Machine element or mechanism – Control lever and linkage systems – Elements
Patent
1997-02-26
1998-08-04
Luong, Vinh T.
Machine element or mechanism
Control lever and linkage systems
Elements
74538, 74533, 74575, 74577R, G05G 506
Patent
active
057877610
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to automatic slack adjustment for systems involving the use of a cable for transferring an applied force between two parts of the system. An example system of that kind is a vehicle brake system in which the brake is controlled by a manually operable actuator connected to the brake assembly through a flexible cable. It will be convenient to hereinafter describe the invention with particular reference to that example, and it is to be understood that the invention has wider application.
2. Description of the Prior Art
In a vehicle brake system there needs to be a limit on the extent of actuator movement required to transfer the brake assembly between the brake fully-on and brake fully-off conditions. By way of example, excessive actuator movement can be dangerous because of the time required to fully apply the brakes in an emergency. Actuator movement will increase as a natural consequence of the brake friction lining wearing during use, and some form of cable slack adjustment is required to compensate for that wear and keep the actuator movement within reasonable limits.
One form of prior art cable slack adjuster incorporates two drive parts which forms a drive connection between the brake lever and the cable. One drive part comprises a pawl and the other drive part comprises a tensioning reel. The pawl is pivotally connected to the lever and is engagable with the tensioning reel, which is connected to the cable. The drive connection enables the lever to impart an actuating force to the cable during movement of the lever between a rest and a fully actuated position. The two drive parts are normally biased into engagement except at the rest position of the lever where the pawl is forced out of engagement from the reel, typically by engaging a stop secured to the support structure. Once disengaged, slack adjustment can occur through movement of the tensioning reel relative to the pawl, and typically this is achieved by a spring acting on the tensioning reel which biases the tensioning reel to rotate in a cable tensioning direction.
While a cable slack adjuster of this type is able to operate automatically, it is prone to malfunction because of its sensitivity to changes which naturally occur within the system under normal use conditions.
One particular problem is the tendency of the slack adjuster to over adjust, such that inadequate running clearance exists within the brake assembly when the brake actuator is at the rest position, or to under adjust such that insufficient slack is taken up. This can occur as the movement of the tensioning reel to take up slack in the cable is dependent on the relationship between competing forces acting on the reel. These competing forces are typically the loads imposed on the reel by the cable and the force imposed on the reel by the spring. As these forces may vary under continued use of the system, the adjuster can malfunction by the spring force becoming the two dominant force which will cause the adjuster to over adjust, or conversely becoming too weak relative to the cable tension which will result in the adjuster taking up insufficient slack.
Another problem is that the slack adjuster may malfunction through failure of the pawl to properly engage the tensioning reel. Typically the pawl includes at least one tooth which is engagable with a series of teeth located on the reel and failure is particularly prone to occur if the pawl teeth only partially engage with the reel teeth, which may cause the pawl teeth to fracture or slip out of engagement with the reel.
U.S. Pat. No. 4,819,501 to Kraus discloses a cable slack adjuster of the above type which aims to address the problem of over adjustment. The slack adjuster disclosed includes an arrangement which controls the amount of slack which is taken up through the positioning of a sliding pawl mounted to the reel. The position of the sliding pawl is dependent on the amount of movement of the lever in the applied stroke, and slack is taken
REFERENCES:
patent: 3621959 (1971-11-01), Gale et al.
patent: 4138905 (1979-02-01), Konishi
patent: 4512210 (1985-04-01), Gurney
patent: 4515036 (1985-05-01), Dotson
patent: 4819501 (1989-04-01), Kraus et al.
patent: 4841798 (1989-06-01), Porter et al.
patent: 4854187 (1989-08-01), Walters
patent: 5001942 (1991-03-01), Boyer
patent: 5067366 (1991-11-01), Gandiglio
patent: 5205184 (1993-04-01), Noel et al.
patent: 5272935 (1993-12-01), Heinemann et al.
patent: 5533420 (1996-07-01), Perisho
Luong Vinh T.
PBR Automotive Pty. Ltd.
LandOfFree
Cable slack adjuster does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cable slack adjuster, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cable slack adjuster will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1166379