SECTION 5 Full Vehicle Analysis

Topics Covered Analysis Communicators Preparation for Quasi-Statics Driveline Demo model

Communicators In this section, more detailed information is given about how to setup the powertrain/driveline model for an Adams/Car full vehicle SDI analysis, including a Quasi-Static setup. In order to communicate with the Adams/Car full vehicle SDI test-rig, a number of input communicators has to be fed to it. In the online help under section Working with Communicators”, all input communicators to the SDI testrig are listed. In the table below only those that are related to the powertrain/driveline are presented. The last column shows the communicators which are the minimum requirement for running Driving Machine closed loop events (referred to as “machine” controlled events). The other communicators are only needed for the Driving Machine Smart-Driver events. In these events a low degree of freedom (DOF) vehicle model pre-calculates a speed trajectory profile based on the vehicle limit values. The low DOF vehicle model needs additional information about the full vehicle and powertrain properties.

Communicators input communicator Class Minor role Recieves Min Requirement for machine closed loop events cis_crankshaft_ratio parameter_real any   cis_diff_ratio Real parameter variable for final drive ratio, from the powertrain subsystem. cis_drive_torque_bias_front cis_engine_idle_rpm cis_engine_revlimit_rpm cis_engine_rpm solver_variable Adams/Solver variable for engine revolute speed, in rotations per minute, from the powertrain subsystem. yes cis_engine_speed Adams/Solver variable for engine revolute speed, in radians per second, from the powertrain subsystem. cis_engine_map spline Engine torque map from powertrain subsystem. cis_max_engine_braking_torque Engine torque at zero throttle cis_max_engine_driving_torque Engine torque at full throttle (100%)

Communicators cis_max_engine_speed parameter_real any Output from powertrain subsystem (maximum engine rpm value). yes cis_max_gears parameter_integer Output from powertrain (maximum number of allowed gears). cis_min_engine_speed Output from powertrain subsystem (minimum engine rpm value, used for shifting strategy). cis_transmission_efficiency   cis_transmission_input_omega solver_variable The transmission input engine variable from the powertrain template. Expressed in radians per second cis_transmission_spline spline Spline for transmission gears (output from powertrain: reduction ratios for every gear).

Preparation for Quasi-Statics The approach to support Quasi-Static setup for an Adams/Driveline model that uses an ac_dyno element to apply the engine torque, is to modify the state variable rpm_input. This state variable calculates the engine speed in revolutions per minute and is normally used when calculating the engine torque in a dynamic analysis. But if the requirements below are satisfied, the torque calculations also become valid in Quasi-Static setup equilibrium analyses.

Preparation for Quasi-Statics There are in total three requirements that need to be fulfilled in order to support Quasi-Static setup analysis when using an ac_dyno to drive the engine: There must be only one active ac_dyno present in the assembly The ac_dyno element is required to be setup as per below: Dyno type = Torque Function type = Throttle Demand An output communicator with the matching name “engine_rpm_sse” (engine rpm steady state equilibrium) has to exist in the model.

Preparation for Quasi-Statics If an ac_dyno is not used in the assembly, that is, you have modeled your own engine torque implementation, you are still able to use the Quasi-Static setup capability if the following conventions are applied: The engine torque has to be dependent on throttle demand and engine speed. Throttle demand value of 100 should produce maximum engine torque for the specific engine speed. Engine speed expression used in the engine torque calculation needs to be setup in a way that it is still valid in the Quasi-Static setup analysis. The user can use the modified rpm_input state variable expression. A recommendation is also to use the wheel speeds that are calculated in the way that is done in the shared Adams/Driveline brake system template. It is required that the different powertrain/driveline components properly inherit the calculated Quasi-Static wheel speeds in the initial velocity analysis. This can be accomplished by correctly setting up the initial condition motions.

Driveline Demo Model In the Adams/Driveline shared database, the full vehicle assembly JEEP_RWD_SDI.asy is prepared for Adams/Car SDI analysis. Here are the used subsystems and templates in the demo vehicle Overview of these systems in the assembly is shown. The powertrain/driveline related communication from and to the full vehicle SDI test-rig and the internal communication used for the Quasi-Static setup is presented as well. The green “In” arrows shows communicators to a certain subsystem while the blue “Out” arrows lists the information sent from the subsystem.

Demo Model

Brake System Brake system Starting from the brake system, calls are made to the VAR1004 subroutine that calculates the wheel speeds values during the Quasi-Static setup equilibrium phase. These speed values are then published to other subsystem via the output communicators listed below: left_front_wheel_omega right_front_wheel_omega left_rear_wheel_omega right_rear_wheel_omega The inputs to the brake system are mainly brake_demand (received from the SDI testrig) and the tire forces (from the wheel templates). The id’s of the tire forces are passed as parameters in the VAR1004 calls

Driveline Driveline This rear-wheel drive model uses the rear wheel speeds from the brake system to calculate the transmission output speed to be used in the Quasi-Static setup analysis phase, as per the equation below: transmission_output_omega_sse = (left_rear_wheel_omega+right_rear_wheel_omega)/2*diff_ratio The transmission output shaft speed is then communicated to other subsystems (used in the engine system in this case). Another output from this system is the diff_ratio which is used by SDI testrig. The diff_ratio parameter value is taken from the reduction gear ratio set in the differential gear arrangement Note that the transmission output speed (that is, the speed of the input propeller shaft) in equation above is not used in any dynamic analysis, where the speed is instead determined by dynamic torque from the gearbox, resistance torque from the differential gear parts, inertia and compliance effects of the propeller shaft, different lash effects, and so on.

Gearbox and Engine Gearbox The gearbox model uses the transmission_demand and clutch_demand from the SDI testrig and publishes to the testrig the gear ratios for all gear positions (transmission_spline), highest gear position number (max_gears) and a scalar value between 0 and 1 which represent a transmission efficiency value.This value is used in (Driving Machine) SmartDriver events. The gearbox input shaft speed (transmission_input_omega) is published to the SDI testrig as well. Since this gearbox does not switch gears during the quasi-static simulation, the transmission_demand information is only used to calculate the gear ratio value (gear_ratio) for the initial gear position. This value is used in the Quasi-Static setup analysis by the engine subsystem.

Gearbox and Engine Engine The engine template has in this case the largest portion of the powertrain/driveline related communication with the SDI testrig. The input from the SDI testrig to the engine is the throttle demand (throttle_ demand) while it publishes information different dynamic engine speed and engine torque quantities. In the Quasi-Static setup analysis, the engine speed is calculated as below: engine_rpm_sse = gear_ratio * transmission_output_omega_sse where the gear_ratio parameter value is received from the gearbox subsystem and the Quasi-Static speed of the transmission output shaft (transmission_output_omega_sse) comes from the driveline subsystem