System Decription
Adaptive Cruise Control (ACC) System Description
The adaptive cruise control (ACC) system automatically controls the vehicle speed, within the set speed, to maintain a safe distance to the vehicle ahead.
Operation Criteria
- When there is no vehicle ahead, the ACC maintains the set speed.
- When there is a vehicle ahead, the ACC maintains a set distance within the set speed.
- If the vehicle ahead pulls over out of the way, the ACC accelerates the vehicle to the set speed and maintains that speed.
- The ACC measures the distance from the vehicle ahead using the millimeter wave radar, and it determines if the target vehicle driving ahead is in the same lane by using inputs from the vehicle speed sensor and the yaw rate sensor.
- If the ACC detects a slow vehicle and the distance to the vehicle ahead is closing, the vehicle speed is reduced primarily by closing the throttle, and additional slowing is accomplished by using the brakes. If the vehicle ahead is too close, an alarm sounds.
- If a slower vehicle ahead accelerates, the throttle is opened to accelerate the vehicle (up to the set speed) to maintain the following distance.
Basic ACC Pattern
- Radar detection: Max. 0.06 mile (100 m) ahead in a 16 degree field of view
- Vehicle operating speed: 25-90 mph (40-145 km/h)
ACC Unit
The ACC unit obtains information from external sensors and switches that are connected to their respective control units.
ACC Operation Range:
- Setting speed range is 25-90 mph (20-145 km/h)
- Setting following distance from vehicle ahead is 1.0-2.0 seconds
- Maximum deceleration is 0.30 G
Millimeter Wave Radar
The millimeter wave radar is installed on the main bracket attached to the front bulkhead. The main bracket allows the radar angle to be adjusted ±3 degrees vertically by moving the main bracket adjusters.
The millimeter wave radar has these functions:
Basic distance function
The millimeter wave radar radiates 76-77 GHz radar waves up to a range of 100 m (328 ft) ahead, 16 degrees horizontally, 3.9 degrees vertically, and it receives the reflected waves. In doing so, it can calculate the distance to the vehicle ahead, the relative speed (the difference in speed between the two vehicles), and its position. This data is sent to the ACC unit.
Aiming function
The millimeter wave radar has a horizontal auto-aiming function range of ±3 degrees and is directed by ACC unit.
Self-diagnosis function
The millimeter wave radar has a self-diagnostic function, it sends this information to the ACC unit.
Sensitivity-lowering detection function
When the detecting performance of the radar is deteriorated by dirt, dust, or other contaminants, it signals the condition malfunction to the ACC unit until the performance is restored.
Adjuster-misalignment detection function
When more than ±5 degrees of adjuster misalignment is detected while driving, it signals the condition to the ACC unit.
Brake Fluid Pressure Sensor
The brake fluid pressure sensors are installed in the right and left sides of the brake line 4-way joint. The brake fluid pressure is converted to a signal (voltage value) and is output to the ACC unit. The ACC unit is always monitoring the ACC brake operation and the brake pressure controlled by the signal sent from the brake fluid pressure sensor.
How to Troubleshoot DTCs
Check the DTCs with the HDS. Make a copy of the freeze data, then clear the DTC.
Before troubleshooting, check and note these items:
- Ask the client about the conditions when the problem occurred, and try to reproduce the same conditions for troubleshooting.
- If the symptom does not appear and the ACC indicator does not come on during the test-drive, but troubleshooting is done based on the DTC, check for poor connections or loose terminals at all connectors related to the circuit that you are troubleshooting.
- After the troubleshooting or repairs are done, clear the DTCs, and test-drive the vehicle under the same conditions as when the DTC was originally set. Make sure the ACC indicator does not come on.
- The ACC system sometimes stops control because of the environment (weather, road conditions, driving conditions, etc.). A DTC may be stored in these cases.
DTCs may be stored even when the system is normal:
DTC 83: ACC does not come on
Performance of the millimeter wave radar is not stable. (Driving behind a target vehicle that caused unstable reception.)
DTC 84: ACC indicator does not come on
Target vehicle comes closer than the millimeter wave radar detecting limits (The target vehicle brakes suddenly, etc.).
DTC 85: ACC indicator does not come on
Extensive driving on a rough road or a winding road, or VSA system detects a problem.
DTC 86: ACC indicator does not come on
Abnormal tire pressure, flat tire
DTC 87: ACC indicator does not come on
ACC brakes work continuously, or ACC brake control is temporarily prohibited by a communication line error detected between the ACC unit and VSA modulator-control unit.
DTC 88: ACC indicator does not come on
Millimeter wave radar temperature is high, millimeter wave radar supply voltage is too low, or out of detection condition.
DTC 89: ACC indicator does not come on
Front wheel spin
DTC 91: ACC indicator does not come on
Vehicle skidded, spun out, or there was an abrupt steering wheel movements.
DTC 93: ACC indicator does not come on
Front tire problem (different diameter of tires, flat tire, or large air pressure differential).
DTC 94: ACC indicator does not come on
Rear tire problem (different diameter of tires, flat tire, or large air pressure differential).
DTC 95: ACC indicator does not come on
Power supply voltage is too high.
DTC 96: ACC indicator does not come on
Power supply voltage is too low.
DTC 99: ACC indicator does not come on
Detects acceleration or deceleration that is out of the normal system operating range.
DTC 100: ACC indicator does not come on
CMBS initial check is incomplete.
DTC 101: ACC indicator does not come on
Rear wheel locked (driving with the parking brake applied, or the parking brake stuck).
DTC 107: ACC indicator comes on
Millimeter wave radar aiming is incomplete.
Adaptive Cruise Control (ACC) Unit Inputs and Outputs
Millimeter Wave Radar Inputs and Outputs
