WHAT DOES VDC, TCS, ABS, or CVT MEAN?

25th May 2014 by Admin

In this newsletter like any article on motor vehicles there is a plethora of TLAs (three letter acronyms).

So to help with the understanding of the articles, included below is a number of technical terms used this edition and some short definitions.

Anti-lock Braking System (ABS) - When you apply your brakes, you want your car to slow down, but you also want to be sure that you don’t lose control. For this reason, many modern cars are fitted with anti-lock braking systems (ABS) which allow the driver to stop the car in the shortest distance possible without locking the wheels and skidding or spinning out of control. The other aspect is that a car cannot be steered if the car is skidding, so ABS also allows the driver to continue to steer the vehicle while the brakes are applied.

Brake Assist (BA), - Brake Assist measures the speed and force of brake application to determine whether the driver is attempting an emergency stop. If such an emergency is determined, the system applies additional brake pressure to allow the driver to take full advantage of the Antilock Braking System (ABS).

CVT Transmission or Nissan’s version X-Tronic - Traditional automatic transmissions use a set of gears that provides a given number of ratios (or speeds). The transmission shifts gears to provide the most appropriate ratio for a given situation: Lowest gears for starting out, middle gears for acceleration and passing, and higher gears for fuel-efficient cruising.

The CVT replaces the gears with two variable-diameter pulleys, each shaped like a pair of opposing cones, with a metal belt or chain running between them. One pulley is connected to the engine (input shaft), the other to the drive wheels (output shaft). The halves of each pulley are moveable; as the pulley halves come closer together the belt is forced to ride higher on the pulley, effectively making the pulley’s diameter larger.

Changing the diameter of the pulleys varies the transmission’s ratio (the number of times the output shaft spins for each revolution of the engine), in the same way that a 10-speed bike routes the chain over larger or smaller gears to change the ratio. Making the input pulley smaller and the output pulley larger gives a low ratio (a large number of engine revolutions producing a small number of output revolutions) for better low-speed acceleration and getting the vehicle to move. As the car accelerates, the pulleys vary their diameter to lower the engine speed as car speed rises. This is the same thing a conventional transmission does, but instead of the old feel of gears changing, the CVT continuously varies the ratio so is just a smooth transition -- hence its name.

For the undemanding drivers CVTs are both elegantly simple and efficient, as the engine is almost always operating at maximum efficiency.

A bit of trivia – The history of the CVT transmission suggests that Leonardo DaVinci sketched the first CVT in 1490. Dutch automaker DAF first started using CVTs in their cars in the late 1950s, but technology limitations made CVTs unsuitable for engines with more than around 100 horsepower. In the late 80s and early 90s, Subaru offered a CVT in their Justy mini-car, while Honda used one in the high-mileage Honda Civic HX of the late 90s. Improved CVTs capable of handling more powerful engines were developed in the late 90s and early 2000s, and CVTs can now common place.

Electronic Brakeforce Distribution (EBD) - In a regular braking system, when the brake pedal is applied, the brake fluid travels to the brakes and the pressure of the fluid forces the two pistons to push out, resulting in the brake shoes or pads being applied. What EBD does is it electronically monitors, through sensors, the conditions of the road, the feel of pressure on the brake pedal, and vehicle weight, to determine when to apply pressure to the brakes. The sensors are designed to monitor the movements of the wheels and determine based on weight, which wheels may need the maximum force applied, as per the condition met.

Traction Control System (TCS), - Traction control helps limit tyre slip in acceleration on slippery surfaces. In the past, drivers had to “feather” the accelerator pedal to prevent the wheels from spinning on slippery pavement. Many of today’s vehicles employ electronic controls to limit power delivery for the driver, eliminating wheel slip and helping the driver accelerate under control.

Vehicle Dynamic Control (VDC) - This standard feature—sometimes called stability control—continuously monitors your steering and braking actions, senses any oversteer or understeer, and compensates by reducing engine speed and/or applying brake pressure to specific wheels.

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