That twisting road connecting the high Tagaytay ridge to the Taal lakeside town of Talisay is a favorite of mine, the many tight turns going down or back up all concentrated into a short and intense few minutes of absolute focus.  And the ride I had that weekend was proving to be an excellent match.

IMG20150613144531

We had a microhatch that balanced handling and riding comfort so well, my kids in back didn’t mind the roller coaster I had turned it into, steering the car through the twisties as if it were on rails. The whole family was with me so there was no messing around with making the tires squeal when coasting in and then powering out of turns. Ironically, I kept the speed well inside the safe zone with some race track tactics I’ve picked up along the way.

IMG20150613132416Cruise into the approach of a tight downhill turn, brake strong before the turn-in point to get the speed down smartly, downshift for engine braking (and for keeping revs spooled up), then ease-off the brakes at the turn in. Foot off the gas until the apex, then power out the back end of the turn. Give it a few shakes, wait till we’re back on a bit of a straight, then shift back up to ease off on the gearbox. The balance between braking and downshifting was good enough that when I checked the wheels at a rest stop, the brakes were just normal hot, never coming close to overheating into uselessness.

On the climb back up to the Tagaytay ridge, I used both momentum and torque to retake the twisties, keeping approach speeds moderate and downshifting at the moment when I felt the engine just touch that pre-stall shudder. Surprisingly, the torque boost I got with the downshifts saw me overtaking not just big slower vehicles but even compact and mid-size sedans that, on paper, had the power to keep me in their rear-view mirror all day long.

All in all, an intense 30 minutes of driving on a surprising ride that was familiar in strange ways. All that shifting for engine drag or torque boosting? Routine on any manual transmission, yes, maybe slightly less natural on a semiautomatic with its overrides, okay, but not something you’d expect doing at all on a continuously variable transmission, not on a CVT. But this particular ride was the Mirage CVT, the award-winning high efficiency microhatch that has an ace up its sleeve with some surprising performance perks.

Not your usual CVT

jatco-cvt-7-slides-400The Mirage CVT variants are equipped with the JATCO CVT7 transmission. First introduced in 2012 and now standard as well on other makes, the CVT7 is the first continuously variable transmission with an auxiliary gearbox.

Connecting the CVT to the engine crankshaft is a torque converter that uses fluid pumping to transfer force from the engine’s impeller to the transmission’s rotor. On conventional automatic transmissions, that torque converter would “lock-up” when the vehicle reaches cruising speed—meaning a clutch would press in to make a solid connection and eliminate “slippage” between the rotating impeller and rotor. But on CVT’s that don’t have to shift from one discrete gear to another, that solid link-up kicks in soon after roll-out.

” the JATCO CVT7 introduced a planetary gearbox that now adds a second, lower forward speed range labelled B “

IMG20150615134009What defines a CVT are those variable-diameter pulleys with slope-sided grooves that widen to let the steel belt sink in lower or gradually narrow to lift the belt up and out—the wider the groove (the further apart the walls), the smaller the pulley diameter, the narrower, the bigger. At roll-out, the driving pulley is set small with a widened groove, the driven pulley set big with a narrower one. Driving a bigger pulley deepens the gear reduction (making more engine revolutions go into each turn of the wheels), driving a smaller pulley makes it shallow. As the car accelerates, gear reduction is made shallower, the driver pulley becomes bigger with a narrowing groove, the driven pulley gets smaller with a widening one.

Where before the only mechanism between the pulleys and the driveshaft was a clutch assembly for going into forward or reverse, the JATCO CVT7 introduced a planetary gearbox that now adds a second, lower forward speed range labelled B. Putting it in B would deepen the gear reduction on the transmission’s output, resulting in higher torque though at a lower operating speed range.

maxresdefault

With the auxiliary gearbox, the CVT7’s ratios range from the exceptionally deep 1:4.07 on its low B starting ratio, to the exceedingly tall 1:0.55 of its top overdrive ratio in standard D (compare these to the 1st gear 1:3.54 and 5th gear 1: 0.80 ratios on the Mirage’s MT variant). To deliver this wide a ratio spread with a typical CVT would’ve entailed much larger and heavier pulleys with a deeper oil bath. Instead, the CVT7 works with a lighter, more compact pulley set and a smaller and tighter-wrapping steel belt, elegantly making these deliver the requisite ratios by splitting these into overlapping standard D and low B ranges.

D and B

The differences in torque delivery are obvious. To go uphill with a fully loaded car, putting it in B would be the natural choice to not strain (or even stall) the engine. But, once you hit the flats, you’d want to be in D to be able to accelerate all the way to cruise speed and maybe beyond.

For the B drive, I’d guess the CVT7 uses the biggest and heaviest components in the planetary gearbox—with the ring-gear engaged and turning the driveshaft through the multiple planetary gears on the carrier set.

Equally obvious is the difference in engine drag you’d be getting if you took your foot off the gas when in D or B. In D, very little engine braking comes in when you let off the gas. Though it’s still there, the drag is light, hinting at a direct connection between pulleys and driveshaft without much in the way of intervening gears. In B, the story is very different: letting off the gas results in instant drag from an idled engine.

I’d speculate that the gear sets for B are left to free-wheel and be drawn along with the spinning driveshaft when D is selected, to minimize the difference in their rotational speeds. This would explain why toggling between D and B on the fly is so fast. As far as I can tell, un-clutching the D set from the driveshaft happens simultaneously with clutches pressing in to engage the ring and carrier gears of the B set, and vice-versa. Such simultaneous sequences, and so confidently executed, can only be done if the target gear is already spun up, ready to be clutched in and primed to take on torque.

These said, when and how would you shift on the fly between D and B? Choosing which gear to roll-out on is simple enough. With the car still stationary, your foot on the brake, simply choose which gear to roll-out with. But once you’re rolling, could you, would you, shift down to B? You’re instincts serve you well if you hesitate. After all, this is a CVT with its Achilles Heel of a drive belt.

There are some important caveats to discuss, things never done on a CVT, but shifting on the fly from D to B, and vice versa, is not only possible, the auxiliary gearbox on the CVT7 even seems tuned to some spirited D/B toggling. With the car already rolling, shifting between D and B is so fast that it reminds me of the sequence on a good dual-clutch transmission, a DCT. As a matter of fact, toggling between drive modes is much faster than the initial roll-out shift from N to D which will see you waiting a full second before feeling the torque converter kick in and start to push against the brakes.

Gradual is good

First off, you roll-out a CVT, never launch it. That old trick of popping the selector from N to D while already redlining the engine is a sure recipe for a wreck.

” Attempt a launch and you’ll likely hear the racket of a linked metal belt disintegrating in the confines of the CVT box. So don’t do it. “

The JATCO CVT7 is rated for maximum torque of 133lb-ft, a figure determined by the strength of the steel belt driving and being driven by the pulleys, and a maximum that gives a 79% margin to the 74lb-ft of peak torque at 4000rpm produced by the Mirage’s 1.2L 3-cylinder MIVEC engine. Now factor in shift-shock forces that can spike torque to ten times normal with the sudden engagement of the converter and you’ll get the picture. Attempt a launch and you’ll likely hear the racket of a linked metal belt disintegrating in the confines of the CVT box. So don’t do it.

IMG20150613145916

And, on a more subtle note, always roll out a CVT from a stop, don’t stomp on the gas pedal to recover it from rolling back down a slope (nor even from a reverse run after going through neutral, if that needs mentioning at all). Step on the brakes before putting her in D, then wait for the torque converter to eventually kick in and push against the brakes. Release the brakes and step gently on the gas only after the car has rolled a little on idle power. If you are on an uphill slope and the grade proves too much for D (you’ll feel the car slipping back), step on the brakes again, pop it in B, then do your roll-out sequence once more, and from the top.

That part about always waiting for the torque converter to kick in and push against the brakes before rolling off and only lastly stepping on the gas will, for one thing, give the CVT a chance to wring out all the slack from the drive belt before you accelerate, and more importantly, with practice, will burn something critical into muscle memory.

” Light, flexible and intricate components like … CVT belts will remain intact so long as changes in tension remain gradual … Burn that into doctrine and you’ll be fine. “

Here’s an old school analogy for you: the legendary UH-1 “Huey” medium-lift chopper of Vietnam War vintage was flown with the rotors always having enough pitch to give them positive lift in flight, even when the chopper is descending, the lift still there though not enough to counter the craft’s weight. Rotary-wing pilots had it trained into them that the main rotor should never be allowed to go into neutral lift until the chopper is back on the ground.

Why? When you eventually need to recover from the descent, pulling on the collective to put more pitch on the blades will likely cause too sudden an increase in opposing forces (lift versus momentum) and result in rotor separation. Yup, that means the spin-blurred rotor disc will go one way while the suddenly quiet fuselage you’re in goes another. Light, flexible and intricate components like rotor assemblies and CVT belts will remain intact so long as changes in tension remain gradual, not percussive (or traumatic, if you like things sensory). Burn that into doctrine and you’ll be fine.

Smart acceleration

Coming out of a gentle roll-out with engine revs under 2000rpm, you’ll notice a weak tug and a slight dip in rpm when you reach 20km/h. That’d be the lock-up clutch on the torque converter clamping down and making a solid link between the impeller and the rotor. And that’s when I think the CVT’s control unit hits its zone and starts active adjustments to the pulleys. In other words, when lock-up gives it something solid to work with, the CVT goes into full dynamic control of the pulleys, adjusting these in realtime to keep them at the best diameters.

” Popping into B on the fly to accelerate faster is like shifting on a semiautomatic, you don’t take your foot off the gas. “

IMG20150616093356With the selector in standard D, try pegging your RPM after passing 20km/h and you’ll find that it’s easy to stay at say 2000 (for a gentle climb to cruising speed) or 3000rpm (for a slightly more spirited approach) with very little trimming on your accelerator while your speed climbs steady and smooth. It’s a strangely satisfying sensation seeing the revs exactly where you intend these to be while watching the speedometer needle sweep smoothly up … you just know your milking that MIVEC engine for every bit of torque it squeezes out of each drop of fuel.

With your gear ratios already managed by the CVT, there are a lot more reasons to manage your RPMs and smooth out your acceleration. With a full car on flat terrain, staying at 2000rpm will slowly bring you to a cruising speed of around 85km/h, trim up to 2250rpm and you’ll reach the 100km/h mark. Go higher, say up to 3000rpm on the climb up to a 100km/h cruise and you’ll find yourself not only throttling back as you reach the high 90’s but also realizing that you’ve just rushed something that maybe you didn’t really need to.

Toggling for a boost

IMG20150615083214Now, finally: “downshifting” into B on the fly.

Popping into B on the fly to accelerate faster is like shifting on a semiautomatic, you don’t take your foot off the gas. In fact, you can even start throttling up right before going to B.

Keep your cruising revs between 2000 and 3000rpm at any speed and the Mirage will be in the ideal energy state for dropping into B when you need a torque boost (either for an overtake or an uphill climb). That pop into B will make the revs quickly climb by 1000rpm even if you don’t increase throttle, and by about 2000rpm if you do step harder on the gas just before shifting. Since the engine’s peak torque happens at 4000rpm, keeping your cruising revs between 2000 and 3000rpm gives you enough elbow room to reach and hover at the peak torque mark during a B sprint.

” B actually puts you in a lower speed range and there are rpm/speed levels you could be at in D when you shouldn’t even think of downshifting into B. “

IMG20150616094013You don’t even have to look at your instrument cluster to know when you’re in the zone for a downshift. If you’re cruising while pressing down on the gas pedal by just a fraction and nowhere near the mid-point, you’re good to go. If you had to do a sprint in D to settle in behind a car you plan on overtaking, just ease off the gas first, pause for a moment to bank more momentum with time instead of throttle, and that should settle the revs back down to the vicinity of 2000rpm. And, just like that, you’re ready to pop into B for the overtake.

It’s also a good idea to stay in B until you complete the overtake and re-enter you’re lane. A premature return to D will have the effect of an upshift, of course, and could rob you of the torque that got you out and ahead in the first place. Besides, staying in B is a good way to have some engine braking potential in case oncoming traffic forces you to re-enter your lane behind another slow vehicle. At the end of the exercise, the overtake or sprint all done, shifting back into D could also be without ever letting up on the gas … like I said, toggling between D and B is like shifting on a semiautomatic.

An important point: recall that B actually puts you in a lower speed range and there are rpm/speed levels you could be at in D when you shouldn’t even think of downshifting into B. Say you’re already going pedal to the metal in D with revs reaching 5000rpm as you approach 100km/h in a sprint. This is definitely not the time to pop into B since doing so will immediately spike engine revs into the red zone which starts at 6500rpm. That rpm spike won’t just put the CVT belt at risk but could harm the engine as well.

Toggling to brake

” Brake first, get the speed down closer to where you want it, then pop into B to get the drag that’ll let you ease off and not ride the brakes. “

IMG20150613144550On the flipside of things, don’t ever brake by just idling the engine and downshifting into B. If you’re coming off a speed run, the effect would be the equivalent of that hot-rod launch we’ve already covered. Engine braking with a pop into B should only be done to sustain drag, not initiate it. Brake first, get the speed down closer to where you want it, then pop into B to get the drag that’ll let you ease off and not ride the brakes.

When dealing with sharp curves, especially on a winding descent down hilly terrain, it’s best to use some watered down racetrack braking techniques. Brake firmly before the turn-in point, not a hard race brake, just a firm one to get your speed down to where you can safely take the turn, then pop the selector into B just before easing up and not coming entirely off the brakes.

The point of all these is to slow down first and mitigate the RPM spike that’ll suddenly follow the downshift, keep it as low as possible, keep it, again, gradual. Turn the process into a mantra: “hard brake, pop into B, ease off the brakes, turn.” Then, as you come out of the turn, accelerate a bit in B before popping back into D. Though, maybe you’ll want to stay in B if the roads are winding, turns following right after the other.

Braking or sport … or power

The draw of CVTs has been their greater efficiency over conventional automatic transmissions. Fixed, multiple gears simply can’t beat the physics of having dynamic ones that are constantly kept in their ideal ratios given the car’s speed and load. Mitsubishi Philippines’ assertion of 21km/l on an EUR combined cycle test is not only credible, you’d wonder why it isn’t higher.

IMG20150615134044Even the JATCO innovation of an auxiliary gearbox on the Mirage’s CVT7 transmission was meant to gain engineering efficiencies in terms of size, weight, temperature and noise. But this self-same innovation had added a dimension that elevates the CVT controls above a pop car’s elementary forward and reverse, adding a low speed range with higher torque and engine drag potential that even Mitsubishi has been challenged in labelling properly.

In some markets, the low range is labelled B, for “braking,” in other markets its marked S, for “sport.” The B accurately describes one effect, but just one effect of the low range. The S could be more appropriate, though it invites the misperception that it simply changes the algorithms controlling the gearbox, like how sport mode lengthens the stay on each gear in an automatic transmission.

Clearly, the control set on the CVT7 is entirely new, but I can think of one similar innovation in the past that’s similar. Remember that very first Mirage from the 1980s, the one badged here as the Mitsubishi Colt? It had a curious second stick for shifting between E and P. E for economy, P for power. Toggling between either one simply changed the final ratio on the drivetrain. E shallowed up the reduction, P kept it somewhat deep to deliver higher torque.

The D on a CVT is fine, it’s the typical label for standard drive on an automatic, no need to think of it as E, or as the economical setting. But that B, or S, well, think of it instead as the Power gear and you’ll get a more complete picture of how and when to use it. All the better for making the most of the CVT7 which definitely has game, and which can be gamed. The overall weight that they saved with the auxiliary gearbox might as well be measured at the per ounce price of gold, that’s how much it enhances the driving experience on the Mirage CVT.

IMG20150613145348

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s