BRAKE CONTROL SYSTEM

Multi-terrain Anti-lock Brake System (Multi-terrain ABS)

1. The multi-terrain ABS operates in conjunction with the multi-terrain select. This function detects off-road driving in sand, mud, gravel, dirt and so on based on signals from the yaw rate sensor assembly, the speed sensor and the ECM, and then automatically switches to the ABS control most appropriate for the road condition.

2. This function is intended to improve the braking feeling when driving off-road without negatively affecting on-road braking control performance.

   

   

Electronic Brake Force Distribution (EBD)

1. This function controls the brake force that acts on the rear wheels in accordance with the changes in the vehicle conditions such as load factors or deceleration, in order to ensure excellent braking performance.

   

   

2. During cornering braking, this function controls the brake force that acts on the left and right wheels in accordance with the vehicle conditions. This ensures vehicle stability and excellent braking performance.

   

   *a

   Brake Force

   *b

   Control Moment

Brake Assist

1. During the brake assist, the skid control ECU calculates the speed of the brake pedal application based on the signals from the master cylinder pressure sensor and then determines the intention of the driver to make an emergency brake application. If the skid control ECU determines that the driver intends to make an emergency brake application, this function activates the hydraulic brake booster assembly to increase the brake fluid pressure, which increases the brake force.

   

Traction Control (TRC)

1. The TRC helps prevent the drive wheels from slipping if the driver depresses the accelerator pedal excessively when starting off or accelerating on a slippery surface. Simultaneously with the hydraulic brake control of the drive wheels, the skid control ECU makes a request to the ECM to effect engine output control. This produces the drive force that suits the driving conditions, in order to ensure the proper start-off acceleration.

   Figure 2. Driving on Road with Different Surface Friction Characteristics

   

   *A	Models without TRC	*B	Models with TRC
   *1	ECM Engine Output Control	*2	Brake Actuator Assembly Hydraulic Brake Control
   *a	Brake Slipping Drive Wheel	*b	Slippery Surface

Active Traction Control (A-TRC)

1. When the vehicle drive mode is L4F* or L4L*, the A-TRC helps restrain wheelspin by controlling the brake hydraulic pressure that is applied to the spinning wheels, and distributes the drive force that would have been lost through the slippage to the remaining wheels in order to achieve an effect that is similar to Limited Slip Differential (LSD).

   Tech Tips

   *: When multi-terrain select is on (models with multi-terrain select)

2. The A-TRC independently controls the brake hydraulic pressure to the four wheels in accordance with the extent of the slippage at the wheels, as detected by the skid control ECU.

   

   

   w/o A-TRC

   *1	Slippery Surface
   *2	No Traction
   *3	Engine

Vehicle Stability Control (VSC)

1. The following are 2 examples that can be considered circumstances in which the tires exceed their lateral grip limit. The VSC is designed to help control the vehicle behavior by controlling the engine output and the brakes of each wheel when the vehicle is under one of the conditions indicated below:

   

   *a

   Front Wheel Skid Tendency (Understeer) When the front wheels lose grip in relation to the rear wheel

   *b

   Rear Wheel Skid Tendency (Oversteer) When the rear wheels lose grip in relation to the front wheels

2. To determine the condition of the vehicle, sensors detect the steering angle, vehicle speed, vehicle yaw rate, and vehicle's lateral acceleration, which are then calculated by the skid control ECU.

3. Whether or not the vehicle is experiencing a front wheel skid is determined by the difference between the target yaw rate and the vehicle's actual yaw rate. When the vehicle's actual yaw rate is smaller than the target yaw rate (which is determined based on the vehicle speed and steering angle) that should be generated when the driver operates the steering wheel, it means the vehicle is making a turn at a greater angle than the target locus of travel. Thus, the skid control ECU determines that there is a large front wheel skid tendency.

   

   *a

   Actual Locus of Travel (Actual Yaw Rate)

   *b

   Locus of Travel Based on Target Yaw Rate

4. Whether or not the vehicle is experiencing a rear wheel skid 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). When the vehicle's slip angle is large, and the slip angular velocity is also large, the skid control ECU determines that the vehicle has a large rear wheel skid tendency.

   

   *a	Travel Direction of Vehicle's Center of Gravity	*b	Movement of Vehicle
   *c	Slip Angle	-	-

5. When the skid control ECU determines that the vehicle exhibits a tendency to experience a front wheel skid or a rear wheel skid, it decreases the engine output and applies the brakes of the front or rear wheels to control the vehicle's yaw moment. The basic operation of the VSC is described below. However, the control method differs depending on the vehicle's characteristics and driving conditions.

6. When the skid control ECU determines that there is a large front wheel skid tendency, it takes countermeasures in accordance with the extent of that tendency. The skid control ECU controls the engine output and applies the brakes of the rear wheels and front wheel on the outer circle of the turn in order to help restrain the front wheel skid tendency.

   Figure 3. Front Wheel Skid Dampening at Right Turn

   

   *a

   Brake Force

   *b

   Control Moment

7. When the skid control ECU determines that there is a large rear wheel skid tendency, it takes countermeasures in accordance with the extent of that tendency. It applies the brakes of the front and rear wheels of the outer circle of the turn, and generates an outward moment of inertia in the vehicle, in order to restrain the rear wheel skid tendency. Along with the reduction in the vehicle speed caused by the braking force, excellent vehicle stability is ensured. In some cases, the skid control ECU applies the brake of the front wheel on the outer circle of the turn, as necessary.

   Figure 4. Rear Wheel Skid Dampening at Right Turn

   

   *a

   Brake Force

   *b

   Control Moment

Trailer Sway Control

1. If the vehicle is towing a trailer with an inappropriate hitch load, trailer sway could be caused by crosswinds, imbalance caused by load, or the driver's steering. Trailer sway control reduces trailer sway by controlling the engine output and the braking of each wheel.

   

   *1	Without Trailer Sway Control
   *2	Side Wind
   *3	With Trailer Sway Control
   *4	Brake Control + Engine Output Control

   Note

   
   

   • Trailer sway control is a part of the VSC function. Accordingly, if the VSC OFF mode or VSC is not functioning normally, trailer sway control will not operate.

   • Trailer sway control will be unable to stabilize the vehicle if a trailer is being towed which cannot be physically controlled due to the influence of the vehicle, road surface, driving conditions and so on.

2. The skid control ECU detects the occurrence of trailer sway based on signals from the yaw rate sensor assembly and the steering angle sensor.

3. Trailer sway can be reduced by decelerating the vehicle. When the skid control ECU detects trailer sway, it controls the brakes of each wheel while simultaneously requesting engine output control from the ECM and reducing vehicle speed.

4. Moreover, by using brake control to reduce the yaw moment caused by trailer sway, trailer sway can be reduced more quickly than by simply decelerating the vehicle.

5. The slip indicator light on the combination meter assembly flashes when trailer sway control is in operation. Also, the stop light illuminates to inform vehicles behind that the vehicle is decelerating.

   

   *a	Trailer Sway	*b	Deceleration Force Caused by Brake Control and Engine Output Control
   *c	Yaw Moment Caused by Trailer Sway	*d	Control Moment Caused by Brake Control

   

Hill-start Assist Control

1. When the vehicle starts off on a steep or slippery hill, the vehicle may start to descend backward while the driver switches from the brake pedal to the accelerator pedal, thus making it difficult for the vehicle to start off. To prevent this from occurring, the hill-start assist control temporarily (approximately 5 seconds at the maximum) applies the brakes to the 4 wheels in order to prevent the vehicle from descending backward.

2. Without the hill-start assist control, the driver must quickly and precisely switch from the brake pedal to the accelerator pedal. With the hill-start assist control, however, the driver can start off easily and operate the pedal in a relaxed manner, because the hill-start assist control prevents the vehicle from descending backward.

   

Downhill Assist Control

1. When the vehicle is descending a steep hill and the engine brake alone cannot provide a sufficient deceleration force while the transfer drive mode is in L4F or L4L, downhill assist control effects 4 wheel brake control to maintain a constant, low vehicle speed. Thus, the vehicle is able to descend in a stable manner without causing the wheels to lock.

2. When the vehicle descends a steep hill without downhill assist control, the driver must pay close attention to the brake and accelerator pedal maneuvers. However, with downhill assist control, the driver can concentrate on the steering operation, without accelerator or brake pedal operation.

3. Downhill assist control enables the vehicle to maintain stability because it can descend a slippery hill at low speeds without causing the wheels to lock.

   

CRAWL

1. The CRAWL is a driving support system that regulates the engine output and the brake force, enabling the vehicle to be driven at a constant speed on rough ground or slippery roads.

2. When the vehicle drives across rough ground such as extremely bumpy rough roads, the driver needs to pay attention to the steering, braking and acceleration operations. However, with the CRAWL, the driver can concentrate on steering, without worrying about the accelerator pedal or brake pedal.

   

3. The CRAWL ensures good vehicle stability in situations such as when the vehicle is running on a slippery or steep road because the chances of the wheels spinning or locking are minimized by regulating the engine output and the brake force.