Automotive Anti-Lock Braking
Delphi Automotive uses VisSim in combination with the VisSim/Real-TimePRO addon as a powerful rapid prototyping environment. In the past, it took months of special machine shop work, circuit design, hand-coded software development and in-car testing to determine whether a design was feasible for production. Now, with the combination of fast and powerful block diagram-based modeling and simulation software from Visual Solutions and highly reliable, noise-immune data acquisition cards from National Instruments, such testing can be done in days.
The Prototype In-Car Configuration
Delphi Automotive Design Engineer Gary Fulks configured a system of VisSim running on a laptop with two PCMCIA DAC Card 1200s, 16 analog inputs, 4 analog outputs and 16 digital I/Os. With their complex control system, they achieved closed-loop sampling rates of over 200Hz running a 100MHz Pentium laptop. VisSim/Real-TimePRO is capable of closed-loop sampling rates of up to 20000Hz depending upon the complexity of the closed-loop system and the CPU speed.
In the test car at Delphi, control wires were duct taped to the vehicle, and the laptop with VisSim was secured to the passenger seat of the car. Gary drove around the test track, stomping on the brake to demonstrate his algorithm running on the laptop. Very impressive. Also a fun job to have at Delphi.
HIL Control and Data Logging
Closed-loop control as well as data logging can easily be developed and configured with VisSim. Once the sensors and equipment under test are installed in the vehicle, it is a simple matter to mount the laptop in the passenger seat, secured with a standard 2" nylon web tie-down, then plug in the ribbon cables to the DAQ Card 1200s, and turn on the laptop. Because it is difficult to view the laptop display during daylight driving, an LED display panel, driven by the digital I/O of the DAQ Card, is used for critical function monitoring. Five-minute runs with stripcharts tracking user inputs, pedal pressures, accelerations, and controller outputs are typical.
In over a year of use, VisSim has never failed during a real-time run. The system has proven robust under the harsh demands of vigorous brake testing, lack of good electrical ground, wide temperature and humidity variations common to Ohio, and general garage lab treatment.
VisSim is also used in lab bench situations, such as automated performance testing of hydraulic valves. Using map blocks, it is easy to create time-based test sequences and correlate sensor outputs with command inputs. The wide array of plotting capability and data export makes it easy for data analysis. VisSim has been an important addition to the set of tools for automotive design and test at Delphi.
Download the Anti-lock Braking Model
If you are signed in, you can download the dynamic VisSim model below. It uses PID control of brake torque to maintain tire slip at the optimal point to maximize braking torque. Tire friction is determined via a mu-slip look-up table "mu-slip.txt". The built-in VisSim global optimizer is used to find PID coefficients that give shortest stopping distance.