Let’s say a few words about the operation of the Toyota system of brake force distribution EBD.
The EBD (Electronic Brake force Distribution) system is designed to redistribute the braking forces between the front and rear wheels, as well as the wheels of the right and left sides of the car, depending on driving conditions. EBD operates as part of a traditional 4-channel electronically controlled ABS.
When braking a rectilinearly moving car, a load redistribution occurs – the front wheels are loaded, and the rear wheels, in turn, are unloaded. Therefore, if the rear brakes will develop the same force as the front, the likelihood of locking the rear wheels will increase. Using wheel speed sensors, the ABS control unit senses this moment and controls the input force. It should be noted that the distribution of forces between the axles during braking substantially depends on the mass of the load and its placement.
The second situation, when the intervention of electronics becomes useful, occurs when braking in a corner. In this case, the external wheels are loaded and the internal ones are unloaded, respectively, there is a risk of their blocking.
1 – ABS modulator, 2 – brake master cylinder, 3 – speed sensors, 4 – ABS control unit, 5 – brake cylinder (front right wheel), 6 – brake cylinder (rear left wheel), 7 – brake cylinder (rear right wheel ), 8 – brake cylinder (front left wheel), 9 – pressure reducing valve, 10 – holding valve, 11 – pump, 12 – accumulator.
Based on the signals from the wheel sensors and the deceleration sensor (or acceleration sensor), the braking conditions of the wheels will be determined and, using a combination of valves, it will regulate the fluid pressure supplied to each of the wheel mechanisms. The adjustment is carried out in three modes: increase, decrease and hold pressure.
EBD is not valid
Holding Valve (Port A)
Pressure Reducing Valve (Port B)
Speaking about the operating principles of the new Toyota brake systems, one cannot bypass the most advanced of them used on Land Cruiser 100 cars. Its main difference is that instead of the traditional vacuum, a hydraulic booster is used here.
1. The functioning of the elements
1. Pump and pump motor – pump brake fluid from the reservoir into the accumulator.
2. The hydraulic accumulator is used to store liquid under high pressure created by the pump. The battery is filled with compressed nitrogen..
3. Pressure switches. Designed to control the pressure in the accumulator and give a control signal to turn on the pump. The PH sensor is used to control the pump, the PL sensor gives a signal at too low a pressure.
4. Bypass valve. Returns brake fluid to the reservoir to relieve excess pressure during continuous pump operation due to a malfunction.
5. The main brake cylinder. Serves to create pressure in the brake line during normal braking.
6. Hydraulic brake booster. Regulates the pressure in the accumulator in accordance with the force on the brake pedals and directs the fluid from it to the booster chamber.
7. Pressure regulator. Monitors the pressure in the rear brake circuit to achieve optimal distribution of braking forces between the front and rear wheels. When the front brakes fail, the regulator does not function.
8. Solenoid valves “SA1”, “SA2”. Distribute pressure when activated ABS or normal braking.
9. Holding and dumping valves. Distribute the pressure supplied to the wheel brake cylinders when ABS is triggered.
2. Pump, accumulator, pressure switches and pressure relief valve
If the pressure in the accumulator drops below the value set for the PH sensor, it is turned off, as a result of which the control unit activates the pump motor.
Brake fluid passes from the pump through the non-return valve to the accumulator, creating an increased pressure in it, which is then used during normal braking or during ABS operation.
If the pressure in the accumulator becomes higher than the value set for the PH sensor, it turns on, after which the control unit turns off the pump for several seconds.
In the event of a PH sensor malfunction that causes the pump to operate continuously, a bypass valve opens to prevent excessive pressure build-up..
If the pressure in the accumulator drops below the value set for the PL sensor, it will be turned off and the control unit will turn on the BRAKE brake system status indicator and a warning sound. At the same time, ABS is prohibited..
3. The functioning of the brake master cylinder (GTZ) and brake booster
1. Pressure increase mode (Lo, low pressure).
The force from the brake pedal is transmitted through the rod and the main piston to the internal piston of the GTZ. Since the force of the main return spring is higher than the force of the return spring of the regulator, the piston of the regulator moves with increasing pressure in the GTZ.
As a result, the spool valve moves forward and closes channel “A” between the reservoir and the amplifier chamber (located behind the main piston) and opens channel “B” between the accumulator and the amplifier chamber. As a result, brake fluid under pressure enters the booster chamber, increasing the braking force and lowering the resistance of the resistance on the brake pedal.
When pressure is created in the booster chamber, the force developed by it exceeds the force of the main return spring, as a result of which the fluid pressure in the front brake circuits also increases. At the same time, pressure from the booster chamber is applied to the rear brakes.
In the initial stage of braking, the pressure in the amplifier supplied to the reactive disk is small, and it does not deform.
2. Pressure increase mode (Hi, high pressure).
If the pressure is high, then the force on the reaction disk increases, as a result of which it deforms and moves the spool valve using the reaction rod. This increases the resistance on the brake pedal. The result is the operation of the system with a variable gain, which is greater, the greater the pressure.
3. Hold mode.
In this position, the force on the brake pedal and the force developed by the pressure in the GTZ are in equilibrium. The forces acting on both sides of the regulator piston are also balanced. Spool valve closes simultaneously channels “A” and “B”.
4. Pressure Relief Mode.
When the force on the brake pedal decreases, the pressure in the GTZ drops. The regulator piston and slide valve move backward, opening channel “A” between the tank and the amplifier chamber. The pressure in the amplifier is reduced to a level that balances the force exerted on the pedal.
5. Operation mode in case of malfunction.
If the pressure in the accumulator is absent for any reason, pressure does not flow to the regulator. As a result, braking forces are not enhanced and pressure is not applied to the rear brakes. Since the pressure does not affect the external piston, it remains stationary in the initial position. The pressure in the front brake circuits created by the internal piston of the GTZ increases in proportion to the force on the brake pedals.
4. ABS functioning
1. Valves SA1 and SA2 are switched during normal braking using the front brakes and during ABS operation. Under normal braking, the channel on the side of the GTZ is open, during ABS operation the channel on the side of the amplifier’s chamber is open.
2. The system has 3 solenoid and 3 vent valves located in each circuit that turn on and off during ABS operation.
3. During normal braking, all electronic valves are turned off (OFF).
4. During ABS operation, the valves are switched as shown in the table below. At this point, the channel between the GTZ and the front brakes is closed to avoid vibrations on the brake pedal and increase its sensitivity.
The condition of the / / m valves with ABS.
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