29 Robot 29 Robot Wheel Robot Wheel 29

From the intelligent wheel bearing to the “robot wheel”

Bernd Gombert

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ered as well. Mechanical and braking ele- The increasing ments are being replaced by mechatronic compo- nents thereby leading to higher functi onality with requirements placed increased safety. When referring to the further developments in on motor safety, the vision of “zero accidents” (autonomous and accident-free driving) has to be menti oned. Why is the trend heading Aft er slip control braking and driving stability sys- towards electromobility? tems, driver assistance systems known as ADAS (Advanced Driver Assistance Systems) are now be- Environmentally-friendly electrical mobility is the ing created as a further requirement for making expected trend and will become a real alternati ve this vision a reality. Figure 2 The fi rst electric , built in 1835 [1] Figure 4 Lohner-Porsche with four wheel hub motors to the current state of the art. Innovati ve technolo- By-wire technology, amongst others, is one of the in 1900 [1] gies, high oil prices and the increasing ecological nate the and since the prerequisites for the implementati on of ADAS. It awareness of many people are reasons, why elec- wheel rotated as the rotor of the direct current In order to compensate for the lack of range, of- monitors the current traffi c situati on and acti vely tromobility is increasingly gaining worldwide ac- motor around the stator, that was fixed to the fered by a vehicle only powered by electricity, supports the driver. By-wire means, that all the ceptance. wheel suspension. The drive therefore operated Porsche developed the “Semper Vivus” in the same driver’s important commands are transferred di- without mechanical friction losses with an im- year, a vehicle with a petrol-electric drive system The requirements placed on motor vehicles are rectly via a control signal. pressive efficiency of 83 percent. The output of (mixte - the term range extender is used to de- constantly growing, in terms of fuel consumpti on, Developing and launching such innovati ve prod- each was a maximum of 7 horse- scribe this system today), which was the precursor comfort, and safety, as well as in terms of emis- ucts on the market is of utmost importance to power, whereby the normal output was to all automobiles today with hybrid drives. The in- sions. maintain and increase the competi ti veness of 2.5 horsepower and 120 rpm. However, at ternal combusti on supplied electricity for The need of vehicles, that excel due to low emis- manufacturing companies. this time up to now, the size of the battery was both electric motors via a generator. It was also sions is increasing, because of the growing aware- a decisive weakness. The 44-cell lead acid bat- possible to acti vate the gasoline engine aft er start- The electric drive was transferred to the wheel ness of CO emissions, coupled with legal require- tery with 300 ampere hours and 80 volts had a ing the vehicle so that the electric motor func- 2 unit more than one hundred years ago. As early ments, such as inner city tolls for vehicles with range of 50 kilometers. The battery weighed ti oned as a generator to charge the batt ery. Both as 1896, Ferdinand Porsche made a patent ap- excessive CO emissions and the desire of govern- 410 kilograms with a vehicle weight of nearly motors could also be used together if necessary. 2 plication for his electric wheel hub motor. ments for less dependence on instable oil and gas one ton. Porsche developed the first vehicle equipped Modern hybrid electric vehicles (HEV) also save suppliers – the begin of zero emission. with electric motors in the wheel hub for Loh- fuel by storing kineti c energy released during brak- Along with the environmental situati on, the need ner & Co. coachbuilders in Vienna, that at first ing and delivering it to the electric motor during of more comfort and safety must also be consid- did not have the functions, associated with a hy- accelerati on to support the internal combusti on brid vehicle since the engine. The latt er is switched off when the vehicle wheel hub motor was is stati onary or during slow travel. However, if full the only drive in the power is required again, both the internal combus- vehicle. The first Lohner Porsche with two wheel hub motors on the steered front was presented at the Great Exhibi- tion in Paris in 1900. The electric motors Figure 3 Lohner-Porsche at the Great Exhibiti on in were located on the Paris in 1900 [1] in order to eliminate complex The racing version of the Lohner-Porsche devel- transmissions from oped during the same year was equipped with the crankshaft to the four-wheel drive and the batt eries for the four wheel, that were sus- power generators alone weighed 1800 kg. Despite 29 ceptible to faults. It its high weight, the racing sti ll managed a speed Figure 5 Lohner-Porsche Mixte with gasoline and Figure 1 Patent specifi cati on and design of F. Porsche’s wheel hub motor [1] was possible to elimi- of 60 kilometers per hour. electric drive (1901) [1]

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ti on engine and the electric motor power the ve- ciency when converti ng energy and the increase in mobiles can already be seen in the same applica- hicle. The advantages of splitti ng the power in this temperature of the batt eries, associated with this ti ons and similar technologies and is inevitable in way are, that a smaller internal combusti on engine when charging and discharging. The best charging the future. Nowadays it is the vision, that fully inte- is required and the excellent characteristi cs effi ciency is available at 50 to 70 % charge. A larger grates the technologies of the automobile of the of the electric motor improve the accelerati on. mass is required, however, for operati on with par- future with the modernity of the robot. ti al charge. Most HEV have a parallel confi gurati on, i.e. the ve- If the automobile and robot are reduced to their hicle has an electric motor and a large batt ery, as core components, it is possible to recognize the ba- well as the mechanical drive train, that runs from sic similarity of the classic machines present: Pow- the internal combusti on engine to the wheels. Parallels to er train, control system, body and . The drive of an arti culated in a robot is therefore In the case of the series confi gurati on, on the other comparable in principle with the drive of a wheel in hand, the wheels are driven by one or more elec- developments in a vehicle. It therefore stands to reason that spati al tric motors and instead of the mechanical connec- and functi onal units are integrated in a similar ti on to the wheels, the internal combusti on engine roboti cs manner as is the case with robots. This combina- powers a generator, that generates electricity for ti on is referred to as “robot wheel” below. these motors. This type of is also If one raises the questi on as to which parallel tech- known as a plug-in HEV. nologies have undergone similar development and in which directi on the car of the future is heading, While the fi rst hybrid vehicles used bulky lead acid one observes that the origins of the mechatronic batt eries, the batt eries in today’s vehicles are con- approach and the trend towards autonomy origi- An outlook for the siderably smaller. Toyota and Honda, who have al- nate in roboti cs. ready made very signifi cant progress in marketi ng automobile of the effi cient hybrid vehicles with reduced fuel con- In the past, however, robots have always been one sumpti on, use lighter and more environmentally- step ahead of the automobile in this respect and future Figure 7 The intelligent Schaeffl er wheel module friendly nickel-metal hydride batt eries (NiMH) in- the automobile has made great progress in the that all forces and moments in the wheel can be stead of lead batt eries. The long operati ng life of meanti me. A conti nuous convergence has been The fi rst promising step towards the robot wheel seen at any ti me. This means, that such wheel bear- these batt eries is an additi onal advantage. Howev- taking place during the last few decades in parti cu- is the development of the intelligent wheel bear- ings form the basis for more extensive assistance er, the disadvantage is the somewhat weak effi - lar, so that the complete fusion of robots and auto- ing by the Schaeffl er Group. This involves, for ex- systems beyond ABS or ESP, with which the longitu- ample, building on the modular concept in which dinal and transverse dynamics of the vehicle can be Leonardo da Vinci design elements of the wheel bearings’ surround- controlled for the safety of the passengers. ings are linked to the Asimo (Honda) bearing. Combining Unimate (GM) Stanford Arm Aibo (Sony) mechanical and elec- tronic components, such as sensors for measuring wheel and 1495 1961 braking force, is an ad- 1969 diti onal development 1999 trend. 2000 The sensors integrated into the wheel bearing 2004 unit form the basis 1997 for the development. 1955 These sensors measure 1886 the distribution of 1600 IMTS - Bus stresses in the wheel Toyota Prius (Toyota) bearings during various Citroen DS driving conditi ons such Motorized carriage as accelerati on or brak- (Daimler) ing. The common per- 29 manent wheel force Figure 8 Longitudinal and transverse dynamics of the vehicle for the safety of the Figure 6 Developments in roboti cs and the automobile sector measurement means, passengers

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New Techno- -By-Wire- Semi-By-Wire Full-By-Wire Literature logies Modules Paral Integraon Complete Integraon [1] Historical archive of Porsche AG (www) [2] MIT study about the Wheel Robot, 100 % ADAS http://www.carbodydesign.com/detail. php?id=742, 2005

Robot Wheel

Integrated corner module

Intelligent wheel bearing

2008 2013 2020

Figure 9 From the intelligent wheel bearing to the robot wheel

Alongside the wheel hub motor, steering and technologies, one can expect that these concepts damping will be integrated in the center point of will soon become reality. The usage level of elec- the wheel. At fi rst, the wheel will contain mecha- tronics and the intelligent linking and merger of tronic components for damping and electric components also therefore increases the level of with the relevant sensor signal processing vehicle autonomy. and electronic components, such as ti re pressure monitoring, (ti re guard) as well as subsystems of the chassis control unit (integrated “corner mod- ule”). A fi nal step will involve integrati ng electric steering into the corner module. The implemen- tati on of the robot wheel will enable each of the four wheels to be driven, braked, steered and damped individually and acti vely via “by wire” commands. One can imagine this system to be similar to a skateboard in that the power generati on system 29 and drive are mounted in a “platf orm”. If one con- Figure 10 “Skateboard principle” with chassis and siders future energy storage systems or body [2]

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