Mtz Intake

COVER STORY

Intake System

The First Continuously Variable Intake System in the New Eight-Cylinder Engine from BMW

The new BMW V8 petrol engine is the first standard production engine in the world to be equipped with an intake module in which the length of the intake ports can be continuously varied. As a completely new development, this is the initial implementation of the concept of ideal adaptation of the lengths of the ports to the desired engine speed characteristics. The torque and therefore the engine output have been considerably increased, especially at high engine speeds. Pierburg, the system supplier, has succeeded in realising a complex yet at the same time light-weight module by the specific use of light-weight materials such as magnesium and plastic.

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MTZ 3/2002 Volume 63

The Authors 1 Introduction

At present, the new V8 petrol engine is the basic engine in the new BMW 7 Series. In addition to the desired reduction in fuel consumption, an increase in the rated output of the engine was a further important requirement of the technical specification. On the one hand, the high torque characteristics of the predecessor engine in the lower engine speed range were to be exceeded if at all possible and, on the other hand, a considerable increase in torque was required at high engine speeds. The intake system plays the central role in the implementation of these requirements. The rigid resonance-type intake system concept used in the predecessor engine was unable to meet these requirements. Within the framework of concept examinations, numerous designs and variants were discussed and analysed by BMW and the system supplier, Pierburg. On the basis of simple, rigid intake systems, Pierburg has implemented new charging and weight optimisation options since 1990 by means of consistent further development in the fields of production technology and materials technology. Milestones within this development include:  the first variable intake system on the German market  the introduction of shell technology  the introduction of composite design (diecast metal and injection moulded plastic parts)  the world's first standard production diecast magnesium variable intake system  the first variable intake system with three port lengths. On the basis of this experience, a new “milestone” was developed in the form of the intake module for the new eight-cylinder engine [1] with 3.6 and 4.4-litre capacity variants. Thanks to the achievement of a world first in the variable adjustment of the length of the intake ports in standard production, the goal of optimum resonance pipe supercharging throughout a wide engine speed range was achieved, Figure 1.

for use in standard production as a result of lowest space requirements with full port variability, Figure 2. An internal drum rotates in an outer, rigid, enginemounted housing. The rigid sections of the housing form the outer walls of the port, while the inner wall is formed by the hollow drum. The intake air is distributed in the hollow drum and enters the intake ports via the apertures, which are positioned in the drum. Rotating the drum enables the continuous variation of the lengths of the individual ports without changing the exterior dimensions of the intake system. 2.2 Structure

The design of the variable intake manifold used here is far more complex than the principle model. Boundary conditions such as adaptation to a V-engine and requirements such as durability, manufacturing and cost optimisation result in additional characteristics. The intake manifold, Figure 3, is comprised of two main elements:  air-guiding, plastic inner assembly  diecast magnesium outer housing. All port length adjustment is implemented in the inner assembly. Due to the sub-division of the cylinders into two banks, length adjustment had to be implemented by two counter-rotating adjustment units. In order to minimise space requirements, the adjustment units are interlocked. Each adjustment unit is comprised of four "rotors", which are mounted

Dipl.-Ing. Klaus Hirschfelder ist Leiter Konstruktion und Versuch Motorperipherie bei der BMW Group, München.

Werner Völkl ist Teamleiter Konstruktion Saugmodule bei der BMW Group, München.

Hans-Ulrich Kühnel ist Leiter Entwicklung Ansaugsysteme bei der Pierburg AG, Neuss.

Dr.-Ing. Walther Sinn ist Leiter Entwicklung elektrische Aktuatoren bei der Pierburg AG, Neuss.

Dipl.-Ing. Armin Huck ist Leiter MechanikVersuch Ansaugsysteme bei der Pierburg AG, Neuss.

1 Introduction

2 Design of the Intake Manifold

In the following, the functional principle, the structure and the drive unit of the intake manifold are discussed. 2.1 Functional Principle

The advantages of variable intake systems were scientifically investigated as early as the 1960s [2]. Of the possible basic concepts, only the drum principle is suitable


Figure 1: Host of measured torque curves

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Intake System

2.1 Functional Principle

Figure 2: Functional principle of an intake manifold (principle according to [2])

2.2 Structure Figure 3: Schematic structure of the intake manifold

together on a shaft. In the case of each rotor, a ring element forms the inner geometry of the intake port; the spokes and hub link the ring to the shaft. In order to optimise the flow, the inlet aperture into the rotor ring is shaped as a bellmouth. The outer limit of the individual ports is structured in segments. Two sides of a port's cross-section are formed by one housing shell; the following shell forms the end. The intake port is sealed by the

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rotor ring, Figure 4. Nine housing shells are therefore necessary to depict the entire outer port geometry of the intake manifold. Due to the repetitive geometry, only five moulded parts are required. The last one, the ninth, is merely a flat end cover. The eight-cylinder engine’s package is favourable for such a principle, but unfavourable as regards adjustment, as the rotors of the relevant banks have to be adjusted counter to one another. Counterrotation and additional functions such as

the necessity of the shaft bearings are unfavourable boundary conditions for the use of identical parts. Nevertheless, only one type of rotor is required for all eight intake ports. Implementation of the structure of the outer port assembly was possible with only five different housing shells, Figure 5. The rotors and housing shells are manufactured from glass fibre-reinforced Duroplast. The determining factors in the selection of this material were:  the mouldability of complex geometries under adherence to stringent component tolerances  the high moulding and temperatureresistance of the phenol resins. The hollow steel rotor shafts offer the best rigidity/weight ratio. A gear is welded onto the end of each shaft. Synchronised and counter-rotating shaft adjustment is guaranteed via these low-play spur gears. The application of force from the electric drive unit to the intake manifold, which is necessary for adjustment, occurs at only one shaft. The force flows via a spiral gear coupling which engages in the inner toothing of one spur gear. The magnesium outer shells form the load-bearing “spine” of the intake system, and guarantee the external leak-tightness of the intake module. On the inside, these carry the plastic functional unit; on the outside, they form the link to the cylinder heads and the throttle valve assembly. Magnesium was selected as the material for the two half-shells for reasons of weight optimisation. This is used in a highly-pure form in order to ensure durability without any further corrosion protection measures. The half-shells are bolted air-tight to one another via a CIP (cured in place) gasket. Due to stringent casting tolerances, mechanical processing predominantly involves drilling the threaded holes for the threaded connections and milling the connecting face. The inner assembly is elastically linked to the outer assembly. In this manner, the intake module is acoustically unobtrusive and can be rigidly bolted to the cylinder head without additional decoupling. The maximum adjustment range of the intake system is limited to 260° due to the structure of the two rotor shaft units. The operating range is limited to 236°. If required, the entire angle range can be traversed through in less than one second. Up to an engine speed of 3500 rpm, the system remains at its longest setting (length of port up to intake valve 670 mm). The shortest port length, 230 mm, is set at maximum engine speed.


COVER STORY

Intake System 2.2 Structure

2.3 Structure of the Drive Unit

The electric drive motor unit, which is positioned at the rear of the intake module, adjusts the rotor shaft units via a worm gear. Bearing feedback from the drive unit to the engine control system is carried out via an integrated potentiometer, Figure 6. The design of a drive is dependent on the following variables:  torque requirements  adjustment speed  maximum ambient temperature  adjustment frequency. A DC motor, which has also proven its worth in other BMW applications, and which also provides sufficient reserves when attached to internal combustion engines, was chosen as the drive. Stepping-down is carried out via a single-stage worm gear. The worm gear ratio is the result of the torque required at the drive and the torque supplied by the DC motor, i. e. the torque which can be provided under rated conditions during continuous operation at maximum ambient temperature. This requirement was fulfilled with a single-stage worm gear unit. The polyamide worm gear is moulded directly onto the drive shaft. At the same time, it is also the bracket for the angle sensor slider. During assembly, the drive unit is centred with the intake module's drive shaft via a low-play gear coupling. Diecast aluminium is used for the drive unit housing. This material ensures adequate thermal dissipation from the DC motor. At the same time, mechanical processing of the motor mount and the drill hole for the gear shaft ensures the necessary degree of accuracy for the worm gear unit. The drive unit is completed via a multifunctional contact unit. This integrates all electrical connections to the inside and outside, the angle sensor and seals, the drive unit itself and the seal for the interface to the intake module. The basic material of the contact unit is a high-temperature-resistant, fibre glass-filled polyamide. The contact unit's two gaskets are moulded on. In order to improve adhesion onto the basic material, both gaskets are additionally mechanically anchored via undercutting. A single-turn potentiometer is used as an angle sensor. The potentiometer PCB is glued onto the contact unit with a UV-activated adhesive. The electrical connection to the injected contact comb is designed as a bonded connection.

Figure 4: Schematic structure of the port geometry: Sides 1 and 2 via housing ring ”n“, side 3 via housing ring ”n+1“, side 4 via rotor ring

Figure 5: Exploded view of the housing shells and rotors

2.3 Structure of the Drive Unit

3 Development

From the original concept to the standard product, the intake manifold passed

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Figure 6: Schematic depiction of the drive unit


COVER STORY

Intake System

3.1 Charge Cycle Design

through several development stages [3]. In addition to the classic A, B and C sample stages, the completely new type of adjustment principle led to a multitude of basic questions which had to be answered. Development was carried out in the form of intensive, iterative interaction between simulation and testing, with all efforts being constantly directed towards defining the optimum form for intake system function and durability [4]. 3.1 Charge Cycle Design

Figure 7: Examination of areas of separation in the intake area

Figure 8: Compari- son of the standard rotor and the proto- type variant

Simulation was heavily involved in the basic design of the intake system. An initial model of the intake module was drawn up on the basis of the key engine data. Due to the complex port geometries, the approach of simple calculation with the substitute system of pipes and vessels was not helpful. In order to enable multidimensional calculations, the intake manifold was depicted entirely as a 3D model (in the program Fire). This model was integrated into the corresponding 1D engine model (program Promo). Interconnected 3D / 1D calculations provided information regarding status data such as pressure and flow behaviour at each point of the intake system at any point in time during a working cycle, Figure 7. In order to maximise the “ram effect” of the intake system, the pressure wave fronts at the transition point between the manifold volume and the actual resonance pipe must be reflected as evenly as possible. The main conclusion of these simulations was the design of precisely this point of reflection. The bell-mouth form which was calculated was converted into rotor prototypes and optimised to its final form on the flow test rig, Figure 8. A considerable increase in volumetric efficiency was achieved via the creation of an “additional volume”. A link to the “additional volume” between the plastic assembly and the lower magnesium shell was created via housing shell apertures in the area of the longest port setting. Measurements revealed that, at higher engine speeds, a considerable percentage of the air flow is guided into the intake ports via the additional volume, Figure 9. 3.2 Development of the Parts

Figure 9: Increase in torque via additional volume

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Tract leak-tightness is vital if the resonance pipe is to function. A slight internal leak within the intake system instantly leads to pressure loss, which negates the desired supercharging effect. In the case of the intake manifold, solutions had to be found for various areas in order to ensure leak-tightness:


COVER STORY

Intake System

During intake manifold assembly, the port transitions from the plastic assembly to the outer magnesium shell are sealed with an FIP (formed in place) gasket.  The joints between the individual housing ring shells are designed as a plug-in system. The housing rings engage into one another throughout the entire contour. In addition, the contours in the assembly form a cavity, into which adhesive is inserted prior to the joining process.  A solution had to be found for joining two counter-rotating components – the rotor ring and housing ring shells: Comparative measurements revealed that significant volumetric efficiency losses occur in the case of even minor leakage. However, auxiliary contacting sealing elements for tolerance compensation were not allowed to significantly increase the torque required to adjust the intake system. In addition, geometrical implementation was not permitted to impede the port cross-section. A radial-acting seal concept proved to be the best solution from a number of variants. Both sides of the rotor are equipped with a continuous groove, into each of which a slit steel ring is inserted. On assembly of the rotors in the housing ring assembly, this sealing ring is supported on a shoulder in the housing rings. The sealing ring is slightly pre-tensioned and firmly seats the steel housing ring in the 

plastic housing rings. The sealing effect results from the labyrinth which is created. The free movement of the adjustment unit is vital as regards the constant function of continuous port variability. Axial contact between the rotors and the adjacent housing rings had to be avoided and shaft bearing friction had to be minimised. The former was solved by the adherent attachment of the rotors onto the shaft: The shaft and hub are designed in a square shape. Leaf springs are inserted into the rotor hub on two adjacent surfaces of the square. These guarantee firm rotor seating and the induction of torque for port adjustment. In the assembly process, rotor fixation is completed without additional components or operations when the pushing-on process has been completed; component tolerances can be balanced out by measuring the pushing-on process. Each of the shafts is equipped with three sliding bearings. The bearing at the spur gear is designed as an axial bearing. For reasons of installation space, the bearing seats are designed as coupled sintered metal bearings. These are coated when the relevant housing rings are being injected. The supporting bearings are manufactured from fibre glass-filled polyamide. All bearing points and gears are lubricated

with high-performance grease, which combines a low coefficient of friction with outstanding temperature and media resistance. The intake system's operational adjusting range is 236°. In this case, the characteristic adjustment curve is optimally attuned to the relevant engine capacity (3.6 or 4.4 litres) and is stored in the engine control module. Depending on the relevant actual position of the intake system, which is reported to the digital engine electronics (DME) by the integrated potentiometer and the current nominal values from the characteristic engine map, the position control system generates a clocked voltage signal for the DC motor. Pierburg has developed the position control system software in close co-operation with BMW. The characteristic values required for this were determined in a comprehensive series of tests. Certain auxiliary functions were implemented in addition to the position control system. Each time a new installation is carried out (on assembly in the plant, replacement of the drive unit or replacement of the entire intake module), the system is automatically calibrated. As a result, clearances to the mechanical stops in the intake module can be minimised, in order to enable the fullest possible use of the installed adjustment range.

3.3 Test of Durability

Figure 10: Back-fire test on a bursting test rig

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4.1 Casting 3.3 Test of Durability

In a multitude of endurance tests, the overall module proved its durability in the face of mechanical, thermal and chemical stress. Engine and vehicle endurance tests and extreme tests on individual test rigs revealed, during the development phase, limits of stability under loading and – in the standard product – durability. For example, the module was successfully tested in excessive resonance dwell tests on vibration test rigs, in back-fire tests on bursting test rigs and adjustment endurance tests on functional test rigs, Figure 10. In the development phase, various individual component tests with respect to material selection and component design were additionally carried out. As in the case of any intake manifold, engine vibrations and pressure pulsations represent the mechanical stress excitation variables during operation. In combination with the large, moving suspended masses prespecified via the component geometry, all of the variable intake system’s elements were subjected to high loading values. Component optimisation led, on the one hand, to the cross-sectionrelated reduction of high, local peak loads and, on the other hand, to the minimisation of excessive increases between force excitation and response. One and threedimensional vibration tests and simulations were the main tools used in designing and verifying components.

Figure 11: Casting cell of the upper magnesium shell

4 Production

The intake system is manufactured in Pierburg’s Nettetal production plant. All manufacturing stages for the production of diecast aluminium and magnesium intake manifolds are carried out here [5], including casting, cutting and assembly.

4.3 Cutting

4.1 Casting

The Nettetal production plant is equipped with one of the most modern d iecast magnesium part production facilities in Europe. This is mainly used for intake manifold shells. Up to 2500 tonnes of magnesium are processed each year. Continuous material analysis guarantees the quality of the cast parts. Modern casting cells, Figure 11, with a clamping force of up to 1400 tonnes form the central units of the magnesium foundry. Handling robots carry the cast parts to a cooling basin and the deburring station. Downstream of this, 100 % leak testing ensures that no parts containing casting defects are passed on.


Figure 12: Dosing robot for the adhesive

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Intake System

4.2 Cutting

Stringent casting tolerances have been implemented thanks to a casting-friendly design and casting process optimisations. As a result of this, cutting has been considerably reduced. Necessary cutting is carried out on CNC machine tools, all of which are equipped with the additional facilities required to process the magnesium (first certified magnesium processing using aqueous emulsions).

4.3 Assembly

4.3 Assembly

The intake module of the V8 engine is predominantly assembled on automated conveyor belt lines. At the picking stations, cast parts and bought-in parts – such as the Duroplast components, for example – are manually inserted into the workpiece carrier mounting facilities. Assemblies are pre-assembled in individual square conveyor belts before being fully assembled to form the finished product on the final belt. On the first square conveyor belt, adhesive is dosed onto the Duroplast housing shells. The plastic components are fed fully-automatically into a dosing station in sets. A robot, Figure 12, moves along the complex contour with a dosing head. The connected robot and barrel pump control system guarantees the constant quality of the adhesive bead. The plastic assembly is assembled in the following square conveyor belt. In the first operation, each workpiece carrier is equipped with eight rotors with preassembled gaskets and springs, a pair of shafts and the first housing ring. Second, the circlips for securing the axial bearing are pushed into position. This is followed by the construction of the overall assembly in a complex rotor press-on station. The rotors are mounted in the hub, placed onto the relevant shaft and pushed into position via a pressing head. The high joining forces of approximately 1 kN are introduced via the hub. In order to align the components precisely, the distance between the rotor and the relevant housing ring is continuously measured during the pressing-on procedure. Once a defined nominal dimension has been achieved, the joining process is automatically stopped. In this manner, the constant position of the rotors in relation to the outer port geometry can be guaranteed throughout the entire assembly. The addition of component/manufacturing tolerances is thereby avoided. The assembly is constructed successively. Following each rotor, the next corresponding housing shell is manually removed from the dos-

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Figure 13: Rotor press-on station

Figure 14: Comparison of the torque curves between t he predecessor engine and the new eight-cylinder engine


COVER STORY

Intake System

ing belt and positioned onto the assembly, Figure 13. Following the assembly of the final, concluding housing shell, five “anchor ties” are laterally inserted into the housing shell apertures and riveted in the subsequent station as the final inner assembly production operation. On the final belt, the magnesium shells and the plastic assembly are assembled. The inner assembly is manually inserted; the upper magnesium shell is joined and subsequently bolted automatically. Following the completion of the intake system by bolting this to the drive unit and the pressure sensor, the module is subjected to a final inspection. The leak-tightness of the intake module is determined by subjecting it to a static vacuum and checking the loss in pressure. The function of the adjustment unit is checked via movement cycles between extreme port lengths, short, long, short. In this case, adherence to the limit values by the adjustment current, travel and time is checked. Important process data are monitored at all stations during production. For example, the force-travel of all pressing processes is monitored, and bolting stations are torque/rotary angle-controlled. Only if the data lie within the prespecified limit values are the assembled parts or assemblies passed on to the next stages. All intake systems are provided with a barcode within the framework of quality assurance and in order to ensure traceability. Relevant product data such as the

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final inspection measurement values are individually stored and archived under this code, Figure 14.

auf den Ladungswechsel mittels gekoppelter 1D-3D-Strömungsberechnung. In: MTZ 61 (2000), Nr. 4 [5] Langner, F.: Ansauganlagen vom Konzept bis zur Serie. Vortragsreihe im HdT Haus der Technik, Essen, April 2001

5 Teamwork

Processing in simultaneous engineering teams with experts from various disciplines formed the basis for the successful completion of the first continuously variable intake manifold system for the BMW V8 petrol engine as a unique product. This was only made possible by the committed and competent work of the specialist departments and persons involved at BMW, Pierburg and the suppliers. A demanding concept has been developed into a high-performance product within a short period of time. Together with further innovations in the new BMW V8 engine, this has led to the creation of an inspiring major assembly. The fully-variable intake system has enabled the realisation of ambitious goals with regard to torque and power output. References [1] Hirschfelder, K.; Hofmann, R.; Jägerbauer, E.; Schausberger, Ch.; Schopp, J.: Der neue BMW Achtzylinder-Ottomotor. In: MTZ 62 (2001), Nr. 9, S. 630–640 [2] Lenz, H. P.: Gemischbildung bei Verbrennungsmotoren; Springer-Verlag, Wien, New York 1990 [3] Sanders, M.; Kühnel, H.-U.: Entwicklung von Saugrohren in der Praxis. In: MTZ 55 (1994), Nr. 7/8 [4] Durst, B.; Thams, J.; Görg, K.-A.: Frühzeitige Beurteilung des Einflusses komplexer Bauteile


Mtz Intake

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