Introduction to ACC adaptive cruise system

Adaptive cruise control (ACC: adaptive cruise control) is an upgrade to the traditional cruise control system. This system can not only keep the vehicle at the speed set by the driver, but also keep the vehicle and the vehicle in front of it at the speed set by the driver. measured by time distance. The stop-and-go adaptive cruise system (ACC Stop & Go) can automatically follow the vehicle in front until it stops or start at the driver's command. Note: ACC is not a safety system, obstacle detector or collision warning system, but a comfort system. The driver must always maintain control of the vehicle and take full responsibility for the vehicle. The ACC function can assist the driver, but it cannot replace the driver's driving. Even if ACC is activated, the driver must drive with caution and obey the speed limit. (Basic principles, precautions)

According to the national standard GB/T20608-2006, the main function of the adaptive cruise control (ACC) system is to control the vehicle speed to adapt to the movement of the vehicle ahead based on specific information. This information includes:

(1) Distance from the front workshop;

(2) The motion status of the vehicle (equipped with ACC);

(3) Driver's operating instructions (see figure ACC system working principle).

Based on the above information, the controller (called "ACC control strategy" in Figure 1) sends control instructions to the actuators to perform longitudinal control while providing status information to the driver.

How the ACC system works

The purpose of ACC is to reduce the driver's labor intensity, ensure driving safety, and provide driver assistance in a convenient way by automatically controlling the longitudinal movement of the vehicle.

ACC system status

The status of the ACC system can be divided into three types: ACC off status, ACC waiting status and ACC working status. The status of the ACC system and its transition are shown in Figure ACC system status and its transition.

• ACC is closed. No direct operation can trigger the ACC system.

• ACC waiting state The ACC system does not participate in the longitudinal control of the vehicle, but can be triggered by the driver at any time to enter the working state.

• ACC working state The ACC system controls the vehicle's speed and/or inter-vehicle headway.

ACC system states and their transitions

*Manual and/or automatic operation after self-test. Manual switching realizes the conversion of ACC between closed and non-closed states. The system will automatically close ACC after detecting an error.

1. ACC function limitations

• The minimum settable desired speed of ACC is 30 km/h.

  
  

• The maximum settable desired speed of ACC is 150km/h.

  
  

• ACC can only achieve limited braking force and cannot achieve emergency braking.

  
  

• For safety reasons, ACC cannot be activated when ESP is turned off.

  
  

• The brakes are overheated.

  
  

• When ACC is working, if the driver steps on the accelerator pedal, the vehicle will be taken over by the driver. All functions of the ACC system will be suspended.

2. ACC operating environment restrictions

• The driver must adjust the following distance based on the traffic flow ahead and current weather conditions, such as rain and snow, and set the ACC system appropriately. Drivers need to ensure that the vehicle can be slowed to a stop within their field of vision at all times. ACC is suitable for use on highways and roads with good road conditions, but is not suitable for use on complex urban road conditions, tunnels or mountain roads. For safety reasons, do not use ACC when visibility is poor, or when driving along slopes and curves, or on slippery roads (such as ice, snow, wet or waterlogged roads).

  
  

• Target selection may be delayed or interfered with when entering and exiting curves. In these situations the ACC vehicle may not brake as expected or brake too late. At this time, the driver must actively step on the accelerator pedal to control the vehicle instead of ACC; or step on the brake pedal, or press the ACC button on the multi-function steering wheel to cancel the ACC system.

  
  

• In some cases (the relative speed of the vehicle in front is too high, the lane change is too fast, or the safety distance is too small, etc.) the system does not have enough time to reduce the relative speed or maintain an appropriate distance between the vehicle and the vehicle in front. In this situation the driver must react appropriately, such as actively applying the brakes to reduce the vehicle's speed. When an emergency occurs and the instrument prompts "Take over request", the driver must actively control the vehicle.

  
  

• In some environments, detection may be affected or delayed. For example, when the radar reflection cross-section of the target is too small (it may be a bicycle, a carriage, or a pedestrian), the system will be at risk of being unable to confirm the distance to the vehicle in front, which will A situation that results in a delayed or inability to respond to such vehicles. In such situations the driver needs to control the vehicle speed.

  
  

• Vehicles equipped with special loads or special equipment; ACC cannot detect items or accessories installed on other vehicles that protrude from the sides, rear ends or roofs of the vehicle. If the vehicle in front is equipped with the above-mentioned special loads or special equipment and overtakes such a vehicle, be sure to turn off ACC. The driver should actively apply the brakes depending on the situation.

  
  

• Heavy rain, water mist, ice, snow or sludge may deteriorate the function of the radar sensor, causing the ACC to temporarily shut down. When this happens, the instrument cluster display will display the corresponding message, and the sensor should be cleaned as required. Once the radar sensor returns to normal status, ACC can be reactivated.

  
  

• Strongly reflected radar signals (e.g. in multi-storey car parks, tunnels, etc.) can deteriorate the function of the radar sensor.

3. Restrictions on the choice of vehicles ahead

The selection of relevant vehicles ahead is set by combining sensor data from the body's surroundings with its own sensor data. Therefore, the reliability of forward target selection must be guaranteed by the quality of sensors around the vehicle body and the surrounding environmental conditions. For these reasons, ACC may have incorrect recognition and responses. When there is a problem with the selection of the target vehicle ahead, ACC may have the following two reactions:

• If the relevant target vehicle directly ahead is not correctly selected by the system, ACC will accelerate the vehicle to the desired speed set by the driver.

  
  

• If an irrelevant vehicle ahead, such as a car in an adjacent lane, is mistakenly selected as the target vehicle directly ahead, ACC will slow down the vehicle.

  
  

In both cases, the driver must actively take over control of the vehicle.

4. No response to certain targets

• The ACC system cannot respond to stationary targets. The driver needs to take over vehicle control to prevent being affected by stationary targets. This is very likely to occur when approaching the rear of a traffic jam or a vehicle waiting at a traffic light. If ACC detects a vehicle that is turning or changing lanes, and there is another vehicle parked behind the vehicle, it is impossible for the system to respond to the stationary vehicle, and the driver should actively apply the brakes depending on the situation.

  
  

• ACC cannot react to oncoming or lateral passing vehicles.

  
  

• Generally speaking, the ACC system only works for motor vehicles driving on the road, and has no response to pedestrians, animals, etc.

2. Button layout & basic operations

Human-machine interface information is mainly divided into two categories:

• Human-machine interface output: used to inform the driver of the current status of the system. Instruments are used to display visual information, while speakers are used to display audible information (such as alarm sounds).

  
  

• Human-machine interface input: used by the driver to output commands to the ACC system to control the ACC system.

  
  

Definition: The on/off switch is also usually called the main switch.

• ACC turned on: ACC turned on means that the ACC system is ready, but the ACC system has not yet intervened in vehicle control. ACC will only control vehicle speed if ACC is turned on and ACC is activated (see next page). Turning on ACC is a prerequisite for ACC activation.

  
  

• ACC is off: The ACC system is completely off, and ACC cannot be activated in this state.

  
  

suggestion:

• When the driver turns on ACC, the text prompt ACC ON/ ACC is turned on is briefly displayed.

  
  

• When the driver turns off ACC, the text prompt ACC OFF/ACC is turned off is briefly displayed.

1. Human-machine interface output

ACC Active/CANCEL activation/cancellation (required)

ACC activation: When the ACC system is activated and the vehicle is being controlled by the ACC system to reach the speed set by the driver. In other words, the vehicle can accelerate or decelerate automatically.

ACC canceled: When the ACC system is in a canceled state or is not activated. Unless the driver reactivates the ACC system, the system will not take control of the vehicle.

It is important for the driver to be aware of the current status of the system at all times. The driver must be able to tell whether the vehicle is capable of responding automatically. Both of the above states must be clear and distinct.

Based on this, it is recommended:

• When ACC is in the canceled state, hide ACC information as much as possible

• When ACC is active, relevant information is displayed in color or highlighted.

• The ISO standard ACC symbol is displayed when the system is activated and is not displayed when the system is canceled/shut down.

• When canceling ACC, it is best to use the text prompt "ACC Cancel/ACC Cancel"

Object valid found the target vehicle (required)

If a vehicle ahead is detected, "Target vehicle found" will be displayed on the instrument, after which the vehicle may respond automatically.

Generally, a vehicle symbol is displayed on the instrument to indicate that the target vehicle has been found:

Take over request requests the driver to take over (required)

When the deceleration of the system's automatic braking is insufficient to avoid a collision, the system will request the driver to take over to remind the driver to take braking action;

Warn with a short, clear sound, display a warning graphic on the instrument panel or turn the target vehicle's graphic red (a red triangle icon indicates a request for the driver to take over)

Target vehicle location (optional)

Refers to the distance between the target vehicle in front and itself: display a dynamic car graphic on the instrument and display its distance

Target vehicle speed (optional)

The speed of the target vehicle ahead detected by the ACC vehicle: Most ACC systems do not display the speed of the target vehicle.

Safe distance warning (optional)

When the distance to the vehicle in front is too close and ACC is turned off or the driver is overtaking, a warning will be displayed; usually the same graphic as the driver's takeover request is displayed, but no sound prompt is used (can be shared with "Request Driver to Take Over" same display)

2. Human-machine interface input

Most OEMs choose the ACC setting joystick as the input device. It is recommended to install the setting lever on the left side and at a higher position to avoid accidental operation by the driver's knees.

General joysticks only provide knobs and built-in LED lights, while high-end joysticks have knobs that can be pushed and pulled in addition to rotating.

The joystick should be able to be depressed and lifted in the direction of the instrument, and it should also be able to be depressed and lifted in the direction of the steering wheel.

High-End Joystick Recommendations

High-end interface

The high-end interface brings a more comprehensive ACC experience to drivers, and information can be displayed and better distributed.

The time interval information is displayed as the actual following distance between the two vehicles, and the expected distance is displayed as a distributed numerical value, making it easier for the driver to judge whether the time interval needs to be increased or decreased.

When the system is turned off, all ACC information disappears, but the driver can still adjust the time interval and desired speed. If the driver adjusts the time interval or desired speed at this time, the relevant information is only displayed for 2 seconds. In passive mode, all information is displayed in grayscale/dimmed form to draw the driver's attention to the passive state.

In failure mode, the ISO symbol is displayed and other ACC information is hidden.

• Slow down and stop

  If the vehicle ahead brakes and stops, ACC will also decelerate and stop, keeping the car at a standstill.

  
  

• parking phase

  If ACC has decelerated the car to a stop, ACC will not automatically exit when the brake pedal is depressed.

  If any of the following situations occur during parking, the electronic parking brake will automatically activate and ACC will automatically exit:

  Ø Unlock seat belt

  Ø Open the driver's door

  
  

• Start after parking

  As long as the vehicle in front starts moving again within 3 seconds after the parking phase, ACC will automatically start the car. If the vehicle in front stops for more than 3 seconds, it needs to be reactivated through the "RES" button or the accelerator pedal.

1. The driver actively increases speed

When the vehicle is in ACC cruising, the driver actively steps on the accelerator pedal to put the vehicle into the driver-initiated speed-up state. When the driver releases the accelerator pedal, ACC will resume cruising at the set speed and continue cruising.

2. Driver takeover request

When ACC braking cannot maintain a safe distance from the vehicle in front (such as when the relative speed of the vehicle in front and the own vehicle is too high), the ACC system will issue a driver takeover request. When the driver receives this request, he should take the initiative to take over the vehicle, otherwise There may be safety hazards.