Synchronized gearbox

Details Synchronized gearbox Synchronized gearbox

2000-03-28

2001-09-18

Marmor, Charles A (Department: 3681)

Machine element or mechanism

Gearing

Interchangeably locked

C074S333000, C074S339000, C192S01800B, C192S066200

Reexamination Certificate

active

06289757

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a motor vehicle gearbox.
The invention relates more particularly to a motor vehicle gearbox of the type which is provided with at least two parallel shafts, the primary and secondary, respectively linked in rotation to a vehicle engine and, via a transmission, to at least one vehicle wheel, and of the type in which one of the shafts supports at least one first idler pinion engaging with a second fixed pinion supported by the other shaft, the first pinion being capable of being linked in rotation to the shaft which supports it to transmit motive power from the engine to the vehicle wheel.
DISCUSSION OF THE BACKGROUND
There are known numerous gearboxes which permit the establishment of various gear reduction ratios by interlocking of idler pinions on their shafts.
In the case, for example, of a gearbox with two parallel shafts, when a user initiates the change from a first gear reduction ratio to a second gear reduction ratio by means of a gear shift lever, the first idler pinion corresponding to the first ratio is “released” from the first shaft supporting it before the second idler pinion corresponding to the second ratio is in turn interlocked on the first shaft. Since the operation is extremely fast, the first shaft continues to turn at a speed close to that which it had when the first idler pinion was interlocked thereon. The second idler pinion, which for its part is driven by a second fixed pinion of the other shaft with which it is engaged, turns at a speed substantially different from that of the first shaft by virtue of a different gear reduction ratio.
To ensure that it can be interlocked on the first shaft, the second idler pinion must be brought beforehand to a speed of rotation substantially equal to that of the first shaft.
This is the function conventionally assigned to devices known as synchronizers.
Each idler pinion is coupled to an axially declutchable device, generally operated by an axially movable band driven by the displacement of an operating fork parallel to the shaft supporting the idler pinion.
Once clutched, the device permits the idler pinion to be frictionally in rotation to its shaft in such a way that it progressively leads to an adequate speed of rotation without transmitting a large torque at the same time.
In a second step (the pinion and shaft turning at the same speed), the device then permits the idler pinion to be linked to the shaft by means, for example, of a toothed coupling, thus establishing a gear reduction ratio of the gearbox.
Such a device is advantageous in that interlocking of the idler pinions on their shafts can be facilitated thereby. In fact, since the majority of interlocking devices are provided with toothed couplings, it is important that the idler pinions be synchronized beforehand with their shaft(s) before being interlocked, in order to limit tooth wear and to guarantee noiseless operation of the interlocking device.
On the other hand, the devices provided with synchronizers have the disadvantage of using a synchronizer based on idler pinions, thus considerably increasing the axial space requirement and weight of the gearbox.
In addition, in the case of a so-called robotized gearbox, or in other words a gearbox in which the different members are shifted by pilot-controlled actuators, these actuators being operated by an electronic control unit on which the vehicle operator acts, the use of synchronizers is particularly difficult. In fact, compared with a conventional operating system with selection fingers and forks, operation of the synchronizers by actuators is particularly inappropriate, since the actuators occupy considerable space.
SUMMARY OF THE INVENTION
To remedy these disadvantages, the method according to the invention no longer comprises bringing the pinion to be interlocked to a speed close to that of the shaft on which it must be interlocked, but instead comprises bringing the shaft on which it must be interlocked to a speed close to that of the pinion to be interlocked.
With this objective the invention proposes a gearbox of the type described hereinabove, characterized in that it is provided with controlled declutchable means permitting the primary shaft to be accelerated or braked selectively in order to synchronize the speed of the idler pinion with that of the shaft supporting it before linking it in rotation to the said shaft, and being capable of accelerating the primary shaft as long as its speed is lower than that of the idler pinion and of braking the primary shaft as long as its speed is higher than that of the idler pinion.
According to other characteristics of the invention:
the declutchable means for accelerating the primary shaft are provided with means for temporarily linking the primary shaft in slipping rotation to the secondary shaft;
the means for linking the primary shaft in rotation to the secondary shaft are provided with a first toothed gear coaxial with the primary shaft, which gear engages with a second toothed gear supported by the secondary shaft and linked in rotation thereto, the second gear being capable of being temporarily linked in rotation to the primary shaft via a slipping device for coupling of acceleration;
the controlled declutchable means for braking the primary shaft are provided with means for temporarily linking the primary shaft in slipping rotation with the gearbox case;
the means for linking the primary shaft in rotation to the gearbox case are provided with a fixed frustoconical bearing surface of the gearbox case, coaxial with the primary shaft, to which the primary shaft can be linked temporarily via a slipping device for coupling of braking;
the slipping devices for coupling of acceleration and of braking are provided with a common contact wheel, which is linked in rotation to the primary shaft by splines, which is provided with two oppositely disposed annular frustoconical bearing surfaces, and which is capable of being driven slidingly along the primary shaft
toward a first active extreme axial position in which a first annular frustoconical bearing surface cooperates by friction with a complementary annular frustoconical bearing surface of the said first toothed gear, to accelerate the primary shaft,
or toward a second, opposite active extreme axial position in which a second annular frustoconical bearing surface cooperates by friction with the fixed, annular and complementary frustoconical bearing surface of the gearbox case, to brake the primary shaft,
by passing through an indexed intermediate axial rest position;
the annular bearing surfaces are frustoconical;
the annular frustoconical bearing surfaces are plane, and the contact wheel is a clutch disk covered with a friction lining material;
the slipping devices for coupling of acceleration and coupling of braking comprise an electromagnetic clutch, in which two radial cages coaxial with the primary shaft, supported respectively by the first toothed gear and by the fixed frustoconical bearing surface of the gearbox case, are capable of cooperating selectively in slipping manner with two ends of a rotor in two portions integral with the primary shaft to accelerate or brake respectively the primary shaft when a magnetic flux is established between a rotor portion and a clutch cage;
the electromagnetic clutch is a metal-powder clutch;
the gearbox is provided with a motorized pump, in which a fixed case supporting axial pistons is integral with the gearbox case, in which a control plate is linked in rotation to the primary shaft of the gearbox, and which is capable of operating selectively as a hydraulic motor or hydraulic pump to accelerate or brake respectively the primary shaft;
the gearbox is a robotized gearbox which is provided with automated control means acting on the declutchable means for acceleration and braking of the primary shaft, and automated means for interlocking the idler pinions on the shafts supporting them.


REFERENCES:
patent: 805978 (1905-11-01), Menges
patent: 858764 (1907-07-01), Sears
patent: 860649

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