The ABS system integrates itself with the brake caliper, rotor and wheel assembly, using sensors to measure individual wheel speeds to detect impending lock-up.Illustrations courtesy Daimler-Chrysler Corporation
The brake-system module works with the system computer to control the amount of brake pressure applied to each wheel.Illustrations courtesy Daimler-Chrysler Corporation
FEATURED IN VEHICLE OPS
No matter what type of patrol vehicle you drive, it’s almost a certainty the vehicle was derived from a production-based civilian model. In most cases, that isn’t a bad thing because your vehicle has benefited from billions of dollars of research and millions of miles of testing.
Advances in automotive technology are always considered cutting edge at the time they are presented. Witness Volvo’s “revolutionary” idea of placing the industry’s first three-point seatbelts in vehicles in 1959. At the time, such technology was unheard of, but consumer demand forced other manufacturers to follow suit. Soon, three-point safety harnesses were available in law enforcement vehicles.
Since then, advances in automotive technologies have placed microcomputers in your patrol vehicle that are smarter than the spaceships of just a few decades ago. One of the newest areas of computer assistance in vehicles has been in dynamic vehicle control technology. This technology was once limited to the highest of high-end vehicles, but it has trickled down into mainstream vehicles, including police patrol vehicles. With the introduction of new patrol vehicle options like the Dodge Charger, cutting-edge dynamic vehicle control technology is now as far away as the order sheet at your local dealership.
Because most law enforcement driver-training programs are behind the curve when it comes to this technology, this guide is the first of two that will provide a condensed explanation of newer technologies, how they work, what they feel like when deployed and what to do if your vehicle has them. In this column, I will address the anti-lock braking system (ABS) and traction control.
What It Is
As officers, we learned in our EVOC classes that a skidding tire is useless for control and stopping power. The theory behind the ABS is simple: Keep the tires from locking up, and the car will stop sooner and safer. By keeping the wheels moving, this allows the tires to maintain rolling friction. This friction allows the driver to stop easier, safer and steer the vehicle around the hazard rather than into it. The ABS has been around for some time now, but many officers still have no idea how it really works.
How It Works
The ABS includes four basic components: speed sensors, the pump, valves and a computer controller. The speed sensor is attached to each brake/wheel assembly and measures how fast the wheel is turning. The computer uses this information to determine the difference in speed of each wheel relative to the others. If one wheel is slowing down much faster than the rest, it’s usually a sign the brake/wheel is ready to lock up. On a four-channel ABS, which most patrol vehicles use, there is a valve in each brake line. When the system senses lock-up on a particular brake/wheel, it uses the valve to regulate pressure to that brake/wheel. No matter how hard you press the brake pedal, the valve prevents any further pressure from making it to that particular brake/wheel. The valve then releases pressure to the brake/wheel as needed. Once the system begins to stabilize, the ABS pump replaces the lost pressure the valve removed. This all happens in milliseconds.
What It Feels Like
When an ABS activates, the valve/pump system repeatedly adjusts brake pressure to each brake/wheel during the hard-braking conditions. The see-saw effect of the two results in a pulsation in the brake pedal, which can be mild or severe, depending on the cost of the vehicle and what generation system is installed. Newer ABS uses electronic brake-force metering instead of mechanical means so it can react quicker and, ultimately, more precisely.
What To Do If You Have It
The entire idea behind driver training is to hopefully prevent you from ever needing an ABS. But if you do, it will help you if you remember to do the following. First, do not pump the brake pedal thinking that the pulsations mean something’s wrong—it’s normal. This was a large problem when the ABS was first introduced into law enforcement fleets without proper training. Officers were braking hard, felt the pulsation, thought something was wrong, pumped the brakes and crash. If you aren’t sure about the pulsation level and feeling provided by your patrol vehicle’s ABS, take it out to an empty parking lot, run it up to 35 mph or so and stand on the brake pedal. As you come to a stop, feel the pulsation and steer left or right to get a feel of what the ABS is doing to help you maintain rolling friction.
This leads to the second point. An ABS will help you stop shorter in some situations, but the best course of action in an emergency situation is usually to steer around the hazard, not stop before it. A study by the Insurance Institute for Highway Safety (IIHS) in 1996 determined that vehicles equipped with an ABS were overall no less likely to be involved in fatal accidents than vehicles without. The study stated that although cars with an ABS were less likely to be involved in accidents fatal to the occupants of other cars, they are more likely to be involved in accidents fatal to the occupants of the ABS-equipped car, especially single-vehicle accidents.