Land Rover Discovery: Adaptive Front Lighting System (AFS)

The Adaptive Front lighting System (AFS) headlamp assembly contains an additional carrier frame which provides a location for the horizontal actuator. The projector module has a central pivot point which allows the module to move horizontally in response to operation of the horizontal actuator.

The AFS actuators are bi-polar (2 phase) dc stepper motors which are driven by a power output from the AFS power module located in the headlamp assembly. Each stepper motor receives its position information from the headlamp Levelling control module via the applicable AFS power module.

When the actuators are powered to their requested positions, a holding current is applied to maintain the actuator position.

The actuators do not supply a positional feedback signal to the headlamp Levelling control module. Each stepper motor requires referencing each time the AFS system becomes active. When the AFS system is active, each vertical actuator is driven to the low beam position and each horizontal actuator is driven to an inboard position until a mechanical stop in the actuator is reached. Once the stop is reached a step counter in the headlamp Levelling control module is set to zero and the actuator is then powered to the operating position as determined by the AFS software.

The AFS is controlled by a Headlamp Levelling Control Module (HLCM). The HLCM is a dual function control module which can process and control the headlamp Levelling and the AFS headlamp systems. The same module is used on vehicles without AFS but fitted with xenon headlamps.

The system operates by the HLCM receiving inputs from the Engine Control Module (ECM) for engine running signal, the Anti-lock Brake System (ABS) control module for steering angle and vehicle speed and a reverse gear input from the transmission.

The HLCM processes these signals and provides an output to the headlamp Levelling motors to adjust the headlamp horizontal aim according to vehicle speed and steering angle.

NOTE:

NOTE: In markets with DRL, the AFS system will not operate when the DRL are active.

The HLCM is connected on the High Speed (HS) Controller Area Network (CAN) bus to receive information from other vehicle systems. The HLCM is connected to the AFS headlamps on a dedicated LIN bus. The HLCM calculates, using input data from other systems, the required position of the horizontal adjustment of the projector modules. The position information is then output on the LIN bus to the AFS Headlamps. The HLCM outputs the appropriate signals to drive the AFS stepper motors in the headlamp to the appropriate position.

The horizontal position of the projector modules is dependent on a number of input variables. The position is determined by vehicle speed and steering angle. When reverse gear is selected, the projector modules are moved to the straight ahead position to avoid glare to other road users.

The angles of each projector module differ to give the correct spread of light, for example, when turning left, the left hand projector module will have a greater swivelling angle than the right hand projector module.

AFS Operation

When the HLCM receives an ignition on signal, the control module performs the initialization procedure which ensures that the headlamps are correctly aligned on both their vertical and horizontal axes.

The AFS swivel initialization starts less than 1 second after the headlamp Levelling initialization is activated to ensure that the headlamps are at or below the 0 degree position in the vertical axis, thus preventing glare to oncoming vehicles. The AFS swivel initialization is completed in less than 2.5 seconds. The left and right AFS actuator motors are powered from the 0 degree position to a small movement to the inboard position, then another small movement to the outboard position and then back to the 0 degree position.

Failure Mode

In the event of a failure of the AFS system, a warning indicator in the Instrument Cluster (IC) is illuminated to warn the driver. The AFS warning indicator illuminates when the ignition is in power mode 6 (ignition on) or greater and will flash continuously until the fault is rectified. The AFS warning indicator will also be illuminated if a failure of the steering angle sensor or the vehicle speed signal is detected.

Illumination of the AFS warning indicator does not necessarily mean that there is a fault with the AFS system. The fault may be caused by a failure of another system such as steering angle sensor or the vehicle speed signal missing, preventing the AFS system operating correctly.

The HLCM performs a diagnostic routine every time AFS is requested. If any fault is found, the HLCM will suspend the operation of the AFS function.

If the AFS Levelling system has failed with the xenon projector module in a position other than the correct straight ahead position, the HLCM will attempt to drive the projector module to a position a small amount lower than the standard position. If the swivel function has failed, the HLCM will lower the projector module using the Levelling actuator motors to a position much lower than standard to prevent excess glare to oncoming vehicles.

The HLCM software can detect an internal failure of the HLCM control circuits. The HLCM will power the projector modules to the zero position and prevent further operation.

Faults can be investigated by interrogating the HLCM using a Land Rover approved diagnostic tool to check for fault codes.

Headlamp Beam Diagram

1. Conventional headlamp beam distribution
2. AFS swivel headlamp beam distribution

Halogen / Xenon HeadlampTail Lamp Assemblies

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