Patent Application
20080167157
1. Field of the Invention
The present invention relates to automatic transmissions and gear trains. In particular, this invention relates to an improved automatic transmission with a fully engaging center support.
2. Description of Related Art
A motorized vehicle typically includes a power train having an engine, a multi-speed transmission, and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times. The number of forward speed ratios that are available in the transmission determines the number of times the engine torque range is repeated. Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicles and, therefore, required relatively large engines that could produce wide speed and torque ranges. This, in turn, resulted in increased engine wear and tear and reduced engine efficiency. Therefore, manually-shifted transmissions were the most popular form used in motor vehicles.
With the advent of three- and four-speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity. This form of transmission improved the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduced the step size between ratios and therefore improved the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration.
One aspect of the instant invention is a redesign of an automatic transmission that has a high failure rate in its present application. The United States Postal Service (USPS) fleet has 145,000 vehicles on the road, each with a service life of 25 or more years. These vehicles rely on the conventional 180C transmission and/or the conventional 700R4 transmission. The 700R4 transmission was introduced into the fleet as an alternative to remanufacturing the 180C. This transmission has a much higher torque capacity than the standard 180C, but also has inherent failure characteristics which are revealed when it is required to perform within the requirements of a postal delivery vehicle duty cycle. High vehicle down time due to inherent 700R4 transmission design problems have plagued this fleet for the past 15 years. During the last 15 years, the USPS has utilized local and regional re-builders to supply replacement products to keep their fleet on the road. The 700R4 transmission is a GM unit that has been in the marketplace for many years. This unit was not designed for the Postal LLV application and had to have a modified conversion kit to adapt to the USPS vehicle. This kit included a drive shaft, an adapter plate, a shift linkage, and a torque converter. Because there was no controlled testing and evaluation at the inception of this 700R4 transmission, there were high failure rates in the field.
The 700R4 transmission historically fails in four ways.
1. Three/four clutch failure.
2. Two/four band failure
3. Rear planetary failure
4. Case lug failure.
The nature of the use of the 700R4 transmission by the USPS results in constant shifting from first gear to second gear and back down to first gear. This shifting sequence typically occurs hundreds of times per vehicle in one day of service. The 700R4 transmission was designed to shift first to second to third and then to fourth. The converter clutch would then be applied, and the driver and vehicle would proceed to a destination. Thus, most of the transmission's useful service would be spent in third and fourth gears. The 700R4 transmission as used by the Postal Service does not see such a sheltered life. After repeated first to second and then second to first shifts, the pinion gears within the 700R4 gear train begin to spall.
Spalling of the gears results in very small, yet very hard pieces of steel flaking off the pressure angle surface of each pinion gear. These pieces of steel are washed away from the pinion gears by the oil that lubricates and cools these same gears; thus, the pieces of hard steel are suspended in the oil. As the oil circulates, in this case by being pumped to all critical areas of the transmission, these pieces of metal act as an abrasive on all parts they contact. As one might suspect, the abrasive action of the steel particles wears the surfaces of all mating and moving parts. As gear deterioration progresses, the hard steel particles become more concentrated in the oil and become lodged in the valves of the valve body. This results in the transmission not shifting properly and burning the three/four clutch and the two/four band. The case lugs are worn as a result of the forces placed on it by the center support when the sprag (which is nested in the center of the center support) is held in first gear and/or slammed during a two-to-one down shift.
One manner of providing an automatic transmission with improved deterioration resistance and an increased effective life forms the subject matter of commonly owned U.S. Pat. No. 7,195,578 to Dalenberg et al., the entire disclosure of which is incorporated herein by reference as non-essential material. As discussed in that patent, a reduction in the load each gear must transfer is provided by adding a fourth pinion gear to the carrier, in combination with certain other operations, to reduce the amount of torque transferred by each gear. Adopting the modifications outlined in the Dalenberg et al. ('578) patent permits the system to be kept free of harmful contamination and functioning properly for a longer period.
According to the present invention, an automatic transmission assembly is constructed or modified to minimize effects of wear thereon and maximize its operational life. The assembly, which includes a transmission case, has a modified ring-shaped center support that is to be secured against rotation within the transmission case. A center support plate, which is attachable to and detachable from the ring-shaped center support, includes protrusions thereon that engage between cooperating protrusions defined on the transmission case to secure the ring-shaped center support against rotation within the transmission case. The ring-shaped center support is modified by incorporating bores adapted to receive fasteners to attach the center support plate to the center support. In a preferred configuration, the bores are threaded bores, the fasteners are screws receivable in the threaded bores, and the protrusions are lugs defined on an outer circumference of the center support plate and lugs defined on an inner circumference of the transmission case. The invention is particularly useful when the modified ring-shaped center support is a worn, original equipment support that has deteriorated in function.
The invention additionally concerns a process of modifying an automatic transmission assembly so as to minimize effects of wear thereon and maximize operational life thereof. In this process, bores, adapted to receive fasteners by which a center support plate is attachable to a center support of the automatic transmission assembly, are incorporated into the center support, and the center support plate is attached to the center support with the fasteners. The center support with the center support plate attached is then placed into a transmission case so that lugs or other protrusions on an outer circumference of the center support plate engage between cooperating lugs or other protrusions defined on the transmission case to secure the ring-shaped center support against rotation within the transmission case.
For simplicity and illustrative purposes, the principles of the present invention are described by referring to various exemplary embodiments thereof. Although the preferred embodiments of the invention are particularly disclosed herein, one of ordinary skill in the art will readily recognize that the same principles are equally applicable to, and can be implicated in other compositions and methods, and that any such variation would be within such modifications that do not part from the scope of the present invention. Before explaining the disclosed embodiments of the present invention in detail, it is to be understood that the invention is not limited in its application to the details of any particular embodiment shown, since of course the invention is capable of other embodiments. The terminology used herein is for the purpose of description and not of limitation. Further, although certain methods are described with reference to certain steps that are presented herein in certain order, in many instances, these steps may be performed in any order as may be appreciated by one skilled in the art, and the methods are not limited to the particular arrangement of steps disclosed herein.
An improvement to the planetary gear assembly is now described. It will be understood by those of ordinary skill in the art that the original equipment planetary gear assembly shown in
The re-engineered planetary gear assembly shown in
More particularly, current state of the art configurations use four (4) pinion planetary arrangements such as the four pinion planetary arrangement 60 illustrated in
According to this invention, case lug failure is repaired by installing a custom center support plate, which, when installed on the altered original center support, guarantees maximum center support engagement to the case. This engagement insures that this point of failure is eliminated for the remaining life of the transmission.
Over time, the lug engagement locations 84, the side walls delimiting the center support recesses 88, or both become worn and deteriorate, leading to circumferential play 90 between the center support 86 and the lug engagement locations 84 and, therefore, the case 80 as a whole. If the metal in the case center support area is worn away, a malfunction will occur. This malfunction manifests itself in a “no-move” situation.
The improved three/four clutch set shown in
While the invention has been described with an emphasis on particular embodiments thereof, those skilled in the art may make various modifications to the described embodiments of the invention without departing from the scope of the invention. Although the invention has been described and disclosed in various terms and certain embodiments, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved, especially as they fall within the breadth and scope of the claims here appended. Those skilled in the art will recognize that these and other variations are possible within the scope of the invention as defined in the following claims and their equivalents.
This application claims the priority of U.S. Provisional Application Ser. No. 60/873,023, filed Dec. 6, 2006, the entire disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60873023 | Dec 2006 | US |
