Bristling with patents, next Mazda3 plots return to comparo podium
The zippy C-segment compact Mazda3 has always been a comparison-test darling at Motor Trend, handily nipping, zipping, and zooming its way around most competitors to a podium finish in every comparison and Big Test it’s competed in … except the last one. In July 2016 it slipped to fourth, primarily by virtue of how much the competition has been forced to up its game. Well, Mazdarati, take comfort: For the next-gen 3 arriving in 2019, Mazda will be rolling out some serious next-level (patented) jinba ittai “horse-and-rider-as-one” shizzle.
The whole jinba ittai shtick is about strategically removing elements of isolation so as to enhance the lines of communication the car provides between the driver and the road. Getting the slop out, if you will. The headline-grabbing update for 2019 is the multipatent-protected 2.0-liter Skyactiv-X engine. Final calibration and testing are not yet complete, but relative to today’s Skyactiv-G 2.0-liter gas engine, it is expected to deliver between 10 and 30 percent more torque and sufficient economy improvement to allow a shortening of the axle ratio for a double whammy in terms of slop-free acceleration.
EPA figures won’t be available until much closer to launch, but we’re told to expect a boost of between 20 and 30 percent. That would rank Skyactiv-X even with the fuel economy of the 2.2-liter Skyactiv-D diesel engine or nearly so, but at a cost that’s not quite halfway between that of the G and D engines. How’d they manage this trick? By firing this gasoline-powered engine like a diesel.
Engine nerds might recognize the concept of running a compression ignition engine on gasoline. The idea has been kicked around for decades under names such as DiesOtto and HCCI (for homogeneous-charge compression ignition). These engines all attempted to run on the diesel cycle, lean and mostly unthrottled, during steady-state and low-load cruising conditions. They would then revert to normal spark ignition during hard acceleration or high loads. Managing the transition between easily controlled spark ignition and much more difficult to control compression ignition has proven extremely challenging. Most big companies have long since abandoned the technology.
Tiny Mazda’s hack is to set the engine’s compression ratio too low to ignite gasoline and then to initiate compression ignition of a homogeneous lean air-fuel mixture by using a tiny kernel of locally rich air and fuel right near the spark plug. The flame front from this explosion doesn’t need to travel too far before boosting cylinder pressure enough to ignite the rest of the air and fuel. Yes, you read that right—compression ignition is being initiated with a spark plug. It’s still compression ignition, mind you, but the pressure rise in the cylinder is less instantaneous than with a true diesel, so you don’t get the clatter, and the bottom end of the block doesn’t take nearly the same beating that the Skyactiv-D’s does. (The X engine does get mild reinforcements down there, mostly to the bed plate.)
Another bonus: The combustion is vastly cooler than with complete spark ignition, which nearly eliminates NOx production, so there’s no need for a costly lean-NOx trap, and with fuel injection pressures that also roughly split the difference between modern gas and diesel DI (figure 7,500–10,000 psi), we’re told that particulate emissions are about on par with typical gasoline direct-injection engines such as the Skyactiv-G. So it shouldn’t need a particle trap until all GDI engines require them.
Mazda invited journalists to Germany to sample three 2019 Mazda3 prototypes fitted with Skyactiv-X engines and manual or automatic transmissions, and although there’s still some drivability tuning work to be done, they felt darned near ready for prime time. Most notably, it’s impossible to discern any transition between full spark combustion and compression ignition without looking at the computer screens in the car. Acceleration indeed felt brisk and linear, and the cars cruised easily at speeds of 100 mph (160 km/h) and above. There’s no sound from the Roots-type compressor, which ensures enough surplus air in the cylinder for compression ignition. It also aids in providing the swirl needed to ensure the late squirt of fuel that creates that rich mix by the plug. Note that Mazda never calls it a supercharger because the comparatively low-pressure air it supplies is not intended to boost performance. The biggest “flaw” still in need of tuning out is a pre-ignition knocking sound when lightly rolling onto the throttle. It was most noticeable on the manuals—the automatics generally called for a downshift whenever this occurred.
Other arrows in the jinba ittai quiver include new seats that mount more rigidly to the body and support the pelvis in an orientation equivalent to when the person is walking. This supposedly encourages an S-curve to the spine and enables the same dynamic balance instincts that stabilize the head when walking. A considerably reinforced chassis improves torsional rigidity by 30 percent with a specific goal toward reducing the delay in energy transfer between diagonal corner inputs. Then at the corners, an effort has been made to make the energy transfer from a bump to the sprung mass more linear. The effective spring rate of the tire has been reduced 10 percent to lower the initial input of smaller bumps. The forces that do transmit through the wheel are then directed through revised lower control arm geometry that increases their vertical loading and into dampers that are better aligned with the suspension motion, and through bushings that are mostly a bit firmer. All of this is to reduce the delay in directing these inputs to the driver. Actual spring and damping rates change very little from the current car.
Two other patents on the Skyactiv Vehicle Dyamics front: The rear trailing twist-beam’s main torsion element morphs from a constant shaped U-section to a more complex shape that flares out at the ends. This reportedly boosts camber stiffness by 50 percent, preventing potential misalignment and toe-angle change during wheel travel. The other one is aimed at ensuring that all this direct-response stuff doesn’t overwhelm the car with noise and vibration. A patented “matrix resin material,” the constituent chemical makeup of which Mazda is keeping mum about, is designed to absorb vibration and dissipate it as heat. Some 7.5 meters of this stuff are strategically located in 16 areas of the body, and perhaps they work, because the prototypes never seemed “abuzz” with vibrations sneaking in through the stiffer bushings.
The mostly urban drive route didn’t include enough ride/handling events to pass judgment on Skyactiv Vehicle Dynamics, but with past as prologue and considering the source, these concepts certainly provide plenty of cause for optimism for the fourth-gen 3 returning to a high podium finish in its debut comparison test.