Machine element or mechanism – Control lever and linkage systems – Elements
Reexamination Certificate
1999-09-23
2001-09-04
Luong, Vinh T. (Department: 3682)
Machine element or mechanism
Control lever and linkage systems
Elements
C074S523000, C074S567000, C074S575000, C074S57700S, C074S578000, C074S529000, C074S535000, C074S536000, C074S540000, C074S545000, C074S501600, C074S516000
Reexamination Certificate
active
06282980
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to vehicle parking brakes and, in particular, to a self-adjusting actuator mechanism for automatically taking up cable slack introduced in the parking brake cable over time and/or during installation.
Vehicle parking or emergency brakes are typically actuated by a pivoting foot-operated or hand-operated actuator lever positioned adjacent the driver. The parking brake actuator is typically fixed to the vehicle by means of a mounting bracket, or the like, and attached to a brake cable connected to a vehicle parking brake system. The actuator lever is typically pivotably mounted on the bracket and adjustable between a ‘brake-released’ position and one or more ‘brake-applied’ positions. The brake cable is attached to the actuator lever so that rotation of the lever in the ‘brake-apply’ direction increases tension in the brake cable, thereby applying the parking brakes to the vehicle wheels to impede rotation thereof. A position lock is provided to releasably lock the lever in a ‘brake-applied’ position and a release mechanism is provided to selectively permit rotation of the lever back to the ‘brake-released’ position.
A problem well-known in the art is induced cable stretch, occurring as the parking brake system is repeatedly cycled, which detrimentally affects the performance of the brake by reducing the maximum available braking force. Cable slack is also unavoidably introduced during the initial installation of the parking brake system and must be accommodated.
One approach for automatically reducing slack in the brake cable involves providing a socalled self-adjusting actuator which typically adds an intermediate element to an otherwise standard parking brake actuator assembly. Such actuators are disclosed in U.S. Pat. Nos. 4,841,798 to Porter et al., 4,850,242 to Hass et al., and Japanese Patent Application No. 56-119762 to Kokai. Typically, this intermediate element, known variously in the art as a self-adjusting cam, cable drum, or cable pulley, is rotatably connected to the mounting bracket independent of the actuator lever. The brake cable head is attached to the rotatable cam, rather than to the lever directly, and the cam is selectively lockable to the lever, for rotation therewith when locked, by a suitable clutch means. When the actuator lever is positioned in the ‘brake-released’ position, the cam is permitted to rotate independently of the lever, and suitable spring means are provided to bias the cam in the brake-apply direction relative the lever, thereby causing the cam to rotate to automatically remove any slack present in the brake cable. A minimum residual tension in the cable is thus maintained when the parking brake is not activated. When the lever is rotated out of the ‘brake-released’ position, the clutch automatically locks the cam to the lever, thereby permitting lever rotation to tension the cable and apply the vehicle parking brakes.
In many prior art self-adjusting parking brake actuators, the actuator lever and the cam are concentrically mounted, as shown in Porter et al., Hass et al. and Kokai, It is well-known that concentric designs yield a constant mechanical advantage vis-à-vis lever load and induced cable tension. Such parking brake actuators offer a fixed amount of cable travel per a given unit of lever travel, and, thus, a constant mechanical advantage to the operator. Generally speaking, however, brake system cable travel versus cable load is not a constant relationship. Larger amounts of cable take up under relatively light loads, are required at the initiation of the brake application stroke, and smaller amounts of cable travel are required under substantially higher cable loads as the end of the brake application stroke is reached. Due to their constant mechanical advantage, concentric actuators can require relatively long levers to balance mechanical advantage and cable take up requirements of the vehicle application, especially if the surrounding environment limits the range of lever motion available. Practically, this typically requires that the actuator mechanism have a very high mechanical advantage to ensure that the maximum input force required from an operator is not too large. This disadvantageously increases the overall size of the actuator, however,
Providing a device which varies the mechanical advantage as the lever is rotated in the ‘brake-apply’ direction would advantageously permit the ratio of cable movement to lever movement to be decreased as the lever is rotated in the ‘brake-apply’ direction, thereby reducing the overall force required of the operator in applying the parking brakes to the vehicle. Such devices are known and typically involve an eccentric positioning of the lever pivot and cam pivot axes, as shown in U.S. Pat. Nos. 5,211,072 to Barlas et al., U.S. Pat. No. 5,477,746 to Perisho et al. and U.S. Pat. No. 5,546,828 to Golarz. In such devices, at the onset of parking brake application, the input force required to take up the initially low tensioned cable is small (i.e. low mechanical advantage), but the input force requirements (and the mechanical advantage) rapidly increase as the parking brake is further applied and the brake cable is further tensioned.
Known eccentric self-adjusting parking brakes, however, have the disadvantage of having mechanisms which require additional components and/or complexly-shaped components to achieve the desired cable takeup, as shown in the devices of in Golarz et al., Barlas et al. and Perisho et al. The production costs of such devices, however, is correspondingly increased. Further, such devices require additional space to achieve the motions required by their respective stroke envelopes. Clearly, space is an ever-precious commodity as automobiles become smaller in the face of demands for increased fuel efficiency, and the like. Thus, many current vehicle applications have environmental space requirements which do not permit known eccentric designs to be utilized.
Thus, there is a need for a high performance, cost-effective, and reliable self-adjusting parking brake actuator that does not suffer from the disadvantages described above.
SUMMARY OF THE INVENTION
The device of the present invention offers an eccentrically-mounted self-adjusting parking brake actuator which is compact in comparison to known eccentric designs and offers greatly improved performance over known concentric designs. The present invention thereby offers increased performance for a given actuator size, in terms of environmental space required by the actuator in operation, over both the eccentric and concentric designs of the prior art.
In one aspect, the present invention provides a lever mechanism for applying tension to a cable comprising a bracket, a lever assembly, the lever assembly rotatably mounted to the bracket about a lever axis for rotation between a first position and a second position, a position lock for releasably locking the lever assembly in the second position, a cam member for connection to the cable, the cam member having a radius, the cam member rotatably mounted on the lever assembly for rotation about a cam axis, the cam axis offset from the lever axis by a distance less than the cam member radius, a spring for rotatably biasing the cam member in a direction tending to increase tension in the cable, the spring extending between the cam member and the lever assembly, and a clutch assembly mounted on the lever assembly, the clutch assembly actuatable to selectively prevent rotation of the cam member relative to the lever assembly, the clutch assembly actuatable upon rotation of the lever assembly.
In a second aspect, the present invention provides a mechanism for variably tensioning a vehicle parking brake cable comprising a bracket, a lever rotatably mounted to the bracket, the lever rotatable about a lever axis, the lever rotatable between a brake-release position and a brake-apply position, the lever axis defining an axial direction, a position lock for releasably locking the lever in the brake-apply position, a cam member
Bereskin & Parr
Luong Vinh T.
Ventra Group Inc.
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