7.2.11 Parking brake system with mechanical drive
Simple and cheap layout of impact on the brakes of the rear wheels involves the use of cables and a lever (or pedal), which is located inside the passenger compartment. The principle of operation of this system is as follows: while moving the parking brake lever, the drive cables are moved. They act on the brake mechanisms, thus preventing the wheels from turning (the elements of the parking brake system are shown in Figure 7.1). The lever inside the passenger compartment is mounted on the ratchet gear, which allows fixing it in the working position. A signal switch is installed under the lever on the instrument panel in order to inform the driver that the parking brake is currently applied.
Note
From the lever inside the passenger compartment the force is transmitted to the brakes by the means of cables. One, two or three cables are used in the design of the parking brake drive. The most common layout has three cables: one front (central) and two rear. The front cable is connected to the lever in the passenger compartment, the rear cables - with the brakes of the right and left wheels, respectively. An equalizer or balance weight is used for connecting the front cable to the rear and evenly transmitting the force.
As well as any other mechanism, the parking brake needs to be adjusted. For this purpose, adjustment of length of cables by means of the adjusting nut, which is installed often on the equalizer, is provided. Return of the system to the initial position (removal from a brake) is made at transfer of the manual lever to the corresponding position by means of a pull-back spring. The spring can be located on the front cable, the equalizer or directly on the brake mechanism.
The braking mechanisms of the parking system can be of different types. Thus, in case if drum brakes are applied behind, the parking brake system uses brake mechanisms of working brake system. Only in this case blocks are pressed not at the expense of the wheel brake cylinder, but at the expense of influence of a cable of system on the driving lever of pads. In case if the brakes are of disc type, then there are two options: either transfer the force via the drive lever to the brake caliper of the service brake system and thereby fix the wheel, or make the rear brake disc composite (meaning that the brake disc will be made so that its inner surface will be act as a brake drum).
Interesting
It is advisable to always use the parking brake in order to prevent acidization of the cables. Because, in case of an emergency and unforeseen situation on the road, it will not be possible to use the parking brake system as emergency one, with sour drive cables.
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