Smart Cars, Part 1

Anti-lock braking & traction control

 


 

JP Molnar | From the November/December 2006 Issue Wednesday, November 15, 2006

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.

The ABS

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.

There are many possible reasons for this, but it’s probable that because most consumers were never trained in ABS braking techniques, the misnomer grew that, somehow, the ABS was the cure-all to all bad driving decisions. In addition, in an overheated braking system, an ABS will not function if the brakes are so hot they can’t produce enough stopping power to lock up a particular brake/wheel, a problem for drivers who rely on an ABS to stop them after repeated brake applications at high speed, such as a police officer in a pursuit. True, the basic hydraulic brake system works, but brake fade will delay implementation of the ABS.

So, when managing your patrol vehicle in a pursuit or Code-3 response, remember that if you get the brakes too hot, you may be out of luck. No matter how good the ABS is, a 5,000-lb. patrol car can stop only so fast, and steering hard around a hazard means a violent weight transfer in a matter of milliseconds. Plan ahead to avoid needing ABS in the first place.

Emergency Brake Assist

There’s a new braking technology married to the ABS called emergency brake assist. This system is available on police models of the Dodge Charger and Magnum, the Ford Expedition and numerous civilian vehicles. According to Chrysler, drivers often apply the brakes quickly in an emergency, but they do not apply them hard enough. Emergency brake assist detects a situation in which emergency braking is required by measuring the speed with which the brake pedal is depressed and relays this information to the electronic control unit. If it registers an unusually high pedal speed, the system registers an emergency braking situation, and automatically increases pressure to the brakes in conjunction with the ABS. In the police package Charger and Magnum, emergency brake assist is also integrated into the electronic stability control system.

Traction Control

What It Is

When power is transferred from your patrol vehicle’s transmission to the drive wheels, it must go through a differential. The differential splits the power to each drive wheel. A differential is necessary because when your vehicle goes around a corner, the inside tires turn at a different rate than the outside tires because the outside tires take a larger arc through the corner. In older vehicles and many patrol vehicles, the differential is open, which means power always transfers to the wheel/tire with the least amount of traction. If you ever tried to do a burnout in your car growing up and kept getting a single rubber stripe instead of two side-by-side, it was most likely because you had an open differential. Most front-wheel-drive vehicles still function on this principle to minimize “wander” under hard acceleration.

Back in the 1960s and 1970s, you achieved traction control by either taking your foot off of the gas or spending a few extra bucks on a traction-aid differential like a limited-slip. The limited-slip differential is currently present in Ford Crown Victoria Interceptors, older Caprices and most police package SUVs. In four-wheel-drive (4WD) vehicles like the Expedition and Tahoe, it’s usually only present in the rear axle. With this differential, a clutch pack inside the differential assembly constantly reallocates the amount of available power to the wheel with the most traction. The amount of power split (i.e., “slip”) still allows for the difference in speed between inside and outside wheels in a corner, but since both tires get power, they maintain much better traction when accelerating. This leads us to the next generation of electronically controlled traction control devices found on the Dodge Charger, Magnum and Durango, but not available on the Impala Police Package or Crown Vic.

How It Works

Modern day traction control systems essentially use the speed sensors in an ABS to measure an increase in acceleration of a particular wheel relative to the others. Once the traction-control system measures one wheel spinning more quickly than the others, it automatically pumps the brake to that wheel to reduce its speed and reduce wheel slip. In many newer cars with smart transmissions and throttle-by-wire, some vehicles also incorporate the ability to reduce engine power when it senses traction loss.

What It Feels Like

Do you remember the old Wendy’s advertisements with the little old lady protesting, “Where’s the beef ?” Well, you might feel the same way when a traction-control device takes over. Your first instinct will be that something has broken on your patrol car. The gas pedal will go to mush, and you will look in the rear view to see who threw out the anchor. Relax. This is normal. Once the system determines that you are indeed worthy to have full power again, the car will leap back to normal, which can surprise you if you aren’t prepared. If it sounds like the jury is still out on traction control, you’re right. I own a vehicle with traction control, and I’ve sampled traction control systems from Mercedes Benz, Dodge, Chrysler, Chevrolet and others. In some cases, they might help, but the bottom line is tires give you traction, not power. If you have no traction in snow or ice because your tires simply won’t grip, the most a traction control system can do is moderate a bad situation because any application of the throttle will cause the system to either decrease power or shut down power altogether. In bad weather, a two-wheel-drive vehicle with traction control is still no match for a regular all-wheel-drive or 4WD.

What To Do If You Have It

First, make sure you have the right tires for the season on your patrol vehicle. Second, drive smoothly with the throttle so you never have to use the traction-control system. Third, make sure you have enough space when merging into traffic in inclement weather or accelerating hard from a stop or corner because when the system activates, you will slow down, making traffic approaching behind you arrive a lot sooner. Once activated, there isn’t much you can do besides pull your foot out of the throttle or wait until the system does its thing.

Conclusion

Anti-lock braking and traction control are just two of many new technologies finding their way into today’s patrol vehicles. I will feature more vehicle control technologies in future issues, show you how they work and tell you when they could end up just outside your squad room. In the meantime, take the time to explore what you already have in your patrol car that can help keep you safe on the roads.

Sources

• About.com

• Bosch Corporation

• Daimler/Chrysler Corporation

• General Motors

• Ford Motor Company



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JP MolnarJP Molnar, Law Officer's Cruiser Corner columnist, is a former state trooper and has been teaching EVOC since 1991 for numerous agencies.

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