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Engine Integration
The Integration of an Engine Series into Various Vehicle Types using the Example of the BMW Inline Six-cylinder Engine
By Johannes Liebl, Norbert Klauer,Andreas Müller and Claus Otto Griebel A decisive characteristic of BMW vehicles is the powertrain.The sixcylinder engine with its superior refinement is the core engine for all model lines. Using the recently revised inline six-cylinder engine as an example, this article shows how BMW succeeds in building cars that offer “ sheer driving pleasure” by making systematic use of the scope for vehicle-specific adaptation.The engine not only serves to set BMW apart from its competitors but also to allow different positioning of the various BMW model lines. 1
Introduction
The BMW range of engines comprises all the most frequently used numbers of cylinders, from a 1.6-litre inline four-cylin-
You will nd the gures mentioned in this article in the German issue of ATZ 1/2001 beginning on page 8.
Einsatz einer Motorbaureihe in verschiedenen Fahrzeugtypen 22am Beispiel des BMW-Reihensechszylinders
der to the exclusive V12 with a capacity of 5.4 litres. Figure 1 shows the allocation of the different engine families to the current BMW range of vehicles. The inline sixcylinder as the core BMW engine is used for all model series. For this reason, BMW’s engine development philosophy can be shown using the main development priorities for the newly revised inline six-cylinder basic engine and its adaptation for use in different models as examples. The aim is to use this engine not only for differentiation against competitors but also to create differences in positioning within the BMW model range.
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The New BMW Six-cylinder Engine
In 1999, 58 percent of BMW cars sold, representing an output of 437,000 units, had an inline six-cylinder engine. The share of inline six-cylinder engines has increased continuously in the last few years, Figure 2. This above-average increase has been made possible by the fact that the inline six-cylinder engine is used as the core engine in the Roadster and the “Sports Activity Vehicle” and is also offered in 7-Series models as an entry-level engine. The next section explains the basic engine functions and the development progress achieved since the launch in 1990.
2.1 Smooth Operation The inline six-cylinder engine won its reputation as an engine with legendary smoothness early on and this has been continually confirmed throughout the internal combustion engine’s long maturity period, despite the fact that modern engine tech-
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Engine Integration
nology can be extensively optimised by means of powerful development methods, new components and materials. The reason for this is the interior balance of mechanical forces and moments in the basic engine. The engine can be regarded as inherently well-balanced, Figure 3. In BMW’s capacity segment between 2.0 and 3.0 litres that is covered by the inline six-cylinder engine, different engine types are available on the market. It is possible to compare different concepts by calculating the resultant effect of all free forces and moments at the engine mounts. Consideration of reactions from the valve gear completes the observation of the engine system as a whole. The relationship between the most important engine layouts is impressive proof, as shown in Figure 4, of the physical advantage of the inline six-cylinder engine.
2.2 Power Output and Torque Through the development measures since its launch in 1990, – resonance-effect intake system and double VANOS variable camshaft control since 1998, – double-flow exhaust system in the most recent revision stage along with dethrottling measures in the entire air intake system, the inline six-cylinder engine has further consolidated its lead in terms of power output/torque related to swept volume. A uniform, high maximum torque of 100 Nm/l is obtained between 3,500 and 4,500 rpm as well as a maximum specific output of 57 kW per litre. At least 90% of the maximum torque is available between 1,500 and 6,000 rpm, which documents the leading position of the new BMW six-cylinder engine in a most impressive way, Figure 5. Combined with the exceptional smoothness of an inline six-cylinder engine, a turbine-like power flow is achieved across an engine-speed range of above-average width.
on the road is particularly noteworthy when related to its fuel consumption. The BMW 330i’s road performance is that of a sports car, but with the consumption of a lower midsize-class car. Exhaust emissions are well below the strictest ULEV exhaust emission limits. The new inline six-cylinder generation thus documents BMW’s engine development objectives most impressively: to achieve without compromise top values for all engine functions that at the same time represent the benchmarks for performance, consumption, emissions and acoustics. These form an excellent starting point for successful integration into different vehicle concepts.
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One Engine – Different Styles of Vehicles
As explained in Section 2, BMW uses the inline six-cylinder engine in all its current model lines. The power unit therefore not only has to meet specific vehicle requirements but also to determine them as an important element in the entire vehicle while maintaining the key engine characteristics. For example, the new 3.0-litre engine in the BMW Z3 Roadster underlines the car’s dynamic character without compromises, whereas the same engine makes the BMW 530i a comfortable saloon in the upper middle-class segment, due to its unique refinement. As the top engine in the 3-Series, it stresses the special sports character of the 3-Series
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Coupé with its synthesis of dynamism, smoothness and comprehensive sound design. As the basic engine for the new BMW X5, the special torque characteristic of the new 3.0-litre version, as explained in section 2.2 above, provides supreme strength in all driving situations, Figure 7.
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Differentiation Measures
Figure 8 is an overview of the components that the development engineer has at his disposal for the optimum adaptation of an engine to differing vehicle requirements. The conventional method of adaptation that has been in use for a long time is to adapt the powertrain to specific vehicle requirements such as rolling resistance, vehicle weight or the speed range to be provided. A new feature in this respect is that vehicle-specific components and assemblies such as the exhaust or intake air systems are developed not only to have an influence on basic engine functions that is as uniform as possible throughout the various model lines, but also specifically for “sound design”. The development engineers have further important elements at their disposal for differentiating between vehicles if they can dispense with a mechanical connection between the accelerator pedal and the throttle, which is actuated by a motor, and also in the form of increasingly powerful engine management systems. The potential of the individual elements is explained below by reference to various examples.
2.3 Road Performance and Fuel Consumption Figure 6 shows how performance has improved in the past ten years, using acceleration from 0 to 100 km/h and fuel consumption as indicators. The latest top 3-Series model, the BMW 330i, has improved considerably on the top model in 1990, the BMW 325i. Acceleration of the manualgearbox version from 0 to 100 km/h in 6.5 s is an excellent figure for a large midsize saloon. The performance achieved by this car
ATZ Automobiltechnische Zeitschrift 103 (2001) 1
Matrix of the vehicle engine program
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Engine Integration
4.1 Driveline The driveline, with the gearbox, propeller shaft, final drive and half-shafts, is the “classic” vehicle adaptation element. The final drive ratio is normally matched individually to every model and the different speed ranges occurring in various markets. In individual cases for special models or special markets, the overall spread of the gear ratios or the characteristic of the torque converter may be specially adjusted.
ible. With a differentiated switching characteristic for the exhaust gas flap according to the selected gear, Figure 11, the sound can be additionally matched to the different refinement standards required in different speed areas by the vehicle versions. The required sound characteristic at the tailpipe is achieved by varying the exhaust system switching characteristics.
4.3 Intake Air Path
Figure 9 shows the difference in pulling power in first gear for different vehicle applications of the new 3.0-litre engine. In the BMW X5, drive-off pulling power is 50% higher than in the BMW 330i saloon at the same engine torque.
There is further potential for sound design in the intake air path. Realisation seems only to be of value for certain vehicle versions, however, since legal regulations, the package situation and the need to handle an additional, dominant sound source require special adaptation values.
4.2 Exhaust System
4.4 Throttle Butterfly
Due to the position of the catalytic converters close to the engine, the double-flow exhaust system on the BMW 330i provides an excellent basis for a high-performance engine charge cycle and sufficient concept potential for optimising acoustics within the package of a compact sports saloon.
Figure 12 shows vehicle-specific throttle butterfly progression in first gear for the BMW Z3 3.0 and the BMW X5 3.0. A steep layout was chosen for the BMW Z3 in order to achieve no-compromise dynamism. In the BMW X5’s first gear, good off-road engine control was a priority, so that progression is considerably flatter, i. e. there is more pedal travel at the driver’s disposal for sensitive torque build-up.
Another notable feature of the technical concept is the exhaust gas flap, with a mapped characteristic controlled by the engine management system. This device selects two damping systems of different pattern in the main silencer. Low-frequency damping can thus be stronger at low revs and full load in order to achieve the refinement criterion for the exhaust system of a luxury saloon and a sonorous engine sound at the same time, Figure 10. At medium revs, it is possible to accentuate the engine orders in the sound at the tailpipe in such a way as to give the driver a load feedback that reflects the power of the engine. At high revs, low flow noise and, most importantly, low back-pressure can be realised, the latter being an important precondition for high specific engine performance. Overall, it has proved possible to design a sound that is an important element in the character of this sports saloon. The degree of freedom of a fully variable, controllable exhaust flap has another conceptual advantage. Identical exhaust system components can be used for different vehicle versions with different acoustic characteristics and/or requirements such as the Coupé, saloon, Touring or convert-
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The progression becomes steeper towards the higher gears in all models, Figure 13. This maintains the impression of dynamism, as reserves of pulling power become smaller in the higher gears.
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For the Bayerische Motoren Werke AG (BMW), a company with “engines” in its name, the engine is the core element for the different model lines. It influences the most important brand characteristics such as performance, dynamism, refinement and driving pleasure. The permanently increasing, brand-independent market demand for lower fuel consumption, exhaust and noise emissions can only be achieved with highly developed engines. Through targeted development of the scope for adaptation in its vehicles, it is possible to cover the entire BMW vehicle program from the 3-Series to the Z3 and from the 5-Series and the X5 up to the 7-Series and at the same time to give each vehicle category its own individual characteristics.
References [1]
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4.5 Engine Management Applying engine management parameters for transient behaviour can have a significant influence on the impression of dynamism or refinement, as shown in Figure 14 for the BMW 330i and the BMW Z3 3.0. During acceleration, a temporary excess in the acceleration measured at the driver’s seat rail can be achieved by fast opening of the throttle butterfly and a rapid increase in the ignition angle on the BMW Z3. This increases the impression of dynamism while reducing refinement slightly.
Summary
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Müller, A.; Riedl, W.; Griebel, C.O.: Neue Abgasanlagen für den BMW Z3 Roadster, Potentiale zur Ausprägung eines typischen Roadster-Sounds. In: ATZ 101 (1999), Nr. 6, S. 464–469 Liebl, J.; Müller, A.; Griebel, C.O.: Soundgestaltung in der Antriebsentwicklung für den BMW Roadster. Vortrag auf dem 8. Aachener Kolloquium Fahrzeug- und Motorentechnik, Aachen 1999 Schmidt, G.; Liebl, J.; Müller, A.: Laufkultur – eine Domäne der BMW Antriebstechnik. In: MTZ 61 (2000), Nr. 5, S. 300–306 Albrecht, F.; Fischer, H. D.; Kiefer, W.; Mertl, R.; Otto, E.; Griebel, C. O.: Die Technik der neuen BMW Sechszylindermotoren. In: MTZ 61 (2000), Nr. 9, S. 563–548 Klauer, N.; Griebel, C. O.; Otto, E.; Burger, A.: Der neue BMW 330i. In: ATZ 102 (2000), Nr. 7/8, S. 558–564 Liebl, J.; Klauer, N.; Müller, A.; Griebel, C.O.: Der Motor – Ein entscheidendes Differenzierungsmerkmal bei BMW. Talk on the AVL-Tagung Motor und Umwelt 2000
On the BMW 330i, the layout was chosen for a good compromise without overshooting between refinement and sports-style driving. The same layout strategy is used for deceleration processes by a faster reduction of the ignition angle and throttle butterfly closure on the BMW Z3 than on the BMW 330i.
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