motor vehicle level 3 hydraulic components resource 3

Motor Vehicle Level 3

Hydraulic Components

Resource 3

Motor Vehicle Level 3Resource 3

Aims


To recognize the role of a hydraulic system within an ABS system

Objectives

By the end of the session you will be able to:

•Identify Hydraulic ABS components•Recognize the various channel set ups available for ABS systems•Identify basic maintenance procedures for hydraulic systems. •Describe the operation of hydraulic components and their need.



Revision

•ABS prevents wheel lock up under heavy braking, it also gives the driver steering control under a skid•Without ABS the brakes can be applied with enough force to lock the wheels making the vehicle uncontrollable (no traction between the tires and the road surface.•ABS controls each wheel separately by fluctuating the brake pressure when the wheel is deemed to be near locking. •If ABS fails, normal braking will not be affected.



Hydraulic ABS components

ABS Actuator•Controls the hydraulic brake pressure to each disc brake calliper or cylinder•This is based upon information received from sensors, so that the wheel speed can be controlled.



Hydraulic ABS Components

The actuator provides three operating modes to control the wheel speed•Pressure Holding•Pressure Reduction•Pressure Increase



Toyota ABS set up



Actuator positions-pressure reduction

•Pressure reduction- the inlet valve is closed, this opens the return valve. •Thus, decreasing the brake pressure, reducing the risk of locking. •Any left over fluid will return to the reservoir.



Actuator positions- pressure holding

•When the ECU (Electronic Control Unit) senses there is an enough drop in pressure to prevent wheel locking the return valve and the pressure is maintained.



Actuator positions-pressure increase

•If the wheel speed sensors indicates that the wheel is spinning freely, the input valve will be open, causing pressure increase to slow down/stop the vehicle.



ABS channel set ups

•Depending on the vehicle, will depend on what channel set up there is, the most common ones are:-



Four-channel, four-sensor ABS

•Speed sensor on all four wheels •Separate valve for all four wheels. •With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.



Three-channel, three-sensor ABS

•Speed sensor and a valve for each of the front wheels•one valve and one sensor for both rear wheels. •Rear wheel speed sensor is located on the axle.

•This system provides individual control of the front wheels, so they can both achieve maximum braking force. •The rear wheels, however, are monitored together; they both have to start to lock up before the ABS will activate on the rear. •Therefore, it is not as effective



One-channel, one-sensor ABS

•One valve, which controls both rear wheels, and one speed sensor, located in the rear axle.•The rear wheels are monitored together and they both have to start to lock up before ABS operation.



Basic Maintenance

It is important to change the brake fluid at the correct intervals, if not the brake fluid will lose it’s properties and will be less effective.•Investigation•Investigate what other basic maintenance is needed on ABS systems.



Summary

We have today....•Identified Hydraulic ABS components•Recognized the various channel set ups available for ABS systems•Identified basic maintenance procedures for hydraulic systems. •Described the operation of hydraulic components and their need.



motor vehicle level 3 hydraulic components resource 3

Documents

hydraulic components

hydraulic brake pressure

hydraulic systems

abs system slide

wheel speed pressure

abs systems

vehicle uncontrollable

sensor abs speed sensor