Brakes – Operators – Spring
Reexamination Certificate
2001-10-04
2004-03-02
Lavinder, Jack (Department: 3683)
Brakes
Operators
Spring
C303S003000, C303S011000, C303S015000, C303S020000
Reexamination Certificate
active
06698555
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a motor vehicle parking brake control device.
With today's vehicle transmissions (synchronized, power-shifting or automatic transmissions), the parking brake is typically set by means of a mechanical rod assembly that blocks rotational movement of the transmission gears or the vehicle wheels by means of positive fit. In connection with improving ease of use, gears have been configured with electrically actuated gear switches, so that the change gear command can be performed by the driver by means of a push-button. Such a servo control could also be used in connection with the parking brake. With the use of continuously variable speed transmissions, which can realize a non-positive stationary state by adjusting to a infinitely high transmission ratio, the transition from the non-positive stationary state into the park position (and vice versa) is done without interrupting the braking effect of the vehicle. Thus, a goal is have a parking brake (mechanical, positive-fit locking of a drive-side gear) which can be locked and unlocked by transmission of an electrical command.
Because the operational safety of the vehicle depends on the function of the parking brake to a very large degree, the construction and design should be operationally safe, that is to say, redundant. Above all, this concerns the reliable execution of driver wishes for locking or unlocking, and preventing accidental locking while driving and accidental unlocking in a stationary state (e.g., through loss of auxiliary power, short circuit in the power circuit, and the like). Therefore, the electrical control unit should provide a return notification about the current state of the parking brake at all times.
To recognize the parking brake state, at least the two end positions of the parking brake, “locked” and “unlocked,” must be detected. Path sensors or end switches could be used, wherein they detect the position of the parking brake activation mechanism, and when each end position is reached, a contact is closed. However, because the activating mechanism end positions are strongly dependent on tolerances and wear, the corresponding signals cannot be triggered with sufficient accuracy. Reliability of path sensors can be adversely affected by abrupt movements of the activating mechanism. If an electrical parking brake is to be retrofitted, it is difficult to install path sensors or end switches into existing transmission housings without changing the existing transmission structure.
In general, the parking brake contains a detent with teeth that can engage the teeth of a gear of the drive train, so that a positive fit is produced and rotational movement of the drive train gear and thus movement of the vehicle is prevented. While engaging the parking brake from its disengaged position in the stationary state, sometimes, according to the teeth interval or the ratio of the tooth width to the gap width, the tip of a tooth of the detent can be positioned on the tip of a tooth of the gear. This tooth-on-tooth position prevents the entire mechanical activation chain from reaching its end position for the engaged position. However, an extremely small movement of the vehicle is sufficient to snap the detent into the next tooth gap. In the tooth-on-tooth position, a path sensor would not recognize that the locking position has been reached.
It is also conceivable to position a path sensor directly on the hydraulic piston in order to monitor the piston motion. However, this requires great expense in terms of construction because either pressure-tight or pressure-compensating implementations for contact switches or a complex rod assembly connecting to the hydraulic piston would be necessary.
U.S. Pat. No. 5,370,449 describes an electrically activated friction-fit parking brake, in which a pressure sensor is used to determine whether the brake is depressed (low pressure) or released (high pressure). As soon as the pressure sensor reports a high pressure, which corresponds to a released brake, the preselected transmission gear is set. However, no sensor signal is used for the transition region of the braking effect, that is, between total braking effect and the released state, so that this region remains undefined and there is uncertainty in the transmission control. Thus, there is the risk that the transmission could enter a non-positive engagement before the brake is released. Also, the brake could be released before the transmission is engaged, so that on a slope, a vehicle not in gear could roll uncontrollably. With the control of positive-fit parking brakes, other problems occur beyond those of non-positive parking brakes.
SUMMARY
Accordingly, an object of this invention is to provide a control device for the parking brake of a motor vehicle, by means of which the previously mentioned problems can be overcome.
A further object of the invention is to provide such a control device which is reliable and which enable vehicles to be equipped at a later time and in a simple way with an electrical control unit for a parking brake.
A further object of the invention is to provide such a control device which enables a freely selectable installation, has a simple construction, and is maintenance-friendly.
A further object of the invention is to provide such a control device which handles the system-dependent tooth-on-tooth position as a normal operating condition (engaged position) and enable diverse plausibility checks.
These and other objects are achieved by the present invention, wherein a control device for a parking brake includes at least one hydraulic cylinder and one pressure sensor that detects the pressure in the hydraulic cylinder directly or indirectly. The hydraulic piston of the hydraulic cylinder is connected mechanically to engagement elements of the parking brake, so that the parking brake is forced into an engaged or disengaged position in dependence on the hydraulic pressure. The pressure sensor outputs pressure signals that represent the state of the parking brake and that are evaluated by an electrical control unit. The pressure signals of the pressure sensor are evaluated relative to at least two predetermined pressure threshold values. A first pressure threshold value is defined to correspond to the engaged state of the parking brake. A second pressure threshold value, which is different from the first pressure threshold value, corresponds to the disengaged state of the parking brake. As a rule, the second pressure threshold value is greater than the first pressure threshold value.
The control or evaluation unit recognizes at least three pressure ranges: a lower pressure range, in which the parking brake is engaged, an upper pressure range, in which the parking brake is disengaged, and a middle transition range. An unambiguous return message about the instantaneous state of the parking brake activation is provided to the control device at all times. Signals are provided that enable a locking circuit to be designed so that the demands for high reliability are satisfied.
In connection with additionally available input signals, such as commands from the operator, output speed, solenoid valve voltage, ignition, engine speed, and the like, many different plausibility queries and error messages can be generated due to detection of the pressure range. The signals of the control and evaluation unit can be used for a return notification to the operator and/or for controlling the transmission. These can also be used to diagnose faults relative to hydraulic and/or electrical problems.
The pressure sensor can be mounted in a simple way directly to the piston chamber or to a channel that is connected to a connecting line running between the valve arrangement and the piston chamber of the hydraulic cylinder. Thus, the position to attach the pressure sensor can be freely selected. This permits a maintenance-friendly design that is simple in terms of construction. The electrical parking brake unit can also be retrofitted in a simple way. Preferably, a pressure
Hoess Bruno
Poehlman Michael
Schäfer Helmut
Deere & Company
Lavinder Jack
Pezzlo Benjamin A
LandOfFree
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