This article will first discuss how level sensors work, which information is measured and evaluated and what special characteristics the sensors have.
Level sensor evaluation for comfort and safety functions
Modern vehicles have a number of new features which assist the driver in making driving safer and more pleasant. Some increase comfort and others improve safety. Two functions which fall into the category of adaptive driver assistance systems are chassis control and headlight beam adjustment. Both functions are controlled based on information from the chassis.
Dynamic chassis control improves both safety and vehicle comfort. The driver selects their preferred “driving feel”, such as sporty for a more energetic drive or comfort for longer journeys. The control unit dynamically adjusts the chassis. Level sensors installed on the chassis in the control arm provide the control unit with the information it needs for its control algorithms to make the adjustment.
Modern LED vehicle headlights have a much longer range than conventional halogen systems and the risk of blinding other road users is increased. For this reason, EU regulations require that vehicles with headlights more powerful than 2000 lumens are equipped with dynamic headlight beam adjustment.
If a vehicle is loaded in the rear, the rear of the vehicle sinks and the headlights point slightly upwards. If the vehicle is loaded to such an extent that this effect causes other road users to be blinded, the headlights must be adjusted downwards. This is a rather static alteration and it is made using relatively simple headlight adjustment mechanisms. However, this mechanical adjustment has only a limited effect while driving. In a moving vehicle, the height of the headlights is also altered by dynamic effects such as uneven ground. Therefore, in order to dynamically adjust the range and height of the front headlights to suit the road conditions, level sensors continually measure the vehicle’s level and their information is sent to control units in a similar way to the chassis control.
Functional principle
A level sensor, also known as a rotation angle sensor, is designed to detect the change in angle of a car’s control arm. Control arms are connecting elements installed on individual wheel mounts perpendicular to the direction of travel. They guide the wheel carrier in an approximately vertical direction and transmit the shear forces between wheel and body, stabilizing the wheel alignment. The movement of the control arm is transmitted to the sensor via a coupling linkage. The design of the sensor which monitors this movement is divided into two entirely separate parts: a mechanical part and an electronic part. The mechanics translate a change in the angle of the sensor’s drive axle into a rotational movement of a diametrically magnetized magnet in the sensor.
The sensor’s electronics work contactlessly using 2D Hall elements arranged below a rotating magnetic field. The rotating magnetic field produces an electrical voltage in the live Hall semiconductors which is perpendicular to the magnetic field and the flow of current. The Hall elements are arranged geometrically so that the magnetic field rotating above them generates a sine and a cosine signal. The electronics are fully potted to protect against moisture. In their output stage, they use mathematical offsetting, processing and filtering to generate the electrical control signals which are converted into an analog, PWM, 12-bit, 150 to 2000 Hz or PSI5 output signal equivalent to the input.
This control signal, also known as a transfer function (TF), is the common language of the sensor, which converts the mechanical movement of the chassis into a signal, and the control unit, which receives the signal and calculates the mechanical change based on it. The X-axis of the TF always represents the position and the Y-axis always represents the signal. This transfer function can differ depending on the customer, control unit and chassis. The transfer function is transmitted both to the front headlight beam adjuster control unit and the chassis control unit, where it is analyzed as described and used for dynamic adjustment of the respective function.
Beyond use in a vehicle, the angle sensors can also have other applications such as measuring the angle of robot arm axle bearing points, in double wishbone axles, for determining wheel travel over a linkage, for HID control and for active suspension adjustment.
Vehicle-specific sensor development and production
Level sensors are installed in many vehicle types with different chassis. This means the control arms with the sensors are not standard products; they are different for every vehicle. They also have to function in the vehicle for several years in all types of extreme ambient conditions. This demands specific environmental qualifications, robustness and technical maturity. The sensor is compact and mounted appropriately for the conditions. The mechanical and electronic parts are completely separate from one another. To protect against moisture, the electronics are appropriately sealed at the mounting point so that it remains moisture-tight over the long term. The magnet itself has an additional coating to protect against the elements.
The variety of vehicle types means each sensor requires a customer-specific mechanical and electrical interface. This must be compact. For this reason, the plug connectors have a modular design and differ from customer to customer. The lever also differs from vehicle to vehicle. This means there is a large amount of variation in assembly. All these conditions require flexibility in design and manufacture of the sensors while maintaining quality. The sensor systems are robust, completely redundant, fully end-of-line programmed and traceable. Over nearly fourteen years, Swoboda has manufactured many millions of level sensors for numerous different customers and vehicles and they are currently in their third generation.
Summary
An angle sensor can of course be used regardless of the propulsion type. The sensors are used in conventional vehicles with combustion engines as well as modern hybrid or full-electric vehicles from many large OEMs in the USA, Europe and Asia.
The level sensors have been produced at Swoboda in very high quantities since 2007 and in many varieties. They are used in many different vehicle types by leading automobile manufacturers. These sensors are also known as rotation angle sensors. They use 2D Hall effect sensors to measure mechanical movements of the chassis they are installed on. Their output signals control headlight beam adjustment and chassis settings to maintain comfort and safety.
Sensor information is the basis for the function of numerous active and passive safety systems. Safety and driver assistance systems have become more and more capable in recent years through the many innovations in new sensor development. Swoboda has been producing level sensors globally in their millions for nearly fourteen years, using state-of-the-art technology and for a number of different customers and vehicles. The development departments are currently also working on inductive level sensors and linear sensors. The company also supplies acceleration, wheel speed, cam shaft and combination sensors.
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