Transfer case for amphibious vehicle and design method

Abstract

The transfer case for the amphibious vehicle comprises a transfer case shell and further comprises a first shaft located in the transfer case shell and used for power input, a second shaft responsible for power output to a spray pump and an intermediate shaft serving as a front axle output shaft and a rear axle output shaft. The front end of the first shaft is supported in an inner circular hole of an external spline at the front end of the second shaft through a needle bearing, and the needle bearing is fixed with the shaft through a shaft retainer ring; the rear end of the first shaft is supported on the transfer case shell through a first deep groove ball bearing, a spline is machined at the shaft end of the first shaft, a transmission connecting flange is installed at the shaft end of the first shaft and axially fixed through a fastening nut set, the transmission connecting flange is connected with a transmission, and a spline is machined in the middle of the first shaft as well. A driving gear is fixed to the first shaft through a spline and a sleeve. The system comprises a transmission route and an arrangement form which are simple in structure and convenient to operate, and the problem that the transmission efficiency is reduced due to the fact that the power transmission route of the amphibious vehicle is too long can be solved.

Description

Technical Field

[0001] The invention relates to the technical field of transmission systems for amphibious vehicles, in particular to a transfer case for amphibious vehicles and a design method thereof. Background Art

[0002] The transmission system is the core of an amphibious vehicle. The purpose of research on the transmission system and transfer case design of an amphibious vehicle is to ensure that the vehicle can guarantee power transmission and transmission efficiency on land or on water. Currently, the power transmission route of an amphibious vehicle is too long, resulting in reduced transmission efficiency.

[0003] Therefore, a transfer case for an amphibious vehicle and a design method are proposed. Summary of the invention

[0004] The object of the present invention is to provide a transfer case for an amphibious vehicle and a design method thereof.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention proposes a transfer case for amphibious vehicles, comprising a transfer case housing, a first shaft in the transfer case housing for power input, a second shaft responsible for power output to a spray pump, and an intermediate shaft as the output shaft of the front and rear axles, wherein the front end of the first shaft is supported in the inner circular hole of the external spline at the front end of the second shaft by a needle bearing, and the needle bearing is fixed to the shaft with a shaft retaining ring; the rear end of the first shaft is supported on the transfer case housing by a deep groove ball bearing, the shaft end of the first shaft is processed with a spline, and a connecting flange for connecting a transmission is installed, which is axially fixed by a fastening nut group, the transmission connecting flange is connected to the transmission, the middle of the first shaft is also processed with a spline, and a driving gear is fixed to the first shaft through a spline and a sleeve, and the driving gear is meshed with a driven gear outside the intermediate shaft.

[0007] A coupling sleeve 1 is provided at the connection between the second shaft and the first shaft, and the external splines of the second shaft, the upper external splines of the first shaft and the coupling sleeve form a water operation gear position of the actuator.

[0008] Preferably, the intermediate shaft adopts a differential structure, and the differential structure includes a differential case and a planetary gear set. The planetary gear set includes planetary shafts, planetary gears, front axle half shafts, rear axle half shafts and half shaft gears. The planetary gears in the planetary gear set are fixed to the differential case by the planetary shafts, and the front axle half shafts and the rear axle half shafts are fixed together with the half shaft gears through spline matching and shaft retaining rings; the shaft ends of the front axle half shafts and the rear axle half shafts are both processed with splines, and are respectively equipped with front axle connecting flanges and rear axle connecting flanges, the front axle connecting flange is connected to the front axle half shaft through a universal joint, and the rear axle connecting flange is connected to the rear axle half shaft through a universal joint; both ends of the differential case are supported on the transfer case housing through two deep groove ball bearings, and the extended part of the driven gear is processed with splines, which is loosely sleeved on the differential case through a bushing and meshes with the driving gear.

[0009] Preferably, the connection between the external splines on the differential case and the external splines on the driven gear is wrapped with a second coupling sleeve, and the external splines on the differential case, the external splines on the driven gear and the first coupling sleeve constitute a land four-wheel drive gear position.

[0010] Preferably, the first shaft and the second shaft are located on the same axis and are parallel to the intermediate shaft.

[0011] Preferably, the transfer case is lubricated by splash lubrication.

[0012] Another object of the present invention is to provide a design method for an amphibious vehicle transfer case, comprising the following steps:

[0013] S1. Parameter calculation and selection of transfer case parts;

[0014] S2, shaft structural design;

[0015] S3. Transfer case control mechanism design.

[0016] Preferably, the step S1 includes the following:

[0017] S1.1: Selection of the module of meshing parts;

[0018] S1.2: Gear pressure angle selection;

[0019] S1.3: Selection of helix angle of helical gear;

[0020] S1.4: tooth width selection;

[0021] S1.5: Selection of tooth addendum coefficient.

[0022] Preferably, the step S2 includes the following:

[0023] S2.1: Determination of the diameters of the first shaft, the second shaft and the intermediate shaft:

[0024] S2.1.1: Structural design of each shaft section from left to right;

[0025] S2.1.2: Design of the length of each shaft segment from left to right;

[0026] S2.2: Appearance design of some parts:

[0027] S2.2.1: Transfer case design;

[0028] S2.2.2: Design of driving and driven gears;

[0029] S2.2.3: Spline design.

[0030] Preferably, the step S3 includes the following:

[0031] S3.1: Selection of transmission control mechanism: select one of direct control and remote control;

[0032] S3.2: Selection of transmission operating mechanism locking device: Select one from the self-locking device and the interlocking device.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention designs a novel transmission system for amphibious vehicles. The system includes a transmission route and layout form with a simple structure and convenient operation, which can solve the problem that the power transmission route of amphibious vehicles is too long, resulting in reduced transmission efficiency. The design of the system is committed to improving the structural design of the transmission system, making the amphibious vehicle structure more compact, thereby reducing the weight of the transmission system, the difficulty of operation and the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the transfer case structure;

[0036] Figure 2 is a schematic diagram of the first axis structure;

[0037] Figure 3 is a schematic diagram of the second axis structure;

[0038] Figure 4 is a schematic diagram of the intermediate shaft structure;

[0039] Figure 5 Modeling schematic diagram for driven gear;

[0040] Figure 6 Sketch out the spline design;

[0041] Figure 7 It is a schematic diagram of the spline shaft;

[0042] Figure 8is a schematic diagram of the joint sleeve;

[0043] Fig. 9 It is a cross-sectional view of the coupling sleeve and the shift fork structure.

[0044] In the figure: 1-transmission connecting flange; 2-driving gear; 3-first shaft; 4-joint sleeve 1; 5-needle bearing; 6-deep groove ball bearing 1; 7-second shaft; 8-transfer case; 9-rear axle connecting flange; 10-deep groove ball bearing 2; 11-rear axle half shaft; 12-planetary shaft; 13-planetary gear; 14-half shaft gear; 15-differential case; 16-joint sleeve 2; 17-driven gear; 18-front axle half shaft 2; 19-front axle connecting flange. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] The present invention provides a transfer case for an amphibious vehicle, such as Figure 1 As shown:

[0047] The first shaft 3 is the input shaft, and the power is transmitted from this shaft to the transfer case. The front end of the first shaft 3 is supported by a needle bearing 5 in the inner circular hole of the external spline at the front end of the second shaft 7, and the needle bearing 5 is fixed to the shaft with a shaft retaining ring; the rear end of the first shaft 3 is supported on the transfer case housing 8 by a deep groove ball bearing 6, and the shaft end is processed with splines and equipped with a transmission connecting flange 1, which is axially fixed by a tightening nut group. The transmission connecting flange 1 is connected to the transmission, and the middle of the first shaft 3 is also processed with splines. The driving gear 2 is fixed to the first shaft 3 through splines and sleeves, and meshes with the intermediate shaft driven gear 17.

[0048] The external splines of the second shaft 7, the external splines on the first shaft 2 and the coupling sleeve 4 form the water operation gear of the transfer case. When not working, the coupling sleeve has its internal splines tightly matched with the external splines on the first shaft 3, and the transfer rod can be operated. The operating mechanism makes the shift fork push the coupling sleeve 4 to slide axially, so that the internal splines of the coupling sleeve 4 are engaged with the external splines on the second shaft 7. In this way, power can be transmitted from the first shaft 2 (input shaft) to the second shaft 7 (jet pump output shaft) through the coupling sleeve 4 in sequence for output.

[0049] The intermediate shaft adopts a differential structure. The planetary gear 13 in the planetary gear set inside the structure is fixed to the differential case 15 by the planetary shaft 12. The front axle half shaft 18 and the rear axle half shaft 11 are fixed together with the half shaft gear 14 through spline cooperation and shaft retaining ring; the ends of the two half shafts are processed with splines, and are respectively equipped with a front axle connecting flange 19 and a rear axle connecting flange 9. The front axle connecting flange 19 is connected to the front axle half shaft 18 through a universal transmission device, and the rear axle connecting flange 9 is connected to the rear axle half shaft 11 through a universal transmission device; both ends of the differential case 15 are supported on the transfer case 8 through deep groove ball bearings 10, and the extended part of the driven gear 17 is processed with splines, which is loosely sleeved on the differential case 15 through a bushing and meshes with the driving gear 2.

[0050] The external splines on the differential case 15, the external splines on the driven gear 17 and the second coupling sleeve 16 constitute the land four-wheel drive gear. When not in operation, the second coupling sleeve 16 is tightly matched with the external splines on the driven gear 17 by its internal splines, and the transfer rod can also be manipulated. The shift fork is used to push the second coupling sleeve 16 to slide axially through the operating mechanism, so that the second coupling sleeve 16 is engaged with the external splines on the differential case 15, which can drive the entire intermediate shaft to rotate, so that the power can be transmitted from the first shaft 3 to the entire intermediate shaft through the driving gear 2, the driven gear 17, the coupling sleeve 16, and the differential case 15 in sequence to achieve the front and rear axle four-wheel drive output.

[0051] The transfer case is lubricated by splash lubrication.

[0052] The design method of a transfer case for an amphibious vehicle proposed by the present invention is as follows:

[0053] Calculation of the dimensions of transfer case components:

[0054] Selection of module of meshing parts:

[0055] When selecting the gear module, the following principles should be followed:

[0056] First, choosing a smaller module helps increase the number of gear teeth and increase the tooth width. This will increase the overlap of the gear meshing, which helps reduce the noise generated when the gear is running. Therefore, in order to reduce noise, the module should be reasonably reduced and the tooth width should be appropriately increased.

[0057] Secondly, if the goal is to reduce the mass of the gear, the module should be increased and the tooth width should be reduced accordingly. This choice can make the gear structure more compact and reduce the overall mass.

[0058] From a process perspective, in order to ensure manufacturing convenience and efficiency, it is recommended that each gear adopt the same module. However, from a strength perspective, each gear may require a different module to meet its specific load-bearing requirements.

[0059] For passenger cars, reducing gear working noise is particularly important, so the gear modulus should tend to be smaller. For trucks, due to their large load requirements, reducing mass is often more important than reducing noise, so the gear modulus should be larger.

[0060] In summary, when selecting the gear module, factors such as noise, quality, process and strength need to be considered comprehensively to ensure that the selected module can meet the performance requirements and ensure the feasibility of manufacturing.

[0061] The selected modulus value should comply with the national standard GB / T 1357-2008 "Module of cylindrical gears for general machinery and heavy machinery", see Table 4-1. The first series should be given priority, and the modules in brackets should be avoided as much as possible.

[0062] Table 4-1 Module of cylindrical gears for general machinery and heavy machinery

[0063]

[0064] This embodiment is designed for the HSB amphibious vehicle transfer case, and has the comprehensive capabilities of multiple working conditions such as rapid water and land rescue, towing rescue and water pump fire fighting, with a curb weight of ≤1.95t, a passenger capacity of ≥9 people, a payload of ≥1t, and a rescue towing force of ≥1.5t.

[0065] Table 4-2 shows the curb weight analysis:

[0066] Table 4-2 Curb weight analysis

[0067]

[0068] Considering the application scenario, reducing mass is more important than reducing noise, so a larger module should be selected. Therefore, the module m=4 is selected for gears 2 and 3.

[0069] Most of the meshing teeth of the meshing sleeve adopt involute tooth shape. Due to technological reasons, the modulus of the meshing teeth on the same transfer case is the same. The selection range is: 2.0 to 3.5 for passenger cars and trucks with a total mass ma of 1.8 to 14.0t; 3.5 to 5.0 mm for trucks with a total mass ma greater than 14.0t. Selecting a smaller modulus value can increase the number of teeth, which is beneficial for shifting. Therefore, the modulus m=2 is selected for the meshing sleeves 1 and 2.

[0070] Pressure Angle

[0071] When the pressure angle of the gear is small, its overlap will increase accordingly, but at the same time the stiffness of the gear teeth will also decrease. This design can reduce the dynamic load of the gear when it enters and exits the meshing, making the transmission process smoother, thereby helping to reduce noise and improve transmission efficiency and stability.

[0072] According to relevant national regulations, the standard pressure angle is set at 20°, so the master and slave gears of the transfer case are designed with this standard 20° pressure angle. In the design of the meshing sleeve engagement teeth, the optional pressure angles include 20°, 25° and 30°. After comprehensive consideration and comparison, the design of this embodiment selects 30° as the pressure angle of the meshing sleeve engagement teeth to better meet the actual use requirements and ensure smooth and reliable transmission.

[0073] Helix Angle

[0074] Helical gears are widely used in transmissions and transfer cases. When selecting the helix angle of a helical gear, it is necessary to pay attention to its effect on the gear working noise, gear tooth strength, and the axial force generated. When a larger helix angle is selected, the meshing overlap of the gears will increase accordingly, making the gears work more smoothly and reducing noise. At the same time, as the helix angle increases, the strength of the gear teeth will also increase. However, when the helix angle exceeds 30°, its bending strength will suddenly drop, while the contact strength will continue to increase.

[0075] Therefore, from the perspective of enhancing the bending strength of the gear, it is not recommended to use an excessively large helix angle. Generally speaking, a helix angle between 15° and 25° is a more appropriate choice. Based on this consideration, the transfer case gears designed in this embodiment all use a helix angle of 20° to ensure that the gears have sufficient strength while also achieving smooth and low-noise transmission.

[0076] Tooth width

[0077] In order to shorten the axial dimension and reduce the mass as much as possible, a smaller tooth width should be selected. On the other hand, the advantage of the stable transmission of the helical gear is weakened by the reduction of the tooth width, and the narrow tooth width will also increase the working stress of the gear. If a wider tooth width is selected, the gear will tilt due to the deformation of the shaft during operation, causing uneven force on the gear along the tooth width direction, resulting in eccentric load, reduced load capacity, and uneven wear in the tooth width direction.

[0078] The tooth width b is usually selected according to the gear module (m).

[0079] For helical teeth, b=kc*m, if kc is 8.5, then the tooth width b=44.

[0080] Addendum coefficient

[0081] Generally, the tooth addendum coefficient is taken as 1.00.

[0082] Shaft structure design

[0083] The diameter of the first shaft is determined as Figure 2 As shown:

[0084] 1) Structural design of each shaft section from left to right

[0085] D1: minimum diameter, install the fastening nut shaft section, D1 = 14mm;

[0086] D2: spline shaft section, module 1, number of teeth 30, pressure angle 30°;

[0087] D3: transition shaft section, D3 = 35 mm;

[0088] D4: transition shaft section, take D4 = 40mm;

[0089] D5: The shaft section connecting the external spline and the internal spline gear, with a module of 2, a number of teeth of 24, and a pressure angle of 30°; D6: The positioning shoulder of the gear formed with the shaft section on the left, with D6 = 80 mm;

[0090] D7: The shaft section is connected by external spline and coupling sleeve, module 3, number of teeth 24, pressure angle 30°;

[0091] D8: forms the locating shoulder of the bearing with the right shaft section, take D8 = 40mm;

[0092] D9: Shaft section at needle roller bearing, D9=30mm.

[0093] 2) Design of the length of each shaft segment from left to right

[0094] L1: Determined by the interference relationship of the external fastening nut assembly, L1 = 20mm;

[0095] L2: Spline shaft section, determined by the interference relationship of the external flange assembly, take L2 = 36mm;

[0096] L3: Considering the structural design of the bearing end cover, the transition shaft section needs to reserve extra length, so L2 = 50mm; L4: transition shaft section, L4 is 42.75mm;

[0097] L5: tooth width 45mm, this shaft section should be 2-3mm smaller than the tooth width, so L4=43mm;

[0098] L6: positioning shoulder, L = 55.75mm;

[0099] L7: The shaft section connected by the external spline and the coupling sleeve. According to the width of the coupling sleeve, L6=30mm;

[0100] L8: According to the fitting relationship of the joint set, take L7 = 3mm;

[0101] L9: According to the bearing installation relationship, take L8=35mm.

[0102] The structural design of the second axis, such as Figure 3 As shown:

[0103] 1) Structural design of each shaft section from left to right

[0104] D1: minimum diameter, install the fastening nut shaft section, D1 = 14mm;

[0105] D2: spline shaft section, module is 1, number of teeth is 30, pressure angle is 30°;

[0106] D3: end cover transition shaft section, D3=35;

[0107] D4: Install the bearing shaft section. According to the deep groove ball bearing model, D4 = 40mm;

[0108] D5: forms the locating shoulder of the bearing with the left shaft section, take D5 = 60mm;

[0109] D6: forms the locating shoulder of the bearing with the right shaft section, take D8 = 80mm;

[0110] D7: The shaft section is connected by external spline and coupling sleeve, module 3, number of teeth 24, pressure angle 30°;

[0111] D8: Inner hole diameter. Based on the outer diameter of the first axis needle roller bearing, we can get D8=47mm.

[0112] 2) Design the length of each shaft section from left to right.

[0113] L1: Determined by the assembly interference relationship of the external fastening nut, L1=20mm.

[0114] L2: Spline shaft section, determined by the interference relationship of the external flange assembly, take L2=53.5mm.

[0115] L3: Considering the structural design of the bearing end cover, additional length needs to be reserved for this transition shaft section, so L2 = 45mm.

[0116] L4: bearing shaft section. From the bearing assembly relationship, we can get L4=29.5mm.

[0117] L5: Positioning shoulder, L5=34mm.

[0118] L6: Positioning shoulder, L6=27.5mm.

[0119] L7: The shaft section is connected by the external spline and the coupling sleeve. According to the sliding stroke of the coupling sleeve, take L7=15mm.

[0120] L8: Inner hole depth. According to the assembly relationship of the needle roller bearing on the first axis, L8 can be taken as 35mm.

[0121] Structural design of intermediate shaft (differential shaft)

[0122] Take the first axis 3 as an example. Figure 4 The intermediate shaft (differential shaft) assembly is shown.

[0123] Parts design

[0124] Transfer case

[0125] The transfer case is a casting. In this embodiment, the transfer case is designed using groove and boss commands to complete the dimensions according to the three-axis assembly relationship. Create a sketch to make a boss, and process the shaft shoulders for bearing positioning and the semicircular hole boss for installing the fork shaft on the two side walls of the housing, and drill the bolt installation holes. The upper case also needs to reserve an area for the shift fork to move.

[0126] Driving gear and driven gear

[0127] Design two gears and calculate the data: the number of teeth of the active gear z1 = 53, the pitch circle diameter is 212mm, and the tooth width is 45mm; the number of teeth of the driven gear z2 = 40, the pitch circle diameter is 160mm, and the tooth width is 45mm. Record the above data, use the SolidWork gear generator to input the data, and automatically generate the gear. Change the save mode to stp, open it with CATIA software, draw sketches separately, make grooves and splines respectively, and the splines are as follows Figure 5 As shown, arraying is then performed to complete the three-dimensional design.

[0128] Spline Design

[0129] Use the spline calculation software to input the module, number of teeth, pressure angle, displacement coefficient, connection length, and accuracy grade to calculate the pitch circle diameter, base circle diameter, and major and minor diameters of the internal and external splines.

[0130] 1) Draw the base circle diameter, pitch circle diameter, and major and minor diameters in the sketch tool;

[0131] 2) Draw equidistant points on the pitch circle (number of points = 2*number of teeth);

[0132] 3) Draw a straight line from the center point to any point A and take the midpoint B;

[0133] 4) Draw a circle at point B with radius AB, intersecting the base circle at C;

[0134] 5) Draw a circle at point C with AC as radius, and the part that intersects with the major and minor diameters is the tooth profile (approximately);

[0135] 6) Trim the excess lines, mirror and remove the excess lines again, and invert the tooth root arc (radius = 0.3);

[0136] 7) The internal and external splines are the same;

[0137] like Figure 6 Shown is a sketch of the internal and external splines.

[0138] like Figure 7As shown in the figure, the external spline is generated on the cylindrical boss in the same way to complete the spline shaft modeling.

[0139] like Figure 8 As shown, the internal spline groove is generated to complete the internal spline modeling of the coupling sleeve.

[0140] like Fig. 9 The figure shows a cross-sectional view of the coupling sleeve and the shift fork structure, and this method is also used to complete the modeling and assembly.

[0141] Design of transfer case control mechanism

[0142] Requirements for transmission control mechanisms

[0143] 1) To prevent the transmission from automatically shifting and automatically disengaging, a self-locking device should be provided in the operating mechanism.

[0144] 2) To ensure that the transmission will not be engaged in two gears at the same time, an interlocking device should be provided in the operating mechanism.

[0145] Transmission operating mechanism classification

[0146] 1) Direct control

[0147] The direct-operated shift lever and its shift control device are integrated on the transmission cover, allowing the driver to directly operate the shift lever, thereby driving the shift control device in the transmission cover to complete the shift action. This design has significant advantages, such as clear shift positions, fast and smooth shifting. Its structure mainly consists of a shift lever, a fork-shaped shift lever, a shift block, a shift fork shaft, and a shift fork. This type of operation is particularly common and practical when the driver's seat is close to the shift lever.

[0148] 2) Remote control

[0149] When the shift lever is far from the driver's seat, it cannot be directly placed on the transmission cover, so a set of connecting rods is required between the shift lever and the transmission to achieve remote control. For this reason, a set of transmission rods is added between the shift lever and the transmission, forming a unique remote control method. This design not only reduces the space occupied by the shift lever in the cab, but also makes the cab more spacious and more comfortable to ride.

[0150] Transmission control mechanism locking device

[0151] Function: Ensure the reliable operation of the transmission to prevent gear skipping, gear shifting and reverse gear shifting by mistake.

[0152] Composition: self-locking, interlocking, reverse lock.

[0153] 1) Self-locking device

[0154] ① Function

[0155] It prevents the transmission from automatically shifting out of gear while driving, ensures full tooth length engagement, and gives the driver a good feel.

[0156] ②Composition

[0157] It consists of a groove on the fork shaft, a spring, a round head pin, etc.

[0158] ③ Locking principle

[0159] The round pin falls into the groove under the action of the spring pressure, thus preventing it from moving out and falling out of gear. At the same time, there is a clear hand feeling when the round pin falls into the groove. The size of the two self-locking grooves ensures full tooth engagement.

[0160] 2) Interlocking device

[0161] Function: Prevent two gears from being engaged at the same time, causing gear confusion.

[0162] Type: pin-ball type, self-locking interlocking two-in-one type, rotating jaw type.

[0163] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0164] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A transfer case for an amphibious vehicle, comprising a transfer case housing (8), characterized in that: The invention also comprises a first shaft (3) for power input in a transfer case housing (8), a second shaft (7) for power output to a spray pump, and an intermediate shaft as an output shaft of a front and rear axle. The front end of the first shaft (3) is supported in an inner circular hole of an outer spline at the front end of the second shaft (7) through a needle bearing (5), and the needle bearing (5) is fixed to the shaft with a shaft retaining ring; the rear end of the first shaft (3) is supported on the transfer case housing (8) through a deep groove ball bearing (6), the shaft end of the first shaft (3) is processed with a spline, and is equipped with a transmission connection flange (1), which is axially fixed by a fastening nut group, and the transmission connection flange (1) is connected to the transmission, and the middle of the first shaft (3) is also processed with a spline, and a driving gear (2) is fixed to the first shaft (3) through a spline and a sleeve, and the driving gear (2) is meshed with a driven gear (17) outside the intermediate shaft. A coupling sleeve (4) is provided at the connection between the second shaft (7) and the first shaft (3); the external splines of the second shaft (7), the upper external splines of the first shaft (3) and the coupling sleeve (4) form a water operation gear position of the transfer case.

2. The transfer case for an amphibious vehicle according to claim 1, characterized in that: The intermediate shaft adopts a differential structure, and the differential structure includes a differential case (15) and a planetary gear set. The planetary gear set includes a planetary shaft (12), a planetary gear (13), a front axle half shaft (18), a rear axle half shaft (11) and a half shaft gear (14). The planetary gear (13) in the planetary gear set is fixed to the differential case (15) by the planetary shaft (12). The front axle half shaft (18) and the rear axle half shaft (11) are fixed together with the half shaft gear (14) through spline matching and a shaft retaining ring; the front axle half shaft (18), the rear axle half shaft (11) are fixed to the half shaft gear (14) through spline matching and a shaft retaining ring; The shaft ends of the differential case (15) are processed with splines, and are respectively equipped with a front axle connecting flange (19) and a rear axle connecting flange (9). The front axle connecting flange (19) is connected to the front axle half shaft (18) through a universal transmission device, and the rear axle connecting flange (9) is connected to the rear axle half shaft (11) through a universal transmission device; both ends of the differential case (15) are supported on the transfer case (8) through deep groove ball bearings (10), and the extended part of the driven gear (17) is processed with splines, which is loosely sleeved on the differential case (15) through a bushing and meshes with the driving gear (2).

3. The transfer case for an amphibious vehicle according to claim 2, characterized in that: The connection between the external splines on the differential case (15) and the external splines on the driven gear (17) is wrapped with a second coupling sleeve (16); the external splines on the differential case (15), the external splines on the driven gear (17) and the first coupling sleeve (16) constitute a land four-wheel drive gear position.

4. The transfer case for an amphibious vehicle according to claim 1, characterized in that: The first shaft (3) and the second shaft (7) are located on the same axis and are parallel to the intermediate shaft.

5. The transfer case for an amphibious vehicle according to claim 1, characterized in that: The transfer case lubrication method adopts splash lubrication.

6. A design method for an amphibious vehicle transfer case comprising any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Parameter calculation and selection of transfer case parts; S2, shaft structural design; S3. Transfer case control mechanism design.

7. The design method of a transfer case for an amphibious vehicle according to claim 6, characterized in that: The step S1 includes the following: S1.1: Selection of the module of meshing parts; S1.2: Gear pressure angle selection; S1.3: Selection of helix angle of helical gear; S1.4: tooth width selection; S1.5: Selection of tooth addendum coefficient.

8. The design method of a transfer case for an amphibious vehicle according to claim 6, characterized in that: The step S2 includes the following: S2.1: Determination of the diameters of the first shaft, the second shaft and the intermediate shaft: S2.1.1: Structural design of each shaft section from left to right; S2.1.2: Design of the length of each shaft segment from left to right; S2.2: Appearance design of some parts: S2.2.1: Transfer case design; S2.2.2: Design of driving and driven gears; S2.2.3: Spline design.

9. The design method of a transfer case for an amphibious vehicle according to claim 6, characterized in that: The step S3 includes the following: S3.1: Selection of transmission control mechanism: select one of direct control and remote control; S3.2: Selection of transmission operating mechanism locking device: Select one from the self-locking device and the interlocking device.

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