Two-way clutch assembly having selective actuation

192 clutches and power-stop control – Clutches – Automatic

Reexamination Certificate

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Details

C192S085060, C192S09300C

Reexamination Certificate

active

06745880

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, generally, to bi-directional or “two-way” clutch assemblies and, more specifically, to a two-way clutch assembly having selective actuation. In addition, the two-way clutch assembly of the present invention is particularly adapted for use in connection with a brake, clutch, or other holding device in a transmission to provide low and reverse gears.
2. Description of the Related Art
Generally speaking, land vehicles require three basic components. These components include a power plant (such as an internal combustion engine), a power train and wheels. The power train's main component is typically referred to as the “transmission.” Engine torque and speed are converted in the transmission in accordance with the tractive-power demand of the vehicle. Transmissions include one or more gear sets, which may include an inner gear, intermediate planet or pinion gears that are supported by their carriers, and outer ring gears. Various components of the gear sets are held or powered to change the gear ratios in the transmission. In addition to such planetary gear sets, driveline components may further include multi-disc friction devices that are employed as clutches or brakes. The multi-disc pack clutch is a friction device that is commonly employed as a holding mechanism in a transmission, transfer case or differential or the like. In addition, multi-disc friction devices also find use in industrial applications, such as wet brakes, for example, to brake the wheels on earth-moving equipment.
The multi-disc pack clutch or brake assembly has a clutch sub-assembly including a set of plates and a set of friction discs that are interleaved between one another. The plates and friction discs are bathed in a continual flow of lubricant and in “open pack” mode normally turn past one another without contact. The clutch or brake assembly also typically includes a piston. When a component of a gear set is to be held, as for example during a particular gear range, a piston is actuated so as to cause the plates and friction discs to come in contact with respect to one another. In certain applications, it is known to employ several multi-disc pack clutch devices in combination to establish different drive connections throughout the transmission, transfer case, or differential to provide various gear ratios in operation, or to brake a component.
When the discs are not engaged, there often remains a differential rotational speed between the drive and driven members that the clutch or brake bridges. Relative rotation between the friction discs and the plates during open-pack mode creates drag. This condition results in parasitic energy losses, reduces the efficiency of the transmission, transfer case or differential, and ultimately results in lower fuel efficiency.
In addition to multiple friction devices, one-way clutches are frequently employed in transmissions, transfer cases, and differentials to selectively transmit torque in one rotational direction, but not in the opposite rotational direction. To this end, one-way clutches typically include an inner race, an outer race, and an engagement mechanism disposed therebetween. The engagement mechanism is operable to lock the inner and outer races together thereby transmitting torque in one relative direction. The engagement mechanism is further operable to allow freewheeling rotation between the inner and outer races in the opposite rotational direction. Engagement mechanisms commonly used in one-way clutches of the related art include pawls, sprags, and rollers. A cage, along with biasing members, such as springs, are also sometimes employed to retain the pawls, sprags, or rollers between the inner and outer races as well as to selectively assist in the change of operational modes between torque translation and freewheeling actuation of the clutch, depending on the direction of rotation between the inner and outer races.
As noted above, one-way clutches of this type have been employed in numerous applications in transmission, transfer cases, and differentials. For example, one-way clutches have been employed in conjunction with friction clutches and planetary gear sets to effect low and reverse gear ratios in conventional transmissions. While this arrangement has worked well for its intended purpose, some disadvantages remain. For example, the friction clutch remains a source of significant parasitic losses due to inherent drag between the friction plates when the clutch is operating in “open pack” mode. Specifically in the case of low and reverse gears, the associated friction clutch operates in open pack mode when the transmission is in gears 2-5 and therefore generated parasitic losses in each of these gears. Still, the clutch is necessary for providing the proper holding torque in low and reverse gears. Accordingly, there remains a need in the art for a mechanism that can provide the appropriate holding torque for both low and rear gears in the transmission and yet results in less parasitic losses than are presently attributable to the multiple plate friction clutch used for this purpose. In addition, there is a need in the art for a device that continues to perform the functions of the one-way clutch as described above, particularly where the output speed-of the transmission exceeds the input speed resulting in engine compression braking.
Partially in response to this problem, bi-directional or “two-way” overrunning clutches have been proposed in the related art for use in these circumstances. These bi-directional overrunning clutch assemblies typically employ an inner race, an outer race, and a plurality of rollers, pawl, or sprags as the engagement mechanism disposed therebetween. Some of the bi-directional overrunning clutches of the type known in the related art are, for the most part, designed to be self-actuating. While they appear to present a solution to certain problems identified above, they have not been widely employed in transmission, transfer cases, and differentials of the related art. These self-actuating bi-directional overrunning clutches are relatively mechanically complex and have certain physical limitations and drawbacks. One such drawback is that the inner and outer races of the presently known bi-directional clutches generally travel over a large angular distance between the engagement in one rotational direction to the engagement in the opposite rotational direction. This makes for undesirable driving conditions by causing hard lockups when changing directions and also brings about a short mechanical life due to the severe inherent impact forces of the engagement. Additionally, the self-actuating bi-directional clutches known in the related art cannot be selectively engaged in an efficient manner or to optimize the vehicle power output in response to varying driving conditions.
In an attempt to overcome these problems, bi-directional overrunning clutches that may be selectively actuated to change the direction of torque translation and overrunning operation have been proposed in the related art. Unfortunately, these devices generally suffer from the disadvantage that they are mechanically complex, difficult to control and are generally not cost effective.
Accordingly, there remains a need in the art for a bi-directional clutch that can be selectively actuated and controlled in a manner to provide driving comfort and offer efficient operating modes for various driving conditions while at the same time facilitating the reduction in parasitic losses derived from conventional multi-disc friction devices. Furthermore, there remains a need in the art for a controllable bi-directional overrunning clutch assembly that can be quickly and easily shifted to provide either torque translation or freewheeling operation in either rotational direction. In addition, there also remains a need in the art for a bi-directional clutch assembly that can be effectively shifted between operational modes without jamming of the engagement mechanism or other fa

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