Headlight Vertical Aim Control (LWR)

Headlight Vertical Aim Control (LWR)

Headlight Vertical Aim control is used to adapt the position of the headlights automatically to the vehicle load condition.

Headlight Vertical Aim Control has the following features:

- 1 stepper motor for each left and right headlight assembly.
- Activation of stepper motors in parallel on left and right sides (common driver IC).
- Possibility of diagnosing missing connections to stepper motors (line break) and short circuits in windings (motor fault).

Referencing of Stepper Motors

The position of the stepper motors is initially uncertain after LWR is activated. First of all, a reference run is carried out which takes place in two phases for the purpose of improving accuracy. The object of the reference run is to guarantee a fixed initial position (calibration) for the headlights.

Automatic Setpoint Generation

Automatic LWR derives the setpoint for the headlight range from two ride-level sensors. These sensors are mounted on the front and rear axles. They are used to determine the difference in ride height between the front and rear axles.

The input signals (0.3-4.7 V) of the ride-level sensors are measured with the engine running or lights ON cyclically at intervals of 20 ms. Voltage values <0.3 V and >4.7 V are interpreted as faults. The LM registers a fault entry "Sensor, ride level, front, faulty" or "Sensor, ride level, rear, faulty".

Dynamic Headlight Vertical Aim Control

The effect of dynamic LWR, is that the headlight aim is corrected immediately in critical driving situations (extreme braking; heavy acceleration).

In this way, reduced headlight aim under certain circumstances (e.g. during braking) is immediately corrected by the process of the head lights being "raised".

Also, the dazzling of other road users is eliminated during acceleration by the process of the headlights being "lowered".

The problem of incorrect interpretations (e.g. irregular road surface) is avoided by the use of more signals than just the ride-level signals.

It can usually be assumed that a braking operation is always accompanied by a simultaneously actuated brake-light switch. However, the brake-light switch is not actuated during acceleration. The vehicle speed is included in the correction calculation,

Dynamic Compensation During Braking:

Because of the "system knowledge" that compensation of the headlight aim during braking is particularly more important when braking at high speeds, dynamic LWR can dampen compensation of the headlight aim at low speeds.

Dynamic compensation during braking begins "gradually" above the minimum speed of approx.40 km/h (25mph) and reaches its full effect from a speed of approx.80 km/h (50mph).

As long as the brake light switch is not actuated, there is no dynamic compensation for braking.

Dynamic Compensation During Acceleration:

Acceleration is more "probable" the lower the initial speed is. Absolute accelerating performance decreases as speed increases because the vehicle is being driven in higher gears and therefore less torque is available.

Complete dynamic compensation takes place during acceleration as long as the speed is less than approx.50 km/h (31mph). The effect of dynamic compensation decreases increasingly above this speed and disappears from a speed of approx.110 km/h (68mph).

When the brake light switch is actuated, there is no dynamic compensation for acceleration.

Activation of Stepper Motors

Functions of the software driver for activating the stepper motors:

- Positioning of stepping motors (powering, acceleration and deceleration).
- Carrying out a reference run (each time LWR is activated).
- Inclusion of current actual step counter.
- Setpoint/actual-value comparison of step position
- Activation of stepping-motor driver.