Power-shiftable gear, especially two-speed planet gear

Details Power-shiftable gear, especially two-speed planet gear Power-shiftable gear, especially two-speed planet gear

1996-08-01

1997-12-23

Wright, Dirk

Planetary gear transmission systems or components

Fluid drive or control of planetary gearing

Fluid controlled mechanical clutch or brake

475140, F16H 6106

Patent

active

057002207

DESCRIPTION:

BRIEF SUMMARY
The invention concerns a power-shiftable gear, especially a two-speed gear preferably designed as planet gear. The ratios of said gear are shifted by hydraulically actuatable friction clutches. The friction components (inner and outer discs) of the friction clutches are engaged by spring tension and disengaged by oil pressure.
In a power-shiftable gear disclosed in WO 89/08796, two speeds can be shifted. When shifting the speeds, friction clutches (one of said friction clutches acts as brake) are alternatively disengaged and engaged. The friction clutches are engaged by plate springs. When both friction clutches are pressureless, that is, engaged, the input and output (parking brake) are blocked.
Due to the relatively strong forces of the plate spring, the pressure medium (hydraulic oil) is removed from the respective pressure chambers to the tank within a very short time. The time needed for disengaging the friction clutches depends on the delivery rate of a source of pressure medium (pump).
By inserting non-return valves with chokes in parallel therewith in the line leading to the pressure chambers, it can be ensured that the alternative disengaging and engaging of the friction clutches be adjusted in a manner such that the friction clutch to be engaged is engaged only when the friction clutch to be disengaged is disengaged.
The non-return valves, added around the chokes, are disposed so that upon opening the oil current can flow unchecked into the respective pressure chamber. When closing, the oil current removed from the pressure chamber is choked drawn into the tank.
The moment of closing can be affected by the valves mentioned. The engaging operation itself, that is, the timed torque intake of the friction clutch, cannot be affected thereby. As soon as the piston working upon the friction components in the sense of engaging has overcome the clearance (sum of the spacings of the inner and outer discs of a friction clutch in a disengaged state), the torque transmissible by the friction components suddenly increases to a maximum valve. Since the engaging operation takes place in a very short time, this makes an abrupt change itself noticeable, especially during a downshift from the second to the first speed, which is felt as especially unpleasant.
An older not previously published proposal of the applicant (international patent application PCT/EP93/02421)-which is the point of departure of the instant invention-relates to means which prevent, during a gear change, that the full locking force acts first upon the friction components of the friction clutches. Thus, the torque curve can, in particular, be affected so as to avoid an abrupt change.
This invention is based on the problem of further improving the pressure and torque curves when downshifting or upshifting.
The stated problem is solved by a power-shiftable gear, especially a two-speed gear designed as planet gear, having at least one friction clutch the friction components of which are engaged by spring tension and disengaged by oil pressure, one line leading to a pressure chamber and in which is a store formed by one cylinder and one spring-loaded piston with a non-return valve and a choke in parallel with it.
Hereby is prevented, in the first place, that when clearance between the friction components is reduced to a value of zero or near zero, the full spring tension act upon the friction components. In addition, the store is situated in the line leading to the pressure chamber of the friction clutch in a manner such that during engaging the friction clutch the phase lasting until the torque begins to be taken over is shortened. Loss of traction practically does not occur.
In a preferred embodiment, when the friction clutch is disengaged, the piston assumes a position in which the store has a minimum of storage capacity.
Since the store is practically empty when the friction clutch is disengaged, it is very advantageously possible during the beginning of engaging of the friction clutch, that is, with the line connected with the tank and engaged

REFERENCES:
patent: 5098354 (1992-03-01), Kuwayama et al.
AN 89-208046 & DE A 3844126 (Akebono) Derwent Publ.

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