192 clutches and power-stop control – Transmission and brake – Motor vehicle
Reexamination Certificate
2001-10-19
2003-03-04
Bonck, Rodney H. (Department: 3681)
192 clutches and power-stop control
Transmission and brake
Motor vehicle
C188S00300R, C303S003000
Reexamination Certificate
active
06527096
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention pertains to a control device for the parking lock of a motor vehicle with at least one actuating drive element that can be operated by triggering means, with which at least one locking device of the parking lock can be brought from an engaged position, into which it is pressed by a retaining force, into a disengaged position.
For current vehicle transmissions (synchronized, power-shifting or automatic transmissions), the parking lock is usually set manually via a mechanical linkage in order to block the rotational motion of gear or vehicle wheels with a positive lock. As part of increasing driver comfort, transmissions have been designed with an electrically operated shifting of gears, so that the gear-shift command from the driver is done by pushing a button. It would make sense for the parking lock also to be incorporated into this servo operation. When infinitely variable transmissions, which can implement a non-positively locked stop by setting an infinitely high transmission rate, are used, the actuation of the parking lock ought to be automated so that the transition from the non-positive stop to the park position (and vice versa) takes place without interruption of the braking force of the vehicle. It is therefore sought to design the actuation of the parking lock (a mechanical, positive locking of an output-side gearwheel) such that setting and releasing the lock takes place by transmission of an electric command.
Since the operating safety of the vehicle depends quite crucially on the functioning of the parking lock, its design and layout should be operationally secure, that is, redundant. This pertains above all else to the reliable execution of the driver's desire for locking and unlocking, the prevention of unintended locking during travel and of unintentional unlocking while stopped (due, for instance, to failure of auxiliary power, a short circuit in the power circuit and the like).
The problem underlying the invention is viewed to be the specification of a control device for the parking lock of the initially mentioned type, by which means the aforementioned requirements are met. In particular, the control device should permit safe, reliable actuation of the parking lock. It should be possible for it to be manufactured in a simple, economical manner and constructed such that it can be retrofitted into existing transmissions without significant difficulties.
SUMMARY OF THE INVENTION
According to the invention, at least two triggering means acting independently on the actuating drive element are provided, which interact with the actuating drive element such that movement of the locking device out of the engaged position into the disengaged position or, conversely, from the disengaged position into the engaged position takes place only if the two triggering means are triggered with changeover signals in the same sense.
This can be implemented in various ways. For instance, the actuating drive element can be a magnetic solenoid plunger which engages the locking device when it is de-energized and disengages it when it passes current. The triggering means can be electrical switches situated in the power circuit of the solenoid plunger and actuated by an electrical controller via electrical switching signals.
A preferred embodiment of the invention provides an electro-hydraulically operated controller. The drive element here is preferably a hydraulic actuating piston under initial spring tension, which brings the parking lock into its disengaged position upon application of pressure. The triggering means are expediently constructed as electrically triggerable hydraulic valves, which can be brought against the force of a spring by electrical signals from an idle position into an active position. 3/2-way solenoids come into particular consideration.
In this case, the hydraulic valves convert electrical commands into hydraulic commands. In particular, they are connected, in conjunction with the check valves, such that a change of state for the parking lock (unlocking or locking) takes place only if both hydraulic valves switch in the same sense. If both hydraulic valves are in the de-energized state, then the actuating drive element, specifically, the actuating piston, is connected to the non-pressurized sump and inflow from the pressure source to the sump is cut off, so that the actuating drive element, and with it the parking lock, is in the engaged, locked position. If power is applied to both hydraulic valves, their magnetic slides are pushed against the force of their respective restoring springs into the position in which the actuating drive element is connected to the pressure source and separated from the sump. Under the force of the system pressure from the pressure source, the actuating drive element moves into its disengaged, unlocked position against the force of the parking lock spring providing retaining force.
The check valves mentioned in claims 5 and 6 are connected in opposite directions and are preferably held in their closed positions by restoring springs. With a sufficiently high hydraulic pressure, the check valves can be opened against the spring force.
Independently of the state (engaged or disengaged) in which the parking lock is situated, this state is preserved if only one hydraulic valve is changed over. Such a changeover can be initiated, for instance, by an unintentional electrical signal (e.g., by an electrical short circuit to ground or to a 12-V power source).
It is expedient for a spring-loaded input check valve, which blocks flow back to the pressure source in case of loss of system pressure that may unexpectedly occur during travel and can thus preserve pressure on the actuating drive element, to be placed in the inlet path of pressure flow to the hydraulic valves. In this way, a sudden engagement of the parking lock during travel due to loss of pressure in the system (pump damage, leakage in the system, etc.) is prevented. The design can be such that the pressure in the actuating drive element can be maintained for approximately 10 min, so that time remains for the vehicle user to bring the vehicle to a controlled stop after the appearance of a warning message.
The two hydraulic valves are preferably implemented as economical slide valves, which normally exhibit a certain leakage, depending on the temperature of the hydraulic fluid and the pressure differential. If, for instance, the first hydraulic valve should lose power and switch back due to a cable breakage or the like during travel, i.e., with a disengaged parking lock, it is possible for the piston chamber of the actuating piston to be slowly emptied back into the sump via internal leakage of the second hydraulic valve. Specifically to prevent this, a preferred refinement of the invention provides that the piston chamber of the actuating piston be connected to the pressure source via an additional valve arrangement.
A pressure-maintaining check valve, which prevents a backflow from the piston chamber to the pressure source, and a throttle point are expediently arranged in series in a connection line linking the piston chamber to the pressure source. Thus, the piston chamber of the actuating piston can also be supplied directly from the pressure source via the pressure-maintaining check valve and the throttle point when the parking lock is completely released—that is, when the piston chamber is under pressure, the actuating piston is moved into the disengaged position and the leakage compensation valve is opened—so that pressure is maintained even in case of leaks. In case of a pressure drop during travel, the pressure-maintaining check valve prevents the piston chamber from being emptied by a backflow via the connection line to the sump (due to leakage of the first hydraulic valve). For the case where the actuating piston is to be brought into its engaged position by the hydraulic valves connecting the piston chamber to the sump, the throttle point limits the inflow to the piston chamber and thus permits a sufficient fluid drainage
Falck Peter
Hoess Bruno
Kilworth Timothy
Kugler Uwe
Schäfer Helmut
Bonck Rodney H.
Deere & Company
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