System Description

1. This vehicle is equipped with VDIM. 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, TRAC, VSC and electronic power steering. However, VDIM integrates these systems to improve "driving, turn and stopping," 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.
   Fig 1: VDIM Flow Diagram

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
4. The VDIM manages all functions, such as the ABS with EBD, BA, the TRAC, and the VSC. It is operated by the electronically controlled brake system, which regulates brake hydraulic pressure. The regenerative braking cooperative control and steering cooperative control functions are 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 when it becomes unstable due to loss of tire traction. In contrast, in order to maintain stable vehicle control, the VDIM starts controlling the brake, hybrid and steering systems in accordance with changes in vehicle 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, BA, the TRAC and the VSC independently, according to the vehicle dynamics. In contrast, the VDIM provides smooth control by seamlessly integrating all those functions.

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 optimum hydraulic control is independently performed on all four wheels.
2. At the same time, the electronically controlled brake system performs control of the normal brakes, ABS, TRAC, VSC and BA in accordance with the operations of the driver.
3. There is a hydraulic backup mechanism that applies master cylinder pressure generated by the driver to the wheel cylinder if brake control stops. In addition, as a fail safe mechanism, if the brake control is malfunctioning, the system by passes the malfunctioning components and continues to perform brake control using the remaining functioning components. A power backup unit (brake control power supply) is also used to ensure a stable supply of power to the system.
   Fig 2: Electronically Controlled Brake System - Communication Diagram

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   HINT:

   The master caution indicator light will come on and a check brake system message will be displayed on the multi-information display if the electronically controlled brake system control cannot be performed.

HINT:

The yaw rate sensor and acceleration sensor are combined in a single unit. This unit communicates with the skid control ECU via CAN communication.

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 - Communication Diagram

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   1. Operation description

      The skid control ECU detects wheel lock based on speed signals it receives from the wheel speed sensors. Based on this information, the skid control ECU controls the solenoid valves. The solenoid valves are used to prevent wheel lock by controlling the hydraulic pressure applied to the brakes at each wheel. The ABS warning light will come on when the system is malfunctioning.

      HINT:

      The master caution indicator light will come on and a check ABS message will be displayed on the multi-information display if the ABS control cannot be performed.

2. EBD (Electronic Brake force Distribution) The EBD control utilizes the ABS to properly distribute brake force between the front and rear wheels in accordance with driving conditions. When braking while cornering, it also controls the brake force distribution between the right and left wheels, helping to maintain vehicle behavior.
   Fig 4: EBD - Communication Diagram

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   1. Operation description

      The skid control ECU receives a speed signal from each wheel speed sensor, and uses these signals to detect locking of the wheels. The ECU uses this information in order to determine appropriate control of the solenoid valves. The solenoid valves control the hydraulic pressure applied to the brake cylinder at each wheel. In this way, the solenoid valves are used to control the brake force distribution between the front and rear, and left and right wheels. The brake warning light / red (malfunction) will come on if there is a malfunction in the EBD system.

      HINT:

      The master caution indicator light will come on and a brake malfunction message will be displayed on the multi-information display if the EBD system is malfunctioning.

3. BA (Brake Assist)

   The primary purpose of the brake assist system is to provide auxiliary brake force to assist a driver who cannot generate a brake force large enough during emergency braking, thus helping to maximize the brake performance of the vehicle.

   Fig 5: BA - Communication Diagram

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   1. Operation description

      The skid control ECU receives the brake pedal stroke sensor signal and the hydraulic 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 valves. The solenoid valves then control the pressure applied to each wheel cylinder.

      The ABS warning light will come on to indicate a malfunction in the BA system.

      HINT:

      The master caution indicator light will come on and a check ABS message will be displayed on the multi-information display if the BA system is malfunctioning.

4. TRAC (Traction Control)

   The TRAC 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 6: TRAC - Communication Diagram

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   1. Operation description

      The skid control ECU detects wheelspin by receiving signals from each speed sensor and the hybrid vehicle control ECU via CAN communication. The skid control ECU sends signals via CAN communication to the hybrid vehicle control ECU in order to control driving torque. The skid control ECU controls brake hydraulic pressure using the solenoid valves. The slip indicator light blinks when the system is operating. When there is a malfunction in the TRAC system, both the brake warning / yellow (minor malfunction), master caution indicator (VSC warning) and slip indicator light will come on.

      HINT:

      The master caution indicator light will come on and a check VSC system message will be displayed on the multi-information display if the TRAC system is malfunctioning.

5. 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 7: VSC - Communication Diagram

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   1. Operation description

      The skid control ECU determines the vehicle operating conditions based on signals received from the wheel speed sensors, yaw rate and acceleration sensor, and steering angle sensor. The skid control ECU sends signals via CAN communication to the hybrid vehicle control ECU in order to control driving torque. The skid control ECU controls brake hydraulic pressure using the solenoid valves. The slip indicator light will blink, and the skid control buzzer will sound when the system is operating. If a malfunction occurs in the VSC system, both the brake warning / yellow (minor malfunction), master caution indicator (VSC warning) and slip indicator light will come on.

      HINT:

      The master caution indicator light will come on and a check VSC system message will be displayed on the multi-information display if VSC cannot be performed.

1. The hill-start assist control generates four-wheel hydraulic pressure when the brake pedal is no longer depressed while the vehicle is stationary in order to prevent the vehicle from moving backward.

   HINT:

   The hill-start assist control will operate when the brake pedal is further depressed while all of the following conditions are met:

   • Shift lever is in a position other than P.
   • Accelerator pedal is not depressed.
   • Vehicle is stationary.
   • Parking brake is not applied.

1. The VDIM system uses coordinated control consisting of VSC and electronic power steering. By integrating these preventive safety functions, the VDIM system ensures higher driving stability and maneuverability performance.
2. If the vehicle loses stability due to tire slippage, this function uses brake control to apply hydraulic pressure to the wheels. At the same time, the electronic power steering provides steering torque assist control to facilitate the driver's steering maneuvers.

1. When a failure occurs in the ABS with BA, TRAC or VSC systems, the ABS warning, brake warning / yellow (minor malfunction), master caution indicator (VSC warning) and slip indicator lights come on and the ABS with BA, TRAC and VSC operations will be disabled. In addition, when there is a malfunction that disables EBD operation, the brake warning light / red (malfunction) also comes on and EBD operation is prohibited.
2. If control is disabled due to a malfunction during operation, control will be disabled gradually. This is to avoid sudden vehicle instability.

1. VSC operation can be disabled using the Techstream (See PRECAUTION ).