The Mazda6 Saloon and Tourer are available with Mazda’s pioneering and award-winning SKYACTIV-D turbo diesel engine, in 150ps and 175ps guise, and SKYACTIV-G direct injection petrol engine, in 145ps and 165ps trim. These engines are joined by the SKYACTIV-MT manual and SKYACTIV-Drive automatic transmissions, both of which feature six forward ratios.
When developing the Mazda6, the project engineers eschewed the current trend of exploiting tried and tested technology such as forced induction and downsizing engines and opted instead for a fundamental rethink that would allow them to optimise every aspect of these innovative engines. The result is a combination of exceptionally high levels of economy, refinement and flexibility without compromising performance.
The exceptional economy and cleanliness of these engines is further enhanced by Mazda’s ingenious i-ELOOP technology. I-ELOOP, short for intelligent energy loop, is Mazda’s proprietary capacitor-based brake energy regeneration system. This uses an electric double-layer capacitor rather than a dedicated battery to quickly capture and temporarily store electricity. Once fully charged – which takes less than 10 seconds under deceleration – the capacitor can power the Mazda6’s electrical systems such as the climate control and audio systems for up to a minute.
SKYACTIV-D – Mazda’s diesel engine
2016 updates include Transient Control and Mazda’s Natural Sound Smoother technology.
When developing the SKYACTIV-D engine, Mazda’s engineers focussed on radically optimising the engine’s compression ratio to achieve superior air-fuel mixture levels and more uniform combustion, which in turn resulted in lower levels of nitrous oxides and a higher expansion ratio for better economy.
As a result, the advanced twin-turbo SKYACTIV-D diesel engine features an exceptionally low 14:1 compression ratio that not only sets new standards of efficiency and performance but also complies with all global emissions regulations.
When the compression ratio is lowered, compression temperature and pressure at top dead centre decrease. Consequently, ignition takes longer even when fuel is injected near top dead centre, enabling better mixture of air and fuel. This alleviates the formation of NOx and soot because the combustion becomes more uniform without localised high-temperature areas and oxygen insufficiencies.
Due to this lower compression ratio, the maximum in-cylinder combustion pressure for SKYACTIV-D is markedly lower than Mazda’s previous-generation 2.2-litre MZR-CD diesel engine. In turn, this lowered the weight of the engine by a full 10 per cent compared to the previous diesel engine, and has reduced the mechanical friction of the engine by a further 20 per cent.
The SKYACTIV-D’s cylinder block is made from aluminium, rather than cast iron, saving a full 25kg over Mazda’s outgoing large capacity diesel engine. Thinner cylinder walls and an integrated exhaust manifold have dropped the weight of the cylinder head by 3kg, while the crankshaft and pistons are 25 per cent lighter than those in Mazda’s previous-generation 2.2-litre MZR-CD diesel engine, significantly lowering the engine’s reciprocating masses.
One of the key challenges of a low-compression diesel engine is that it results in a compression-ignition temperature that is too low for reliable cold starts and efficient cold-temperature operation. To combat this, Mazda’s powertrain engineers opted for the following technical innovations:
In addition, two key updates added to the 2.2-litre SKYACTIV-D in 2016 are designed increase responsiveness and reduce engine noise: Transient Control and Mazda’s Natural Sound Smoother Technology (NSS).
By reducing turbo lag and boosting torque, Transient Control provides a more positive throttle response, ensuring that the Mazda6’s diesel engine reacts better than ever to the driver's intentions, while refinement has been enhanced thanks to the introduction of Mazda’s Natural Sound Smoother (NSS) technology.
Designed to cleverly reduce diesel knock noise during starting and low-speed acceleration, NSS suppresses resonance from the piston and connecting rod by using a dynamic damper inside the piston pin to suppress diesel knock, while three critical frequency bands in which engine components typically vibrate most loudly are supressed by Mazda’s Natural Sound Frequency Control. It deactivates the engine timing in 100 microsecond waves thereby causing the pressure waves caused before, after and during combustion to cancel each other out, with the end result being less combustion induced vibration. Working in unison these two technologies have reduced diesel engine resonance in the cabin of the Mazda6.
SKYACTIV-G – Mazda’s new generation petrol engine
With up to 80 per cent of the energy contained in fuel lost within a vehicle’s powertrain, the engineers on the Mazda6 development team adopted a radical high-compression approach to boosting the outright efficiency of the direct injection SKYACTIV-G petrol engine.
The result of this clean-sheet approach to the SKYACTIV-G’s development was an incredibly high compression ratio of 14:1 – that delivers a 15 per cent increase in fuel efficiency and an equally impressive 15 per cent hike in torque across the entire rev-range, compared to Mazda’s previous 2.0-litre petrol engine.
Although increasing the compression ratio considerably improves thermal efficiency, it also increases the chances of knocking – unwanted premature ignition – as the temperature at top dead centre also rises.
In the SKYACTIV-G petrol engine, the top dead centre temperature is lowered by halving the level of residual exhaust gas from eight to four per cent, and introducing an extended and looped four-two-one exhaust system that prevents exhaust gas leaving one cylinder being forced into the combustion chamber of another.
In addition, the piston heads were fitted with cavities to prevent the initial combustion flame from hitting the piston and interfering with the flame’s growth, and low-temperature oxidation – an exothermic reaction in which the bonds within the molecules of petrol break and produce energy – was exploited to further boost torque across the rev range.
Particular attention was also paid to the reduction of inertial weight and mechanical friction, with the following results –
i-ELOOP and i-stop – Economy-enhancing technology for all
The exceptional economy of cleanliness of these engines is further enhanced by Mazda’s ingenious i-ELOOP technology – standard on both 150ps and 175ps diesels models and 165ps petrol models. This proprietary capacitor-based brake energy regeneration system employs an electric double-layer capacitor rather than a dedicated battery to quickly capture and temporarily store electricity.
Opting for an Electric Double-Layer Capacitor (EDLC) rather than a dedicated battery allowed Mazda’s SKYACTIV engineers to neatly sidestep the limited charging and power storage potential of the lead-acid batteries. When fully charged – which can take as little as 10 seconds under deceleration – the capacitor can store enough energy to power the Mazda6’s electronic components for up to a minute.
After detailed studies of the typical deceleration and acceleration cycle, Mazda’s engineers determined that a typical deceleration phase lasts only about 10 seconds. Hence the decision to use a capacitor rather than a lead-acid battery. The system uses a 12V-25V variable voltage alternator to efficiently generate power from the moment the accelerator is released, fully charging the electric double-layer capacitor in as little as 7-10 seconds – well within a single deceleration cycle.
After recharging, the DC/DC converter steps down the voltage of the electricity in the EDLC to 12V to power components like the climate control and audio systems. Any surplus electricity goes to the battery. A full capacitor charge is enough to run the vehicle’s electrical systems for a minute.
i-ELOOP is therefore the perfect companion for i-stop, since there is no need to revert to battery power even when Mazda’s idle-stop system has shut down the engine. Together the two systems can boost economy by up to 10 per cent, depending on driving conditions, delivering up to 68.9mpg on the combined economy cycle and tax-friendly CO2 emissions from just 107g/km.
Developed entirely in-house, Mazda’s innovative i-stop technology made its debut in 2009 on petrol versions of the Mazda3 and Mazda5. Now significantly enhanced for its application in Mazda’s current generation of SKYACTIV-Engines, i-stop is still the only idle-stop system that uses combustion energy for restarting the engine, and only requires an electric-powered starter motor to provide a small degree of momentum during the initial restart phase.
In addition to delivering meaningful fuel savings, this restart system enables incredibly quick and smooth restarts that put it competitively above rival systems. The Mazda6 with SKYACTIV-G petrol power features a restart time within 0.35 seconds, while the SKYACTIV-D diesel is just behind at 0.40 seconds.
SKYACTIV-Drive and SKYACTIV-MT – Mazda’s new generation of automatic and manual transmissions
To exploit the full potential of the superb SKYACTIV-D and SKYACTIV-G powerplants in the Mazda6, Mazda’s engineers developed two dynamic new six-speed gearboxes – the SKYACTIV-MT manual and the SKYACTIV-Drive automatic transmission.
Like the engines they are allied to, these two transmissions are the direct result of convention-defying thinking – rather than develop a range of transmissions to meet the different requirements of its global markets, Mazda’s drivetrain engineers took the bold decision to develop just two new six-speed transmissions to effectively deliver what each market demanded.
SKYACTIV-Drive automatic transmission
The SKYACTIV-Drive six-speed lock-up automatic transmission – available on the 145ps SKYACTIV-G petrol and 150ps and 175ps versions of the SKYACTIV-D diesel engine – brings together the best attributes of conventional step automatic transmissions, continuously variable transmissions and dual clutch transmissions in one compact and lightweight package.
The key requirements for the SKYACTIV-Drive automatic transmission were excellent fuel efficiency, a direct and engaging feel, smooth and quick shifts and prompt responses. This resulted in the development of a torque converter with a lock-up clutch, which locks the torque converter’s turbine to the impeller to improve fuel economy and enhance the driver’s feeling of connectedness.
The lock-up range was fully maximised, a move enabled by a significant reduction in noise, vibration and harshness characteristics of the SKYACTIV-D engine, SKYACTIV-Chassis and SKYACTIV-Body. Lock-up performance was also enhanced by employing a multiple-disc clutch with optimised oil flow for heightened cooling performance.
The SKYACTIV-Drive automatic transmission also features an advanced hydraulic mechatronic control module. By locating this control module inside the transmission, rather than outside the gearbox, the accuracy of oil pressure monitoring has been significantly improved.
To boost shift quality and response, the SKYACTIV-Drive also features a direct linear solenoid system that accurately controls hydraulic pressure for exceptional responsiveness. The result is a smooth and highly efficient gearbox that delivers up to seven percent better economy along with a direct feel and quick shift pattern – qualities aimed squarely at the enthusiastic driver.
SKYACTIV-MT manual transmission
The SKYACTIV-MT is a lightweight six-speed manual transmission that is available on all four petrol and diesel engine options. It has been designed to deliver crisp wrist-flick gear changes, like those enjoyed by Mazda MX-5 drivers. The key element to achieving this quick and decisive gearshift action is a larger gear lever ratio, but this in turn effectively reduces the internal stroke.
To counter this, Mazda’s transmission engineers developed a small module spline that allows for exceptionally precise synchroniser and torque transmissions even with the desired 45mm short gear lever stroke. Shift effort gradually falls away during the gearshift action, resulting in a reassuring resistance during the initial movement of the gear lever, followed by a lighter touch to create the tangible feeling of the gears meshing cleanly in to place.
Other features of the Mazda6’s SKYACTIV-MT transmission include a down type system with first gear located on top of the change system, a lock ball type synchroniser for smoother shifts and a shift load canceller. A slide ball bearing reduces unwanted resistance during rotational and sliding movements and a common second and third gear reduces the inertia of the non-synchronised side by 37 per cent over Mazda’s previous generation manual transmission.
In pursuit of the ultimate shift quality, Mazda’s engineers developed 30 different configurations of a triple-shafted gear train with a common gear for second and third before final selection of a geartrain that delivered low-weight construction, a light shift effort, high efficiency and a wide gear ratio.
By reviewing the function of each component, common first and reverse gears were also adopted, further reducing weight, enabling the length of the secondary shaft to be reduced by a full 20 per cent and doing away with the need for the reverse idle shaft.
The result was a significant reduction in the number of moving parts and an overall weight reduction of by 3kg, with individual parts being up 16 per cent lighter than before. These combine to deliver a one per cent increase in fuel economy.