BMW 4 cylinder: 6 cylinder smoothness, 5 litre eco

BMW’s latest 5 Series marks the introduction of 4-cylinder engines into the F10 platform. Until now, it’s been all 6-cylinders or V8s.

Powertrain manager Jan Kretschmer revealed what’s been keeping them busy at the launch of the 520d variant, on the debut of this September’s F11 Touring.

My, they’ve been well-occupied, it seems. ‘4 cylinder engines are always a bigger challenge for our engineers,’ he explained; even ones like this, with counter-rotating balancer shafts.

They have, as you know, a different (‘and higher’) level of NVH – noise, vibration, harshness. ‘You have to consider this before you even start with the development and installation.

‘Luckily, our Body-In-White department is able to conduct a lot of simulation work (big investment in computer technology over the past half-decade facilitates this). This means we can predefine possible weaknesses where extra stiffening may help – or, actually, stiff areas where some weakness may be beneficial!

‘They start this 5 years before the vehicle hits the road.’

Concurrently, his powertrain team will be working to provide the smoothest possible engine for eventual implementation. With the 184hp (135kW) 2.0-litre diesel, Kretschmer explained the process was one of evolution. ‘We were tasked with further refining an already high-level engine, rather than reinventing it.’

Two key development areas were prioritised here:

•    Engine Mountings: ‘These must be isolated. We fit electronically driven semi-hydraulic engine mounts, with 2 characteristics. At idle and low rpm, they are ‘weaker’, to absorb low-level vibration. When driving, there are fewer engine vibrations, so we stiffen them to improve handling.’

•    Fluctuating Torque: ‘This is harder to isolate on 4-cylinder engines than 6-cylinders. On manual models, we fit a pendulum-type flywheel which minimises these oscillations and reduces the booming rear axle effect. The 8-speed auto has a new torque converter with a twin-damper system that provides isolation.’

Minimisation of fluctuating torque is the aspect he is most proud of, as it is extremely significant. ‘We have reduced it going into the transmission by 60 percent.

‘This helps us drive the car more at lower rpm, with longer gear ratios on the manual and new gearshift profiles on the auto. With the new 8-speed, this alone has led to a 9 percent improvement in fuel efficiency!’

in doing so, Kretschmer has created a ‘5-litre’ engine for the 5 Series (that’s 5 litres per 100km – 56.5mpg). Don’t think his efforts have gone unnoticed by the Board, either.

‘This is the volume model for the 5 Series, so the pressure has been on us to further improve.’ Good job, really, that he’s done just that.

+ Do you think BMW makes the best 4-cylinder engines on the market?
+ Would you consider a 520d?
+ If not, what are the main reasons stopping you chosing diesel?