(EPS) with GMR-Based Angular and Linear Hall Sensor

October 2008
Electric Power Steering (EPS)
with GMR-Based Angular and Linear Hall Sensor
Application Note
V 0.1
Sensors
Edition 2008-10-23
Published by
Infineon Technologies AG
81726 München, Germany
© 2007 Infineon Technologies AG
All Rights Reserved.
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Electric Power Steering
Electric Power Steering (EPS) with GMR-Based Angular and Linear Hall Sensor
Revision History: 2008-10-23, V 0.1
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Electric Power Steering
Table of Contents
Table of Contents
Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1
1.1
Electric Power Steering with GMR-based Angular Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2
2.1
EPS Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
EPS Electric Control Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3
3.1
3.1.1
3.1.2
3.2
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
Infineon Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Infineon Angle Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
TLE5011 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
TLE5012 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Infineon’s Linear Hall Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
TLE4990 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
TLE4997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
TLE4998P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
TLE4998S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
TLE4998C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4
Rotor Position Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5
Steering-Angle Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6
Torque Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
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Electric Power Steering
List of Figures
List of Figures
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Figure 13
EPS Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
EPS Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
EPS Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Possible setup for rotor position detection (1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Possible setup for rotor position detection (2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Additional angle error vs. motor-speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Excitation signal of one coil vs. rotor position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Possible Setup for Steering-Angle Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Torsion Bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Torque Sensor - Rotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Torque Sensor - Stator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Torque sensor - Concentrator with Sensor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Application Note
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List of Figures
Application Note
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Electric Power Steering
Electric Power Steering with GMR-based Angular Sensors
1
Electric Power Steering with GMR-based Angular Sensors
1.1
Introduction
Power steering is a system for reducing the steering effort on cars by using an external power source to assist in
turning the wheels.
Electro Hydraulic Power Steering (EHPS) is an advanced system that uses conventional hydraulic power steering
with an electric motor-driven hydraulic pump.
Electric Power Steering (EPS) is the latest system in which the electric motor (“E-motor”) is attached directly to the
steering gearbox without a hydraulic system. Sensors detect the motion of the steering column and a processor
module applies assistive power via an electric motor. This allows varying amounts of assistance depending on
driving conditions.
With electronic systems becoming more and more common in cars, EPS is the future power steering system that
they will use. Unlike its conventional counterpart, EPS is active only during the actual steering process. It also
eliminates maintenance on steering hydraulics and cuts fuel consumption by as much as 0.4 l/100 km.
2
EPS Systems
Different EPS systems are in use (see Figure 1).
Column Type
Pinion Type
Dual Pinion Type
APA Rack Type
Source: IQPC Advanced Steering Systems, ZF Lenksysteme, Dr.G.Ruck, May 2006
Figure 1
EPS Systems
Which EPS type will be used depends on the steering rack force (see Figure 2).
The column drive is used for small and lower mid-sized cars. The motor is located in the passenger compartment.
Its advantage is its better performance at reduced temperatures, and sealing.
The pinion drive is used for mid-sized cars, and the dual pinion drive is used for upper mid-sized cars. Both of
these drives are located in the engine compartment.
Another possibility is the rack drive. This type is appropriate for large vehicles such as Sports Utility Vehicles
(SUVs) and trucks.
Application Note
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Electric Power Steering
EPS Systems
Steering Rack
Segments Force [N]
Car
SUV/Trucks
Upper Segment
Upper
Middle Segment
Middle Segment
Lower
Middle Segment
Small Car
Mini
15000
14000
13000
12000
11000
10500
10000
9500
9000
8500
8000
7500
7000
6500
Column
Pinion
Dual Pinion APA - Rack
With
advanced
steering
technology
Servolectric with 12V
Source: IQPC Advanced Steering Systems, ZF
Lenksysteme, Dr.G.Ruck, May 2006
EPSc high
…
Figure 2
EPS Application
2.1
EPS Electric Control Unit
Each EPS Electric Control Unit (ECU) handles the data from different sensors. The sensors send information
about the steering torque, driving speed, and the steering angle. Figure 3 is an example of a block diagram of an
EPS ECU. Using this information from the sensors, the ECU calculates the necessary steering assist and controls
the 3-Phase Driver.
+12VRail
2x TLE5011/12
XC866/8
Torque Sensor
Torque
TLE5011
TLE4998
Differential Hall
IC
Speed
Tracker
TLE4250/51
8-Bit
Microcontroller
XC866
(optinal)
Steering
Angle
Sensor Interface
8-Bit
Microcontroller
SupplyICs
TLE 6361
TLE 6389
TLE4941/42
Fail Safe
16-/32-Bit
Microcontroller
3-Phase Driver IC
TLE 7183F
TLE 7189F
TLE 718X
Steering Angle
Sensor
Electric
Power
Steering
ECU
Rotor
Position
TLE5011/12
Current Sense
(Shunt
Substitute )
2xTLE4990/98
XC2364
Master
CAN/LIN
Transceiver
TLE6251DS/G,
OptiMOS-T 40V
IBP180N04S3
-02
IBP180N04S3
-H2
x6
Rotor Position
TLE6258,6285G
HS-CAN-Bus
Figure 3
EPS Block Diagram
Application Note
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Electric Power Steering
Infineon Sensors
3
Infineon Sensors
3.1
Infineon Angle Sensors
Infineon offers some angle sensors based on GMR technology. This section gives a short overview of Infineon’s
angle-sensor portfolio. For more detailed information, please refer to the products’ individual datasheets.
3.1.1
TLE5011
The TLE5011 is a 360° angle sensor that detects the orientation of a magnetic field. This is achieved by measuring
sine and cosine angle components with monolithic integrated GMR elements. The data communications are
accomplished with a bi-directional SSC Interface that is SPI compatible.
The sine and cosine values can be read out. These signals can be processed digitally to calculate the angle
orientation of the external applied magnetic field. This calculation can be easily done by using a COordinate
Rotation DIgital Computer (CORDIC) algorithm.
It is also possible to connect more than one TLE5011 to one SSC Interface of a microcontroller for redundancy or
any other reason. In this case the synchronization of the connected TLE5011 is done by a broadcast command.
Each connected TLE5011 can be addressed by a dedicated chip-select pin.
3.1.2
TLE5012
The TLE5012 is also a 360° angle sensor. Compared to the TLE5011, this sensor calculates the absolute angle
on chip with an implemented CORDIC. This angle value and additional register values can be read out with a bidirectional SSC Interface that is SPI-compatible. A Pulse-Width-Modulation (PWM) protocol and an Incremental
Interface are also implemented.
An angle error smaller than 1.0° will be achieved over temperature and lifetime using an internal autocalibration
algorithm. This autocalibration is only helpful in applications with an angle range more than 360°. The sensor
calculates the calibration parameters and updates the new parameters within a timeslot or within the following
angle range.
A revolution counter is also implemented within the TLE5012. This counter counts every full rotation. It is a 9-bit
signed value, so ±256 revolutions could be measured.
3.2
Infineon’s Linear Hall Sensors
Infineon offers a variety of linear Hall sensors with different programming, package and interface options. This
section is a general overview of our sensor portfolio. For more detailed information, please refer to the datasheets
for each product.
Table 1
Overview of Infineon’s linear Hall sensors
Product
Programming
Package
Interface
TLE4990
Fuses
PG-SSO-4-1
Analog
TLE4997
EEPROM
PG-SSO-3-10
Analog
TLE4998P
EEPROM
PG-SSO-3-10
PG-SSO-4-1
PWM
TLE4998S
EEPROM
PG-SSO-3-10
PG-SSO-4-1
Digital, SENT
TLE4998C
EEPROM
PG-SSO-3-10
PG-SSO-4-1
Digital SPC
Application Note
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Electric Power Steering
Infineon Sensors
3.2.1
TLE4990
The TLE4990 is Infineon's basic linear Hall sensor with analog signal processing and fuse programmability. The
sensor is end-of-line programmable, meaning that its gain and sensitivity can be set in a two-point calibration in
the module. Due to its thin PG-SSO-4-1 package, it fits in small air gaps. The TLE4990 has been field-proven over
the last few years and is well established for automotive applications such as gas-pedal position sensing.
3.2.2
TLE4997
The TLE4997 has been designed to improve on some of the shortcomings of an analog compensation scheme as
the one used in the TLE4990 and most competing products, including offset and sensitivity drifts over temperature,
range of the programmable parameters, and accuracy. The signal processing in the TLE4997 is entirely shifted to
the digital domain, making the influence of the programmed parameters completely deterministic. Temperature
effects of the Hall probe can readily be compensated for by pre-calibration in Infineon's fabrication. The TLE4997
is also the first sensor on the market that offers independent, programmable parameters for both first- and secondorder temperature coefficients of the application sensitivity. The TLE4997 has an analog, ratiometric output and
can be used as a robust replacement for potentiometers. It comes in a small 3-pin PG-SSO-3-10 package and is
therefore suited for use in the limited space inside magnetic circuits.
3.2.3
TLE4998P
The TLE4998 family is the successor of the TLE4997, providing innovations on the interface side. The signal
processing concept is based on the TLE4997 design, offering high-precision analog-to-digital signal conversion
and a deterministic digital signal processing. The TLE4998P features a PWM interface in which the duty cycle
carries the Hall signal information. It offers 12-bit resolution on the output, and combined with accurate detection
on the microcontroller side, is more accurate than an analog interface.
3.2.4
TLE4998S
The TLE4998S is equivalent to the TLE4998P except for the interface, which is implemented as SAE's1) Single
Edge Nibble Transmission (SENT) standard. SENT offers a low-cost alternative to CAN and LIN, but still
incorporates a coded digital signal transmission with a Cyclic Redundancy Check (CRC) to check the validity of a
transmission. Apart from an industry-leading 16-bit Hall value, the transmitted SENT frame includes 8-bit
temperature information and 4-bit sensor status information. The status information finally allows for a massive
improvement of overall system safety.
3.2.5
TLE4998C
The TLE4998C features a Short PWM Code (SPC) protocol, which is an extension to the standard SENT protocol
and therefore has all the advantages already present in the TLE4998S such as high resolution, status,
temperature, and CRC information. The sensor does not, however, send out the measured values indefinitely, but
only after being triggered by the ECU. This functionality permits synchronized transmission of data. The protocol
makes it possible to select one of four sensors, which are connected to a single bus line.
1)
SAE: Society of Automotive Engineers
Application Note
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Electric Power Steering
Rotor Position Sensor
4
Rotor Position Sensor
The rotor position is very important for correct commutation of the motor, independent of the motor type
(Permanent Magnet Synchronous Motor (PMSM); Brush Less Direct Current (BLDC); Asynchronous Motor
(ASM)). For detection of rotor position, a TLE5011 or TLE5012 could be used as depicted in Figure 4 a.Figure 5.
Pinion
Gear
EC-Motor
Magnet
Sensor
Figure 4
Possible setup for rotor position detection (1)
EC-Motor
Pinion
Gear
Magnet
Sensor
Figure 5
Possible setup for rotor position detection (2)
The angle information tells the system which coil has to be excited next. The angle detection has to be done very
fast. Depending on the number of poles used and the rotation speed, an additional error has to be considered for
the electrical commutation, which is depicted in Figure 6. With one pole pair, the electrical 360° (one period)
matches the mechanical 360° (one rotation). With a rotor with two pole pairs, the switching in the coils has to be
done two times faster. This means the electrical period must be completed within a half rotation (Figure 7).
Application Note
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Electric Power Steering
Rotor Position Sensor
Additional Angle Error vs. Application Speed
(Sensor Update Rate = 80µs)
100
Angle Error [°]
10
1
0,1
PP=1
0,01
100
PP=2
1000
PP=3
PP=4
PP=5
10000
100000
Motor-Speed [1/min]
Figure 6
Additional angle error vs. motor-speed
Excitation Signal
of one coil with 1
polpair
Excitation Signal
of one coil with 2
polpairs
Mech. Angle
0°
Figure 7
360°
180°
Excitation signal of one coil vs. rotor position
Application Note
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Electric Power Steering
Steering-Angle Sensor
5
Steering-Angle Sensor
The steering angle indicates where the driver wants to go. This information is also used by other systems such as
the Electronic Stability Program (ESP), Active Front Steering (AFS), Adaptive Front Lighting (AFL), and so forth.
The steering-angle sensor unit is mounted on the steering column, mostly within the passenger compartment.
It is important to determine an angle value at power-on. This true power-on functionality is achievable by the
nonius principle. This is patented by Robert Bosch GmbH; Figure 8 shows an example of how one might build
such a steering-angle sensor.
Source: 2nd Advanced Steering Conference; Ms. Schiebel; May 2007
Figure 8
Possible Setup for Steering-Angle Sensor
This module consists of three gear wheels. One hub gear wheel is mounted on the steering column and represents
the steering angle ϕ. The two smaller gear wheels differ by one or more teeth, and there is a magnet in both of
them. These magnets, with diametrical magnetization, each rotate above an angle sensor. Due to the different
number of teeth, one gear wheel turns faster than the other one. The two measured angle values have the
following output characteristics Figure 9:
Gear wheel ψ andθ [°]
360°
360°
Figure 9
720°
1080°
1420°
Absolute measuring rangeφ [°]
Output
With this principle it is possible to determine an unambiguous steering angle over more than four full turns of the
steering wheel. In addition, no standby current is needed. At every startup the sensor knows its position as a result
of having both angle values.
Application Note
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Electric Power Steering
Torque Sensor
6
Torque Sensor
The power-steering control unit uses a torque sensor as the main input for determining the amount of steering
assistance needed. The steering column is split into two parts: The input shaft, from the steering wheel to the
torque sensor; and the output shaft, from the torque sensor to the steering shaft coupler. The input and output
shafts are separated by a torsion bar (Figure 10), where the torque sensor is located. The torque sensor
measures the shift angle between input and output shaft. One possible torque sensor from Moving Magnet
Techologies (MMT) is described below. Please note that this design is covered by a patent1) and should give only
an idea how to implement torque sensing with linear Hall sensors.
Input Shaft
Output Shaft
Torsion Bar
Figure 10
Torsion Bar
The sensor by itself is split into two parts, the rotor and the stator. The rotor, a multipole magnet ring, is mounted
on one side of the shaft (Figure 11).
Multipole Magnet Ring
Figure 11
Torque Sensor - Rotor
The stator consists of two parts. They are made of soft ferromagnetic material, and are mounted on the opposite
side of the torsion bar (Figure 12).
Stator
Figure 12
Torque Sensor - Stator
1) US patent 2004-0011138
Application Note
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Electric Power Steering
Torque Sensor
To detect the shift angle, a stationary fixed concentrator is necessary. This concentrator also contains the linear
Hall sensor and is put over the stator (Figure 13). When torsion occurs between input and output shaft, a flux
variation is detected by the sensor, which is proportional to the shift angle.
This information is processed by the EPS ECU, which controls the EC motor via the 3-Phase Driver IC
Sensor (e.g. TLE4998)
Fluxconcentrator
Stator
Figure 13
Torque sensor - Concentrator with Sensor
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----------------------------------------------------------------------------------------------------------------------------------------------------Application Note
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