Machine element or mechanism – Control lever and linkage systems – Hand operated
Reexamination Certificate
1998-07-28
2001-05-01
Marmor, Charles A (Department: 3681)
Machine element or mechanism
Control lever and linkage systems
Hand operated
C074S491000, C074S502600
Reexamination Certificate
active
06223621
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates in general to hand-actuated brakes, and more particularly to braking systems exhibiting an increase in mechanical advantage over the range of motion of a brake lever.
BACKGROUND OF THE INVENTION
Numerous types of bicycle brake mechanisms are known in the art, including drum brakes, cantilever brakes, disk brakes, caliper brakes and linear-pull brakes. One common feature of these brake mechanisms is that the braking force is a function of the force applied to a brake cable extending between the brake mechanism and a brake lever assembly (FIG.
9
); a corresponding condition exists for hydraulic brakes. Various mechanisms have been incorporated in braking systems to increase the braking force during lever actuation, providing the rider with increasing braking power or mechanical advantage for slowing the bicycle. The present invention is an improvement to braking systems exhibiting increasing mechanical advantage.
Typically, a brake lever assembly consists of a brake handle including a finger grip bar and a cable pulling arm. The brake lever is attached to the bicycle handlebar by a mounting bracket for pivotal movement relative to the mounting bracket about a fixed axis. The brake cable is attached to the cable pulling arm a select distance from the fixed axis. As the finger grip bar is squeezed by a rider, the cable pulling arm pivots, increasing the tension on the brake cable, thereby actuating the brake mechanism. Once the brake mechanism is adjusted, the braking force is a function of how hard the finger grip bar is squeezed. How hard the finger grip must be squeezed and how far it must travel to provide a given braking force is known as the “feel” of the brakes.
Bicyclists, particularly avid bicyclists, each have a preferred feel for their bicycle brakes. Riders tend to anticipate the braking force that will result based upon the feel of their brakes. This feel is particularly important in high performance bicycling, such as off-road mountain biking, where too much braking force under certain conditions can cause the wheels to lock, resulting in a potentially dangerous loss of rider control. Likewise, too little braking force can have disastrous consequences. Thus, not only is a particular brake feel a matter of user preference, in performance situations a consistent feel contributes to rider safety. To complicate matters, as brake pads wear, the feel of the brakes can vary, particularly during off-road biking where dirt and grit increase brake pad wear and where brakes must be used often and aggressively.
With conventional brake lever assemblies, in order for a bicyclist to obtain a desired feel for the brakes, the brake mechanism itself must be adjusted. This is a time consuming and difficult process requiring special tools. Adjustments are particularly difficult under field conditions where a bicyclist either does not have the necessary tools or does not want to take the time to adjust the brake mechanism.
An alternative to adjustment of the brake mechanism to alter the brake feel known in the art, is providing a structure in the brake lever for varying the perpendicular distance between the fixed axis and the brake cable. This distance is known as the pivot arm. Known prior art devices provide a plurality of holes along the length of the brake lever at various distances from the fixed axis. While this structure does provide for coarse adjustment of the brake feel, the adjustment is only between pre-selected distances between the fixed axis and the point of attachment of the brake cable. Thus, only a limited number of pivot arm distances, and therefore brake feels, are available. In addition, while this structure does not require disassembly of the brake mechanism to adjust the brake feel, it does require disassembly of the brake lever assembly to reposition the point of attachment of the brake cable to the brake lever. Thus, adjustment of the brake feel with this structure is time consuming and requires tools which might not be available under field conditions.
Another prior art device employs a slotted brake lever whereby the point of attachment of the brake cable is allowed to transition between varying distances with respect to the fixed axis. Although the noted device provides a varying brake feel and more braking power, the device also suffers from several drawbacks. The most significant drawback is the abrupt transition of the mechanical advantage and hence, the force applied to the brake cable. The mechanical advantage is inversely proportional to the pivot arm. The smaller the pivot arm, the greater the power or braking force applied to the brake cable. Therefore, it is crucial that the increase in mechanical advantage be smoothly varying and therefore predictable.
Other devices achieve a mechanical advantage increase over the lever rotational range even with fixed cable attachment points, thereby eliminating complex slotted mechanisms while still providing increasing braking power. The brake mechanisms described above, however, all have in common a single axis design feature. The brake lever is pivotally attached to the mounting bracket and as the brake lever is drawn toward the handlebar, the lever sweeps across a single plane of motion. This type of design has several ergonomic drawbacks. In such conventional brake lever designs the rider's hand is forced to slide across the front surface of the finger grip bar and/or the knuckles are pinched upwards as the lever is drawn closer to the handlebar. This configuration not only results in uncomfortable rubbing and chafing of the rider's hand across the finger grip but also weakens the gripping power as the rider's hand is pinched upwards away from the handlebar. Providing a brake lever that simply rotates about a its longitudinal axis alone does not eliminate these drawbacks. Even so configured, the angle that the brake lever forms with respect to the handlebar is typically quite large to provide sufficient lever travel and the rider's hand is positioned further away from the pivot axis to provide the desired braking power. Such a configuration places the lever too far away from the rider's hand, especially for riders with smaller hands, and positions the weaker fingers at the maximum power region on the finger grip away from the pivot axis and the strongest fingers closer in where they are less effective in producing powerful braking.
Thus, it is desirable to provide a brake lever assembly that provides a comfortable brake lever that is easy to reach and that rotates about a second axis to follow the natural arcuate motion of the rider's hand during lever actuation, eliminating friction between the fingers and the finger grip bar while sweeping toward and downward along the handlebar to provide sufficient braking power with desired brake feel. A primary characteristic of the invention is that the arcuate or rotational motion of the brake lever is converted into a rectilinear force that boosts the braking power as the lever is drawn toward the handlebar.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a two-axis brake lever assembly that converts the rotational force imparted to the brake lever into a rectilinear force drawing the lever toward the handlebar.
It is a further object of the invention to provide a two-axis brake lever assembly that follows the natural motion of a rider's hand as the rider's fingers sweep toward and below the handlebar, the brake lever rotating to prevent any rubbing between the rider's fingers and the finger grip bar.
It is a further object of the invention to provide a two-axis brake lever assembly including a brake lever that is positioned substantially parallel to the handlebar, providing comfortable lever reach for the rider's hand and maximizing the braking power imparted by each finger to the finger grip bar, thereby providing “compacted” mechanical advantage benefits over conventional single axis brake levers.
A brake operating device accor
Cheever John D.
Jordan Brian T.
Solberg Kent A.
Wesling Kevin F.
Zimberoff David J.
Marmor Charles A
Perkins Jefferson
Piper Marbury Rudnick & Wolfe
SRAM Corporation
Waddell Tisha D.
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