Honda un-veiled their Multimatic transmission when they launched the EK-generation Civic in late 1995. This gearbox has since become a reference standard by which automatic gearboxes are judged. We ran a technical article on the Multimatic a couple of years ago, translating the technical article (in japanese) from Honda's Japan web-site. Here in this 4th article of my "Executive Civic" series, I will focus on the Multimatic's driving experience.
Honda's Multimatic or MMT is developed from the conventional CVT transmission but with numerous Honda improvements that overcomes the weaknesses of the traditional CVT-box. When MMT was first introduced, Honda said they applied for and held as many as 50 patents on the many developments they specifically developed for MMT. For e.g. MMT does not use a torque converter. Rather the engine flywheel couples directly to MMT which in turn couples via a viscous coupling clutch system to the driving wheels. This gives superior power transfer characteristics compared to standard automatic gearboxes. What's so great about MMT is it being a CVT gearbox, is able to continously change the effective gear ratio to perfectly complement the drive of the car to the requirement of the driver's right foot. But while conventional belt-driven CVT gearboxes are severely limited in their power handling capacity, Honda's MMT is additionally able to handle power as high as 130ps from the 3-stage VTEC D15B engine.
Like all great inventions, the operating principle of the CVT gearbox is surprisingly simple. The core construct is the use of two cones to form a V-shaped gear. The image on the right is a diagramatic view of two placements of two sets of such cones In the first placement above, the two cones are placed with their tips a short distance apart. Note points 'A' on both cones. The distance between the corresponding points (A) on both cones is a certain distance (say 5mm for the sake of this explanation). Now take a look at the second placement at the bottom. The two cones are now placed so that their tips touches each other, i.e. they are placed as close as possible. Now take a look at points 'B' on both cones. The distance between points B on both cones is the same (5mm for this illustration) as the first placement but notice that now the points are higher or further from the center of the cones in this second placement.
So if we take a flat belt, say 5mm in width, and wrap it around the two sets of cones, it is clear that the belt will wrap around at a lower point on the first top set, or closer to the center of the cones, compared to the second set. If you look at it carefully, the belt and cone combination therefore forms the equivalent mechanical construct of a small gear-wheel (the first set of cones) connected to a large gear-wheel (the second set of cones). And if we link the first set to the engine flywheel and the other to the drive shafts, then it will work similarly to the case of a gearbox running high-geared. By using a hydraulic mechanism to dynamically move the two cones in and out relative to each other, the belt will correspondingly ride higher or lower. We can now use a computer to control the two sets of conical gears so that when one set is moved apart, the other set is moved corespondingly closer so as to maintain the connecting belt's tension. So now we have a set of two gears that can continously vary their ratios, i.e. we now have a gearbox with continously variable gearing ! The moving-GIF on the left attempts to show this mechanism in action for 1 set of conical gear.
Understanding this basic principle of how the Multimatic CVT gearbox works is crucial to understanding the unique advantages MMT/CVT has over the regular automatic or manual gearboxes that works with a set of discrete ratio'ed gears.
Honda programmed the Multimatic ECU to generally emulate the characteristic of the standard automatic gearbox for normal driving. When the the throttle is gently squeezed, the gearbox bites and the car moves off, gradually gaining speed while engine rpm slowly climbs. However, engine rpm will only climb to a certain rpm and will thereafter remain steady at that rpm. For most people, this will usually be ~2500rpm. The car will steadily - and not too slowly in fact - keep accelerating right up to around 90 - 100kph. Indeed for relaxed driving, one can be running the engine at no more than ~2500rpm all day and still be accelerating briskly, cruise around at speeds of up to 100kph, even overtake !
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| Multmatic Mode Selector Knob 'E' is for Economy 'D' (the dot) for Drive and 'S' is for Sports |
A huge change comes during "performance driving". Honda equipped their Multimatics with three driving modes of E(conomy), D(rive), and S(port), selectable via a knob on the gearbox console. The main difference between the three modes is how high the rpms will climb at WOT and part-throttle. For best performance, obviously one should immediately switch the knob to 'S' mode.
Drive the 3-stage VTEC D15B with a Multimatic gearbox. Cruise leisurely at 90kph and when you need to overtake the car in front quickly, simply flick the dial to 'S' and floor the throttle. Engine rpm shoots up almost instanteously while the car's speed remains at around 90kph. This is the "clutch slip" phenomena of MMT that is much talked about. Once the engine's rpm reaches ~7000rpm, it stays there and the car now lurches forward, accelerating at a comparatively wild pace. 160kph quickly comes up on the speedometer with seemingly little or no effort. The engine may be 'only' 1.5l in displacement but with VTEC screaming in full glory at 130ps (for the 3-stage VTEC D15B), traditional concerns like "power band" or "flat point in the power curve" becomes totally irrevelant.
What actually happens at WOT with the Multimatic gearbox is the engine rpm surges up straight to the engine's max power point. Multimatic box slips the gear-ratio so that the engine revs pass all rpms below 7000rpm without driving the car much. The car's inertia and mass has little or no effect on the rpm climb because the car hardly changes speed, the gearbox acting like a flexible "rubber-band" that allows the engine to change rpm at will without little change to the speed of the car - almost as if the gearbox was running in neutral !! Once the engine rpm reaches ~7000rpm only then will Multimatic engage and transfer drive to the front wheels. This means at WOT, the engine hardly has to contend with pulling the car while at lower rpms - and lower power. It only starts to pull the car after it is screaming at 7000rpm and is delivering 130ps in its full glory.
Spinning at 7000rpm while the car is moving at 90kph has another effect. At this relationship, Multimatic would have varied the effective gear ratio to very high, multiplying engine torque as high as possible as a result. To understand the significance of this, we should take a look at a discrete fixed ratio gearbox first. Taking a manual as illustration, at any one time the car must be in a certain gear. Now, the driving torque at the front wheels are multiplied by first the gear which is in use and then the final drive. Using the EK3 manual as a reference, at any one time, it must be in either 1 of its 5 forward gears. 3rd gear for e.g. has a ratio 1.172 while final drive is 4.058. So in 3rd gear at around 90kph, the engine will be spinning at ~3800rpm. The driving torque at the front wheels will be engine torque at ~3800rpm multiplied by 4.76 (minus a reduction factor due to power loss at the gearbox of course). With Multimatic however, the engine only start pulling the car after it reaches 7000rpm. Revving at 7000rpm at 90kph with stock 185/65/R14 tyres (on the EK3) means the effective gear-ratio maintained by MMT is now ~8.75, multiply engine torque by 80% more compared to the manual box !
Therefore it can be clearly seen that Multimatic has two big advantages over the normal discrete ratio gearbox. Take again the scenario of cruising at 90kph and then overtaking the car in front as fast as possible.
With the discrete fixed ratio gearbox, the car will typically initially be in 5th gear. So we first down-shift. If we down-shift to 3rd, engine revs will be ~3800rpm. This is 'low-cams' region. The gearing ratio multiplies engine torque by 4.76 and even at WOT, the engine will have to start pulling the car from 3800rpm onwards (and where it's generating relatively low power). And it will have to pull all the way through until ~6000rpm before VTEC activates the wild cam profiles and then to 7000rpm before it can finally generating 130ps. VTEC fans are well familiar with this situation of course, we call it waiting for VTEC to 'kick' in. In very tight situations, indeed we have to down-shift further but 90kph in 2nd gear is already 5800rpm. Red-line in the 3-stage VTEC D15B is 7200rpm so very soon we will have to shift up again. Indeed, even 2nd gear ratio is only 1.782 giving a final multiplication factor of 7.23, still below the 8.75 with the case of Multimatic. And we can't shift into 1st gear at 90kph !
In the Multimatic on the other hand, upon WOT, engine rpm surges almost instantaneously to the engine's max-power rpm. The effective gear-ratio is also changed to the maximum possible for the prevailing speed. All these means the car accelerates at the maximum rate possible. As the speed picks up, the gear-ratio will start to drop in order to maintain 7000rpm. Acceleration slows down correspondingly but most importantly we now see that because Multimatic maintains the highest possible gear-ratio at WOT at any speed, this allows the car to accelerate at the maximum possible rate at all times the throttle is kept at WOT ! No need to worry about down-shift. No power-band or VTEC kick-in point considerations. Maximum acceleration is available any time by just quick stomp of the right foot !
Nothing is perfect of course and Honda still have to work within the constraints of physical laws. The clutch system used on MMT being a viscous coupling system still imposes a higher power loss compared to a manual gearbox though lower than that of the conventional torque-converter based automatic. Also at WOT, there is still a finite time needed for engine revs to reach 7000rpm from whatever initial rpm the engine was running at. This leads to an operational attribute not dissimilar to "throttle lag". Consequently, for overtaking manuveurs in tight conditions, some planning is still needed for maximum performance and safety.
For all its unbeatable strengths however, the Multimatic still have one unfortunate limitation which Honda couldn't overcome despite all their brilliance. The CVT belt is prone to slipping when it is asked to transmit too much power between the two sets of conical pulleys. Indeed in older non-Multimatic CVT gearboxes, it's been even known to snap from the power. For Multimatic, Honda is able to improve it to handle a very high 130ps power limit. But ultimately for Honda, 130ps is to be honest, not that high in power. Thus rather unfortunately Honda is not able to equip their more powerful models with the Multimatic gearbox.
Lately there have been reports about Multimatic failures. I myself have come across quite a few cases of this from readers of TOVA. In this section, I would like to put forward a few of my own ideas and opinions about this topic.
The first and perhaps most important thing to highlight about Multimatic's reliability and robustness must be to highlight that it is still a gearbox and as gearbox goes, some degree of common-sense and indeed 'tender-loving-care' would not go amiss. Actually the same goes for the other types of gearboxes - both automatic and even manual gearboxes will suffer failure with 'over-casual' usage. Let me explain what I mean by this.
In many cases where I have come across a Multimatic gearbox failure, after asking for some details, I have always found that the owner had been 'over-enthusiastic' and had modified his engine for more power. The 3-stage VTEC D15B especially already produces 130ps so any modifications will quickly push the power output to above 130ps. The thing is Honda designed the Multimatic gearbox to operate with a max of not much above 130ps. But the 'problem' with such an energetic combination as a 130ps 3-stage VTEC D15B with Multimatic is that where before, one was stuck with the old paradigm that little 1.5l engines with automatic gearboxes will never deliver good performance, now the relative performance of a 3-stage VTEC D15B/Multimatic combo can be encouragingly fast !! One can quickly understand the famous adage 'Power is Never Enough'. With the relative ease it is to squeeze even more power out of the little D15B, one can quickly see the scenario for a broken gearbox. But please do not misunderstand me here. I have seen EK3 Civic Ferio Vi's being modded with various devices like HKS Super Power Flow and even the HKS AFR. And they have been running fine. I think the key is a good degree of care and sensible usage. After all if one goes around running at 7200rpm the whole day, any gearbox and any engine will quickly blow up !
Sometimes problems attributed to Multimatic's supposed lack of reliability can be traced to driving style. It's not really entirely the fault of the driver since the automatic gearbox in many ways encourages this style by its convenience. For e.g. many people when forced to stop halfway up an up-hill climb (say in the up-ramp of a multi-storey carpark) will simply leave the gearbox engaged and in order to keep the car from rolling backwards, simply apply light pressure on the throttle. Think about it. The engine is revving lightly (perhaps 2000rpm) generating drive to the wheel. But this drive is just enough to keep the car stationary. So somewhere in between something is giving way, generating friction in the process, to keep enough force on the wheels so that the car is kept from rolling down backwards. And that something is the gearbox. Indeed if we do this 'stunt' with a manual gearbox, we'll quickly burn the clutch. With a normal auto gearbox the torque converter over-heats leading to premature failure. And it's no different in the Multimatic as the viscous clutch slips in order to generate the friction and this in turn will burn up the clutch. It's the same at move off time, since many people have also developed the habit of simply letting go the brakes and then pumping the throttle to get to car moving upwards. I think that in such scenarios, it is not only Multimatic which will fail if we keep doing this - indeed any gearbox will fail.
A similar case also applies to the scenario where one has come up against a tall obstacle, perhaps a rather high kerb for e.g. Again the 'lazy method' is to simply apply more and more throttle until the car makes the 'jump' and this will lead to excessive stress on any gearbox. The common wisdom given by experienced drivers here is to reverse the car a bit (check that there's room to reverse !) and then get the car moving steadily forward, and using a combination of the forward momentum and light throttle, to get the car smoothly up and over the obstacle.
I can go on with more examples but I think these illustrations are enough to explain that no gearbox is indestructible and the Multimatic certainly is not. Like all gearboxes, a certain amount of restraint and common sense will not go amiss when using the Multimatic and will contribute tremendously to its reliability and durability.
In today's public roads, there will be many occasions where the Multimatic will shine. In a typical relaxed drive, the driver will be cruising in a high gear, usually 5th, at a moderate speed. In such cases, despite the superior power loss characteristic of the manual, Multimatic will definitely put more power to the ground at WOT quicker, thus allowing the car to accelerate faster earlier. So in many cases on the public roads, Multimatic will indeed be able to outshine even the manual gearbox. For EK3 Civics such situations might even be the norm, for the driver who is willing to compromise comfort and practicality for all-out performance will seldom be willing to be driving constantly at high rpms and a low gear or to constantly 'row-the-gears' especially for a trivial task like overtaking the lorry (or truck) in front.
I have tried my best to show-case the unique strengths of Honda's great Multimatic gearbox in this article, carefully balancing it with a close look at the need for proper driving techniques and care. In the process, I hope I have managed to clearly explain the many advantages of Honda's Multimatic and all CVT gearboxes.
Wong KN
January 2003
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