Patent Application
20180320768
The disclosure relates to a multiple-mode continuously-variable transmission (CVT) for a motor vehicle.
A majority of modern motor vehicles use a transmission to enable a power-source, such as an internal combustion engine, to power the vehicle across a wide range of road speeds with desired acceleration and efficiency. Frequently such transmissions are automatic or self-shifting. Such transmissions can automatically change gear ratios as the vehicle moves, freeing the driver of the vehicle from having to shift gears manually. Like other transmission systems on vehicles, a transmission allows an internal combustion engine, best suited to run at a relatively high rotational speed, to provide a range of speed and torque outputs necessary for driving the vehicle in various conditions. A transmission can offer a fixed number of gear ratios or be configured as a continuously-variable transmission (CVT) that can change steplessly through a continuous range of effective gear ratios.
In general, a CVT can change through an infinite number of effective gear ratios between a maximum gear ratio and a minimum gear ratio. A typical continuously variable transmission includes two adjustable pulleys, each having two sheaves. A belt or any suitable endless rotatable device, such as a continuous loop cable or chain, typically runs between the two pulleys, with the two sheaves of each of the pulleys sandwiching the belt therebetween. Frictional engagement between the sheaves of each pulley and the belt couples the belt to each of the pulleys to transfer a torque from one pulley to the other. One of the pulleys may function as a drive pulley so that the other pulley can be driven by the drive pulley via the belt. The gear ratio is the ratio of the torque of the driven pulley to the torque of the drive pulley. The gear ratio may be changed by moving the two sheaves of one of the pulleys closer together and the two sheaves of the other pulley farther apart, causing the belt to ride higher or lower on the respective pulley.
A multiple-mode continuously-variable transmission (CVT) assembly for connecting to an external power-source is disclosed herein. The assembly includes a continuously-variable speed-ratio unit having an input member and a multiple fixed speed-ratio unit having another input member, wherein the multiple fixed speed-ratio unit is operatively connected the continuously-variable speed-ratio unit. The assembly also includes a first torque-transmitting device operatively connected to each of the input members of the continuously-variable speed-ratio unit and the multiple fixed speed-ratio unit. The first torque-transmitting device is configured to receive torque from the external power-source. The assembly also includes an output member operatively connected to each of the continuously-variable speed-ratio unit and the multiple fixed speed-ratio unit and configured to carry an output torque from the assembly.
The multiple-mode CVT assembly may also include an assembly housing configured to retain each of the continuously-variable speed-ratio unit, the multiple fixed speed-ratio unit, and the first torque-transmitting device.
The first torque-transmitting device, the continuously-variable speed-ratio unit, and the multiple fixed speed-ratio unit may be connected in series. In such an embodiment, the first torque-transmitting device may be directly connected to the input member of the continuously-variable speed-ratio unit and the continuously-variable speed-ratio unit may be directly connected to the input member of the multiple fixed speed-ratio unit. Additionally, the multiple fixed speed-ratio unit may be directly connected to the assembly output member.
Alternatively, the continuously-variable speed-ratio unit and the multiple fixed speed-ratio unit may be connected to the first torque-transmitting device in parallel. In such an embodiment, the continuously-variable speed-ratio unit and the multiple fixed speed-ratio unit may be configured to selectively transmit the power-source torque to the assembly output member.
The multiple-mode CVT assembly may also include a second torque-transmitting device arranged between the first torque-transmitting device and each of the continuously-variable speed-ratio unit and the multiple fixed speed-ratio unit. In such a case, the second torque-transmitting device may be configured to selectively connect the first torque-transmitting device to the respective input member of one of the continuously-variable speed-ratio unit and the multiple fixed speed-ratio unit.
The assembly housing may be additionally configured to retain the second torque-transmitting device.
The continuously-variable speed-ratio unit may be configured to transmit the torque from the power-source to the assembly output member in direct drive through overdrive modes. Furthermore, the multiple fixed speed-ratio unit may be configured to transmit the power-source torque to the assembly output member in underdrive through direct drive modes.
The continuously-variable speed-ratio unit may be configured as a continuously-variable transmission (CVT). Such a CVT may include a variable diameter input pulley and a variable diameter output pulley connected via a chain.
The multiple fixed speed-ratio unit may be configured as a multi-speed automatic gearbox.
The first torque-transmitting device may be configured as a fluid coupling, i.e., a torque converter, or a friction plate clutch.
A motor vehicle having such a multiple-mode CVT assembly connected to an internal combustion engine is also disclosed.
The above features and advantages, and other features and advantages of the present disclosure, will be readily apparent from the following detailed description of the embodiment(s) and best mode(s) for carrying out the described disclosure when taken in connection with the accompanying drawings and appended claims.
Referring to the drawings in which like elements are identified with identical numerals throughout,
The vehicle 10 also includes a multiple-mode continuously-variable transmission (CVT) assembly 18 for connecting the power-source 12 to the drive axle(s) 14. The power-source is mounted in the vehicle 10 externally with respect to the multiple-mode continuously-variable transmission (CVT) assembly 18, i.e., the multiple-mode continuously-variable transmission (CVT) assembly 18 may be operatively connected to the power-source 12 and be appropriately fastened thereto. The CVT assembly 18 includes an assembly input member 18-1 configured to receive the power-source torque Ti. The CVT assembly 18 also includes a continuously-variable speed-ratio torque transmitting unit 20. The continuously-variable torque transmitting unit 20 provides a continuous range of effective speed ratios between the input and output members. As shown in
As understood by those skilled in the art, in the variable-diameter pulley system, the speed ratio of the continuously-variable torque transmitting unit 20 is changed by moving the two sheaves of one of the input and output pulleys 24, 26 closer together and the two sheaves of the other pulley farther apart. The V-shaped cross section of the torque-transmitting element 28 causes the element to ride higher on one of the pulleys 24, 26 and lower on the other. Such movement of the respective sheaves of the pulleys 24, 26 changes the effective diameters of both pulleys, and, in turn, changes the overall speed ratio of the torque transmitting unit 20. Because the distance between the respective pulleys 24, 26 and the length of the torque-transmitting element 28 does not change, generally, both pulleys are adjusted simultaneously.
The CVT assembly 18 also includes a stepped multiple fixed speed-ratio unit 30. The multiple fixed speed-ratio unit 30 may include an appropriate gear-train (not shown), which may be configured as a parallel-shaft manual or automatically shiftable gear-train, or an epicyclic automatically shiftable multi-speed gear-train, each providing a discrete number of speed-ratios as understood by those skilled in the art. The multiple fixed speed-ratio unit 30 is operatively connected to the continuously-variable speed-ratio unit 20. Specifically, as shown in
As shown in
As shown in
In the multiple-mode CVT assembly 218, the assembly housing 36 may be additionally configured to retain the second torque-transmitting device 38. The continuously-variable speed-ratio unit 20 may be configured to transmit the power-source torque Ti to the assembly output member 18-2 in direct drive through overdrive modes, such as at elevated road speeds of the vehicle 10. In other words, the continuously-variable speed-ratio unit 20 may be configured to operate in modes where the ratio of the power-source torque Ti to the output torque To is smaller than 1:1 and, conversely, the ratio of rotational input speed from the power-source 12 to rotational speed of the assembly output member 18-2 is greater than 1:1. On the other hand, the multiple fixed speed-ratio unit 30 may be configured to transmit the power-source torque Ti to the assembly output member 18-2 in underdrive through direct drive modes, such as during launch of the vehicle 10 from rest and to enable vehicle stop/start operation. In other words, the multiple fixed speed-ratio unit 30 may be configured to operate in modes where the ratio of the power-source torque Ti to the output torque To is greater than 1:1 and, conversely, the ratio of rotational input speed from the power-source 12 to rotational speed of the assembly output member 18-2 is smaller than 1:1.
Overall, in the multiple-mode CVT assemblies 118 and 218, the continuously-variable speed-ratio unit 20 and the multiple fixed speed-ratio unit 30 are employed to facilitate distinct, substantially non-overlapping, speed-ratios and road-speed ranges. Therefore, the continuously-variable speed-ratio unit 20 is configured as an “asymmetric” CVT, wherein the term “asymmetric” is employed herein to denote that the continuously-variable speed-ratio unit is only used in a limited range of speed-ratios, such as overdrive numerical ratios. Accordingly, the multiple fixed speed-ratio unit 30 is configured to transmit the power-source torque Ti in numerically higher ratios to permit effective launch of the vehicle 10 from rest and propulsion at lower road speeds. Furthermore, in the embodiments of the multiple-mode CVT assemblies 118 and 218 described above, the multiple-mode CVT assembly is intended to arrange the continuously-variable speed-ratio unit 20 and the multiple fixed speed-ratio unit 30 such that the continuously-variable speed-ratio unit transmits the power-source torque Ti in lower, such as overdrive numerical ratios, and higher road speeds of the vehicle 10. Such arrangement of either of the CVT assemblies 118 and 218 enable enhanced efficiency of the particular CVT assembly and may also facilitate usage of a reduced power-consumption actuator 29.
The detailed description and the drawings or figures are supportive and descriptive of the disclosure, but the scope of the disclosure is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed disclosure have been described in detail, various alternative designs and embodiments exist for practicing the disclosure defined in the appended claims. Furthermore, the embodiments shown in the drawings or the characteristics of various embodiments mentioned in the present description are not necessarily to be understood as embodiments independent of each other. Rather, it is possible that each of the characteristics described in one of the examples of an embodiment may be combined with one or a plurality of other desired characteristics from other embodiments, resulting in other embodiments not described in words or by reference to the drawings. Accordingly, such other embodiments fall within the framework of the scope of the appended claims.
