Machine element or mechanism – Gearing – Interchangeably locked
Reexamination Certificate
2001-07-12
2002-11-26
Wright, Dirk (Department: 3681)
Machine element or mechanism
Gearing
Interchangeably locked
C074S473120, C477S099000
Reexamination Certificate
active
06484598
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an actuator for a change speed shaft of a motor vehicle automatic transmission.
BACKGROUND OF THE INVENTION
In motor vehicles having an automatic transmission shifting between the various gearbox positions, including the parking position, is done by means of a gearshift lever usually arranged above the transmission tunnel of the vehicle. The gearshift lever is coupled to a change speed shaft of the transmission via a traction cable or linkage.
BRIEF SUMMARY OF THE INVENTION
The invention provides an actuator for a change speed shaft of a motor vehicle automatic transmission comprising no gearshift lever to be actuated manually so that the space provided in conventional vehicles for the gearshift lever can be put to use for other purposes.
The actuator in accordance with the invention comprises:
a housing, an actuating shaft rotatably mounted in the housing, an electric motor with a rotor, a reversible low-loss reduction gearing by which the rotor of the electric motor is directly coupled to the actuating shaft, an energy storing means storing an amount of energy required for driving the actuating shaft independently of the electric motor, an electronic controller for driving the electric motor in response to control signals, a coupling means for coupling the actuating shaft to the change speed shaft, rotation of the actuating shaft by the electronic motor and through the coupling means being converted into angles of rotation of the change speed shaft which correspond to the control signals.
The actuator in accordance with the invention is an electromechanical positioner activated by electrical control signals. The electrical control signals can be generated by switches actuated manually located anywhere as desired in the vehicle, for example, on the dashboard or on the steering wheel.
An objective of the invention is to ensure that the automatic transmission is switched to the parking position when the ignition key is removed with the vehicle stationary, i.e. the driver not being forced to select the parking position before removing the ignition key. To satisfy this requirement, selecting the parking position must also occur even when there is a power failure to the electric motor. It is for this case that an energy storing means is provided storing an amount of energy required for driving the actuating shaft independently of the electric motor. The actuating shaft is thus powered in normal operation by the electric motor through the reduction gearing and in emergency operation via the energy storing means. To permit eliminating a mechanical selector device, however, which is hardly achievable with the necessary reliability, the invention provides for both the energy storing means in emergency operation and the electric motor drive in normal operation being permanently coupled to the actuating shaft. The electric motor thus works against the energy storing means, for example, a tensioned spiral spring, and the energy storing means entrains in emergency operation the electric motor through the reduction gearing which then translates to a higher speed. This concept requires, on the one hand, a particularly rugged electric motor and, on the other, a low-loss design of the reduction gearing.
In accordance with one advantageous embodiment of the invention a brushless external rotor motor is provided as the electric motor, particularly suitable being a 28-pole 4-phase external rotor motor. To permit positional control a rotary shaft encoder is employed achievable by two Hall sensors assigned to the rotor. Such a rotary shaft encoder permits sensing the absolute angles of rotation of the rotor. Driving the stator windings is done by extremely low-impedance FET-type power semiconductors.
A particularly low-loss reduction gearing suitable for communicating a high torque is achieved by a two-stage design. The first stage is a belt drive with a small diameter pulley on the rotor of the electric motor coupled to a larger diameter pulley via belts, more particularly V-belts. The second stage is a planetary gearing, the sun gear of which is connected to the larger diameter pulley for joint rotation and the and planet carrier of which is coupled to the actuating shaft. The reduction ratio of such a two-stage reduction gearing is, for example, approx. 40 to 1.
A further objective of the invention is to ensure that in the absence of an explicit positioning command to the controller any shift action is excluded.
This objective is achieved by one further embodiment of the invention in that the actuating shaft can be selectively arrested in its various discrete rotary positions by a latch active in the non-operated condition, unlatching requiring a current pulse to a solenoid which maintains the latch temporarily in the release position. The solenoid has two exciter windings each independent of the other. The first exciter winding is driven in normal operation by the controller when a positional control is translated. The other exciter winding is driven by a signal derived from the vehicle ignition lock when the ignition key is removed and the vehicle is stationary. For this signal, energy needs to be available independently of the vehicle voltage which, however, may be small and, for example, achievable by a storage capacitor coupled to the vehicle electrics via a decoupling diode.
REFERENCES:
patent: 5531303 (1996-07-01), Raszkowski
patent: 5901608 (1999-05-01), Takeyama
patent: 6367344 (2002-04-01), Vogt et al.
patent: 19734023 (1998-02-01), None
patent: 19823767 (1998-12-01), None
patent: 19857714 (1999-06-01), None
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
TRW Automotive Electronics & Components GmbH & Co. KG
Wright Dirk
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