Vehicle height sensor (ride height sensor)

01

Choose the sensing principle and mounting

US patent 6,234,654 B1, on a height sensor for headlight beam axis levelling, describes conventional height sensors that convert vertical movement of the suspension arms relative to the body into a rotation through a link mechanism and read that rotation with an angular sensor: either a rotating magnet whose flux change is read by a magnetic detecting element, or a slit disc read by a photo-interrupter. It notes that the link needs space above the suspension arms and adds parts to assemble. [1]

The same patent describes an ultrasonic alternative fixed to the body and aimed at the road, which it says can be disturbed by road irregularities, weeds and snow, and claims a coil-based sensor in which an exciting coil on the suspension arm and a pickup coil on the body face each other, the vehicle height being calculated from the pickup voltage. [1]

Headlamp levelling is one regulatory reason for fitting a height sensor. UN Regulation No. 48 (paragraph 6.2.6, in the English text published by Japan's Ministry of Land, Infrastructure, Transport and Tourism) requires the dipped-beam cut-off to stay within set inclination limits under all the static load conditions of its Annex 5: for a headlamp lower edge below 0.8 m, between −0.5% and −2.5% with an initial aim of −1.0% to −1.5%; above 1.0 m, between −1.0% and −3.0% with an initial aim of −1.5% to −2.0%. Where a levelling device is needed to meet these limits, paragraph 6.2.6.2.1 says it shall be automatic; that text also permits manually adjusted devices operable from the driver's seat with a stop at the initial inclination. [3]

Editorial calculation: a 1% change in inclination moves the cut-off 0.25 m at 25 m, so the full −0.5% to −2.5% band spans about 0.5 m at that distance; the height sensor and levelling actuator together must keep the beam inside it as load changes. Check which revision of R48 applies to your vehicle, since amendments change the levelling requirements. [3]

For measurement rather than control, Cosworth's mini laser ride height sensor measures the distance to the road from 50 mm to 450 mm for motorsport ride height logging, using a class 2 laser at 650 nm with 100 kLux ambient light immunity and a replaceable protective window. [2]

Give the supplier the vehicle or axle, the function (headlamp levelling, suspension control or test logging), the mounting points on body and suspension arm or the road-facing position, the travel or distance range, required output (analogue voltage, PWM, SENT or other) and calibration, accuracy, supply, connector, operating temperature and sealing.

02

Set the range, output, accuracy, supply and sealing

The Cosworth data sheet lists a 0–5.0 V DC analogue output with a calibration of 80 mm/V, resolution from ±0.02 mm at 50 mm to ±0.80 mm at 350 mm, linearity from ±0.06 mm to ±2.5 mm over the same distances, thermal drift of ±0.06% per °C and response time under 2.5 ms. It runs on 10–28 V at 80 mA, operates from 0 to +75 °C, is rated IP67, weighs 62 g and measures 13 × 49.5 × 40 mm; its range can be taught to a narrower span so the 0–5 V output covers it, and if the beam is interrupted the output holds the last valid value for up to 200 ms before dropping to 0 V. [2]

Editorial calculation: the 400 mm span from 50 mm to 450 mm over a 5 V output gives the stated 80 mm/V (400 ÷ 5). [2]

Editorial note: for link-arm sensors the output depends on link length and mounting geometry as well as the sensor, so agree the calibration on the vehicle at the reference height.

03

Specify a contactless link-arm sensor for production vehicles

The link-arm design described in the patent above is still the production form, with the angle read contactlessly. KYOCERA AVX's sensor 91970 is a Hall-effect position sensor for height and level control in vehicles: it measures an angle range of ±45° and gives a single-channel analogue output of 0.5–4.5 V from a 5 V supply, with independent linearity of 1% or better. It operates from −40 °C to +100 °C, is sealed to IP6K9K in the mounted state and uses an AMP 114-18063-21 connector, coding A. KYOCERA AVX states that the Hall sensors detect magnetic field changes without mechanical contact, which reduces wear. [4] [1]

Editorial calculation: 4.0 V of output span (0.5 to 4.5 V) over 90° of rotation is about 44 mV per degree, and 1% linearity of that span is ±40 mV, or about ±0.9°. With an assumed 100 mm lever, ±45° corresponds to about ±71 mm of arm travel (100 × sin 45°), so the lever length chosen at the mounting sets how much ride-height change the sensor sees per volt. [4]

Editorial note: the 0.5 V and 4.5 V end points leave the 0–0.5 V and 4.5–5 V bands outside the measuring range; ask the supplier whether the control unit should treat an output in those bands as a fault, and compare this with the Cosworth laser sensor, which outputs 0–5.0 V and drops to 0 V after 200 ms if its beam is blocked. [4] [2]

04

Link rod and lever, angle sensing element, coil pair, laser or ultrasonic head, and electronics

The rows split by what is measured: a link and lever turn suspension travel into an angle, while a coil pair, laser or ultrasonic head measures distance directly, and the patent notes that ultrasonic heads can be disturbed by road irregularities, weeds and snow. [1]

05

Supply, output, measuring range, linearity, resolution, temperature and sealing for a height sensor order

The example values here come from one laser sensor for test logging; for a production link-arm sensor compare against data such as KYOCERA AVX's ±45°, 0.5–4.5 V and IP6K9K, and agree the calibration on the vehicle. [2] [4]

06

Send the vehicle, mounting and signal data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Vehicle: [model; axle]
Function: [headlamp levelling; suspension control; test logging]
Mounting: [body and arm points or road-facing position]
Range: [travel or distance]
Signal: [output type; calibration; accuracy]
Power: [supply; current]
Environment: [temperature; sealing; washdown]
Connector: [type]
Volume: [quantity]

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