Engine - Overview - N52: Other BMW Z4 E85/E86 рестайлинг

Power Output

The terms "power output per liter" and "power to weight ratio" are used for comparing individual engine designs with each other. The power output per liter indicates the highest effective power output of the engine per liter of displacement (kW/l).

Compared to the M54 at 55kW/l, the power output of the N52 has been further increased to 61.7 kW/l.

The power to weight ratio indicates the construction weight per kW output (kg/kW). The lower the construction weight as a function of power output, the more efficient the power yield. The power to weight ration of the N52 also set new standards. Compared to the M54 at 1.0kg/kW, the N52 has been further reduced to 0.82kg/kW.

M20

BMW 6-cylinder engines have undergone a constant optimization process over time starting with the M20. The M20, which used 2-valves per cylinder, also featured a timing belt for the camshaft drive and adjustable valves. Over the years, The M20 was available with carbureted as well as fuel injected versions throughout the 1970's and 80's.

M30

The M30 which also featured 2 valve per cylinder technology and adjustable valvetrain, did not use a timing belt. The M30 was available in larger displacements up to 3.5 liter. The "big six", which the top engine in the BMW engine lineup, would later be succeeded by the new BMW V-8 engines in 1993.

M50

The successor to the M20, the M50 featured many new innovations when introduced in 1992. The M50 engine technology included 4-valves per cylinder, Dual overhead camshafts and direct stationary ignition (RZV). This engine also used fully sequential injection controlled by DME 3.1 engine management.

M50TU

The M50 was "technically upgraded" with the addition of VANOS in 1993. The new VANOS system allowed for intake camshaft timing changes which improved horsepower and torque curves. The "TU" variant also featured cylinder selective knock control, Hot Film air mass sensing and secondary ignition monitoring.

M52

The M52, which includes many of the features on the M50TU, utilized Siemens engine control. It was introduced in 1996 to comply with OBDII regulations. The M52 also provided a slight increase in horsepower and a large increase in torque over the M50TU.

M52TU

In 1999, the M52 was further refined by the addition of Double VANOS and an electronically controlled throttle. The new "TU" engine also used innovations such as a variable intake runner length, "near engine" catalytic converters and secondary air injection.

The use of aluminum on the M52TU also extended to the crankcase as well. This would pave the way for future improvements in engine materials.

M54/M56

The M54/M56 variants used much of the technology available at that time, however customer and legislative demands would mean that further improvements would be needed.

With these design goals in mind, BMW brought forth the latest engine construction technology. The "new generation 6" innovations include a new composite magnesium/aluminum engine block, Valvetronic II, electric coolant pump, volumetric flow controlled oil pump and a 3-stage intake manifold.

The new construction configuration allows a weight savings of 10kg (22 lbs.) over the previous generation of six cylinder engines.

Scheme 59

Innovative Solutions

The N52 engine concept allowed for a substantial weight savings of 10Kg (22lbs.) over its predecessor the M54. The primary contributors to the total weight savings are the new composite magnesium-aluminum crankcase and the lightweight exhaust manifold. Also, the magnesium bedplate and cylinder head cover also played a significant role in overall weight reduction.

The overall lightweight engine package allows for and improved power to weight ratio as well as an improvement in fuel consumption.

The N52 engine also features several innovations designed to further improve the overall engine. Aside from the composite crankcase there is a new Valvetronic II system which has been improved from the original version. The new 3-stage DISA intake manifold is constructed from a high temperature lightweight material. The belt driven coolant pump from previous engines has been replaced by an electric coolant pump. This allows the addition of a single belt drive. There is also a volumetric flow controlled oil pump to supply the required oil for VANOS operation.

Scheme 60

Technical Data (N52B30)

TECHNICAL DATA (N52B30) DESCRIPTION CHART

Scheme 61

Components

The N52 engine consists of the following components/systems

Scheme 62

1. 6-cylinder, 4-valve in-line, friction optimized engine
2. Two-piece crankcase in composite magnesium-aluminum structure
3. Trapezoidal connecting rods (weight optimized)
4. Aluminum silicon (Alusil) cylinder head
5. Timing case integrated in crankcase and cylinder head
6. Cylinder head gasket with silicon sealing lip
7. VALVETRONIC II
8. Weight-optimized double VANOS
9. Volumetric flow-controlled oil pump
10. Electrically controlled coolant pump
11. Crankcase ventilation with integrated heater
12. 3-stage DISA

Crankcase

Since magnesium cannot be used in all areas of engine construction, the new N52 crankcase is a composite design. The crankcase consists of an aluminum/silicon insert which is cast inseparably in a magnesium alloy.

The crankcase is a two piece design with a separate bedplate also cast from magnesium. Also a notable change from previous designs is the timing cover which is now cast as an integral part of the engine block.

The aluminum silicon insert provides the threaded connections for the transmission mounting, cylinder head and crankshaft main bolts. The insert provides the coolant passages as well. This is to prevent coolant contact with the magnesium portion of the engine block.

Scheme 63

The use of magnesium is a new concept for production passenger vehicles. BMW has developed special processes for the development of the N52 crankcase. A special magnesium alloy (AJ62) is used which has excellent properties which reduce the possibility of corrosion and allow favorable machining characteristics.

Scheme 64

The cylinder bore consists of an Alusil structure, there are no iron cylinder liners as with previous 6 cylinder designs. The cylinder bores cannot be machined, however this design still allows for planing of the deck surface if needed.

Scheme 65

Bedplate

The N52 engine uses a split crankcase, the upper section is made from a composite magnesium/aluminum structure. The lower portion, which is used to increase rigidity, is designed as a bedplate structure made from magnesium.

Scheme 66

There are sintered steel inlays (arrow) for the main bearings to take up forces which would not be suitable for magnesium alone.

Between the bedplate and crankcase, a liquid sealer is injected under high pressure into a machined groove This process is critical in service applications.

Scheme 67

Crankshaft

The crankshaft is cast iron with 7 main bearing journals. The trigger wheel for the crankshaft position sensor is between cylinders 5 and 6. Due to the design of the timing chain module, the crankshaft snout is modified to facilitate removal during service.

Scheme 68

Piston and Connecting Rod

As with previous engine designs, the pistons are manufactured from aluminum and have 4 valve reliefs.

The underside of the pistons are cooled with oil spray jets as in the past.

The connecting rods are weight optimized by tapering the "small end" of the rod. This method reduces weight without reducing strength.

The "big end" of the connecting rod is "cracked" to create to proper centering of the bearing cap without the use of dowel pins. This further contributes to the overall weight reduction. Each connecting rod uses pairing codes (1) to allow the correct rod cap to be matched to the connecting rod.

The connecting rods are divided into weight categories and can only be replaced as a set.

Scheme 69

Cylinder Head

The N52 uses an aluminum (AluSil) cylinder head with a cast bridge to mount the VVT actuator motor for the Valvetronic II system.

Scheme 70

Cylinder Head Cover

The cylinder head cover is also cast from magnesium alloy as well. The cylinder head cover provides an important mounting point for the VVT motor. The rear of the motor is supported by an aluminum bolt which attaches to a bracket on the cylinder head cover.

All of the bolts which attach the cylinder head cover to the cylinder head are made from aluminum. When performing repairs which involve the removal of the cylinder head cover be sure to replace the bolts and use the proper torque/angle procedure as outlined in the repair instructions.

Scheme 71

Valvetrain

The valvetrain on the N52 uses the familiar 4 valve per cylinder arrangement used on previous engines. The N52 valvetrain also uses the proven Valvetronic technology which was introduced on the N62.

Scheme 72

Camshaft

The total weight of the N52 is additionally reduced by the lighter camshafts. The total weight of the camshafts has been reduced by approximately 25% using "hydroforming" technology during the manufacturing process.

The hydroforming process starts with a steel tube on which hardened camshaft lobe "rings" are fitted. The camshaft assembly is then placed into a die. The steel tube is then subjected to an internal water pressure of up to 4000 bar. The tube then conforms to the inside of the die and achieves the desired shape. The camshaft lobes are then polished to the desired finish.

The weight savings is approximately 600 grams (21 oz) per camshaft.

Scheme 73

VANOS

Additional weight savings is also found on the VANOS system as well. The design of the VANOS is similar to that found on the N62.

The VANOS units are compact and use the "vane-type" construction which is less complex and easier to service than previous 6-cylinder VANOS designs. The VANOS units have integrated sprockets and are attached to the camshaft via a central bolt.

Due to the different spread ranges for the intake and exhaust camshaft, the VANOS units cannot be interchanged. Doing so would cause considerable engine damage.

Scheme 74

Intake Manifold

The intake manifold is manufactured from lightweight thermo-plastic. The manifold provides the mounting for the 2 airflap actuators for the three-stage DISA system as well as the electronic throttle flap actuator.

Scheme 75

Crankcase Ventilation

The crankcase ventilation system is attached to the rear of intake manifold. The system is now heated to prevent moisture from affecting system operation during low ambient temperatures. The heating system is controlled by the MSV70 engine management system via a relay.

Scheme 76

Exhaust Manifold

The exhaust manifold has been modified to offer substantial weight savings over the previous design. The mounting flange has been lightened by using sheet steel with a new sealing design. The flange is approximately 2mm thick, as compared to the M54 design which is approximately 12mm thick.

Scheme 77

The manifold uses a new circular seal which contains graphite. The new design features a thin-walled catalyst which reaches operating temperature faster. This eliminates the need for secondary air injection on some applications. The catalysts are also mounted near the engine as in the past. There are also provisions for the mounting of the pre and post catalyst oxygen sensors.

Scheme 78

Gaskets/Seals

In order to prevent contact corrosion, a non-conductive gasket is placed between select engine components. This is the function of the oil pan and cylinder head gasket.

The oil pan separates the aluminum oil pan from the magnesium crankcase (bedplate). The cylinder head gasket separates the aluminum cylinder head from the magnesium crankcase.

The cylinder head gasket features a sealing lip which protrudes from the block. This lip prevents dirt and splashing water from bridging the sealed joint, which prevents contact of these metals.

Scheme 79

Scheme 80

Particular care must be taken to ensure that the gaskets are not damaged during service. If gasket damage occurs, contact corrosion could form between the aluminum of the cylinder head and the magnesium of the crankcase within a relatively short period of time.

If the damage to the gasket were deep enough, the steel in the core of the gasket could also have an effect on the corrosion process.

Bolts

Due to the magnesium construction, any ancillary components which are attached to the engine exterior are connected by aluminum bolts.

The aluminum bolts are needed to prevent contact corrosion. Conventional steel cannot be used in magnesium for any reason. The aluminum bolts can be identified by a blue colored bolt head and their light weight.

Scheme 81

Also, the aluminum bolts can only be used once and must be replaced after each use.

When replacing components requiring aluminum bolts, torquing procedures must be strictly followed.

Torquing procedures include specific guidelines to prevent under or over torquing of the attachment bolts.

The procedures are outlined as follows

1. The bolt is tightened to a specific application torque to remove any slack between the components to be joined.
2. The bolt is then tightened using the "angle torquing" method.

Also, during any service procedures which involve coolant such as cylinder head replacement, the bolt holes must be blown dry immediately. Coolant must not be allowed to sit in any holes, this prevents any corrosion which could be caused by the coolant coming into contact with magnesium components.

Oil Pump

The high oil volume demands of the VANOS system on the N52 create a need for an oil pump that can deliver a high volume of oil when needed. Also, the pump needs to be able to cut back on the oil delivery volume when the requirements are not as great.

This occurs when the VANOS is not as active, for instance during cruise situations.

This new oil pump is a "volume controlled" design which not only meets the oiling requirements, but also contributes to improved fuel economy and emissions.

Scheme 82

The advantages of a volumetric-flow controlled oil pump

1. Favorable space/efficiency ratio
2. Provides sufficient hydraulic pressure and volume for valve control systems
3. Reduced volumetric flow fluctuations
4. Hydraulic energy not converted into thermal loss
5. Reduction of premature oil ageing
6. Reduced sound emissions

Electric Water Pump

The coolant pump on the N52 is designed as an electrically driven centrifugal pump. The output of the wet-rotor electric motor is controlled electronically by the electronic module (EWPU) located under the connection cover of the motor.

Scheme 83

The EWPU is connected via the bit-serial data interface to the DME engine control unit. The engine control unit determines the necessary cooling capacity from the engine load, operating mode and the data from the temperature sensor and sends the corresponding instruction to the EWPU control unit.

The coolant in the system flows through the motor of the coolant pump, thus cooling both the motor as well as the electronic module.

The coolant also lubricates the bearings of the electric coolant pump.

Note. Particular care must be taken when performing servicing work to ensure that the pump does not run dry. When the pump is removed, it should be stored filled with coolant. The bearing points of the pump could seize if the pump were not filled with coolant. This could jeopardize subsequent start-up of the pump thus rendering the entire heat management system inoperative (the pump not starting up could cause serious engine damage). If the pump should ever run dry, the pump wheel should be turned by hand before finally connecting the coolant hoses. The system should then be immediately filled with coolant. Particular care must be taken during assembly to ensure that the connector is clean and dry and the connections are undamaged. Diagnosis should be performed only with the approved adapter cables. The information provided in the repair instructions must be observed.

Map Controlled Thermostat

The map controlled thermostat is located externally near the electric water pump. The thermostat is controlled by the ECM an operates in conjunction with the N52 Heat Management System.

Scheme 84

Oil-to Water Heat Exchanger (5 Series)

The oil-to-water heat exchanger is connected both to the oil circuit as well as to the water circuit of the engine. This arrangement ensures that the coolant quickly heats up the engine oil when the engine is cold and the coolant cools the engine oil when the engine is hot. Shortening the warm-up phase contributes to reducing the overall fuel consumption. The engine oil is cooled in order to extend its service life.

Scheme 85

Vacuum Pump

Just as with the N62 engine, the N52 has little vacuum available in the intake manifold to operate certain components.

The N52 engine uses a vacuum pump driven by the camshaft chain drive.

The vacuum pump supplies vacuum to the brake booster and the exhaust flap damper. The exhaust flap damper system no longer requires the vacuum storage reservoir used on past models. This is due to the use of the vacuum pump. The flap operation is no longer affected by variations in intake manifold vacuum.

Scheme 86

Alternator

The alternator is a 180 amp unit manufactured by Valeo. The alternator uses a one way clutch on the pulley. The alternator is capable of over-running when the battery is in a full state of charge. This prevents the inertia created by the rotating alternator from causing belt slippage on deceleration. Also, the service life of the belt tensioner is increased.

The alternator communicates with the ECM via the BSD line.

Note. the one way clutch is also used on Bosch alternators as well (N52).

Scheme 87

Magnesium - New Material In Engine Construction

Until now, magnesium has not been explored as an option for a material for engine construction. Recently, the realization is that the weight savings potential of aluminum has been exploited to its fullest. This is one of the primary factors in the decision to use magnesium as engine building material. The light weight and low density of magnesium make it an outstanding option to aluminum.

Magnesium, which has very good casting properties, makes it possible to manufacture large components with high surface quality. Despite the high accuracy of the cast parts, subsequent machining of function areas is, however, in the majority of cases unavoidable.

These excellent properties are, however, offset by several problematic aspects in the use of magnesium and its alloys. The former serious problem of corrosion has in the meantime been substantially alleviated by the development of distinctly more corrosion resistant alloys. The alloy used for the N52 is designated AJ62.

Nevertheless, a distinct corrosion risk still exists if the material-specific fundamentals described in the following are disregarded. Non-approved materials that come in contact with magnesium must not be installed.

This means only genuine BMW spare parts must be installed. The materials of the add-on parts must either be compatible with AJ62 or shielded by a seal/gasket from the magnesium casing. For these reasons, it is important to strictly adhere to the corresponding information provided in the repair instructions.

Electrochemical Properties

Metals are divided into noble (precious) and base metals. Gold, for example, is a noble metal and sodium a very base metal. The other metals are distributed over this division. When two metals such as iron and magnesium in contact with each other are placed in an electrically conductive liquid, e.g. a salt solution, the base metal will break down or dissolve and go into solution.

At the same time, electric current flows from the noble metal to the base metal. Under certain conditions, the base metal will deposit itself on the noble metal.

Scheme 88

Magnesium is a base metal. Its surface is therefore very susceptible to other materials. The magnesium alloy used in the N52, however, is completely different: By mixing other metals the negative properties of the pure metal are essentially cancelled out so that it is capable of satisfying the demands made of it.

An electrical voltage occurs between the two metals in the electrolyte. All metals can be classified based on this voltage. Iron assumes a mid-position in the voltage range while, on the other hand, aluminum and particularly magnesium are base. The greater the voltage difference between the metals, the faster electrochemical corrosion takes place.

The described laboratory situation can also easily occur on the engine when two metals make direct contact and the contact surface is moistened by splash water for instance. So-called contact corrosion takes place. A gap between the contact surfaces in which moisture can collect further promotes the occurrence of contact corrosion.

Contact corrosion can be avoided by keeping the contact surfaces dry or wetting them with electrically non-conductive engine oil. For this reason, all contact surfaces in the engine involving magnesium, aluminum and steel pose no problems.

Physical Properties of the Materials

Magnesium and aluminum have a virtually identical coefficient of expansion which, however, is almost double that of steel

1. Magnesium: 0.0026% per °C
2. Aluminum: 0.0023% per °C
3. Steel: 0.0011% per °C

The melting temperature of magnesium also barely differs from that of aluminum. On the other hand, the melting point of steel is considerably higher

1. Magnesium: 650 °C
2. Aluminum: 660 °C
3. Steel: 1,750 °C

The electrical conductivity of aluminum and magnesium is considerably better than that of steel. These materials are therefore particularly suitable for shielding electromagnetic interference (e.g. from the ignition spark).

No problems are encountered when connecting aluminum and magnesium as both materials have the same coefficient of expansion. However, no steel screw/bolts can be used on the N52 engine due to the fact that the coefficient of expansion of steel is only half as much. When the engine heats up, a steel bolt expands at only approximately half the rate of the crankcase. Conversely, there is the risk that a screw connection could become loose as the engine cools down. For this reason, aluminum bolts/screws are used at the decisive points.

VALVETRONIC II

With the introduction of the N52, the 6-cylinder, engine is now also equipped with the load control system based on the valve timing gear. The VALVETRONIC I system that was used on the 8-cylinder and 12-cylinder engines already achieved a substantial increase in efficiency.

Scheme 89

BMW has further developed this concept with the VALVETRONIC II.

The results of this further development are

1. Increased engine dynamics
2. Increased efficiency
3. Improved emission values

These results underscore BMW-specific standards. This engine that features the following optimizations further enhances the Ultimate Driving Machine.

1. The top engine speed has been increased to 7,000 RPM
2. The specific power output has been increased to 63.4 kW/l (85 hp/liter).
3. The specific engine torque is 100 N.m/l over a broad engine speed range
4. Distinctly increased valve acceleration values and friction-optimized transmission elements result in an even more responsive engine
5. CO2 emissions reduced
6. The world's most stringent exhaust emission regulations are complied with

Load Control

The illustration on the left below shows the conventional method with the slightly higher loss. The reduced loss can be clearly seen in the illustration on the right. The upper area represents the power gained from the combustion process in the petrol engine. The lower area illustrates the loss in this process.

Scheme 90

The loss area can be equated to the charge cycle, relating to the amount of energy that must be applied in order to expel the combusted exhaust gasses from the cylinder and then to draw the fresh gasses again into the cylinder. Apart from the full load setting, the intake of fresh gasses in a throttle valve controlled engine always takes place against the resistance offered by the throttle valve to the inflowing gasses. The throttle valve is virtually always fully opened during intake on the VALVETRONIC-controlled engine. The load is controlled by the closing timing of the valve.

Compared to the conventional engine where the load is controlled by the throttle valve, no vacuum occurs in the intake manifold. This means no energy is expended for the purpose of producing the vacuum. The improved efficiency is achieved by the lower power loss during the intake process.

A minimum vacuum in the intake system is required for the crankcase ventilation and evaporative (purge) systems. The throttle valve is slightly adjusted for this purpose.

Design/Function

The VALVETRONIC II consists of the fully variable valve lift control combined with the variable camshaft control (double VANOS). The valve lift is controlled only on the intake side while the camshaft is adjusted also on the exhaust side.

The throttle-free load control is implemented by variable valve lift of the intake valve, variable valve opening timing of the intake valve and variable camshaft spread of the intake and exhaust camshaft.

In terms of this load control principle, the VALVETRONIC II corresponds to the VALVETRONIC I introduced on the N62 engine.

System optimization includes modification of the valve gear kinematics, a modified actuator motor and the adapted spread range of the VANOS units.

The main differences are

1. The plain bearing on the intermediate lever to the eccentric shaft has been replaced by a roller bearing, thus reducing the friction in the valve timing gear.
2. Guidance of the intermediate lever is more precise. Only one spring is now required to guide and hold the intermediate lever.
3. The moved mass of the valve timing gear has been reduced by 13%.
4. The lift range of the intake valves has been improved. The maximum lift has been increased to 9.9 mm but more importantly the minimum lift has been further reduced to 0.18 mm.

The overall result is supported by further improvements in the intake manifold and exhaust dynamics.

Scheme 91

Scheme 92

The N52 is equipped with a compact, infinitely variable vane-type VANOS unit for the intake and the exhaust side. The VANOS units can be easily disassembled and assembled. They are designed as an integrated component in the chain drive and are mounted with a central bolt on the respective camshaft. When de-pressurized, a coil spring holds the VANOS unit in the base position.

The VANOS units are controlled by oil pressure from the 4/3 proportional solenoid valves. The valves are located in the front of the cylinder head and are controlled by the ECM. The ECM regulates the VANOS based on factors such as engine RPM, load and coolant temperature.

The operation of the VANOS units is similar to the N62 engine.

Scheme 93

Scheme 94

When servicing the VANOS units, the repair instructions must be followed precisely. The VANOS unit can no longer be dismantled and they must not be interchanged as they have different spread ranges for the intake camshaft and exhaust camshaft. Installing the wrong VANOS unit can cause considerable engine damage.

Differential Intake Air Control (DISA)

The torque developed in an engine greatly depends on the quality of the fresh gas charge during the induction stroke.

Oscillations are induced in the intake air mass during the induction strokes of the individual cylinders, i.e. by the downward movement of the pistons. These oscillations are in turn superimposed by oscillations that arise from pressure peaks as soon as the moved air mass of an intake cylinder comes up against the closing intake valves.

When two oscillations are superimposed, the resulting oscillation is known as the resonance oscillation or sympathetic vibration. The resonance can be an amplification or an attenuation of the initial oscillation or vibration.

Whether a pressure peak or a pressure hole is applied before the intake valves at the cylinder at the start of the induction stroke depends on the path the superimposed oscillations have covered in the intake area and on the engine speed, i.e. the gas speed.

The desire for high torque over a broad engine speed range necessitates an increasingly diverse range of air intake systems for internal combustion engines. The geometry and control of the intake manifold therefore have a considerable influence on the quality of the charge cycle. An intake manifold with a fixed length would provide an optimum cylinder charge only at a certain engine speed.

For this purpose, the M54 is equipped with a two-stage differentiated intake manifold (DISA) with a DISA valve (flap). The DISA valve is activated by means of a solenoid and an upstream vacuum accumulator.

The options of boosting torque over a defined engine speed window are limited. Since the N52 reaches a maximum engine speed of 7,000 RPM, the previous 2-stage DISA would produce a torque lag in the mid engine speed range. The N52 is equipped with a 3-stage DISA in order to provide high torque also in the medium engine speed range.

The result of these three stages is illustrated in the diagram below. The switched stages of the DISA achieve a high torque over the entire engine speed range. This principle is realized by means of an intake manifold changeover facility with two DISA actuators and an overflow pipe in the intake area.

In contrast to the previous system that was controlled with vacuum, the two DISA actuators are now operated by electric motors.

Scheme 95

The electric motors and DISA actuators form one unit. The two DISA actuators differ in size. The DISA actuator 2 is installed in the overflow pipe and the DISA actuator 1 is installed in the intake air manifold ahead of the resonating intake runner.

Scheme 96

Stage 1 - Idle/lower engine speed range

The DISA actuators 1 and 2 are closed in the idle speed and lower engine speed range. The air drawn in flows past the throttle valve into the resonance pipe. The air mass is split in the resonance pipe and is routed further via the collector runner and the intake resonating runners into the individual cylinders. In this way, a comparably large air mass is made available to three cylinders.

Stage 2 - Medium engine speed range

DISA actuator 2 is open in the medium engine speed range. In this example it is assumed that the intake valves of the first cylinder are just closing. The gas movement produces pressure peaks at the closing intake valves.

This is continued via the resonating and manifold runners at the next cylinder in the firing order thus improving fresh gas charge of the next cylinder to be charged.

Stage 3 - Upper engine speed range

Both DISA actuators are opened in the upper engine speed range. Also in this case it is assumed that the intake valves of the first cylinder are just closing. The pressure peaks ahead of the closing intake valves are also utilized in this case. The intake air mass is now routed via the resonance, overflow and manifold runners.

DISA Actuators

Together with the drive, the DISA valve (flap) forms one unit. The DISA valve is driven by an electric motor and a gear mechanism.

The electronic control is integrated in the DISA actuator. The DISA actuator is driven by a pulse width-modulated signal from the DME MSV70.

There are only two possible positions: The valves (flaps) can either be closed or opened, i.e. when activated, the motor moves the valve to the respective end position.

Electronic Oil Condition Monitoring

There is no dipstick including the guide tube on the N52 engine. This represents a convenience function for the customer while enabling more accurate recording of the engine oil level.

The engine oil level is measured by an oil condition sensor (OZS) and indicated in the central information display (CID). The engine oil temperature and the oil condition are also registered or calculated by the oil condition sensor. The signal from the oil condition sensor is evaluated in the ECM. The evaluated signal is then routed via the PT-CAN, SGM and the K-CAN to the instrument cluster and to the CID.

Registering the engine oil level in this way ensures the engine oil level in the engine does not reach critically low levels thus protecting the engine from the associated damage. By registering the oil condition, it is also possible to determine when the next engine oil change is due. Over filling the engine with oil can cause leaks - a corresponding warning is therefore given.

Scheme 97

Function Of The Oil Condition Sensor

The sensor consists of two cylindrical capacitors arranged one above the other. The oil condition is determined by the lower, smaller capacitor (6). Two metal tubes (2 + 3), arranged one in the other, serve as the capacitor electrodes. The dielectric is the engine oil (4) between the electrodes. The electrical property of the engine oil changes as the wear or ageing increases and the fuel additives break down.

The capacitance of the capacitor (oil condition sensor) changes in line with the change in the electrical material properties of the engine oil (dielectric). This means that this capacitance value is processed in the evaluation electronics (7) integrated in the sensor to form a digital signal.

The digital sensor signal is transferred to the DME as an indication of the status of the engine oil. This actual value is used in the DME to calculate the next oil change service due.

The engine oil level is determined in the upper part of the sensor (5). This part of the sensor is located at the same level as the oil in the oil pan. As the oil level drops (dielectric), the capacitance of the capacitor changes accordingly. The electronic circuitry in the sensor processes this capacitance value to form a digital signal and transfers the signal to the DME.

A platinum temperature sensor (9) is installed at the base of the oil condition sensor for the purpose of measuring the engine oil temperature.

The engine oil level, engine oil temperature and engine oil condition are registered continuously as long as voltage is applied at terminal 15. The oil condition sensor is powered via terminal 87.

Scheme 98

Faults/Evaluation

The electronic circuitry in the oil condition sensor features a self-diagnosis function. A corresponding error message is sent to the DME in the event of a fault in the oil condition sensor.

Electronic Oil Level Indicator

The oil level is measured in two stages

1. Static oil level measurement while the vehicle is stationary
2. Dynamic oil level measurement during vehicle operation

Static Oil Level Measurement At Engine OFF

This is only a reference measurement as the oil condition sensor (OZS) is flooded when the engine is turned off and can only detect the minimum oil level. The oil level is measured correctly only when the engine is running (see DYNAMIC OIL LEVEL MEASUREMENT DURING VEHICLE OPERATION ).

After switching on the ignition, the static oil level measurement provides the driver with the opportunity of checking whether there is sufficient engine oil for safely and reliably starting the engine.

1. It is important that the vehicle is parked horizontally otherwise the oil level measurement may be incorrect.
2. Select on-board computer function "Service" -> "Oil level".

If there is sufficient engine oil for safe and reliable engine start, a graphic appears in the CID in the form of an engine with a green oil sump.

Scheme 99

If the oil level is close to minimum, the graphic appears with a yellow oil sump and an oil dipstick that represents the low oil level in yellow.

A top-up request +1 liter additionally appears as a text message. The display will not change if less than 1 liter of oil is topped up. MAX is indicated only after topping up a quantity of 1 liter.

Scheme 100

If the oil level drops below minimum, the graphic appears with a red oil sump and an oil dipstick that represents the low oil level in red.

A top-up request +1 liter will additionally appear as a text message.

The display will not change if less than 1 liter of oil is topped up. MAX is indicated only after topping up a quantity of 1 liter.

Scheme 101

If the oil level is above maximum, the graphic appears with a yellow oil sump and an oil dipstick that represents the high oil level in yellow.

A text message is also displayed for the driver.

Scheme 102

Cooling System

On most engine systems to date, the delivery capacity of the coolant pump has been designed with the greatest possible cooling requirement of the engine. In the majority of cases, this large volume of coolant is not required.

As a result, the excess coolant will circulate through the thermostat ina small circuit. The new design of the cooling system utilizes an electric coolant pump which minimizes engine power losses and allows for increased fuel economy by a more efficient method of engine heat management.

Heat Management

The engine control unit controls the coolant pump according to requirements: low output in connection with low cooling requirements and low outside temperatures; high output in connection with high cooling requirements and high outside temperatures.

The coolant pump may also be completely switched off under certain circumstances, e.g. to allow the coolant to heat up rapidly during the warm-up phase. However, this only occurs when no heating is required and the outside temperature is within the permitted range.

Scheme 103

The coolant pump also operates differently than conventional pumps when controlling the engine temperature. To date, only the currently applied temperature could be controlled by the thermostat. The software in the engine control unit now features a calculation model that can take into account the development of the cylinder head temperature based on load.

In addition to the characteristic map control of the thermostat, the heat management system makes it possible to use various maps for the purpose of controlling the coolant pump. For instance, the engine control unit can adapt the engine temperature to match the current driving situation.

This means that four different temperature ranges can be implemented

1. 112°C ECO mode (economy)
2. 105°C Normal mode
3. 95°C High mode
4. 80°C High + mapped thermostat mode

The coolant control sets a higher cylinder head temperature (112°C) if the engine control unit determines ECO mode based on the current operating conditions.

The engine is operated with relatively low fuel consumption in this temperature range as the internal friction is reduced.

An increase in temperature therefore favors lower fuel consumption in the low load range. In HIGH and mapped thermostat mode, the driver wishes to utilize the optimum power development of the engine. The cylinder head temperature is therefore reduced to 80°C.

This results in improved volumetric efficiency, thus increasing the engine torque. The engine control unit can therefore set a certain operating mode adapted to the respective driving situation. Consequently, it is possible to influence fuel consumption and power output by means of the cooling system.

Intelligent Heat Management

This concept of intelligent heat management opens up potentials for engine functions and the vehicle operator. The previous section dealt with the various operating modes in connection with heat management. However, an electrically driven coolant pump makes available even further options. For instance, it is now possible to warm up the engine without the recirculating the coolant or to allow the pump to continue to operate after turning off the engine to facilitate heat dissipation.

The advantage offered by this type of pump are listed in the following table

FUEL PUMP ADVANTAGE

Cooling System Comparison (Belt Driven Vs. Electric Coolant Pump)

The belt driven coolant pump circulates the coolant as a function of engine speed. The circulated coolant can only be influenced by the mapped thermostat for temperature control purposes.

The system switches between the small and large circuit. In other words, between the circuit which flows through the radiator (large circuit) and the circuit which flows only between the engine block, coolant pump and thermostat.

This means that the cooling capacity is dependent upon engine speed.

Scheme 104

The advantages of the conventional cooling system are still utilized in the cooling system with the electric coolant pump. However this system also provides further options.

For instance, the cooling capacity of the system can now be adapted by means of freely variable volumetric coolant flow. It is possible to deactivate the coolant pump while the engine is warming up or to allow it to continue to operate when the engine has been turned off.

As illustrated in the following graphic, this results in the field in which the speed related to the cooling capacity can be controlled independently. This field is limited by the MAX and MIN speed of the coolant pump.

Scheme 105

Note. Due to the design of this coolant pump, a special filling and bleeding procedure is implemented for service. Refer to WORKSHOP HINTS for more information.

Electronically Controlled Coolant Pump

Particular care must be taken when performing servicing work to ensure that the pump does not run dry. When the pump is removed, it should be stored filled with coolant. The bearing points of the pump could seize if the pump were not filled with coolant.

This could jeopardize subsequent start-up of the pump thus rendering the entire heat management system inoperative (the pump not starting up could cause serious engine damage). If the pump should ever run dry, the pump wheel should be turned by hand before finally connecting the coolant hoses. The system should then be immediately filled with coolant.

Particular care must be taken during assembly to ensure that the connector is clean and dry and the connections are undamaged.

Diagnosis should be performed only with the approved adapter cables. The information provided in the repair instructions must be observed. Due to this coolant pump, a special filling and bleeding procedure must be implemented for servicing

1. Fill system with coolant via the expansion tank (AGB). Top up coolant level to lower edge of expansion tank.
2. Close expansion tank.
3. Switch on ignition.
4. Set heating to maximum (temperature), switch on blower (lowest stage).
5. Press accelerator pedal module to floor for at least 10 seconds. The engine must NOT be started.
6. Bleeding via EWP takes about 12 minutes. Then check coolant level in expansion tank, top up to MAX marking if necessary.
7. Check cooling circuit and drain plugs for leaks.
8. If the procedure needs to be repeated several times, allow DME to completely de-energize (remove ignition key for app.. 3 minutes) and then repeat procedure as from item 3.

Note. Connect battery charger if battery charge level is low.

Thread Repair

When repairing threads on magnesium or aluminum components, the repair instructions recommend the use of HelicoilT repair kits. These kits are available with aluminum repair thread inserts.

Engine Repairs

Any engine repair which involves the replacement/removal of the cylinder head requires special attention. The bolt holes must be blown dry immediately after cylinder head removal. It is not acceptable to wait until the engine is ready for reassembly. Leaving the coolant standing in the head bolt holes until reassembly will increase the possibility of contact corrosion. Engine coolant should not come into prolonged contact with magnesium engine components.

Note. Be sure to wear approved eye protection when using compressed air to dry the bolt holes.

Scheme 106

Machining (metal Cutting) Magnesium

The jobs that are most frequently carried out in connection with this material as part of servicing applications are considered to be non-critical. The small amount of metal chips that occurs, e.g. when recutting threads, requires no special extraction systems or special facilities.

If, on the other hand, extensive machining is to be performed on magnesium crankcases, particular care must be taken to ensure that no explosive hydrogen can collect in the collection containers for metal chips and moisture can escape from the container.

Moisture in this context only refers to water or compounds containing water. The following information must be observed for metal removing machining processes

Although with regard to metal removal or machining properties magnesium alloys offer very good prerequisites for dry machining, today wet machining processes are state-of the-art, involving the use of either cutting oil or emulsion. The greatest hazard potential in metal removal machining processes is posed by the metal chips (swarf). Particularly wet or moist metal chips are hazardous while, on the other hand, metal chips moistened in oil will not ignite easily.

Magnesium and water can react to form magnesium hydroxide and hydrogen. For this reason, there is a risk of a hydrogen explosion in machining processes involving emulsion if the hydrogen that is constantly formed can collect and reach a critical concentration. For this reason, it is important to ensure that the moisture in the collection container can escape or drain off.

In addition, metal chips and swarf must be conveyed at a very fast rate out of the emulsion otherwise a saponification or hardening process may occur making the emulsion unusable.

The range of cutting materials known from aluminum machining processes can also be used for magnesium machining, i.e. high speed steel, hard alloy or carbide and polycrystalline diamond (PCD).

Special Measures For Grinding

The preconditions for wet machining in grinding processes are to be considered from different aspects than the standard metal cutting machining processes. This is due to the fact that fine metal chips (grinding dust) are produced in grinding processes. As from a certain mixing ratio with air, this grinding dust can combust explosively following possible ignition from spark created from grinding or welding work. If wet grinding is not possible or too inconvenient, the grinding dust produced must be extracted and precipitated with water in a separator.

Important Precondition

Any work on magnesium that forms dust must not be performed without a suitable extraction facility.

The specific surface of the respective product, i.e. the surface-to-volume ratio represents an important criterion for the hazard potential of the magnesium. Solid components pose no problems from a safety point of view. Even when subjected to high temperatures for all intents and purposes they cannot combust.

On the other hand, chips, particles and powder are considerably more reactive. The critical temperature at which dry, fine metal chips can ignite is at 450 - 500°C. Cutting tools that have improper edge geometries or blunt edges can give rise to such temperature levels during dry machining processes. Sparks caused by tool collisions or when machining steel represents a further source of danger. If, despite all precautionary measures, a magnesium fire occurs, on no account must water or extinguishing agents containing water be used (release of hydrogen, detonating gas explosion!). ABS powder extinguisher, carbon dioxide and nitrogen are also unsuitable as extinguishing agents.

Keep suitable metal fire extinguisher ready at hand! The proper classification for a fire extinguisher capable of handling magnesium fire is Class D. DO NOT use class A, B or C fire extinguishers in magnesium fires. This could create a more hazardous situation.