2 Vehicle Stability Control (VSC) Il VSC è un sistema attivo di sicurezza, che rileva la tendenza al sovrasterzo o al sottosterzo della vettura e attua le dovute correzioni agendo sui singoli freni e sul motore.VSC:The VSC system ensures the vehicle's cornering stability. When the vehicle becomes unstable during cornering, the computer applies the brakes and reduces the engine output to stabilize the vehicle.During understeer: Rear inner brake generate an inward force.During oversteer: Outer front brake generate an outward force.SottosterzoSovrasterzo
3 VSC Funzionamento Eccessiva velocità su strade tortuose Improvvisi ostacoli da evitareVSC is an active safety system that automatically helps to control vehicle’s lateral slip when the driver must make a sudden turn to avoid an obstacle, to take a sharp curve on an icy road, or handle some other situation that may exceed his/her ability to control the vehicle. VSC, however, does not and can not overcome the rules of physics.Curve su strade ghiacciate
4 Forze generate in curva Fc = m v2/RDuring cornering, the centrifugal force pulls the vehicle outside of the turn. This force becomes greater the faster the vehicle’s speed and the smaller the turning radius. The centrifugal force (Fc) can be expressed according to the following formula:Fc = m. (N)Where m: vehicle mass (kg), v: vehicle speed (m/s) , Rk: radius of the curve (m). This means the centrifugal force is exponentially proportional with the vehicle speed and inversely proportional with the curve radius.Ordinarily, the vehicle sustains this centrifugal force through the grip force of the tires and continues driving in the steered direction. However, if the centrifugal force becomes higher than the tires grip force, the vehicle starts to slide sideways. In other words, the vehicle remains stable in a curve as long as the centrifugal force (Fc) does not exceed the sum of the tires’ grip force (Fg) between the road and the tires.(1) Fc < Ff or m.v2/rk < .m.gFrom this formula we can easily determine the maximum speed in a given curve:(2) vmax = .rk.g Does not depend on the vehicle massF1F1F2F2
5 Coefficiente di attrito - laterale Slittamento tolleratoForza laterale:Massima forza laterale:A 0% dello slittamentoFs= s.m.gSlip* = 0% s = max. Fs = max.Slip* = 100% s = 0 Fs = 0*Slittamento longitudinale1Asfalto asciuttoAsfalto asciuttoAsfalto bagnatoAsfalto bagnatoGhiaccioSince µs (in lateral direction) is expressed in relation to longitudinal slip, maximum side force is reached when the slip is 0% and becomes 0 when the slip is 100%.Maximum side force is at 0% slip ratio in longitudinal direction.Ghiaccio20406080100Rapporto di slittamento (%)
6 Cerchio (ellisse) di Kamm Direzione di marcia teoricaFR (forza risultante)Limite di aderenza del pneumaticoFd (Forza traente)FmaxFS (forza laterale)FR (forza risultante)Massima trazione o massima forza frenanteFB (forza fenante)Kamm's Circle is a model illustrating the distribution of forces on the wheels and the connection between dynamic driving forces and friction.From this circle it becomes clear that when a side force is combined with the maximum braking force (steering during emergency brake operation) or drive force (steering during sudden acceleration), the vehicle will drift.Max forza di aderenza laterale
7 VSC Concetto base del VSC: “Ball in Bowl” (palla nella scodella) Condizione a cui è soggetto il veicoloScodella:Prestazioni del veicoloCondizioni di aderenzaAccelerazioneTRCVSCVSCABS:Maintain stability and control by preventing wheels from locking during hard brakingTRC:Maintain stability and control by preventing drive wheels from spinning during accelerationVSC:Maintain stability and control during corneringCurvaFrenataABS
8 Limite fisico del veicolo VSCScodella:Prestazioni del veicoloLa diminuzione del coefficiente d’attrito corrisponde ad un rimpicciolimento della scodella (Limite fisico)Sistemi di sicurezza durante:Frenata: ABSAccelerazione: TRCCurva: VSCAccelerazioneVSCTRCCurvaCondizione incontrollabileBallABSCurvaFrenataLimite fisico del veicoloin movimentoConceptual diagram of Ball-in-Bowl:In this diagram, the Ball represents the vehicle state of motion, and the Bowl the vehicle performance. The Ball jumping out over the edge of the Bowl indicates the uncontrollable state of the vehicle. Under a general driving condition, the Bowl is sufficiently large and deep compared with the motion of the Ball, so that the vehicle is in a stable state. When the Ball motion becomes suddenly sharp because of a rapid steering, or when the vehicle runs on a wet or snow- or ice-covered road, having a low coefficient of friction, the Bowl becomes smaller and the Ball goes over the Bowl edge, making it possibly difficult to control the vehicle.ABS and TRC are systems to retain stability at the braking and driving direction edges of the Bowl.VSC aims at stabilizing the vehicle during cornering, and assists the driver in making the appropriate steering operation.Diagramma concettuale Ball-in-Bowl
9 VSC Informazioni per il guidatore: Funzioni di controllo: Indicatore luminosoCicalinoFunzioni di controllo:Controllo della potenza:Corpo farfallatoControllo della forza frenante:VSC, attuatore freni*Nota: VSC non estende il limite fisico!Controllo incondizioni diaderenza criticaLimite fisico*VSCSenza VSCInformazione (avanzata) per il guidatoreFmax = .m.gVSC functions:Information function (Advanced information):VSC realizes a guarding function by suppressing the vehicle side slip during critical cornering.The VSC has also a hazard information function to let the driver recognize that there is an impending hazard to the vehicle or tire grip: Through an indicator light and the sound of a buzzer, it informs the driver of imminent stability problem. This prompts the driver to safer driving.Vehicle stability control function (Critical cornering guard):Throttle controlBrake actuator control
10 Principio 1 Sovrasterzo Sottosterzo Understeer: The front wheels lose grip and slide outwards and the vehicle’s line of travel bulges outwards of the curve. In this condition the vehicle tends to move straight ahead.Oversteer: The rear wheels lose grip and slide outwards and the vehicle’ line of travel wedges inwards of the curve.SottosterzoSovrasterzo
11 Variazione del momento d’imbardata M (Nm) VSCLa ECU controlla la tendenza sovrasterzante/sottosterzante frenando opportunamente le ruote in grado di creare un momento opposto alla imbardata attuale del veicolo in curva.5000Posteriore inPosteriore outInterno curvaVariazione del momento d’imbardata M (Nm)5000Forza frenanteFx (N)Anteriore inFxFxMMMMIn the graph we can see what yaw moment is generated in relation to brake force on individual wheels.Front out:Generates a stable outward moment.Rear in:Generates an inward yaw moment, since the brake force is created on one side of the vehicle and not in the gravity point.Front in: Moment depends of the size of braking:Initially, at low brake pressure, an outward inward moment is generated.When brake pressure increases, being the front inner wheel with low vehicle weight during cornering, the wheel will lock and side slip. No yaw moment will be generated in this case, the vehicle goes straight out.Rear out: Moment depends of the size of braking:At low brake pressure, an outward moment is generated, or the vehicle tends to go straight out instead of through the corner.When the brake force is increased, the wheel will eventually lock and slip. When this happens, the tire can not transmit any side force and an inward moment will be generated.Control must include:Variation of cornering moment caused by shift of load (during braking) F = .m.gDrop of cornering force due to friction limit of tires (maximum side force and braking force are different in size)5000FxFxEsterno curvaAnteriore out
12 VSC Controllo del sottosterzo/sovrasterzo: Δv= riduzione di velocitàControllo del sottosterzo/sovrasterzo:Miglioramento della stabilità in curva per riduzione della velocitàForza centrifuga Fc: Fc = m . v²/rBilanciata dalla forza di aderenza laterale FAlte velocità di percorrenza, una leggera decelerazione produce una grossa riduzione della forza centrifuga.ΔvvAderenza in curva FFcFEffect of improved cornering stability through speed reduction:The sum of cornering force of respective wheels needed for cornering becomes greater in proportion to the square of the vehicle speed. Therefore slight deceleration during high speed travel causes a sharp drop of cornering force needed for cornering. The effect of improved stability is remarkable.Velocità veicolo v
13 Sottosterzo Determinazione di una situazione di sottosterzo Traiettoria reale (imbardata reale)Traiettoria ideale (imbardata calcolata obiettivo)Sottosterzo: Imbardata attuale < Imbardata calcolataOversteer/Understeer:To determine the condition, the vehicle detects the steering angle, vehicle speed, vehicle’s yaw rate, and the vehicle’s lateral acceleration, which are then processed by the ABS and VSC ECU.The vehicle posture is permanently monitored by the above sensors, which send information to ABS and VSC ECU.Understeer is determined by the difference between the target yaw rate and the vehicle’s actual yaw rate.When the vehicle actual yaw rate is smaller than the target yaw rate, determined by the vehicle speed and steering angle. It means the vehicle is making a turn at a greater radius, or in other words, the vehicle slides outwards of the curve and tends to move straight ahead.(misurata dal sensore d’imbardata)(calcolata da velocità veicolo e angolo di sterzo)
14 Sottosterzo Yaw rate: ….. ? Determinazione del sottosterzo Understeer detectionFrom vehicle speed and steering angle, the ECU calculates a target yaw rate.If the actual vehicle’s yaw rate, measured by the yaw rate sensor, is lower than the theoretically calculated one, the ECU determines that there is a large tendency to understeer. If a vehicle drives at 20 m/sec through a corner with a radius of 50 m. The time it needs to drive ¼ of the complete circle (90°) = ds/dv2..r. / 20.4 = sec.During this 90° corner, the vehicle has rotated around the z-axle for 90°. The speed in which the vehicle is rotated (yaw-speed) = ds/dt90°/dt or 90°/ sec. = 22,785°/sec. or rad/sec.If the yaw rate sensor outputs a voltage that represents a lower yaw-speed than calculated, understeer is detected.v = 20 m/sec.R = 50 md = 90°
15 Sottosterzo Coppia di controllo Momento di controllo del Sottosterzo Perdita di aderenzaQuesta forza viene limitata per via della ridistribuzione del carico in curva (minor carico sulle ruote interne alla curva maggior carico su quelle esterne)Forza FrenanteUndersteer is suppressed by braking on the rear axle to reduce speed and generate an inner yaw moment by applying more brake pressure to the inner wheel as the outer. For further speed reduction, once the vehicle is back on track (according to the ECU) the front wheel brakes can also be applied for vehicle speed reduction.Forza Frenante
17 Angolo di slittamento () SovrasterzoDeterminazione di una situazione di sovrasterzoAngolo di slittamento ()Direzione di marcia del centro di gravità del veicolo (calcolata dal sensore di G e dalla velocità del veicolo)Traiettoria del veicolo (calcolata dal sensore angolo di sterzo e dalla velocità del veicolo)Sovrasterzo: Grande slittamento e grande velocità angolareOversteer is determined by the values of the vehicle’s slip angle () and the vehicle’s slip angular velocity (time-dependent changes in the vehicle’s slip angle) (rad/sec.). When the vehicle’s slip angle is large (actual yaw rate is larger than target yaw rate) and the slip angular velocity is also large, the ECU determines that the vehicle has a large oversteer tendency.
18 Sovrasterzo Momento di controllo del sovrasterzo Coppia di controllo Forza frenantePerdita di aderenzaPerdita di aderenzaOversteer is suppressed by braking the outer front wheel. This way an outward yaw moment is generated (towards the outer side of the cornering vehicle).Despite the sliding rear wheels, still there is some side force, which can be transmitted. Therefore during heavy oversteer condition the rear outer wheel also receives some brake pressure (not locking), to generate additional outward yaw moment.
21 Sensore a semi-conduttore Segnali di InputSensore di decelerazioneGL1: G-signal 1 Inclinato in avanti: 0,4 – 2,3 V Inclinato in dietro: 2,3 – 4,1 V GL2: G-signal 2 (0,4 - 4 ,1 V) Inclinato in avanti : 2,3 – 4,1 V Inclinato in dietro : 0,4 – 2,3 VDecelerazione (longitudinale)Sensore a semi-conduttoreDeceleration sensorThe sensor is the same as used for the ABS. The two semi-conductor sensor output a voltage linear to the deceleration they sense. Since they are opposed 90° to each other, and installed so that each has an angle of 45° in the longitudinal direction. Each semi-conductor sensor element is provided with a weight which is moved by the deceleration force applied to the vehicle. The semi-conductor itself converts the weight’s movement into electrical signal (voltage output), and outputs them to the Skid Control ECU.These output signals have linear characteristics and the output signals (0,4 - 4 ,1 V) contains information on all horizontal movements of the vehicle (lateral and longitudinal acceleration can be detected by a single G-sensor).In recent models (Corolla, Avensis……) deceleration sensor is combined with yaw rate sensor.Decelerazione (laterale)
22 Segnali di Input Sensore angolo di sterzo Alla ECU ABS TRC & VSC Alla ECU delle sospensioniFoto interruttoriSteering angle sensorA high precision steering angle sensor consists of a microcomputer and three photo interrupters (SS1, SS2 and SSC). The slotted disc passes the dent of the photo interrupters. The signals that are detected by the SS1 and SS2 photo interrupters are converted by the microcomputer into serial signals that are output to the Skid Control ECU.The SSC photo interrupters are used for detecting the neutral position of the steering wheel and performing a self-check of the steering angle sensor.Note: Since the slots in the disc are not equally divided over the disc circumference, the direction of rotation can be determined.Disco forato
23 Segnali di Input Sensore angolo di sterzo BOSCH Steering angle sensor BOSCH
24 Segnali di Input Sensore angolo di sterzo From the moment the IG switch is turned on, the steering angle sensor sends the content of its counters to the engine ECU. When there is no rotation of the steering wheel, the counters are empty. Once a rotation occurs, the new counter content is transmitted constantly.In the Bosch systems, a CAN communication (multiplex) is used. The basic operation however, is the same.
25 Segnali di Input Sensore angolo d’imbardata Fc = m x 2v x Yaw rate sensorThe yaw rate sensor uses a tuning-fork shaped vibration type rate gyro. Each resonator consists of a vibrating portion and a detecting portion. The detection portion is rotated over 90° to the vibrating portion. A piezoelectric ceramic piece is attached to both portions. The characteristic of this piece is to become distorted when voltage is applied to it and generate voltage when an external force is applied to distort the ceramic.To detect yaw rate, alternating current is applied to the vibrating portion, which causes it to vibrate. Then, the yaw rate is detected from the detection portion according the amount and direction of distortion of the piezoelectric ceramic piece, which is caused by the Coriolis-force that is generated around the resonator.Note (Coriolis force):In rotating systems (like the yaw rate sensor tunig fork) an additional force is generated if a point of mass moves with velocity v, an acceleration is created, called Coriolis acceleration. Coriolis acceleration: 2v x
26 Segnali di Input Sensore angolo d’imbardata Fc = m x 2v x Forza di CoriolisFc = m x 2v x : velocità angolare v : velocità radiale m : massaCoriolis effectA vibrating element (vibrationg resonator), when rotated, is subjected to Coriolis effect that causes secondary vibration to the original vibrating direction.By sensing the secondary vibration, the rate of turn can be detected.The Coriolis effect is named for the French physicist and mathematician Gustave Gaspard de Coriolis ( ). An assistant professor of mathematics at the “Ecole Polytechnique” in Paris from 1816 to 1838.Coriolis is best remembered for his 1835 seminar paper “Equations du mouvement relatif des systèmes de corps”, in which is demonstrated that the laws of motion could be used in a rotating frame of reference if an extra force called the coriolis acceleration is added to the equations of motion.A typical example of the Coriolis effect is that exhibited by wind patterns on Earth.Convection cells in the atmosphere set up a wind flow from the poles toward the equator (with a north-south orientation). The Earth’s rotation, however, causes these linear flows to develop a sideways (orthogonal) component of motion. This “bends” the wind from a north-south to an east-west direction.Apparent deflection of an object on a northerly trajectory (Coriolis effect)
27 Segnali di Input Sensore tasso d’imbardata Imbardata (deg/sec.) Tensione d’uscitaSensore tasso d’imbardata2,4 - 2,6 VGYAW: massa VYS: alimentazione +5V YAW: segnale sensore in volt YSS: linea schermata YD: linea di diagnosiSvolta a SxSvolta a DXGYAWTasso d’imbardataVYSYAWSens. tasso d’imbardata Sens.deceleraz.YSSECU dello slittamentoYDSensore di decelerazione: GL1: G-signal 1 (0,4 - 4 ,1 V) GL2: G-signal 2 (0,4 - 4 ,1 V)Yaw rate sensor output voltage over the YAW line is linearly proportional to the yaw moment applied to the vehicle body.Left turn corresponds to voltage level between 0,5 V to 2,5 V, while right turn corresponds to 2,5 V to 4,5 V.The yaw rate sensor receives +5V power supply from the Skid Control ECU over the VYS line and grounded over the GYAW terminal. Permanent diagnosis is carried out between the sensor and the ECU over the YD diagnosis line, and in case of malfunction is detected within the sensor, a digital code is sent over this line to the ECU.GL1GL2
28 Segnali di Input Informazione da altri sensori Sensore di velocità Interruttore luci stopInterruttore TRC OFFSensore di pressione del cilindro maestroInterruttore livello liquido freni
31 Sens. Tasso d’imbardata Sistemi BoschNei sistemi Bosch, e ora anche negli attuali sistemi Denso è utilizzata una linea di comunicazione CAN tra i sensori angolo di sterzo, tasso d’imbardata e la ECU di controllo dello slittamento.YGND YIGASS2 SS1Sens. Tasso d’imbardataECU dello slittamentoVehicles made by TMUK (Corolla ZZ12# series and Avensis AZT22#, AZT, CDT25# series) are equipped with Bosch type VSC (ESP) system. In these models a CAN communication is used to send TRC & VSC control information from yaw rate sensor and steering angle sensor info to Skid control ECU.Sens. Angolo di sterzo
32 UARTÈ stato impiegato come sistema di comunicazione ad alta velocità fino ad essere soppiantato dl sistema CANIn order to control engine power output in case TRC or VSC are active communication is necessary between the engine ECU and Skid control ECU (ABS&TRC&VSC ECU). This is performed over a Universal Asynchronous Receiver Transmission (UART). This is an international recognized serial communication, which is unidirectional and occurs over a pair of separated transmit and receive communication lines.In order to have communication in both directions, in total 4 lines (2x2) are used with the speed of 9,6 kbps.
33 UART Dettaglio delle comunicazioni ABS,TRC ENGINE ECU & VSC ECU ENG- NEOTRC-TRC+ENGINE ECUABS,TRC& VSC ECUBecause the serial communication is to slow for fast changing signals, NEO (engine speed) is communicated over a separate wire.Information from TRC to engine ECU (torque control is required) goes over the ENG- and ENG+ lines while f.e. stop light switch info is informed to the TRC ECU by the engine ECU over TRC- and TRC+.
34 Attuatore Posizione (con ECU dello slittamento) This slide shows the location of the ABS, TRC and VSC actuator. ECU portion is integrated onto the actuator.
35 Attuatore Costruzione interna This slide shows the internal construction of the hydraulic actuator as a cut drawing.The additional valve for master cylinder cut and reservoir cut can be clearly seen. Also it is well visible that the reservoirs are in fact spring loaded hydraulic accumulators.
36 Attuatore NG Avensis Sottosterzo 1 Circuito diagonale The ABS/TRC actuator is capable of controlling the wheel brakes of each wheel individually. When the VSC system is operative and the brake of one or more wheels are applied, the ABS will prevent wheels from locking.Understeer controlDuring understeer situation, the rear brakes are applied to reduce vehicle speed. The diagram below shows the VSC system operating in the pressure increase mode similar as during TRC operation.In order to correct the wheel slip, the inner front wheel brake is applied.
37 Attuatore LC Wagon Sottosterzo Circuito per asse Pressure from the accumulator is used, guided through the accumulator cut solenoid valve (sometimes indicated STR), which is then applied to the rear wheel brakes. Holding and reduction solenoid valves control the brake pressure.NOTE: On the above slide, the inner rear brakes are in the increase mode, the outer rear brake cylinders are in reduction mode.
38 Attuatore NG Avensis Sovrasterzo Circuito diagonale VSC operation is not different with other vehicles. However, in practice due to the fact, it is a 4WD vehicle, driving force is transmitted over the 4 wheels. This means that, unless a sudden steering manouvre is executed, the vehicle will start side slipping over its 4 wheels. In that case, the control can differ from the normal under or oversteer control.
39 Attuatore LC Wagon Sovrasterzo Circuito per asse Master cylinder cut solenoid valves closed off, while the reservoir cut solenoid valves supply the ABS pumps with brake fluid.Pressure control is carried out by the ABS solenoid valves (hold and reduction).
41 Controllo della potenza Veicolo con ETCS-iInizio contollo farfallaInizio controllo freniControllo freni completatoIntensità della sbandataControllo farfalla completatoAngolo di apertura della farfallaOn vehicle with ETCS-i (Electronic Controlled Throttle System), the engine torque during VSC operation is reduced by closing the throttle valve. As we can see it from the graph, this control starts even earlier as the brake control.AltaPressione alle pinze frenitempo
42 Controllo della potenza Veicolo senza ETCS-iInizio taglio carburanteInizio controllo freniControllo freni completatoIntensità della sbandataTaglio carburante completatoCoppia motriceOn vehicles without ETCS-i, such as, Corolla TS, engine torque is reduced by cutting off the fuel injection.AltatempoPressione alle pinze freni
43 DiagnosiSimilar to the initial check of the ABS and TRC system, since the same actuator is used for all three systems, an initial check for the VSC is also performed.As a result, the VCS OFF and SLIP indicator light goes on for 3 seconds after the ignition is turned on.If the ECU stores a DTC in memory, CHECK VSC can be read on the multi-information display while the VSC OFF indicator turns on.In addition a VSC sensor check can be performed in test mode. The steering wheel position sensor and yaw rate sensor can be checked in a more sensitive way.
44 Suggerimenti per l’assistenza LS430, GS, RX, LC 90, 100 & 120Quando si sostituisce (disconnette) il sensore tasso d’imbardata, ECU dello slittamento e sensore di GÈ necessario eseguire l’inizializzazione del sensore tasso d’imbardata e di decelerazione!Selezionare la posizione “P” del A/TPortare il quadro ONPonticellare Ts CG (E1) 4 volte o più in 8 sec.Non muovere il veicolo per 15 sec.la spia del VSC OFF si spegne, la spia VSC inizia a lampeggiare