Transmission types explained

[Eric]

Transmission types explained
By Eric Peters
for immediate release

We don't have "three on the tree" (column-shifted three-speed manual transmissions) anymore, but what we do have is a profusion of different transmission types -- both manual and automatic -- each doing things no old-stlye transmission could have dreamed of.

It could use a little explaining.

It used to be that there were just two basic types of transmissions to choose from -- manuals and automatics. The manual transmissions had a clutch you needed to engage and disengage -- while the automatics you simply left in "drive" and went about your business. There were no electronics; no "help" of any kind -- and no overdrive ratios to improve fuel economy, either.

That's about as complex as it got.

Enthusiast drivers generally preferred manual transmissions because of the greater control and precision they offered -- and also because there was less parasitic power loss through the torque converter, a round, fluid-filled device found near the front of an automatic transmission that spins with the engine and uses the force of hydraulic fluid under pressure to transmit the engine's power through the transmission's main shaft and internal planetary gears to the drive wheels. But because there is no actual mechanical connection between the engine and transmission in a conventional automatic -- just the force of the fluid spinning inside the converter -- a significant portion of the engine's available power was lost.

This is why, all else being equal, the stick-shift version of a given car would usually be quicker (or at least, more responsive) than the same car with an automatic. The stickshift car also tended to get better mileage -- again, because less of the available power was lost through the "slippage" inherent to an old-style automatic and its fluid-driven torque converter. Finally, absent modifications, few factory-produced automatics were capable of delivering performance-type gear changes that made the most of the engine's ouput. (Hence the derisive term, "slushbox.")

The only real advantage the automatics of the past had was convenience and ease of use. The fluid coupling enabled the driver to idle "in gear" without stalling the engine -- because of the torque converter and the use of hydraulic fluid/pressure to transmit power. Also, the driver didn't have to worry about what gear to select or when; you just put it in "D" and that was that.

But the performance gap has narrowed considerably in the last decade -- and thanks to efficient "lock-up" torque converters (now common) that physically connect the engine to the transmission at least part of the time (mostly when the car is at road speed) by means of a special clutching mechanism, the parasitic power losses associated with automatics have been reduced to the point where a stick car has only a slight performance/fuel economy advantage over the identical car with an automatic. Sometimes, the automatic is actually more efficient (for example, the new Chevy HHR; the automatic version of which gets slightly better fuel economy than the same model with a stickshift).

Meanwhile, automatics have been programmed, via electronic controls, to be capable of delivering the crisp, high-performance shifts enthusiasts demand. Many offer a level of operator control and precision that simply did not exist in years past -- right from the factory, with no special modifications needed. Some modern automatics are even capable of "learning" your driving preferences and adjusting shift feel and quality to suit. Many even let you control gears changes and firmness yourself, if you like.

So-called "adaptive" automatics acan alter their operating characteristics based on the habits/driving style of the person driving. For example, let's say you're an enthusiast driver who likes to punch it and really put the car through its paces. Or maybe you like smooth, imperceptible gear changes -- and have a very light foot. Adaptive automatics -- such as offered by Mercedes-Benz, BMW, Lexus and other automakers -- take note of your driving syle and tailor the shift firmess (harder fr enthusiast drivers, or softer for those who just like to cruise) and timing (right at redline, for maximum performance; or less aggressively, for a smoother experience) according to the way you drive. The most performance-oriented units even "know" to hold a lower gear in hard cornering or other extreme situations, just like you'd do with a manual.

It's like having a custom-made race transmission -- only better, because you don't have to sacrifice civility to get good performance. The modern adaptive automatic delivers both. Even those without this more advanced capability typically can at least switch from one pre-programmed mode to another at a moment's notice. Drive most any new car equipped with an automatic and you'll notice a button or switch that lets you select either "sport" or "normal" modes -- depending on what you'd like the car to do. With sport mode enagaged, you'll typically get firmer upshifts and these will occur at higher engine speeds, to maximize acceleration. To get the best fuel economy -- or smoother shift feel -- simply switch it back to "normal." Some cars with this feature also have a "winter" mode that starts the car out in second gear to aid traction and keep you from becoming stuck.

Another really neat development is the "shiftable" function found on many modern automatics that provides a degree of manual control over gear changes. There is typically a secondary gate for the shift lever -- or buttons marked with "+" and "-" symbols to denote upshifts or downshifts. The driver either taps the gearshift lever (or buttons) to move the transmission through the gears manually. But there is no clutch -- and the transmission's electronics do not allow full control over either upshifts or downshifts, as on a true manual transmission. The electronics will usually not allow the driver to shift down to first (or second) gear until the car's speed has dropped below a certain pre-set level; this is a fail-safe to keep the driver from accidentally grenading the tranny or over-speeding the engine. Also unlike a true manual transmission, you cannot raise the engine RPMs and "dump the clutch" for a dragstrip-type launch from a standing start. That's because, being a true automatic, there is no clutch. You just hit the gas and go.

Modern manuals transmissions, meanwhile, have sprouted extra gears -- with five and six speeds now common -- that use extra "deep" overdrive ratios as their fifth or six gear to maximize fuel efficiency and lower cruise engine speed. For example, the Chevy Corvette has a six speed manual with a final ratio in sixth gear that permits the engine to lope along at what is basically a fast idle, even at 80-mph. Engineers have used overdrive transmissions to get the best of both worlds: ferocious off-the-line acceleration, combined with the potential for decent fuel economy at steady-state cruise. The new Corvette -- a 400 horsepower spprts car -- can achieve highway fuel economy in the mid-20s, comparable to the four-cylinder compact economy-cars of 20 years ago.

The latest twist on the manual gearbox is the use of electronics and actuators to operate the clutch -- so all the driver has to do is change gears. Toyota's MR2 has such a feature -- called Sequential Shift Manual Transmission -- as do some high-end BMWs and Ferraris. The technology is derived from F1 open wheel racing, where the fastest, most consistent shifts can mean the difference between winning and losing. In cars like the MR2 and BMW M5 sedan, there is no third pedal for the cluch -- just a pedal for the brake and for the gas, as on an automatic-equipped car.

To start the car, you don't depress the clutch and turn the key -- remember, there is no clutch, at least, not as far as the driver is concerned. You just move the shifter gate to the neutral position, depress the brake and key the engine to life. The computer has declutched for you -- no fuss, no muss .

Now, even though you aren't moving and the engine is running, it's not wanting to stall -- exactly what would not happen with a regular stickshift -- unless of course you manually pushed in the clutch, or moved the shift lever to neutral. The car doesn't stall because the car's electronics know you aren't moving and thus have declutched for you. You can even roll back now, if you want to -- just ease off the brake. The car will remain declutched -- even when you move the gate to the "+' "-" area and the dash display says you're in first gear.

To get going, just hit the gas. The computer will engage the clutch for you and off you go. It's not "grabby" -- and feels just like an automatic car accelerating off the line. To get the next gear, it's your responsibility to tap the shifter (or the paddle buttons on the steering wheel) "+" to move up, "-" to go down.

Easy as that. The computer handles the actual process of disengaging the clutch, moving the internal forks around and getting you to second, third, fourth -- whatever. Reverse works the same way. And unlike a conventional manual transmission-equipped car, it is not possible to stall the car when accelerating from a stop, miss a shift, or over-rev the transmission and blow up the engine. It's failsafe -- and idiot proof.

Whether this will catch on, though is another matter. Efficiency is not everything, and by taking away responsibility for handling the clutch from the driver, the fun of the stickshift experience has been lessened consideably. Functionally, the system behaves very much like the previously discussed automatics with manual-shift function or "sport" programs.

The last type of transmission available today is neither an automatic nor a manual -- nor a combination of these two. It is an entirely different animal known as the Continuously Variable Transmission (CVT). Instead of a torque converter, valve body and internal gears, the CVT uses pulleys and a metal belt to transfer engine power to the drive wheels. The pulleys have the ability to expand or contract continuously, effectively increasing or decreasing the "gear" ratio and hence the tension of the drive belt. Honda and Nissan are among the automakers offering CVT echnology -- which is also used in some hybrid models such as the Mercury Mariner hybrid SUV.

This arrangement eliminates the need for conventional gears altogether, and with them, the need for shifts. Under acceleration, the driver of a CVT-equipped car will notice the engine speed move upward in a smooth, linear progression, without the drop-off between gear changes ? and the attendant ?shift shock? one experiences with a regular automatic.
Even under full throttle, the CVT driver can sip his coffee without worrying about spillage during upshifts.

Because the engine can accelerate to its optimum operating range and stay there, straight line performance with the CVT is excellent ? as good, in fact, as it would be with a manual transmission. Maybe more so. Essentially, the CVT is always in the ?right? gear for conditions, so there?s no lag time between upshifts and downshifts, or ?hunting? for the right gear with this puppy. The engine computer relays information to the CVT, which uses hydraulic pressure to expand or contract either or both pulleys as necessary.

The selector ranges (?Park,? ?Reverse,? ?Neutral,? and ?Drive?) are typically the same as in other cars with automatic transmissions. The CVT even ?creeps? from a stop if you let off the brake -- just like a car with a conventional automatic.

Another nice thing about the CVT is that it?s a simpler design than a conventional automatic. There are only a couple of moving parts and no gears to strip or grind. That should translate into fewer and less expensive repairs down the road -- as well as better fuel economy potential.

END

[MeanMeosh]

We don't have "three on the tree" (column-shifted three-speed manual transmissions) anymore, but what we do have is a profusion of different transmission types -- both manual and automatic -- each doing things no old-stlye transmission could have dreamed of.

There are places in the world where the old style "column shift" manual still exists. In India, there's a car called the Ambassador that uses the column shift manual, and I believe it uses a 3-speed to boot. The car is truly a throwback - it's a 4 door sedan that looks kind of like an old style Packard or Studebaker, and hasn't been meaningfully redisigned since the 1950's (it's still being produced and sold, although its popularity has declined as more and more import models find their way into the country). Along with the column shift, the car contains many other "throwback items", including the trusty front and rear bench seat (with no seat belts), tube tires, and non-pressurized radiator (which really comes in handy, since antifreeze isn't exactly found in abundance in rural areas of the country).

- Sriram

[Dave Brand]

In India, there's a car called the Ambassador that uses the column shift manual, and I believe it uses a 3-speed to boot. The car is truly a throwback - it's a 4 door sedan that looks kind of like an old style Packard or Studebaker, and hasn't been meaningfully redisigned since the 1950's (it's still being produced and sold, although its popularity has declined as more and more import models find their way into the country).

When BMC brought out a new Morris Oxford in1958 they sold the tooling for the old model to Hindustan - the Ambassador is still built using that same tooling, which will now be around 50 years old! Current production uses Mitsubishi engines - gearboxes will be four-speed, as the original Oxford never had a three-speed.

Visually the only changes they have made are a different grille & a redesigned dash.

[Eric]

I wish they'd bring that car here.. but the federales won't let it happen. Killjoys!

[Kwozzie1]

It is an entirely different animal known as the Continuously Variable Transmission (CVT). Instead of a torque converter, valve body and internal gears, the CVT uses pulleys and a metal belt to transfer engine power to the drive wheels. The pulleys have the ability to expand or contract continuously, effectively increasing or decreasing the "gear" ratio and hence the tension of the drive belt.

When living in London during the '70s I owned for a time a Daf 55. Dafs had Variomatic transmission and I guess were the forerunner to the modern CVTs. Daf was later bought out by Volvo. Volvo now owned by Ford

[Eric]

It is an entirely different animal known as the Continuously Variable Transmission (CVT). Instead of a torque converter, valve body and internal gears, the CVT uses pulleys and a metal belt to transfer engine power to the drive wheels. The pulleys have the ability to expand or contract continuously, effectively increasing or decreasing the "gear" ratio and hence the tension of the drive belt.

When living in London during the '70s I owned for a time a Daf 55. Dafs had Variomatic transmission and I guess were the forerunner to the modern CVTs. Daf was later bought out by Volvo. Volvo now owned by Ford

Yes, the industry'sbeen fooling around with CVTs for some time; it was mainly a matter of making them "user friendly" and of course the additonal pressure of ekeing out a few more MPGs!

[D_E_Davis]

When BMC brought out a new Morris Oxford in1958 they sold the tooling for the old model to Hindustan - the Ambassador is still built using that same tooling, which will now be around 50 years old! Current production uses Mitsubishi engines - gearboxes will be four-speed, as the original Oxford never had a three-speed.

Visually the only changes they have made are a different grille & a redesigned dash.

It's quite possible they blocked one speed, ala the Austin A90 in the Austin-Healey. Those Ambassador taxis I rode in, in India, were using only three gears.

[Kwozzie1]

Yes, the industry'sbeen fooling around with CVTs for some time; it was mainly a matter of making them "user friendly" and of course the additonal pressure of ekeing out a few more MPGs!

Yep, and also to make them okay to drive through shallow water.

A sunday arvo, outside a English pub in Kent, ......"hey Rex lets go through the ford". Why not says I...even though there is a perfectly good bridge along side
Strangely mid stream no drive....belts wet and slipping in the pulleys.

Much laughter from pub patrons

[Eric]

Yes, the industry'sbeen fooling around with CVTs for some time; it was mainly a matter of making them "user friendly" and of course the additonal pressure of ekeing out a few more MPGs!

Yep, and also to make them okay to drive through shallow water.

A sunday arvo, outside a English pub in Kent, ......"hey Rex lets go through the ford". Why not says I...even though there is a perfectly good bridge along side
Strangely mid stream no drive....belts wet and slipping in the pulleys.

Much laughter from pub patrons

I BET!

On the CVTs - I've driven probably a dozen vehicles with 'em. Most are very smooth; some (Nissan Murano) genuinely funt o drive/sporty (as autos go). A few were not so impressive - too much noise; felt "strained" and like parts were going to begin flying everywhere at any moment (Ford).

[Dave Brand]

Red]Yes, the industry'sbeen fooling around with CVTs for some time; it was mainly a matter of making them "user friendly" and of course the additonal pressure of ekeing out a few more MPGs!

The early DAF CVTs used rubber belts driving in tension, which severely limited the power they could transmit. Modern CVTs use a steel-block belt which drives in compression.i

[Kwozzie1]

In India, there's a car called the Ambassador that uses the column shift manual, and I believe it uses a 3-speed to boot. The car is truly a throwback - it's a 4 door sedan that looks kind of like an old style Packard or Studebaker, and hasn't been meaningfully redisigned since the 1950's (it's still being produced and sold, although its popularity has declined as more and more import models find their way into the country).

When BMC brought out a new Morris Oxford in1958 they sold the tooling for the old model to Hindustan - the Ambassador is still built using that same tooling, which will now be around 50 years old! Current production uses Mitsubishi engines - gearboxes will be four-speed, as the original Oxford never had a three-speed.

Visually the only changes they have made are a different grille & a redesigned dash.

The Morris Oxford was popular in NZ, along with the Austin Cambridge. My grand mother had an Austin 40 (Devon) which had a cable operated 4 peed column change. trouble was between summer and winter the cable used to expand or contract so some gearchanges were not that smooth.