Advanced Steering Design Options

Rack and Pinion Advanced Steering System, Rack and Pinion Tilt 3 Universal Joint Steering System, Relay and Pitman Advanced Steering System and Relay and Pitman Simple Steering System has various design options which can toggle various compliances and frictions in the steering system. Steering system consists of following design options.

In the Relay and Pitman Advanced Steering System and Relay and Pitman Simple Steering System, the steering gear can be switched from relay type to pitman type. This can be toggled by using parameter variable 'pvs_steering_gear_type'. Where, '1' and '2' are mapped to Relay and Pitman respectively.

Steering column to body compliance introduced damping in between steering column part and the body. This is achieved by using point torque 'pts_steering_column_to_body' actuator. This can be toggled by using parameter variable 'pvs_steering_column_body_compliance'. The damping value can be set by using parameter variable 'pvs_steer_column_to_body_damping'.

Steering column compliance is induced in between auxiliary steering column and steering column. An additional dummy part is introduced in between them for the compliance. The auxiliary steering column is connected with universal joint to the dummy part and dummy part is connected by revolute joint and point torque actuator to the steering column (Figure 1)

The steering column compliance can be of type Linear or Nonlinear. This can be toggled by using parameter variable 'pvs_steering_column_compliance'. Where, '0', '1' and '2' are mapped to None, Linear and Nonlinear respectively.

The point torque 'pts_steering_column_compliance' actuator introduce required torque depending upon the selection of the steering column compliance.

The parameters required for the compliance are torsional stiffness (gps_steering_column_comp_kt), torsional damping (gps_steering_column_comp_ct) and nonlinear spline (gss_steering_column_compliance). These are read from "steer_compliance.ste" file stored in steering_assist.tbl of the acar_concept database.

I-shaft compliance is introduced in between upper and lower intermediate shafts. This can be toggled by using parameter variable 'pvs_ishaft_compliance'. Where, '0', '1', '2' and '3' are mapped to None, Lash, Linear and Nonlinear respectively.

The point torque 'pts_ishaft_compliance' actuator introduce required torque depending upon the selection of the I-shaft compliance.

The parameters required for the compliance are:

- torsional stiffness (gps_ishaft_comp_kt),

- torsional damping (gps_ishaft_comp_ct) and

- nonlinear spline (gss_ishaft_compliance).

These are read from "steer_compliance.ste" file stored in steering_assist.tbl of the acar_concept database.

In the Rack and Pinion Tilt 3 Universal Joint Steering System the intermediate shaft compliance is divided into two separate design options upper and lower intermediate shaft compliance. This can be toggled individually by using parameter variable 'pvs_upper_intermediate_shaft_compliance' and 'pvs_lower_intermediate_shaft_compliance' for upper and lower intermediate shaft compliance respectively. Where, '0', '1' and '2' are mapped to None, Linear and Nonlinear respectively.

The point torque 'pts_upper_ishaft_compliance' and 'pts_lower_ishaft_compliance' actuators introduce required torque depending upon the selection of the choices of the upper and lower intermediate shaft compliances.

The parameters required for the compliance are:

- torsional stiffness (gps_upper_ishaft_comp_kt, gps_lower_ishaft_comp_kt),

- torsional damping (gps_upper_ishaft_comp_ct, gps_lower_ishaft_comp_ct) and

- nonlinear spline (gss_upper_ishaft_compliance, gss_lower_ishaft_compliance).

These are read from "steer_compliance.ste" file stored in steering_assist.tbl of the acar_concept database.

The lash is introduced between upper and lower intermediate shafts. This can be toggled by using parameter variable 'pvs_ishaft_compliance''. The point torque 'pts_ishaft_compliance' actuator introduces required torque depending upon the lash value that calculates output angle based on the 3D spline (gss_lash). You can specify the desired lash value and the nature of spline in the property file (steer_compliance.ste).

The lash is active if the 'gps_ishaft_lash' value is greater than zero.

The following diagram shows implementation of Intermediate shaft compliance and lash (Figure 2)

The column compliance is induced in between intermediate shaft lower and intermediate shaft lower dummy. This can be toggled by using parameter variable 'pvs_column_compliance'. Where, '0', '1' and '2' are mapped to None, Linear and Nonlinear respectively.

The point torque 'pts_column_compliance' actuator introduces required torque depending upon the selection of the choices of the column compliance.

The parameters required for the compliance are:

- torsional stiffness (gps_column_comp_kt),

- torsional damping (gps_column_comp_ct) and

- nonlinear spline (gss_column_compliance).

These are read from "steer_compliance.ste" file stored in steering_assist.tbl of the acar_concept database.

In the Relay and Pitman Advanced Steering System and Relay and Pitman Simple Steering System, shaft compliance is induced in between sector shaft and pitman arm. This can be toggled by using parameter variable 'pvs_shaft_compliance'. Where, '0' and '1' are mapped to Off and On respectively.

The torsion spring 'ues_shaft_compliance_relay' for relay and 'ues_shaft_compliance_pitman' for pitman configuration introduces required torque depending upon the stiffness and damping value.

The parameters required for the compliance are torsional stiffness, torsional damping or nonlinear spline which can be define itself in torsion spring. The variable 'pvs_shaft_compliance_stiffness' should be greater than '0.0' if the shaft compliance is 'on', else it will be considered as 'off'.

The 'pvs_shaft_compliance_stop_angle' value is used to apply torque through point torque 'pts_sector_shaft_stop_angle' if the sector shaft rotate through the specified value in either directions.

The modelling fidelity can be improved to accurately model on center handling, steering performance, and drift by turning on the friction. The friction between lower, upper u-joint and steering wheel can be activated by using parameter variable 'pvs_lower_ujoint_friction_active' for lower u-joint, 'pvs_upper_ujoint_friction_active' for upper u-joint and 'pvs_steering_wheel_friction_active' for steering wheel.

For Relay and Pitman Advanced Steering System and Relay and Pitman Simple Steering System additional friction forces related to steering gear are modeled. The friction between steering shaft, piston, sector shaft and idler arm can be activated by using parameter variable 'pvs_gear_input_friction' for housing to input shaft joint, 'pvs_piston_friction' for piston to gear housing joint, 'pvs_sector_shaft_friction' for sector to gear housing joint and 'pvs_idler_arm_friction' for idler to body joint. Idler arm friction can be used only if the pitman type gear configuration is selected.

You can modify the parameters of the friction 'frs_lower_ujoint', 'frs_upper_ujoint', 'frs_steering_wheel', 'frs_gear_input_friction', 'frs_piston_friction', 'frs_sector_shaft_friction' and 'frs_idler_arm_friction' selectively.

The compliance between rack housing and body/subframe can be improved by activating rack housing mid-mounts using parameter variable 'pvs_rack_housing_midmount'. Where, '0', '1' and '2' are mapped to None, Mid-Mount One and Mid-Mount Both. The position of the mid-mounts can be controlled by using hardpoints 'hps_rack_house_mid_mount_1' and 'hps_rack_house_mid_mount_2' respectively.

In the Rack and Pinion Tilt 3 Universal Joint Steering System the isolators are provided for upper and lower intermediate shaft. The upper and lower isolator can be individually activated using parameter variable 'pvs_upper_isolator' and 'pvs_lower_isolator' respectively. When the upper isolator is active the fixed joint between "upper_isolator_dummy" and "upper_ishaft_compliance" parts is replaced with the bushing. Similarly, lower isolator bushing is attached between "lower_isolator_dummy" and "intermediate_shaft_lower" parts.

In the Rack and Pinion Tilt 3 Universal Joint Steering System dash seal compliance option is provided. You can connect dash seal to support upper/lower intermediate shaft or steering shaft using switch part as per requirement. By default the dash seal compliance is active. You can toggle it by using parameter variable 'pvs_dash_seal_compliance'. If you deactivate the compliance then dash seal part is connected using fixed joint to the body if you use the steering in full-vehicle assemblies.

Also you can simulate real condition by activating the friction in dash seal compliance. This will induced friction between connected part and the dash seal part. You can toggle it by using parameter variable 'pvs_dash_seal_friction'.

To simulate the installation of steering column universal joints, your template based product offers the user optional specification of U-Joint phase angles. The user can specify 2 phase angles for Rack and Pinion Advanced Steering System and 3 phase angles for Rack and Pinion Tilt 3 Universal Joint Steering System.

For 2 U-joint phasing system the first phase angle applies to the upper u-joint, the second phase angle applies to the lower u-joint. Similarly, for 3 U-joint phasing system the first phase angle applies to the upper u-joint, the second phase angle applies to the middle u-joint and the third phase angle applies to lower u-joint.

The orientation is such that a positive angle indicates clockwise rotation of the u-joint looking down the steering column. The second phase angle is defined as being relative to the first phase angle (Figure 3) and the third phase angle is defined as being relative to second phase angle.

The U-joint phasing can be activated by using parameter variable 'pvs_ujoint_phase'. The angles can be specified using parameter variables 'pvs_u_joint_phase_angle_1', 'pvs_u_joint_phase_angle_2', 'pvs_u_joint_phase_angle_3' respectively.

In the Rack and Pinion Tilt Bracket Steering System the slider location design option is provided. You can select slider location either at the intermediate or upper steering column shaft to allow articulation of the column during tilt adjustment. You can toggle it by using parameter variable 'pvs_tilt_bracket_slider_location' where, '1' and '2' are mapped to Upper Shaft, and Intermediate Shaft.

When you select Upper Shaft, one translation degree of freedom is released between steering wheel and auxiliary steering column and when you select Intermediate Shaft one translation degree of freedom is released between intermediate shaft lower and intermediate shaft upper.

Also you can set angle of Tilt Bracket to Body during runtime using Tilt Bracket Angle. The parameter variable 'pvs_tilt_bracket_angle' is used to set tilt angle.

The torsion bar can be used to specify different torsion bar modeling options like linear, linear with stop angle, geometric, geometric with stop angle and nonlinear spline options for providing compliance between steering shaft and pinion shaft.

The force or torque actuator provides the steering assist force to the rack or torque to the motor. The below figure shows the flow chart of steering assist implementation. The steering assist has different options like None, Hydraulic, EPAS Column, EPAS Rack Simple, EPAS Rack Complex, EPAS Pinion and EPAS Second Pinion.

When "None" is selected, it deactivates steering assist force. When "Hydraulic" is selected, it activates steering assist force at the rack. When different EPAS options are selected, it activates respective steering assist torque at the motor.

The Figure 5 shows the flow chart of hydraulic assist Implementation. It directly apply steering assist force to the rack.

The Figure 6 shows the flow chart of EPAS Column Assist Implementation which applies steering assist torque to the motor.

See EPAS Boost Options (Rotational Sforce) Implementation.

The Figure 7 shows the flow chart of EPAS Rack Simple Assist Implementation which applies steering assist torque to the motor. See EPAS Boost Options (Rotational Sforce) Implementation.

The Figure 8 shows the flow chart of EPAS Rack Complex Assist Implementation which applies steering assist torque to the motor. See EPAS Boost Options (Rotational Sforce) Implementation.

The Figure 9 shows the flow chart of EPAS Pinion Assist Implementation which applies steering assist torque to the pinion motor. See EPAS Boost Options (Rotational Sforce) Implementation.

The Figure 10 shows the flow chart of EPAS Second Pinion Assist Implementation which applies steering assist torque to the pinion motor.

The flowchart below demonstrates how EPAS Boost Type options used to calculate motor torque (Rotational Sforce) which applies steering assist torque to the respective motor based on the selection of EPAS boost type.

The following table shows the design options implemented in the steering templates.