Hydraulic backflow type three-gear automatic transmission for bulldozer

Abstract

The invention discloses a hydraulic backflow type three-gear automatic transmission for a bulldozer, which relates to the field of transmission equipment and comprises a hydraulic backflow transmission device, a compound planetary gear shifting and speed regulating device and a reversing device which are connected in sequence. The transmission device is specially designed for meeting the working characteristics that the bulldozer is complex in working condition, large in load fluctuation and higher in backward speed than forward speed, the engine can be effectively prevented from stalling while low-speed torque increasing is achieved, and the transmission efficiency is excellent; and each speed regulation section has a stepless speed regulation function, so that more operation working conditions can be adapted, and the driving comfort is improved. In addition, the transmission is compact in structure and convenient to arrange, and serialization is easy to achieve.

Description

Technical Field

[0001] The invention relates to the field of transmission equipment, and in particular to a hydraulic reflux type three-speed automatic transmission for a bulldozer and a shifting method thereof. Background Art

[0002] Bulldozer is an important engineering machinery, which plays an irreplaceable role in engineering fields such as land reclamation and leveling, infrastructure construction, and mining. The working conditions of bulldozers are complex, and their working objects are mainly relatively hard earth and stone, and the homogeneity of soil is poor. When cutting soil and bulldozing, bulldozers often have short-term peak loads, which can easily cause the engine to be forced to shut down. Therefore, as a common component of hydromechanical transmission systems, hydraulic torque converters have been widely used in engineering vehicles with their unique low-speed torque increase characteristics. However, the problems of low transmission efficiency and narrow high-efficiency range of hydraulic torque converters have always existed, which has become a global problem that has plagued the wider application of hydromechanical transmission systems. Therefore, how to break the constraints of the existing structure and find a new transmission system that can achieve low-speed torque increase and has excellent transmission efficiency has become a new topic in recent years. Summary of the invention

[0003] The present invention aims to disclose a hydraulic reflux three-speed automatic transmission suitable for a bulldozer, which can have higher transmission efficiency and wider speed regulation range while ensuring low-speed torque increase characteristics, has a compact structure and is convenient for serialization.

[0004] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0005] A hydraulic reflux three-speed automatic transmission for a bulldozer, comprising a hydraulic reflux transmission device, a compound planetary gear shifting and speed regulating device and a reversing device connected in sequence;

[0006] The hydraulic reflux transmission device is composed of a first transmission shaft, a first gear, a second transmission shaft, a variable displacement hydraulic element, a fixed displacement hydraulic element, a third transmission shaft, a second gear, a third gear, a fourth gear, a first planetary row sun gear, a first planetary row planet carrier, a first planetary row ring gear, and a fourth transmission shaft;

[0007] The compound planetary gear shifting and speed regulating device is composed of a first brake, a fourth transmission shaft, a second planetary row sun gear, a second planetary row planet carrier, a second planetary row ring gear, a third planetary row sun gear, a third planetary row planet carrier, a third planetary row ring gear, a second brake, a fifth transmission shaft, a large wheel hub, and a first clutch;

[0008] The reversing device is composed of a fifth transmission shaft, a fourth planetary gear sun gear, a fourth planetary gear carrier, a fourth planetary gear ring, a third brake, a small wheel hub, a second clutch, and a sixth transmission shaft.

[0009] Preferably, the first transmission shaft is the input shaft of the transmission, and the engine is directly connected to the first transmission shaft; the fourth gear and the first planetary gear sun gear are fixedly mounted on the first transmission shaft; the third gear is fixedly mounted on the first planetary gear carrier; the first planetary gear ring is fixedly mounted on the fourth transmission shaft; the first gear and the second gear are respectively fixedly mounted on the second transmission shaft and the third transmission shaft; the variable displacement hydraulic element drive shaft is fixedly connected to the second transmission shaft, and the fixed displacement hydraulic element drive shaft is fixedly connected to the third transmission shaft.

[0010] Preferably, the first transmission shaft, the second transmission shaft and the third transmission shaft are parallel to each other; the first gear and the fourth gear are meshed with each other; the second gear and the third gear are meshed with each other; the first planetary gear carrier is sleeved on the first transmission shaft; the fourth transmission shaft serves as the output shaft of the hydraulic reflux transmission device, and transmits power to the compound planetary gear shifting and speed regulating device.

[0011] Preferably, the second planetary gear sun gear and the third planetary gear ring are fixedly sleeved on the fourth transmission shaft; the third planetary gear carrier and the large wheel hub are fixedly sleeved on the fifth transmission shaft; the second planetary gear ring is fixedly connected to the third planetary gear sun gear; in the actual transmission process, the rotation speed of the second planetary gear ring and the third planetary gear sun gear is always the same; the rotating end of the first brake is fixedly sleeved on the second planetary gear carrier, and the rotating end of the second brake is fixedly sleeved on the second planetary gear ring, and the second planetary gear carrier and the second planetary gear ring can be braked by the first brake and the second brake respectively; the first clutch The two ends are respectively fixedly sleeved on the second planetary gear ring and the large wheel hub, and the locking and separation of the second planetary gear ring and the large wheel hub can be freely controlled through the first clutch; the fourth planetary gear ring is fixedly sleeved on the fifth transmission shaft; the fourth planetary gear sun gear and the small wheel hub are fixedly sleeved on the sixth transmission shaft; the rotating end of the third brake is fixedly connected to the fourth planetary gear carrier, and the braking of the fourth planetary gear carrier can be achieved through the third brake; the two ends of the second clutch are respectively fixedly sleeved on the fourth planetary gear carrier and the small wheel hub, and the locking and separation of the fourth planetary gear carrier and the small wheel hub can be freely controlled through the first clutch.

[0012] Preferably, the second transmission shaft is fixedly connected to the variable displacement hydraulic element drive shaft via a shaft sleeve; the third transmission shaft is fixedly connected to the fixed displacement hydraulic element drive shaft via a shaft sleeve.

[0013] In the above scheme, the gears and planetary gear transmission elements are fixedly sleeved on the corresponding transmission shafts through splines.

[0014] Preferably, the first brake, the second brake and the third brake are all wet brakes.

[0015] Preferably, the first clutch and the second clutch are both wet clutches.

[0016] Preferably, the variable displacement hydraulic element and the fixed displacement hydraulic element are both axial piston hydraulic elements with a pump / motor dual working mode;

[0017] The variable displacement hydraulic element and the fixed displacement hydraulic element form an axial piston pump-motor closed system;

[0018] Among them, the maximum control displacement of the variable displacement hydraulic component is not less than the rated displacement of the fixed displacement hydraulic component.

[0019] The present invention also provides a shifting method of a hydraulic reflux type three-speed automatic transmission for a bulldozer, wherein the second clutch and the third brake respectively control the forward and reverse movement of the vehicle;

[0020] When the third brake is closed, the fourth planetary gear carrier is fixed, and the rotational speeds of the fourth planetary gear sun gear and the fourth planetary gear ring gear are opposite; when the second clutch is engaged, the fourth planetary gear sun gear and the fourth planetary gear carrier are rigidly connected, and the fourth planetary gear is in a locked state.

[0021] When the first brake is closed, the transmission operates in the first gear, and the system speed ratio of the transmission is

[0022]

[0023] Where i1 and i2 are the transmission ratios of the fixed axis gears i1 and i2 respectively, and k1, k2 and k3 are the characteristic constants of the first, second and third planetary gears respectively;

[0024] When the second brake (21) is closed, the transmission operates in the second gear, and the system speed ratio of the transmission is

[0025]

[0026] When the first clutch (24) is engaged, the transmission operates in the third gear, and the system speed ratio of the transmission is

[0027]

[0028] In summary, the beneficial effects of the present invention are:

[0029] (1) The hydraulic reflow type three-speed automatic transmission involved in the present application can significantly improve the transmission efficiency of the bulldozer while ensuring the low-speed torque increase characteristics.

[0030] (2) It has a wider speed regulation range and the ability to actively adjust the speed within each speed regulation range, which is beneficial to improving driving comfort and improving work efficiency.

[0031] (3) Different torque increase coefficients and speed regulation ranges of each gear can be obtained simply by adjusting the specifications of the pump, motor and planetary gear, which is conducive to the convenient and quick construction of a series of product solutions.

[0032] (4) Affected by the hydraulic reflux transmission device, the present invention has excellent buffering and shock absorbing performance.

[0033] (5) The transmission described in the present application has a compact structure and is easy to arrange. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 The transmission principle diagram of the torque converter (a-turbine; b-pump wheel);

[0036] Figure 2 is the power flow transmission direction of the torque converter (c-rotating flow; d-eddy current);

[0037] Figure 3 It is the transmission principle diagram of the present invention;

[0038] Figure 4 The speed / torque transmission relationship and power transmission direction of the gears and planetary gears in the hydraulic reflux transmission device in the reflux transmission mode;

[0039] Figure 5 The speed / torque transmission relationship and power transmission direction of the gears and planetary gears in the hydraulic reflux transmission device in the split transmission mode;

[0040] Figure 6 The maximum efficiency curve of the hydraulic return transmission device under load conditions (ΔP = 270bar);

[0041] Figure 7 This is the minimum efficiency curve of the hydraulic return transmission under load conditions (ΔP=350bar).

[0042] In the above drawings:

[0043] 1-first transmission shaft; 2-first gear; 3-second transmission shaft; 4-variable displacement hydraulic element; 5-fixed displacement hydraulic element; 6-third transmission shaft; 7-second gear; 8-third gear; 9-fourth gear; 10-first planetary row sun gear; 11-first planetary row planet carrier; 12-first planetary row ring gear; 13-first brake; 14-fourth transmission shaft; 15-second planetary row sun gear; 16-second planetary row planet carrier; 17-second planetary row ring gear; 18-third planetary row The first planetary gear is the sun gear of the first planetary gear row; the second planetary gear row is the sun gear of the second planetary gear row; the third planetary gear row is the ring gear of the fourth planetary gear row; the fourth planetary gear row is the ring gear of the fourth planetary gear row; the fourth planetary gear row is the ring gear of the fourth planetary gear row; the sixth planetary gear row is the sun gear of the first planetary gear row; the first planetary gear row is the sun gear of the first planetary gear row; the second planetary gear row is the sun gear of the first planetary gear row; the fourth planetary gear row is the sun gear of the first planetary gear row; the fourth planetary gear row is the sun gear of the first planetary gear row; the fourth planetary gear row is the sun gear of the first planetary gear row; the fourth planetary gear row is the sun gear of the first planetary gear row; the sixth planetary gear row is the sun gear of the first planetary gear row; the fourth planetary gear row is the sun gear of the first planetary gear row; the sixth planetary gear row is the sun gear of the first planetary gear row; the sixth planetary gear row is the sun gear of the first planetary gear row; the sixth planetary gear row is the sun gear of the first planetary gear row; the seventh planetary gear row is the sun gear of the first planetary gear row; the eighth ... DETAILED DESCRIPTION

[0044] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0045] Research has found that the ability to form a power cycle means that the transmission system has an energy storage function; the existence of circulating power is the fundamental reason why the torque converter has the low-speed torque-increasing characteristic.

[0046] See also Figure 1-Figure 7 As shown, the present invention replaces the internal return of hydraulic machinery with the external return of hydraulic machinery, and provides a hydraulic return type three-speed automatic transmission suitable for bulldozers, such as Figure 3 The transmission includes a hydraulic reflux transmission device, a compound planetary gear shifting and speed regulating device and a reversing device connected in sequence, which achieves low-speed torque increase and has excellent transmission efficiency.

[0047] The hydraulic reflux transmission device is composed of a first transmission shaft 1, a first gear 2, a second transmission shaft 3, a variable displacement hydraulic element 4, a fixed displacement hydraulic element 5, a third transmission shaft 6, a second gear 7, a third gear 8, a fourth gear 9, a first planetary row sun gear 10, a first planetary row planet carrier 11, a first planetary row ring gear 12, and a fourth transmission shaft 14;

[0048] The compound planetary gear shifting and speed regulating device is composed of a first brake 13, a fourth transmission shaft 14, a second planetary row sun gear 15, a second planetary row planet carrier 16, a second planetary row ring gear 17, a third planetary row sun gear 18, a third planetary row planet carrier 19, a third planetary row ring gear 20, a second brake 21, a fifth transmission shaft 22, a large wheel hub 23, and a first clutch 24;

[0049] The reversing device is composed of a fifth transmission shaft 22 , a fourth planetary gear sun gear 25 , a fourth planetary gear carrier 26 , a fourth planetary gear ring 27 , a third brake 28 , a small wheel hub 29 , a second clutch 30 , and a sixth transmission shaft 31 .

[0050] Among them, the first transmission shaft 1 is the input shaft of the transmission, and the engine is directly connected to the first transmission shaft 1; the fourth gear 9 and the first planetary row sun gear 10 are fixedly sleeved on the first transmission shaft 1; the third gear 8 is fixedly sleeved on the first planetary row planetary carrier 11; the first planetary row ring gear 12 is fixedly sleeved on the fourth transmission shaft 14; the first gear 2 and the second gear 7 are fixedly sleeved on the second transmission shaft 3 and the third transmission shaft 6 respectively; the drive shaft of the variable displacement hydraulic element 4 is fixedly connected to the second transmission shaft 3, and the drive shaft of the fixed displacement hydraulic element 5 is fixedly connected to the third transmission shaft 6.

[0051] The first transmission shaft 1, the second transmission shaft 3, and the third transmission shaft 6 are parallel to each other; the first gear 2 and the fourth gear 9 are meshed with each other; the second gear 7 and the third gear 8 are meshed with each other; the first planetary gear carrier 11 is loosely mounted on the first transmission shaft 1; the fourth transmission shaft 14 serves as the output shaft of the hydraulic reflux transmission device to transmit power to the compound planetary gear shifting and speed regulating device.

[0052] The second planetary gear sun gear 15 and the third planetary gear ring 20 are fixedly sleeved on the fourth transmission shaft 14; the third planetary gear carrier 19 and the large wheel hub 23 are fixedly sleeved on the fifth transmission shaft; the second planetary gear ring 17 is fixedly connected to the third planetary gear sun gear 18; in the actual transmission process, the rotation speed of the second planetary gear ring 17 and the third planetary gear sun gear 18 is always the same; the rotating end of the first brake 13 is fixedly sleeved on the second planetary gear carrier 16, and the rotating end of the second brake 21 is fixedly sleeved on the second planetary gear ring 17, and the braking of the second planetary gear carrier 16 and the second planetary gear ring 17 can be achieved by the first brake 13 and the second brake 21 respectively; the two ends of the first clutch 24 are fixedly sleeved It is sleeved on the second planetary gear ring 17 and the large wheel hub 23, and the locking and separation of the second planetary gear ring 17 and the large wheel hub 23 can be freely controlled by the first clutch 24; the fourth planetary gear ring 27 is fixedly sleeved on the fifth transmission shaft 22; the fourth planetary sun gear 25 and the small wheel hub 29 are fixedly sleeved on the sixth transmission shaft 31; the rotating end of the third brake 28 is fixedly connected to the fourth planetary gear carrier 26, and the braking of the fourth planetary gear carrier 26 can be achieved by the third brake 28; the two ends of the second clutch 30 are respectively fixedly sleeved on the fourth planetary gear carrier 26 and the small wheel hub 29, and the locking and separation of the fourth planetary gear carrier 26 and the small wheel hub 29 can be freely controlled by the first clutch 30.

[0053] In the above scheme, the gears and planetary gear transmission elements are fixedly sleeved on the corresponding transmission shafts through splines.

[0054] As a preferred embodiment, the second transmission shaft 3 is fixedly connected to the drive shaft of the variable displacement hydraulic component 4 through a shaft sleeve; the third transmission shaft 6 is fixedly connected to the drive shaft of the fixed displacement hydraulic component 5 through a shaft sleeve.

[0055] Furthermore, the first brake, the second brake and the third brake are all wet brakes. The first clutch and the second clutch are all wet clutches.

[0056] Preferably, the variable displacement hydraulic element and the fixed displacement hydraulic element are both axial piston hydraulic elements with a pump / motor dual working mode; the variable displacement hydraulic element and the fixed displacement hydraulic element form an axial piston pump-motor closed system (CLHS);

[0057] Among them, the maximum control displacement of the variable displacement hydraulic component is not less than the rated displacement of the fixed displacement hydraulic component. In order to save costs and improve transmission efficiency, the maximum control displacement of the variable displacement hydraulic component in the closed system is generally equal to the rated displacement of the fixed displacement hydraulic component. However, in some cases, in order to obtain a larger speed regulation range, you can also try to use a variable displacement hydraulic component with a maximum control displacement slightly larger than the rated displacement of the fixed displacement hydraulic component.

[0058] Depend on Figure 3It can be seen that the hydraulic reflux three-speed automatic transmission for bulldozers described in the present invention has three gears in each of the forward and reverse directions, and its shifting method is shown in Table 1.

[0059] Table 1 Transmission shifting method

[0060]

[0061] The second clutch 30 and the third brake 28 control the forward and reverse movement of the vehicle respectively;

[0062] When the third brake 28 is closed, the fourth planetary gear carrier 26 is fixed, and the fourth planetary gear sun gear 25 and the fourth planetary gear ring 27 rotate in opposite directions; when the second clutch 30 is engaged, the fourth planetary gear sun gear 25 is rigidly connected to the fourth planetary gear carrier 26, and the fourth planetary gear is in a locked state. By controlling the second clutch 30 or the third brake 28 to cooperate with the first brake 13, the second brake 21, and the first clutch 24 respectively, the vehicle can generate driving force in the forward direction or backward direction in the 1st, 2nd, and 3rd gears respectively.

[0063] When the first brake 13 is closed, the transmission operates in the first gear, and the system speed ratio of the transmission is

[0064]

[0065] Where i1 and i2 are the transmission ratios of the fixed axis gears i1 and i2 respectively, and k1, k2 and k3 are the characteristic constants of the first, second and third planetary gears respectively;

[0066] When the second brake 21 is closed, the transmission operates in the second gear, and the system speed ratio of the transmission is

[0067]

[0068] When the first clutch 24 is engaged, the transmission operates in the third gear, and the system speed ratio of the transmission is

[0069]

[0070] The above-mentioned transmission shifting method can enable the hydraulic reflux three-speed automatic transmission involved in the present invention to significantly improve the transmission efficiency of the bulldozer while ensuring the low-speed torque increase characteristics; it has a wider speed regulation range and has actively adjustable stepless speed change capabilities in each speed regulation section, which is beneficial to improving driving comfort and improving work efficiency; different torque increase coefficients and speed regulation ranges of each gear can be obtained only by adjusting the specifications of the pump, motor and planetary gear, which is conducive to the convenient and quick construction of a series of product solutions.

[0071] The variable displacement hydraulic element 4 and the fixed displacement hydraulic element 5 form an axial piston pump-motor closed system (CLHS). In order to save costs and improve transmission efficiency, the maximum control displacement of the variable displacement hydraulic element in the closed system is generally equal to the rated displacement of the fixed displacement hydraulic element. However, in some cases, in order to obtain a larger speed regulation range, it is also possible to try to select a variable displacement hydraulic element whose maximum control displacement is slightly larger than the rated displacement of the fixed displacement hydraulic element.

[0072] For the convenience of analysis, the displacement ratio ε of CLHS is defined as

[0073] ε=V V / V F =n F / n V (4)

[0074] Wherein, nV and nF represent the rotation speed of the variable displacement hydraulic component and the fixed displacement hydraulic component, rpm; VV and VF represent the displacement of the variable displacement hydraulic component and the fixed displacement hydraulic component, cm3 / r.

[0075] According to the change of the inclination angle of the swash plate of the variable displacement hydraulic element, the displacement ratio of the CLHS exists in two situations: ε>0 and ε<0. When ε>0, the hydraulic return transmission device operates in the return transmission mode. At this time, the speed / torque transmission relationship and power transmission direction of the gear and planetary gear in the hydraulic return transmission device are as follows: Figure 4 shown.

[0076] Depend on Figure 4 It can be seen that in the reflux transmission mode, there is circulating power in the hydraulic reflux transmission device. When the ring gear stops rotating due to excessive load, the power input from the power source can still be stored in the hydraulic reflux transmission device in the form of reflux power and accumulate until the system meets the torque requirement or the CLHS reaches the upper pressure limit. In the reflux transmission mode, the hydraulic reflux transmission device has similar power to the torque converter and can be used for starting or loading operations of bulldozers.

[0077] When ε<0, the hydraulic reflux transmission device operates in the split transmission mode. The speed / torque transmission relationship and power transmission direction of the gears and planetary gears in the hydraulic reflux transmission device are as follows: Figure 5 As shown. At this time, the hydraulic circuit and mechanical circuit in the hydraulic return transmission device transmit power in parallel in both directions, and there is no power circulation in the system. Therefore, in the actual operation of the transmission, the hydraulic return transmission device is only suitable for high-speed and light-load conditions of bulldozers in the split transmission mode.

[0078] According to the transmission characteristics of the power flow in the hydraulic return transmission device, the transmission efficiency of the hydraulic mechanical compound transmission system can be calculated by the meshing power method as follows:

[0079]

[0080] Wherein, ηHMCS is the transmission efficiency of the hydraulic reflux transmission device; ηg is the transmission efficiency of the fixed axis gear, ηg = 0.98; I is the first transmission shaft 1; r1 is the first planetary gear ring 12; p1 is the first planetary gear carrier 10; s1 is the first planetary gear sun gear 11; iab represents the speed ratio of element a to element b; i is the speed ratio of element a and element b relative to element c; ηP-M is the total transmission efficiency of CLHS. The efficiency model of CLHS obtained by fitting the bench test data is:

[0081]

[0082] Wherein, ΔP is the operating pressure difference of CLHS; A is the efficiency fitting coefficient of CLHS.

[0083] Substituting formula (6) into formula (5) can calculate the highest and lowest efficiency characteristic curves of the hydraulic mechanical compound transmission system in the main operating range, which are respectively as follows: Figure 6 , Figure 7 shown.

[0084] Depend on Figure 6 , Figure 7 It can be seen that within the main operating pressure range, the hydraulic-mechanical compound transmission system has better efficiency characteristics, which effectively makes up for the defects of low transmission efficiency and narrow high-efficiency zone of the torque converter.

[0085] The total efficiency of the hydraulic return type three-speed automatic transmission of the present invention can be expressed as

[0086] η PHAT =η HMCS η mn η c (7)

[0087] Where, ηmn is the transmission efficiency of the mechanical stepless transmission. ηc is the transmission efficiency of the reversing device.

[0088] In the first gear, the first brake 13 is engaged, and the second planetary gear and the third planetary gear together form an output coupling mechanical parallel mechanism. At this time, the transmission efficiency of the compound planetary gear shifting speed regulating device is

[0089]

[0090] Wherein, is2-p3 represents the ratio of the rotational speed of the second planetary gear sun gear 14 to the rotational speed of the third planetary gear planet carrier 19; represents the ratio of the rotational speed of the third planetary gear carrier 19 and the second planetary gear sun gear 14 relative to the third planetary gear sun gear 18; It is expressed as the ratio of the rotation speed of the third planetary gear carrier 19 and the third planetary gear ring 10 relative to the third planetary gear sun gear 18; It is expressed as the ratio of the speed of the third planetary gear carrier 19 and the second planetary gear sun gear 14 relative to the third planetary gear ring 20. It can be seen from the calculation that when the planetary gear characteristic constant k∈[1.5,4], ηm2≈0.97.

[0091] In the second gear, the second brake 21 is engaged, and the third planetary gear sun gear 18 is fixed. Power is input by the third planetary gear ring 20 and output by the third planetary gear carrier 19, and ηm2=0.98.

[0092] In the 3rd gear, the first clutch 24 is engaged, the third planetary gear is locked, and ηm3=1.

[0093] The second clutch 30 and the third brake 28 control the forward and reverse movement of the vehicle respectively, which can meet the working characteristics of the bulldozer that the reverse speed is greater than the forward speed. When the second clutch 30 is engaged, the fourth planetary gear is locked, and theoretically there is no power loss, ηc=1. This is conducive to further improving the transmission efficiency of the bulldozer.

[0094] The first planetary gear is a typical differential gear train, which plays a role in power convergence and diversion in the hydraulic reflux transmission device, and largely determines the performance of the system. The first planetary gear sun gear 10 is connected to the engine output shaft as one of the input elements of the first planetary gear, which is conducive to reducing the speed of each rotating element in the hydraulic reflux transmission device and improving the service life of the system. Under starting and load conditions, the hydraulic reflux transmission device of the present invention mainly operates in the reflux transmission mode (ε>0), the system needs to output a larger torque, and the third gear 8 has the same direction of rotation as the first planetary gear sun gear 10. It can be known from the transmission theory of the planetary gear train that at this time, the planet carrier is connected to the third gear 8 as another input element, and the hydraulic reflux transmission device will obtain a larger reduction ratio i 2, which can effectively reduce the system's upper displacement requirements for the fixed displacement hydraulic element (5) and the variable displacement hydraulic element (4), thereby saving costs. The hydraulic return transmission device uses the first planetary gear ring 12 as the output element, so that the hydraulic return transmission device has a speed ratio control range that is more convenient for bulldozer speed matching, which is beneficial to ensure that the planetary gear characteristic parameters of each planetary gear in the compound planetary gear shifting and speed regulating device are controlled between 2 and 3, which is convenient for production and assembly.

[0095] Depend on Figure 4 It can be seen that the power transmission relationship of the hydraulic reflux transmission device in the reflux transmission mode is:

[0096] |P e |+|P p1 |η g η P-M =|Ps1 (9)

[0097] Wherein, Pe is the engine input power, kW; Pp1 is the output power of the first planetary gear carrier 11, kW; Ps1 is the input power of the first planetary gear sun gear 10, kW.

[0098] According to the design theory of planetary gears, when the first planetary gear is an internal and external meshing single planetary gear, the power transmission relationship between the first planetary gear carrier 11 and the first planetary gear sun gear 10 is:

[0099]

[0100] Substituting formula (10) into formula (9) can calculate the low-speed torque increase coefficient K of the hydraulic reflow transmission device.

[0101]

[0102] Wherein, Te is the input torque of the hydraulic reflux transmission device, N; Tr1 is the output torque of the first planetary gear ring 12, N.

[0103] Due to the limitation of assembly space, in the vehicle transmission system, the transmission ratio of a single-stage external gear is generally not greater than 2.8 and not less than 0.6. Therefore, the numerical relationship between i1, i2 and k1 can be expressed as

[0104]

[0105] When ε∈[-1,1], ΔP∈[0,350], the maximum efficiency that the CLHS efficiency model shown in formula (6) can achieve is about 83.7%. Therefore, the maximum torque increase coefficient of the hydraulic return transmission device can be calculated as shown in Table 2.

[0106] Table 2 Maximum torque increase coefficient of hydraulic return transmission device

[0107]

[0108]

[0109] It can be seen from Table 2 that the maximum torque increase coefficient of the hydraulic return transmission device is not less than 7.65, which is far greater than the maximum torque increase coefficient of a general torque converter and can meet the power requirements of general engineering vehicles.

[0110] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A hydraulic reflux three-speed automatic transmission for a bulldozer, characterized in that: It includes a hydraulic reflux transmission device, a compound planetary gear shifting and speed regulating device and a reversing device connected in sequence; The hydraulic reflux transmission device comprises a first transmission shaft (1), a first gear (2), a second transmission shaft (3), a variable displacement hydraulic element (4), a fixed displacement hydraulic element (5), a third transmission shaft (6), a second gear (7), a third gear (8), a fourth gear (9), a first planetary row sun gear (10), a first planetary row planet carrier (11), a first planetary row ring gear (12), and a fourth transmission shaft (14); The compound planetary gear shifting and speed regulating device is composed of a first brake (13), a fourth transmission shaft (14), a second planetary row sun gear (15), a second planetary row planet carrier (16), a second planetary row ring gear (17), a third planetary row sun gear (18), a third planetary row planet carrier (19), a third planetary row ring gear (20), a second brake (21), a fifth transmission shaft (22), a large wheel hub (23), and a first clutch (24); The reversing device is composed of a fifth transmission shaft (22), a fourth planetary row sun gear (25), a fourth planetary row planet carrier (26), a fourth planetary row ring gear (27), a third brake (28), a small wheel hub (29), a second clutch (30), and a sixth transmission shaft (31).

2. A hydraulic reflux type three-speed automatic transmission for a bulldozer according to claim 1, characterized in that: The first transmission shaft (1) is the input shaft of the transmission, and the engine is directly connected to the first transmission shaft (1); the fourth gear (9) and the first planetary gear sun gear (10) are fixedly sleeved on the first transmission shaft (1); the third gear (8) is fixedly sleeved on the first planetary gear carrier (11); the first planetary gear ring (12) is fixedly sleeved on the fourth transmission shaft (14); the first gear (2) and the second gear (7) are respectively fixedly sleeved on the second transmission shaft (3) and the third transmission shaft (6); the drive shaft of the variable displacement hydraulic element (4) is fixedly connected to the second transmission shaft (3), and the drive shaft of the fixed displacement hydraulic element (5) is fixedly connected to the third transmission shaft (6).

3. A hydraulic reflux type three-speed automatic transmission for a bulldozer according to claim 2, characterized in that: The first transmission shaft (1), the second transmission shaft (3) and the third transmission shaft (6) are parallel to each other; the first gear (2) and the fourth gear (9) are meshed with each other; the second gear (7) and the third gear (8) are meshed with each other; the first planetary gear carrier (11) is loosely mounted on the first transmission shaft (1); and the fourth transmission shaft (14) serves as an output shaft of a hydraulic reflux transmission device to transmit power to a compound planetary gear shifting and speed regulating device.

4. The hydraulic reflux type three-speed automatic transmission for bulldozer according to claim 1, characterized in that: The second planetary gear (15) and the third planetary gear ring (20) are fixedly sleeved on the fourth transmission shaft (14); the third planetary gear carrier (19) and the large wheel hub (23) are fixedly sleeved on the fifth transmission shaft; the second planetary gear ring (17) is fixedly connected to the third planetary gear ring (18); in the actual transmission process, the rotation speeds of the second planetary gear ring (17) and the third planetary gear ring (18) are always the same; the rotating end of the first brake (13) is fixedly sleeved on the second planetary gear carrier (16), and the rotating end of the second brake (21) is fixedly sleeved on the second planetary gear ring (17), and the braking of the second planetary gear carrier (16) and the second planetary gear ring (17) can be achieved by the first brake (13) and the second brake (21) respectively; the two ends of the first clutch (24) are respectively fixedly sleeved The second planetary gear ring (17) and the large wheel hub (23) can be freely controlled to lock and separate with the first clutch (24); the fourth planetary gear ring (27) is fixedly sleeved on the fifth transmission shaft (22); the fourth planetary gear sun gear (25) and the small wheel hub (29) are fixedly sleeved on the sixth transmission shaft (31); the rotating end of the third brake (28) is fixedly connected to the fourth planetary gear carrier (26), and the fourth planetary gear carrier (26) can be braked by the third brake (28); the two ends of the second clutch (30) are respectively fixedly sleeved on the fourth planetary gear carrier (26) and the small wheel hub (29), and the locking and separation of the fourth planetary gear carrier (26) and the small wheel hub (29) can be freely controlled by the first clutch (30).

5. The hydraulic reflux type three-speed automatic transmission for bulldozer according to claim 2, characterized in that: The second transmission shaft (3) is fixedly connected to the drive shaft of the variable displacement hydraulic element (4) via a shaft sleeve; and the third transmission shaft (6) is fixedly connected to the drive shaft of the fixed displacement hydraulic element (5) via a shaft sleeve.

6. The hydraulic return type three-speed automatic transmission for bulldozer according to claim 4, characterized in that: The first brake (13), the second brake (21) and the third brake (28) are all wet brakes.

7. The hydraulic return type three-speed automatic transmission for bulldozer according to claim 4, characterized in that: The first clutch (24) and the second clutch (30) are both wet clutches.

8. A hydraulic reflux type three-speed automatic transmission for a bulldozer according to claim 2 or 3, characterized in that: The variable displacement hydraulic element (4) and the fixed displacement hydraulic element (5) are both axial piston hydraulic elements with a pump / motor dual working mode; the variable displacement hydraulic element (4) and the fixed displacement hydraulic element (5) form an axial piston pump-motor closed system, and the maximum control displacement of the variable displacement hydraulic element (4) is not less than the rated displacement of the fixed displacement hydraulic element (5).

9. The shifting method of a hydraulic reflux type three-speed automatic transmission for a bulldozer according to claim 4, characterized in that: The second clutch (30) and the third brake (28) respectively control the forward movement and the reverse movement of the vehicle; When the third brake (28) is closed, the fourth planetary gear carrier (26) is fixed, and the rotational speeds of the fourth planetary gear sun gear (25) and the fourth planetary gear ring (27) are opposite; when the second clutch (30) is engaged, the fourth planetary gear sun gear (25) and the fourth planetary gear carrier (26) are rigidly connected, and the fourth planetary gear is in a locked state. When the first brake (13) is closed, the transmission operates in the first gear, and the system speed ratio of the transmission is Where i1 and i2 are the transmission ratios of the fixed axis gears i1 and i2 respectively, and k1, k2 and k3 are the characteristic constants of the first, second and third planetary gears respectively; When the second brake (21) is closed, the transmission operates in the second gear, and the system speed ratio of the transmission is When the first clutch (24) is engaged, the transmission operates in the third gear, and the system speed ratio of the transmission is

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