Proton X50 1.5L TGDi – Packaging Refinement and Power In A Small 3-Cylinder Engine

The Proton X50 seems to dominate the automotive news cycle with everything from the tentative prices to the car’s suite of active safety systems taking centre stage of the discussion posts on social media.

Another topic of hot discussion is the X50’s 1.5-litre TGDi turbocharged engine. After all, this is the most advanced powerplant to ever feature in a Proton, and the most power-dense, given it produces 177 PS in the case of the 1.5 TGDi from just 1.5-litres of displacement and 3-cylinders.

Needless to say, there’s a whole lot of tech that goes into creating such an engine, and ensuring that it remains reliable for the lifetime of the vehicle.

The powerplant is co-developed by Volvo and Geely, the former having ample experience with downsized turbocharging, through its Drive-E engine programs. Another testament of its reliability is the 1.9-million km of real-world testing that has been done by its developers.

In addition, given the relative scale of Geely Automotive’s global business, the new 1.5-litre turbo engine has already seen service in 550 thousand cars worldwide – so we can be assured it works.

Here’s a quick snapshot of the key specs between the two engine variants fitted in the X50:

You’ll note that besides the difference in power figures, the lower powered ‘1.5L T’ variant uses port injection versus the ‘1.5L TGDi’ which uses direct-injection technology. Geely achieved this by having two different engine head assemblies to offer two different engines at varying power levels. But what is the difference between the two?

Port Injection

Port injection is the more traditional design, where fuel and air are injected into the intake port and premixed before it is sucked into the engine for combustion. The benefits of a port injection system are its reliability, lower costs of manufacturing and reduced carbon build-up around the intake valves. However, it isn’t as efficient as direct-injected engines, produces less power (in most cases), and offers less control over the amount of fuel that enters the combustion chamber.

Direct Injection

Direct injection on the other uses high-pressure injectors to inject fuel directly into the combustion chambers. Hence air and fuel enter the engine from different points. Direct injection is able to create more power, offer a more complete combustion process, and gives manufacturers better control over the amount of fuel that enters the engine – aiding fuel economy. The downsides though are that they’re more expensive, and direct-injected engines tend to have higher carbon buildup around the intake valves. 

With that said, it is an intelligent way for Proton to offer two different engine variants to cater better to customers with varying requirements from their X50's.

But, why they didn’t they just go with a 4-cylinder engine?

Another topic of frequent discussion is the fact that the 1.5-litre engine is a 3-cylinder engine. Now there is nothing new about 3-cylinder engines, car manufacturers have been using them since the 80s, and bike manufacturers, even longer – most people will note that the Perodua Kancil and Kelisa were both powered by 3-cylinder engines, which are still running reliably to this day. Heck even the BMW i8 supercar is powered by a 3-cylinder turbocharged engine.

However, the more informed might note that 3-cylinder engines are not the most refined – in that they produce more vibration especially at idle and low-revs. And as you might surmise, this isn’t good to have in an SUV like the X50.

Why do 3-cylinder engines vibrate so much anyway?

Well, it’s down to their very design. Without geeking out too much, in 4- and 6-cylinder engines, while two pistons travel upwards (typically the first and last) within the engine, the other 2- or 4- pistons respectively are typically travelling downwards within the engine. What this does is almost even out the counteracting forces (upwards/downwards and rotational) within the engine allowing the engine to remain steady within its axis.

In a 3-cylinder engine, which is essentially a 6-cylinder engine cut in half, while the first piston reaches the top of the combustion chamber (TDC) the other two pistons can be on their way down or up (depending on the manufacturer) within the engine. While this does just enough to balance out the up and down forces, it doesn’t balance out the rotational forces caused by the engine’s components, thus a three-cylinder engine always wants to rotate and fall over itself.

In the Proton X50, there are a number of innovations that have been used to mitigate these refinement issues and offer great performance in a small package.  

Here a few highlights:

• High stiffness engine block and head: Starting with a good base – the X50’s engine uses a high-stiffness engine block and head design, this pays dividends in having an engine that will last years of service, resist torsional forces across the engine and offer reduced engine vibration.
• Good balance: In addition to an engine balancer shaft, the X50’s engine also employs a Torsional Vibration Damper (TVD) to absorb the aforementioned twisting forces of the engine during operation. Anti-vibration injectors are also fitted to reduce engine vibration and reduce the characteristic ‘ticking’ noise of direct-injected engines.

• A smooth gearshift: The X50 dual-clutch automatic transmission interfaces with a Dual Mass Flywheel (DMF) equipped with a Centrifugal Pendulum Absorber (CPA), as the name suggests, the entire system works to harmonise the forces of the engine crankshaft before power is transmitted to the transmission.  A downside of a DMF setup is a slight delay in gearshift response, however, it pays dividends with silky smooth up- and downshifts, and improved refinement during engine startup.
• Silent engine accessories: A large quantity of the noise generated in a car doesn’t even come from the engine itself, rather the engine accessories such as the alternator, and various system pumps. To mitigate this, the X50’s engine uses a silent high-pressure fuel pump and silent electrical alternator equipped with an Overrun Alternator Decoupler (OAD) pulley system. Unlike traditional alternators, OAD pulleys are equipped with a one-way clutch, which allows the alternator to momentarily decouple from the engine and ‘freewheel’ when engine speeds drop or during initial startup. OADs are commonly found on modern diesel engines because these engines exhibit more torsional forces during operation. Not only are OAD’s more efficient because they can keep spinning even when the engine speeds are dropping, but they also isolate the alternator and engine from ‘knee-jerk’ vibrations caused by sudden changes in engine speeds.  

In the development of the X50 engine, special attention has been paid to improve efficiency and increase power at every phase of the engine’s operation. And as they say, the proof is in the pudding, with the claimed 0-100 km/h sprint covered in 7.9 seconds, and segment beating performance as proven by the raft of real-world testing exercises members of the media were treated to recently.

Are we ready to put to bed this three-cylinder being lousy engine debate or at least wait till customer testimonials tell us otherwise?