Machine element or mechanism – Gearing – Plural power paths to and/or from gearing
Reexamination Certificate
1997-07-09
2001-02-13
Estremsky, Sherry (Department: 3681)
Machine element or mechanism
Gearing
Plural power paths to and/or from gearing
C074S331000
Reexamination Certificate
active
06186029
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to transmissions and, in particular, to a transmission having dual drive paths and having components arranged such that a “straight-through”, “short drop” and “long drop” version of the transmission can be provided using a large number of common components.
BACKGROUND ART
A type of transmission known as a “power shift” transmission is used in many on-road and off-road applications. In this type of transmission, a torque converter is usually disposed between the vehicle engine and the gear box. The gear box, which typically has automatic shift capability, differs from conventional automobile transmissions in that it uses multiple shafts that mount gear/clutch assemblies, as opposed to planetary units used in conventional automobile automatic transmissions. The gear clutches are selectively engaged to couple the gearbox input with the gearbox output in a ratio determined by the selected gears. This arrangement provides the multiple speed capability for the transmission.
This type of transmission typically includes a forward/reverse shaft which mounts forward and reverse clutch/gear assemblies. This type of transmission also includes at least one countershaft which mounts gears for providing other speeds and utilizes clutches for coupling the gears to the shaft. The forward and reverse clutches determine whether the transmission is in forward, reverse or in neutral (neither clutch engaged), whereas the selective application of the other clutches determine the “range” of the transmission. In transmissions that employ a torque converter, it is known to provide a “lock-up” clutch to mechanically lock the turbine to the pump impeller in order to eliminate slippage and, hence, energy loss when the vehicle is moving.
In conventional transmissions of this type, if four (4) forward speeds are desired, the gear box may be supplied with four pairs of meshing gears and four clutches for selectively engaging the appropriate gear pair. Accordingly, eight speed transmissions might require eight pairs of gears and eight clutches or two input clutches and four pairs of gears.
Transmissions of this type, depending on application, are provided in various configurations. In one configuration known as a “straight-through” configuration, the axis of the input shaft is coincident with an axis of the output shaft. In a “short drop” transmission, the axis of the output shaft is displaced vertically with respect to the axis of the input shaft. In a “long drop” transmission, the vertical distance between the output shaft and input shaft is even greater. In many, if not most instances, the construction and design of these three types of transmissions are substantially different even in situations where all three designs have substantially the same horse power rating. Each is individually designed to provide the necessary vertical distance between the input and the output. Manufacturers of these types of transmissions expend large amounts of dollars for transmission tooling unique to each type of transmission.
DISCLOSURE OF INVENTION
The present invention provides a new and improved transmission of the type used in heavy-duty, off-highway and on/off road applications. The invention is especially suited for “power shift” transmissions. It should be understood, however, that principles of this invention can be applied to other types of transmissions and should not be limited to a “power shift” type transmission.
According to a preferred embodiment of the invention, a multi-speed transmission is disclosed that includes a torque converter having a pump portion adapted to be coupled to a prime mover, such as a vehicle engine and a turbine portion arranged to be fluidly driven by the pump portion. The principle by which drive torque is transmitted between the converter pump and the converter turbine is conventional and does not form part of the present invention.
The transmission includes a gear box portion having at least two inputs and at least one output and further includes shiftable elements, such as clutch actuated gears which rotatably couple the inputs to the output in predetermined ratios depending on which gear clutches are actuated. A first drive mechanism rotatably couples the pump portion of the torque converter to one of the inputs to the gear box portion and establishes a first drive path from the pump portion to the output of the gear box. A second drive mechanism rotatably couples the turbine portion of the torque converter to the other of the inputs and establishes a second drive path from the turbine portion of the torque converter to the gear box output.
In a preferred embodiment of the invention, a first input module is disposed between the pump portion of the torque converter and the first input. In the preferred and illustrated embodiment, the first input module includes gears for directly coupling the pump portion of the torque converter to the first input; the gears chosen for the input module determine the overall ratio for the first drive path.
In the preferred embodiment, a second input module is also provided which includes gearing for rotatably coupling the turbine portion of the torque converter to the other input of the gear box. The gears chosen for the second input module determine the overall ratio for the second drive path.
In the exemplary embodiment, the first drive path comprises a direct drive path in that the pump portion of the torque converter, which is directly driven by the prime mover, is coupled to the output via the gear box portion. This drive path eliminates the slippage normally associated with a torque converter. The second drive path can be termed the torque converter drive path in that the output of the torque converter is coupled to the other input of the gear box. In the preferred and illustrated construction, the torque converter drive path includes forward and reverse clutches and determines whether the transmission is in forward, reverse or neutral.
According to the preferred embodiment of the invention, the first drive path includes a drive clutch for controlling the coupling between the pump portion of the torque converter and the first input.
The disclosed transmission construction can be used to provide a transmission having multiple speeds with a reduced number of gear/clutch assemblies. In a typical power shift-type transmission, four gear/clutch assemblies are required in order to provide four forward or four reverse speeds. With the disclosed invention, a gear box portion can be provided with four gear/clutch assemblies to provide six-eight speeds. This is accomplished by providing different overall gearing for the first and second drive paths. By using different gearing, four speeds can be obtained via the direct drive path and a different four speeds can be obtained by using the torque converter drive path.
The disclosed transmission construction can also provide a retarding function when desired. This is achieved by activating both drive paths so that the pump and turbine portions of the torque converter are driven at relative speeds with respect to each other. As is known, when a vehicle is coasting, the vehicle wheels drive the torque converter via the gear box. By activating both drive paths and providing gearing for the first and second drive paths that are different, the pump and turbine portions of the torque converter can be forced to rotate at different speeds and, in effect, become a energy absorber or retarder.
According to another feature of the invention, a multi-speed transmission is disclosed that includes an input shaft, an output shaft and at least two transmission shafts or countershafts. The axes of the countershafts and the axis of the output shaft are arranged such that the three axes are parallel with respect to each other. In addition, the axes are spaced radially from each other such that the axes are arranged in a triangular relationship. A first gear is rotatably connected to the first countershaft, a second gear is rotatably connected to the second countershaft,
Dana Corporation
Estremsky Sherry
Watts, Hoffmann, Fisher & Heinke Co.
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