Editorial Feature

Inside a Car – Steering Sensors

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Image Credit: oatzpenz studio/Shutterstock.com

The steering wheel is an integral part of a motor vehicle, allowing the driver to control the position of a moving vehicle. Most land vehicles are engineered to have a steering wheel device. 

A complete steering system is made up of more than just a steering wheel to maneuver the car; the system also consists of a steering box connected to the steering wheel, the linkage that connects the steering box to the wheel assembly and a steering sensor.

Figure 1 is a schematic drawing of the steering components of a car. The scope of this article will focus on the steering sensor and how this component is fundamental to the flexibility in the steering control of a vehicle.

A vehicle steering system.

Figure 1. A vehicle steering system. Image Credit: Knowles D. (2003). Today’s Technician: Automotive Suspension and Steering Systems. USA, New York: Delmar Learning, a division of Thomas Learning, Inc.

Steering sensors are crucial for measuring the rotational angle of a steering wheel and communicating this information on navigation. These sensors are used for automated systems that require electronic command steering (ECS) and electric power steering (EPS) systems. Electrical power steering systems require information about the steering-wheel angle, the wheel speed, and the lateral acceleration sensors to interpret the under- or over-steering of a car. Figure 2 is a flowchart of steering angle sensors, mainly in the form of optical, magnetic, inductive, capacitive, and resistive sensors.

Types of steering sensors.

Figure 2. Types of steering sensors. Image Credit: Marek J, Trah H, Suzuki Y, Yokomori I. (2003). Sensors Applications, Sensors for Automotive Applications. WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

These sensors rely on each other for accurate information to connect the steering wheel to the wheels, such as the rate of turn or traction control. They determine where the driver wants to steer, matching the steering wheel with the vehicle’s wheels.

A standard steering sensor is important for controlling power-assisted steering for a number of reasons: firstly to interpret the rotary torque being delivered to the input shaft of the steering wheel, and secondly for navigation of the steering wheel (i.e., the twisting of the steering wheel by the driver).

Steering Sensor – Structure and Functional Principle

Let’s study the structure and position of a steering sensor in relation to the overall body of a car by looking at the Volkswagen car models as an example. In these cars, the power steering sensor by KOYO is cylindrical in shape and is integrated into the rotary disc valve connected to the steering gear embracing the input shaft of the gear component. For cars with an electronic stability program (ESP), the steering angle sensor is fastened to the steering column shaft that sits between the column switch and the steering wheel.

During the maneuvering of a vehicle, the electronics from the torque sensor calculate the signal (i.e., steering angle and steering angle rate) as a reflection of the change in capacitance and then transmits an electrical current to the ECU, the main control unit that determines the direction of the steering wheel.

Upon receiving the electrical signal from the steering sensor, the electronic control unit interprets this current and calculates a control signal that will operate the electric motor unit to power the steering capacity. The torsion bar to the steering wheel system starts to twist, turning the rotary valve against a sleeve component. This turning of the rotary disc then forces oil into the cylinder and creates a lubricated surface to ease the turning of the steering wheel. Completion of the steering action brings the control sleeve and rotary disc valve back into a neutral position.

The steering control system works by manipulating the steering power in response to road speed and conditions (i.e., if the road speed is low, there is a greater degree of power steering is provided, but in the event of increased road speed the power steering capability is reduced).

There are a range of steering sensors, but the optical sensor has become the most popular type of sensor in an application based on its durability, simplicity, and high resolution. 

There are also steering angle sensors, the majority of which contain a microcontroller that reads the sensory information and processes this information into a steering angle by a serial communication network based on the steering wheel position angle and rate of turn.

Applications

The main field of application for steering sensors is in vehicle systems including ESP and EPS. The main location for standard steering sensors in a vehicle is either inside the steering column or mounted beneath the steering wheel component.

Sources and Further Reading

This article was updated on 13th February, 2020.

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