both ends of the gearbox housing and are installed in the gearbox. These forks correspond to the R gear fork shaft, the first and second gear fork shaft, and the third and fourth gear fork shaft, respectively, and can slide on them. It is worth noting that the first and second gear forks and the second gear guide block are connected to form a whole, and are made by an integrated molding process. Such a design not only improves the reliability and durability of the components, but also makes the operation of the entire mechanism smoother, further optimizing the driving experience.

[0036] As a key part of the shift control, we use a lightweight but strong composite material. This material not only reduces the overall weight of the shift control assembly, but also improves its durability. The design of the shift paddle fully considers ergonomic principles, allowing the driver to feel more comfortable and smooth when operating.

[0037] The shift arm serves as a bridge between the shift paddle and the driver's operating interface. By optimizing the structural design and using a more flexible connection method, the shift arm can more accurately convey the driver's intentions and reduce operational errors.

[0038] The R gear guide block is a sliding component, and is sleeved on the middle periphery of the R gear fork shaft, playing a guiding and positioning role. The top of this guide block is uniquely designed, it is perpendicular to the R gear fork shaft and extends upward, such a structure enables the R gear guide block to better perform its function.

[0039] On the other hand, the second-gear guide block is also a sliding component, which is installed on the middle periphery of the first and second gear shift fork shafts, and also plays a guiding and positioning role. It is worth noting that the top of the second-gear guide block is not directly connected to the R-gear guide block, but extends to the R-gear guide block, and the two remain parallel to each other, but there is a certain gap between them. This design allows the second-gear guide block to perform its function independently, while also ensuring coordinated work with the R-gear guide block.

[0040] The fourth gear guide block is slidably sleeved on the middle outer periphery of the third and fourth gear shift fork shafts. The fourth gear guide block is designed so that it can extend to the left, so as to maintain parallelism and spacing with the R gear guide block and the second gear guide block. In addition, the fourth gear guide block is also perpendicular to the shift fork shaft assembly and extends upward to form a gear slot block. Such a design allows the gear slot block to effectively cooperate with the shift fork shaft assembly to achieve a smooth shifting operation.

[0041] A rectangular groove is designed on the surface of the gear slot block, and the plane where the groove is located is parallel to the plane where the shift fork shaft group is located. This design can not only improve the strength and stability of the gear slot block, but also reduce the noise and vibration during gear shifting, and improve driving comfort. In addition, the rectangular groove design can also effectively prevent the jamming phenomenon when engaging the gear, and increase the service life of the gearbox.

[0042] First of all, the R-gear guide block, the second-gear guide block, and the fourth-gear guide block all need to be made of high-strength, wear-resistant, and elastic materials. Such materials can ensure that the guide blocks are not easily worn during long-term use and maintain their guidance and positioning accuracy. At the same time, the elastic material can also absorb the impact of shifting to a certain extent, reducing damage to the gearbox.

[0043] Secondly, machining accuracy is also crucial for these sliding components. The size and shape of each guide block need to be processed strictly according to the design requirements to ensure that they can be accurately mounted on the corresponding fork shaft and maintain an appropriate spacing with other guide blocks. Only in this way can the smoothness and accuracy of gear shifting be ensured.

[0044] In addition, the design of the gear slot block also needs to take into account its processing accuracy. The size and shape of the rectangular slot need to be precisely controlled to ensure smooth cooperation with the fork shaft assembly and avoid jamming during gear shifting. At the same time, the surface of the gear slot block also needs to be specially treated to improve its wear resistance and corrosion resistance.

[0045] As the gear-engaging lug slides precisely in the rectangular groove, the driver can easily and accurately operate the shift lever to switch between different gears. During the gear shifting process, the coordination between the shift lever and the shift shaft is particularly critical. The shift shaft not only serves as the basis for supporting the shift lever, but also provides a stable guide when the shift lever moves, ensuring that the gear-engaging lug always moves smoothly in the rectangular groove, preventing misalignment or jamming during the gear shifting process.

[0046] This embodiment also includes a set of gear sets, which are composed of an input shaft and an output shaft, which are coaxially arranged at intervals, maintaining a certain connection and independence. On the input shaft, the third gear, overdrive gear, first gear and second gear are installed in order, and these gears each undertake different transmission tasks, ensuring the smooth operation of the entire mechanism. Between the third gear and the overdrive gear, a gear sleeve is set, which plays a transition role and cooperates with the third and fourth gear shift forks. By switching the shift forks, different gears can be switched. Similarly, between the first gear and the second gear, a gear sleeve is also set, and cooperates with the first and second gear shift forks. By switching the shift forks, different gears can be switched. At the end of the input shaft, a gear sleeve is set, which cooperates with the R gear shift fork to realize the start and stop of the mechanism. The setting of the entire gear set enables the mechanism to switch at different speeds during operation, meeting various operating requirements.

[0047] The beneficial effects of this embodiment are:

[0048] This embodiment adopts the method of cooperating the guide block assembly and the shift lever to integrate the function of the reversing mechanism into the sleeve and the fixed pin, which simplifies the shift mechanism while retaining the function of the reversing mechanism. It does not require any form of shift reversing mechanism, which not only retains the function of the reversing mechanism but also does not complicate the shift mechanism. It is therefore easier to disassemble and repair. In addition, since the reversing mechanism is eliminated and the overall structure is simpler, many failure problems caused by the reversing mechanism are reduced, and the maintenance rate is greatly reduced. Moreover, for the manufacturer, the simplification of the structure also achieves the effect of energy saving, environmental protection, cost reduction and efficiency improvement.

[0049] Furthermore, the present embodiment also reasonably adjusts the sequence of some shift gears, so that the shift sequence of the shift lever of the present embodiment complies with international standards and driver habits, and is convenient for direct production and use.

[0050] In addition to the above-mentioned embodiments, within the scope disclosed in the claims and the specification of the utility model, the technical features or technical data of the utility model can be reselected and combined to form new embodiments, which should also be regarded as specific embodiments of the utility model and within the protection scope of the utility model.

Claims

1. An overdrive gearbox shift mechanism, characterized in that: include: The shift fork shaft assembly includes a first and second gear shift fork shaft and a third and fourth gear shift fork shaft, which are arranged parallel to each other and spaced apart; The guide block assembly includes an R gear guide block, a second gear guide block and a fourth gear guide block, which respectively correspond to and are sleeved on the R gear shift fork shaft and the first and second gear shift fork shafts and the third and fourth gear shift fork shafts. The top of the guide block assembly extends outward and is arranged in parallel with each other at equal intervals to form a gear shift slot block. A rectangular groove is provided on the surface of the gear shift slot block, in which a shift lever is fitted.

2. The overdrive gearbox shift mechanism according to claim 1, characterized in that: It also includes a shift control assembly, which includes a shift arm, a shift paddle block and a shift shaft. The shift shaft is a cylindrical structure, and a shift paddle block and a shift arm are fixed to one end of the shift shaft. The shift paddle block and the shift arm are connected in a cooperative manner, and the shift shaft passes through the shift lever and is fixed to the shift lever.

3. The overdrive gearbox shift mechanism according to claim 2, characterized in that: It also includes a fork assembly, which includes an R gear fork, first and second gear forks, and third and fourth gear forks, which are respectively corresponding and slidably mounted on the R gear fork shaft, the first and second gear fork shafts, and the third and fourth gear fork shafts, and the first and second gear forks are connected to the second gear guide block and are integrally formed.

4. The overdrive gearbox shift mechanism according to claim 3, characterized in that: The R gear guide block sliding sleeve is arranged on the outer periphery of the middle part of the R gear fork shaft, and the top of the R gear guide block extends upward perpendicular to the R gear fork shaft. The second gear guide block sliding sleeve is arranged on the outer periphery of the middle part of the first and second gear fork shafts, and the top of the second gear guide block extends toward the R gear guide block and is parallel to each other and has a gap.

5. The overdrive gearbox shift mechanism according to claim 4, characterized in that: The fourth gear guide block sliding sleeve is arranged on the outer periphery of the middle part of the third and fourth gear fork shafts, and the fourth gear guide block extends to the left side, and is arranged parallel and spaced apart with the R gear guide block and the second gear guide block and extends upward perpendicular to the fork shaft group to form a gear engaging groove block.

6. The overdrive gearbox shift mechanism according to claim 5, characterized in that: The plane where the rectangular groove arranged on the surface of the gear shifting groove block is located is parallel to the plane where the shift fork shaft assembly is located.

7. The overdrive gearbox shift mechanism according to claim 5 or 6, characterized in that: The shift shaft is located above the gear slot block, and the bottom of the shift lever extends downward to form a gear projection. The width of the gear projection matches the width of the rectangular slot of the gear slot block, and the gear projection can slide transversely in the rectangular slot.

8. The overdrive gearbox shift mechanism according to claim 1, characterized in that: The gear set also includes an input shaft and an output shaft which are coaxially arranged at intervals. A third gear, an overdrive gear, a first gear and a second gear are sequentially sleeved on the input shaft.

9. The overdrive gearbox shift mechanism according to claim 8, characterized in that: A gear sleeve is provided between the third gear and the overdrive gear and cooperates with the third and fourth gear shift forks; a gear sleeve is provided between the first gear and the second gear and cooperates with the first and second gear shift forks; a gear sleeve is provided at the end of the input shaft and cooperates with the R gear shift fork.

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