Powertrain with a multi-speed transmission

Details Powertrain with a multi-speed transmission Powertrain with a multi-speed transmission

1999-12-10

2001-03-13

Marmor, Charles A (Department: 3681)

Planetary gear transmission systems or components

With means to vary drive ratio or disconnect drive

Plural elements selectively braked

C475S313000

Reexamination Certificate

active

06200242

ABSTRACT:

TECHNICAL FIELD
This invention relates to powertrains with multi-speed transmissions and more particularly to transmissions having at least six forward speeds.
BACKGROUND OF THE INVENTION
In an effort to improve the overall performance of a vehicle while also reducing the mass of the vehicle, the number of speed ratios available through the transmission is increased. This permits a more efficient use of the engine operating range while also reducing the size of the engine. The increased number of speed ratios allows for a higher low gear ratio which will result in a reduced size torque converter.
The number of forward speed ratios in power transmissions has increased from two to five over a number of years. Many of the five speed transmissions incorporate two or three interconnected simple or compound planetary gear sets and five or six selectively engageable clutches or brakes. These transmissions quite often include one or more bridging clutches when two interconnected planetary gear sets are utilized. One example of this type of power transmission can be seen in U.S. Pat. No. 5,830,102 issued to Coffey on Nov. 3, 1998.
Currently many manufacturers are considering increasing the number of ratios to six or seven. These transmissions generally contain three planetary gear sets. One such transmission is seen in U.S. Pat. No. 3,946,623 issued Mar. 30, 1976. This prior art transmission incorporates four interconnected planetary gear sets, three clutches and four brakes when more than five speed ratios are to be attained. Another known six speed transmission is shown in U.S. Pat. No. 4,070,927 issued Jan. 31, 1978. A six speed planetary having two simple planetary gear sets is disclosed in U.S. Ser. No. 09/383,429 filed Aug. 27, 1999 and assigned to the assignee of this application.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved multi-speed planetary transmission.
In one aspect of the present invention, the planetary transmission has two compound planetary gear sets and seven selectively engageable torque transmitting mechanisms. In another aspect of the present invention, the torque transmitting mechanisms include four rotating mechanisms and three stationary mechanisms. In yet another aspect of the present invention, one of the stationary mechanisms is a mechanically engaging device.
In still another aspect of the present invention, the ring gear member of one of the planetary gear sets is continually connected for common rotation with an output shaft and the ring gear member of the other planetary gear set is continually connected for common rotation with the carrier assembly member of the one planetary gear set.
In yet still another aspect of the present invention, three of the rotating mechanisms are input drive devices and one of the rotating mechanisms is an interconnecting device. In a further aspect of the present invention, the mechanically engaging device is utilized only in the establishment of a reverse speed ratio. In yet a further aspect of the present invention, two one-way torque transmitting mechanisms are provided to establish reaction members in one of the planetary gear sets.
The present invention employs two planes of planetary gears to provide six forward speed ratios and one reverse ratio. Two compound planetary gear sets are interconnected and controlled by four selectively actuated, rotating torque transmitting mechanisms or clutches and three selectively actuated, stationary torque transmitting mechanisms or brakes. The torque transmitting mechanisms are actuated in combinations of three to establish the reverse speed ratio and the six forward speed ratios which include four underdrive ratios, a direct drive ratio and an overdrive ratio.
The overall ratio (1
st
/6
th
) of the forward speed ratios is greater than 5.2 and the 1
st
to 2
nd
ratio step is less than 1.7. The high overall ratio and the low 1
st
to 2
nd
step ratio permits a tighter torque converter to be incorporated into the transmission. Since the tighter torque converter is more efficient, an increase in overall powertrain efficiency is attained. Typically a one-percent (1%) increase in torque converter efficiency results in a one-half of one percent (½%) improvement in combined fuel economy.
The step ratio between the two highest speed ratios (5
th
and 6
th
) is less than 1.25. The small step size allows a reduction in top gear gradability since the ratio interchange (6
th
to 5
th
) would be substantially imperceptible to the driver. The reduction in top gear gradability typically improves fuel economy.
To further improve the efficiency of the transmission, a mechanical brake, often termed a “dog clutch”, can be employed to establish the reaction members in the planetary gear sets. This brake is engaged without a torque load being present and one of the other selectively engageable torque transmitting mechanisms is actuated to complete the vehicle launch or “garage shift”. This mechanism can be controlled mechanically or hydraulically.


REFERENCES:
patent: 2873625 (1959-02-01), Simpson
patent: 4872376 (1989-10-01), Asada et al.
patent: 4916980 (1990-04-01), Asada et al.
patent: 5383822 (1995-01-01), Pierce
patent: 5690578 (1997-11-01), Hall, III

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