GF46.50-P-0001CE Speed-Sensitive Power Steering (SPS), Function
GF46.50-P-0001CE Speed-Sensitive Power Steering (SPS), Function
MODEL 204.0 /2
- with CODE (213) Speed-sensitive power steering as of Model Year 2009 /modification year 08
MODEL 204.901 /956 /981 /983 /987 /988 /992
- with CODE (213) Speed-sensitive power steering
MODEL 204.302 /303 /347 /349 /357
- with CODE (213) Speed-sensitive power steering
Function requirements, general
^ Circuit 61 ON
Speed-sensitive power steering (SPS), general
The steering wheel's rotary motion is converted into horizontal movement through the steering gear of the rack-and-pinion steering.
The rack-and-pinion steering gear has a constant gear ratio, i.e. the tooth pitch is identical across the entire toothed rack.
Steering assistance is executed hydraulically by a belt driven power steering pump.
The Electronic Stability Program control unit (N30/4) will be introduced into service as of 1.3.2011 (model 204.0/2) or as of 1.6.2011 (model 204.3) in 2 variants:
- ESP control unit, Basic variant (except code (233) DISTRONIC PLUS and model 204.077/277/377)
- ESP control unit, Premium variant (with code (233) DISTRONIC PLUS or model 204.077/277/377)
Up to 28.2.2011 or 31.5.2011 and as from 1.6.2011 (model 204.9) only the Basic variant of the ESP control unit is used.
On model 204.001/002/003/006/025/044/045/047/048/049/065/092/201/202/203/225/245/247/248/249/292, as of 1.9.08 on model 204.041/046/052/054/056/241/246/252/254/256/302/303/347/349/357 and as of 1.6.2011 on model 204.077/277/377 the volumetric flow rate is regulated to meet demand through the power steering pump quantity control valve (Y10/1) installed on the power steering pump. As a result, the flow pressure in the servo system is reduced if power-assisted steering is not required, thereby reducing energy consumption. The volume flow is regulated by the Electronic Stability Program control unit.
To cool the power steering fluid, an oil cooler in the form of a coiled pipe is fitted immediately upstream of the radiator. The oil cooler version depends on the engine mounted in each particular vehicle.
The steering assistance is regulated by the rack-and-pinion steering gear itself. The hand force to be applied to the steering wheel is increased as per a specified characteristics map from a vehicle standstill up to a speed of v = 100 km/h. The hydraulic reaction assembly is adapted to the respective requirement via the speed-sensitive power steering solenoid valve (Y10). Electronic control is provided by the Electronic Stability Program control unit.
The speed-sensitive power steering system consists of the following subfunctions:
^ Speed-sensitive power steering turn operation function sequence
^ Function sequence for SPS [PML] electrically controlled reaction
^ Rack-and-pinion steering straight-ahead driving function sequence
Speed-sensitive power steering turn operation function sequence
If the steering wheel is turned, then the drive pinion is supported on the toothed rack. The rotary valve is rotated over the stabilizer bar against the pilot bushing surrounding it, thus changing the position of the control grooves in relation to one another.
The pressurized oil flow is now fed into the right working cylinder (left steer) or into the left working cylinder (right steer) and causes the axial movement of the toothed rack to the right or left.
The oil is pushed out of the unpressurized working cylinder and flows back into the power steering pump reservoir via the open return grooves of the pilot bushing.
Steering force support is regulated according to the vehicle speed.
Regulation is effected by the speed-sensitive power steering solenoid valve, which is actuated by the Electronic Stability
Program control unit according to vehicle speed.
A differentiation is made here between the following conditions:
^ Function with vehicle speed v = 0 km/h
^ Function with vehicle speed 0 km/h less than v less than or equal to 100 km/h
^ Function with vehicle speed v greater than 100 km/h
Shown on left wheel lock
10 Stabilizer bar
11 Pilot bushing
12 Rotary valve
13 Toothed rack
14 Drive pinion
I Right working cylinder
II Left working cylinder
A Pressurized
B Unpressurized
C Regulated pressure
Y10 Speed-sensitive power steering solenoid valve
Shown with left steer and vehicle speed v = 0 km/h
4 Reaction balls
8 Constant constriction orifice
9 Regulating valve
10 Stabilizer bar
11 Pilot bushing
12 Rotary valve
I Right working cylinder
II Left working cylinder
III High pressure from power steering pump
IV Return flow to power steering pump
A Pressurized
B Unpressurized
Y10 Speed-sensitive power steering solenoid valve
Function with vehicle speed v = 0 km/h
The speed-sensitive power steering solenoid valve receives maximum energy and as a result it is closed against the force of the integrated compression spring. The pressure ratios in the reaction chambers are identical since the supply of oil is stopped. No force is exerted on the reaction balls, no additional torque acts on the surfaces of the rotary valve.
The steering is light as the steering torque applied by the driver (i.e. the force required to overcome the force of the stabilizer bar) is very low. Via the constant constriction orifice the oil flow is passed on to the power steering pump reservoir virtually depressurized.
Shown on left steer and vehicle speed 0 km/h less than v 100 km/h
4 Reaction balls
8 Constant constriction orifice
9 Regulating valve
10 Stabilizer bar
11 Pilot bushing
12 Rotary valve
I Right working cylinder
II Left working cylinder
III High pressure from power steering pump
IV Return flow to power steering pump
A Pressurized
B Unpressurized
C Regulated pressure
Y10 Speed-sensitive power steering solenoid valve
Function with vehicle speed 0 km/h less than v less than or equal to 100 km/h
As the vehicle speed increases, energization of the speed-sensitive power steering solenoid valve decreases continuously; the valve is opened by the force of the integrated compression spring. The controlled pressure is led to the reaction balls via the regulating valve, causing the pressure applied to the surfaces of the rotary valve to increase.
The force on the torsion bar is increased further as a result and the driver has to operate the steering wheel with a higher steering torque. The constant constriction orifice reduces the regulated pressure from the speed-sensitive power steering solenoid valve.
This is then passed on as an almost depressurized backflow to the power steering pump reservoir.
Shown with left steer and vehicle speed v greater than 100 km/h
4 Reaction balls
8 Constant constriction orifice
9 Regulating valve
10 Stabilizer bar
11 Pilot bushing
12 Rotary valve
I Right working cylinder
II Left working cylinder
III High pressure from power steering pump
IV Return flow to power steering pump
A Pressurized
B Unpressurized
C Regulated pressure
Y10 Speed-sensitive power steering solenoid valve
Function with vehicle speed v greater than 100 km/h
The speed-sensitive power steering solenoid valve receives minimum energy. As a result maximum pressure is routed from the speed-sensitive power steering solenoid valve to the reaction balls via the regulating valve, which in turn causes the pressure applied to the surface of the rotary valve to increase to a maximum.
The constant constriction orifice reduces the regulated pressure from the speed-sensitive power steering solenoid valve. This is then passed on as an almost depressurized backflow to the power steering pump reservoir.
Function sequence for SPS [PML] electrically controlled reaction
Electronic control of the speed-sensitive power steering is integrated in the Electronic Stability Program control unit. A certain manual force is set at the steering wheel according to the speed of the vehicle. As vehicle speed increases, the manual effort required to turn the steering wheel increases at the steering wheel (up to v = 100 km/h).
In the Electronic Stability Program control unit, the determined vehicle speed is assigned a nominal current via a performance map. This is then set in the speed-sensitive power steering solenoid valve and influences the oil flow (hydraulic reaction assembly) within the rack-and-pinion steering gear and thus the manual force required to turn the steering wheel.
Actuation of the speed-sensitive power steering solenoid valve is pulsed. The flow control results from the pulse width modulation (PWM) of this cycling.
10 Stabilizer bar
11 Pilot bushing
12 Rotary valve
13 Toothed rack
14 Drive pinion
I Right working cylinder
II Left working cylinder
A Pressurized
B Unpressurized
Y10 Speed-sensitive power steering solenoid valve
Rack-and-pinion steering straight-ahead driving function sequence
When driving straight ahead (steering wheel in center position) the rotary slide of the rotary slide valve is in the neutral position.
The control grooves of the rotary valve and the pilot bushing are aligned such that the oil flow supplied by the power steering pump is routed straight back via the return flow to the reservoir. The working cylinders are therefore unpressurized.
The stabilizer bar is pinned on one side to the rotary valve and on the other side to the drive pinion.
