ASM Brake Hydraulics Model dspace Automotive Simulation Models ASM Brake Hydraulics Model dspace
Automotive Simulation Models ASM Brake Hydraulics Model Real-time brake hydraulics model Key Features Open MATLAB /Simulink model Real-time simulation and offline simulation Complete hydraulics system with full ESP support Description Application Areas The ASM Brake Hydraulics Model is an open Simulink model that simulates the brake hydraulics system required for vehicle dynamics controls like ABS (Antilock Brake System), TCS (Traction Control System), and ESP (Electronic Stability Program). It is typically used together with a vehicle model on a dspace Simulator for hardware-in-the-loop testing of the vehicle s ESP electronic control unit (which usually includes ABS and TCS) or during the design phase of ESP controller algorithms for early validation by offline simulation. Key Benefits All the Simulink blocks in the model are visible, so it is easy to add or replace components with custom models to adapt the brake hydraulics properties perfectly to individual projects. The ASM Brake Hydraulics Model is a complete hydraulics system that includes all the features and functions required for ESP controls. The model can be parameterized completely via ModelDesk s graphical user interface and takes full advantage of ModelDesk s comprehensive parameter management and handling features. Simulation Model Characteristics The modeled ESP braking system consists of a dual-circuit hydraulics system. The model contains all the components like valves, chambers, accumulators, and braking cylinders that are necessary for simulating a standard state-ofthe-art ESP braking system (for example, Bosch, ContinentalTeves, TRW). Offline and Online Simulation The ASM Brake Hydraulics Model can be used in combination with real controllers in a hardware-in-the-loop environment (HIL or online mode), or it can be used for simulating an ESP braking system in combination with software controller algorithms (PC or offline mode). The model supports real-time code generation via Real-Time Workshop from The MathWorks and dspace s RTI for online simulation on a dspace real time system. 2
Brake Hydraulics Model Main Features and Benefits Feature Description Benefit Open Simulink model All model blocks are visible Custom models can easily be added or used to replace model components ModelDesk Graphical user interface with parameter management Easy parameter handling and management Online simulation Real-time simulation on real-time hardware Hardware-in-the-loop simulations with ECUs Offline simulation Simulations as early as the design phase Controller validation in early development stages ASMSignalBus Online tunable parameters Model interoperability Simulation signals are part of a structured Simulink signal bus Direct parameter access during real-time simulations ASM models are easy to combine to create a virtual vehicle Standardized and fast access to model variables (p. 8) Online parameter optimizations and behavior studies (p. 9) An entire virtual vehicle can be simulated (p. 10) Order Information Order Number ASM Brake Hydraulics Model ASM_L_BH Relevant Software and Hardware Hardware Required Minimum system Pentium 3 processor, 800 MHz 512 MB RAM Recommended system dspace Simulator, equipped with Pentium 4 processor, 1.4 GHz or higher Memory 1024 MB RAM DS1005 or DS1006 Software for Online Simulation Required Integrated development environment MATLAB /Simulink from The MathWorks Real-Time Workshop dspace implementation software Real-Time Interface (RTI) dspace experiment software ControlDesk dspace experiment software ModelDesk Operating system www.dspace.com/goto?os_compatibility Optional Other dspace ASM Packages Software for Offline Simulation Required Integrated development environment MATLAB /Simulink from The MathWorks dspace experiment software ModelDesk Operating system www.dspace.com/goto?os_compatibility Optional Other dspace ASM Packages 3
Automotive Simulation Models ASM Brake Hydraulics Feature Overview Features at a Glance Contains all the components of a state-ofthe-art ESP braking system Linear and physical master brake cylinder model Valves with continuously controllable cross-sections Nonlinear, look-up-table-based wheel brake cylinder Offline and online simulation Real-time capable Graphical user interface for parameterization Easy to insert in ASMVehicleDynamics Numerical integration stabilized via local oversampling Modular, library-based implementation Easy variable access Fully integrated into dspace tool chain Brake Hydraulics Model Hydraulics Model Concept The brake hydraulics model consists of the master brake cylinder and the two independent braking circuits. The braking circuit system calculates the pressure in each wheel brake cylinder. Master Brake Cylinder Pre-Charge Valve 1 Change-Over Valve 1 Change-Over Valve 2 Pre-Charge Valve 2 Damper Chamber 1 Pump 1 M Damper Chamber 2 Pump 2 Connection Chamber 1 Connection Chamber 2 Non-Return Valve Reservoir 1 Non-Return Valve Reservoir 2 Reservoir 1 Reservoir 2 Inlet Valve FL Inlet Valve RR Inlet Valve RL Inlet Valve FR Non-Return Valve FL Non-Return Valve RR Non-Return Valve RL Non-Return Valve FR Outlet Valve FL Outlet Valve RR Outlet Valve RL Outlet Valve FR Brake Cylinder FL Brake Cylinder RR Brake Cylinder RL Brake Cylinder FR Schematics of the brake hydraulics. 4
Brake Hydraulics Model Master Brake Cylinder The master brake cylinder transforms the brake pedal position into a cylinder pressure. It consists of a cylinder with a piston that delivers pressure to both braking circuits. There are two models, one linear and one physical. The linear model can be used to convert the pedal position into a pressure directly, for example, if a brake pedal position of 70 percent must produce exactly 70 percent of the maximum braking pressure. The physical model can be used for realistic vehicle simulations or if the data measured for the brake pedal position is to be reused in simulations. Brake Hydraulics Model Components and Characteristics Linear model: Linear conversion of brake pedal position to cylinder pressure Physical model: Massless piston which can move longitudinally in the cylinder body One piston of the master brake cylinder. Hydraulic Valves Valves are used to control the flow of the hydraulic fluid. The flow control valves are modeled as orifices with continuously controllable cross-sections. Components and Characteristics All valves except the non-return valve have continuously controllable cross-sections Model based on the Bernoulli equation Different types of valves included Precharge valve with two different crosssections in the opening state. The crosssection depends on the pressure difference Change-over valve with pressure relief function in the closed state Inlet valve Outlet valve Non-return valve q1 q1 [cm³/s] q2 [cm³/s] p1 p2 Non-Return Valve RL q2 Inlet Valve RL p1 [bar] p2 [bar] q3 q3 [cm³/s] p3 Change-Over Valve p3 [bar] A selection of the valve systems: non-return, inlet, and change-over valves with their characteristics diagrams. 5
Automotive Simulation Models Brake Hydraulics Model Chambers and Accumulators The chamber is modeled as a fixed volume that is filled with a compressible fluid. Components and Characteristics Chamber with fixed volume filled with a compressible fluid, model based on the continuity law Hydropneumatic accumulator, model based on the Hagen-Poisson equation A damper camber. Wheel Brake Cylinder The wheel brake cylinder is based on a look-up table that calculates the cylinder pressure from the cylinder volume. Components and Characteristics Nonlinear Look-up-table based Graph of cylinder pressure versus cylinder volume. Hydraulics Pump The hydraulic pump transports brake fluid back from the accumulator to the master brake cylinder. Its second function is to deliver braking fluid to the inlet valves during active braking without driver intervention. Components and Characteristics Look-up-table based Damper Chamber Pump q p Hydraulics pump with damper chamber. 6
Brake Hydraulics Model Simulation Results The hydraulic model, executed in conjunction with a real ECU, generates a modulated pressure in each brake cylinder as the brake pressure rises. The vehicle model supplies the required wheel and vehicle speeds. Brake Hydraulics Model Graph of modulated cylinder pressure and the resulting wheel and vehicle speeds. Parameterization ModelDesk is a graphical user interface for intuitive model parameterization and parameter set management. It also provides project handling and allows parameter sets to be downloaded to offline and online simulations. Its overall look and feel, basic handling, and workflows are identical to those of other software tools from dspace. For manual parameter entry, ModelDesk provides parameter pages with illustrations for each component. Parameter Management in ModelDesk Parameter page for the precharge and change-over valves with graph of valve characteristics. 7
Automotive Simulation Models Technical Aspects Numerical Stability Subsystem Oversampling To quarantee numerically stable integration of submodels with stiff behavior, local subsystem oversampling is used. The Simulink For Iterator subsytem evaluates stiff differential equations n-times during one major simulation step. Subsystem oversampling for a step response of a first-order delay element. 200µs 200µs 200µs 200µs 200µs 1ms Signal and Parameter Management Parameters Sets The model is preconfigured with default data, so that all the tables and parameters have useful values and are fully functional. ASMSignalBus The ASMSignalBus comprises the relevant signals of all model components in a hierarchical structure. Signals for I/O access with an interface board or for display with a Simulink Scope can be chosen conveniently via a Simulink Bus- Selector. ASMSignalBus displays all the relevant signals in a clear structure. 8
Brake Hydraulics Model Parameters Tunable Online Every parameter in the model is implemented as a single constant block and can be tuned during real-time simulation on a dspace Simulator. ControlDesk provides access to the parameters in online mode. Signal and Parameter Management The brake hydraulics Simulink model with the main components and signals. 9
Automotive Simulation Models ASM Philosophy Concept Model Design Philosophy For optimum support of customer-specific requirements dspace has chosen an open model concept. This means that models are visible to users right down to the level of standard Simulink blocks. Thus the dspace Automotive Simulation Models provide enormous flexibility for projects that require dedicated simulation models. The open model approach allows perfect adaptation to individual projects and requirements. This can be achieved by modifying models or by replacing or adding components. Virtual Vehicle dspace Automotive Simulation Models are a collection of well coordinated models that you can easily combine to build anything from extended models to a whole virtual vehicle. As well as gasoline and diesel engines, there are models for vehicle dynamics and brake hydraulics. Combined models interoperate in one simulation. Several ASM packages can be combined to make up a virtual car. 10
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