science

Variomatic

Variomatic is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Variomatic rather than just read about it. In short: Variomatic is the continuously variable transmission (CVT) of the Dutch car manufacturer DAF, originally developed by Christoffel Sellenraad. It is a stepless, fully-automatic transmission, consisting of a V-shaped drive-belt, and two pulleys, each of two cones, whose effective diameter can be changed so that the "V" belt runs nearer the spindle or nearer the rim, depending on the separation of the cones.

Key takeaways

Variomatic belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Variomatic to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Variomatic from memory before moving on to harder problems.

Reference excerpt

Variomatic is the continuously variable transmission (CVT) of the Dutch car manufacturer DAF, originally developed by Christoffel Sellenraad. It is a stepless, fully-automatic transmission, consisting of a V-shaped drive-belt, and two pulleys, each of two cones, whose effective diameter can be changed so that the "V" belt runs nearer the spindle or nearer the rim, depending on the separation of the cones. These are synchronized so that the belt always remains at the same optimal tension.

History Patented by Milton Reeves in 1889 in the USS and in Fouillaron in 1898. “To solve a thorny weaving problem, the engineer developed a variator system that prevented the thread from cutting when starting the looms”. In 1904, the Fouillaron type G tonneau road vehicle was equipped with a wooden Tonneau body and a De Dion 6 HP single-cylinder engine; the car did not exceed 25 km/h. This vehicle has a very original gear transmission system with extendable pulleys. This invention, which he further developed and adapted to machine tools, was later acquired by the Dutch car manufacturer DAF, and developed into the Variomatic transmission, since continued by a separate company called DVT. The Variomatic was the first commercially successful CVT (as opposed to shifting between separate gears), first marketed on the DAF 600. In theory, this always produces the optimum torque. The Variomatic was introduced by DAF in 1958, also putting an automatic gearbox in the Netherlands for the first time.

Efficiency Because most of the time the engine runs at its most economical speed, the fuel consumption of this car was acceptable, although the fuel efficiency of any mechanical CVT is about 70% (then) to 75% now (Bosch).

Reversing Because the system does not have separate gears, but one (continuously shifting) gear and a separate 'reverse mode' (as opposed to reverse gear), the transmission works in reverse as well, giving it the side effect that one can drive backwards as fast as forwards. As a result, in the former Dutch annual backward driving world championship, the DAFs had to be put in a separate competition because no other car could keep up.

VDT Manual transmission remains dominant in Europe. When DAF was acquired by Volvo in 1974, the Variomatic patents were transferred to a company called VDT (Van Doorne Transmissie), later acquired by Bosch in 1995. VDT continued the development of the CVT and introduced a push-belt system in the Ford Fiesta and Fiat Uno.

Operation

Gear ratio The final drive has two pulleys with moveable conical drums. The distance between the drums is controlled by the engine vacuum in the inlet manifold and engine RPM, through centrifugal weights inside the drums. Between the two pulleys runs a drive belt. As a result of the change in the distance of the conical drums in both pulleys, the diameters and so also the reduction ratio changes continuously.

Differential

With the DAF 600 - 55, each rear wheel was propelled individually by a pair of conical drums and drive belt with the effect of a limited-slip differential: if a drive wheel on slippery road revs up, the other wheel can still transfer the full torque. This results in unusually good traction characteristics, which were also a reason for the successes of the DAFs in rallying. There were several disadvantages that accompanied the lack of a true differential gear. Although each belt could settle (independent of the other) into its optimum position, thus allowing for wheel speed variation, the system was slow to operate and depended on the pulleys being turned. This led to rapid tire wear and placed stress on other transmission components. Snapped drive shafts were common. Low-speed handling in icy conditions was interesting as the system tended to drive the car forward against the influence of the steered wheels. Later cars, the 46, 66, and Volvo variants were fitted with a differentially geared axle. A version with a differential was developed by Williams in the 1993 Williams FW15C CVT Formula One car, but it was banned before being raced. In testing there were problems with the heat production.

Motorscooters The Variomatic is also used in today's motorscooters. It has been a standard part of all common scooters since 1985, and several companies such as Malossi, Polini, Doppler, and Stage6 are offering tuning clutches and variomatic for most common 50, 70 and 125 cc scooters.

Steel link belts The modern CVT works according to the same principle of split pulleys allowing infinitely variable gear ratios. Rather than the pulled rubber drive belts as originally used by DAF, the modern transmission is made more durable by the use of steel link belts that are pushed by their pulleys. This improvement was pioneered by Fiat, Ford, and Van Doorne in the Netherlands from the late 1970s. The gearbox is also under electronic control. One version that incorporates the switch from rubber to steel belts was called the Transmatic.

Availability DAF's Van Doorne's Transmissie is still operating (as of November 2015) in Tilburg, Netherlands. It changed affiliations from the DAF group to Bosch in 1995. The CVT is available from brands such as Audi, Honda, BMW Mini, and Subaru. Tata Motors from India intended to use a Variomatic transmission in its $2500 Nano. The Nissan Primera is offered with this transmission.

References

External links How it Works: The Variomatic Transmission

Illustrations

Variomatic: Belt and pulleys of a Van Doorne transmission — Belt and pulleys of a Van Doorne transmission

Worked examples

Example 1 — a first encounter with Variomatic

Start with the simplest possible case. Write down what Variomatic claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Variomatic before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Variomatic ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Variomatic

In research: Variomatic appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Variomatic in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Variomatic is common in secondary-school and first-year university syllabi. It links to neighbouring topics Automatic transmission tradenames, Automotive transmission technologies, Continuously variable transmissions, so understanding it makes those chapters shorter.
In everyday life: Look for Variomatic outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Variomatic in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Variomatic means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Variomatic out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Variomatic in simple terms?

Why does Variomatic matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Variomatic?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Variomatic.