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

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.

   

Multi-terrain Select

1. The multi-terrain select has the following functions:

   Multi-terrain Select Function	Sends the road mode that is selected by the multi-information switch to the skid control ECU, ECM and 4WD control ECU.
   	Displays a message on the multi-information display prompting the driver to switch to the optimum transfer drive mode if the currently selected road mode and transfer drive mode are inappropriate.
   	Displays an assist message on the multi-information display in order to make switching to the optimum transfer drive mode easier.
   	Automatically switches to the optimum engine output control and switches the brake control function to A-TRC when the selected road mode and transfer drive mode are switched to the optimum position.

2. The screen of the multi-information display is switched by operating the multi-information switch, control is enabled by determining the road mode, and the multi-terrain select indicator light flashes.

   

   *1	Multi-information Switch - ENTER Switch - Menu Switch	-	-
   *a	Multi-terrain Select Selection Screen (Mode Select or Camera Selection)	*b	Multi-terrain Select Selection Screen (Determined Mode Select)
   *c	Road Mode Selection Screen	*d	Road Mode Selection Screen (Determined Road Mode)

3. 4 road modes can be selected: "MUD and SAND", "LOOSE ROCK", "MOGUL" and "ROCK". The recommended road modes for each road condition are listed below.

   Tech Tips

   Road mode recommendations are for reference only. The mode may not be appropriate depending on the road conditions (incline, road surface, road undulation etc.).

   

   *1	MUD and SAND
   *2	LOOSE ROCK
   *3	MOGUL
   *4	ROCK

   

4. The engine output and A-TRC control tendency for each road mode are as follows:

   Multi-terrain Select Road Mode	Transfer Drive Mode	Control
   		Engine Control	A-TRC Control
   MUD and SAND	H4F, H4L, L4F, L4L	Engine output control is performed gradually in response to accelerator pedal operation	The wheel is allowed to slip more than usual
   LOOSE ROCK	L4F, L4L	Engine output control is performed gradually in response to accelerator pedal operation	The wheel is allowed to slip more than usual
   MOGUL	L4F, L4L	Engine output control is performed gradually in response to accelerator pedal operation	The wheel is made to slip more than usual
   ROCK	L4F, L4L	Engine output control is performed gradually in response to accelerator pedal operation	The wheel is made to grip more than usual

5. The driver is informed of multi-terrain select operation by the flashing or illumination of the multi-terrain select indicator light and the slip indicator light. Also, operation assist messages are displayed on the multi-information display.

   System Condition		Indicator Light and Multi-information Display
   		Multi-terrain Select Indicator Light	Slip Indicator Light	Multi-information Display Message
   Operates		○	X	-
   A-TRC Operates		○	▲	-
   A-TRC Control → A-TRC Control Released		○ → X	▲ → X
   Control Commencement Conditions Not Met	Transfer Drive Mode Mismatch	○	X
   	System Malfunction	X	○
   	Vehicle Speed 12 km/h (7.5 mph) or more	X	X
   	During CRAWL Control	X	▲
   	Malfunction Multi-terrain Select	▲	X
   Related System Switching Commencement Conditions Not Met		○	X
   Operation Assist		○	X
   		○	X
   		○	X
   		○	X

   Tech Tips

   ○: Illuminates

   ▲: Blinks

   X: Turns off