192 clutches and power-stop control – Clutches – Axially engaging
Reexamination Certificate
2000-02-09
2001-11-06
Marmor, Charles A (Department: 3681)
192 clutches and power-stop control
Clutches
Axially engaging
C192S070200, C192S10700R, C029S895300, C029S527100
Reexamination Certificate
active
06311815
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to frictional elements such as clutch separator plates used in clutch or brake disc packs for vehicle transmissions and the like and in particular to a separator plate with improved surface features to enhance operation of the disc packs and a method of manufacturing a separator plate with improved surface features.
BACKGROUND OF THE INVENTION
Automotive and industrial automatic transmissions and the like comprise clutch pack assemblies, sometimes also called multi-disc clutch packs. Clutch pack assemblies comprise frictional members, commonly called plates. There are typically two groups of frictional members. A first group comprises plates having a friction enhancing material bonded to the plates, the first group of plates being called friction plates. The second group of plates separates the friction plates and are typically called separator or reaction plates. The separator plates act as reaction members against which the friction plates operate in transferring torque. Typically, one group of plates is internally splined to a first shaft while the other set of plates is externally splined either to a second shaft or a fixed housing as will be discussed more fully below. There will typically be found several clutch pack assemblies in an automatic transmission. Each clutch pack assembly may be selectively used to provide a particular transmission ratio, better known as first gear, second gear, and so on.
To operate effectively, the plates must exhibit high torque transmitting capacity. High torque transmission is related to the coefficient of static friction. It is also desirable for the separator plate to have a large coefficient of dynamic friction which is related to shock and noise prevention as the plate is engaged. Designing for a large torque transmitting capacity, however, may result in a low coefficient of dynamic friction. U.S. Pat. No. 5,535,870 to Takezaki et al. discusses the difficulty in combining in one clutch the characteristics of high torque transmitting capacity, a large ratio of coefficient of dynamic friction to the coefficient of static friction and heat resistance. The '870 patent discloses the combination of two different kinds of commercially available friction members to realize the above characteristics. One friction member has a high coefficient of static friction while the other has a high coefficient of dynamic friction. The '870 patent, however, does not address, among other things, the issue of parasitic drag.
Parasitic drag occurs when the separator plate and the friction plates in a particular clutch pack assembly are not engaged. While in this condition, depending on the particular transmission design, the friction plates, the separator plates or both types of plates may be rotating independent of the other set. This condition is called freewheeling. In some freewheeling situations, the separator plates and the friction plates may be rotating in opposite directions. The plates are in a fluid bath which is used to cool the plates and to reduce wear as the plates are coupled and de-coupled. The fluid bath also carries away debris from the face of the plates. The fluid bath, while beneficial in several respects, does produce drag on the plates. For example, in a transmission where the fluid is transmission fluid, the rotation of the plates through the transmission fluid adjacent the plate is resisted by the transmission fluid. Consequently, energy must be expended to rotate the plates through the transmission fluid. Drag thus acts as a load on the engine in the freewheeling condition and results in, for example, reduced fuel efficiency. Inasmuch as the drag is thus undesired, it may be referred to as a parasitic force.
Additionally, as the plate rotates through the transmission fluid, some rotation of the transmission fluid is effected. Because the plates within a clutch pack assembly are very close to each other, the rotating transmission fluid acts upon the adjacent plates. If, according to the design of the particular transmission, the adjacent plates are moving in the opposite direction or are stopped, the resulting drag is yet another source of parasitic drag.
As discussed above, the presence of fluid between the separator plate and the friction plate in a clutch pack assembly may result in undesired rotation of plates due to drag. In addition to the deleterious effects on efficiency, the undesired rotation may result in an undesired effect referred to as “clunk”. Clunk is most frequently noticed as a transmission is shifted out of neutral into reverse or a forward gear. As plates which are rotating in opposite directions are engaged and the rotation of one of the plates is suddenly reversed or stopped, the clutch pack assembly and associated components are mechanically shocked. This is manifested, in part, by a low frequency noise or clunk and a jolt to the vehicle. Clunk is thus undesired as it is an annoyance to the operator and subjects the transmission to undesired mechanical stresses.
U.S. Pat. No. 5,890,988 to Kasuya et al. discloses the use of a gear brake structure instead of a frictional engagement member such as a clutch pack assembly, to avoid rotation of equipment and thus to avoid the deleterious effects of drag. The '988 patent, however, is limited to eliminating drag caused by freewheeling of the frictional engagement members in the reverse gear only. Thus, parasitic drag produced by other frictional engagement members, such as in the first through fifth gears, is not reduced. Moreover, the gear brake of Kasuya et al. requires a significant alteration to the time proven design of transmissions which is realized only through expensive redesign efforts.
In addition to the shortcomings with respect to drag and clunk, prior art clutch packs suffer from a number of wear related shortcomings. One such shortcoming is the so called “break-in” period. Clutch components are designed to operate using friction between two surfaces initially rotating at different relative speeds in order to match the speed of rotation between the two surfaces. This results in the surfaces being worn down over time. When first placed into operation, there is normally an initial period where the change in characteristics such as drag, coefficient of dynamic friction and coefficient of static friction may be relatively rapid. This is commonly referred to as a “break-in” period. Rapid changes in transmission operation can be unsettling to an operator. Thus, it is desired to have a very short “break-in” period, if any, and a consistent rate of change throughout the remaining useful life of the clutch pack assembly such that any change is not perceived by the operator.
A characteristic which is closely related to the break-in characteristic is the shift characteristic. As the friction plate and separator plate are worn, the contact surfaces of components will vary as the components are worn. As the components wear, the contact area typically increases resulting in changes in the coefficient of friction. If the coefficient of friction increases, shifting may become jerky as the plates “grab” each other. Conversely, if the coefficient of friction becomes too small, shifting time may increase appreciably. Thus, the time required for disengagement of the lower gear and engagement of the higher gear may increase. Depending on the transmission, this may result in, for example, higher revolution rates of the lower gear or in noticeable hesitations in the acceleration. Rapid onset of shifting pattern changes may result in operator consternation while the same changes effected gradually over time are readily adapted to by the operator.
Notwithstanding the '988 patent which replaces an entire clutch pack assembly and the '870 patent which addresses the characteristics of both friction elements, improvements to shortcomings in prior art clutch pack assemblies have typically been directed to improvements in the friction plate. An exception to this is found in U.S. Pat. No. 5,048,654 issued to Yesni
Case Richard L.
Riggle John F.
Ice Miller
Marmor Charles A
Rodriguez Saul J.
Steel Parts Corporation
Taylor Jay G.
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