2Accelerazione/decelerazione (marcia in rettilineo) F = m x aTRCLimite FisicoF = m x a < l x m x gZona di stabilitàAcceleration, decelerationTo change a vehicle speed (acceleration or deceleration) or its direction, a force is needed.Accelerating or decelerating:F = m . a Where m = vehicle mass and a = acceleration (+ or -)This force is transmitted to the road surface through the tires. Therefore the maximum force, which can be transmitted equalsFmax = m . k . g . µlwhere k = vehicle weight on the used wheels/ total vehicle weight. (rear spoilers on racing cars increase the load on the traction wheels)g = 9,81 m/s² and µl = friction coefficient between road and tire.From this can be concluded that every 2WD car can brake faster as it can accelerate (independent from engine power).Q:If Porsche claims that the 911 is able to stop in 5 sec. from 200km/h to 0. What kind of deceleration is than required, and which µ it could be possible.ABSF = m x aDecelerazione
3Anti-lock Brake System (ABS) L‘ABS previene il bloccaggio delle ruote durante la frenata, assicurando la stabilità al veicolo e migliorando la sterzata. Nelle forti frenate su superfici a basso coefficiente di aderenza, la direzionalità del veicolo viene comunque garantita.Anti-lock Brake System (ABS):ABS prevents the wheels from locking up during braking. (a locked wheel is in fact not longer a wheel anymore !)Because ABS allows the wheels to roll, the vehicle maintains directional control (and a high steering performance).
6Anti-lock Brake System (ABS) Cilindro maestroAttuatoreABSFpedalePressione regolataPressione di riferimentoECU di controlloCilindro frenoSensore di velocitàABS antilock braking systems are closed-loop control devices within the braking system, which prevent wheel lock-up during braking and, as a result, retain the vehicle’s steerability and stability.Fb: forza frenante (N)G: Forza peso (N)
7Segnali d’ingresso Sensore di velocità Tipo induttivo (pick-up) Magnete permanentebobinaRuota fonicaAs we saw earlier, ABS system should detect the speed of each wheel in order to be able to instantly calculate the momentary slip ratio (for each wheel) and the deceleration value (also for each wheel). Therefore speed sensors must be used.Inductive speed sensor:Pick-up sensors with a coil inside and permanent magnet, generate a fluctuating signal as teeth are passing by. Inside the ECU the signal is being digitized so that the frequency of the block wave is the measurement value for the wheel speed. The average frequency of two diagonal wheels is used as vehicle speed indication. The wheel speed is compared with the reference speed of the vehicle, calculated as average from the speed of two diagonal wheels. This way always a driven and non-driven wheel, an inner and outer wheel and a high and low-µ wheel are involved in the calculation.Q: What is minimal speed for ABS operation? Is it still possible to use brake tester?For logic, front 7km/h, rear 6km/h. Ref. Speed sensor detects from 2.6 r.p.m. of tire.
8Segnali d’ingresso Sensore di velocità Tipo MRE (sensore attivo) MRE (Magnetic Resistance Element)Sensor OutputTempoClick!AICBRuota fonica magneticaSensor OutputmagneteActive wheel speed sensor:Conventional passive wheel speed sensors detect only from 3 km/h.With the active speed sensors, speed detection is possible from +/- 0 km/h, and the direction of rotation is also detected.Low speed detection is necessary for the DAC or Down-Hill Assist Control system of the new Land Cruiser, to make a low constant downhill speed control possible.This detection of rotation direction (that is not possible with conventional passive wheel speed sensors) is necessary for the HAC or Hill-start Assist Control system of the new Land Cruiser.(For details see HAC & DAC presentation)Tempo
9Segnali d’ingresso Sensore di decelerazione Tipo a semi-conduttore Deceleration sensor:In case of a full time 4WD vehicle, front and rear wheels are connected. When the center differential is mechanically locked, all wheels tend to lock at the same time, resulting in a drastic reduction of control precision. In these cases, ABS is simply inoperative.Even for 4WD vehicles with viscous coupling or “sporty” vehicles with a Torsen differential, there are occasions where the binding force between front and rear axle is too large (very low µ surfaces). Therefore, a deceleration sensor informs the ECU about the vehicle’s deceleration so that the ECU can estimate the vehicle speed, even when all wheels tend to lock.On older models, a photo interrupter type sensor was used. This sensor consists of 2 photo transistors and 2 LED’s, a slit plate and a signal conversion circuit. Depending on the acceleration (or deceleration) amount, the slit plate rotates and LED light is received by the phototransistor. The combinations formed by the 2 pairs of sensing elements divide the rate of deceleration into four levels, which are sent to the ABS ECU.This sensor detects ONLY the longitudinal acceleration level in four discrete steps.Actually, for more precise deceleration measurements, two semi-conductor type sensors are used into one housing. This way the level of deceleration can be measured step-less both in longitudinal and lateral direction.Sensore a semi-conduttore
10Servo-freno a depressione Diagramma del sistemaInterr. luci stopAttuatoreFreniSensore di velocitàSensore di velocitàECUThe brake control circuit is composed of wheel speed sensors, a brake actuator (hydraulic unit with the valves and hydraulic motor included), an ECU, which is recently integrated with the actuator ( refer to corolla NCF218F, page CH34), a stop light switch, a combination meter and a diagnosis connector.TachimetroSpia ABSSpiaimpianto frenanteDLC3
11Servo-freno idraulico Diagramma del sistemaBasically the ABS circuit is almost identical with the one used on conventional brake booster type systems. However, there are some additional signals are input to the ABS ECU to cancel the ABS operation within certain conditions or provide additional information for more precise reference speed calculation.
12Attuatore ABS – con ECU ECU di controllo dello slittamento BOSCH DENSO Actuator in fact consist of actuator portion (hydraulic part) and a skid control ECU part. The above slide shows difference in construction between a BOSCH made and a DENSO made ABS&EBD actuators installed into Corolla ZZE12# and CDE120 series. BOSCH type is installed to TMUK build vehicle, while DENSO made it fitted to TMC made vehicles.DENSO
13ECU Input unit convertitore A/D CPU1 CPU2 RAM EEPROM +B, IG,BATTCPU1Stop light SWInput unit convertitore A/DVelocità ruoteCPU2G-SensorRAMEEPROMSpia ABSOutput circuit, amplifierInput circuit:Receives information from battery voltage and ignition. In addition to this, it receives the information of stop light switch, wheel speeds and G-sensor. The purpose of the input circuit is filtering and digitalization of analogue signal.CPU:Two micro-processors are connected in parallel, and both receives all input information. The purpose of the CPU is to make:-the arithmetical calculations, e.g. to calculating wheels’ circumferential speed, wheels’ deceleration.-logical calculations, for instance determining vehicle reference speed and the comparison of it to the marginal curves stored in the EEPROM,-verification of each others operation.Memory: to store vehicle reference speed curves and to store the software.Output circuit: to produce stable voltage output for the actuator’s operation.Solenoidi,...
14Struttura degli attuatori ABS Le strutture degli attuatori vengono classificate in funzione dei seguenti parametri:Configurazione circuiti frenantidiagonale o per asseNo. di canali usati per la determinazione della velocitàNo. delle valvole a solenoide presenti nell’attuatore4, 6, 8, 11, 12, 14, 15No. delle posizioni che ogni valvola può assumere3-posizioni (vecchi sistemi), 2-posizioni (attualmente utilizzati)Metodo di servo-assistenzaA depressione o idraulicaActuators can be classified in several ways based on the following features:Brake circuit configuration; on front/rear split type, such as on Hilux, Land Cruiser Prado, 6 solenoid valves are used, whilst on diagonal split ones, such as on Camry, Celica, Corolla, RAV4, Avensis etc.) 8 solenoid valves are installed. AsNumber of channels can be 3 or 4 depending on in how control of the rear axle is done. A difference is noted between the Bosch and Denso interpretation. Bosch is quit optimistic by considering the possibility to handle the two rear wheels separately as being a 4-channel control even if control is not applied individually. Denso on the other hand is only considering a system as 4-channel if the system can really apply the individual control of the rear wheels.Number of solenoid valves can vary the most, since additional control devices can be linked to brake system, such as TRC, VSC and Brake Assist. The least number of solenoid valves (4) are used in EP91 series Starlet models, in which the ABS control is done purely based on the wheel deceleration. In all other vehicle, as we will see later, ABS control is achieved based on wheel deceleration and wheel slip control.Solenoid valve positions, which can be 2 or 3. In old ABS systems, like in Lexus UCF10 or Supra JZA80, 4 sets of 3-position solenoid valve was fitted into the actuator, one for each wheel. Therefore this system is called ND4-4/3, which means 4-channel control and 4 pieces of 3-position valve for pressure control.However, this system is NOT discussed during this course. Refer to TEAM Step3, ABS and TRC system. Pub. No: TTM307E
15Attuatore 8/2 – solenoidi/posizioni Cilindro maestroAttuatore freniValvola mantenimento pressioneValvola di riduzione pressione8/2 – position solenoids: 8 valves, 2-positionNowadays, most ABS systems use 8 2-position solenoid valves: a pressure hold and a reduction valve for each wheel.Ant. Sx Post. Dx Post. Sx Ant. Dx
16Attuatore ABS - Solenoidi e valvole Based on the signals received from the 4 wheel speed sensors, the skid control ECU calculates each wheel speed and deceleration, and checks wheel slipping conditions. And according to the slipping condition, the ECU controls the pressure holding and reduction valves in the actuator in order to adjust the fluid pressure of each wheel cylinder in the following 3 modes:Pressure increase, Pressure hold, Pressure reduction
17Quest’area è utilizzata per il controllo ABS AttuatoriTipo 14/2In Europe, the Carina E 190 series was the first model to use 8 2-position solenoid valves.Nowadays, most ABS systems use 8 2-position solenoid valves: a pressure hold and a reduction valve for each wheel. However, due to the rapid development of other control systems, which also use the brake system, more and more solenoid valves are fitted into the actuator, depending on the existence of TRC, VSC and/or BA.Quest’area è utilizzata per il controllo ABS
18Principio di controllo dell’ABS Pr = Pressione dei freni Vv= Velocità veicolo Vw= Velocità ruote = Slittamento ruote aw= Accelerazione ruoteLivello di attivazione (superiore)25% slittamentoLivello di attivazione (inferiore)10% slittamentoAt first the ECU has to determine when one or more wheels tends to lock.A first criteria is the wheel slip. The wheel speed is compared with the reference speed of the vehicle This in case of no brake operation is the average speed of the four wheels. In case of braking this is the average of all not slipping wheels.By measuring wheel speed in small intervals, comparing the measured speeds of each wheel and divide by the time between the intervals, gives the deceleration of each wheel.a = v/ tIf one wheel decelerates faster then the others, the reference speed ( vehicle speed) is recalculated, based on the lower decelerating wheels. This is important when a vehicle is decelerating with skidding wheels or driving over rough roads.Based on the reference speed, two slip borders are set at 10 and 25% slip. The wheel slip is the comparison between the actual wheel speed and the vehicle speed at that interval.When the calculated slip passes the above lowest border, the ABS switches to reduction mode.If a wheel slip reaches the highest border, pressure reduction mode is maintained. (This happens in case of a -jump)A second criteria is purely based on the wheel deceleration.If the measured deceleration is higher than 13 m/s², the ABS switches to holding mode.The level is this high because under normal circumstances 10 m/s² is possible on rough roads.Livello di attivazione (superiore)Decelerazione = 13 m/s²tempo
19Max. forza frenante e forza laterale Forza risultanteForza frenanteForza lateraleWhy a tire that transmits maximum braking force can not transmit the maximum on side force, becomes clear in the friction circle.Since the tire is basically just rubber, the max. transmittable force is equal in every direction. This creates a circle, where acceleration, braking and cornering left and right forces have an equal length.From the circle can be seen that a max. braking force + some side force always creates slip. The further out of the circle the result of both forces, the more slip is generated.Forza lateraleForza frenante
20Coefficiente d’attrito 204060801001Slittamento tolleratoCoefficiente d’attrito in curva sCoefficente di attrito in frenata bAsfalto asciuttoAsfalto asciuttoAsfalto bagnatoAsfalto bagnatoAs we already discussed….This is the most famous graph. Since tires deform due to the force applied, is it impossible to transmit any force without slip. Remarkable is that the highest friction coefficient is reached with a slip between 10 and 30%, depending on road surface, tire construction and vehicle speed. Once over this critical slip, the coefficient drops.All ABS systems are designed to control wheel slip being max. 25%, while the system will increase brake pressure again when 10% slip is reached.GhiaccioGhiaccioRapporto di slittamento (%)
21ABS – velocità obiettivo Aumento pressioneMantenimento della pressioneRiduzione della pressioneDuring emergency braking with ABS, the ECU converts the friction graph into the vehicle speed information. During braking, vehicle speed drops (upper line). For each vehicle speed, 10 and 25% slip means 10-25% lower wheel speed are set out as limits.From wheel speed sensors, the ECU receives the speed of each wheel individual and compares this speed with the target between 10 & 25% slip.A first control the ABS needs to perform is comparing wheel speed with the calculated target based on vehicle speed information.Thus the first control of ABS systems is based on the wheel slip.
22ABS – decelerazione delle ruote A second control is based on the wheel acceleration (deceleration).The deceleration is deviated from the speed. In time seen the speed varies. The more the speed changes (=steep sloops), the higher the deceleration-acceleration, because a=(V1-V2)/t. No change in speed gives no acceleration or deceleration, while vertical speed lines would mean a collision or infinity deceleration.Of course, if the ECU measures wheel speed at certain time intervals, it becomes easy to calculate the deceleration of that wheel. The difference in speed divided by the time between two intervals gives the deceleration.At a fixed deceleration level, the ECU determines that that wheel will tend to lock. The ECU will avoid the brake pressure from increasing when a higher deceleration is measured. (and it turns to holding mode).This control can be seen as a proactive control (before the wheel locks already start the control).a = dv/dt
23Controllo 2WDControllo di riduzione al più basso (ruote su superfici a diverse)Per evitare che il veicolo tenda ad imbardare, la forza frenante applicata alle ruote posteriori è quella calcolata per la ruota sulla superficie a più bassaForza frenante altaSuperficie a elevataControls on 2WD vehicles (low-µ select)With this type of vehicles an ABS system is used with 3 channels : each front wheel is controlled individual and the rear are controlled with one channel. The ABS will operate for the rear wheel channel when one wheel tends to lock. The remaining brake force for the high-µ wheel is unused.Because brake force left and right are equal, there is no yaw moment generated thus enhancing a good track stability, while the high-µ wheel can still transmit a high cornering force. This type of control is called low-µ select.Most ABS system operations are based on wheel slip & deceleration criteria. (Only the Starlet #90 with 4/2 actuator controls only on the deceleration rate)At rapid brake pressure increase on dry smooth road surface and no-driven wheels, the deceleration limit of 13 m/s² will be earlier reached as the slip borders.On low µ surfaces, driven wheels (with a high rotation mass) the slip borders will be reached before the deceleration limit.Superficie a bassaAsse anterioreAsse posteriore
24Controllo 2WDFrenata senza ABS (superfici a diversa)
25Controllo 2WDFrenata ABS (superfici a diversa)
27Controllo 2WD Frenata su superficie a costante Se la decelerazione rimane inferiore a 13m/s2 il mantenimento della pressione è temporizzatoPressure increases until the deceleration limit is reached (phase 1).The system goes to holding mode (phase 2) because the wheel can still be in a stabile situation (high µ surface).If the lowest slip border is passed, reduction mode is selected (phase 3).This reduction last until the deceleration is back under the limit. (In certain conditions - in case of a -jump - reduction is also maintained till the highest slip border of 25% is passed)Holding mode for a fixed time follows.If within this time the wheel acceleration does exceed the limit, pressure remains constant (phase 4).If the wheel does not accelerate fast enough, a fixed time the pressure is reduced further.When the highest acceleration limit is passed, pressure increases again until its back under this limit (phase 5).Then pressure is kept constant until the lowest acceleration limit is passed (phase 6).The wheel is now stabile again and with a fixed pattern pressure is increased until the deceleration limit is reached (phase 7). The fixed times for holding and reduction modes, depend on the hysteresis of the brakes. (drum brakes have a higher hysteresis as disc brakes)When the deceleration limit is passed again, reduction mode is selected like in the previous cycle.
28Controllo 2WDVw = Velocità ruote Vv = Velocità veicolo Vref= Velocità di riferimento del veicolo + 10 % slittamentoaw=accelerazione del veicoloRiduzione Mantenimento AumentoPressione ai cilindri freni
29Controllo 2WD ”veicoli sportivi” 4 canali con sensore di accelerazione lateraleControllo ruote: individuale, riduzione al µ più basso o una combinazione dei dueAccelerazione laterale (m/s2)Riduzione al µ più bassoLeggero sovrasterzoLeggera diminuzione al µ più bassoThe ABS used on the Supra JZA80, Celica ST20# with super strut suspension and MR2 SW20 ’98, however, has 4 channels and an additional lateral deceleration sensor. The use of 4 channels result in a maximum braking force on all wheels, independent from µ.Since braking during cornering creates a higher weight on the outer rear wheel and therefore higher braking force can be applied. This generates however, a yaw moment and a tendency to oversteer.Depending on vehicle speed and lateral acceleration, the ABS controls the wheel brake pressure, individual, low-µ select or a mixture of both.Nessuna imbardataControllo individualeVelocità veicolo (m/s)
30Controllo nei veicolo 4WD As mentioned earlier on 4WD vehicles, due to the large rotation masses and the fact wheels are influencing one another due to internal connections over differentials, the ABS would not be able to carry out the reference speed calculation accurate enough. In order to overcome this problem ECU needs to determine the actual vehicle speed more precisely. A G-sensor is used for this purpose.On older models (w/o) VSC a longitudinal G-sensor was used.BOn recent models (also equipped with VSC) a semi conductor type G-sensor is used, which is capable to detect longitudinal and lateral deceleration as well.Since wheel speed differences on the rear wheels are impossible when the rear differential is locked, ABS becomes useless and is therefore inoperative. When the transfer selector in L4L, also ABS is switched off for improved braking performance.
31Controllo nei veicoli 4WD Sensore di decelerazione (g)A causa della grande quantità di masse in rotazione che s’influenzano l’un l’altra, l’ABS non è in grado di eseguire il calcolo della velocità di riferimento con la dovuta precisione. Per evitare questo problema viene utilizzato un sensore di (G-sensor).Nei veicoli equipaggiati con il VSC è impiegato un sensore di g a semi-conduttore in grado di rilevare accelerazioni longitudinali e laterali
32ABS Pr= pressione frenante Vv= velocità veicolo Ricapitolando possiamo dire che il funzionamento dell’ABS si basa su due criteri di calcolo:Slittamento delle ruote (incremento, mantenimento e riduzione)Decelerazione delle ruote (aumento e mantenimento)Slittamento 25%Slittamento 10%Pr= pressione frenanteVv= velocità veicoloaw= decelerazione ruoteTo summarize we can say, ABS operation is based on two calculation criteria: - wheel slip and wheel deceleration.During braking the vehicle speed decreases as well as the wheel speed. Depending on the µ of the surface and tires , weight acting on the wheel, the deceleration limit is so selected that it will be reached before 10% wheel slip occurs. Whichever comes first, the system holds the brake pressure constant once the deceleration or slip limit is exceeded.The advantage of the deceleration limit control is that the system acts earlier and can compensate for the hydraulic and mechanical delay in the brake system itself. This means that the vehicle remains controllable in every step of the braking.Controlled by wheel slip, which has two levels, the system controls in 3 modes. (increase, hold and reduce)However, in deceleration mode, only one level is set to trigger, which means that the system can only control in 2 modes (increase & hold)It will be clear that the control resulting in the lowest brake pressure is used.Limite di decelerazioneAumento pressioneMantenimento presione
33ABS ed EBD (Electronic Brake force Distribution) Ever since the introduction of EBD on Avensis, a lot of people are still confused about the actual operation, advantages, disadvantages….Therefore, we would like to cover in detail the ABS/EBD brake system thoroughly.
34EBD Reazione del veicolo Grande forza frenante su tutte le ruote genera instabilità direzionaleWhen brake force increases, at a point, in which the force on the rear wheels exceeds the maximum transmittable force and wheels will lock as result.The reason why the rear wheels will lock earlier is very clear: during braking the weight on the rear wheels reduces and sinceFbrakemax = m.g.µ, wherem = weight on the wheel or axle; g = 9,81m/s²; µ = friction coefficientAs long the Fbrakemax on the left and right wheels are equal, the vehicle slips straight out. But what happens if not?
35EBD Funzionamento indipendentemente dal carico: riduce la forza frenante sulle ruote posteriori (frenata in marcia rettilinea)riduce la forza frenante sulle ruote interne alla curva (frenata in curva)The same phenomena on the rear wheels can give a complete different situation.When there is a difference in transmitted force on the rear wheels, also these wheels will receive a side force. Since the vehicle weight is already limited, the additional side force on top of the high braking force can lead to side slip. (downhill on the µ-split)Especially when the vehicle is in a corner, rear wheels losing grip results in spinning of the car. For that reason most ABS systems will control the rear wheels simultaneous, thus no difference in brake force can occur.To prevent locking of one rear wheel the lowest transmittable force is used as being the maximum for the rear axle (low µ select principle).
36EBDSo far we only discussed the ABS system operation. On all these vehicles, for fail safe reasons, a P-valve regulates mechanically the rear brake pressure in relation to the front brake pressure.As can be seen from the graph, depending on the load of the vehicle, the ideal deviation between front and rear brake pressure differs. An LSPV-valve solved this problem on vehicles where the load can differ drastically (wagon types, pick-up, van)To cover with these mechanical limitations and avoid the additional costs for a “sporty” 2WD vehicle system (with G-sensor) a EBD system is developed.ABS with EBD applies the correct braking force to each wheel to compensate for different loads during cornering, (in accordance with the cargo) and heavy straight line braking.
37Dipende dalla decelerazione ruote ABS/EBDABS (slittamento >10%) EBD (slitt.<10% e aw>13 m/s2)AumentoMantenimentoDipende dalla decelerazione ruoteIncreaseHoldReduceWhere the ABS could only control the rear brake pressure simultaneous based on slip and deceleration, with EBD the ECU still controls the brakes according the wheel slip and deceleration, but slightly different.EBD ABS Control:Wheel deceleration exceeding the fixed level results in going to hold mode for that wheel ONLY.In case wheel slip of one rear wheel exceeds the 10% limit, BOTH rear wheels are set to hold mode (conventional ABS operation).In summary we can state that EBD is ordinary ABS, where the control based on wheel deceleration is performed for each wheel individual. ABS based on wheel slip is still acting on both rear wheels together.The EBD is therefore just a software update, while the P-valve needs to be deleted in order to be able to allow rear brake pressure differences.
38ABS/EBD Condizioni di attivazione modalità EBD: aw 13m/s2 e slitt.< 10%la pressione alle pinze freni posteriori viene controllata individualmente.Passaggio alla modalità ABS:aw 13m/s2 e slitt.> 10%la pressione alle pinze freni posteriori viene controllata simultaneamente.Possiamo quindi affermare che l’EBD è semplicemente un aggiornamento del programma del sistema ABS
39Diagnosi e modalità d’emergenza Guasto del sistemaIndicatore ONABSABS & EBDABS &In case a malfunction is detected, the ECU will try to operate all other systems as much as possible.A front sensor signal stops ABS operation but rear wheel locking or deceleration can still be detected. EBD still operates, so only the ABS warning light is illuminated.In case a rear wheel sensor is malfunctioning, both ABS and EBD are not performing. Hitting the brakes would be very dangerous since the rear wheels receive always the same brake pressure (there is no more mechanical P-valve as a fail-safe) as the front.It is not allowed to drive that vehicle! To warn the driver an illumination for ABS & BRAKE (EBD) turns on.
41Brake Assist (BA)Rileva la richiesta di una frenata d‘emergenza e automaticamente aggiunge pressione all’impianto per assicurare le massime prestazioni frenanti!Con assistenzaForza frenanteSenza assistenzaBrake Assist:This system assists the driver's braking effort in an emergency stop, by increasing the braking force.In case of an emergency stop, people often don’t brake hard enough (bleu line).The ECU determines whether or not a strong braking force is need, by measuring the speed of the brake pedal application. (or the rate of increase of brake master cylinder pressure)When emergency braking is detected, the computer controls the hydraulic pressure, in order to increase the braking force (red line).(Like in normal conditions, ABS prevents the wheels from locking-up)When the driver does not step forcefully enough on the brake in an emergency, only a small amount of brake force is generated.The pedal effort might weaken as time passes, causing a reduction of braking force.Based on how quickly the brake pedal is depressed, BA assesses the intention of the driver to apply emergency braking and increases the brake force.After the BA operation, if the driver intentionally releases the brake pedal, the assist operation reduces the amount of Brake Assist.tempo
42Brake Assist (BA) Pressione frenante c Con assistenza d b Senza assistenzaBrake assist interprets a quick push of the brake pedal as emergency braking and supplements the braking power applied if the driver has not stepped hard enough on the brake pedal.In emergencies, drivers, especially inexperienced ones, often panic and do not apply sufficient pressure on the brake pedal.Brake assist system measures the speed and force, in which the pedal is depressed to determine whether the driver is attempting to brake rapidly, and applies additional pressure to maximize braking performance of both conventional brakes and ABS equipped brakes.When the driver intentionally eases up on the brake pedal, the system reduces the amount of assistance it provides.If brake pressure raises faster than a predetermined level, this triggers the brake assist and the system monitors further the reached level of brake pressure.When this pressure does not keep on rising to the ABS operation limit, the brake assist system is activated to increase brake pressure. Even if the driver now ease upon the brake pedal, pressure still continues to rise.Once the max. allowed pressure (ABS operation limit) is reached, the generated pressure of the master cylinder is monitored. When this pressure drops, in the same line, the brake pressure drops.As long there is force applied on the brake pedal, the assistance is kept at the same level and therefore following the driver’s intentions.Once the brake pedal effort is nearly gone, the BA system is cancelled.atempo
43Brake Assist (BA) Sensore di pressione cilindro maestro La ECU tiene conto sia del valore di pressione raggiunto sia della velocità con cui questa pressione aumentaIn order to constantly monitor the pressure in the master cylinder, which in fact is ultimately necessary for Brake Assist operation, a master cylinder pressure sensor has been adopted.Brake assist system measures the speed and force, in which the pedal is depressed to determine whether the driver is attempting to brake rapidly, and applies additional pressure to maximize braking performance of both conventional brakes and ABS equipped brakes.The speed and the brake force applied on the pedal is measured by the master cylinder pressure sensor, in fact measuring how fast the pressure is increasing in the master cylinder (pressure gradient). On LS430 however, a separate brake pedal load sensing switch is installed for more precise control.
44Reservoir cut solenoid valves Brake Assist AvensisReservoir cut solenoid valvesMaster cylinder cut solenoid valveMaster cylinder cut solenoid valveOn the Avenis, brake fluid is coming from the master cylinder, through the reservoir cut solenoid to the ABS pumps. The master cut solenoids must be closed of to avoid leaking the high pressure back to the master cylinder.Posteriore destra e sinistra sono in modalità di mantenimento
45Valvola di scorrimento Brake Assist BALand Cruiser 120 (senza VSC)Brake Assist meccanicoOn Land Cruiser 120-series the VSC is optional equipment. In order to obtain brake assist operation the vehicle w/o VSC is equipped with a “Mechanical Brake” assist. On top of the operation rod present in the traditional brake booster we see the presence of a slide valve and a hook.GancioValvola di scorrimentoAsta di spinta
46Brake Assist BA Brake Assist meccanico Nessuna attivazione del pedale Valvola di controllo “Aperta”Camera a pressione costanteIn idle condition the “Air valve” is in closed position. The “Control valve“ on the other hand is opened so the vacuum present in the “Constant pressure chamber” is also present in the “Variable pressure chamber”. So no movement or assistance No braking.Stantuffo di spintaAsta di spintaValvola pneumatica “Chiusa”Camera a pressione variabile
47Camera a pressione costante Brake Assist BAPedale premuto (BA non attivato)Velocità dello stantuffo = Velocità dell’asta di spintaValvola di controllo “Chiusa”Camera a pressione costanteSPINTAWhen pushing the “Operation rod” there are two possibilities. First possibility: the operating rod speed is equal to the “Power piston” speed. This is the case for normal braking.At first the control valve is closed after which the air valve opens. Atmospheric pressure is introduced so the pressure in the variable chamber rises and because of the pressure difference on both sides of the membrane the power piston is assisted in the forward direction (see next slide).Stantuffo di spintaAsta di spintaValvola pneumatica “Aperta”Camera a pressione variabile
48Camera a pressione costante Brake Assist BAPedale premuto (BA non attivato)Velocità stantuffo di spinta = Velocità asta di spintaValvola di controllo “Chiusa”Camera a pressione costanteSPINTAMOVIMENTOWhen the desired brake performance is reached the air valve will come to a closed state after which a balance position is obtained between the hydraulic pressure in the brake system on one side and the combination of pedal pressure, vacuum in the constant pressure chamber and P(partial vacuum) in the variable pressure chamber.Stantuffo di spintaAsta di spintaValvola pneumatica “Aperta”Camera a pressione variabile
49Camera a pressione costante Brake Assist BABrake Assist meccanicoNessuna attivazione del pedaleValvola di controllo “Aperta”Camera a pressione costanteWhen releasing the brake pedal, the control valve opens and pressure in the variable pressure chamber will lower until equal to the pressure in the constant pressure.Stantuffo di spintaAsta di spintaValvola pneumatica “Chiusa”Camera a pressione variabile
50Camera a pressione costante Brake Assist BAPedale premuto (BA attivato)Velocità stantuffo di spinta < Velocità dell’asta di spintaValvola di controllo “Chiusa”Camera a pressione costanteSPINTASecond possibility: the driver pushes the brake pedal fast. The operating rod speed is higher then the power piston speed.The air valve pushed by the operating rod will move forward more then the power piston and as such will crush the rubber damper (hatchet clear blue section) inside the power piston. Simultaneously the slide valve will be released by the hooks. In this case the control valve will remain closed for a longer travel distance then without the slide valve. This means that also the power piston will travel further forward before reaching the equilibrium position. So brake assist occurs…(see next slide).Stantuffo di spintaAsta di spintaValvola pneumatica “Aperta”Camera a pressione variabile
51Camera a pressione costante Brake Assist BAPedale premuto (BA attivato)Velocità stantuffo di spinta < Velocità dell’asta di spintaValvola di controllo “Chiusa”Camera a pressione costanteSPINTAMOVIMENTONote that when the operating rod is released, the first valve to close will be the air valve. Only then the control valve will open to let the air escape to the vacuum chamber.Stantuffo di spintaAsta di spintaValvola pneumatica “Aperta”Camera a pressione variabile
52Sistema di controllo della trazione - TRC On roads with low coefficient of friction (), such as snowy, icy or wet roads, the drive wheels spin if the vehicle is accelerated quickly, resulting in loss of torque and possibly causing vehicle skidding.The maximum torque that can be transmitted to the wheels is determined by the friction force between the road and tires contact surface.Tdrive / wheel radius < Friction forceIf the attempt is made to transmit torque exceeding that level to the wheels, it will become easy for the wheel to spin.TRC system lowers the engine’s torque, regardless of the driver’s intentions, when the wheels start to spin, while at the same time controlling the brake system, thereby reducing the torque transmitted to the road surface. In this way, stable and rapid starting and acceleration can be achieved.
53Intervallo di tolleranza del TRC FisicaIntervallo di tolleranza del TRC204060801001Asfalto asciuttoAsfalto asciuttoAsfalto bagnatoAsfalto bagnatoGhiaccioOn roads with low µ, the drive wheels spin when the driver wants to accelerate quickly. Since spinning wheels (100% slip) can transmit less force to the road surface and can not transmit any side force, vehicle’s acceleration will be less and fishtailing will occur on FR vehicles.The TRC system maintains the wheel slip between the 10-25% ratio in order to allow the maximum torque to be transmitted to the road surface.GhiaccioRapporto di slittamento (%)
56Nuova generazione TRCETCS-i (Electronic Throttle Control System-intelligent)
57ABS & TRC attuatore 12/2 Modalità normale During normal braking, the reservoir cut solenoid valves are closed.Solenoide d’esclusione liquido vaschetta
58TRC - Modalità d’incremento della pressione Pressione pompaLiquido pressurizzatoTRC on Avensis is very basic: close off the master cylinder by the cut solenoid valves and open the reservoir cut solenoids to supply the pumps with brake fluid.Note that the brake fluid is coming through the master cylinder and not directly from the reservoir. This means that the brake pedal must not be applied, so that the (small) connection between reservoir and master cylinder outlet is open.TRC operationThe fluid pressure that is generated by the pump, is regulated by the pressure regulator valve to the required pressure (regulated mechanically). Thus, the wheel cylinder of the front wheels are controlled in 3 modes: pressure increase, pressure holding and pressure reduction. The diagram above shows the hydraulic circuit in pressure increase mode when TRC is activated.During TRC operation, the pump motor of the brake actuator is activated.Further control is carried out by the ABS part according to the wheel slip.Components: Pressure regulator valve (1) (assembled into the master cyl. cut valve (2,5) Master cylinder cut off solenoid valve (2,5) Reservoir cut off solenoid valves (3,4) Pressure holding valve (6,7,8,9) Pressure reduction valve (10,11,12,13)
59Attuatore ABS & TRC integrato Cilindro maestroIS200ABS & TRC attuatoreSensori di velocità anterioriSensori di velocità posterioriTRC OFF SW TRC OFF indicator ABS warning light SLIP indicatorETCS-i motore e frizioneBrake actuator (ABS and TRC)TRC system on IS200 is the first traction control system of, where engine torque control is carried out by controlling the ignition timing and the throttle opening angle via ETCS-i.Features of TRC: Brake hydraulic circuits are composed of axles. TRC actuator is integrated into ABS actuator by adding three more solenoid valves:pressure regulator valve cut solenoid,master cylinder cut solenoidand reservoir cut solenoid.ECUmotoreABS & TRC ECUBobine
60Solenoidi per TRC, VSC e BA TRC – tipo 14/2 (LS 430)Pressione pompaSuction solenoid valves (for BA)Liquido pressurizzatoSolenoidi per TRC, VSC e BAMaster cylinder cut solenoid valveMaster cylinder cut solenoid valveReservoir cut solenoid valvesSolenoidi per l’ABSBrake actuator (ABS, TRC, VSC and BA)UCF20 from ‘98 production and UCF30The TRC actuator is integrated in the ABS actuator.Additional to the 8 2-position solenoids of the ABS, 2 master cylinder cut solenoid valves, 2 reservoir cut solenoid valves and 2 suction solenoid valves (refer the BA system) are adopted.Again master cylinder is cut off, reservoir cut valve opened, the ABS pump activated and the ABS solenoids control the wheel spin.PosterioriAnterioriEngine ECUSkid control ECUSpeed sensorBrake actuatorSlip indicator light
61TRC integrato – tipo 14/2 (Circuito diagonale RX 300) Cilindro maestroSensore di pressioneMaster cylinder cut solenoid valves2145173611891011Differences RX300 to LS400 (UCF20 ‘98) and LS430 (UCF30):Diagonal brake circuit is used and therefore two additional master cylinder cut solenoid valves are installed (in total 4). The suction valves have been omitted.Brake actuator (ABS, TRC, VSC and BA)This brake actuator consists of 14 two-position solenoid valves, 1 motor, 2 pumps, 2 reservoir, 4 pressure regulator valves (1) and a master cylinder pressure sensor.Amongst the 14 two-position solenoid valves, 4 are used for master cylinder cut (2, 3, 6, 7), 2 for reservoir cut (4, 5), 4 for pressure holding (8, 9, 10, 11) and another 4 for pressure reduction (12, 13, 14, 15).Vacuum booster type brake assist system has been adopted.Front right wheel12131415Front left wheelRear leftRear right
62TRC integrato - tipo 14/2 (Circuito diagonale RX 300) TRC sulle ruote anterioriMaster cylinder cut solenoid valveIn the slide, TRC is active for the front wheels. TRC on the rear wheels can be created by the master cylinder cut solenoid valves.Front right wheelFront left wheelRear leftRear right
63Attuatore (MC RAV4, NG RX300, MMC LS 430) Su alcuni modelli la pompa ABS è cambiata dal tipo a pistoni al tipo trocoidaleGruppo valvole a solenoideMotorePompa trocoidaleECU
64Attuatore (MC RAV4, NG RX300, MMC LS 430) Su alcuni modelli la pompa ABS è cambiata dal tipo a pistoni al tipo trocoidalePompa trocoidaleECU di cotrollo dello slittamentoMotoreGruppo valvole
65Attuatore (MC RAV4, NG RX300, MMC LS 430) La pompa trocoidale viene utilizzata per ridurre la rumorositàTrocoidaleA pistoni (tipo convenzionale)QuantitàQuantitàTempoTempoPiccole pulsazioni Piccole vibrazioniGrandi pulsazioni Grandi vibrazioni
66Attuatore ABS & TRC integrato Servofreno idraulico1: Solenoide d’esclusione accumulatore (STR)2: Solenoide d’esclusione del servo-freno per le ruote posteriori (SA3)3: Solenoide d’esclusione del servo-freno per l’ant. Sx (SA1)4: Solenoide d’esclusione del servo-freno per l’ant. Dx (SA2)2134In combination with the hydraulic brake booster and the 8 2-position solenoids of the ABS, one additional solenoid valve for rear wheel brake master cylinder (booster pressure) cut-off solenoid (SA3) and one accumulator cut-off solenoid (STR) valve is used.When wheel slip is detected, the accumulator solenoid valve opens to apply hydraulic pressure via the pressure holding and reduction solenoids to the rear wheel brakes. (master cylinder cut-off solenoid SA3 is closed)Further control of wheel slip is performed by the ABS.NOTE: una delle ruote posteriori è in modalità di riduzioneRear axleFront axle
67Controllo della potenza Veicolo con ETCS-iIntensità della sbandataInizio contollo farfallaInizio controllo freniControllo freni completatoControllo farfalla completatoAngolo di apertura della farfallaAltaOn 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.Pressione alle pinze frenitempo
68TRC Condizioni di attivazione IDL: OFF Neutral/Parking sw: OFF SPD > 6 km/hTRC switch: ONMemoria guasti attuali della ECU ABS: vuotaECU ABS & TRC non in comunicazione con ITTRC operating conditions:-the main throttle should not be fully closed.-transmission should not be in “P” or “N”.-the vehicle speed should exceed 6 km/h and stoplight off.-the TRC switch should be off.-the ABS should not be operating.-the system should not be in the sensor check mode or diagnostic code output.
70Active Traction Control A-TRC Effetto di slittamento differenziale limitatoMigliori capacità in fuori stradaMaggiore accelerazione su superfici a differentiMaggiore sensibilità con il veicolo bloccato nel fangoMigliorata guidabilità: non è necessario attivare il bloccaggio del differenzialeDisponibile su:LC100 con motore 2UZ-FE (V8)LC 90 con A/TLC 120/125
71Active Traction Control *Differenziale centrale libero
72Active Traction Control Land Cruiser 12#Se una ruota inizia a slittare il sistema si comporta come un differenziale LSDLa funzione LSD si ottiene frenando la ruota che slittaClick!Movie
73Active Traction Control LC120In questo sistema, il differenziale centrale non necessita di blocco come avviene nei veicoli a trazione integrale convenzionale, e ciò consente una morbida manovra in curva (priva di fenomeno di frenatura in curva stretta)Elevata prestazione di trazione (stessa della trazioneIntegrale - 4WD)Morbida manovrabilità(stessa della trazionea due ruote motrici - 2WD)
74Active Traction Control LC100/120 valvole e solenoidiLa resistenza dei solenoidi è stata variata per aumentare la possibilità di attivazione fino a 3 minutiValvole a SolenoideSolenoide di regolazione, di interruzione e di mantenimento della pressioneSolenoidi di interruzione dell’accumulatore e del cilindrio principale (FL/FR)Massimo tempo di attivazioneNew LC100/120Approx. 7.2 Approx. 4.3 3 minutiLC100/90Approx. 5.0 Approx. 3.7 50 secondiNOTE: When the voltage is 13 V (P=R*I²) New Model: 7.2 x (1.81 A)² = WPrevious Model: 5 x (2.60 A)² = 33.8 W