Carquirks talks about the technical aspects of transmissions

The roads that run through the hilly regions of the India called ‘ghats’ are etched in my memory as some of the most fun-to-drive roads around the world. The condition of the roads may not be world class, but it was on the set of twisties just outside the city of Pune that I got my first taste of all-out driving as there was almost never any traffic early in the morning. The feeling of attacking a corner in my 100bhp Fiat hatchback; brake hard and feel the rear squirm before you hit the apex, heel-toe and blip the throttle, shift down to second, and power out like a bat out of hell!

The Transfagarasan highway in Romania been named the best driving road in the world. (Image source: Wikipedia Commons)

As I hit another set of zig-zags, I was really taken in by the connection I felt with the car. Besides the feel of the tyres through the steering and the sound of the motor revving, it was the manipulation of the transmission to eke out the best out of the engine that brought an idiotic grin to my face. I had to know more about this technology that made driving this much fun. Last weeks’ post promised an in-depth look at gearboxes and that’s what you’re going to get today.

(Image source: memegenerator)

An essential part of any modern internal combustion car (today’s electric cars don’t use the same sort of transmissions… yet), the transmission is a part of the drivetrain. To put it simply, the gearbox transfers power and torque from the engine to the wheels. While the idea of a gearbox is quite a recent one in terms of human history, it is actually based on the simple pulley systems that were used ages ago.

The purist petrolheads’ passion; the manual gearbox. (Image source: Wikipedia Commons)

Credit is given to Louis-René Panhard and Émile Levassor for inventing the first manual transmission when they created the first Daimler car engine in the late 1800s. This type of gearbox had multiple gears (also called ratios or speeds), a couple of them for forward movement and at least one for reverse. If you’ve seen a cycle with gears, you’ll understand how gears are meant to work. The larger gears are meant to create initial momentum from stand-still while the smaller gears provide more speed.

After the 1920s synchromesh transmissions became popular. This technology allowed the gears to slip into their cogs with much less resistance and doesn’t require multiple clutch depresses. Most new manual gearboxes now have 5 or 6 speeds where the highest gear is meant to cruise while the second highest gear can be used to reach a cars’ maximum speed.

A manual transmission with 3 forward speeds and one reverse designed by Ford in the 1950s. (Image source: Wikipedia Commons)

Manual gearboxes have been a part of automobiles since their inception and a siren call for petrolheads. Engaging the old time gears required careful timing and throttle manipulation when shifting. Otherwise the gears would not spin at the same speed when engaged and cause that awful grinding sound (shudder). This is where double-clutching came in.

Now that we know about manual ‘boxes, let’s see what automatic transmissions are about. While purists may not like them, the automatic gearbox is here to stay. In addition, there are a lot of reasons why today’s automatic transmissions are better than their manual brethren.

The 1940 Oldsmobile Series 60 was the first car to sport an fully automatic gearbox that did not require any driver input to change gears. (Image source: Wikipedia Commons)

While some say the automatic transmission was invented in 1921 by Canadian Alfred Horner Munro, a Wall Street Journal article credits ZF Friedrichshafen with the invention sometime after World War I. However, it wasn’t until 1940 that the first truly automatic transmission appeared on the Oldsmobile. Today, there are many different types of automatic gearboxes; conventional automatics, continuously variable transmissions (CVTs), automated manuals, and dual-clutch automatics.

This fully automatic transmission was dubbed Hydramatic as the operation of the gears was achieved with hydraulics. (Image source: Wikipedia Commons)

The conventional automatics use a torque converter to transfer power from the engine to the transmission. The transmission chooses the different speeds by engaging electronically controlled, hydraulically operated clutch packs. They tend to shift smoothly but are less efficient due to transmission losses and shift slower than the others. That said, having had the opportunity to drive a Jaguar F-Type with the superb ZF 8-speed torque converter automatic, I can honestly say it shifts quickly and doesn’t blunt performance in the least.

The ZF built 8-speed torque converter automatic is the best of its kind and comes standard on the entire range of Jaguar models (Image source: Jaguar press site & Wikipedia Commons)

CVTs use a belt that runs between two variable-diameter pulleys to give a wide range of ratios and a smooth transition between them. The advantage of a CVT is that the engine can be kept at its most efficient speed while the transmission adjusts to changes in load or road speed. A limiting factor is that because CVTs rely on friction between the belt and the pulleys, they haven’t yet been designed to handle a lot of power. My father’s old Honda automatic is a decent drive in stop-go conditions and on the highway, but is downright unpleasant for spirited driving. When the CVT shifts gear, it is extremely smooth but sudden throttle inputs are not what the gearbox is made for as the shifts feel like a rubber band being pulled and snapped.

The CVT is offered on most of Honda’s smaller models like the Jazz pictured here (Image source: Honda press site & Wikipedia Commons)

The automated manuals are essentially manual transmissions where the clutch and shift actions are carried out by computer-controlled, electronically activated mechanisms. They work without driver interaction just like a conventional automatic gearbox. The Fiat Abarth 595 comes with this transmission as an option. While it makes the hot hatch more efficient when compared to a conventional automatic gearbox, it tends to shift gears in a very jerky manner. A change in driving style can compensate for this but I found it quite irritating as the transmission ponderously searched for the right gear.

A serious chink in the Fiat Abarth 595’s armour is the automated manual. you’d be much better off with the manual option (Image source: Fiat press site)

The dual-clutch automatics, as the name implies have two gear shafts – one for the odd-numbered gears (1, 3, 5, 7) and another for the even-numbered gears (2, 4, 6) – each with its own clutch. Both clutches are used simultaneously with the next gear always pre-selected. As seen on Porsche’s PDKs and VW’s DSG ‘boxes, the benefits from this include seamless shifting and better fuel efficiency through lesser transmission losses. However, they are more sophisticated and expensive than other types of gearboxes and have more moving parts creating more wear.

VW’s DSG dual-clutch automatic gearbox has all the benefits of a torque converter without its pitfalls (Image source: Volkswagen press site & Wikipedia Commons)

The number of ratios or speeds of gears has increased since they were first made. Where the first cars had three speeds, today’s transmissions have many more. Just a few years ago, the industry standard for cars was 5-speed, though now it’s 6, while sports cars have 7 or more. CVTs have potentially infinite number of speeds. Theoretically, a larger number of gear ratios helps keep an engine operating in the most efficient part of its rev band at any given moment. This means that the car will be the more efficient as each ratio will perfectly translate what is needed in each situation. However, the more complex the gearbox, the more wear and the more expensive it is.

A few years ago, there was an idea floating around some automotive forums that if the CVT could handle the Bugatti Veyron’s power, it could potentially reach a much higher speed than its recorded 265.7mph (427.6kmph) (Image source: Wikipedia Commons)

Now that you have basic idea of what all these transmissions are, let’s talk about the gearbox that Honda has patented. In the description of the patent, Honda says they are using a third clutch which will be able to decrease torque removal that occurs with dual-clutch transmissions. The patent application also says that the new transmission will allow “speed change to be more effectively restricted and a speed change response to be increased.”

Dual Clutch Transmission
An image of Honda’s dual-clutch transmission used on the manufacturer’s bikes (Image source: Honda press site)

All this jargon means that it will be more fuel efficient than dual-clutch gearboxes, shift gears faster and more smoothly. With 11 ratios or speeds, the ‘box will also be able to find an ideal gear for the driving situation more easily. While there’s no guarantee that Honda is going to use the technology in its cars, it’s only a matter of time before we see it on the road. Especially considering GM and Ford have a jointly developed 10-speed automatic transmission ready to be fitted to their cars and trucks. Ford is also said to have filed a patent for their own 11-speed conventional automatic unit.


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