Cadence braking

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Cadence braking or stutter braking is a driving technique that involves pumping the brake pedal and is used to allow a car to both steer and brake on a slippery surface. It is used to effect an emergency stop where traction is limited to reduce the effect of skidding from road wheels locking up under braking. This can be a particular problem when different tires have different traction, such as on patchy ice for example. Its use in an emergency requires a presence of mind that the situation itself might preclude. Cadence braking is supposed to maximize the time for the driver to steer around the obstacle ahead, as it allows the driver to steer while slowing. It needs to be learned and practiced. For most drivers of modern cars, it has been entirely superseded by ABS, however it is still a valuable skill for drivers of non-ABS equipped vehicles such as classic cars.

Maximum braking force is obtained when there is approximately 10–20% slippage between the braked wheel's rotational speed and the road surface. [1] Beyond this point, rolling grip diminishes rapidly and sliding friction provides a greater proportion of the force that slows the vehicle. Due to local heating and melting of the tires, the sliding friction can be very low. When braking at, or beyond, the peak braking force the steering is ineffective since the grip of the tire is entirely consumed in braking the vehicle.

Anti-lock braking system performs these operations automatically many times per second in rapid succession. A human driver can perform one lock-release cycle per second with practice[ dubious – discuss ][ citation needed ].

This is done primarily to maintain steering control, at least in part. In wet, hard surfaces, this is useful to reduce somewhat total braking distance. When ABS is present the best emergency stop will usually be obtained by simply pressing very hard on the brakes, forcing the ABS to perform, and steering to avoid the obstacles ahead.

Cadence braking (or any other type of braking) will not help much on extremely slippery surfaces such as ice (in theory it would, but in practice the ice can be so slippery that it makes little difference—a winter tire would make more difference). Also, on very loose surfaces, a quicker stop can be achieved by simply locking the wheels, causing a wedge of loose material to build up ahead of the wheels [2] and create a substantial braking force. This is useful only when stopping in a straight line, because locking the wheels means all steering control would be lost. In such conditions, ABS actually increases the stopping distances. On poor surfaces, in the past, rally drivers timed the pulsing of brake application so as to take advantage of the load transfer as the vehicle pitches forwards and backwards in response to the initial braking effort. With modern, over-dampened, and stiffly sprung suspensions this is less likely to be effective.[ citation needed ]

While cadence braking is effective on most surfaces, it is less effective at slowing the vehicle than keeping the tires continually at the optimum braking point which is called threshold braking. The latter is an expert driving technique that is even more difficult to learn than cadence braking, and again has been largely superseded by ABS.

Threshold braking, or a good ABS, generally results in the shortest stopping distance in a straight line. ABS, cadence and interference braking are intended to preserve steering control while braking.

Related Research Articles

Anti-lock braking system Safety anti-skid braking system used on aircraft and land vehicles

An anti-lock braking system (ABS) is a safety anti-skid braking system used on aircraft and on land vehicles, such as cars, motorcycles, trucks, and buses. ABS operates by preventing the wheels from locking up during braking, thereby maintaining tractive contact with the road surface and allowing the driver to maintain more control over the vehicle.

Brake Mechanical device that inhibits motion

A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction.

Opposite lock Driving terminology

Opposite lock, also commonly known as counter-steering, is a colloquial term used to mean the steering associated with the deliberate use of oversteer to turn a vehicle rapidly without losing momentum. It is typified by the classic rallying style of rear-wheel drive cars, where a car travels around a bend with a large drift angle. The terms "opposite lock" and "counter-steering" refer to the position of the steering wheel during the maneuver, which is turned in the opposite direction to that of the bend.

Electronic stability control Computerized safety automotive technology

Electronic stability control (ESC), also referred to as electronic stability program (ESP) or dynamic stability control (DSC), is a computerized technology that improves a vehicle's stability by detecting and reducing loss of traction (skidding). When ESC detects loss of steering control, it automatically applies the brakes to help steer the vehicle where the driver intends to go. Braking is automatically applied to wheels individually, such as the outer front wheel to counter oversteer, or the inner rear wheel to counter understeer. Some ESC systems also reduce engine power until control is regained. ESC does not improve a vehicle's cornering performance; instead, it helps reduce the chance of the driver losing control of the vehicle.

A traction control system (TCS), also known as ASR, is typically a secondary function of the electronic stability control (ESC) on production motor vehicles, designed to prevent loss of traction of the driven road wheels. TCS is activated when throttle input and engine power and torque transfer are mismatched to the road surface conditions.

Locking differential Forcing two transaxial wheels to spin together

A locking differential is designed to overcome the chief limitation of a standard open differential by essentially "locking" both wheels on an axle together as if on a common shaft. This forces both wheels to turn in unison, regardless of the traction available to either wheel individually.

Aquaplaning

Aquaplaning or hydroplaning by the tires of a road vehicle, aircraft or other wheeled vehicle occurs when a layer of water builds between the wheels of the vehicle and the road surface, leading to a loss of traction that prevents the vehicle from responding to control inputs. If it occurs to all wheels simultaneously, the vehicle becomes, in effect, an uncontrolled sled. Aquaplaning is a different phenomenon from when water on the surface of the roadway merely acts as a lubricant. Traction is diminished on wet pavement even when aquaplaning is not occurring.

Electronic brakeforce distribution or electronic brakeforce limitation (EBL) is an automobile brake technology that automatically varies the amount of force applied to each of a vehicle's wheels, based on road conditions, speed, loading, etc. Always coupled with anti-lock braking systems (ABS), EBD can apply more or less braking pressure to each wheel in order to maximize stopping power whilst maintaining vehicular control. Typically, the front end carries more weight and EBD distributes less braking pressure to the rear brakes so the rear brakes do not lock up and cause a skid. In some systems, EBD distributes more braking pressure at the rear brakes during initial brake application before the effects of weight transfer become apparent.

Stiction is the static friction that needs to be overcome to enable relative motion of stationary objects in contact. The term is a portmanteau of the words static and friction, perhaps also influenced by the verb stick.

Skid mark

A skid mark is the visible mark left by any solid which moves against another, and is an important aspect of trace evidence analysis in forensic science and forensic engineering. Skid marks caused by tires on roads occur when a vehicle wheel stops rolling and slides or spins on the surface of the road. Skid marks can be analyzed to find the maximum and minimum vehicle speed prior to an impact or incident. Skidding can also occur on black ice or diesel deposits on the road and may not leave a mark at all.

Traction, or tractive force, is the force used to generate motion between a body and a tangential surface, through the use of dry friction, though the use of shear force of the surface is also commonly used.

Threshold braking or limit braking is a driving technique most commonly used in motor racing, but also practiced in road vehicles to slow a vehicle at the maximum rate using the brakes. The technique involves the driver controlling the brake pedal pressure to maximize the braking force developed by the tires. The optimal amount of braking force is developed at the point when the wheel just begins to slip.

Fishtailing is a vehicle handling problem which occurs when the rear wheels lose traction, resulting in oversteer. This can be caused by low friction surfaces. Rear-drive vehicles with sufficient power can induce this loss of traction on any surface, which is called power-oversteer.

Slippery rail

Slippery rail, or low railhead adhesion, is a condition of railways (railroads) where contamination of the railhead causes trains to experience less adhesion (grip). This can lead to wheelslip when the train is taking power, and wheelslide when the train is braking. The most common cause of contamination is fallen moist leaves that lie on and cling to the top surface of the rails of railway tracks. The condition results in significant reduction in friction between train wheels and rails, and in extreme cases can render the track temporarily unusable. In Britain, the situation is colloquially referred to as "leaves on the line".

Braking distance concept in traffic law

Braking distance refers to the distance a vehicle will travel from the point when its brakes are fully applied to when it comes to a complete stop. It is primarily affected by the original speed of the vehicle and the coefficient of friction between the tires and the road surface, and negligibly by the tires' rolling resistance and vehicle's air drag. The type of brake system in use only affects trucks and large mass vehicles, which cannot supply enough force to match the static frictional force.

S-AWC is the brand name of an advanced full-time four-wheel drive system developed by Mitsubishi Motors. The technology, specifically developed for the new 2007 Lancer Evolution, the 2010 Outlander, the 2014 Outlander, the Outlander PHEV and the Eclipse Cross have an advanced version of Mitsubishi Motors' AWC system. Mitsubishi Motors first exhibited S-AWC integration control technology in the Concept-X model at the 39th Tokyo Motor Show in 2005. According to Mitsubishi Motors, "the ultimate embodiment of the company's AWC philosophy is the S-AWC system, a 4WD-based integrated vehicle dynamics control system".

All Wheel Control (AWC) is the brand name of a four-wheel drive (4WD) system developed by Mitsubishi Motors. The system was first incorporated in the 2001 Lancer Evolution VII. Subsequent developments have led to S-AWC, developed specifically for the new 2007 Lancer Evolution. The system is referred by the company as its unique 4-wheel drive technology umbrella, cultivated through its motor sports activities and long history in rally racing spanning almost half a century.

Road slipperiness

Road slipperiness is a condition of low skid resistance due to insufficient road friction. It is a result of snow, ice, water, loose material and the texture of the road surface on the traction produced by the wheels of a vehicle.

An automobile skid is an automobile handling condition where one or more tires are slipping relative to the road, and the overall handling of the vehicle has been affected.

Crosswind stabilization (CWS) is a relatively new advanced driver-assistance system in cars and trucks that was first featured in a 2009 Mercedes-Benz S-Class. CWS assists drivers in controlling a vehicle during strong wind conditions such as driving over a bridge or when overtaking a semi-truck. CWS uses yaw rate, lateral acceleration, steering angle, and velocity sensors to determine how much assistance to give the driver in a certain scenario whether it be at different speeds or while turning. Using different components throughout the vehicle like brakes, differentials, and suspension, CWS can implement the readings from force sensors to properly assist the driver in a given situation.

References

  1. ↑ Tyre-road friction and tyre slip
  2. ↑ Automotive Brakes By Jack Erjavec p359 "A locked tire allows a small wedge of snow to build up ahead of it, which allows it to stop in a shoreter distance thana rolling tire."


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