LMS Imagine.Lab Driving Dynamics: Steering Systems Solutions Marc Alirand BizDev Driving Dynamics 1D division
Building a real time model of a hydraulic steering system Using AMESim Know-How The rendering of the hydraulic steering system was not sufficient for taking care of on centre feeling. The customer asked LMS Imagine to improve its internal tool thanks to Hydraulic knowledge in AMESim. Dynamic effect was first analysed in AMESim, secondly coded into C s-function and the new model was validated against experiments. Couple volant [N.m] 10 5 0-5 mesure modèle Page 2 2013-09-24-10 -1-0.5 0 0.5 1 Angle volant [rad]
Application #1 Hydraulic steering systems Goal: Explore low frequency vibrations like judder or nibble. A recognized state-of-the-art software in Hydraulics to model the piping circuit (rigid and hose), the rotary valve and the cylinder. Interfaces to most of the 3D MBS software for the suspension geometry Extended friction models to enable matching the Physics and thus induced vibrations. friction valve input pressure for... torque around Z (complex) a Y force (simple) housing rack housing connection Page 3 2013-09-24
Application #2 Electro hydraulic steering systems Goal: Assess the transition between hydraulic and electric steering with EHPS systems. The Active Front Steering system: a clear multi disciplinary approach when taking care of the electric drive and planetary gear set for variable ratio in parking manoeuver coupled with the hydraulic assistance, Functional or detailed view of the electric motor driving the pump in case of EHPS. First view of the controller to drive the motor. Page 4 2013-09-24
Standard structure of an electric steering system Column/Pinion/Rack Assist A hierarchy inside the controllers and what does what A control logic dedicated to control the torque assistance. A control logic dedicated to control the motor current. An adaptive offer (model complexity) that depends on the supplier or OEM needs. Torque Control Additional Compensations Vehicle velocity Torque from torque sensor 0 Iqin Idin PI PI Uq Ud Inverse Park Transform Uu, Uv, Uw PWM Inverter Motor Steering Gear θmeas Idmeas Park Transform Ivmeas Iqmeas Iumeas Current Control Page 5 2013-09-24
Application #3 EPS Scalability for functional or detailed analyses Goal: Different analyses require different model assumptions implying modeling scalability. Under hood motor with heat influence on motor performances may be of interest. Take advantages of a software able to go from power electrics and controller (Field control) to simple current control involving the technology of the motor to very simple functional approach of the electric motor. Page 6 2013-09-24
Application #4 EPS Gearing and reducer for steering systems Goal: Tackle any technologies of electric steering systems. Use the 1D mechanical library and its advanced friction models as well as screw-nut and worm gear models for reversibility and worm shaft possible translation. Handles belt drive system with cable and pulley as a first functional modelling approach. Page 7 2013-09-24
Application #5 EPS Testing the control logic with more Physics Goal: Include more Physics to test the control logic of your EPS Take benefit of existing and validated models to introduce design variability of the motor technology with thermal dependencies and gearing systems in your control logic testing using simple interface to Simulink (real time capability). Page 8 2013-09-24
AMESim Demonstrator Page 9 2013-09-24
Connections to the vehicle: rack and steering angle The suspension geometry allows going from the rack displacement to the wheel steering angle. This is the way for AMESim to take care of caster angle/offset for the steering system. If the customer is not interested in the vehicle itself but in the previous geometry contributions, the 1D Mechanical library can be used. ( z, y n, z opp) z y (, n,0) z z y y Action/Reaction Principle & Power Conservation Fz M z z Fyr M y r n z n Page 10 2013-09-24
Connections to the vehicle: rack and steering angle To have access to the right forces in car park maneuvers with the Van Der Jagt effect, Modularity in suspension modeling for including Jacking effects when steering Z K Z ( z, y ) K rack dz dt K Z z K z Z y K r y r Page 11 2013-09-24 Action/Reaction Principle & Power Conservation Z K Fz z Z Fyr y K r F K F K
Steering system parameters influencing the most on-center driver feeling Which are the parameters influencing the most the quality of a steering system from an OEM point of view? Which are the criteria to be considered? Since we are considering on center driver feeling analysis, the vehicle has to be taken into account. Page 12 2013-09-24
Steering system parameters influencing the most on-center driver feeling Maneuvers of Concerned The idea was to analyse two criteria more or less linked to almost the same feeling and not two criteria linked to a compromise to be reached. The compromise has been left to the OEM. Criteria and Measurements P 1 P 2 The definition of the criteria uses some post processing in the AMESim sketch plus the Export Setup facility. Page 13 2013-09-24
Steering system parameters influencing the most on-center driver feeling Parameters The analysis will focus on the contribution of 4 friction forces, the rack/pinion ratio, the pump characteristics, the valve cross section, the column stiffness. Optimization A Monte Carlo analysis to find the parameter (V vector) contributions in the two criteria (Note). Criteria = V T.Q.V A RSM to match the results and easily analyse the contributions. The Q matrix contains the coefficient of the polynomial functions of the RSM. The RSM give the weight of the parameter contribution and its variations allowing to know which are the parameters that are the most relevant for the two criteria. Page 14 2013-09-24
Integrating the EPS and ESP control logic to the vehicle model to validate the controllers Steering system parameter validation versus static experiments. Steering system analysis on a K&C test rig. Coupling the ESP, the EPS to the vehicle model for on road tests. ABS/ESP supplier Controller Problem Posing Vehicle post processing EPS Supplier Controller Rear Vertical Suspension Page 15 2013-09-24 Vehicle Model TNO Tire Model Aerodynamics Model
Integrating the EPS and ESP control logic to the vehicle model to validate the controllers Difficulties to identify all the parameters of the steering system but importance of worm gear reversibility. Page 16 2013-09-24
How to manage mechanical vibrations GUIDANCE tests: the steering wheel angle is imposed, the tires are simulated with springs Tire Simulated Force Rack displacement Steering System Steering Torque Steering Angle T Y Sensor rack?? SteerWheel DISTURBANCE tests: the force is imposed to the rack and the steering wheel angle is free. Rack Force Rack displacement Steering System Steering Angle Acceleration No Driver Torque T SteerWheel Sensor?? F rack The rotary velocity of the motor is also sensed. Page 17 2013-09-24
How to manage mechanical vibrations Only a mechanical view easily understandable and portable since the model does not consider any assistance (assistance in Simulink) Since only Signal & Mechanical libraries are used, pay for only a standard AMESim license. Take the advantage of a Design Exploration integrated tool with Export Setup to prepare the parameters and criteria for doing DOE, sensitivity analyses, parameter identification or optimization. Page 18 2013-09-24
How to manage mechanical vibrations Friction Models For low force input (even lower than the rack friction force) the type of friction model will allow force transmission in stiction of not. Simple to complex friction models (Karnopp, Reset/Integrator, Dahl and LuGre) depending on the expected rendering. Page 19 2013-09-24
How to manage mechanical vibrations optimization for DISTURBANCE and GUIDANCE tests and for different levels of force inputs. An in-phase motion of the steering wheel and the motor at low frequency and an out-of-phase motion at the resonance (around 15 Hz). The motor necessary has a node of zero velocity with extra contribution of the worm gear assembly. Page 20 2013-09-24
How to manage mechanical vibrations Worm Gear Contributions The worm wheel can still rotate around the node (no motion of the motor inertia) thanks to the Belleville washer assembly (stiffness and hysteresis). The worm shaft can translate under tire force inputs bringing steering wheel to be shacked. A clear coupling between the rotation and the translation of the worm gear that plays a role in steering feel. Page 21 2013-09-24
Application #8 Rear steering system with electric actuator Goal: Assess the actuation capability of the electric motor and reducer to pilot the rear suspension toe and camber angles, Connecting a MBS model of the suspension allows to verify the motor and reducer sizing and the potential dynamic couplings of the two systems. Page 22 2013-09-24 2012-01-0974 2012-01-0550
AMESim model from a Steering supplier Page 23 2013-09-24
References in Steering Systems Published papers and presentations Wintrebert E, Alirand M., Coupling study of the Mechanics of the front suspension with the Hydraulics of a power assisted steering systems, SIA Conference on Hydraulics and Transportation, Roanne, France, 1999, p 1-7 Schuster M., Simulation of power steering system using AMESim, European AMESim Users Conference, Paris, France, 2000, Alirand M., Lebrun M., Richards C., Front wheel vibrations A hydraulic point of view, SAE Paper n 2001-01- 0490, 2001, pp 1-14 Warinner, Bires., Lanhart., Chassis application of AMESim, North American AMESim Users Conference, Detroit, MI, 2004, Rommel B., The use of AMESim to model electromechanical power steering (EPS) systems, European AMESim Users Conference, Strasbourg, France, 2006, Alirand M., Petrucelli L., Barale E., From hydraulic to electric steering system: conceptual modeling and impact on fuel economy, 5 th Int. Conference on Advanced Chassis Systems, October 2010, Torino, Italy Ramirez Ruis I., Fricke D., Stachel D., Garcia J., A 6 DOF Bench Test on a New Active Kinematics Rear Suspension for Functional Development, SAE paper n 2012-01-0550, 2012, pp 1-8 Ramirez Ruis I., High Performance Electromechanical Actuator for Active Rear Axle Kinematics of a Sports Car, SAE Paper n 2012-01-0974, 2012, pp 1-15 Page 24 2013-09-24
Thank you Steering Systems Solution