When Mazda first announced its Skyactiv technology some years ago, many people thought it referred only to the new engine family that would power new models for the rest of this decade. However, Skyactiv is actually a package that encompasses the powerplant, transmission, drivetrain, chassis and body structure. The technologies of Skyactiv will be incorporated in all future Mazda models and the new CX-5 is the first one which has all of them (the updated Demio and Mazda3 in some markets has only the new Skyactiv engine).
Skyactiv technology was developed by Mazda as an alternative to hybrid and EV solutions to address the issues of fuel-saving and protection of the environment. While hybrid powertrains do a good job of addressing these issues, they are still costly at this time. Rather than spend a lot of time and money trying to develop hybrid or EV technology, Mazda has instead focussed on taking the efficiency of the internal combustion engine (ICE) to the next level. It has done so well that one of the new Skyactiv engines has been able to achieve up to 30 kms/litre – comparable to the Honda Jazz Hybrid (based on official claims by both companies).
|The ideal Internal Combusion Petrol Engine
The ICE has been around over 100 years. Manufacturing processes, supply chains and numerous complementary industries are geared towards designing, making and maintaining this type of engine. It is because the ICE is so entrenched that the move towards other types of powertrains running on alternative fuels has been slow. Besides the enormous R&D cost of developing such powerplants, massive new investments are needed to switch over manufacturing processes. For instance, batteries – greatly in demand for hybrids and electric vehicles (EVs) – cannot be made fast enough because there are insufficient factories.
It’s also because of the massive investments required that the automobile companies expect governments to ‘share’ in the cost by providing subsidies for the purchase of hybrids and EVs. They don’t expect the subsidies to be forever but for a sufficient period of time to enable production of such vehicles to reach a critical mass when economies of scale can kick in and prices become acceptable to consumers.
Unless something catastrophic forces use of the ICE to stop altogether, it is likely that we’ll see it as the primary powerplant for automobiles for many more decades. In the meantime, mindful of the need to stop pollution from worsening, governments are introducing stricter emission regulations and also demanding fuel consumption to be reduced significantly.
Thus, the most significant of the Skyactiv technologies is the new generation of engines Mazda has developed. Pursuing ideal combustion in the ideal engine design was the most important objective and after identifying the four factors that limit efficiency – exhaust loss, cooling loss, pumping loss and mechanical loss – the engineers looked for ways to minimize these losses.
One of the most significant breakthroughs in this area was the compression ratio which was set to 14:1 for both petrol as well as diesel Skyactiv engines. For those unfamiliar with this, the compression ratio for petrol engines has been typically around 10:1 and for diesels, 18:1 or higher.
Higher compression ratios have usually meant that higher octane fuel (RON98 or higher) must be used to avoid knocking (pre-combustion) but the Skyactiv petrol engine can run properly on RON95 which is the minimum fuel grade in Malaysia. Some of the features of the engine which make it possible to run such a high compression ratio on RON95 include an injector spray pattern that more efficiently cools the air intake, a new and optimized design on the top of the piston and smoother flame propagation. By creating a stratified air-fuel mixture around the sparkplug, it has also been possible to fire up a cold engine smoothly.
There are enormous implications to this radical change in the compression ratio, with the result being greatly improved efficiency leading to lower fuel consumption and cleaner exhaust emissions. So impressive is the Skyactiv-G engine, as it is referred to, that Ward’s Auto (an authoritative industry publication in America) picked it as one of the 10 Best Engines in the World for its 2012 list.
There’s also the advanced Skyactiv-Drive, a 6-speed automatic transmission which is not a CVT but has a conventional design with a more compact torque converter. The transmission’s efficiency is exceptionally high (4 – 7% savings in fuel consumption) and said to be comparable to dual-clutch transmissions/CVTs with an extra wide lock-up range that reduces power losses. With more sophisticated electronic and oil pressure controls, direct shifting also quickens transitions and improves acceleration.
The chassis element was incorporated Skyactiv technologies because this is the area that gives the Zoom-Zoom character. Sacrificing that character in the pursuit of better fuel efficiency and losing that character would have taken away one of the reasons why many people love their Mazdas. One of the challenges the engineers faced was to maintain Jinba-itai which is a Japanese term for ‘rider and horse as one’; it refers to the ‘unity’ between the car and the driver and was first mentioned in the development of the MX-5.
The other challenges in this area were to find the right balance of comfort and handling, and to make the driver feel confident at high speeds. These required a lot of development work on the track and the engineers had to rethink all the concepts of suspension design and tuning and find new approaches to take.
One example: to make the car agile in corners at low to medium speeds without compromising ride comfort, the engineers reduced the vertical impact at the rear suspension, making for less dependence on the tyre’s transitional vertical load. Raising the attachment point of the rear trailing arms by 43 mm also improved the anti-lift geometry and less left means the rear tyres stay more firmly planted on the road – with less pitch, the driver will have a better sense of stability and security.
On its own, as mentioned earlier, the powertrain could be improved to quite a large extent to be more fuel-efficient and powerful but to achieve higher fuel efficiency also meant that weight savings were necessary – but without compromising safety. This is the tricky part for engineers because lightening a vehicle body means using lighter or less materials but the structure still needs to be strong enough to withstand the enormous forces of a collision during an accident.
Since engineers began to use powerful computers for their work and could carry out finite element analysis and highly complex simulations, structural design has advanced greatly. But for the Mazda engineers developing the Skyactiv body, higher targets were set which included (compared to previous equivalent models) rigidity that would be at least 30% greater and weight reduction of at least 8%. And this was to be achieved while ensuring that the models would have the best crash safety performance.
Three main areas received attention to meet the targets – structural optimization, manufacturing processes and usage of materials. Using computer-aided engineering (CAE) to optimize calculations, strength targets were set for numerous critical elements in the structure. From this, a multi-load path was determined which could effectively disperse collision forces before they reached the occupants. The more advanced bonding process during manufacturing also helped to improve rigidity and had the additional benefit of lower noise, vibration and harshness (NVH). Needless to say, there is greater use of high-tensile steel – which is lighter but stronger – and depending on the model, the increase is up to 20%. That helps rigidity and yet overall weight could be lowered by 8% (depending on the model).
Mazda is confident that the Skyactiv body can meet or even exceed the toughest crash test requirements in North America, Europe, Japan and China. In fact, since its launch, the CX-5 has already been named a “Top Safety Pick” for 2012 by the American Insurance Institute for Highway Safety. This is the highest possible safety rating in the independent organisation’s crash tests.
|CX-5 is the first Mazda model with the complete set of Skyactiv technologies
Click here to read more about the new CX-5
With its Skyactiv technologies, Mazda believes that it can offer customers the fuel economy benefits that they expect more and more of without the higher technology cost of taking the hybrid system approach. This is not to say that Mazda does not believe or want to offer hybrids and in fact, it is rumoured that the company is already at work on a hybrid model which will be launched in a year or two. And whatever model it is, that Zoom-Zoom character must be present… otherwise it’s just not a Mazda.
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