1. Field of the Invention
This invention relates generally to synchronizing clutches. In particular, the present invention relates to a multiple friction member synchronizing clutch.
2. Description of Related Art
In general, the components of a clutch interact negatively, or, when the rotating plates are interacting, the system has not been actuated to do so; its initial home position is with the different rotating components engaged. In these systems, when the components are actuated, they cease interaction, for example actuating the clutch pedal in a vehicle to disconnect the engine from the rest of the drive train.
In a positively engaged system, such as those found in vehicle transmissions, the effects are slightly different. In the initial position, the components are disengaged. As they are actuated, the components begin to interact, simultaneously with the synchronizer components of the transmission, as the shifter is moved from the neutral position through the gate of the desired gear. FIGS. 1A and 1B illustrate the differences between these known systems.
As illustrated in FIG. 1A, the clutch design's home position, dictated by the force mechanism used, is generally with the rotation components engaged and the user (whether it be human or computer input) actuator disengaged. Thus, as illustrated in FIG. 1B, upon user engagement of the actuator there is disengagement of rotating components; this is the negative engagement.
In a simple clutch a driving flywheel and driven clutch plate are brought into physical frictional interaction through different spring and actuation mechanisms. The actuating system rides on a bearing, which allows the clutch assembly to be linearly actuated while rotating. When actuated the clutch plate is forced into the flywheel by a pressure plate, which holds the force generating spring mechanism, usually either a diaphragm spring or spring/rocker arm system.
Another clutch variation utilizes a friction system in which a pattern of annularly mounted rotating friction members on one component interact with the friction surface other the opposing component. The force-derived friction is generated by the progressive rotational resistance of a generated torque at the connection point of each friction member. As the friction member mounted component is linearly actuated into contact with the other component's friction surface, the multiple friction member clutch system introduces frictional forces between the rotating components. These forces, as in a plate clutch, are great enough that when harnessed under controlled engagement and fed into the proper mechanical system, are capable of overcoming the inertia of a stationary vehicle or load.
In a synchronized straight drive transmission, a frictional interface between the gear of interest and the collar that selects the gears on that particular shaft is present to control the internal rotations of the transmission. When a gear is selected the clutch connection between the engine and transmission is first interrupted by the operator. The operator then selects the desired ratio. If the gear is selected from a vehicle's stationary position then no internal transmission rotations are needed to be matched and final engagement has occurred. The operator then gradually reintroduces clutch engagement to allow friction to be generated within the clutch, transmitting rotation from the engine through the transmission and causing movement of the vehicle. If the gear is selected while the vehicle is already moving, the synchronizer's role becomes more prevalent. The clutch is still initially disengaged, but when this action happens, a rotational discrepancy exists between the rotations of the input and output shafts within the transmission as a result of changing to a different gear ratio. The synchronizer uses a small amount of friction between the gear selector components and the driving components of each gear to better match their rotations so as to preserve the integrity of other components within the transmission and make driving with a manually shifted transmission easier on the operator.
The friction components are designed to be spatially efficient and therefore employ systems that can fit in a tightly toleranced transmission to keep actuation distance to a minimum. One such system employs the use of frictionally toleranced rings and/or squash springs, which compound axially together as the shifter is moved from neutral to final engagement of that gear. As the ring components combine and interact the friction between them coordinates the rotations of their respective shafts allowing for easier, more controlled final engagement, usually an interference type using dog teeth. Another engagement system utilizes a tight fit between cone-type structures, usually mounted axially on the gear selector collar, and housings on the corresponding gear. As the shifter is moved from a neutral position, the synchronizer cones are forced tightly into their housings, which create the friction that coordinates the rotations of the shaft.
Other mechanical systems have been developed to reduce the coordination required by the operator to work a straight drive transmission. The first of these is a powered actuating system that controls the clutch for the operator based on the operators other actions and how they trigger the system. In an example of this case, prior to the gear shifter being actuated the operator must reduce engine load by easing off the accelerator, which, when sensed, is when the clutch is disengaged by the actuating system. When the gear is selected, and thus actuated into engagement within the transmission, the operator begins reintroducing engine power and the clutch is automatically reengaged.
Volkswagen utilized a vacuum powered version of this system, which derived actuation force from engine intake pressures as a function of the changing engine conditions associated with selecting different gears. Citroen also had a variation of this system, which utilized a hydraulically actuated clutch controlled by the sequential gear selecting actions of the operator. Another variation of this system utilizes a button on the shifting lever, which the operator uses to control the actuation of the clutch.
These types of systems also operate very closely to a modern semi-automatic sequentially arranged transmission system in which a computer controls all of the different component, clutch, and gear selection, actuations based an basic operator input.