Development and Implementation of a Powertrain Electrical System Simulator with Computer-Controlled Fault Generation

To manage the function of a vehicle’s engine, transmission, and related subsystems, almost all modern vehicles make use of one or more electronic controllers running embedded software, henceforth referred to as a Powertrain Controller System or PCS. Fully validating this PCS is a necessary step of vehicle development, and the validation process requires extensive amounts of testing. Within the automotive industry, more and more of this validation testing is being performed using Hardware-in-the-Loop (HIL) simulators to automate the extensive test sequences. A HIL simulation typically mates the physical PCS to a closed-loop real time computer simulation of a powertrain. Interfacing the physical PCS hardware to a powertrain simulation requires the HIL simulator to have extensive signal input/output (I/O) electronics and simulated actuator electrical loading. To accomplish this needed interface with off-the-shelf I/O devices and to provide needed automated faulting of actuator loads, Ford's VPACS-HIL simulator development has led to the creation of the CAPESS electrical load system. The CAPESS is a computercontrolled, automatic, powertrain electrical system simulator. The CAPESS combines a user-defined collection of load boards in a standard rack-mount chassis. The CAPESS receives configuration and fault instructions from an external computer via a simple networking interface, but has on-board automatic protection to provide high-speed response to any failure conditions. Currently there are two forms of a load board – a standard load board and an ignition spark-coil load board. Both types of load board use solid-state circuitry, contain on-board signal processing, and allow the user to rapidly reconfigure electrical loads. Since implemented in 2000, the CAPESS has functioned very well as a key element of Ford's VPACS-HIL powertrain simulator. This paper will describe the structure, functions, and features of the CAPESS. Lessons learned in the design process and technologies employed in the design will be presented as well. INTRODUCTION To support the testing of complex Powertrain Controller Systems (PCS), Ford Motor Company has for some time supported the development of Hardware-in-the-Loop (HIL) test environments. In particular, the VPACS-HIL powertrain simulator is the result of extensive development efforts, with most of the early focus directed in two areas: creating powertrain models that can execute in real-time, and designing an I/O system that can properly interface to a physical PCS. The function of these primary VPACS-HIL simulation elements has been previously examined [1,2]. Another necessary element is equivalent actuator electrical loading, which presents PCS electrical sensing circuitry with appropriate electrical impedances. This avoids unintended PCS detection of electrical faults. In early implementations of the VPACS-HIL system, two standalone electrical load boxes contained the equivalent actuator electrical loads: a standard load box contained a series of fixed resistive and inductive loads mounted to boards, while a spark-coil box contained a fixed set of spark plug charging coils. Both load boxes included some modest signal processing circuitry that converted actuator driving signals to input state signals that are compatible with off-the-shelf I/O devices. As the role of the VPACS-HIL system was refined to target PCS design-validation testing, including the key area of OBD (On-Board Diagnostics) validation, it was clear that the current load boxes were not sufficient. There were several main goals of a next-generation actuator electrical load simulator: provide the ability to generate all needed actuator electrical fault modes under computer control, create a modular and expandable load system that is easy to configure, and incorporate robust system electronics and layers of protection that will ensure long-lasting and safe operation. This nextgeneration electrical load simulator also had to work with existing VPACS-HIL simulators without any significant modification. 2006-01-1599 Development and Implementation of a Powertrain Electrical System Simulator with Computer-Controlled Fault Generation Changjiang Wang and Tim Cardanha Ford Motor Company David D. Wentzloff Massachusetts Institute of Technology Copyright © 2006 SAE International The resulting system has been named the CAPESS – Computer-controlled, Automatic, Powertrain Electrical System Simulator. Each CAPESS consists of a standard form-factor chassis containing a combination of three types of printed circuit boards: a single central processing / control board, standard load boards, and spark-coil load boards. All actuator electrical loads for a given PCS are provided by a user-specified combination of standard electrical load boards (providing resistive and/or inductive loads) and spark-coil load boards. The remainder of this paper will detail the CAPESS’ design and lessons learned during the development process, and will describe the resulting robust performance of the CAPESS during extensive use on multiple VPACS-HIL installations. HARDWARE DEVELOPMENT The hardware development process for the electrical system simulator had to address several important goals: functioning with all current and all foreseen future VPACS-HIL simulator designs, generating all needed actuator electrical operating modes and fault modes, flexibly providing all needed types of loads, and reliably running without human presence for many hours at a time. Initial development brainstorming and competitive benchmarking led to selecting a hardware framework consisting of a standard computer chassis with a backplane, holding a collection of circuit boards. Each load board would contain the equivalent actuator electrical loads as well as all needed fault insertion switching and all supporting circuitry for switch control, signal conditioning, and safety protections. A single central processing board would control the operation of all load boards, based on control instructions received from the primary simulation computer. Based on existing VPACS-HIL equipment form factors and an evaluation of backplane and circuit board space requirements, a standard 6U (1U = 1.75 inches) high, 320-mm deep, 19-inch wide rack-mount chassis was selected. Initial development intent was to develop a single load board that would support all actuator electrical loads, but unique signal conditioning requirements led to the development of two separate load boards: a standard load board is used to provide appropriate loads to most PCS output drivers, while a spark-coil load board is specially designed to load the PCS ignition drivers. Fig. 1 illustrates the resulting CAPESS board arrangement, as well as the final backplane assignment: a custom-defined VME bus was adopted for both communication between boards and for power distribution. Fig. 1: Schematic of a full CAPESS installation. For a number of reasons, including available board surface area and grouping convenience, each standard load board and spark-coil load board was laid out with eight channels. Within a given type of load board, all eight channels have identical circuit layouts. For both types of load boards, each channel has two essential elements supporting the primary load circuit: an extended H-bridge switching circuit, and signal conditioning circuitry. The common H-bridge switching implementation is detailed below, while each load board type’s signal conditioning circuitry is detailed in later sections.