Electronic Stability Control (Esc) System Components: Overview Hyundai Equus II

Scheme 4

Description of ESC

Optimum driving safety now has a name: ESC, the Electronic Stability Control.

ESC recognizes critical driving conditions, such as panic reactions in dangerous situations, and stabilizes the vehicle by wheel-individual braking and engine control intervention.

ESC adds a further function known as Active Yaw Control (AYC) to the ABS, TCS, EBD and EDC functions. Whereas the ABS/TCS function controls wheel slip during braking and acceleration and, thus, mainly intervenes in the longitudinal dynamics of the vehicle, active yaw control stabilizes the vehicle about its vertical axis.

This is achieved by wheel individual brake intervention and adaptation of the momentary engine torque with no need for any action to be taken by the driver.

ESC essentially consists of three assemblies: the sensors, the electronic control unit and the actuators.

The stability control feature works under all driving and operating conditions. Under certain driving conditions, the ABS/TCS function can be activated simultaneously with the ESC function in response to a command by the driver.

In the event of a failure of the stability control function, the basic safety function, ABS, is still maintained.

Scheme 5

Description of ESC Control

ESC system includes ABS/EBD, TCS and AYC function.

ABS/EBD function The ECU changes the active sensor signal (current shift) coming from the four wheel sensors to the square wave.

By using the input of above signals, the ECU calculates the vehicle speed and the acceleration & deceleration of the four wheels.

And, the ECU judges whether the ABS/EBD should be actuated or not.

TCS function prevents the wheel slip of drive direction by adding the brake pressure and engine torque reduction via CAN communication.

TCS function uses the wheel speed sensor signal to determine the wheel slip as far as ABS function.

AYC function prevents unstable maneuver of the vehicle. To determine the vehicle maneuver, AYC function uses the maneuver sensor signals (Yaw Rate Sensor, Lateral Acceleration Sensor, Steering Wheel Angle Sensor).

If vehicle maneuver is unstable (Over Steer or Under Steer), AYC function applies the brake pressure on certain wheel, and send engine torque reduction signal by CAN.

After the key-on, the ECU continually diagnoses the system failure. (Self-diagnosis)

If the system failure is detected, the ECU informs driver of the system failure through the BRAKE/ABS/ESC warning lamp. (fail-safe warning)

Scheme 6

Scheme 7

Scheme 8

Scheme 9

Scheme 10

1. ESC Non-operation: Normal braking. ESC NON-OPERATION REFERENCE CHART Solenoid valve Continuity Valve Motor pump TC Valve IN (NO) OFF OPEN OFF OFF OUT (NC) OFF CLOSE Operation In this position, the inlet valve and the TCS valve are open, the electrically operated shuttle valve and the outlet valve are closed. ESV: Electric reversing valve.
2. ESC operation ESC OPERATION REFERENCE CHART Solenoid valve Continuity Valve Motor pump TC Valve Under steering (Only inside of rear wheel) IN(NO) OFF OPEN ON ON OUT(NC) OFF CLOSE Over steering (Only outside of front wheel) IN(NO) OFF OPEN OUT(NC) OFF CLOSE Operation The on/off booster builds up a pressure of approx. 10 bar in order to enable the ESC pump to suck brake fluid at low temperatures. In this position, the inlet valve is driven in a pulsed cycle. The TCS valve is closed. The outlet valve remains closed. The electrically operated shuttle valve is opened. The hydraulic pressure is led to the wheel brakes which are to be applied for a brief period of time.

Scheme 11

Scheme 12

Scheme 13

Scheme 14

1. Normal Braking ABS OPERATION MODE REFERENCE CHART Solenoid valve State Valve Passage Inlet valve (NO) OFF OPEN Master cylinder[]Wheel cylinder Outlet valve (NC) OFF CLOSE Wheel cylinder[]Reservoir When braking, the hydraulic pressure in the TMC is increased. The pressure reaches the wheel brake via the current less open inlet valve IV. The current less closed outlet valve OV is closed. For the sake of simplicity the diagram is limited to only the solenoid valve pair of one brake circuit. The wheel speed is reduced as the brake pressure increases, in the extreme case until the wheel locks.
2. Dump Mode DUMP MODE REFERENCE CHART Solenoid State Valve Passage Inlet valve (NO) ON CLOSE Master cylinder[]Wheel cylinder Outlet valve (NC) ON OPEN Wheel cylinder[]Reservoir If the wheel speed decreases, there is still a tendency to lock; the brake pressure on the corresponding wheel must be reduced accordingly. For this, the outlet valve OV is opened, the inlet valve IV remains closed. The brake pressure to the low-pressure accumulator is reduced. The wheel in danger of locking gains speed again.
3. Hold Mode HOLD MODE REFERENCE CHART Solenoid State Valve Passage Inlet valve (NO) ON CLOSE Master cylinder[]Wheel cylinder Outlet valve (NC) OFF CLOSE Wheel cylinder[]Reservoir When a wheel (or several) tends to lock the inlet valve IV is first closed to avoid a further increase in brake pressure. The outlet valve OV remains closed: the brake pressure is kept constant.
4. Increase Mode INCREASE MODE REFERENCE CHART Solenoid State Valve Passage Inlet valve (NO) OFF OPEN Master cylinder[]Wheel cylinder Outlet valve (NC) OFF CLOSE Wheel cylinder[]Reservoir For optimum brake from the certain wheel acceleration a brake pressure increase is necessary. For this, the inlet valve IV is opened and the outlet valve OV is closed. The pump of the unit starts to run and aspirates the necessary quantity of fluid from the Low-pressure accumulator, in order to produce the necessary brake pressure for the pressure increase phase in seconds. With an increase in the brake pressure the wheel speed is reduced. These control phases are repeated until the ABS control unit no longer detects any tendency of the wheels to lock. NOTE: During ABS control function, the brake pedal only moves in accordance with the volume requirement of the wheels. Because of a sudden change in friction coefficient this pedal movement may increase slightly.

Scheme 15

Description

The VSM is an electronic control system that can provide vehicle stability, control car-to-car distance and offer parking convenience through the integrated control of the damping, braking and driving forces using the suspension system and the Smart Cruise Control (SCC) system on the basis of Electronic Stability Control (ESC) system.

It consists of the high-performance Smart Cruise Control (SCC), Pre-safe Seat Belt (PSB), and the cluster and warns the driver with warning sound, warning lamp, and the belt vibration in accordance with driving condition. When emergency condition, it can protect the driver from critical injury by controlling the seat belt and brake.

Scheme 16

SCC: Smart Cruise Control

PSB: Pre-safe Seat Belt

The EBD system (Electronic Brake force Distribution) as a sub-system of the ABS system is to control the effective adhesion utilization by the rear wheels.

It further utilizes the efficiency of highly developed ABS equipment by controlling the slip of the rear wheels in the partial braking range.

The brake force is moved even closer to the optimum and controlled electronically, thus dispensing with the need for the proportioning valve.

The proportioning valve, because of a mechanical device, has limitations to achieve an ideal brake force distribution to the rear wheels as well as to carry out the flexible brake force distribution proportioning to the vehicle load or weight increasing. And in the event of malfunctioning, driver cannot notice whether it fails or not.

EBD controlled by the ABS Control Module, calculates the slip ratio of each wheel at all times and controls the brake pressure of the rear wheels not to exceed that of the front wheels.

If the EBD fails, the EBD warning lamp (Parking brake lamp) lights up.

The ESC system is the shorten word of Electronic Stability Control system. This system recognizes a critical driving condition by Yaw-rate sensor, Lateral acceleration sensor and Steering angle sensor. And then it stabilizes the vehicle by a individual wheel braking and engine torque control through CAN communication. Among components of this system, the yaw-rate & lateral G sensor is installed on the lower of the center console. The yaw-rate and lateral G sensor are installed together in the one container which is called as "Sensor cluster". When the vehicle is moving around a vertical axis, the yaw rate sensor senses the vibration changes of the plate-fork installed in the yaw-rate sensor. When the vehicle's yawing is sensed and the yaw velocity reaches a certain velocity, the ESC control is activated. The lateral G sensor senses a vehicle's lateral acceleration. A small element in the sensor is attached to a deflectable lever-arm. The HECU recognizes a vehicle's direction and a lateral acceleration by the lateral G sensor.

Scheme 17

1. The ESC OFF switch is for the user to turn off the ESC system.
2. The ESC OFF lamp is on when ESC OFF switch is engaged.

Scheme 18

Scheme 19

Scheme 20

Scheme 21

1. Turn ignition switch OFF and disconnect the negative (-) battery cable
2. Remove the crash pad side cover.
3. Remove the lower panel. (Refer to the «CRASH PAD»(ref-417751-S11778651202011083000000) )
4. Remove the lower crash pad switch assembly by using the scraper and then disconnect the connectors.
5. Check the continuity between the switch terminals as the ESC OFF switch is engaged.

It is used when the driver wants to disable the VSM function and repeats ON and OFF).

1. VSM ON (No lamp in the cluster) It warns with warning sound and so on when detecting any crash condition with previous car. It controls braking right before crash condition.
2. VSM OFF ("VSM OFF" Lamp ON)

1. When the drivers disable the VSM function, the lamp (VSM OFF) is turned ON and the function does not work. NOTE: VSM function is also disabled OFF when VDC OFF.

Scheme 22

Scheme 23

Scheme 24

Scheme 25

1. Turn ignition switch OFF and disconnect the negative (-) battery cable
2. Remove the crash pad side cover.
3. Remove the lower panel. (Refer to the «CRASH PAD»(ref-417751-S11778651202011083000000) )
4. Remove the lower crash pad switch assembly by using the scraper and then disconnect the connectors.
5. Check the continuity between the switch terminals as the VSM OFF switch is engaged.

Steering Wheel Angle Sensor detects rotating direction of the vehicle. Rotating direction detected by the sensor is communicated with HECU as CAN signal involving information about the angle through CAN communication line.

HECU detects speed of the steering wheel handling and the angle with this CAN signal. HECU also uses this signal as the input signal to control anti-roll.

Scheme 26