ENHANCEMENT OF VEHICLE STABILITY BY ACTIVE GEOMETRY full report
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ENHANCEMENT OF VEHICLE STABILITY BY ACTIVE GEOMETRY
CONTROL SUSPENSION SYSTEM
In recent years, there has been increased need to develop high-performance suspension for high-power engines ,especially active chassis control systems have been developed and mass-produced in the market to compromise vehicle ride and handling performance simultaneously,
The conventional active chassis control systems control the vehicle phenomenon such as body roll, yaw, and pitch using hydraulic actuators with the same direction as acting load. So, their hardware and control algorithms are complex and it often happens that cost is high. Figure 1 shows the concept of the conventional active chassis control system. In this paper, AGCS control concept has been introduced and its performances were analyzed with the ADAMS full vehicle model. The simulation results of AGCS system show the improved handling performance. In addition ,the subjective tests were performed to evaluate the AGCS performance for lane change and steady-state cornering .
Figure 1. Concept of the conventional active chassis control system.
2. AGCS OVERVIEW
The kinematics arrangement of the suspension link changes toe angle, which is largely affecting running stability, as the running condition changes. The AGCS system is a device to optimize the toe angle of a rear wheel by controlling the position of a rear suspension link. Figure 2 shows the comparison between the conventional active chassis control system and AGCS system. It consists of actuators, control lever (these are mounted in rear sub frame) and ECU as shown in Figure 3. ECU is adjusting actuator stroke based on the vehicle speed and steering angle. Then the control lever is rotating downward or upward around hinge. It moves the inboard mounting point of the rear wheel assist link to maintain optimal bump toe-in value.
Sensor part has vehicle speed sensor and steering angle sensor. Vehicle speed sensor reads the vehicleâ„¢s speed, and the steering angle sensor reads the driverâ„¢s steering amount . Control part commands the actuator by estimating lateral acceleration acting on the vehicle based on the
data from the vehicle speed sensor and the steering angle sensor. Actuator part is producing the optimal toe angle of the rear outside wheel by controlling the position of the link mounting point of rear wheel based on the command from the control part.
The concept of AGCS is intelligent, and it overcomes many negative points of conventional active suspension systems. AGCS has simple control logic and hardware equipment. Moreover, if energy supply goes off in conventional system the performance becomes failure mode but in AGCS, vehicle performance will be equal to passive suspension. At situations accompanying rolling such as high speed cornering the equal to passive suspension. At situations accompanying rolling such as high speed cornering the AGCS system estimates lateral acceleration acting on the vehicle based on the data from vehicle speed sensor and steering angle sensor. Based on the estimated lateral acceleration, it moves the actuator to increase rear outside (Figure 4).Since abrupt steering at high speed produces large centrifugal force on the vehicle, the rear part of the vehicle slips outward (AGCS OFF in Figure 5).Thus, it is difficult for the vehicle to show stabilized steering performance. The AGCS system prevents the vehicle from leaning, which increases grip force of the rear wheels, thereby decreasing the rear-sway (AGCSON in Figure 5).
3. CONTROL LOGIC
The control logic of the AGCS system is investigated in this section. The objective of the logic philosophy was to maximize the positive effect of the AGCS on the precise situations. The most important aims to accomplish are:Â¢ Actuation starting points at constant levels of lateral acceleration for all speeds in order to guarantee homogenous effect
Â¢ Definition of different control maps with increasing AGCS application strokes with increasing lateral acceleration levels for better progressivity and natural effect on the handling response of the vehicle The definition of all the logic has been done bearing in mind the control parameters available for the set-up:
Â¢ Vehicle speed
Â¢ Steering wheel angle
Â¢ Steering wheel rate (actually this value is calculated)
Only an additional throttle position has been used for the consideration of the power-off in turn situation.The idea to be applied in the control logic is to establish the starting point of the actuation of the AGCS at a certain level of lateral acceleration of the vehicle. This level will be determined based on the steady-state characteristics of the vehicle for different speeds, therefore with
a given steering wheel angle and speed the system will establish the corresponding steady state acceleration and decide the actuation of the AGCS. Additionally different mappings will be defined based on the steering wheelangle rate.This will inform about the level of non-steady state (or
transient) situation of every driving condition of the vehicle. The more transient the situation will be the sooner and the more aggressive the system will act on the suspension. Figure 6 shows the control logic flow of the AGCS system.
Figure 2. Comparison between the conventional active
chassis control system and AGCS;
4. SIMULATION AND TEST RESULTS
In this section, in order to verify the effectiveness of AGCS the step steer input simulation is performed using full vehicle ADAMS model (Mechanical Dynamics Inc,2002). The vehicle model comprises double wishbone front suspension and multi-link rear suspension (Figure7). The AGCS ADAMS model consists of assist link ,control lever and actuator. Control lever is connected to
the assist link with the bushing and also connected to the sub frame by the revolute joint. The connecting part between the actuator and the control lever is modeled with a contact element of ADAMS. As the actuator generates translational motion, the control lever will rotate about the revolute joint, and assist link mounting point moves downward.
4.1. Step Steer Input Simulation
Step steer input maneuver is simulated to investigate the transient response in AGCS OFF and ON condition .Vehicle speed is 140 KPH and steering wheel angle is 50degrees. Figure 8 shows the results of vehicle response for the step steer input. It can be noted that the overall
trends in AGCS ON condition have superior performance when compared to those in AGCS OFF condition .Especially, in case of maximum magnitudes of body sideslip angle are considerably reduced in AGCS ON condition (Table 1).
4.2. Sinusoidal Input Simulation
Also, the sinusoidal input maneuver is performed to investigate the transient handling performance. Initial vehicle speed is 140 KPH and steering wheel angle is sinusoidal as in Figure 9(a). Figure 9(b)(d) show the results of transient response for the sinusoidal input. Like
the step steer input, it can be noticed that AGCS ON vehicle has superior handling performance than AGCSOFF vehicle. In particular, it can be found that magnitude reduction of side slip angle is large in case AGCS ON condition (refer to Table 2).
4.3. Subjective Test
In order to establish the level of influence of the AGCS effect, The rear suspension were installed with AGCS hardware such as actuator, control lever for road testing in Figure 10 (ECU is not seen in the Figure). The subjective evaluations are performed to cover the principal aspects of the handling performance that are affected by AGCS system. Test driver tries two kinds of driving case, AGCS off and on condition for single lane change and quasi steady-state cornering.
The vehicle characteristics are also evaluated whenturning in steady-state or quasi steady-state situation. All Table 1. Maximum magnitudes comparison in step steer
input simulation. Item AGCS off AGCS on
Roll angle 3.99 deg 3.58 deg (10.3%)
Yaw rate 15.79 deg/s 14.52 deg/s (8.0%)
Side slip angle 3.77 deg 2.7 deg (28.43%)
Figure 8. Step steer input simulation results.
Figure 9. Sinusoidal input simulation result
In this paper, AGCS to improve handling performance as the active chassis control system is suggested. The summaries of results are as follows1) The AGCS system is applied on the rear suspension to regulate bump toe-in using the electric actuator which varies the geometry of assist link, and enables to improve road grip and extend the slipping point.(2) Because the control direction is perpendicular to the acting load in regulating wheel toe-in, the system is inherently more efficient than conventional systems that control in the same direction as the acting load.(3) AGCS system has superior handling performance when compared to the conventional system in step input simulation results and subjective tests.
CatalÃƒÂ . A. (2004). Dry Handling Tuning of AGCS
Systems with Hyundai NF. IDIADA Technical Reports
SC 050507-1. Spain.
Lee, U. K. (1994). Suspension System for Vehicle. Patent
No. U.S. 5,577,771. USA.
Lee, U. K. (1996). Vehicle Suspension System for a
Steerable Wheel. Patent No. U.S. 5,700,025. USA.
Lee, U. K. (2001). Suspension System for Vehicles. Patent
No. U.S. 6,182,979. USA.
Mechanical Dynamics Inc. (2002). ADAMS/Car Userâ„¢s
Namio, I. and Junsuke, K. (1990). 4WS technology and
the prospects for improvement of vehicle dynamics.
SAE Paper No.
INTERNATIONAL AUTOMOBILE JOURNAL