192 clutches and power-stop control – Transmission and brake – Motor vehicle
Reexamination Certificate
2003-01-13
2004-11-30
Rodriguez, Pam (Department: 3683)
192 clutches and power-stop control
Transmission and brake
Motor vehicle
C188S031000
Reexamination Certificate
active
06823976
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a parking brake, especially for an automatic transmission for a motor vehicle or for an automatized, manual, motor vehicle shift.
BACKGROUND OF THE INVENTION
Normally, with motor vehicles automatic transmissions possess a mechanically acting parking brake apparatus, in which, for example, when in park, a blocking pawl drops into a tooth gap of a parking brake gear. The gear is connected to the output shaft of the transmission and thus to an axle of the vehicle. Mechanical and electrohydraulic systems are known to be used as operative connectors between a parking brake and its regulatory apparatus in the interior of the motor vehicle. Mechanical operative connectors, for instance, comprise encased push/pull cables between a selector lever affixed to the body, an electro-hydraulic transmission control placed in the automatic transmission as well as to the parking brake activation apparatus located within the transmission housing. A purely electrical activation connection between the automatic transmission regulating apparatus in the interior of the vehicle and the electrohydraulic transmission control demands, as a condition, the conversion of the electrical signal into the mechanical movement of a pawl to block/unblock the parking brake. Essential advantages of the purely electrically executed actuation between the operative apparatus of the automatic transmission and the electrohydraulic transmission control are found in an acoustic decoupling of the operative apparatus from the input drive string of the motor vehicle and the free choice of the location of the regulating apparatus in the interior of the vehicle.
DE 43 22 523 A1, for instance, describes an electrohydraulic control device for an automatic transmission of a motor vehicle, with an electrically based operative connection between the regulatory apparatus in the interior of the vehicle for the automatic transmission and the electrohydraulic transmission control, wherein the shift stages D, R, and N are effected by the application of pressure to individual shifting members, while the stage P automatically engages upon loss of pressure in all connected shifting members.
This arrangement leads to the fact, that not only in stage P, but also in all shifting stages of the gear-shift lever, upon loss of pressure, the parking brake is actuated. The engagement of the parking brake is executed, in this case, by a spring accumulator, its release being carried out, in contrast, hydraulically. The supply of the necessary pressure for applying the said brake is effected by means of a pressurized oil circulation system, which is inherent in the automatic transmission. In order to be able to release the engaged parking brake in case of failure of the electrical voltage supply, or of a defect in the electronic control device of the automatic transmission, or yet a failure in the transmission oil supply, additionally an emergency disengagement arrangement is provided, by means of which the parking brake can be mechanically released.
DE 41 27 991 C2, for example, likewise discloses a parking brake system for a motor vehicle automatic transmission, with an electrically based operative connection between the regulatory apparatus of the automatic transmission, which is in the vehicle interior and the shiftable parking brake mechanism, wherein the parking brake is engaged by means of a mechanical spring accumulator and released by means of an electrohydraulic transmission control functioning at an elevated pressure. For this purpose, the activation rod, by which the parking brake is caused to engage and/or release, simultaneously serves as a piston in a single action cylinder-piston combination. For the release of the parking brake and for its retention in a released condition, the cylinder is subjected to pressure by a solenoid valve admitting pressurized oil. The hydraulic pressure is, advantageously, supplied directly from the pressurized oil circulation of the automatic transmission, which also furnishes the hydraulic transmission control. In the selected gear shift position P, the solenoid valve is in the closed position and the cylinder is freed of pressure. In the non-pressurized stance, the cylinder pushes the parking brake into the engaged position. The force for this action of the cylinder is supplied by the spring force of the spring accumulator. In one embodiment, the proposal is to provide an elevated pressure reservoir tank with a check valve, in order to hold the parking brake disengaged for a specified time if the motor stalls and pump pressure fails.
Finally, the generic DE 198 34 156 A1 discloses a parking brake system for an automatic transmission in a motor vehicle, wherein the parking brake pawl, as a result of sliding induced by a spring accumulator, falls into its restraining place and can be freed by means of hydraulic pressure, which is supplied by the oil circulatory system of the automatic transmission. At the same time the spring accumulator is pretensioned. For the prevention of an involuntary engagement of the parking brake upon loss of pressure, a hydraulic parking brake activation device provides a mechanical detent by one or more balls. The ball detent action is activated by an electromagnet, in which an activating rod is placed in a linearly sliding motion as a result of energization of the electromagnet. When this occurs, the balls are brought into the locking position by the activating rod which has a diameter equivalent to that of the ball. As long as the electromagnet is energized, just so long is the parking brake held in its non-braking position. A blocking mechanism which can carry out this operation requires, counter to the available opposing force of the spring accumulator, only a relatively small activation force to effect a linear motion in the activation rod which must be brought away from the electromagnet. The holding force of the ball detents, which likewise must be brought away from the electromagnet, is very small. The design criteria for the electro magnet are, the required pulling force for the activation of the braking mechanism, the path of the activation and the necessary holding power. In the case of a locking mechanism in accord with DE 198 34 156 A1, the activation path measures about 3 mm. Since it is known that the attraction force of an electro magnet decreases rapidly as separation therefrom increases, the result is that the electromagnet, with a relatively large activation path of the locking mechanism, must have correspondingly large dimensions. As a result of this, mounting space problems can arise and an unwanted large power must be provided to energize the electromagnet, which must be supplied, as a rule, by the electronic transmission control.
Thus, the present invention has the purpose of improving an electrohydraulically controlled parking brake, in accord with the generic state of the technology, in regard to a minimizing of the necessarily consumed electrical capacity and a reduction of the mounted space of the parking brake activation apparatus.
In accord with the invention, this purpose is achieved with a parking brake, which possesses the features of the principal claim. Further advantageous embodiments of the invention are evident in the subordinate claims.
SUMMARY OF THE INVENTION
The invention proceeds from the concept of a known parking brake system, in which a parking brake locking pawl for the blocking of a transmission is hydraulically disengaged, wherein, the required hydraulic energy for this action is advantageously supplied by the electrohydraulic control unit of the transmission. An advantageous activation element of the releasing arrangement of the parking brake is a hydraulically actuated cylinder, which is in mechanical connection with the parking pawl. Simultaneously, with the withdrawal of the parking pawl from its engagement, a spring accumulator is pretensioned, by means of the spring force of which, the parking brake, upon a depressured positioning of the hydraulic release element, engages. The now
Davis & Bujold P.L.L.C.
Rodriguez Pam
ZF Friedrichshafen AG
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