Collision Avoidance System Field Operational Test
6 BRAKE CONTROL SYSTEM (Task B3)
6.1 Brake System Development
The objective of this task is to replace the Original Equipment Manufacturer’s (OEM) brake components in FOT deployment vehicles with Delphi Chassis and Energy Systems hardware and software that meets the FOT requirements.
The ACAS brake system will be a DBC 7.2 System that provides state-of-the art, full performance, wheel lock control to optimize the vehicle car stopping distances while maintaining the electrical and diagnostic interface. The development of brake controls to meet both the vehicle requirements and the ACAS/FOT program requirements are being accomplished through common best engineering practices at Delphi. The safety analysis and vehicle level verification of the brake system will be accomplished to ensure production-level confidence the brake system. The brake system will include an "autobraking" feature in addition to the braking features and functions that were previously on the vehicle before replacement with the Delphi Brake System.
Milestones and Deliverables
The brake system design milestone is completed. This work was accomplished as a result of laboratory testing with hardware-in-the loop. Testing of the brake controls design for the autobraking feature using a dedicated chassis mule has been performed. The installation of hardware on the Prototype mule has been conducted with plans to update the hardware and software with production release levels after testing and calibration for the Buick.
Deliverable Number 9, the Brake Actuator System Design Summary report dated June 30, 2000 has been provided to NHTSA.
This section describes how functional requirements are accomplished using the DBC 7.2 System. The programs utilizes a dedicated vehicle identical to the prototype vehicle to conduct the brake systems development, system verification and vehicle level testing.
The hydraulic modulator unit (HCU) of DBC 7.2 incorporates Anti-lock Brake (ABS), Traction Control (TCS) and vehicle stability enhancement and provides pressure modulation capabilities into the vehicle base brake system. The major components of the modulator are: a casting/body with internal cross drills and an Electro-Hydraulic pump and motor.
An electronic control unit (ECU) of DBC 7.2 contains a microprocessor-based device that controls the hydraulic modulator in a manner that allows all vehicle requirements to be satisfied. The includes the following physical content:
The ECU processes the input signals and converts them to digital form. The control algorithms are stored in non-volatile memory to achieve the vehicle performance requirements. The ECU performs diagnostic checks on internal and external hardware. It stores fault codes in non-volatile memory when a fault is detected. The ECU converts control commands to physical outputs (pulse width modulation control). It is assembled to the HCU to meet all vehicle performance requirements relative to the vehicle environment.
In addition to ABS and TCS the brake system provides a capability which aids the driver over a wide range of driving conditions and maneuvers. This vehicle stability feature, hereafter designated Traxxar, helps the driver to maintain the intended path during oversteer or understeer conditions.
Figure 6.1 depicts the HCU/ECU and the vehicle level of integration. The wheel speed, yaw rate / lateral accelerometer and steering angle sensors are inputs to the ECU for the algorithms. The hydraulic paths to each brake corner are indicated and the communications link to the power train controller for engine communications.
6.1 HCU/ECU and Vehicle Level of Integration
System Performance and Interfaces
The DBC 7.2 ABS/TCS/Traxxar System provides state-of-the-art, full performance, wheel lock control to optimize stopping distance, steerability, and vehicle stability along with acceleration slip control to optimize vehicle launch and traction capabilities. In addition, the Traxxar System is capable of correcting vehicle over- and understeer conditions, with or without driver braking, to significantly improve overall vehicle safety. The brake system shall also perform an autobraking function based upon decel commands from the Adaptive Control Processor and vehicle control algorithm. This autobraking function is very limited relative to absolute deceleration authority achieved by the vehicle. The autobraking feature is achieved based upon an open-loop control strategy where the ACC processor issues the braking request over a Class 2 communication protocol.
The DBC 7.2 system uses a fully sealed connector for all signal and power interfaces. The pin assignments are documented by production drawings for this program. The harness connector uses a mechanical assist mechanism to reduce the insertion force and is oriented for upward modulator installation in the vehicle. The system power is provided by battery voltage and the ECU monitors the battery supply for acceptable levels of voltage. Battery inputs are used to supply power to the electronics, the pump motor and solenoids. System diagnostics enable and disable functions per production specifications for operating voltage ranges.
The brake system includes two power grounds. The pump motor uses a vehicle power ground and the other ground for all other devices including the internal solenoids. The ECU has the capability to communicate with other vehicle systems, sensors, and offboard diagnostic test equipment. Specific software messages are designed to pass back and forth to the ACC processor. These messages contain brake control, status, sensor, and diagnostic information as appropriate.
The DBC 7.2 system provides the indication to the brake lamp relay during autonomous braking. During the autobraking scenarios a high side drive output drives the brake lamp relay which results in the brake lamps being lit during the autobraking function. Figure 6.2 shows high-level system interface block diagram.
Figure 6.2 System Interface Block Diagram6.2 System Verification
During system development, verification of the DBC 7.2 system is conducted per industry and federally regulated standards. The brake system is classified as a safety critical system and thus treated accordingly.
The scope and purpose of this test is to determine if the messages are sent by the software at the specified rate. The test setup follows specific test procedures to test the applicable software version such that the communication bus is monitored for message transmissions. Delphi Engineering practices for production programs for brake system verification are followed.
The communication interface between the DBC 7.2 brake system and the vehicle was tested on the functional bench during the design and development phases. This test setup incorporates hardware-in-the-loop to simulate sensor inputs for control algorithm testing. An example of a typical test consists of verification of message periodicity.
A second phase of brake system verification occurred at the vehicle level. The vehicle level tests were conducted in full compliance with the FMVSS Requirements. Additionally, an ABS/TCS/Traxxar/ACC test and verification plan for the ACAS/FOT program was used to direct the maneuvers to be performed and the test surfaces on which the tests were performed.
The vehicle level testing of the brake system will be conducted on a dedicated mule vehicle which is identical to the ACAS/FOT Prototype vehicle. This engineering development vehicle has identical brake hardware and performance capabilities. This vehicle is dedicated to support brake system development, testing, and verification of ACAS/FOT braking requirements. Corrective actions will be taken as necessary to ensure that all quantitative targets are met.
6.3 Vehicle Builds
Development and refinement of the ACAS brake system for integration into the final vehicles.
Both the chassis mule and the prototype vehicles have the Delphi Brake System integrated on the vehicle. The release level of hardware is identical on both vehicles and significant production testing for production programs has occurred over the past two years. The calibration and tuning of the brake system for this program is the central focus. The engineering mule contains instrumentation used for calibration and data collection. This vehicle will be utilized as a resource for development and testing in support for the prototype vehicle.
The initial build of prototype vehicle with the Delphi brake system is complete. Work completed includes:
This vehicle will be updated with an integral ECU and the harness will be removed. The software will be flashed in the ECU. The rapid prototyping hardware will also be removed from prototype vehicle trunk. In summary, the brake system will all be contained underhood within the engine compartment of the prototype vehicle.
Plans are in place to update the prototype hardware toward the end of the third quarter 2000. Additional details for brake system integration, calibration and testing are provided in the Gantt Chart in Figure 6.3.
Plans through December 2000 for Task B3
Testing and calibration of the software package on the Chassis Brake Engineering vehicle will be the primary focus over the next six months. The objective shall be to provide a production software package that meets vehicle requirements for a safe, reliable, smooth and quiet brake system. Engineering support for specific areas within Delphi such as ABS, TCS, Vehicle Stability Enhancement, and calibration engineering will support achieving standard brake system metrics and requirements. Approved software releases resulting from the above tests shall be used to support and update the ACAS/FOT prototype vehicle per the master schedule.
6.3 Task B3 Schedule
[TITLE PAGE] [TABLE OF CONTENTS]
[1 Executive Summary] [2 Introduction] [3 System Integration] [4 Forward Radar Sensor]
[5 Forward Vision Sensor] [6 Brake Control System] [7 Throttle Control System]
[8 Driver-Vehicle Interface] [9 Data Fusion] [10 Tracking & Identification] [11 CW Function]
[12 ACC Function] [13 Fleet Vehicle Build] [14 Field Operational Test]
[Appendix A] [Acronyms]