Simulation helps build better brakes

Livonia, MI--Engineers at Light Vehicle Braking Systems (LVBS), a division of LucasVarity plc, are using a virtual reality environment to perform dynamic vehicle braking performance simulations. According to the company, the system allows it to begin brake system development before a prototype is built, and have a well-tested, high-confidence system by the time the vehicle is ready.

"The ability to precisely simulate vehicle dynamics can help reduce development time by letting us do some of the development here at the lab rather than on a real asphalt test track," says Mark Elwell, LVBS lead engineer at the simulation lab. He adds that the system makes it possible to cut weeks and months out of the cycle.

LVBS has been using simulation as an engineering tool since 1991. Engineers previously used an open-loop system (OLS) to support brake-control system algorithm development. However, re-sulting brake control system outputs could not be fed back into the system to modify sensor input signals--making it difficult to mimic the real-world scenario.

"The OLS is an extremely useful tool," Elwell said, "but it's not nearly as sophisticated as our two closed-loop virtual reality systems." Of the two, one is a non-real-time desktop simulation (CLSDT), and the other a hardware-in-the-loop simulation (CLSH). Both were built from the ground up as brake system development tools.

LVBS has also built a virtual reality vehicle or Driver Interface Module (DIM), complete with recorded track sound and images. Using the DIM, development engineers "drive" the products they're working on to test the braking system. In this instance, brake control system outputs are fed back into the simulation to continuously modify the vehicle dynamics, thus closing the action/response/reaction loop. The result: a real-time simulation that mirrors real-world events.

Actual brake hardware and control systems are incorporated into the simulation house from a hydraulic chamber. The chamber houses the entire brake system--calipers, rotors, linings, drums, proportioning valves, jounce hoses, and other system components under test.

The hydraulic chamber also provides the hydraulic apply system and all of the sensors and interfaces required to integrate the hardware into the simulation. It can handle brake systems intended for sub-compact cars to medium-duty trucks.

When an engineer "drives" the DIM, which is built from the front half of an actual vehicle chassis, he or she sees an animation of the test track projected on a screen in front of the "vehicle," hears actual road sounds through a multi-speaker sound system, and even "feels" actual brake pedal feedback.

A brake fixture mounted under the hood of the DIM and identical to those used in the hydraulic chamber allows engineers to test their products. It uses the same master cylinder, vacuum booster, and pedal installed in the actual vehicle to reproduce "real" feedback sensations.

Sensors for steering wheel angle, throttle and clutch position, gear selection, brake switch, and wheel cylinder pressures send real-time analog signals to the simulation software. High-resolution visual images created from CAD drawings of a proposed real-world test track are projected in front of the DIM.

Such images include a 1.5-mile banked oval, a skid-traction area with wet and dry surfaces, a traction-control hill with 10 and 20% grades and low-friction strips, and a vehicle landing area. Cones for lane-change maneuvers can be set up on a straight section of the oval, and in the skid-traction area. Drivers can select a passenger car, minivan, pickup truck, and any of several viewing perspectives.

"Hardware in the loop has proven to be an extremely useful tool," said Elwell. 'With it we can automate test procedures and get dependable, repeatable results regardless of vehicle or real-world weather conditions."