System Description

VDIM (Vehicle Dynamics Integrated Management) DESCRIPTION
1. This vehicle is equipped with VDIM (Vehicle Dynamics Integrated Management) It is a concept of vehicle motion control that integrates brake control, drive force control and steering control.
2. Conventional vehicles use a combination of independent functions such as ABS, TR(A)C, VSC, EPS and VGRS. However VDIM integrates these systems to improve "drive, turn and stop", the motion performance of the vehicle in other words.
3. In conventional vehicles, control starts at the limit of the vehicle However VDIM exercises control before the limit is reached, creating a smooth vehicle response This expands the limits of the vehicle, and increases driving pleasure Also, with the cooperative control function with the A/T, the vehicle has smooth, natural acceleration.
  
  Fig 1: VDIM - Diagram
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
4. The VDIM manages all functions, such as the ABS with EBD, brake assist, TR(A)C, and VSC. It is operated by the electronically controlled brake system, which regulates brake fluid pressure The steering cooperative control function is also available Thus the VDIM is able to perform comprehensive management.
5. Conventional brake control systems begin to control either the braking or motive force in order to stabilize the vehicle motion when it becomes unstable due to loss of tire traction. In contrast, in order to maintain stable vehicle control, the VDIM commences controlling the brake and steering systems in accordance with changes in balance before the vehicle becomes unstable. As a result, smooth vehicle control is achieved.
6. Conventional brake control systems manage all related functions, such as the ABS with EBD, brake assist, TR(A)C and VSC independently, according to the vehicle dynamics In contrast, the VDIM provides smooth control by seamlessly integrating all those functions.
ELECTRONICALLY CONTROLLED BRAKE SYSTEM DESCRIPTION
1. The system detects the degree of brake pedal operation with a brake pedal stroke sensor and two master cylinder pressure sensors, and calculates the optimum hydraulic brake force. The hydraulic pressure source is adjusted based on this so that the optimum hydraulic control is independently performed on all four wheels.
2. Meanwhile, the electronically controlled brake system performs control of the normal brakes, RBS (Regenerative Brake Cooperative Control System), ABS, TR(A)C, VSC and brake assist in accordance with the operations of the driver.
3. There is a hydraulic backup mechanism that applies brake master cylinder pressure generated by human power to the wheel cylinder when the brake control stops. In addition, as a fail-safe mechanism, when the brake control is malfunctioning, the system excludes the malfunctioning sections and continues to perform brake control on the normal sections. A power backup unit (brake control power supply) is also used to ensure a stable supply of power to the system.
  
  Fig 2: Skid Control ECU - System Diagram
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
FUNCTION DESCRIPTION
1. ABS (Anti-lock Brake System)
  The ABS helps prevent the wheels from locking when the brakes are applied suddenly and firmly or applied on a slippery surface.
  
  Fig 3: ABS (Anti-Lock Brake System) - System Diagram
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  1. Operation description
    The skid control ECU detects the wheel lock condition by receiving vehicle speed signals from each speed sensor, and sends control signals to the solenoid valve The solenoid valve avoids wheel lock by controlling the oil pressure of each wheel cylinder.
    
    The ABS warning light comes on when the ABS system is malfunctioning.
2. EBD (Electronic Brake Force Distribution)
  The EBD control utilizes the ABS, performing proper brake force distribution between the front and rear wheels in accordance with driving conditions. When braking while cornering, it also controls the brake forces of the right and left wheels, helping to maintain proper vehicle control.
  
  Fig 4: EBD (Electronic Brake Force Distribution) - System Diagram
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  1. Operation description
    The skid control ECU receives the speed signal from each speed sensor to detect, the slip condition of the wheels and sends the control signal to the solenoid.
    
    The solenoid valve controls the oil pressure of each wheel cylinder and splits the control power properly between the front and rear wheels and the right and left wheels.
    
    The ABS warning light and brake warning light / red (malfunction) come on to indicate a malfunction in the EBD system.
3. BA (Brake Assist)
  The primary purpose of the brake assist system is to provide auxiliary brake force to assist the driver who cannot generate a brake force large enough during emergency braking, thus helping to maximize the vehicle's brake performance.
  
  Fig 5: BA (Brake Assist) - System Diagram
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  1. Operation description
    The skid control ECU receives the brake pedal stroke sensor signal and the oil pressure signal from the master cylinder pressure sensor to determine whether brake assist is necessary or not. If brake assist is deemed necessary, the skid control ECU will send control signals to the solenoid valves. The solenoid valves then control the pressure applied to each wheel cylinder.
    
    The ABS warning light comes on to indicate a malfunction in the BA system.
4. Regarding changing of TR(A)C and VSC operation permission / disablement through VSC OFF switch.
  1. Changing modes
    Through the VSC OFF switch, the vehicle can be changed to normal mode, TR(A)C OFF mode and VSC OFF mode.
    
    Fig 6: Identifying VSC OFF Switch
    Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    1. Normal mode
      When the vehicle is in TR(A)C OFF mode or VSC OFF mode, and the VSC OFF switch is pressed for a short amount of time, the vehicle changes to normal mode. During normal mode, TR(A)C and VSC operation is possible. After the power switch is turned ON, the vehicle is in normal mode.
    2. TR(A)C OFF mode
      When the vehicle is in normal mode and the VSC OFF switch is pressed for a short amount of time, the vehicle changes to TR(A)C OFF mode. During TR(A)C OFF mode, the combination meter's slip indicator light illuminates, and TR(A)C operation is disabled. During TR(A)C OFF mode, if the vehicle speed increases, the vehicle automatically returns to normal mode.
    3. VSC OFF mode
      When the vehicle is stopped and the VSC OFF switch is pressed for 3 seconds or more, the vehicle changes to VSC OFF mode. During VSC OFF mode, the multi-information display shows a VSC OFF display, and the combination meter's slip indicator light illuminates. Also, VSC and TR(A)C operation are disabled. During VSC OFF mode, even if the vehicle speed increases, the vehicle does not return to normal mode.
5. TR(A)C (Traction Control)
  The TR(A)C system helps prevent the drive wheels from slipping when the driver depresses the accelerator pedal excessively while starting off or accelerating on a slippery surface.
  
  Fig 7: TR(A)C (Traction Control) - System Diagram
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  1. Operation description
    The skid control ECU detects the vehicle's slip condition by receiving signals from each speed sensor and the hybrid vehicle control ECU via CAN communication The skid control ECU controls driving torque together with the hybrid vehicle control ECU via CAN communication. Driving torque control is carried out by controlling brake fluid pressure with the solenoid valve.
    
    The slip indicator light blinks when the system is operating. When there is a malfunction in the TR(A)C system, the brake warning light / yellow (minor malfunction) and slip indicator light come on and a DTC will appear on the multi-information display.
    
    The VSC OFF switch stops traction control operation.
    
    HINT:
    
    When the VSC OFF switch is pressed, the vehicle changes to TR(A)C OFF mode, and TR(A)C operation is disabled. During TR(A)C OFF mode, if the VSC OFF switch is pressed again or the vehicle speed increases to 50 km/h (31 mph), TR(A)C operation becomes possible. During TR(A)C OFF mode, the SLIP indicator light illuminates.
6. VSC (Vehicle Stability Control)
  The VSC system helps prevent the vehicle from slipping sideways as a result of strong front or rear wheel skid during cornering.
  
  Fig 8: VSC (Vehicle Stability Control) - System Diagram
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  1. Operation description
    The skid control ECU determines the vehicle condition by receiving signals from each speed sensor, yaw rate and acceleration sensor and steering angle sensor. The skid control ECU controls driving torque together with the hybrid vehicle control ECU via CAN communication. Driving torque control is carried out by controlling brake fluid pressure with the solenoid valve.
    
    The slip indicator light blinks and the skid control buzzer sounds when the system is operating. When there is a malfunction in the VSC system, the brake warning light / yellow (minor malfunction) and slip indicator light come on and a DTC will appear on the multi-information display.
    
    The VSC OFF switch stops VSC operation.
    
    HINT:
    
    When the VSC OFF switch is pressed for 3 seconds or more with the vehicle stopped, the VSC system changes to VSC OFF mode. If the VSC OFF switch is pressed again with the system in VSC OFF mode, the TR(A)C and VSC systems can be operated. When the system is in VSC OFF mode, the SLIP indicator light and VSC OFF indicator light illuminate.

BRAKE HOLD SYSTEM

The brake hold operation occurs when the brake pedal is depressed and the vehicle is fully stopped. Under brake hold, the wheel cylinder oil pressure of the 4 wheels is maintained, and the vehicle's fully stopped condition is sustained. When the acceleration pedal is depressed, the wheel cylinder oil pressure is automatically released. Also, depending on the vehicle conditions, the electric parking brake operates.

Fig 9: Brake Hold System Diagram

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

TRANSMITTING ECU TRANSMITTER AND COMMUNICATION METHOD REFERENCE

Transmitting ECU (Transmitter)	Receiving ECU (Receiver)	Signals	Communication Method
Skid control ECU	Electric parking brake ECU	Stop light switch signal Brake hold status Vehicle speed Electric parking brake lock command	CAN communication system
Electric parking brake ECU	Skid control ECU	Electric parking brake lock status Electric parking brake control permission status	CAN communication system
Hybrid vehicle control ECU	Skid control ECU	Accelerator pedal idling signal Accelerator pedal opening percentage signal Shift position signal Vehicle load signal	CAN communication system
Yaw rate and acceleration sensor	Skid control ECU	Yaw rate and acceleration sensor signal	CAN communication system
Pad switch ECU (Brake hold switch)	Skid control ECU	Brake hold operation request	CAN communication system
Skid control ECU	No 1 meter ECU	Brake hold standby indicator light ON signal Brake hold operated indicator light ON signal	CAN communication system
Skid control ECU	Main body ECU	Stop light ON signal	CAN communication system
Main body ECU	Luggage room junction block (Rear junction block ECU)	Stop light ON signal	CAN communication system
Center airbag sensor	Main body ECU	Driver's side seat belt buckle switch signal	CAN communication system
Skid control ECU	Warning buzzer	Warning buzzer signal	Serial communication line
Skid control ECU	Brake actuator	Hydraulic pressure command signal	Serial communication line
Speed sensor	Skid control ECU	Wheel speed signal	Serial communication line
Driver's side door courtesy switch	Skid control ECU	Driver's side door courtesy switch signal	Serial communication line
Hood courtesy switch Luggage door courtesy switch	Main Body ECU	Hood courtesy switch signal Luggage door courtesy switch signal	Serial communication line

Operation description
1. Brake hold system indicator lights and stop light.
  - When brake hold can be operated, the combination meter's brake hold standby indicator light illuminates in green. When brake hold is operating, the brake hold operated indicator light illuminates in amber Also, when brake hold is operating, even if the driver is not depressing the brake pedal, the stop lights illuminate.
  - When the brake hold system is malfunctioning and the brake hold switch is pressed, the brake hold standby indicator light blinks in green. For other malfunctions, the warning light of the malfunctioning area illuminates.
  Fig 10: Identifying Brake Hold System Indicator Lights And Brake Hold Switch
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Brake hold system operation standby conditions (all conditions below must be met).
  - Brake hold switch is pushed [A]
    HINT:
    
    If the power switch is turned OFF, brake hold will stop operating
  - Brake hold system is normal
  - Driver side door is closed
  - Driver side seat belt is fastened
  - Engine hood is closed
  - Luggage compartment door is closed
3. Brake hold system operation conditions (all conditions below must be met)
  - Brake hold system is in operation standby state
  - Shift lever is in position other than P or R
  - Driver is depressing brake pedal and vehicle is fully stopped [B]
  - Driver is not depressing accelerator pedal
  - Vehicle is not on steep decline
4. Brake hold system operation stop conditions (one of the conditions below must be met)
  - Driver depresses accelerator pedal [C]
  - Shift lever is moved to P position
  - While brake pedal is depressed, shift lever is moved to R position
    
    Fig 11: Identifying Brake Hold Standby Indicator Lights ON And OFF Position
    Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
ELECTRIC PARKING BRAKE SYSTEM LINKED OPERATION
HINT:

If the driver is depressing the brake pedal, the parking brake linked operation will not occur.
1. Parking brake automatic operation condition while brake hold system is operating (one of the conditions below must be met)
  - Driver side door is opened
  - Driver side seat belt is unfastened
  - Engine hood is opened
  - Luggage compartment door is opened
  - Brake hold has operated and 3 minutes or more have passed
2. Parking brake release
  Before driving the vehicle, release the parking brake
3. Brake hold system operation standby end condition (automatic) (either of the conditions below must be met)
  - As a result of opening of driver side door, opening of engine hood, opening of luggage compartment door or unfastening of driver side seat belt, parking brake linked operation occurs
  - While driving the vehicle, opening of driver side door, opening of engine hood, opening of luggage compartment door or unfastening of driver side seat belt occurs
4. Brake hold system operation standby end condition (manual) (either of the conditions below must be met)
  - While driving vehicle, brake hold switch is pushed
  - While vehicle is stopped and brake pedal is depressed, brake hold switch is pushed
5. Brake hold system malfunction condition (one of the conditions below must be met)
  HINT:
  
  If a brake hold system malfunction occurs, brake hold will stop operating.
  - Hybrid control system malfunction
  - Electric parking brake system malfunction
  - Electronically controlled brake system malfunction
    HINT:
    
    Even if the electronically controlled brake system is malfunctioning, the parking brake linked operation can operate.

STEERING COOPERATION CONTROL
1. The VDIM system effects coordinated control consisting of the electronically controlled brake system, EPS (Electric Power Steering), and VGRS (Variable Gear Ratio Steering) By integrating these preventive safety functions, the VDIM system ensures excellent driving stability and maneuverability of the vehicle.
2. If the vehicle loses stability due to slippage, this function effects brake control by applying hydraulic pressure to the wheels At the same time, the EPS provides steering torque assist control or active steering wheel angle control and the VGRS provides variable gear ratio steering control to facilitate the driver's steering control.
DYNAMIC RADAR CRUISE CONTROL
1. When a greater deceleration than usual is required while driving in vehicle control mode, braking force is generated by the brake hydraulic pressure control in accordance with the signal from the distance control ECU.
PRE-COLLISION CONTROL
1. The pre-collision system predicts frontal collisions with other vehicles or obstructions By winding up the seat belts prior to collision, and performing brake control and brake assist control, it lessens the impact during the collision.
2. The extreme high frequency radar recognizes if there is a vehicle or obstruction on the road ahead, and the distance control ECU makes a judgment (from the position and speed of the object, the road surface) of whether or not a collision is unavoidable.
3. The distance control ECU sends this information via CAN communication to the seat belt control ECU, suspension control ECU and skid control ECU to operate each control element of the pre-collision system.

FUNCTION OF COMPONENTS

Components	Functions
Skid control ECU	Processes the signals from each sensor to perform brake control for ABS, TR(A)C, and VSC In addition, it communicates with the hybrid vehicle control ECU to output a control signal
Gateway ECU	Transmits data between ECUs connected to a different bus in the CAN communication system
Hybrid vehicle control ECU	Controls the driving torque output during the operation of TR(A)C and VSC by communicating with the skid control ECU
Brake control power supply	Provides the system with a supplementary power supply by discharging the electric charge of the capacitor When the vehicle power voltage (12 V) is low and an electric charge is accumulated in the power back up unit's capacitor, the electric charge is discharged
Speed sensor	Detects the wheel speed and inputs the results to the skid control ECU
Brake pedal stroke sensor	Detects the brake pedal stroke volume and inputs the results to the skid control ECU
Yaw rate and acceleration sensor	Detects the yaw rate (axial rotation) and the forward, rearward and lateral acceleration, and inputs the results to the skid control ECU
Steering angle sensor	Detects the steering angle and direction, and outputs the results to the skid control ECU via CAN communication
Accumulator pressure sensor (PACC)	Built into the brake actuator to detect the accumulator hydraulic pressure and inputs the results to the skid control ECU
Stop light switch	Detects the brake operating conditions and inputs the results to the skid control ECU
VSC OFF switch	Switches off the TR(A)C and VSC operation
Brake hold switch	Permits the brake hold operation
Brake fluid level warning switch	Detects a reduction in the level of the brake fluid in the reservoir
ABS motor relay (ABS MTR1, ABS MTR2)	Controlled by the skid control ECU Supplies power to the pump motor
Skid control buzzer	Sounds intermittently to inform the driver that the VSC is active Sounds intermittently to warn the driver of a reduction in accumulator hydraulic pressure in the brake actuator, an abnormality in the power supply system, or a reduction in the vehicle power voltage (12 V)
Brake fluid reservoir	Stores brake fluid for the brake master cylinder system and power supply system
Brake master cylinder	Generates pressure in accordance with the force of the brake operation
Brake stroke simulator cylinder	Generates a natural pedal stroke in accordance with the pedal force of the driver during system operation (integrated with the brake master cylinder)
Stroke simulator cut valve (SCSS)	Sends brake fluid pressure generated in brake master cylinder to brake stroke simulator cylinder during system control
Accumulator	Accumulates the hydraulic pressure generated by the pump for the power supply system
Pump motor	Pumps up the brake fluid from the reservoir and supplies the accumulator with high hydraulic pressure
Brake actuator	Controls the hydraulic pressure of each of the four wheel cylinders using the output signal of the skid control ECU
Master cylinder pressure sensor (PMC1, PMC2)	Built into the brake actuator to detect the pressure of the brake master cylinder and inputs the results to the skid control ECU
Wheel cylinder pressure sensor (PFR, PFL, PRR, PRL)	Built into the brake actuator to detect the brake hydraulic pressure of each wheel cylinder and inputs the results to the skid control ECU
Master cut solenoid valve (SMC1,SMC2)	Switches the brake hydraulic pressure route according to if normal brakes are used, or if VDIM (ABS, TR(A)C and VSC) control is used
Linear solenoid valve (SLA##, SLR##)	Controls the wheel cylinder hydraulic pressure during normal brake operation and VDIM (ABS, TR(A)C and VSC) control SLA## are solenoids for controlling pressure increases, while SLR## are solenoids for controlling pressure decreases
Relief valve	Prevents excessive high pressure in the power supply system It relieves the system by sending brake fluid to the reservoir when the pump has operated continuously, for example, during an accumulator hydraulic pressure sensor malfunction
ABS warning light	Comes on to inform the driver that a malfunction in the ABS or BA has occurred Blinks to output DTC
Brake warning light / red (malfunction)	Comes on when a malfunction which has a possibility of influencing brake performance has occurred Comes on when the brake fluid level is low
Brake warning light / yellow (minor malfunction)	Comes on when there is a malfunction in the normal brakes or a minor malfunction in the brake system which does not impair driving
Slip indicator light	Blinks to inform the driver that ABS, TR(A)C and VSC are operating Comes on when the VSC OFF switch is on to inform the driver of the TR(A)C and VSC operation prohibited state or that a malfunction in the TR(A)C and VSC system has occurred
Brake hold standby indicator light / green	Comes on when the system is in the brake hold control permission state Blinks when a malfunction has occurred during brake hold control selection
Brake hold operated indicator light / amber	Comes on when the brake hold is operating
Multi-information display	Comes on to inform the driver that a malfunction in the electronically controlled brake system or VSC system has occurred Displays output DTC

FAIL-SAFE
1. When a failure occurs in the ABS with BA, TR(A)C and VSC systems, the ABS warning light and the brake warning light / yellow (minor malfunction) come on and ABS with BA, TR(A)C and VSC operations will be prohibited In addition to this, when there is a failure that disables the EBD operation, the brake warning light/ red (malfunction) also comes on and the EBD operation is prohibited.
2. If control is prohibited due to a malfunction during operation, control will be disabled gradually. This is done to avoid sudden vehicle instability.
MAINTENANCE MODE
1. VSC operation can be disabled by operating the Intelligent tester or Techstream.
  HINT:
  
  Refer to the Intelligent tester or Techstream operator's manual for further details.