Staying on track

Jan. 1, 2020
ABS, traction and stability control systems open the door for a host of new pre-accident systems.

If you wanted to tag the last 20 years of auto development with a movie title, none could be more suitable than “The Fast and the Furious.” Computer-generated modeling and advanced production methods have shaved years off the design and implementation process. Technological upgrades now leap from drawing boards to showrooms in a matter of months.

As the evolution of the automobile has become supercharged, an interesting “power struggle” has erupted between driver and vehicle. On one side, auto manufacturers have delivered new levels of power and performance to all areas of the market. Buyers of even the most basic economy cars now can count on plenty of horse-power and “bang-for-your-buck” fun. Unfortunately, putting all this muscle in the hands of millions of drivers facing countless distractions during their daily commutes sometimes means one thing: trouble. The kind of trouble that causes accidents. Knowing this, carmakers have provided the occasional revolution, or outright coup d’état, in the driver’s seat.

Anti-lock braking systems (ABS), traction and stability control systems take command when circumstances, such as poor driving decisions or poor road conditions, warrant. If that wasn’t power enough, these “pre-accident” systems are evolving, incorporating additional vehicle systems as they take on more driving and safety responsibilities. They’re also commanding greater miles of roadway each year as they become standard features on more vehicles. Here’s a look at the past, present and future of these systems and how they’re shaping the automotive world.

Control technology:

The building blocks of safety

Understanding pre-accident, or control, technology is tantamount to knowing how your home theater system works. Both require a modular approach. Both build upon relatively simple or basic constructs, adding more features until they create a complex system capable of producing a number of functions.

For example, in your home entertainment center, you start with a television and DVD player and then add a receiver, speakers and other components. In the end, you have a system that produces multiple combinations of image and sound. With an automobile, start with braking, and add throttle control and power disbursement. The result is optimal stopping and directional control created by the interplay of several electronic systems under the guidance of one.

Module 1: ABS

ABS came to market in the mid-1980s, first in BMW and Mercedes-Benz models fitted with brake technology developed by Robert Bosch GmbH. Headquartered in Stuttgart, Germany, Bosch works mostly with German auto manufacturers, which explains why many pre-accident systems first appear in German automobiles.

ABS operates by sensing and preventing wheel lockup during hard braking situations, such as braking while a vehicle slides on ice. The function of ABS is to restore traction during deceleration. It does this by automatically slowing and increasing wheel spin until the wheels create the traction necessary to stop.

ABS uses four basic components: speed sensors, pump, valves and controller. Located at each wheel or sometimes in the differential, the speed sensors indicate when a wheel is about to lock up. The valves act to release pressure on the brakes, and the pump replaces the pressure. The controller acts as the computer that monitors speed sensors and controls the valves.

The controller continually searches for unusual deceleration in the wheel: for example, rapid decelerations that typically precede a wheel lockup. When left unchecked, these decelerations cause the wheel to stop much more quickly than the vehicle, sending the vehicle into a skid. To prevent this, the controller reduces the pressure to the brake until it detects acceleration. Then it increases the pressure until it detects deceleration again. ABS acts so quickly — cycle times can reach 15 per second — tire speed does not significantly change. The result is that tires slow down at the same rate as the vehicle. Because the system automatically keeps the tires near the point of lockup without allowing them to actually lock, maximum braking power is yielded and maximum stopping power is produced.

Anti-lock braking systems come in three different types, based upon channel number (how many valves are individually controlled) and the number of speed sensors. Four-channel/four-sensor ABS schemes feature a speed sensor and separate valves for each wheel. The controller monitors each wheel individually to make sure it achieves maximum braking force. This system provides the most effective braking of the three.

In a three-channel/three-sensor ABS scheme (typically used on pickup trucks with four-wheel ABS), each of the front wheels has its own sensor and valves, while both rear wheels share the same valves and one sensor located on the rear axle. This system provides individual control and maximum braking force of the front wheels. Because the rear wheels are monitored together, they both have to start to lock up before the ABS activates. The drawback here is that one of the rear wheels can lock and thereby reduce brake effectiveness.

Pickup trucks with rear-wheel ABS sometimes feature a one-channel/one-sensor scheme, where the valves operate only the rear brakes and the single sensor is located on the rear axle. Operating the same as the system on the rear of a three-channel scheme, both rear wheels are monitored together and both have to start to lock up before the ABS takes command. As with the three-channel system, one of the rear wheels could also potentially lock.

Module 2: traction control

Following ABS to the market, traction control — or more specifically, acceleration slip regulation (ASR) — uses the same operational premise: maintain as much traction as possible between the tires and the road. In this case, traction is maintained while the vehicle is accelerating.

Building on the ABS model, traction control uses the brakes along with the throttle to maintain adhesion between the vehicle’s tires and the pavement. Traction control works by preventing wheel spin in low-traction situations, such as snowy or wet roads, by adjusting torque at the rear wheels. In some cases, the brakes are automatically applied. At other times, power is redistributed to the wheel(s) with the most traction. These actions typically are achieved either through a series of quick braking pulses or redirection of engine torque through directional clutches in the rear differential.

Module 3: stability control

Electronic stability control (ESC) systems also use braking and throttle control elements to help drivers maintain control of their vehicles. These systems control yaw — the lateral movement of the vehicle’s front or back end (side skidding).

Stability control systems typically integrate ABS and traction control along with a yaw-sensing feature usually referred to as a rotational-speed sensor or yaw-rate sensor. The yaw-rate sensor, along with information on steering wheel angle, wheel speed and accelerator position, will allow the control unit to determine if the vehicle is rotating in a turn. If the system determines there is too much yaw, it activates a brake or a combination of brakes and sometimes throttle control, until it determines the vehicle is stable.

Stability control systems are marketed under a number of names. Mercedes systems are referred to as Electronic Stability Programs (ESPs), while BMW systems are marketed as Dynamic Stability Control (DSC) and Cornering Stability Control (CSC). Delphi markets a TRAXXAR system, but automakers use a variety of their own monikers, including AdvanceTrac for Ford and Active Safety for some General Motors (GM) models. While these systems share a basic architecture, each operates and offers different levels of performance according to its own engineering. For example, GM’s Active Handling Chassis Control System, which is built by Delphi, allows more oversteer for the Corvette than other vehicles. Greater oversteer allowance is designed to give the Corvette more sports car-like handling.

More systems, integration coming

The next generation of pre-accident systems offers upgrades in the form of more effective ABS and traction and stability control systems, along with integration of other systems. Phil Cunningham, director of Chassis Systems Product Planning for TRW, notes that his company has integrated suspension and steering control into its Active Roll Control (ARC) system, a stability control system designed to prevent rollovers in vehicles such as SUVs.

In an ARC setup, stabilizer bars linking both sides of the suspension connect to computer-controlled actuators. These actuators use hydraulic pressure to move the ends of the bars. When an accelerometer detects lateral movement during cornering, a computer signals for increased hydraulic pressure. Hydraulic pressure, produced by the power-steering pump and controlled by a separate valve, powers the actuators to move the stabilizer bar — reducing body lean and holding the vehicle flatter. In 2002, TRW and GM integrated ARC in the GM Safari.

Ford has followed suit by being the first auto manufacturer to engineer its own anti-roll system. Integrated first on the 2003 Volvo XC90, Ford’s Roll Stability Control (RSC) continuously monitors roll potential and intervenes when it calculates a vehicle is approaching a rollover situation. RSC utilizes a gyroscopic sensor to determine body roll angle and roll rate. It correlates this information approximately 150 times per second with data collected from other sensors, for example, yaw rate with lateral and linear acceleration. When a vehicle approaches an unstable situation, RSC reduces engine power and/or applies brakes to the appropriate wheels until vehicle stability is returned.

The Lincoln Aviator and Navigator already feature RSC. Ford plans to integrate RSC on 2005 models of the Explorer, Expedition and Mercury Mountaineer. Lexus and Range Rover will offer similar systems on their vehicles.

Because SUV owners often use their vehicles to tow boats and campers, which can create stability problems, BMW’s new X5 3.0d will feature a stability system that monitors the pendulum-like motions of the trailer. At speeds above 40 mph, the system’s sensors begin searching for excessive motion. If so, the engine output is cut and the brakes are applied automatically until the trailer goes back in line with the vehicle, says the automaker.

Regardless of what type of stability system a vehicle may use, Nick Zielinski, GM’s chief engineer for advanced vehicle integration, says engineers will continue upgrading the functionality of system modules and sensors. “This means tapping into an ever-increasing number of sensors for additional input to help system actuators, the mechanisms that activate stability control actions, react sooner and more effectively. We’re talking about reaching a whole new level of control,” says Zielinski.

One system for total protection

Frank Lubischer, director of braking systems for TRW, says along with controlling vehicle direction and motion, pre-accident systems also will branch out into a total protection system for drivers and passengers. “Stage one will be crash prevention,” he says. “Stage two will integrate interior safety systems to protect vehicle occupants in the most effective manner. For example, yaw sensors will help tell the passive restraint system to pull the driver back into a more effective driving position. Airbags will be tied into this system, too, and will activate in a manner that best protects the occupants.”

Lubischer and Cunningham explain that automotive engineers have begun looking at the chassis as one fully integrated, central system tied into other vehicle systems. The chassis is becoming both brain and cocoon, designed to protect passengers while commanding all vehicle operations to work together in a way that provides the safest, most efficient traveling experience possible.

Delphi uses this same philosophy to build its line of Unified Chassis Control (UCC) systems, which similarly integrate performance and safety systems into one scheme. Currently, Delphi is able to integrate offerings, such as its Active Front Steering (AFS) and Active Rear Steering (ARS) with braking systems.

Delphi also has introduced other pre-accident systems that have the potential to be integrated. These include its Lane Departure Warning system (TRW has built a similar system), which sends out audible warnings when a vehicle begins to leave its driving lane, and its Forewarn Adaptive Cruise Control with Driver Alert system. Forewarn uses a vehicle’s braking and throttle systems to automatically manage vehicle speed to maintain a headway gap (following distance) selected by the driver. The driver sets the cruise control and following distance. The vehicle responds by maintaining the set speed, automatically slowing when approaching slower traffic and accelerating when appropriate. It’s almost enough to make you consider bringing along a good book the next time you drive. Almost.

Final word: a new era for repair?

Looking at all the innovations in vehicle control systems and how far we’ve come in the last decade, it’s tempting to wonder if the day isn’t far off when getting from point A to point B simply will be a matter of programming a vehicle autopilot. Though that’s probably further off than we may think or hope, these technology enhancements will continue to be finessed and of course, will ultimately impact the way a vehicle is serviced. 

These systems are tied into a number of parts and other systems that technicians regularly work on. Remember, too, these systems rely on greater numbers of monitors and sensors placed around wheels and other vehicle areas. Remind your technician customers to be aware of their locations to avoid damaging them.

The industry should also be aware of the direction diagnostics might take based on the growing presence of pre-accident systems. As electronic and computer-based systems become more prevalent in automotive construction, on-board computers may be used to search for accident damage and repair information, using the thousands of bits of data normally collected by these systems to prevent accidents. Vehicles will be able to tell their drivers what happened to them and where they hurt.

With that done, perhaps the next step auto designers take is the one we’ve spent years waiting on — programming vehicles to automatically arrive at a shop the moment they’re in need of repairs.

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