17-05-2012, 11:22 AM
4 wheel steering. (4WS)
4ws Writeup.pdf (Size: 865.44 KB / Downloads: 130)
DISCLAIMER:
I personally love 4ws, I think it makes the car more responsive and fun to drive. If you don't like it that's great.
Note: This is mainly about the USDM 4th gen prelude 4ws system as that's what I have, I'll include info on the 3rd
gen and 5th gen JDM and EDM as I see fit or as I come across it. Everything here is either from personal
experiance or from reading everything I could find, if you think anything is incorrect let me know, but please have
info to back it up with.
Purpose:
I'm writing this so there will be a central source of information on the USDM 4th gen 4ws system.
Why am I writing this?
I'm sick and tired of seeing people answer questions about 4ws with totally incorrect info. On almost every prelude
forum when someone asks about 4ws they get answers that are totally incorrect, probably from people who have
never owned or even driven a 4ws prelude. After sifting through all that crap while tring to complete my swap I
decided that I'd try and group all the info I could find about it in one spot so here we go!
The absolute first thing I want to address is this, the ECU has nothing to do with the 4ws system. Reread that. I'll
say it again, the ECU has *NOTHING* to do with 4ws. If you don't believe me go check the wiring digrams, you
can find them here:
then explain how I have an Accord P0F ECU in the lude and the 4ws works! This is probably the most common
misconception out there relating to 4ws. So everyone out there telling peeps that they have to buy a 4ws ECU stop
it, you're wrong. From what I can tell the 4W on the ECU simply means that it came out of a 4ws car. As for the 4W
ECU's with 4 plugs, no idea what the 4th one is for but it's not for 4ws. Ok, now that that's cleared up lets get to it.
[/rant]
From the service manual:
Outline:
The electronically controlled power assisted 4WS (4-wheel steering system) consists of the hydraulic power
steering system that steers the front wheels, the rear actuator that steers the rear wheels, the 4WS control unit,
and the sensors that detect the car's speed and other steering conditions. The front steering gearbox and the rear
actuator are connected by a wire harness. The rear steering angle is controlled electrically, allowing the rear
wheels to be set at any designated steering angle.
System Operation:
The 4WS control unit receives input from the Vehicle Speed Sensor (VSS), front main steering angle sensor, and
the font sub steering angle sensor. The 4WS control unit calculates the vehicle speed, steering turning angle,
steering speed and steering direction to determine the best angle to steer the rear wheels.
The rear wheels are turned by a motor built into the rear steering actuator. The motor is actived by the power circuit
in the 4WS control unit. The actual steering angle of the rear wheels is detected by the rear main steering angle
sensor, and the rear sub steering angle sensor. The 4WS control unit adjusts the angle according to the difference
between the sensed steering angle of the rear wheels and the targeted steering angle of the rear wheels.
Features of rear wheel steering:
The electronically controlled power assisted 4WS sets the rear wheels at the best steering angle for the car's
speed, steering rotation speed, steering wheel angle, etc.