The Active Steering Wheel Returns function always resets the steering wheel to its central position, for example following a turning operation. A configurable function shall be implemented that actively supports the steering wheel return. Active steering wheel return shall be available after the system is started.

The function damps the steering wheel motion.

By providing additional power, the Steering Power Assistance function makes the steering easier for the driver. A ramping is used for activation and deactivation of the Steering Power Assistance function.

The currently consumed battery current is periodically transmitted by the EPS via the network.

Limiting of the power used by the EPS is applied for the stability of the onboard electrical system. The function limits the power consumption of the EPS to a maximum value.

The function limits the power consumption of the EPS to a maximum value. The limit of the current limitation is determined by this function is dependent on the voltage at the component's load input.

The maximum electrical current that the EPS may draw from the onboard electrical system is limited. The EPS is informed of how much battery current may be drawn from the onboard electrical system via FlexRay network.

In the case of the special event "curb push-off", there may be damage to steering and axle components. One remedy for reducing the forces is to reduce the assisting force provided by the steering system. This is the function of this feature.

The friction detection function is used to detect friction between the steering pinion and the wheels.

The EPS is used as an actuator for vehicle dynamics and driver assistance functions, by means of torques being requested via the driving dynamics interface and/or EPS-internal functions being influenced by different factors.

In the case of driver assistance systems, information regarding whether the driver's hands are on the steering wheel or not is required. The function Hands-Off Detection provides this information.

Steering hysteresis is taken to mean that when steering from the center, a different manual torque operates to that which operates when steering back to the center (friction hysteresis). If system-related hysteresis deviates from the target characteristics, this software function is used to adjust hysteresis effects strategically.

As a result of the arrangement of the cardan joints, sinus-shaped torque superimposition of the steering moment occurs which is compensated by this feature for the steering actuator.

Owing to the performance call-off and the installation position in the engine compartment, the steering may be subjected to temperature loads.

The EPS servotronic function allows the customer to park using low steering moments.

External functions such as the parking maneuver assistant use the EPS via this function as an actuator for adjusting target positions.

The Friction Compensation function detects and compensates for frictional forces palpable to a driver.

The function is used to protect the mechanical steering stop by means of situation-related reduction of the EPS motor torque before the mechanical steering stop.

The function Inertia compensation offers a means of functional compensation for the possibility of a subjective impression of inertia (caused by the steering system's self-inertia).

Depending on the input signals, the system is able to switch different types of steering tuning (e.g. economic, basic, sports tuning). The requirements for the types of tuning to be stored and the behaviour during the actual switching process are formulated below.

The function restricts the rack travel to a certain value (target value) so that the fact that the end stop has been reached is displayed haptically (=relating to or based on the sense of touch) for the driver.

The function of Compensation Of Constant And Transverse Gradient Pull relieves the driver from manual torque during relatively long passages with a cambered road surface and/or a vehicle with constant pull. The function actively provides a torque that counteracts the effects of the cambered road surface and constant pull for straightline driving.

Based on the irregularities of the front wheels and/or fluctuations in manual torque free-rolling or braked rotary vibration of the steering wheel (LDS) can occur over the entire speed range. This function provides that the driver cannot detect the LDS fluctuations in steering moment up to the fourth harmonic order of the wheel frequency in the steering moment.

The temperature of the steering shall be transmitted by the EPS via the signal defined in the message catalog.

The Limp Home mode of operation ensures that the EPS is still operational in case of the following scenarios:

• Outage of RPS signals
• Loss of torque sensor signals (index- and/or angle-signals)
• Failure in one half-bridge in the Power Module

The EPS provides limited assistance in these cases instead of the panic-mode shutdown, that means rendering none of assistance.

Limp-Home Mode or emergency mode can also be initiated by other ECUs, such as the or the . Uniform handling is needed in these cases regardless which ECUs cause them.

Electric motor design (lamination shape, rotor, winding) is provided by Thyssenkrupp Presta Chassis Hungary Ltd. (Budapest), mechanics designed by Thyssenkrupp Presta Chassis GmbH (Eschen).

Peak Phase current limitation	120 A
Max. Battery Current Limitation	85 A
Battery voltage	11,5 V
Line Effective Voltage (Phase/Phase)	6.2 V
Sizing temperature (Wires, magnets)	80 °C

Speed [rpm]	Torque [Nm]	Mechanical Power [W]
0	5.513	0
1 128	5.437	642.1
2 255	2.772	654.7
4 143	1.246	540.6
4 486	0	0

Construction	12/8 slot/pole, V-magnet structure, segmented stator
Active Rotor Length	63 mm
Stator Inner/Outer Diameter	48/85 mm
Overall Size (Length/Diameter)	135.5 x 93 mm
Total Weight	3 500 gr

Steering Maneouvers to be satisfied

• BMW Steering Maneuver 1 –
• BMW Steering Maneuver 2 –
• BMW steering Maneuver 3 –
• BMW steering Maneuver 5 –

Thermal properties for heat transfer from the ECU

The function of the Torque and Angle Sensor is the detection of steering shaft torque, the detection of the steering shaft angle.

Torque sensing functionality detects the torsional deflection angle of a torsion bar which is integrated into the steering shaft. For the steering angle measurement an additional multiturn module is implemented which provides a signal to calculate the absolute steering angle within the steering ECU. The multiturn module provides a true power on sensor signal.

The applied sensor is the Hella TAS Gen2 sensor. It consists of a rotor build as simple metal part and a stator build as printed circuit board equipped with an . On the there is one excitation coil and a set of receiver coils implemented planar with conducting paths for one sensor.

The excitation coil is part of an LC oscillator and generates a concentric magnetic field. This magnetic field induces a current in the rotor. As a consequence the rotor generates a second magnetic field that superposes and couples back to the receiver coils. The induced voltage levels in the receiver coils correspond to the rotor position. The ASIC of the sensor measures these voltages with a ratiometric technique, calculates the rotor position and transmits a linear output signal over the steering angle to the ECU.

For angle sensing, the gear consists of two gear-wheels. Combining a 40 degree and a 296 degree measurement ranges the absolute steering angle is calculated via the Vernier algorithm.

Controlling the electric motor (PMSM) requires a robust Rotor Position Sensor with high resolution and high noise suppression.

Operating Principle

A two pole neodymium or ferrite magnet is fixed at the end of the motor shaft. The orientation of the magnetic field is measured with a magneto-resistive sensor fixed between the electric motor and the ECU.

Sensor

The applied sensor is the Infineon TLE5900D Giant Magneto-Resistive (GMR) sensor. It has a fully redundant design, containing two sensor ICs 180 degrees shifted to each other. It provides analog sine and cosine output voltages that describe the magnet angle in a range of 0 to 360 degrees, as the following figure it shows. No turn counting functionality is provided by the sensor.

Performance

Characteristic Features:

• Main Processor: Freescale MPC5744 is based on the Architecture. It is designed for safety applications requiring a high Automotive Safety Integrity Level (ASIL), having 384 kBytes SRAM, 64 kBytes tightly coupled local data SRAM with and 2,5 MBytes on-chip flash memory including ECC.
• Dedicated Watchdog Processor: a Freescale MC9S08SG32 16-bit microprocessor with 32 kBytes flash- and 32 kBytes RAM, high sophisticated I/O-, interrupt- clock-management-, timer- and communication-facilities.
• Two Auxiliary Processors to take care of the Rotor Turn Position Sensor's signals: Microchip PIC12LF1822 (8-Pin Flash Microcontrollers with nanoWatt Technology. They have high-­performance core, running at 32 MHz, with 2 kW/4 kByte program memory, 256 byte EEPROM, 128 byte SRAM).

Structural Components:

• Main PCB containing the vast majority of the electronic components, such as the main , the Watchdog- and the Auxiliary Processors, the Power Supply Unit and the communication Interfaces, the bridge-neutraliser circuit, phase disconnector switching elements, as well as their drivers and the power MOSFET's avalanche-detection circuits.
• PCB containing a magnetoresistive angle sensor (KMZ60), for angular control, two Hall-sensor latches (MLX92211), signal enhancer op-amps, and the two Auxiliary RPS Processors (PIC12LF1822).
• Power Module is composed of 3 pieces of half-bridge to control the PMSM, snubber elements for the power MOSFETs (N-channel, 40V, 1.25mOhm, 270A STV270N4F3).

Functional Features:

• Voltage Measurement:

  The Main Processor and the Watchdog Processor monitor all the power supply rails

  • each component's (GDU, RPS Auxiliary Processors, / ),
  • the star-point voltage of the PMSM,
  • the battery voltage,
  • the voltage-drop on a 0.5mOhm shunt (computing the phase current and the input).
• Temperature Measurement:

  There are several critical points in the ECU hardware whom temperature are measured continuously

  • three positions on the Power Module (central points of the half-bridges),
  • one NTC-sensor on the Main PCB, (see the PCB-layout),
  • the dual-core Main Processor (MPC5644P) includes two junction temperature sensors (per core), that monitors the device temperature and delivers analog and digital output signals.
• PMSM Controlling:

  Complex steering algorithms are running on the ECU hardware. These high- sophisticated algorithms (according to the input parameters, such as torque index/angle, electric motor position, gear-position, vehicle weight, vehicle speed) controls the PMSM, as the actuator of the EPS control system as a whole.

• Communication:

  The ECU of the R8 EPS uses FlexRay which is a scalable, flexible high-speed, real-time communication system with a time-triggered approach. The FlexRay node transceiver is TJA1081 which allows for the use of wake-up frames on the FlexRay bus.

The following figure shows a detailed block diagram of the BMW R8 ECU hardware.

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