192 clutches and power-stop control – Transmission control and clutch control – Common control
Utility Patent
1999-05-05
2001-01-02
Bonck, Rodney H. (Department: 3681)
192 clutches and power-stop control
Transmission control and clutch control
Common control
C192S03000R, C192S090000
Utility Patent
active
06167995
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to clutch release mechanisms for a motor vehicle friction clutch for use with a motor vehicle transmission, especially commercial or utility vehicle transmissions, with subdivided shifting or switching steps. More particularly, the present invention relates to a release mechanism actuatable by compressed air.
2. Description of the Related Art
A release mechanism is known from German patent publication DE 197 16 600 A1. This known release mechanism in which the releasing force is generated by air pressure and the extent of the release actuation is predetermined by a hydraulic system coupled with a clutch pedal is basically constructed for use with vehicle transmissions, especially in commercial or utility vehicle transmissions, which are constructed with or without subdivided switching steps. Transmissions in which the switching steps are subdivided comprise a subdivided stage which can be switched on or off as desired by the driver or an intermediate gear by means of which the switching steps, provided per se, can be switched by, for example, a half switching step. Thus, for example, when the subdivided stage is not activated switching can be carried out in the following gear sequence: 1
st
, 2
nd
, 3
rd
, etc. When the subdivided stage or intermediate gear is activated, the gears are then displaced by, for example, a half switching step, so that shifting can be carried out in the following gear sequence: 1½. . . 2½. . . 3½, etc. When the subdivided shifting stages or intermediate gears are selectively switched on or off, it is important to ensure that the motor vehicle clutch is in its fully released state for carrying out this shifting process. This requires accurate detection of the release state. For example, an electric switch can be arranged at the clutch pedal, so that the electric switch is activated when the clutch pedal is completely depressed and initiates shifting through the shifting stages. However, a problem associated with this mechanism is that there is no exact relationship between clutch pedal actuation and the actual release state in the case of air pressure actuation of the clutch, so that even when the clutch switch initiates shifting, it is possible that the clutch is not yet in its fully released state.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a release mechanism for a friction clutch in a motor vehicle which has none of the problems cited above. The release mechanism may be employed in a motor vehicle transmission such as, for example, a commercial or utility vehicle transmission with subdivided switching steps. By means of the inventive release mechanism, the release position required for initiating the shifting processes of the transmission can be detected in a reliable and assured manner.
According to one aspect of the invention, this object is met by a release mechanism for a friction clutch of a motor vehicle transmission, particularly a commercial or utility vehicle transmission, with subdivided switching steps and which includes the following: a release member which is displaceable by means of application of compressed air for carrying out release processes, a valve arrangement for selective supply of compressed air for acting upon the release member, a measurement arrangement for detecting an actual release position of the release member. The valve arrangement carries out the application of pressure medium on the release member depending on (1) a reference variable which is provided by an actuation arrangement and which represents a reference release position of the release member, and (2) the detected actual release position.
According to another aspect of the invention, there is provided a measurement arrangement constructed in such a way that when the detected actual release position exceeds a predetermined switching threshold release position, a shifting signal is provided for shifting the subdivided switching steps.
According to still another aspect of the present invention, the measurement arrangement which is provided in this release mechanism in any case is accordingly used simultaneously to indicate when a predetermined release position has been reached in which shifting can be initiated insofar as a shifting command has been given by the driver of the vehicle. That is, there is no need to provide separate sensors or other detection elements which detect the instantaneous release position or which allow direct conclusions concerning the instantaneous release position. Since the release position of the release member can be detected by the measurement arrangement in a certain and very precise manner, the shifting process can, if desired, also be carried out in a precise manner when the desired release position exists.
In one embodiment of the release mechanism according to the invention, it is preferably provided that the shift signal is reproduced by a shifting force for shifting the subdivided switching steps. This means that a force is delivered directly by means of the measurement arrangement when the shifting can be carried out, wherein this force is then utilized simultaneously and preferably directly for carrying out these shifting processes.
For example, the measurement arrangement may include a switch device which adjusts a supply of pressure fluid generating the shifting force depending on the detected actual position.
The switch device preferably comprises:
(1) a pressure fluid feed in fluid communication with a pressure fluid source;
(2) a pressure fluid outlet for communicating pressure fluid supplied from the pressure fluid source to the transmission; and
(3) a valve unit which provides a fluid connection between the pressure fluid inlet and the pressure fluid outlet when the detected actual release position exceeds the switching threshold release position.
Therefore, in accordance with the detected release position, fluid pressure can be communicated from the pressure fluid source at an appropriate point in time and the shifting process can be triggered by corresponding shifting commands.
The valve device preferably includes:
(1) a valve element which is pretensioned or resiliently urged toward at closing position in which the pressure fluid connection between the pressure fluid inlet and the pressure fluid outlet is interrupted or otherwise disconnected; and
(2) a valve actuation element which is movable or displaceable in accordance with the actual release position and through which the valve element can be moved into an open position so as to define the pressure fluid connection between the pressure fluid feed and the pressure fluid outlet when the predetermined switching threshold release position is exceeded.
In order to relieve this pressure fluid system, it is proposed that the valve device also has a pressure fluid discharge which is in fluid communication with the pressure fluid outlet for discharging pressure fluid to a reservoir, the surroundings or the like when there is no pressure fluid connection between the pressure fluid inlet and the pressure fluid outlet.
The construction of the valve device in the release mechanism according to the invention can be simplified in that the valve actuation element acts on the valve element when the predetermined switching threshold release position has been reached and, in so doing, interrupts the fluid connection between the pressure fluid discharge and the pressure fluid outlet and, when further displaced, the valve actuation element carries along the valve element against its pretensioning for producing the pressure fluid connection between the pressure fluid inlet and the pressure fluid outlet. This means that an additional valve function can even be integrated in the valve device by means of the cooperation between the valve actuation element and the valve element.
When the pressure fluid is compressed air, the existing pneumatic system in utility vehicles can be utilized in a simple manner to provide the shifting for
Bonck Rodney H.
Cohen & Pontani, Lieberman & Pavane
Mannesmann Sachs AG
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