SSPS (Speed Sensing Power Steering)

Transcription

1 SSPS (Speed Sensing Power Steering) 1. GENERAL INFORMATION Overview In the conventional constant power assist steering system, the steerability gets lighter as vehicle speed rises, and this may cause a dangerous situation. Where as having heavy steerability in high speed driving makes it difficult to manipulate the steering wheel when vehicle is in stop. This steering system solves this problem as the steerability is changed according to the vehicle speed, which is called Speed Sensitive Power Steering (SSPS). SSPS, by providing appropriate steerability to a driver according to the changes of vehicle speed, gives steering stability. The power steering control unit adjusts the hydraulic pressure to reaction plunger by controlling the pressure solenoid valve located in the gear box to optimize the steerability. In other words, the steering wheel gets lighter by adjusting steerability in stop or low speed and provides steering stability by adjusting steering wheel to become heavier in high speed. SSPS (Speed Sensitive Power Steering) NOTICE If the SSPS solenoid valve is defective, the power steering assembly should be replaced.

2 Function Input/Output of SSPS Control Unit IG Power Ground CAN HIGH CAN LOW SSPS Configuration PCV Spring Filter Spool Pressure Connector SSPS CONTROL UNIT Balance line Pinion valve Valve Meter Cluster (SSPS warning lamp) Trouble Diagnosis Valve body Right Left A / CON A / BAG BRAKE ST NG SP AXLE CLUTCH T/C M/T A/T valve Reaction fi line Plunger ˆ œ Steering gear box PCV (Pressure Control Valve) This valve controls the hydraulic pressure supplied to reaction device by moving the spool valve according to the changes of solenoid valve. This device increases the steerability effect by binding the input shaft with supplied hydraulic pressure from PCV. valve This valve determines the valve spool position in PCV with the electric current supplied from SSPS control unit.

3 Valve Location Cannot be replaced The SSPS control unit controls the amount of electric current to the solenoid valve according to the vehicle speed. In other words, the solenoid valve controls the hydraulic pressure applied to reaction plunger by changing the valve spool position that is linked with solenoid valve according to the amount of electric current. The changes of hydraulic pressure applied to input shaft according to the pressure changes applied to the reaction plunger provide proper steerability based on the amount of electric current. Specifications Description Voltage Rating Current Rating Resistance Specification DC 12 V 1.0 A 6.7 ± 1 Ω

4 Operation 1. During parking and low speed driving Return port 1) The SSPS control unit outputs nearly maximum electrical current. 2) The solenoid rod pushes the PCV spool to the right side. 3) The hydraulic pressure coming from pump is not supplied to the reaction device as the spool orifice is cut off. 4) The hydraulic pressure is cut off and the manipulation of steering wheel becomes lighter. 2. In medium and high speed driving Inlet port valve valve Hydraulic pressure (cut off) A / CON A / BAG BRAKE ST NG SP AXLE CLUTCH T/C M/T A/T Hydraulic pressure (cut off) Return port Inlet port 1) The shaft operating force of solenoid rod is reduced due to the reduction of output current from the SSPS control unit. 2) The coil spring pulls the PCV spool toward solenoid valve to open it. 3) The hydraulic pressure from pump flows to pinion reaction area through orifice and applies reaction force to reaction plunger. 4) At this time, the reaction plunger transmits the reaction force to V-groove in input shaft to provide heavy steerability.

5 SSPS Control Unit 1. To provide proper steerability to a driver, the SSPS control unit controls the solenoid valve by receiving the vehicle speed and the throttle position data via CAN communication. 2. The SSPS control unit controls the working current for the solenoid valve with PWM type duty ratio of 333 Hz frequency and sets the target current to 1A during 1 second after the ignition is ON. 3. When a trouble occurs in the system, the SSPS control unit generates a trouble code using fail safe function Pin No Function Ignition Power Supply CAN HIGH Ground Warning Lamp (SSPS) CAN LOW Self Diagnosis Location SSPS unit

6 System Control The SSPS system, according to the vehicle speed, enables to achieve proper steering characteristics by controlling hydraulic pressure to reaction plunger located in input shaft of power steering gear box. In other words, the SSPS control unit enhances the parking conveniences by controlling duty type current control. It provides heavy steerability with low current as the vehicle speed increases. Also, it provides light steerability with high current as the vehicle speed decreases. 1. During parking and low speed driving During parking and driving in low speed, the control unit supplies approx. 1 A of electric current to solenoid valve. Then, the spool located in PCV compresses the upper spring and elevates upward, and the working pressure from oil pump (A port) is not able to flow to the reaction plunger (C port). As a result, the pressing force from the reaction plunger disappears and the steerability enhances. Spring Spool Connector PCV Filter Pressure Balance line Current [A] Pinion valve Valve body Vehicle speed [km/h] Right Left A / CON A / BAG BRAKE ST NG SP AXLE CLUTCH T/C M/T A/T valve Reaction line Plunger Steering gear box

7 During high speed driving During high speed driving, the control unit supplies weak electric current to solenoid valve. Then, the spool located PCV moves from top to bottom, and the working pressure (A port) from oil pump is applied to reaction plunger (C port) through B port. As a result, the pressing force from reaction plunger against input shaft is increased and the steerability becomes heavier. Spring Spool PCV Filter Pressure Balance line Pinion valve Valve body Right B Port Connector Left valve Reaction line Plunger Steering gear box