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es Instrument Clusters

Topics covered in this presentation:

Analog Instrument Clusters Digital Instrument Clusters Instrument Gauges and Computers

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es Typical Analog Instrument Cluster

The speedometer is usually situated in a prominent position.

It has a pointer that lines up with numerical values, which indicate vehicle speed in miles per hour (MPH).

The speedometer also has an odometer to measure distance traveled.

The tachometer displays engine speed in revolutions per minute (RPM).

An instrument cluster displays the status of a vehicle’s systems.

The rev limit (red area) indicates the maximum engine speed allowed, before damage can occur.

Tachometer

Rev limit

Odometer Pointer

Speedometer

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Warning lamps are usually positioned around the perimeter of an instrument cluster. They may have red, green, blue or orange lenses.

They are used to indicate system information such as oil pressure, parking brake, battery status, direction indication, hi beam, ABS, choke, etc.

Typical Analog Instrument Cluster

The gauges usually have a symbol to represent their function.

The fuel gauge displays the amount of fuel that is left in a fuel tank. Fuel quantity is measured in gallons. The temperature gauge displays engine coolant temperature.

Fuel gauge

Warning lampsTemperature gauge

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es Typical Instrument Cluster Construction

The front of the instrument cluster is protected by a transparent cover or lens.

The instruments are fitted into, or are part of, the instrument housing.

They are aligned / secured in place by a support housing that may also be a fascia with indication markings.

A printed circuit electrically connects components in the instrument cluster. Display illumination bulbsare often inserted from the rear.

The instrument cluster is usually made of plastic and is held in position with screws.

PCB

Support housing

Transparent cover or lens

Speed, fuel and temperature

gauges

Instrument housing

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es Mechanically Driven Analog Speedometer

The speedometer cable links between the speedometer head and the transmission housing.

It has an inner cable that is a flexible wire with a drive gearon one end. It moves within a stationary outer housing.

When a vehicle is moving, it transfers motion through a gear linkage and rotates the speedometer inner cable.

At the speedometer head in the instrument cluster, a small magnet rotates. The resulting magnetic force moves the speedometer pointer.

Flexible inner cable

Outer cable housing

Speedometer head

Transmission housing

Cable inner wire and gear

Drive gear

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Trigger wheel

Transmission housing

Speed sensor

Analog or digital display

Computer (ECU)

Electronically Driven Speedometer

The transmission housing contains an output shaft with a trigger wheel.

A vehicle speed sensor is positioned next to the trigger wheel.

The computer (ECU / BCM) processes the input signal and converts the information into drive signals, for either analog or digital speedometers.

Some analog systems do not use a computer. The frequency of the incoming signal is converted to a voltage, which is used to drive a stepper motor that deflects the pointer.

Analog signal

When a vehicle is moving, the sensor produces a signal that relates to vehicle speed.

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Battery

Ignition switch

Switching / ignition pulses

Tachometer

Coil switching device

Ignition coil

Ignition Coil Driven Analog Tachometer

When an engine is running, the primary winding of the ignition coil is switched on and off to produce a spark.

The tachometer is connected to the minus (switching) terminal of the ignition coil.

The switching pulses trigger the analog pointer in the tachometer to display engine speed in revolutions per minute (RPM).

The switching rate is proportional to engine speed.

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Analog or digital drive

Trigger wheel

Speed sensor

Computer (ECU)

Digital tachometer

Analog tachometer

Analog signal

Sensor Driven Analog/Digital Tachometer

The crankshaft is fitted with a trigger wheel, which rotates while the engine is running.

The computer (ECU / BCM) processes the input signal and converts the information into drive signals, for either analog or digital tachometers.

A speed sensor is positioned nextto the trigger wheel. It produces a signal that relates to engine speed.

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Fuel consumption

Warning/status lamps

Climate control

Tachometer Main display

Typical Digital Instrument Cluster

The digital instrument cluster is lightweight and easy to read.

It can have digital displays for speed, fuel level, climate control, distance traveled etc.

There will also be lamps for warning / vehicle status, and direction indication.

The displays may be LCD, LED, or vacuum fluorescent. Incoming data is processed by the Body Computer Module (BCM).

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Digital/ switch

Analog

Input stage

Processing stage

Output stage

Input. Processing. Output.

The input stage processes both analog and digital inputs.

Weak or noisy digital signals are conditioned, ready for processing.

Typical Instrument / Body Computer (BCM)

Analog voltages are converted to digital signals by the A/D converter and / or amplifier, ready for processing.

Some input devices require a reference voltage to function. This is provided by the BCM’s power supply.

The instrument computer has three main stages of operation:

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Digital/ switch

Analog

Input stage

Processing stage

Output stage

CPU

Typical Instrument / Body Computer (BCM)

The “brain” of the computer is the processing stage.

The CPU stores input data in random access memory (RAM).

The output stage switches the required actuators.

CPU operation is controlled by a software program, stored in read only memory (ROM).

It compares input data against expected data and switches appropriate output drivers.

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Fuel level sensor Lamp

BCM

Digital display

Speaker

5V

The resistance of the fuel level sensor changes with fuel quantity.

The BCM processes the input data and produces an output signal to drive a digital or analog display.

The BCM may also switch on a lamp, or use a speaker to warn the driver that the fuel tank is nearly empty.

Fuel Level Circuit

Typical Body Computer Circuits

This causes a corresponding voltage change at the BCM’s analog input.

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Oil pressure switch

BCM

Lamp

Speaker

12V

Typical Body Computer Circuits

When engine oil pressure is correct, the oil pressure switch is closed.

The BCM will switch on a warning lamp or speaker, when 12V is measured at its input.

When engine oil pressure is too low, the oil pressure switch is open.

The voltage at the BCM input is zero.

The voltage at the BCM input is 12V.

Oil Pressure Circuit