Mechanically assisted steering system Rack and Pinion Rack

Mechanically assisted steering system

Rack and Pinion

Rack & Pinion Operation • As the pinion rotates it moves the rack either left or right • Note that the rack teeth are all the same • What effect would narrowing the teeth have?

Variable Pitch Rack and Pinion • By moving the pitch of the rack teeth closer together you gain a mechanical advantage • Less effort is required at the steering wheel to get more movement/steering movement from the rack

• The pitch narrows at either end of the rack. • Which means you only gain the mechanical advantage when the steering is near full lock.

Advantages • When would having this be advantageous? • When turning tight corners, parallel parking & ‘U’ turns.

ELECTRIC POWER ASSISTED STEERING

Inputs, Processes & Outputs 101010010100101 Inputs 00101 Outputs 110010010100101 Sensors 100101001010010 Actuators 10010 Outpu Power Inputs 0010100101010 ts Control 01010 Supply Units 101010010100101 Ground 110010010100101 Diagnos 00101 tic 100101001010010 Output 10010100101010 -------ECU-------Processing

Types of Electric PAS Systems • Electro Hydraulic Steering • Full Electric Steering • (Assignment Question)

What Is It. Electrically powered steering uses an electric motor to drive either: • THE POWERED STEERING HYDRAULIC PUMP (ELECTRO HYDRAULIC) (not common) • OR THE STEERING LINKAGE DIRECTLY (FULL ELECTRIC). The powered steering function is therefore independent of engine speed, resulting in significant energy savings. However, the hydraulic pump system is facing quick extinction due to rapidly advancing electric power steering technologies

ELECTRO-HYDRAULIC P. A. S. THE ADVANTAGES OVER HYDRAULIC PAS ARE: 1 MORE COMPACT 2 SIMPLIFIED INSTALLATION 3 REDUCTION IN ENERGY CONSUMPTION 4 P. A. S. AVAILABLE DURING TOWING

FULL ELECTRIC POWER ASSISTED STEERING. THESE SYSTEMS ARE TOTALLY CONTROLLED BY ELECTRICS AND ELECTRONICS THEY HAVE THE SAME ADVANTAGES AS ELECTROHYDRAULIC AND ALSO. • No Fluid Leaks • System can be speed sensitive • Less components / less weight REMEMBER – IF THE PAS FAILS YOU ARE STILL ABLE TO OPERATE THE VEHICLE STEERING – FAILSAFE!!

The Components ELECTRIC MOTOR STEERING INPUT SENSORS ELECTRONIC CONTROL UNIT ACTUATING MECHANISM THE ENTIRE ELECTRIC POWER STEERING SYSTEM IS INTEGRATED INTO A COMPACT UNIT. SO THERE IS NO LONGER ANY COMPLEX WIRING ARRANGEMENTS.

ELECTRIC MOTOR A DC. Unit which has its armature revolving inside permanent magnets. It is reversible to allow for left and right turns. The current input is changed in relation to the required torque input (assistance) Can be mounted on the steering column inside the vehicle (under the dash), or built into the steering rack.

The Mighty Hyundai Atoz Rack

Column Mounted Motor VW

Steering Input Sensors • These are needed to provide the E. C. U. With the following information • Direction of the steering • Speed of which the steering is turned • Torque being applied to the wheel Is connected to the pinion gear shaft. It registers the steering wheel lock and/or the current position of the steering. • Known as a Steering Moment Sensor

Steering Moment Sensor • Is a potentiometer that is connected to the torsion bar. • It registers a rotational angle of the torsion bar in relation to the intermediate spindle.

The Steering Sensor Housing The steering moment sensor is located in a housing. The sensor housing is located on the worm gear shaft above the gear. The sensor housing is connected to the control unit.

Electronic Control Unit The control unit calculates a torque, and if it exceeds a nominal value , the control unit assumes that a steering assistance is required. Receives information from the steering sensors and the engine speed sensors. This data is processed and related to the pre-programmed power assistance characteristics, fail safe and self diagnostic functions are provided. (dash warning light)