Drivers- Adaptive Front Lighting System

8/12/2019 Drivers- Adaptive Front Lighting System

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Performant Mechatronic Drives for AFS

Herbert Trummer, SONCEBOZ SA

Keywords: Motors, Actuators, Position Sensors, Mechatronics, Weight / Size Reduc-

tion

1 Introduction

The individual design of the car front but also various technical functions are thedrivers for the design progress of headlamp systems. With further developmentof adaptive Front light Systems, there will be more motors and actuators in the

headlamp to perform the different movements for the bending light, adaptivelighting, levelling, variable hi/low beam etc. These new functions require possib-ly higher duty cycles and higher loads i.e. for LED modules which lead to morepowerful motion drives.

Design aspects and new technical functions make that space becomes more andmore valuable in the front part of a car. Due to safety requirements like for ex-ample pedestrian friendly headlamps (EU directive 2003/102/EC), space for con-trolled displacement to absorb impact energy is extremely important .

Moreover car manufacturers are looking for potentials of weight reduction due tothe necessity to reduce fuel consumption and CO2 emissions. A study of the IFEUin Heidelberg says that 10kg less weight reduces CO2 emission by approx. 1g/km.

In order to fulfil the increased specification and at the same time to reduce theoverall size and the weight of the components of a front light system, higherefficiency of motors and actuators over the whole temperature range and integra-ted mechatronic drives may well be a good solution.

2 The challenge at very low temperature

The different motors and actuators in a modern front light system must guaranteecorrect movements over a wide temperature range from -40 to + 130C. An idealmotor or actuator would need to have a constant torque respectively force overthe whole temperature range. In reality, various factors, especially mechanicalone reduce the torque/force quite considerably.

Thats the reason why most electrical motors or actuators are strongly oversizedfor normal function temperature. Therefore they fulfil the torque or force specifi-

cation at -40C but induce a higher weight and space requirement.


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233Performant Mechatronic Drives for AFS

Figure 1: Typical force vs temperature curve of a Linear Actuator for Levelling

2.1 Higher force at -40C

One of the main reasons for the torque / force drop at very low temperature isthe viscosity of typical lubricants in bearings. The high viscosity of the greaseat very low temperature may increase the residual torque of a ball bearing by afactor two.

Special Silicon based lubricants would offer low residual torque but they are not

allowed due to their out-gassing characteristics, which can damage reflectors ofthe lighting system.

A possible way forward is to apply a patented alternative bearing concept em-ploying pivot bearings instead of ball bearings. The lead screw or the motor shafthas spherical pivots on their ends which are held between springs. The very smallcontact surface linking the pivots and springs guarantees a low residual torquewhich is not influenced by increasing viscosity of grease.

At very low temperatures a linear actuator with pivot bearing for LVL or DBL ap-

plication has output forces more than 2 times higher than the same version withball bearings. Thus its possible to fulfil the specification with a motor of smallersize. In some applications the specification may be fulfilled using a motor with adiameter of 25mm instead of 35mm. In such a case the effect is about 45% lessweight which represents up to 60 g for a LVL actuator. This may seem little, butmultiplied by 6 motors or actuators, two headlamp units could produce a savingof about 0.36 kg.


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Figure 2: Force increase by factor 2.4. at -40C with Levelling actuator with pivot bearing

3 Size reduction through integration

Motors and actuators have important interactions with other components of thehead lamp system. On the electrical side we have motor controllers which maybe integrated into the head lamp or centralized in an external controller. Severalfunctions require sensors for position feedback for reference or even the absoluteposition. Finally there is a mechanical interface between the head lamp mecha-nics and the motor or actuator.

Taking of-the-shelf-components and assembling them to the complete systemis one possibility to realize the different motion elements. However expensivecabling and space consuming construction may result. Higher integration of ac-tuator, sensor and electronics allow a reduction in space as well as cabling, calib-ration and mounting costs.

Figure 3: Xenon Headlight with high integrated DBL Actuator including Sensor and Driver electronics.


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An integrated design that allows direct contact of the motor, position sensor, mo-tor driver and the connector with one single PCB makes it possible to reduce theoverall volume by about 20% compared with a solution based on single compo-

nents.

Figure 4: Integrated Actuator solution with sensor and driver for minimal space requirement

4 Position Sensors

In a head lamp system there are linear as well as rotary movements to control.Due to aspects like higher safety or precision, and for On-Board Diagnostics OBDit may be necessary to have a position feedback signal. Depending on the functionthese signals may range from a simple digital reference point to a precise absoluteposition feedback. Besides the functional aspects and technical specification thereare other requirements: Simple and low cost design Non sensitive to temperature and other environmental influences Variable angle or stroke for absolute position

Non Contact for high life expectancy

While the reference point signal is rather easy to realize by using a bipolar ma-gnet and a digital Hall probe, absolute position sensors are more challenging.Using a patented solution (based on a moving magnet with a sinusoidal shape ora sinusoidal magnetization and a Hall probe giving two signals with a phase shiftof 90), robust and precise sensors can be made.


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Figure 5: Absolute position sensor using magnets with sinusoidal magnetization

Figure 6: Absolute position sensor using magnets with sinusoidal shape for linear or rotary movements

The induction B varies as a function of the movement of the magnet with sinu-soidal shape. Thus the two output signals of the Hall probe Bx and Bz with a 90phase shift are generated.


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Figure 7: Absolute position output signal Bx/Bz based on angle of the magnetic field for high immunity

The measuring mode based on the angle of the magnetic field of the absoluteposition sensor makes the system highly insensitive to temperature effects andmechanical tolerances. The achievable intrinsic non-linearity is typically betterthan +/- 0.5 % of the full stroke.

Integration of the position sensor into the actuator or motor may lead to impro-ved precision, smaller size and simpler cabling.

5 Conclusion

Todays designers of moving parts in headlamp system are under pressure due todemands of increasing performance, dynamics and reliability and reduction ofsize, weight and cost. An integrated approach with mechatronic systems, inno-vative solutions like the pivot bearing or the integration of new sensor concepts,may help to cut the Gordian knot.

6 References

Hella KGaA Hueck & Co, Technical Information Light Pedestrian Protection.

Studie zum Potential des Leichtbaus zur Reduktion des Transportenergiekonsums

Institut fr Energie- und Umweltforschung Heidelberg GmbH (IFEU).

Linear Actuator of the screw-nut type. Sonceboz SA

MMT Moving Magnet Technologies (FR) Besanon (Member of Sonceboz Group)

Drivers- Adaptive Front Lighting System

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