Small step ratio reduction composite planetary gear set

Abstract

The application discloses a small-step-ratio deceleration composite planetary gear train, which comprises a shell, an input component, an output component, a first planetary gear train, a second planetary gear train, a first brake, a second brake, a first clutch and a second clutch. The first planetary gear train and the second planetary gear train are coaxially arranged. The input component is coaxially connected with a first ring gear. The output component is coaxially connected with a first carrier. A first sun gear is coaxially connected with a second carrier. One end of the first brake is fixedly connected with the shell, and the other end is connected with a second sun gear. One end of the first clutch is connected with the second sun gear, and the other end is connected with the first ring gear. One end of the second brake is fixedly connected with the shell, and the other end is connected with a second ring gear. One end of the second clutch is connected with the second ring gear, and the other end is connected with the output component. The application can transmit a smaller deceleration ratio.

Description

Technical Field

[0001] This invention belongs to the field of planetary transmission technology, specifically relating to a small-ratio speed reduction composite planetary gearbox. Background Technology

[0002] A traditional planetary gear set consists of a sun gear, a ring gear, and a set of planet gears. Traditional planetary gear sets can be used to form automatic or semi-automatic transmissions. Ordinary transmissions usually consist of multiple sets of planetary gears, a wet clutch, and a torque converter.

[0003] The primary function of a vehicle's transmission is to enable speed changes during driving. Traditional vehicle transmissions typically have gear ratios (the ratio between each gear; for example, if the first gear ratio is 6 and the second gear ratio is 4, then the gear ratio is 6 / 4 = 1.5) between 1.5 and 3. This large gear ratio necessitates the use of a torque converter in the transmission design to buffer the speed and torque changes during gear shifts, preventing damage to the engine or transmission mechanism due to high speed differences. Especially during vehicle start-up, a torque converter is often used to achieve a smooth start, providing a flexible connection between the engine and transmission to cushion the vibrations and shocks caused by changes in engine speed and torque. However, torque converters also reduce efficiency, consume engine power, and increase the power required for cooling.

[0004] Therefore, without adding a hydraulic torque converter, the traditional planetary gear set has too large a step ratio and cannot adapt to the slow changes in vehicle speed. In order to adapt to the speed changes of the transmission, it is urgent to design a small step ratio multi-gear reduction compound planetary gear set. Summary of the Invention

[0005] In view of this, the present invention provides a small-order-ratio deceleration composite planetary gearbox that can transmit a smaller reduction ratio.

[0006] This invention is achieved through the following technical solution:

[0007] A small-ratio speed reduction compound planetary gearbox includes: a housing, an input component, an output component, a first planetary gearbox, a second planetary gearbox, a first brake, a second brake, a first clutch, and a second clutch;

[0008] The first planetary gear set includes: a first gear ring, a first planet carrier, and a first sun gear; the second planetary gear set includes: a second sun gear, a second gear ring, and a second planet carrier.

[0009] The first and second planetary gear sets are arranged coaxially; the input component is coaxially connected to the first gear ring; the output component is coaxially connected to the first planetary carrier, and the first sun gear is coaxially connected to the second planetary carrier.

[0010] One end of the first brake is fixed to the housing, and the other end is connected to the second sun gear; when the first brake is engaged, the second sun gear is connected to the housing, and the second sun gear is braked.

[0011] One end of the first clutch is connected to the second sun gear, and the other end is connected to the first gear ring; when the first clutch is engaged, the second sun gear is connected to the first gear ring, that is, the second sun gear is connected to the input component;

[0012] One end of the second brake is fixed to the housing, and the other end is connected to the second gear ring; when the second brake is engaged, the second gear ring is connected to the housing, and brakes the second gear ring.

[0013] One end of the second clutch is connected to the second gear ring, and the other end is connected to the output component; when the second clutch is engaged, the second gear ring is connected to the output component, that is, the second gear ring is connected to the first planetary carrier.

[0014] Furthermore, by controlling the engagement or disengagement of the first brake, the second brake, the first clutch, and the second clutch, eight different operating conditions can be combined to obtain eight different transmission ratios.

[0015] The eight operating conditions are as follows:

[0016] The first brake and the second brake are engaged, and the first clutch and the second clutch are disengaged;

[0017] The first clutch and the second brake engage; the first brake and the second clutch disengage.

[0018] The first brake and the second clutch engage; the first clutch and the second brake disengage.

[0019] The first clutch and the second clutch are engaged, and the first brake and the second brake are disengaged;

[0020] The first brake and the first clutch are engaged, and the second brake and the second clutch are disengaged;

[0021] The second brake and the second clutch engage, while the first brake and the first clutch disengage;

[0022] The first brake, the second brake, the first clutch, and the second clutch are all disengaged;

[0023] The first brake, the second brake, the first clutch, and the second clutch are all engaged.

[0024] Furthermore, under the condition that the first and second brakes are engaged and the first and second clutches are disengaged:

[0025] The second sun gear is connected to the housing via the first brake, therefore its rotational speed ω6 is 0. The second ring gear is connected to the housing via the second brake, therefore its rotational speed ω7 is 0. Let R1 be the ratio of the number of teeth on the first sun gear to the number of teeth on the first ring gear. The formula for calculating the transmission ratio Kt1 of the compound planetary gear set under this condition is as follows:

[0026] Under these conditions, ω6 = 0 and ω7 = 0, therefore the rotational speed of the second planetary carrier is ω8 = 0 and the rotational speed of the first sun gear is ω5 = 0.

[0027] Then the transmission ratio i from the first balcony wheel to the first gear ring is 4 53 for:

[0028] i 4 53 =(ω 5- ω4) / (ω 3- ω4)=-1 / R1 formula (1)

[0029] Since ω5 = 0, the rotational speed of the first planetary carrier ω4 = the rotational speed of the output component ω2, and the rotational speed of the first gear ring ω3 = the rotational speed of the output component ω1, then formula (1) can be converted to:

[0030] i 4 53 =(0-ω2) / (ω1-ω2)=-1 / R1 formula (2)

[0031] Substituting Kt1=ω1 / ω2 into formula (2), we get:

[0032] (0-1) / (K t1 -1)=-1 / R1 Formula (3) is transformed to finally obtain K t1 =1+R1.

[0033] Furthermore, under the operating conditions of the first clutch and the second brake being engaged, and the first brake and the second clutch being disengaged:

[0034] The second sun gear is connected to the first ring gear via the first clutch, therefore the rotational speed ω6 of the second sun gear is the same as the rotational speed ω3 of the first ring gear. The second ring gear is connected to the housing via the second brake, therefore the rotational speed ω7 of the second ring gear is 0. Let R1 be the ratio of the number of teeth of the first sun gear to the number of teeth of the first ring gear, and R2 be the ratio of the number of teeth of the second sun gear to the number of teeth of the second ring gear. The formula for calculating the transmission ratio Kt2 of the compound planetary gear set under this condition is as follows:

[0035] Under these conditions: ω6=ω3, ω7=0;

[0036] Then the transmission ratio i from the first balcony wheel to the first gear ring is4 53 for:

[0037] i 4 53 =(ω 5- ω4) / (ω 3- ω4)=-1 / R1 formula (1)

[0038] Since ω3 = ω1 and ω4 = ω2, formula (1) can be transformed into:

[0039] i 4 53 =(ω5-ω2) / (ω1-ω2)=-1 / R1 formula (4)

[0040] The transmission ratio i from the second sun gear to the second ring gear is... 8 67 for:

[0041] i 8 67 =(ω 6- ω8) / (ω 7- ω8)=-1 / R2 formula (5)

[0042] Since ω6=ω3=ω1, ω8=ω5, ω7=0, formula (5) can be converted to:

[0043] i 8 67 =(ω1-ω5) / (0-ω5)=-1 / R2 formula (6)

[0044] Combining formulas (4) and (6), we can obtain:

[0045] ω5=ω1R2 / (1+R2) Formula (7)

[0046] Substituting Kt2=ω1 / ω2 and formula (7) into formulas (4) and (6) respectively, the final calculation yields K t2 =(1+R1+R2+R1R2) / (1+R2+R1R2).

[0047] Furthermore, under the operating conditions of the first brake and the second clutch engaged, and the first clutch and the second brake disengaged:

[0048] The second sun gear is connected to the housing via the first brake, therefore its rotational speed ω6 is 0. The second ring gear is connected to the first planetary carrier via the second clutch, therefore its rotational speed ω7 is the same as the rotational speed ω4 of the first planetary carrier. Let R1 be the ratio of the number of teeth on the first sun gear to the number of teeth on the first ring gear, and R2 be the ratio of the number of teeth on the second sun gear to the number of teeth on the second ring gear. The formula for calculating the transmission ratio Kt3 of the compound planetary gear set under this condition is as follows:

[0049] Under these conditions: ω6=0, ω7=ω4;

[0050] Then the transmission ratio i from the first balcony wheel to the first gear ring is 4 53 for:

[0051] i 4 53 =(ω 5- ω4) / (ω 3- ω4)=-1 / R1 formula (1)

[0052] Since ω4=ω2 and ω3=ω1, formula (1) can be transformed into:

[0053] i 4 53 =(ω5-ω2) / (ω1-ω2)=-1 / R1 formula (4)

[0054] The transmission ratio i from the second sun gear to the second ring gear is... 8 67 for:

[0055] i 8 67 =(ω 6- ω8) / (ω 7- ω8)=-1 / R2 formula (5)

[0056] Since ω6=0, ω8=ω5, ω7=ω4=ω2, formula (5) can be converted to:

[0057] i 8 67 =(0-ω5) / (ω2-ω5)=-1 / R2 Formula (8)

[0058] Combining formulas (4) and (8), we can obtain:

[0059] ω5=ω2 / (1+R2) Formula (9)

[0060] Substituting Kt3=ω1 / ω2 and formula (9) into formulas (4) and (8) respectively, the final calculation yields K t3 = (1+R2+R1R2) / (1+R2).

[0061] Furthermore, under the condition that the first and second clutches are engaged and the first and second brakes are disengaged:

[0062] The second sun gear is connected to the first ring gear via the first clutch, therefore the rotational speed ω6 of the second sun gear is the same as the rotational speed ω3 of the first ring gear. The second ring gear is connected to the first planetary carrier via the second clutch, therefore the rotational speed ω7 of the second ring gear is the same as the rotational speed ω4 of the first planetary carrier. That is, ω8 = ω5, ω7 = ω4 = ω2.

[0063] ω6=ω3=ω1, the formula for calculating the transmission ratio Kt3 of the compound planetary gearbox under this working condition is as follows:

[0064] Under this operating condition: ω6=ω1, ω7=ω2

[0065] i 4 53 =(ω5-ω4) / (ω3-ω4)=(ω5-ω2) / (ω1-ω2)=-1 / R1

[0066] i 8 67 =(ω 6- ω8) / (ω 7- ω8)=(ω1-ω5) / (ω2-ω5)=-1 / R2

[0067] From the above formula, we can obtain: ω5=(R2ω1+ω2) / (1+R2)

[0068] Furthermore, the transmission ratio Kt4 = 1.

[0069] Beneficial effects:

[0070] (1) This invention provides a small-ratio reduction compound planetary gear set, which can transmit a small reduction ratio, wherein the geometric reduction value X of the transmission ratio is between 1.05 and 1.15, that is, the transmission ratio of the compound planetary gear set can decrease within this range. By using this compound planetary gear set, the rotational speed can be continuously varied within a small speed ratio range, increasing the number of gears in the transmission, allowing the vehicle speed to change slowly during the starting phase, and eliminating the need for a hydraulic torque converter in the design of the vehicle transmission. This is of great significance for the research and development of future high-speed and high-efficiency transmission mechanisms.

[0071] (2) The present invention provides a small-scale reduction compound planetary gear set, which uses two simple planetary gear sets, two clutches and two brakes. By separating and combining different clutches and brakes, eight different motion forms can be combined to obtain eight different transmission ratios. By switching the transmission ratio of this reduction scale, the vehicle can have a small change in speed and torque when shifting gears, thereby reducing vibration and impact during shifting gears, and thus reducing dependence on hydraulic torque converter.

[0072] (3) By calculating the transmission ratio under different working conditions, the present invention can obtain at least four different decreasing transmission ratios, and the torque of the input component and the output component can also be multiplied, with the transmission ratio close to 1, and the four transmission ratios form a geometric series close to 1.

[0073] In summary, this invention achieves multi-row functionality using only a small number of simple planetary gear sets. Furthermore, by employing traditional planetary gears instead of double internal meshing gears, it achieves multi-row functionality, resulting in higher manufacturing costs and greater manufacturability. The kinematic chain of this invention can be opened and closed at will, and the transmission ratio can be controlled automatically, thereby minimizing clutch wear and increasing service life. Attached Figure Description

[0074] Fig. 1 A simplified diagram of the speed-up design of this invention;

[0075] Fig. 2 This is a diagram illustrating the speed-up design model of the present invention;

[0076] Fig. 3 A three-dimensional model diagram for the speed increase of this invention;

[0077] Wherein, 1-input component, 2-output component, 3-first gear ring, 4-first planetary carrier, 5-first sun gear, 6-second sun gear, 7-second gear ring, 8-second planetary carrier, 9-first brake, 10-second brake, 11-first clutch, 12-second clutch, 13-housing. Detailed Implementation

[0078] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0079] This embodiment provides a small-order-ratio deceleration composite planetary gearbox; see appendix. Figs. 1-3 It includes: housing 13, input component 1, output component 2, two simple planetary gear sets, two clutches and two brakes;

[0080] The two simple planetary gear sets are a first planetary gear set and a second planetary gear set; the first planetary gear set includes: a first gear ring 3, a first planet carrier 4, and a first sun gear 5; the second planetary gear set includes: a second sun gear 6, a second gear ring 7, and a second planet carrier 8.

[0081] The two brakes are the first brake 9 (abbreviated as B1) and the second brake 10 (abbreviated as B2);

[0082] The two clutches are the first clutch 11 (abbreviated as C1) and the second clutch 12 (abbreviated as C2);

[0083] The overall connection relationship of the composite planetary set is as follows:

[0084] The first planetary gear set and the second planetary gear set are arranged coaxially; the input component 1 is coaxially connected to the first gear ring 3; the output component 2 is coaxially connected to the first planetary carrier 4; and the first sun gear 5 is coaxially connected to the second planetary carrier 8.

[0085] One end of the first brake 9 is fixedly connected to the housing 13, and the other end is connected to the second sun gear 6. When the first brake 9 is engaged, the second sun gear 6 is connected to the housing 13, thereby achieving braking of the second sun gear 6.

[0086] One end of the first clutch 11 is connected to the second sun gear 6, and the other end is connected to the first gear ring 3. When the first clutch 11 is engaged, the second sun gear 6 is connected to the first gear ring 3, that is, the second sun gear 6 is connected to the input component 1.

[0087] One end of the second brake 10 is fixedly connected to the housing 13, and the other end is connected to the second gear ring 7. When the second brake 10 is engaged, the second gear ring 7 is connected to the housing 13, thereby achieving braking of the second gear ring 7.

[0088] One end of the second clutch 12 is connected to the second gear ring 7, and the other end is connected to the output component 2. When the second clutch 12 is engaged, the second gear ring 7 is connected to the output component 2, that is, the second gear ring 7 is connected to the first planetary carrier 4.

[0089] Both clutches can be hydraulic clutches, independently controlling each simple planetary gear set, or they can be interactive clutches, allowing one clutch to engage while the other disengages.

[0090] Working principle: The transmission ratio Ki of each simple planetary gear set is defined as the ratio of the number of teeth on the ring gear to the number of teeth on the sun gear. The transmission ratio Kt of the entire compound planetary gear set is defined as the ratio of the input speed to the output speed, Kt = Vinput / Voutput. Two clutches and two brakes, as motion control elements, are defined as elements that restrict one degree of freedom of the system and make its motion state controllable. Utilizing this kinematic configuration, by combining control elements, a compound planetary gear set with proportionally decreasing transmission ratios is obtained. The transmission ratio is controlled by the control elements. From the transmission ratios K1 and K2 of the two simple planetary gear sets, by adjusting appropriate values ​​of K1 and K2, the geometrically decreasing transmission ratio Kt of the compound planetary gear set can be obtained, with a geometric reduction value of X.

[0091] In the reducer configuration, the input of the compound planetary gear set is the first ring gear 3 connected to the input component 1, and the output is the first planet carrier 4 connected to the output component 2. The first sun gear 5 is connected to the second planet carrier 8. The second sun gear 6 and the second ring gear 7 are both controlled by motion control elements. When the first brake 9 is applied, the second sun gear 6 is braked. When the first clutch 11 is engaged, the second sun gear 6 is connected to the input component 1. When the second brake 10 is engaged, the second ring gear 7 is braked. When the second clutch 12 is engaged, the second ring gear 7 is connected to the output component 2. The specific control logic table is shown in the table below:

[0092]

[0093]

[0094] As can be seen from the table above,

[0095] ④ Under condition Kt1: The second sun gear 6 is connected to the housing 13 via the first brake 9, therefore the rotational speed ω6 of the second sun gear 6 is 0. The second ring gear 7 is also connected to the housing 13 via the second brake 10, therefore the rotational speed ω7 of the second ring gear 7 is also 0. Let R1 be the ratio obtained by dividing the number of teeth of the first sun gear 5 by the number of teeth of the first ring gear 3. The formula for calculating the transmission ratio Kt1 of the compound planetary gear set under this condition is as follows:

[0096] Since under this operating condition: ω6=0, ω7=0, then the rotational speed of the second planetary carrier 8 is ω8=0, and the rotational speed of the first sun gear 5 is ω5=0;

[0097] The transmission ratio i from the first balcony wheel 5 to the first gear ring 3 is... 4 53 for:

[0098] i 4 53 =(ω 5- ω4) / (ω 3- ω4)=-1 / R1 formula (1)

[0099] Since ω5 = 0, the rotational speed ω4 of the first planetary carrier 4 is equal to the rotational speed ω2 of the output component 2, and the rotational speed ω3 of the first gear ring 3 is equal to the rotational speed ω1 of the output component 1, then formula (1) can be converted to:

[0100] i 4 53 =(0-ω2) / (ω1-ω2)=-1 / R1 formula (2)

[0101] Substituting Kt1=ω1 / ω2 into formula (2), we get:

[0102] (0-1) / (K t1 -1)=-1 / R1 Formula (3) is transformed to finally obtain K t1 =1+R1;

[0103] ② Under condition Kt2: The second sun gear 6 is connected to the first ring gear 3 via the first clutch 11, therefore the rotational speed ω6 of the second sun gear 6 is the same as the rotational speed ω3 of the first ring gear 3. The second ring gear 7 is connected to the housing 13 via the second brake 10, therefore the rotational speed ω7 of the second ring gear 7 is 0. Let R1 be the ratio of the number of teeth of the first sun gear 5 to the number of teeth of the first ring gear 3, and R2 be the ratio of the number of teeth of the second sun gear 6 to the number of teeth of the second ring gear 3. The formula for calculating the transmission ratio Kt2 of the compound planetary gear set under this condition is as follows:

[0104] Under these conditions: ω6=ω3, ω7=0;

[0105] The transmission ratio i from the first balcony wheel 5 to the first gear ring 3 is... 4 53 for:

[0106] i 4 53 =(ω 5- ω4) / (ω 3- ω4)=-1 / R1 formula (1)

[0107] Since ω3 = ω1 and ω4 = ω2, formula (1) can be transformed into:

[0108] i 4 53 =(ω5-ω2) / (ω1-ω2)=-1 / R1 formula (4)

[0109] The transmission ratio i from the second sun gear 6 to the second ring gear 7 is... 8 67 for:

[0110] i 8 67 =(ω 6- ω8) / (ω7- ω8)=-1 / R2 formula (5)

[0111] Since ω6=ω3=ω1, ω8=ω5, ω7=0, formula (5) can be converted to:

[0112] i 8 67 =(ω1-ω5) / (0-ω5)=-1 / R2 formula (6)

[0113] Combining formulas (4) and (6), we can obtain:

[0114] ω5=ω1R2 / (1+R2) Formula (7)

[0115] Substituting Kt2=ω1 / ω2 and formula (7) into formulas (4) and (6) respectively, the final calculation yields K t2 =(1+R1+R2+R1R2) / (1+R2+R1R2);

[0116] ③ Under condition Kt3: The second sun gear 6 is connected to the housing 13 via the first brake 9, therefore the rotational speed ω6 of the second sun gear 6 is 0. The second ring gear 7 is connected to the first planetary carrier 4 via the second clutch 12, therefore the rotational speed ω7 of the second ring gear 7 is the same as the rotational speed ω4 of the first planetary carrier 4. Let R1 be the ratio of the number of teeth of the first sun gear 5 to the number of teeth of the first ring gear 3, and R2 be the ratio of the number of teeth of the second sun gear 6 to the number of teeth of the second ring gear 3. The calculation formula for the transmission ratio Kt3 of the compound planetary gear set under this condition is as follows:

[0117] Under these conditions: ω6=0, ω7=ω4;

[0118] The transmission ratio i from the first balcony wheel 5 to the first gear ring 3 is... 4 53 for:

[0119] i 4 53 =(ω 5- ω4) / (ω 3- ω4)=-1 / R1 formula (1)

[0120] Since ω4=ω2 and ω3=ω1, formula (1) can be transformed into:

[0121] i 4 53 =(ω5-ω2) / (ω1-ω2)=-1 / R1 formula (4)

[0122] The transmission ratio i from the second sun gear 6 to the second ring gear 7 is... 8 67 for:

[0123] i 8 67 =(ω 6- ω8) / (ω 7- ω8)=-1 / R2 formula (5)

[0124] Since ω6=0, ω8=ω5, ω7=ω4=ω2, formula (5) can be converted to:

[0125] i 8 67 =(0-ω5) / (ω2-ω5)=-1 / R2 Formula (8)

[0126] Combining formulas (4) and (8), we can obtain:

[0127] ω5=ω2 / (1+R2) Formula (9)

[0128] Substituting Kt3=ω1 / ω2 and formula (9) into formulas (4) and (8) respectively, the final calculation yields K t3 = (1+R2+R1R2) / (1+R2);

[0129] ④ Under Kt4 operating condition: The second sun gear 6 is connected to the first ring gear 3 through the first clutch 11, so the speed ω6 of the second sun gear 6 is the same as the speed ω3 of the first ring gear 3. The second ring gear 7 is connected to the first planetary carrier 4 through the second clutch 12, so the speed ω7 of the second ring gear 7 is the same as the speed ω4 of the first planetary carrier 4. That is, ω8=ω5, ω7=ω4=ω2, ω6=ω3=ω1. The calculation formula for the transmission ratio Kt3 of the compound planetary gear set under this operating condition is as follows:

[0130] Under this operating condition: ω6=ω1, ω7=ω2

[0131] i 4 53 =(ω5-ω4) / (ω3-ω4)=(ω5-ω2) / (ω1-ω2)=-1 / R1

[0132] i 8 67 =(ω 6- ω8) / (ω 7- ω8)=(ω1-ω5) / (ω2-ω5)=-1 / R2

[0133] From the above formula, we can obtain: ω5=(R2ω1+ω2) / (1+R2)

[0134] Furthermore, with a transmission ratio of Kt4 = 1, the compound planetary gear set undergoes overall rotation;

[0135] ⑤ Under Kt5-Kt8 conditions: There is no practical application value, but it can supplement the use of this embodiment under certain conditions, such as when the kinematic chain is fully opened or closed.

[0136] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A small-order-ratio deceleration composite planetary gearbox, characterized in that, include: Housing, input component, output component, first planetary gear set, second planetary gear set, first brake, second brake, first clutch, and second clutch; The first planetary gear set includes: a first gear ring, a first planet carrier, and a first sun gear; the second planetary gear set includes: a second sun gear, a second gear ring, and a second planet carrier. The first and second planetary gear sets are arranged coaxially; the input component is coaxially connected to the first gear ring; the output component is coaxially connected to the first planetary carrier, and the first sun gear is coaxially connected to the second planetary carrier. One end of the first brake is fixed to the housing, and the other end is connected to the second sun gear; when the first brake is engaged, the second sun gear is connected to the housing, and the second sun gear is braked. One end of the first clutch is connected to the second sun gear, and the other end is connected to the first gear ring; when the first clutch is engaged, the second sun gear is connected to the first gear ring, that is, the second sun gear is connected to the input component; One end of the second brake is fixed to the housing, and the other end is connected to the second gear ring; when the second brake is engaged, the second gear ring is connected to the housing, and brakes the second gear ring. One end of the second clutch is connected to the second gear ring, and the other end is connected to the output component; when the second clutch is engaged, the second gear ring is connected to the output component, that is, the second gear ring is connected to the first planetary carrier.

2. The small-order-ratio deceleration composite planetary gearbox as described in claim 1, characterized in that, By controlling the engagement or disengagement of the first brake, the second brake, the first clutch, and the second clutch, eight different operating conditions can be combined to obtain eight different transmission ratios. The eight operating conditions are as follows: The first brake and the second brake are engaged, and the first clutch and the second clutch are disengaged; The first clutch and the second brake engage; the first brake and the second clutch disengage. The first brake and the second clutch engage; the first clutch and the second brake disengage. The first clutch and the second clutch are engaged, and the first brake and the second brake are disengaged; The first brake and the first clutch are engaged, and the second brake and the second clutch are disengaged; The second brake and the second clutch engage, while the first brake and the first clutch disengage; The first brake, the second brake, the first clutch, and the second clutch are all disengaged; The first brake, the second brake, the first clutch, and the second clutch are all engaged.

3. A small-order-ratio deceleration composite planetary gearbox as described in claim 1 or 2, characterized in that, Under the condition that the first and second brakes are engaged and the first and second clutches are disengaged: The second sun gear is connected to the housing via the first brake, therefore its rotational speed ω6 is 0. The second ring gear is connected to the housing via the second brake, therefore its rotational speed ω7 is 0. Let R1 be the ratio of the number of teeth on the first sun gear to the number of teeth on the first ring gear. The formula for calculating the transmission ratio Kt1 of the compound planetary gear set under this condition is as follows: Under these conditions, ω6 = 0 and ω7 = 0, therefore the rotational speed of the second planetary carrier is ω8 = 0 and the rotational speed of the first sun gear is ω5 = 0. Then the transmission ratio i from the first balcony wheel to the first gear ring 4 53 for: i 4 53 =(ω5 - ω4) / (ω3 - ω4)= -1 / R1 Formula (1) Since ω5 = 0, the rotational speed of the first planetary carrier ω4 = the rotational speed of the output component ω2, and the rotational speed of the first gear ring ω3 = the rotational speed of the output component ω1, then formula (1) can be converted to: i 4 53 = (0 - ω2) / (ω1 - ω2) = -1 / R1 formula (2) Substituting Kt1=ω1 / ω2 into formula (2), we get: (0-1) / (K t1 -1)=-1 / R1 Formula (3) is transformed to finally obtain K t1 =1+R1.

4. A small-order-ratio deceleration composite planetary gearbox as described in claim 1 or 2, characterized in that, Under the condition that the first clutch and the second brake are engaged, and the first brake and the second clutch are disengaged: The second sun gear is connected to the first ring gear via the first clutch, therefore the rotational speed ω6 of the second sun gear is the same as the rotational speed ω3 of the first ring gear. The second ring gear is connected to the housing via the second brake, therefore the rotational speed ω7 of the second ring gear is 0. Let R1 be the ratio of the number of teeth of the first sun gear to the number of teeth of the first ring gear, and R2 be the ratio of the number of teeth of the second sun gear to the number of teeth of the second ring gear. The formula for calculating the transmission ratio Kt2 of the compound planetary gear set under this condition is as follows: Under these conditions: ω6=ω3, ω7=0; Then the transmission ratio i from the first balcony wheel to the first gear ring is 4 53 for: i 4 53 =(ω5 - ω4) / (ω3 - ω4)= -1 / R1 Formula (1) Since ω3 = ω1 and ω4 = ω2, formula (1) can be transformed into: i 4 53 =(ω5 - ω2) / (ω1 - ω2)= -1 / R1 Formula (4) The transmission ratio i from the second sun gear to the second ring gear is... 8 67 for: i 8 67 =(ω6 - ω8) / (ω7 - ω8)= -1 / R2 Formula (5) Since ω6=ω3=ω1, ω8=ω5, ω7=0, formula (5) can be converted to: i 8 67 =(ω1-ω5) / (0-ω5)=-1 / R2 formula (6) Combining formulas (4) and (6), we can obtain: ω5=ω1R2 / (1+R2) Formula (7) Substituting Kt2=ω1 / ω2 and formula (7) into formulas (4) and (6) respectively, the final calculation yields K t2 =(1+R1+R2+R1R2) / (1+R2+R1R2).

5. A small-order-ratio deceleration composite planetary gearbox as described in claim 1 or 2, characterized in that, Under the condition that the first brake and the second clutch are engaged, and the first clutch and the second brake are disengaged: The second sun gear is connected to the housing via the first brake, therefore its rotational speed ω6 is 0. The second ring gear is connected to the first planetary carrier via the second clutch, therefore its rotational speed ω7 is the same as the rotational speed ω4 of the first planetary carrier. Let R1 be the ratio of the number of teeth on the first sun gear to the number of teeth on the first ring gear, and R2 be the ratio of the number of teeth on the second sun gear to the number of teeth on the second ring gear. The formula for calculating the transmission ratio Kt3 of the compound planetary gear set under this condition is as follows: Under these conditions: ω6=0, ω7=ω4; Then the transmission ratio i from the first balcony wheel to the first gear ring 4 53 for: i 4 53 =(ω5 - ω4) / (ω3 - ω4)= -1 / R1 Formula (1) Since ω4=ω2 and ω3=ω1, formula (1) can be transformed into: i 4 53 =(ω5 - ω2) / (ω1 - ω2)= -1 / R1 Formula (4) The transmission ratio i from the second sun gear to the second ring gear is... 8 67 for: i 8 67 =(ω6 - ω8) / (ω7 - ω8)= -1 / R2 Formula (5) Since ω6=0, ω8=ω5, ω7=ω4=ω2, formula (5) can be converted to: i 8 67 =(0-ω5) / (ω2-ω5)=-1 / R2 Formula (8) Combining formulas (4) and (8), we can obtain: ω5=ω2 / (1+R2) Formula (9) Substituting Kt3=ω1 / ω2 and formula (9) into formulas (4) and (8) respectively, the final calculation yields K t3 = (1+R2+R1R2) / (1+R2).

6. A small-order-ratio deceleration composite planetary gearbox as described in claim 1 or 2, characterized in that, Under the condition that the first and second clutches are engaged and the first and second brakes are disengaged: The second sun gear is connected to the first ring gear via the first clutch, therefore the rotational speed ω6 of the second sun gear is the same as the rotational speed ω3 of the first ring gear. The second ring gear is connected to the first planetary carrier via the second clutch, therefore the rotational speed ω7 of the second ring gear is the same as the rotational speed ω4 of the first planetary carrier. That is, ω8 = ω5, ω7 = ω4 = ω2, ω6 = ω3 = ω1. The formula for calculating the transmission ratio Kt3 of the compound planetary gear set under this condition is as follows: Under this operating condition: ω6=ω1, ω7=ω2 I 4 53 =(ω5-ω4) / (ω3-ω4)=(ω5-ω2) / (ω1-ω2)=-1 / R1 I 8 67 =(ω6-ω8) / (ω7-ω8)=(ω1-ω5) / (ω2-ω5)=-1 / R2 From the above formula, we can obtain: ω5=(R2ω1+ω2) / (1+R2). Further, we can obtain that the transmission ratio Kt4=1.

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