Scheme 2
Introduction
The Servotronic does not regulate the steering force support in a conventional way by using the engine speed, rather it is dependant upon the car's road speed. The Servotronic regulates the hydraulic pressure in the power-steering pump. Adaptation of the hydraulic pressure to the car's road speed has the effect of
- High steering force support at low road speeds
- Minimum steering force support at high road speeds
This means that minimum force is required for steering force at slow road speeds. As the road speed increases the steering force support is continuously reduced. Contact to the road surface therefore becomes more direct and steering is more precise. Consequently, steering is very comfortable and maneuverability is maximized, for instance when parking and maneuvering at slow speeds.
New : In E83 the Servotronic is integrated in its own control unit.
The Servotronic is available as special equipment (option 216).
E83 Servotronic System Overview
General overview
Scheme 3
The primary role of the torsion bar is to generate the return forces for the steering.
A centering unit is integrated in the steering box.
The centering unit supports centering of the steering when the steering wheel is in the center position.
The centering unit characteristic is another variable for steering system design.
Inputs/outputs
Scheme 4
System circuit diagram
Scheme 5
Brief Description Of Components
The following control units are involved in the Servotronic
- Servotronic control unit (SVT) The SVT control unit specifies the nominal values for controlling the Servotronic valve (hydraulic pressure). The SVT control unit is connected to the PT-CAN (powertrain CAN) and K-Bus (body bus). For more information, refer to «E83 SERVOTRONIC CONTROL UNIT (SVT)»(/bmw/x3/e83-2003-2006/remont/manual-power-steering/#steering-and-wheel-alignment-service-techniques__e83-servotronic-control-unit-svt) .
- DSC control unit (Dynamic Stability Control) The DSC control unit delivers the car's road speed signal. The DSC control unit and SVT control unit are connected by the PT-CAN.
- DME or DDE (Digital Engine Electronics or Digital Diesel Electronics DDE) The Servotronic receives the signal of whether the engine is running from the DME or DDE over the PT-CAN. The Servotronic only activates the Servotronic valve when the engine is running.
- Instrument cluster (KOMBI) The instrument cluster delivers the terminal status (e.g. terminal 15 ON) and the kilometer reading. The following actuators are controlled by the Servotronic
- Servotronic valve The Servotronic valve is an electro-hydraulic converter located in the power-assisted steering oil circuit. The Servotronic valve restricts the hydraulic current and consequently reduces the hydraulic pressure. The Servotronic valve is activated by a characteristic curve delivered by the SVT control unit. For more information, refer to «E83 SERVOTRONIC VALVE»(/bmw/x3/e83-2003-2006/remont/manual-power-steering/#steering-and-wheel-alignment-service-techniques__e83-servotronic-valve) .
System Functions
The Servotronic is based upon the following system functions
- Initialization of the Servotronic
- Recording of the speed
- Supplying the Servotronic valve with power
- Undervoltage detection and overvoltage detection
Initialization Of The Servotronic
The Servotronic is active from terminal 15 ON.
A short initialization phase for the Servotronic (under 1 second) is necessary when the engine starts in order to reach the characteristic curve for a low road speed as fast as possible.
A plausibility check for supplying the Servotronic valve is performed during the initialization phase.
Recording Of The Speed
The road-speed signal is calculated by the DSC and supplied to the PT-CAN. The Servotronic specifies an acceleration value for plausibility of the road-speed signal. A road speed is calculated from the acceleration value.
At a low acceleration the road-speed signal supplied by the DSC is used.
At a higher acceleration the Servotronic control unit calculates the road speed internally. The road speed is stored in the Servotronic control unit.
Supplying The Servotronic Valve With Power
The Servotronic valve is supplied with power in response to the car's road speed. The power-assisted steering characteristic is memorized in a characteristic curve. The characteristic curve specifies the power based on the car's road speed.
The characteristic curve is written using 16 reference points.
The Servotronic valve is no longer supplied with power when the engine is OFF (over the PT-CAN). Minimum steering force support is set (high road speed) when the Servotronic valve is no longer supplied with power.
Equally, the Servotronic valve is also no longer supplied with power if there is a fault-memory entry.
Undervoltage Detection And Overvoltage Detection
The Servotronic valve is no longer supplied with power under the following conditions
- Supply voltage less than 9 volts
- Supply voltage higher than 17 volts
Voltage dips during ignition faults are detected.
Switch-On Conditions
Switch-on conditions for the Servotronic are
- Terminal 15 ON
- The engine must be running
The Servotronic only activates the Servotronic valve when the engine is running.
When the engine has started and there a road-speed signal is not supplied the Servotronic sets the maximum steering force support.
If a plausible road-speed signal is detected the Servotronic valve is activated by the characteristic curve.
If there is still not a (or not a plausible) road-speed signal 5 seconds after the engine has started the minimum steering force support is set.
E83 Servotronic Control Unit (SVT)
Installation location
Scheme 6
The SVT control unit is housed in the device holder behind the glove box.
The position of the Servotronic control unit in the device holder is different for RHD cars.
Construction
The SVT control unit is connected to the wiring harness by a 12-pin connector.
| Pin | Type | Description |
|---|---|---|
| 1 | A | Activation for the Servotronic valve |
| 2 | E | Measurement input for the Servotronic valve |
| 3 | V | Terminal 30 (power supply) |
| 4 | M | Terminal 31 (earth) |
| 5 | E/A | Powertrain CAN High |
| 6 | E/A | Powertrain CAN Low |
| 7 | ||
| 8 | ||
| 9 | ||
| 10 | ||
| 11 | ||
| 12 | E/A | Body bus (K-bus) |
| A = Output | ||
| E = Input | ||
| E/A = Input/output | ||
| M = Earth | ||
| V = Supply | ||
| For current specifications regarding pin assignment, please refer to BMW diagnosis system | ||
PIN ASSIGNMENT X83, 12-PIN
How it works
The following signals are transmitted on the PT-CAN
- Car road speed
- The engine must be running
- Odometer reading
The Servotronic is not switched off if the signal for the kilometer reading is absent (no impairment to function). "Kilometer reading 0000" is entered under environment related conditions in the fault-memory entry.
The SVT control unit goes into the idle state (sleep mode) 30 seconds after terminal R OFF.
At terminal 15 ON the SVT control unit is reawakened.
E83 Servotronic Valve
The Servotronic valve is fitted directly onto the steering box.
Scheme 7
Construction
The Servotronic valve is an electro-hydraulic converter. There is a variable diaphragm in the Servotronic valve. The cross-section dimension of the variable diaphragm lies between 0 and 0.7 mm.
How it works
The Servotronic valve restricts the hydraulic current in the power-assisted steering. The degree of restriction is changed by the current (PWM signal from 250 to 500 Hz) that is used to activate the Servotronic valve. The steering force support characteristic is memorized in a characteristic curve. The characteristic curve is written using 16 reference points. The car's road speed and current are coded for each reference point (road speed: 0 to 250 kph, current: 0 to 0.9 A)