14. Brake system

Models with the ordinary brake system

Braking of the car is carried out by means of double-circuit hydraulic system by means of the block of vacuum strengthening of brakes. On all models external brake disks, both on forward, and on back wheels are established. On forward wheels the ventilated disks for improvement of their cooling are established.

Hydraulic contours are divided on diagonal; one contour operates braking right forward and left back wheels whereas another operates braking of the left forward and right back wheel. Such design provides at least 50 percent efficiency of braking, even at loss of pressure in one of contours. Besides, diagonal division of contours provides full stability when braking the car, even at involvement of one contour.

Brakes are equipped with one-piston supports of floating type - a design minimum on dimensions, providing minimization of transfer of heat of the brake fluid leading to deterioration in work of brakes. In each support two brake shoes which are not containing asbestos are established. One from the inside of a disk and one from external. When braking the hydraulic pressure given to a support moves the piston on the cylinder, pressing an internal brake shoe to a disk. At the same time force of reaction of resistance moves the support case on the directing fingers, bringing into contact with a disk as well an external block. At the same time both slips nestle on a disk with identical effort. At a brake otpuskaniye hydraulic pressure behind the piston falls and the piston comes back to the cylinder, releasing at the same time an internal brake shoe. Now the case of a support moves on the directing fingers back, releasing as well an external block.

Pay attention that cylinders of back supports have smaller diameter, than cylinders of forward supports; the resulting difference in effort of braking between forward and back supports prevents blocking of back wheels at sharp braking, removing at the same time need of installation of valves of adjustment of pressure. Besides in supports of back wheels there are lever and returnable springs providing a possibility of mechanical control with supports by means of the emergency brake.

The main cylinder will transform the effort made for a brake pedal to hydraulic pressure. The double (tandem) design of the main cylinder includes two cylinders operated in parallel and transferring pressure everyone to the contour. In each cylinder there is a piston and a returnable spring. Movement of pistons on cylinders causes a liquid stream on brake lines of each contour which transfers the effort made for a pedal on pistons of supports. Two pistons of the main cylinder are partially connected that equalizes pressure in all four supports at usual braking, and also allows to transmit effort of a pedal to a working contour in case of damage of another without increase in the effort made for a pedal.

The continuous power of the main cylinder is carried out by brake fluid from the tank of brake fluid. The tank is divided into three separate cameras; on one camera on each brake contour and, on cars with the manual transmission, one camera for a coupling contour. Such design provides the guaranteed supply with brake fluid at least of one of contours even in case of leak of liquid from the second. The fact that the tank cannot be completely devastated is a consequence of such feature. Walls of the tank are made of translucent material that allows to make visual check of level of brake fluid, and the unscrewing cover of the tank provides a possibility of addition it. The indicator switch of level of liquid in the tank is a part of a cover of a jellied mouth; when lowering level of liquid to a certain limit the switch provides inclusion of an alarm lamp on the dashboard.

For increase in the effort made from a brake pedal for the main cylinder the block of vacuum strengthening of brakes operating by means of vacuum in the engine pipeline is used.

The models equipped with system of anti-blocking of brakes (ABS)

The ABS system installed in addition on some models prevents blocking of wheels (skid) at sharp braking that not only optimizes a brake way of the car (under any conditions), but also allows to exercise complete control of management of the car at the maximum braking.

Exercising constant control behind the speed of each wheel in relation to other wheels by an electronic method, the system can define the beginning of the moment of blocking of a wheel before control of a situation is not lost. Further, several times in a second modulation (consecutive increase and reduction of pressure attached to a brake support of this wheel) before restoration of complete control of a situation is carried out. The system is divided into three contours providing individual management of each forward wheel and simultaneous management of both back wheels.

Components of system are the electronic actuation device (ECU), four sensors of speed of rotation of wheels, the hydraulic block, brake lines, the special relay / a safety box and alarm lamps established in an instrument guard.

The hydraulic block includes the following components:

   a) the double (tandem) main cylinder operating at normal braking two forward supports
   b) the valvate block which is carrying out modulations of pressure in three brake contours during the work of the ABS system
   c) the accumulator providing a raising of high pressure of brake fluid
   d) the hydraulic pump for feed of the accumulator
   e) the servo cylinder providing supply of liquid under pressure from the accumulator, providing hydraulic strengthening of brakes (instead of the block of the vacuum strengthening used in ordinary brake systems), and also giving of pressure for actuating of back brakes
   f) tank of brake fluid.

Four sensors of speed of rotation of wheels are installed in naves of wheels. Each wheel is equipped with the rotating gear rotor established on a nave. Sensors of speed of wheels are installed in close proximity to these disks. At rotation teeth of rotors provide excitement in sensors of tension of a sinusoidal form which frequency changes according to the speed of rotation of disks. This tension is transferred to the block of the electronic actuation device which carries out recalculation of frequency of a sinusoid in the speed of rotation of each wheel.

The box of safety locks / relay is installed in a motive compartment near the electronic actuation device of the ABS system. In a box there are safety locks of the electronic actuation device, and also the main relay of system and the relay of the hydraulic pump.

The electronic actuation device has ability to self-diagnostics and at detection of defect stops functioning of the ABS system, providing fire of the alarm lamp established on an instrument guard. At the same time the brake system begins to work as the ordinary brake system which is not equipped with the ABS system. If the cause of defect cannot be immediately found at survey, the car should be driven away in representative office of SAAB where the diagnostic equipment necessary for troubleshooting by connection to the electronic actuation device of system is available (address the Section Components of system of anti-blocking of brakes (ABS) - the general information).