The all new F48 BMW X1 is arriving in dealership with an all new engine. The BMW B46 inline 4 cylinder engine replaces the N20 4 cylinder found in the previous X1 as well as much of the BMW lineup. The N20 was a great engine but was not universally loved, complaints of diesel like vibrations and engine racket were the prime offenses to American based BMW owners use to the silky smooth 6 cylinder engines.
In a never ending quest for more performance and efficiency the N20 is being retired and the B46 takes it's place. The B46 is part of the new BMW B family of engines, we dive into what makes this 2.0 liter TwinPower inline 4 special.
The new engine generation is mainly characterized by lower fuel consumption and fewer exhaust emissions (ULEV II). To achieve low fuel consumption, a map-controlled oil pump, characteristic map thermostat and injection system with direct-rail and electric arc wire-sprayed cylinder barrels, among others, are used. All engines also receive an automatic engine start-stop function and intelligent alternator control as a further EfficientDynamics measure.
Due to the similarities between the B38 3 cylinder engine and B46 4 cylinder engine some images shown are of the 3-cylinder engine.
TwinPower Turbo Technologies
TwinPower Turbo is a commonly misunderstood term, often being confused with twin turbo, especially as it was introduced around the time BMW discontinued the twin turbo N54 engine. TwinPower does not mean twin turbo, in BMW nomenclature it is the umbrella term that means the following technologies are used:
- Direct injection
Crankcase / Engine Block Design
Characteristics of crankcase:
- Heat-treated all aluminium crankcase made from AlSiMgCu 0.5
- Electric arc wire-sprayed cylinder barrels
- Weight-optimized main bearing cap of crankshaft with embossing teeth
- Closed-deck design
- Deep Skirt
- Oil ducts for the use of a map-controlled oil pump
- Support of counterbalance shaft(s) in cored tunnel
With the closed-deck design, the coolant ducts around the cylinder are closed from above and provided with coolant bore holes. This design is mainly reserved for BMW diesel engines. Due to the high combustion pressures in the diesel engine, a greater degree of rigidity is required in order that the forces can be safely absorbed. As the gasoline engine uses the same unfinished cast part as the diesel engine, it also benefits from this robust design.
Cooling concept of cylinder head
The B46 engine has a cylinder head with cross-flow cooling. In the case of cross-flow cooling, the coolant flows from the hot exhaust side to the cooler intake side. This has the advantage of providing uniform heat distribution in the overall cylinder head. Loss of pressure in the cooling circuit is also prevented.
Cylinder head gasket
In order to satisfy the high demands of the B46 engine, a triple-layer spring steel gasket is used as the cylinder head gasket.
Electric arc wire spraying
The cylinder walls of the B46 engine are coated with electric arc wire spray (LDS). In this procedure a conductive metal wire is heated until it melts. The melt is then sprayed onto the cylinder barrels at high pressure. This layer of ferrous material is roughly 0.3 mm thick, extremely wear-resistant and facilitates an efficient transfer of heat from the combustion chambers to the crankcase, and from there to the coolant ducts
Counterbalance Shafts of B46 Engine
Due to the operating principle of the piston engine, undesired oscillations occur at the engine housing when driving, which can be transmitted to the vehicle interior. To counteract this negative effect, BMW has already been installing so-called counterbalance shafts in more recent engine generations. Up till now, their role was to cancel out free inertia forces and therefore increase ride comfort. In addition to the inertia forces, so-called 'free moments of inertia' also exist, which can also adversely effect ride comfort. Depending on the engine design and number of cylinders, varying degrees of free inertia forces and free moments of inertia occur.
The B46 engine has two counterbalance shafts which rotate at twice the speed of the crankshaft. The gears of the counterbalance shafts have 48 teeth. The gear of the crankshaft has 96 teeth.
Timing Chain, VANOS and Valvetronic Components
On of the bigger changes on the B46 is the location of the cam shaft timing chain drive. Typically found on the front of the engine, the B family of engines has the chain drive on the transmission side. The inertia of the transmission at this end of the engine significantly reduces the rotary oscillations and also therefore the loads acting on the chain drive.
Note the two different chains that make up the cam drive chain. In the diesel engines, the high pressure fuel pump is driven by this intermediary gear setup. On the gasoline engines the high pressure fuel pump is located on top of the engine so a simple gear transfer sprocket is used.
To facilitate VANOS repairs the VANOS solenoid valve actuators on the B46 are not mounted to the cylinder head, but in the cylinder head cover. Presumably the cylinder head cover (valve cover) can be removed to change the solenoid so the entire engine does not need to be dropped. Additionally the mounting of the VANOS solenoid valve actuators has also changed. They are no longer bolted on, but are attached to the cylinder head cover using a bayonet fitting and retaining clips.
With older VANOS systems, such as that used in the N55 engine, the VANOS units were controlled by separate VANOS solenoid valves integrated into oil ducts in the cylinder head. The oil ducts in the cylinder head are reduced and the adjustment speed is increased by using a VANOS solenoid valve unit and a mechanical VANOS central valve, which is located inside the VANOS unit.
The valve overlap times have a significant impact on the characteristics of the engine. An engine with smaller valve overlap therefore tends to have a high maximum torque at low engine speeds but the maximum power which can be achieved at high engine speeds is low. The maximum power achieved with a large valve overlap on the other hand is higher, but this is at the expense of the torque at low engine speeds. The VANOS provides a solution. It makes a high torque possible in the low and medium engine speed range and a high maximum power in the higher engine speed ranges. A further benefit of the VANOS is the option of internal EGR. This reduces the emission of harmful nitrogen oxides NOx, particularly in the partial load range
The Valvetronic has been further developed for use in the new Bx8 engines. A distinguishing feature of the VVT4 is the Valvetronic servomotor is located outside of the cylinder head. Valvetronic comprises a fully-variable valve lift control and a double VANOS. It operates according to the principle of throttle-free load control. With this system, a throttle valve is only used to stabilize the engine operation at critical operating points and to ensure a slight vacuum for the engine ventilation. A very small vacuum can be produced in the intake pipe by slightly tilting the throttle valve, which allows treated blow-by gases to be introduced into the intake port during naturally-aspirated engine operation.
Due to the construction space, the oil filter housing is suspended in the transverse mounting. The inspection is carried out from the bottom of the vehicle. Using an oil drain plug the Service employee can drain the engine oil from the oil filter module before opening the oil filter cover.
In order to protect the thermally loaded engine components, the engine oil and the transmission oil from overheating, they are cooled using coolant. A mechanical coolant pump circulates the coolant in the cooling circuit. The heat quantities introduced to the coolant are emitted to the ambient air again using a radiator. An electric fan assists the radiator output. The coolant in the B46 engine is mainly circulated via a mechanical coolant pump. Several engines are also equipped with an electrical overrun pump which maintains a trickle of coolant to the bearing seat cooling system of the exhaust turbocharger.
Special features of the B46 cooling system
- Coolant-cooled exhaust turbocharger
- Mechanical coolant pump
- And electric coolant pump
- Characteristic map thermostat
Due to the twin-scroll technology, the B46 engines are equipped with a steel manifold. 'Twin-scroll' means that the exhaust flows are routed via two separate channels to the exhaust turbocharger. The heat produced is absorbed by the coolant which is supplied via a coolant connection on the exhaust turbocharger. When the motor is not running, post-cooling of the exhaust turbocharger is possible with the assistance of an electric coolant pump. This prevents a build-up of heat in the area of the exhaust turbocharger.
Water pump / coolant pump
The coolant pump is a single unit also containing the thermostat. The coolant pump housing is made from the aluminium alloy ALSi9Cu3, the impeller and the thermostat cover are made of plastic. The DME controls the cooling circuit via a map-controlled thermostat.
The coolant is not subject to a change interval, the factory coolant is designed for the entire service life of the engine. Work which requires an opening of the cooling circuit, coolant must be replaced as needed. The cooling system must only be filled with BMW-approved coolant. If the wrong coolant is used, damage to the coolant pumps, coolant hoses, radiators and cylinder head gasket may occur.
The exhaust turbocharger of the B46 engine is a twin-scroll exhaust turbocharger. To facilitate a fast and direct response, the exhaust flows from cylinders 1 and 4, and 2 and 3 are merged and routed to the compressor via two separate channels. This principle is referred to as pulse turbocharging. The exhaust manifold and exhaust turbocharger housing have been designed as one common cast part and cannot be replaced individually. The charging pressure in B46 engines is controlled via an electrically adjustable wastegate valve.
A blow-off valve is not used in current models. Pressure peaks, caused by sudden load shedding due to the inertia of the turbine of the exhaust turbocharger, can be avoided by careful tuning of the Digital Motor Electronics software. With foresighted charging pressure control, pressure peaks can be predicted and reduced by quick adjustment of the electrically-adjustable wastegate valve. Assisted by a delayed load control of the Valvetronic (in the minimum lift direction) or the throttle valve (in the closed direction), the remaining charge air which is produced can be routed to the exhaust emission system via the engine. This form of control thus prevents the exhaust turbocharger shaft from being exposed to excessive torsional stress due to high pressure peaks.
Apparently BMW is fine with a little wastegate rattle at startup. They state if the wastegate valve is opened when cold, pulsation of the exhaust gas may cause vibrations in the wastegate valve, which are perceived as noise. This is not due to a defective component, and is normal running noise. This noise becomes less audible as the temperature of the component increases.
The main high pressure fuel pump (HPFP) is a single-piston high pressure pump by Bosch, similar in concept to the unit on the N20/N55. At this point BMW seems to have resolved all HPFP failures so there should be no concerns about that. The high pressure pump is driven by a triple cam which is attached to the exhaust camshaft. Fuel low pressure is supplied to the high pressure pump via the fuel feed from the in tank electric fuel pump.
The direct rail represents a departure from the familiar systems used up till now. With this system, the high pressure lines have been omitted and the injectors are attached to the rail directly.
Directly connecting the solenoid valve injectors to the rail has the following advantages:
- Less volume needs to be available for high-pressure injection
- Fewer interfaces and therefore less problematic with respect to leaks
- Short cycle times during production due to compact design