Lock-up Clutch for Power-Split Hybrid Transmission

Abstract

A power transmission system includes a first planetary gear set configured to establish a fixed linear speed relationship among a first rotor, an engine crankshaft, and a second rotor. The power transmission system further includes a gear drive assembly configured to alternately and selectively establish a plurality of proportional speed relationships between the second rotor and an output shaft. The gear drive assembly further includes a second planetary gear set having a lock-up clutch configured to selectively couple two rotatable elements of the second planetary gear set.

Description

Technical Field

[0001] The present disclosure relates to the field of automatic transmissions for motor vehicles. More specifically, the present disclosure relates to the arrangement of gears, clutches, motors, and their interconnection in a power transmission. Background Art

[0002] Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse motion. However, certain types of engines are only capable of operating effectively within a narrow speed range. Therefore, transmissions that can efficiently transmit power at various gear ratios are frequently employed. When the vehicle is at low speed, the transmission typically operates at a high gear ratio, so that it multiplies the engine torque, thereby increasing acceleration. At high vehicle speeds, operating the transmission at a low gear ratio allows the engine speed to be associated with a quiet, fuel-efficient cruise. Generally, a transmission has a housing mounted to the vehicle structure, an input typically driven by an engine crankshaft via a launch device such as a torque converter, and an output that typically drives the wheels via a differential assembly that allows the left and right wheels to rotate at slightly different speeds when the vehicle turns. In a front-wheel drive vehicle with a transversely mounted engine, the engine crankshaft axis is typically offset from the axle axis.

[0003] Hybrid electric transmissions further reduce fuel consumption by including one or more reversible electric motors and some type of electrical energy storage device such as a battery. Hybrid electric transmissions improve fuel efficiency in several ways. Most internal combustion engines are most efficient when operating at a relatively high power setting. A hybrid electric transmission allows the engine portion to be operated at a higher power level than is required for propulsion for part of the time, while storing the excess power in the battery. Then, at other times, the engine is turned off and the stored energy is used to propel the vehicle. Although the engine generates the same total amount of energy, it operates at a higher average efficiency. Also, when the brakes are applied, the reversible electric motor can capture the vehicle's kinetic energy and store it in the battery for later use in propulsion. When the vehicle is stationary and thus no propulsion is required, the engine can be turned off to eliminate the fuel that would otherwise be used to maintain the idle speed. The electric motor provides the ability to propel the vehicle with the engine off and to quickly restart the engine if necessary. Summary of the Invention

[0004] In at least one method, a power transmission system is provided. The power transmission system may include a first planetary gear set configured to establish a fixed linear speed relationship among a first rotor, an engine crankshaft, and a second rotor. The power transmission system may further include a gear transmission assembly configured to alternately and selectively establish a plurality of proportional speed relationships between the second rotor and an output shaft. The gear transmission assembly may further include a second planetary gear set having a lock-up clutch configured to selectively couple two rotatable elements of the second planetary gear set. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 is a schematic diagram of a power split power transmission system.

[0006] Figure 2 is a schematic diagram of a power split power transmission system including a lock-up clutch.

[0007] Figure 3 is a schematic diagram of a first transmission gear drive.

[0008] Figure 4 is a schematic diagram of a second transmission gear drive. DETAILED DESCRIPTION

[0009] Embodiments of the present disclosure are described herein. However, it is to be understood that the disclosed embodiments are merely examples and other embodiments may take various forms and alternative forms. The drawings are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Accordingly, the specific structural and functional details disclosed herein are not to be construed as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As will be understood by one of ordinary skill in the art, the various features illustrated and described with reference to any one of the drawings may be combined with features shown in one or more other drawings to produce embodiments not explicitly shown or described. Combinations of the illustrated features provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for a particular application or implementation.

[0010] If a set of rotating elements is constrained to rotate about the same axis at the same speed under all operating conditions, they are fixedly coupled to each other. The rotating elements can be fixedly coupled by means of a splined connection, welding, press fitting, being machined from a common solid, or other means. Slight variations in rotational displacement may occur between fixedly coupled elements, such as displacements due to clearance or shaft flexibility. One or more rotating elements that are all fixedly coupled to each other can be referred to as a shaft. In contrast, when a shift element constrains two rotating elements to rotate about the same axis at the same speed whenever it is fully engaged, and they have different rotational speeds about that axis in at least some other operating conditions, the two rotating elements are selectively coupled by the shift element. If there is a fixed ratio speed relationship between two rotatable elements, they are drivingly connected or coupled.

[0011] A shift element that holds a rotating element stationary by selectively coupling it to a fixed housing is called a brake. A shift element that selectively couples two or more rotatable elements to each other is called a clutch. The shift element can be an actively controlled device such as a hydraulically actuated or electrically actuated clutch or brake, or it can be a passive device such as a one-way clutch or brake. The shift element can be a positive engagement device, such as a jaw clutch or a friction device capable of transmitting torque between elements in the presence of relative rotation. If two elements are fixedly coupled or selectively coupled, the two elements are coupled.

[0012] A gear train is a collection of gear train elements and shift elements configured to impose a specified speed relationship between a set of shafts. If a speed relationship is imposed regardless of the state of any shift element, the speed relationship is fixedly imposed by the gear train. If a speed relationship is imposed only when a particular shift element of the gear train is fully engaged, the speed relationship is selectively imposed by the gear train. The speed of a shaft is positive when the shaft rotates in one direction and negative when the shaft rotates in the opposite direction. A proportional speed relationship exists between a first shaft and a second shaft when the ratio of the speed of the second shaft to the speed of the first shaft is constrained to a predetermined value. If the ratio of the speed of the second shaft to the speed of the first shaft is between 0 and 1, the proportional speed relationship between the first shaft and the second shaft is a reduction gear relationship. Similarly, if the ratio of the speed of the second shaft to the speed of the first shaft is greater than 1, the proportional speed relationship between the first shaft and the second shaft is an overdrive gear relationship. A linear speed relationship exists in an ordered list of shafts when i) the first and last shafts in the ordered list are constrained to have the most extreme speeds, ii) the speeds of the remaining shafts are each constrained to be a weighted average of the speeds of the first and last shafts using predetermined weights, and iii) when the speeds of the shafts are different, they are constrained to be in the listed order, either increasing or decreasing.

[0013] Reference Figure 1, a hybrid electric vehicle (HEV) includes a power-split powertrain 10. The vehicle may include a vehicle system controller (VSC) and a powertrain control module (PCM) 12 for controlling an electric traction battery 14. The battery 14 may have a bi-directional electrical connection such that it receives and stores electrical energy and also supplies energy to an electric traction motor 16. The controller 12 may also control the operation of an internal combustion engine (ICE) 18. Both the motor 16 and the engine 18 are capable of providing power to a transmission 20, which ultimately transfers torque to the wheels.

[0014] The engine 18 transfers power to a torque input shaft such as a crankshaft 22, which is connected to a planetary gear set 24, for example, by a one-way clutch. The crankshaft 22 supplies power to the planetary gear set 24, which includes a ring gear 26, a sun gear 28, and a planet carrier assembly 30. The crankshaft 22 may be drivingly connected to the carrier assembly 30 to supply power to the planetary gear set 24. The planetary gear set 24 may distribute torque to an intermediate shaft, which may be, for example, a second rotor 62.

[0015] The sun gear 28 may be drivingly connected to a generator 32; for example, by a first rotor 34. The generator 32 may engage with the sun gear 28 such that the generator 32 may rotate with the sun gear 28 or not rotate with the sun gear. When the one-way clutch couples the engine 18 to the planetary gear set 24, the generator 32 generates energy as a reaction element of the operation of the planetary gear set 24. Electrical energy generated from the generator 32 may be transferred to the battery 14 through an electrical connection 36. The battery 14 also receives and stores electrical energy through regenerative braking in a known manner. The battery 14 supplies the stored electrical energy to the motor 16 for operation. A portion of the power transferred from the engine 18 to the generator 32 may also be transferred directly to the motor 16. The battery 14, the motor 16, and the generator 32 are each interconnected in a bi-directional electrical flow path through the electrical connection 36.

[0016] The vehicle may be powered only by the engine 18, only by the battery 14 and the motor 16, or by a combination of the engine 18 with the battery 14 and the motor 16. In a first operating mode, the engine 18 is activated to transfer torque through the planetary gear set 24. The ring gear 26 may distribute torque through the second rotor 62 to a stepped ratio gear 38, which may include, for example, meshing gear elements 40, 42, 44, and 46. Gears 42, 44, and 46 are mounted on a countershaft, and the gear 46 distributes torque to a gear 48. The gear 48 then distributes torque to a torque output shaft or countershaft 50. In the first operating mode, the motor 16 may also be activated to assist the engine 18. When the motor 16 is acting in an assist mode, the gear 52 distributes torque to the gears 44 and the countershaft.

[0017] In the second operating mode or the EV mode, the engine 18 is disabled or otherwise prevented from distributing torque to the torque output shaft 50. In the second operating mode, the battery 14 powers the motor 16 to distribute torque through the stepped transmission ratio gear 38 to the torque output shaft 50.

[0018] The torque output shaft 50 is connected to a differential and axle mechanism 56 that distributes torque to the traction wheels 58. The controller 12 controls the battery 14, the engine 18, the motor 16, and the generator 32 to distribute torque to the wheels 58 in the first operating mode or the second operating mode.

[0019] As previously described, the powertrain has two power sources. The first power source is the engine 18, which transfers torque to the planetary gear set 24. The other power source only involves the electric drive system, which includes the motor 16, the generator 32, and the battery 14, where the battery 14 serves as the energy storage medium for the generator 32 and the motor 16. The generator 32 can be driven by the planetary gear set 24 and can alternatively serve as a motor and transfer power to the planetary gear set 24.

[0020] The powertrain 10 may also include a generator brake 54. The generator brake 54 can be disposed, for example, near the first rotor 34. The generator brake 54 can be activated to "brake" or prevent the rotation of the shafts of the generator 32 and the sun gear 28. In this way, the generator brake 54 can be activated so that the engine output power is transferred to the torque output side of the powertrain 10 only through the mechanical path at a fixed gear ratio.

[0021] Now referring to Figures 2 to 4 , the powertrain 10 may also include a lock-up clutch 60. The lock-up clutch 60 can be adapted to lock the planetary gear set 24 of the transmission 20. In Figure 2 at least one method shown, the lock-up clutch 60 is adapted to lock the ring gear 26 and the planetary carrier assembly 30. In Figure 3 at least one other method shown, the lock-up clutch 60 is adapted to lock the sun gear 28 and the planetary carrier assembly 30. In Figure 4 at least another method shown, the lock-up clutch 60 is adapted to lock the ring gear 26 and the sun gear 28.

[0022] Locking the planetary gear set 24 via the lock-up clutch 60 causes the gears of the ring gear 26, central gear 28, and planetary gear carrier 30 to mesh and "lock", thereby transmitting torque from the engine 18 to the transmission 20. In this way, the elements of the planetary gear set 24 rotate in unison at a 1:1 gear ratio. Locking the planetary gear set 24 via the lock-up clutch 60 can reduce or eliminate the meshing losses in the planetary gear set 24, thereby improving the transmission efficiency when in the locked configuration.

[0023] The transmission 20 may include a gear train that may be disposed at, for example, position L1, position L2, or position L3.

[0024] Now referring to Figure 3 , the first gear train 70 may include a first planetary gear set 72 that includes a ring gear 74, a central gear 76, and a planetary gear carrier assembly 78. The first gear train 70 may include a second planetary gear set 80 that includes a ring gear 82, a central gear 84, and a planetary gear carrier assembly 86.

[0025] The central gear 76 is fixedly coupled to the input 62. The planetary gear carrier assembly 78 is fixedly coupled to the ring gear 82. In at least one method, the planetary gear carrier assembly 78 is selectively coupled to the ring gear 74 via the clutch 94. In at least another method, the planetary gear carrier assembly 78 is selectively coupled to the central gear 76 via the clutch 94. In either method, the clutch 94 can be used as a "lock-up clutch" for the first planetary gear set 72.

[0026] In at least one method, the brake 98 selectively couples the planetary gear carrier assembly 78 to the housing to selectively hold it stationary, or selectively couples both the planetary gear carrier assembly 78 and the ring gear 74 to the housing to selectively hold them stationary. In this way, the first gear train 70 can provide four forward speeds with a reverse clutch. In at least another method, the first gear train 70 does not include the brake 98. In this way, the first gear train 70 can provide four forward speeds without a reverse clutch.

[0027] The ring gear 74 is selectively coupled to the central gear 84 via the clutch 90. The ring gear 74 is also selectively coupled to the planetary gear carrier assembly 86 via the clutch 92. The planetary gear carrier assembly 86 is fixedly coupled to the output 50.

[0028] In at least one method, the brake 96 selectively couples the sun gear 84 to the housing to selectively hold it non-rotating. In at least another method, the first gear train 70 does not include the brake 96 or the brake 98. In this way, the first gear train 70 can provide three forward speeds without a reverse clutch.

[0029] Various power flow paths between the input shaft 62 and the output shaft 50 are established by selective engagement of the clutches and brakes of the first gear train 70. As shown in Table 1, the engagement of the shift elements in combinations of two or three establishes four forward gear ratios and one reverse gear ratio between the input 62 and the output 50. X indicates that a shift element is required to establish the power transfer path.

[0030] Table 1

[0031] Ratio 90 92 94 96 98 First 5.442 X X Second 2.905 X X Third 1.539 X X Fourth 1.000 X X Reverse -7.248 X X Alt 1 -2.537 X X Alt 2 1.000 X X Alt 3 1.000 X X

[0032] Now referring to Figure 4 , the second gear train 100 may include a first planetary gear set 102 that includes a ring gear 104, a sun gear 106, and a carrier assembly 108. The second gear train 100 may include a second planetary gear set 110 that includes a ring gear 112, a sun gear 114, and a carrier assembly 116.

[0033] The sun gear 106 is fixedly coupled to the input 62. The carrier assembly 108 is fixedly coupled to the ring gear 112. The brake 120 selectively couples the ring gear 104 to the housing to selectively hold the ring gear non-rotating.

[0034] The ring gear 104 is selectively coupled to the carrier assembly 116 by a clutch 124. The carrier assembly 116 is fixedly coupled to the output 50. In at least one method, the brake 122 selectively couples the sun gear 114 to the housing to selectively hold it non-rotating. In at least another method, the second gear train 100 does not include the brake 122. In this way, the second gear train 100 can provide three forward (e.g., reduction drive) speeds without a reverse clutch.

[0035] In at least one method, the ring gear 104 is selectively coupled to the sun gear 106 via a clutch 126. In at least another method, the ring gear 104 is selectively coupled to the planet carrier assembly 108 via the clutch 126. In at least another method, the planet carrier assembly 108 is selectively coupled to the sun gear 106 via the clutch 126. In these methods, the clutch 126 can be used as a "lock-up clutch" for the first planetary gear set 102.

[0036] Various power flow paths between the input shaft 62 and the output shaft 50 are established by selective engagement of the clutches and brakes of the second gear train 100. As shown in Table 2, the engagement of the shift elements in combinations of two or three establishes four forward gear ratios and one reverse gear ratio between the input 62 and the output 50. X indicates that a shift element is required to establish the power transfer path.

[0037] Table 2

[0038]

[0039]

[0040] Although the exemplary embodiments have been described above, it does not mean that these embodiments describe all possible forms covered by the claims. The words used in the specification are descriptive words rather than limiting words, and it should be understood that various changes can be made without departing from the spirit and scope of the present disclosure. As previously mentioned, the features of the various embodiments can be combined to form other embodiments of the present invention that may not be explicitly described or illustrated. Although the various embodiments may be described as providing advantages over one or more desired characteristics or being superior to other embodiments or prior art implementations, those of ordinary skill in the art recognize that one or more features or characteristics may be compromised to achieve the desired overall system attributes, depending on the specific application and implementation. These attributes may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, maintainability, weight, manufacturability, ease of assembly, etc. Therefore, embodiments described as being less than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the present disclosure and may be desirable for a particular application.

[0041] According to the present invention, a power transmission system is provided, the power transmission system having: a first planetary gear set configured to establish a fixed linear speed relationship between a first rotor, an engine crankshaft, and a second rotor; and a gear transmission assembly configured to alternately and selectively establish a plurality of proportional speed relationships between the second rotor and an output shaft, and including a second planetary gear set having a locking clutch configured to selectively couple two rotatable elements of the second planetary gear set.

[0042] According to an embodiment, the second planetary gear set includes a first rotatable element, a second rotatable element fixedly coupled to the second rotor, and a third rotatable element.

[0043] According to an embodiment, the first rotatable element is a first planetary carrier assembly, wherein the second rotatable element is a first sun gear, and wherein the third rotatable element is a first ring gear.

[0044] According to an embodiment, the locking clutch is configured to selectively couple: the first sun gear to the first planetary carrier assembly; the first sun gear to the first ring gear; or the first ring gear to the first planetary carrier assembly.

[0045] According to an embodiment, the gear transmission assembly further includes a third planetary gear set having a fourth rotatable element, a fifth rotatable element, and a sixth rotatable element fixedly coupled to the output shaft.

[0046] According to an embodiment, the fourth rotatable element is a second planetary carrier assembly, wherein the fifth rotatable element is a second sun gear, and wherein the sixth rotatable element is a second ring gear.

[0047] According to an embodiment, the first planetary carrier assembly is fixedly coupled to the second ring gear.

[0048] According to an embodiment, the first ring gear is selectively coupled to the second planetary carrier assembly.

[0049] According to an embodiment, the above invention is further characterized in that a first brake is configured to selectively hold the second sun gear from rotating.

[0050] According to an embodiment, the first ring gear is selectively coupled to the second sun gear.

[0051] According to an embodiment, the above invention is further characterized in that a second brake is configured to selectively hold the first planetary carrier assembly from rotating.

[0052] According to an embodiment, the above invention is further characterized in that a second brake is configured to selectively hold the first ring gear from rotating.

[0053] According to an embodiment, the first planetary gear set includes a first rotatable element fixedly coupled to the engine crankshaft, a second rotatable element fixedly coupled to the first rotor, and a third rotatable element drivably connected to the second rotor.

[0054] According to an embodiment, the invention further features a lock-up clutch configured to selectively couple two of the first rotatable element, the second rotatable element, and the third rotatable element.

[0055] According to an embodiment, the first rotatable element is a planetary carrier assembly, the second rotatable element is a sun gear, the third rotatable element is a ring gear, and the lock-up clutch is configured to selectively couple: the sun gear to the planetary carrier assembly; the sun gear to the ring gear; or the ring gear to the planetary carrier assembly.

[0056] According to an embodiment, the invention further features a generator brake configured to selectively hold the first rotor stationary.

[0057] According to an embodiment, the plurality of proportional speed relationships includes at least four positive speed relationships.

[0058] According to the present invention, there is provided a power transmission system having: an engine; a first electric machine; a second electric machine; a first planetary gear set including a first rotatable element fixedly coupled to the engine crankshaft, a second rotatable element fixedly coupled to the first electric machine, and a third rotatable element drivably connected to an intermediate shaft; and a gear transmission assembly configured to alternately selectively establish a plurality of proportional speed relationships between the intermediate shaft and an output shaft and including a second planetary gear set having a lock-up clutch configured to selectively couple two rotatable elements of the second planetary gear set.

[0059] According to the present invention, a power transmission system is provided, the power transmission system having: a first planetary gear set configured to establish a fixed linear velocity relationship between a first rotor, an engine crankshaft, and a second rotor, wherein the first planetary gear set includes a first rotatable element fixedly coupled to the engine crankshaft, a second rotatable element fixedly coupled to the first rotor, and a third rotatable element drivably connected to the second rotor; a lock-up clutch configured to selectively couple two of the first rotatable element, the second rotatable element, and the third rotatable element; and a gear transmission assembly configured to alternately selectively establish a plurality of proportional velocity relationships between the second rotor and an output shaft, and including a second planetary gear set having a lock-up clutch configured to selectively couple two rotatable elements of the second planetary gear set.

[0060] According to an embodiment, the first rotatable element is a planetary gear carrier assembly, wherein the second rotatable element is a sun gear, wherein the third rotatable element is a ring gear, and wherein the lock-up clutch is configured to selectively couple: the sun gear to the planetary gear carrier assembly; the sun gear to the ring gear; or the ring gear to the planetary gear carrier assembly.

Claims

1. A power transmission system, comprising: A first planetary gear set configured to establish a fixed linear speed relationship between a first rotor, an engine crankshaft, and a second rotor; And A gear transmission assembly configured to alternately and selectively establish a plurality of proportional speed relationships between the second rotor and an output shaft, and including a second planetary gear set and a third planetary gear set, the second planetary gear set including a first planetary carrier assembly, a first sun gear, and a first ring gear, the first sun gear being fixedly coupled to the second rotor, the second planetary gear set having a lock-up clutch configured to selectively couple two of the first planetary carrier assembly, the first sun gear, and the first ring gear, the third planetary gear set having a second planetary carrier assembly, a second sun gear, and a second ring gear, the second planetary carrier assembly being fixedly coupled to the output shaft, and the first planetary carrier assembly being fixedly coupled to the second ring gear.

2. The power transmission system according to claim 1, wherein the lock-up clutch is configured to selectively couple: The first sun gear to the first planetary carrier assembly, or The first sun gear to the first ring gear, or The first ring gear to the first planetary carrier assembly.

3. The power transmission system according to claim 1, wherein the first ring gear is selectively coupled to the second planetary carrier assembly.

4. The power transmission system according to claim 3, further comprising: A first brake configured to selectively hold the second sun gear from rotating.

5. The power transmission system according to claim 4, wherein the first ring gear is selectively coupled to the second sun gear.

6. The power transmission system according to claim 5, further comprising: A second brake configured to selectively hold the first planetary carrier assembly from rotating.

7. The power transmission system according to claim 6, further comprising: A second brake configured to selectively hold the first ring gear from rotating.

8. The power transmission system according to claim 1, wherein the first planetary gear set includes a first rotatable element fixedly coupled to the engine crankshaft, a second rotatable element fixedly coupled to the first rotor, and a third rotatable element drivingly connected to the second rotor.

9. The power transmission system according to claim 8, further comprising: Another lock-up clutch configured to selectively couple two of the first rotatable element, the second rotatable element, and the third rotatable element.

10. The power transmission system according to claim 9, wherein the first rotatable element is a planetary carrier assembly, wherein the second rotatable element is a sun gear, wherein the third rotatable element is a ring gear, and wherein the another lock-up clutch is configured to selectively couple: from the central gear to the planetary gear carrier assembly, or from the central gear to the ring gear, or from the ring gear to the planetary gear carrier assembly.

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