19MTZ worldwide 4/2002 Volume 63

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Crankshaft sealing modules with integral speed sensor technology were developed toassist the automotive industry in its continuing efforts to cut costs, logistics and installa-tion space as well as to meet stricter emission and fuel consumption standards. Thesemodules combine the following functions in a single unit: dynamic sealing, static sealingand the sensing of the crankshaft speed/reference mark. In the light of the successfulintroduction of Freudenberg’s sensor sealing flange module with a PTFE sleeve seal ringand multipole sensor wheel into the series production of the BMW 2.0-litre common raildiesel engine, this article describes the module’s functional requirements, design charac-teristics, main areas of development, requirements for garage and engine plant assemblyas well as future development prospects.

By Uwe Meinig,

Markus von Geisau

and Eric Kammerer

Kurbelwellendichtung

mit integrierter

Drehzahlsensorik

You will find the figures mentioned in this article in the German issue of MTZ 4/2002 beginning on page 280.

Crankshaft Seal with Integral Speed Sensor Technology

20 MTZ worldwide 4/2002 Volume 63

1 Introduction

In addition to the repeated changeoverfrom crankshaft seals near the flywheel tointegral solutions [1, 2] that combine boththe dynamic and static sealing of the crank-shaft to the crankcase in a single sealingbase, and the introduction of PTFE packingswhich improved quality and increased ser-vice life, Freudenberg has after years of in-tense development work made anotherbreakthrough in the integration of addi-tional functions into modules: crankshaftspeed/reference mark sensing for enginemanagement systems. This developmenttook on concrete form in 1998 with the suc-cessful introduction of sensor sealingflange modules with passive sensor wheelsinto the series production of VW 1.0-litreand 1.4-litre spark-ignition engines.

The recent inclusion of a sensor sealingflange module from Freudenberg in theBMW 2.0-litre common rail diesel engineconstituted the first ever use of a modulewith an active multipole sensor wheel inseries production, Figure 1. Unlike the pas-sive sensor wheel, in which the magneticflux is altered by means of a ribbed ortoothed sensor wheel made of ferritic steel,the magnetic flux at the sensor in the activesensor wheel is altered by a magnetizedlayer of elastomer with alternating polarityon its outer diameter.

2 Function Integration andModularisation

Module suppliers create additional benefitsfor their customers by integrating supple-mentary functions into existing products.An important prerequisite for the economicsuccess of such new solutions is the carefulevaluation within the cost framework oftechnical feasibility in the early stages ofdevelopment and, if necessary, of alterna-tive concepts.

A comparison of the concept behind thesensor sealing flange module describedhere and conventional solutions (integralrotary shaft seal and speed/reference marksensor technology via inductive sensor andwith a sensor wheel that is screwed to thecrank web) highlighted significant cost-cutting potential. Other factors also tippedthe balance in favour of the sensor sealingflange module. These included technicalconsiderations such as weight reduction,the close proximity of the sensor technolo-gy to the flywheel (low crankshaft torsionalvibration amplitudes) and the greater lee-way in the configuration of the mass-bal-ancing weights on the crank webs [3]. Inthe concept stage of the developmentprocess, other important factors included

key technical functions, recycling, auto-mated assembly, ease of diagnosis andmaintenance.

3 Integrating Speed SensorTechnology into the SealingFlange

The sensor sealing flange module was de-veloped in response to the automotive in-dustry’s efforts to cut costs and reduce thenumber of logistical interfaces, and the re-sulting move towards the use of modulesand sub-assemblies in this sector. This mod-ule combines in a single unit the previouslyseparate static and dynamic sealing func-tions of the integral rotary shaft seal andthe crankshaft reference mark/speed sen-sor technology for the engine managementunit. The Table compares the system sensorsealing flange module with a conventionalsealing flange that uses a sensor wheelscrewed onto the crank web and an induc-tive speed sensor. The main advantages ofthe sensor sealing flange module relate toits system costs and also to its assembly,weight and installation dimensions.

3.1 Functional RequirementsIn order to allow for a sufficiently accuratestart of the injection and ignition processwith regard to the position of the crank-shaft, the sensor sealing flange modulemust sense the reference mark signal withan accuracy of at least ±2° crankshaft anglewhile, at the same time, taking all mass-produced engine component tolerancesinto account. A speed signal is derived fromthe reference mark signal in the engine

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management unit [4]. In diesel engines, sig-nificantly greater accuracy is generally re-quired of the allocation of the referencemark signal to the position of the crank-shaft. In the true spirit of onboard diagno-sis, a future-oriented module concept mustalso offer the potential for detecting mis-fires.

The high degree of automation in theautomotive industry means that assemblyrobots must be able to easily install mod-ules delivered to the assembly line in spe-cial transportation containers and correctlyposition the sensor wheel in relation to thecrankshaft. Another important develop-ment consideration relates to the car-makers’ customer service requirements: inother words, should a defect arise, thespeed sensor must be quick and inexpen-sive to replace.

1 Introduction

Figure 1: New sensor sealing flange module of Freudenberg

3 Integrating Speed Sensor Technology into theSealing Flange

Table: System comparison of the sensor sealing flange module with a conventional sealing flange with sensor wheel and inductive speed sensor

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clude the fact that they require very littleradial installation space and guaranteehigh signal accuracy in the incrementrange. Compared with passive sensorwheels, these components are not as criti-cal in terms of signal interruption, which inturn means that in practical operation theyallow for comparatively larger sensor gapdimensions.

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3.2 Applied SolutionsFigure 2 and Figure 3 illustrate the layoutof two different types of sensor sealingflange modules. In terms of the sealingfunction, the layout of the sensor sealingflange module basically corresponds to thatof the integral rotary shaft seal [1, 2]. Heretoo, the rotary shaft seal parent panel,which holds both static and dynamic sealsand which has been increased to the size ofthe housing opening, is pressed onto thecylinder crankcase via an aluminiumflange. As has been the case for decades, therotary shaft seal’s sealing lip seals on theground outer diameter of the crankshaftflange.

Figure 2 shows the version in which thepassive sensor wheel is pressed onto thecrankshaft. The sensor wheel, which ismade of 0.8 mm thick deep-drawing quali-ty sheet and has ribbed teeth, is pressed ax-ially onto the crankshaft flange behind thesealing lip. Like conventional solutions, thissensor wheel has 58 teeth, whereby twoteeth have been left out (gash). The sensorwheel is bent at right angles around theseal, so that the toothed wheel work is posi-tioned above the seal packing in a radialalignment. The sensor has a cylindricalhead (with a diameter of 11 mm) and sits ina machined radial bore in the aluminiumflange.

As illustrated in Figure 2, the aluminiumalloy sealing flange body has cast ribs inthe uptake area of the sensor in both radialand circumferential directions. These ribsallow for the easy insertion of the sensoreven during blind assembly (e. g. when theengine is installed in the vehicle). The en-gine cylinder crankcase, which is made ofdiecast aluminium, has a sensor insertionopening in the area of the housing flange tothe gear. The walls of this opening alsohave sensor insertion ribs and are geomet-rically adjusted to suit the correspondingribs on the sensor sealing flange module.The sensor is positioned in relation to thealuminium flange using the sensor headand is secured to the sensor sealing flangemodule using an M6 screw. The screw is atan angle of 30° to the radially positionedsensor head.

This means that the sensor screw can betightened accurately using the prescribedtorque and a wrench inserted through thesensor insertion opening in the cylindercrankcase. When servicing alternative con-cepts, the starter is disassembled to replacethe sensor.

Figure 3 illustrates the sensor sealingflange module featuring multipole encod-ing and the fastening of the sensor wheelin the crankshaft-flywheel screw union.The sensor wheel, which is made of 1 mm-

thick deep-drawing quality sheet, has on itsouter circumference a layer of magnetiz-able elastomer that is approximately 1 mmthick. A high-precision magnetizationprocess is used to magnetize north andsouth poles alternately around the circum-ference. These poles replace the teeth onconventional toothed sensor wheels. Theadvantages of multipole sensor wheels in-

3.2 Applied Solutions

Figure 2: Layout of the sensor sealing flange module with passive sensor wheel pressed onto the flywheel flange

Figure 3: Layout of the sensor sealing flange module mounted on the cylinder crankcase where the multipole sensor wheel is braced between the crankcase flange and the flywheel

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3.3 Main Focus of DevelopmentThe individual components in the sensorsealing flange module are fundamentallybased on conventional technology. How-ever, significant development activity wasrequired before the concept could be imple-mented. The first development tasks thathad to be tackled were the definition of thegeometry of the sensor wheel, includingthe fastening and positioning of the rota-tion angle on the crankshaft, as well as thedevelopment of solutions relating to con-figuration, operating principle, fasteningand assembly and replacability of thespeed/reference mark sensor. These con-cepts were defined in very close co-opera-tion with the customers for two reasons:firstly, the confined installation space and,secondly, the request made by several cus-tomers that the module should be flexibleenough to be used in all engines in an en-gine range with only minimal adjustments.

Customer requests for a fastening and ro-tational positioning of the sensor wheelwithout alterations to the crankshaft al-ready used in series production resulted inthe development of solutions in which thesensor wheel was non-positively and axiallypressed onto the crankshaft flange behindthe seal packing. Another proposed solution,which would have seen the sealing ring seal-ing on the sensor wheel – as is the case witha cassette seal – was rejected for reasons ofexpense and functional reliability (to avoidan additional static sealing problem). In-stead, the sensor wheel is positioned axiallybehind the seal ring in the area that is notwetted by the engine oil, Figure 2.

A sufficient frictional connection be-tween the crankshaft and sensor wheeleven under the effects of changing temper-atures and centrifugal forces was demons-trated in both test drives and comprehen-

sive laboratory tests. An alternative solu-tion to fastening the sensor wheel is thepossibility of positioning it axially in thescrew union between the crankshaft flangeand the flywheel. A defined positioning ofthe circumference can, for example, beachieved using a straight pin pressed intoan additional bore on the front face of thecrankshaft flange, an oblong hole with ra-dial extension or a cylindrical sleeve posi-tioned concentrically to the flange screwthread. In this case, the sensor wheel isbraced axially between the crankshaftflange and the flywheel. This means that,where necessary, a comparatively accurateangular assignment can be achieved be-tween the cranks of the crankshaft and thesensor wheel gashes.

When developing the sensor wheel withmultipole technology for the sensor sealingflange module, which was recently intro-duced into series production at BMW,Freudenberg was able to make use of expe-rience gathered in the manufacturing ofmultipole sensor wheels for ABS applica-tions, which have been in series productionfor several years now. The multipole sensorwheels used in ABS applications are rub-ber-metal components. The elastomer usedin these parts is filled with ferrite powder.The elastomer layer, which is usually vul-canized onto the radial outer edge or frontface of a parent panel, is magnetized evenlyand with great precision on the circumfer-ence with alternating north and southpoles. The advantage of multipole sensorwheels over conventional ABS sensorwheels made of stamped sheet steel is theirhigh pitch accuracy even at high resolutionand the fact that they allow for large airgaps between the surface of the sensorwheel and the sensor.

The fundamental differences betweensensor wheels for ABS applications and

sensor wheels for engine applications in-clude the signal gap (which corresponds tothe gash of two teeth on a passive sensorwheel), an orientation of the toothed wheelwork to an interlocking mark, which is sub-sequently used to align the sensor wheel tothe crankshaft, and the higher ambienttemperatures during operation in engineapplications. The main focus of the devel-opment of the multipole sensor wheel forthe sensor sealing flange module was thefurther development of the existing mag-netising technology to allow the signal gapto be achieved with sufficient angular ac-curacy over the entire sensor air gap range.Just like the ABS multipole sensor wheels,the edges outside the signal gap are ex-tremely accurate.

In view of the high temperature require-ments, a new elastomer mixture also hadto be developed. Furthermore, for the seriesproduction of the multipole sensor wheelfor engine applications, a procedure wasdeveloped that allows for the accuratearrangement of the sensor wheel duringthe magnetisation process to ensure an ac-curate relative position of the signal gap inrelation to the interlocking mark. Figure 4compares the passive and active sensorwheels, both of which have been used in se-ries production.

Inductive, magnetoresistive or Halland/or differential Hall sensors are mostsuitable for measuring the speed and sens-ing the reference mark on the sensor wheel.Given the confined areas involved, a pas-sive inductive speed sensor is not suitablefor this purpose. When the following areaswere taken into account, magnetoresistivesensors were deemed most suitable for thisapplication:■ limiting air gap■ operating temperatures■ installation dimensions■ lower ceiling speed■ availability.

As this sensor was a new development,manufacturers and customers in the auto-motive industry had to carry out extensivesystem performance tests, such as temper-ature change resistance tests, leak tests,EMC tests, vibration acceleration tests,worst case sample tests (min. / max.) ofmaximum gap and angle of the sensorwheel and gap to the crankshaft crank andtests with minimum axial overlap betweenthe sensor wheel and sensor.

The position of the sensor element in re-lation to the outer diameter of the sensorwheel is influenced by the individual com-ponent tolerances of the following parts:cylinder crankcase, crankshaft, sensorwheel, aluminium flange and sensor. Dur-ing engine operation, this list also includes

3.3 Main Focus of Development

Figure 4: Conventional sensor wheel (left) and multipole sensor wheel(right) – both for the sensor sealing flange module

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thermal expansions and the influences ofthe crankshaft’s bearing clearances. Care-fully calculated tolerances in a radial direc-tion were essential to exclude the possibili-ty of a collision between the sensor and thesensor wheel in large series conditionswithin the maximum gap dimensions ofapproximately 1 mm as determined by thesensor, and to ensure the reliable function-ing of the sensor technology. The same ap-plies to circumferential and axial toler-ances.

3.4 Assembling the ModuleThe solution examined in this article, inwhich the sensor wheel is non-positivelypressed onto the crankshaft flange, meansthat, for servicing, the sensor sealing flangemodule has to be assembled using a specialtool. The longitudinal section in Figure 5shows the service assembly tool, the condi-tion of the sensor sealing flange module atthe time it was supplied and the crankshaftflange. The sensor sealing flange module,which comprises a sealing flange and asensor wheel, is delivered with a plastictransportation/mounting sleeve. The pur-pose of this sleeve is to keep the PTFE lip onthe selected sealing flange diameter. It alsoacts as a locking and anti-rotation devicefor the sensor wheel.

The friction torque between the trans-portation/mounting sleeve and the sensorwheel, and between the sleeve and thePTFE sealing lip means that the sensorwheel can be pre-positioned in relation tothe sealing flange. In order to assemble inthe engine, the service assembly tool isscrewed onto the sensor sealing flangemodule by means of three knurled thumbscrews that are distributed around the cir-cumference and are screwed into the corre-sponding bores on the sensor sealing flangemodule’s aluminium flange. With the help

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of a positioning pin on the tool, which ex-tends into a corresponding oblong holewith a radial extension, the tool and sensorwheel are positioned at the correct angle toone another. When the central nut isturned to the right, the unit comprising thetool and the sensor sealing flange module isplaced on the cantering spigot at the crank-shaft end (crankshaft position DP). The in-ner part of the tool is then screwed into thecrankshaft flange using two diametricallyopposed screws. A defined positioning ofthe circumference to the crankshaft is en-sured by a positioning pin that is parallel tothe axis and the screws. The positioning pinalso extends into one of the screwed holeson the front face of the crankshaft.

By tightening the central nut on the tool,the sensor wheel and the sealing flange arepressed un-cantered onto the crankshaftflange at the prescribed angle. The trans-portation/mounting sleeve leans on thefront face of the crankshaft flange. Whenthe central nut is pulled off, the sleeve ispushed through the sensor wheel and intoa ring space within the tool. Once theknurled thumb screws have been loosenedand the tool removed, the aluminiumflange is screwed onto the cylindercrankcase and the oil pan.

The automated assembly of this moduleby industrial robots on the engine assem-bly line is similar to this process. The sensorsealing flange modules are removed from aspecial transportation box by a gripper de-vice. The sensor wheel is then positioned ina circumferential direction by means of apositioning pin and pressed on by a pneu-matic cylinder.

4 Summary and Outlook

At Freudenberg, the automotive industry’sneed to reduce interfaces, cut costs and to

work with a few, high-performance suppli-ers in the long term led to the developmentof the sensor sealing flange module. Thismodule, which is used to seal the cylindercrankcase at the crankshaft end near theflywheel and for speed/reference marksensing for the engine management sys-tem, combines in one single component aPTFE sealing lip, a static housing seal con-tour made of elastomer and the seal ringparent panel. The crankshaft referencemark/speed are sensed by an inexpensive-ly designed sensor wheel made of deep-drawing quality sheet steel that is attachedto the flywheel flange or a multipole sensorwheel and a magnetoresistive speed sensorthat is positioned radially above the sensorwheel.

Numerous requirements had to be takeninto account when developing this module:specification sheet requirements relatingto sealing reliability, speed sensing, resis-tance to temperature and media, fatiguelimit, durability, the replacement of thesensor during servicing and the automaticassembly of the module in series produc-tion. In the concepts described in this arti-cle, the sensor wheel is either pressed ontothe crankshaft flange non-positively withthe assistance of a special tool or braced be-tween the crankshaft and the flywheel.

The second PTFE generation sealing so-lution recently presented by Freudenbergnot only offers decisive benefits in the seal-ing area but also reduces the amount ofspace required and is, therefore, ideallysuited for other stages of the speed mea-surement process, which are certain to beimplemented not only for the crankshaftbut also for other key engine managementinstallation areas. Future emission limits(accurate angular injection and ignition,misfire recognition) and costs, when con-sidered as a whole, will play a decisive rolein this area in the future.

References

[1] Meinig, U.: Dichtungs- und schwingungstech-nische Entwicklungstendenzen am schwung-radseitigen Kurbelwellenende von Pkw-Motoren. Vortrag, Universität Karlsruhe,1. Juli 1997

[2] Guth, W.: Eine leistungsfähige Alternative:Kurbelwellendichtringe aus PTFE. In:ATZ/MTZ-Sonderausgabe System Partners1998

[3] Köhler, E.: Verbrennungsmotoren,Motormechanik Berechnung und Auslegungdes Hubkolbenmotors. Braunschweig / Wies-baden: Verlag Vieweg, 1998, S. 18 ff.

[4] N. N.: Bosch – Ottomotor Management.1. Auflage, Wiesbaden: Verlag Vieweg, 1998,S. 272 ff.

[5] Müller, K. H.: Abdichtung bewegter Maschi-nenteile. Waiblingen: Medienverlag U. Müller,1990

3.4 Assembling the Module

Figure 5: Longi-tudinal section ofservice assemblytool, sensor sealingflange module andcrankshaft flange

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