Planetary gear transmission systems or components – Fluid drive or control of planetary gearing – Impeller-turbine type fluid circuit in series with planetary...
Reexamination Certificate
2001-01-30
2003-05-20
Parekh, Ankur (Department: 3681)
Planetary gear transmission systems or components
Fluid drive or control of planetary gearing
Impeller-turbine type fluid circuit in series with planetary...
C475S280000, C475S302000
Reexamination Certificate
active
06565470
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to an automatic transmission apparatus that transmits power from an engine to an output shaft. More specifically, the present invention relates to a five or six-speed automatic transmission apparatus that expands the direct drive region of the torque converter for front wheel drive to greatly improve the power performance and fuel economy thereof.
2. Background Information
Four-speed automatic transmission apparatuses are well known for driving a front wheel drive vehicle. One example of a four-speed automatic transmission apparatus for a front wheel drive vehicle is shown in FIG.
1
. Transmission
1
of
FIG. 1
is disposed on a first shaft
3
, which is the output shaft of torque converter
2
, while the output of transmission
1
is coupled to a second shaft
5
via a pair of counter gears
4
. Second shaft
5
is coupled with a third shaft
8
via a pair of counter gears
6
and a differential gear
7
so that its output is transmitted to the front left and right wheels.
One conceivable design for the transmission
1
in such a configuration is one that comprises two planetary gear trains, two clutches CA and CB, and three brakes BA, BB and BD, as shown in
FIG. 2A
to FIG.
2
E.
FIG. 3
shows the ON/OFF control of the coupling elements at each speed level of the transmission shown in FIG.
2
and the rotational speed of each structural element A, B, C and D of the planetary gear trains. In the present invention structural element C is the output part of transmission
1
and gear ratios for four forward speeds and one reverse speed are obtained.
As shown in
FIG. 4
, another example of a transmission is illustrated that comprises a pair of planetary gear trains, three clutches CA, CB and CD, and a pair of brakes BA and BB. As seen in
FIG. 5
, the ON/OFF control of the coupling elements is shown at each speed level of the transmission shown in FIG.
4
and the rotational speed of each structural element A, B, C and D of the planetary gear trains. In the present invention structural element C is the output part of transmission
1
and gear ratios for four forward speeds and one reverse speed are obtained.
With these automatic transmission apparatuses, the gear ratios of first speed (1
st
) and fourth speed (4
th
) are normally determined by the maximum tractive force and the maximum speed. Consequently, there are large differences in gear ratio between speed levels. These four-speed automatic transmission apparatuses have inferior power performance in comparison with typical five or six-speed manual transmissions. Also, with the large differences between gear ratios, there is a larger region where the engine speed is low when the torque converter is coupled directly. Consequently, an inefficient region (hydraulic coupling region) of the torque converter must be used more often, resulting in poor fuel economy.
Therefore, it is preferred that automatic transmission apparatuses also have five or six speeds with narrower differences between gear ratios similar to five or six-speed manual transmissions.
To this end, the automatic transmission apparatus shown in
FIG. 6
has been proposed. This apparatus modifies the configuration shown in
FIG. 1
by providing a second shaft
5
with a subordinate transmission ST that comprises a planetary gear train, a direct drive clutch C and a speed-reducing brake B. This configuration achieves an automatic transmission apparatus with five forward speeds, wherein the first through fourth speeds are obtained by outputting the first through fourth speeds of transmission
1
through subordinate transmission ST, while the same is in direct drive mode. The fifth speed is obtained by using subordinate transmission ST to reduce the first speed of transmission
1
.
However, there is a limit to how far the difference between the gear ratios of transmission
1
can be narrowed and it is difficult to achieve gear ratios similar to those of a manual transmission. Moreover, subordinate transmission ST is disadvantageous in that it increases both cost and weight.
In view of the above, there exists a need for an automatic transmission apparatus, which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
SUMMARY OF THE INVENTION
One object of the present invention is to provide an automatic transmission apparatus that expands the direct drive region of the torque converter and greatly improve power performance and fuel economy by providing a five or six-speed automatic transmission apparatus having narrow differences between gear ratios and roughly the same cost and weight of a conventional four-speed automatic transmission apparatus.
Another object of the present invention is provide an automatic transmission apparatus that is more compact in the axial direction by dispersing the structural elements onto two shafts and thus to achieve an automatic transmission apparatus that is suitable for a front-engine, front-wheel-drive vehicle.
Yet another object of the present invention is provide an automatic transmission apparatus that reduces power losses by lowering the rotational speed of the structural elements of the transmission unit.
At least some of the foregoing objects are attained by providing an automatic transmission apparatus in accordance with the present invention. The automatic transmission apparatus of the present invention is a device that transmits power from the engine side thereof to an output shaft and is equipped with a first shaft, a second shaft, a pair of planetary gear trains, first and second pair of counter gears, and a plurality of coupling elements. The first shaft receives power input from the engine side. The second shaft is provided so as to be parallel with the first shaft. The planetary gear trains are disposed on the second shaft. One or both of the planetary gear trains have a first structural element and second structural element to which power is input, a third structural element from which power is output, and a fourth structural element disposed in the power transmission path. The first and second pairs of counter gears couple the first shaft with the structural elements of the planetary gear trains, and each of them has a different gear ratio. The plurality of coupling elements include first, second and third clutches and first and second brakes. The coupling elements are selectively activated in pairs of two elements in order to control the power transmission path. Furthermore, power is input to the first structural element of the planetary gear trains via either the first clutch and the first pair of counter gears, or via the second clutch and the second pair of counter gears. Power is input to the second structural element of the planetary gear trains via the third clutch and the second pair of counter gears. The third structural element of the planetary gear trains is connected to the output shaft. The first brake is provided so as to brake the rotation of the second structural element. Seven speed levels are obtained by selectively activating two coupling elements from among the first clutch, second clutch, third clutch, first brake and second brake. With this automatic transmission apparatus, power from the engine side is input to the first shaft. This power is transmitted to the second shaft via the pair of counter gears, its rotation is modified by the planetary gear trains, and then the power is output from the transmission. A transmission having seven speed levels, including five forward speeds and two reverse speeds, is obtained by selectively activating two coupling elements from among the first clutch, second clutch, third clutch, first brake and second brake.
In the present invention, a transmission having seven speeds and a simple structure is obtained by inputting a different rotational speed to the first structural element of the planetary gear trains of a conven
Exedy Corporation
Parekh Ankur
Shinjyu Global IP Counselors, LLP
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