The Speed Variator: A Brief Introduction

The speed variator is a component that serves two fundamental purposes: it transmits motion with a constant transmission ratio and allows you to continuously vary this ratio from the outside using a specific control device.

Unlike a standard gearbox, which has a fixed reduction ratio, the speed variator features a variable reduction ratio within a wide range. When it is possible to set the output speed to zero, these variators are called infinitely variable or “infinite range” variators.

Types of Continuously Variable Drives

Continuously variable speed drives can be classified as:

• Mechanical: The speed variation is achieved by changing the position of an intermediate element, specifically the one coupling the drive shaft and the driven shaft.

• Hydraulic: The variation is managed by modifying the pressure and flow rate of a fluid that transmits forces and displacements between the components coupled to the drive and driven shafts.

• Electrical: The speed variation is achieved by modifying the current and voltage of an electrical device.

In this focus, we will specifically look at mechanical speed variators, which feature a moving mechanical component that alters the transmission ratio. This element can be either rigid or flexible.

• Rigid Moving Intermediate Element Variators: These are usually distinguished by the shape of the driving component, which can be flat, conical, or spherical. The transmission can feature fixed axes or rotating axes.

• Flexible Moving Element Variators: These are built using belts (generally V-belts) or chains. Shifting the position of the flexible moving element changes the transmission ratio.

The Anatomy of a Speed Variator: Core Components

When analyzing a mechanical speed variator, several key internal components require close attention:

• The Planets (Satellites): Disks featuring a conical cross-section profile.

• The Inner Planetary Rings (Tracks): The area where the planets make contact, creating the necessary friction.

• The Outer Planetary Rings (Tracks): The area where contact is free and exempt from forces.

Precision and careful engineering during component manufacturing are highly strategic to ensure the longevity and practical performance of the variator. Because of the delicate nature of these mechanics, specialized materials must be used. Consequently, the planets and tracks—the very heart of the variator—are made of a special alloy steel known as 100Cr6 and must be strictly ground using specialized machinery.

The lubricant is equally specific: it requires an ATF (Automatic Transmission Fluid), precisely ATF Dexron II. The operating speed range typically falls between 400 RPM and 2800 RPM. It is vital never to exceed the specified maximum torque, as doing so will cause the speed variator to malfunction.

Speed Variator Accessories

To optimize operation, several accessories are available for speed variators:

• Remote Control: A device that allows you to vary the speed without having to manually turn the traditional handwheel. It is essentially a small gearbox connected to a kinematic mechanism that incorporates a clutch. (A kinematic mechanism is a system of rigid components connected to create relative mechanical motion between the elements).

• Gravitational Indicator: An instrument that allows you to estimate the speed of the variator. It provides a rough approximation since it is based on the number of handwheel turns made during adjustment.

• Position Indicator: Slightly more accurate than the gravitational indicator, it reads the physical position correlated to the speed. Like the gravitational indicator, it calculates speed based on the number of turns made by the regulating screw.

• Speed Indicator: This is the most precise and accurate accessory for measuring speed. It features a phonic wheel (tone wheel) mounted integrally with the output shaft. A sensor placed close to the phonic wheel reads the teeth and gaps on its surface, counting the pulses to deliver the real, actual output speed of the variator.