Chapter 7 Instrument and Indicator System
1.Instrument system
Instrument system is ud to indicate the operating condition of engine and vehicle. It includes various meters or gauges on the instrument panel, such as:
●speedometer
●odometer
●trip odometer
●tachometer
●coolant temperature gauge
●amperemeter(or voltmeter)
●fuel gauge
●oil pressure gauge
●air pressure gauge(for air pressure braking system),etc.
2.Indicator system
Indicator system is usually ud to monitor the abnormal or limited operating condition of engine and vehicle. It includes various warning or indicator lights and chimes ,such as:
●Oil pressure warning light
●Low air pressure warning light (for air pressure braking system)
●Low vacuum warning light (for vacuum brake booster)
●Low brake fluid warning light
●Braking signal warning light
●Air cleaner jam warning light
●Low fuel warning light
●Exhaust brake indicator light (for exhaust brake system)
●Turn signal/hazard indicator light
●High beam indicator light
●Charging indicator light
形容结婚的成语●Seat belt reminder light
●Glow plug indicator light (for diel engine)
爱神丘比特
●Low washer fluid indicator light
●Water in fuel filter warning light(for diel engine)
●Rear window defogger indicator light
●4-wheel drive indicator light (for 4-wheel drive vehicle)
●A/T oil temperature warning light (for automatic transmission)
●Engine oil temperature warning light, etc.
3.Speedometer and odometer
Function of speedometer and odometer
Speedometer—It indicates vehicle speed.
Odometer—It records the total distance the vehicle has been driven.
Construction of speedometer and odometer ( magnetic induction type for example)
1-permanent magnet 2-metal(aluminium)ring 3-magnetic screen 4- coil spring
5-speedometer face 6-pointer 7-number rings(decimal odometer) 8,9-worm gears
10-driving shaft
3.3 Operating principle
The magnet is driven by a flexible cable from the transmission. The faster the car goes ,the faster th
e magnet spins. This action produces a rotating magnetic field that drags on the metal ring surrounding the magnet. The faster the spinning, the more drag on the ring. The spinning caus the ring to swing around against the tension of a spring. This, in turn, moves a pointer attached to the ring, which indicates car speed.
The odometer is operated by a pair of gears from the same rotating flexible cable that drives the speedometer. The motion is carried through the gears to the number rings on the odometer indicator. The rings turn to show how many kilometers the car has been driven.
4.Tachometer
4.1 Function of tachometer
The tachometer indicates the engine speed in order to
●Check and adjust engine.
●Monitor the engine operating condition.
●Control the optimum shift timing.
你可安好●Utilize the economical vehicle speed( for low fuel consumption).
4.2 Types of tachometer
There are two types of tachometer respectively for gasoline and diel engine. The circuit varies with the different signal source.
4.3 Tachometer circuit and operation
The following is a typical tachometer circuit for gasoline engine.
Fig. Typical tachometer circuit for gasoline engine
Operation:
This circuit utilizes the capacitor action of charging and discharging.
(1)When contact points clod, the ba electrode of triode T (NPN) doesn’t have offt
voltage and the triode blocks. The capacitor C2 is being charged. The charging circuit is B+→ ignition switch→ R3→C2→D2→B─.
(2)When contact points opened, the ba electrode of triode obtains a positive potential as a
signal voltage and the triode pass. The capacitor C 2 is discharging now. The discharging
circuit is C 2 positive → T → amperemeter →D 1 →C 2 negative. This action will drive the
amperemeter.
(3) When contact points repeat the process (open and clo), C 2 charges and discharges
超级中学
through amperemeter. The average current is in direct proportion to engine speed. Then
the scale of amperemeter can be calibrated to indicate the engine speed. Here the Zener
diode DW stabilizes the voltage to charge C 2 for more accuracy.
5. Fuel gauge
5.1 Function and component parts of fuel gauge
The fuel gauge indicates the fuel level of the fuel tank. It consists of a fuel indicator gauge on
the instrument panel, and a nsor in the fuel tank. The nsor is a variable resistor.
5.2 Types of fuel gauge
There are two basic types:
Electromagnetic fuel gauge Bimetal fuel gauge
5.3 Fuel gauge circuit and operation of electromagnetic type
(1) Electric circuit
猴和马合不合
Fig. Fuel gauge circuit of electromagnetic type
1-left coil 2 –right coil 3-iron armature(or rotor) 4-pointer 5-variable resistor
6-sliding blade 7-float 8,9,10-terminals 11-ignition switch
定格动画如何制作(2) Operation
When the float is low, left coil(called holding coil) has great current and produces strong
magnetic field. This attracts the rotor and the pointer moves leftwards. The fuel gauge
indicates a low level.
As the level changes to higher position, the magnetic field of right coil (deflecting coil)
increas becau of parallel connection with variable resistor, causing the movement of
pointer rightwards to indicate a high level.
By using two coils, the accuracy of the gauge is unchanged by any alteration in battery
voltage, as both are equally affected.
5.4 Fuel gauge circuit and operation of bimetal type
(1) Electric circuit
Fig. Fuel gauge circuit of bimetal type
1-contact point 2-bimetallic strip 3-heating coil 4,11,12-terminal 5,9-adjusting惊蛰图
geared ctor 6-bimetallic strip 7-heating coil 8-pointer 10-spring strip
13-variable resistor 14-sliding blade 15-float
(2) Operation
When the float is low, all resistance of nsor (or variable resistor ) is connected into
circuit. As a small current flows, the coil heats the bimetallic strip in the gauge a little. The
strip bends a little becau of the unequal expansion of the two metals. The pointer moves a
little to indicate a low level
When the float is high, the resistance of nsor becomes smaller. The higher the current,
the more the heating and bending of bimetallic strip in the gauge. The pointer moves across
the scale to indicate a high level.
成都吉他弹唱Note: The voltage stabilizer equipped is to reduce the influence resulting from the
voltage fluctuation of power source.
6. Coolant temperature gauge
6.1 Function and component parts of coolant temperature gauge
The coolant temperature gauge indicates the temperature of engine coolant. It consists of a
temperature indicator gauge on the instrument panel, and a temperature nsor at the water jacket
of engine head. 6.2 Types of coolant temperature gauge
There are two basic types:
Bimetal coolant temperature gauge
Electromagnetic coolant temperature gauge
6.3 Coolant temperature gauge circuit and operation of bimetal type
(1) Electric circuit
Fig. Coolant temperature gauge circuit of bimetal type
1-stationary contact-point 2- bimetallic strip 3-contact tongue 4,5,11-terminal
6,9-adjusting geared ctor 7- bimetallic strip 8-pointer 10-spring piece
(2) Operation
The temperature nsor is a aled tube with a bimetallic strip ,and a heating wire wound
around it. The contact points(moveable and stationary points) has a pre-pressure applied by
the bimetallic strip. When the coolant temperature becomes high, it bends upwards, the
pressure on contact points decreas.
At a low temperature: The bimetallic strip is heated by heating coil and bends up. The
contact points open. As the surrounding temperature is low, the bimetallic strip cools down
easily and the clod time of contact points is long. The average current through the heating
coil in gauge is high. The bimetallic strip bends much, causing the pointer to move rightwards
and indicate a low temperature.
At a high temperature: The bimetallic strip is heated by heating coil and bends up. The
contact points open. On the contrary, the surrounding temperature is high, the bimetallic strip
cools down hardly and the clod time of contact points is short. The average current through
the heating coil in gauge is low. The bimetallic strip bends little, causing the pointer to move
leftwards and indicate a high temperature.
6.4 Coolant temperature gauge circuit and operation of electromagnetic type
(1) Electric circuit
Fig. Coolant temperature gauge circuit of electromagnetic type
1-left coil 2-right coil 3-iron armature(or rotor) 4-pointer 5-nsor(thermistor)
(2)Operation
The circuit nsor is a NTC (negative temperature coefficient) thermistor . When the temperature is high, the resistance is low. When the temperature is low, the resistance is high.
As the coolant temperature changes, the resistance of thermistor changes. This alters the current through right coil and results in a variation of magnetic field. The resultant magnetic fields of left and right coil cau the pointer to move and indicate the coolant temperature, high or low.
7. Oil pressure gauge
7.1 Function and component parts of oil pressure gauge
The oil pressure gauge indicates the oil pressure of engine lubricating system. It consists of a oil pressure indicator gauge on the instrument panel, and oil pressure nsor at the main oil gallery or on the coar filter of the engine.
7.2 Oil pressure gauge circuit and operation
(1)Electric circuit
1-oil chamber 2-diaphragm 3-spring tongue 4- bimetallic strip 5-adjusting gear
6-connecting strip 7,9,15-terminal 8-calibrated resistance 10,13- adjusting geared ctor 11- bimetallic strip 12-pointer 14-spring piece 16-ignition switch
(2)Operation
The operating principle is similar to that of coolant temperature gauge of bimetal type. The main difference is that the contact-point pressure changes with the nsor temperature for coolant temperature gauge, whereas the contact-point pressure changes with the nsor oil pressure for oil pressure gauge.
8. Oil pressure warning light
8.1 Function of oil pressure warning light
Oil pressure warning light warns of low engine oil pressure. If the light flickers or comes on during normal driving, pull off the road in a safe area, stop the engine immediately and call a mechanic to check. Running the engine with the oil pressure warning light on could cau rious damage to the engine.
8.2 Sensor types of oil pressure warning light
There are two types of nsor for oil pressure warning light: Spring tube type and diaphragm type. They operate similarly.
8.3 Construction and operation of diaphragm-type nsor
(1) nsor construction
Fig. Oil pressure warning nsor of diaphragm-type
1-adjusting screw 2-diaphragm 3-moveable point 4-stationary point
