The Synaptic Damping Control System: increasing the drivers feeling and perception by means of controlled dampers
Giordano Greco Magneti Marelli SDC Vehicle control strategies
Stuttgart, 6 May 2008 From ‘passive’ to ‘controlled’ suspension
Vehicle suspension systems should guarantee:
Safety & Comfort handling Passive suspension Comfort vehicle Sport Vehicle Suspension tuning
Soft suspension Rigid suspension Low damping suspension High damping suspension Controlled suspension
Adapt its behavior to different running conditions and to driver requests
Stuttgart, 6 May 2008 2 The Synaptic Damping Control system
Synaptic Damping Control (SDC) is the continuous damping system by Magneti Marelli suited to control vertical vehicle dynamics and body motions, caused by road surface and by driver inputs (steering wheel, accelerator, brake, gears,..), through controlled shock absorbers.
The system is made up of the following components:
4 Electronically controlled shock Command current increases absorbers 1 Electronic Control Unit (ECU)
400 ) 300 daN 3 Body Accelerometers ( 200 Force
100
0 2 Front Hub Accelerometers 0 100 200 300 400 500 600 700 800 900 1000
-100
-200
Embedded SW Control strategies -300 Velocity (mm/s)
CAN node connection Command current increases
Electronically controlled shock absorbers include proportional electro-valves which continuously vary their characteristics from a minimum (low command current) to a maximum (high command current) damping curve.
Stuttgart, 6 May 2008 3 The Synaptic Damping Control system architecture
Front left body accelerometer
Front right body accelerometer
Rear left body accelerometer
Front left hub accelerometer
Front right hub accelerometer
Rear Sensors set ECU shock absorbers Front shock absorbers
CAN network
¾Engine control node; ¾Gear-shift control node; CAN signals from: ¾ABS, EBD, ASR, VDC control node; ¾Steering wheel control node; ¾Body computer node.
Stuttgart, 6 May 2008 4 Vehicle dynamics control functionalities
Which functionalities for a controlled shock absorbers system?
Ride comfort on uneven roads Ride comfort in case of impulsive event ¾Sky-Hook control ¾Hole/bump management control
Software architecture
Lateral dynamics transients Longitudinal dynamics transients ¾Control of body roll ¾Control of body pitch ¾Control of under-oversteer
Stuttgart, 6 May 2008 5 Ride comfort behaviour - modal Sky-Hook control
Modal Sky-Hook control. Function purpose is to adjust suspension damping level to optimise control of body motion and vibrations caused by road irregularities. The control law is based on the “Sky-Hook” theory. Optimization of control parameters ¾Virtual optimization performed by simulation accelerometer ¾Optimization performed on road z(t) M Optimization performed on a 3D vehicle model Continuously adjustable damper k Ecu
accelerometer y(t) m
kt Road holding setup
Crel Best comfort
Fref = Csky z& + Crel(z& − y&) Best road holding Comfort setup
Stuttgart, 6 May 2008 6 Lateral dynamics control
¾The function is deputed to control vehicle behaviour during lateral dynamic transients.
9Basic functionality Æ damping levels of shock absorbers are set in order to smooth body roll motion.
9Advanced functionality Æ control of the understeer - oversteer behaviour of the vehicle by adjusting the front / rear damping level balance
as a function of the actual turn phase (entry, stationary, exit);
as a function of the acceleration (throttle-on) or deceleration (throttle-off) requested by the driver.
Stuttgart, 6 May 2008 7 Lateral dynamics control – philosophy of the control logic
The basic idea: during lateral dynamics transients the control logic increases damping level of shock absorbers.
Steering ∧ wheel angle* day damping Steering wheel Reference level to ∧ Damping level calculation gradient* a singular Model y (Front/rear & inner/outer balance) shock Vehicle speed* absorbers
Gas pedal* * signals form CAN bus
¾The front / rear damping level balance has a strong influence on the understeer / oversteer behaviour.
¾The SDC control logic adjusts in real time the front / rear damping level balance as a function of
9actual turning phase Æ steering wheel angle
9acceleration/deceleration request Æ gas pedal
Stuttgart, 6 May 2008 8 Control of body roll motion
Steering wheel step input at 100 km/h (simulation results).
Steering angle
Roll angle
Stuttgart, 6 May 2008 9 Control of body roll motion
Sine sweep at 120 km/h – 40° steering wheel angle (simulation results).
Zoom
Frequency response diagrams
Stuttgart, 6 May 2008 10 Control of body roll motion
Sine sweep at 120 km/h – 40° steering wheel angle (simulation results).
Stuttgart, 6 May 2008 11 Control of understeer and oversteer during transient cornering
Introduction to the problem
Steering wheel step manoeuvre at 100 km/h (simulation results)
Steering angle
High promptness in turning
Yaw rate
High damping of yaw movement
The front / rear damping level balance has a strong influence on the directional behaviour of vehicles.
Stuttgart, 6 May 2008 12 Control of understeer and oversteer during transient cornering
Sine sweep at 120 km/h – 40° steering wheel angle (simulation results)
Stuttgart, 6 May 2008 13 Control of understeer and oversteer during transient cornering
¾The SDC control philosophy:
the front / rear damping level balance is adjusted in real - time during cornering.
¾The logic intervention is highly tunable:
it is possible to comply to different drive styles and different drivers expectations.
Stuttgart, 6 May 2008 14 Control of understeer and oversteer during transient cornering
For instance, a possible goal may be: the higher promptness in turning, with the higher damping of yaw movement:
Steering wheel step manoeuvre at 100 km/h (simulation results) Steering angle Body slip angle
Yaw rate Roll angle
Second phase of the entry: more damping to the front dampers.
First phase of the entry: more damping to the rear dampers.
Stuttgart, 6 May 2008 15 Control of understeer and oversteer during transient cornering
SDC offers high tuning possibility Æ different set up for the logic intervention can be implemented in order to comply to different goals.
Steering angle
Theoretical graphs……..
Intermediate solution Æ it also guarantees good steer feeling
Yaw rate Yaw rate Tuning parameter
Stuttgart, 6 May 2008 16 Control of understeer and oversteer during transient cornering
Steering wheel step manoeuvre at 100 km/h (experimental results)
Steering angle
……..experimental graphs
Yaw rate
Stuttgart, 6 May 2008 17 Control of understeer in throttle-on manoeuvres
Without understeer control With understeer control
Strong reduction of understeer Understeer effect
Experimental results, front-wheel drive car
Stuttgart, 6 May 2008 18 Control of oversteer in throttle-off manoeuvres
Without oversteer control
Oversteer effect
3 Throttle-off 2
2
1
Counter steer action needed
12 3 Experimental results
Stuttgart, 6 May 2008 19 Control of oversteer in throttle-off manoeuvres
With oversteer control Without oversteer control
Strong reduction of oversteer
US-OS control ON
US-OS control off 1
Experimental results
Stuttgart, 6 May 2008 20 Hole and bump management
The goal of the hole/bump management module is to optimize comfort and road holding in case of wheels impact against an obstacle (positive or negative) on the road.
¾During rectilinear path, the main goal is to optimize comfort.
¾During cornering, the main goal is to optimize road holding
9by reducing hubs vibrations;
9and so reducing yaw rate disturbances and guaranteeing good trajectory control.
¾The SDC hole/bump management module is able to
9rapidly recognize the presence of the event by monitoring vertical accelerations of front wheels;
9recognize the sign of the event (hole or bump);
9act on the rear dampers in a predictive way;
9differently manage symmetrical and asymmetrical events;
9differently manage events during rectilinear path and during cornering.
Stuttgart, 6 May 2008 21 Hole and bump management during rectilinear path
Good comfort Æ reduction of peak to peak of seat guide vertical acceleration
Positive obstacle 100 x 25 mm at 30 km/h. Seat guide vertical acceleration. Experimental results.
Passive Semi-active
17%
Stuttgart, 6 May 2008 22 Hole and bump management during cornering
Cornering manoeuvre at 40 km/h with 80° steering wheel angle. Positive obstacle on the external wheel. Experimental results. Good trajectory control Æ reduction of yaw rate disturbances
Positive obstacle -19% Increment of yaw rate caused by the impact against the rear wheel
A strong reduction of the increment of yaw rate is possible with SDC control
A strong reduction of hubs vibrations is possible with SDC control
Stuttgart, 6 May 2008 23 Longitudinal dynamics control
¾This function controls body pitch movement caused by longitudinal acceleration jerk induced by driver actions on
9gas pedal
9clutch pedal
9gearbox
9brake pedal.
¾Damping levels of shock absorbers are set in order to control dive and squat body motion.
The basic idea: during longitudinal dynamics transients the control logic increases damping levels of shock absorbers.
Stuttgart, 6 May 2008 24 Control of body pitch movement
Tip in/tip out in 1a gear @ 100% gas pedal
Torque engine request TipTiro in (pitch (velocita` velocity) di beccheggio) Passive Controlled 16 . 0
14 . 0 Input driver 12 . 0 10 . 0 PassivePassiva 8.0 65% Controlled
60% Controllata 6.0
4.0 Pitch Angle 2.0
0.0 MaxPeak-to-peak picco-picco
TipRilascio out (pitch (velocita` velocity) di beccheggio)
16.0 14.0 12.0 Pitch Velocity 10.0 PassivePassiva 8.0
59% Controlled deg/s Controllata 6.0 57% 4.0 2.0 0.0 MaxPeak-to-peak picco-picco
Average on different tests
Stuttgart, 6 May 2008 25 Control of body pitch movement
Braking from 100 km/h Brake pressure
Passive Controlled Input driver
Vehicle Speed
ABS (massima velocita` beccheggio) Max pitch velocity
10.0 9.0
8.0 38% 7.0 Pitch Angle 6.0 PassivePassiva 5.0 ControlledControllata 4.0 vel [deg/s] 3.0 2.0 1.0 0.0 abs(v_max beccheggio) Pitch Velocity Average on different tests
Stuttgart, 6 May 2008 26 Conclusions
¾Control strategies, based on the classical Sky-Hook theory, allow a perceptible improvement of comfort performance in case of controlled dampers.
¾The ride comfort application represents only a first step in the use of controlled dampers.
¾The Synaptic Damping Control strategies are designed in order to increase the drivers feeling and perception.
9Improvement of handling characteristics of vehicles
Control of body roll
Control of understeer and oversteer during transient cornering
Control of understeer and oversteer caused by throttle-on and throttle-off
Minimization of yaw rate disturbances caused by impacts against obstacles during cornering
Control of body pitch
9All these control strategies give the vehicle more stability and allow greater driving pleasure, without compromising vertical comfort.
Stuttgart, 6 May 2008 27 ThankThank YouYou !!
Stuttgart, 6 May 2008 28