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Engine protection system
Overheating alarm system Having once cooked the engine I decided to increase my chances of avoiding a major problem next time round. Therefore I have installed a simple system which warns me visually and audibly when the engine gets hot beyond the acceptable limit.
The system is housed in a small plastic box bolted to the inside of the hinged cover below the steering wheel. The buzzer is fitted on top of the circuit enclosure and the LED on the instrument panel housing.
Circuit description:
The coolant temperature sender in the thermostat housing changes its resistance depending on the temperature. Maximum resistance is reached at the lowest coolant temperature. Voltage registered by the temperature gauge on the instrument panel causes the pointer to move up and down the scale as illustrated on the diagram. For the typical engine temperature voltage at the sender terminal should be between 5.5V and 4.5V. These values are approximate and may vary depending on the type of the sender installed in the vehicle.
An op-amp acts as a comparator between the voltage supplied from the thermostat temperature sender and the voltage preset by the R1/Rv divider. If the engine temperature rises, ie. the sender resistance drops, so does the voltage supplied to the inverting op-amp input. When the preset voltage is reached (the temp gauge is about to reach the red area) the op-amp output goes high and drives the transistor which then powers a flashing LED and a piezzo buzzer. With the LED flashing, the buzzer is switched on and off. C1 introduces a hysteresis which prevents activation by intermittent voltage fluctuations.
The circuit requires one op amp (e.g. 741 family), one transistor to drive the LED and buzzer, two capacitors, one variable resistor and a couple fixed value resistors. The choice of components and semiconductors is not critical, as long as they are automotive grade. All parts, including the blinking LED are available form the Maplin Electronics catalogue.
To test the operation of the alarm circuit you will need to disconnect the lead from the temperature sender terminal post and connect a 4.7k potentiometer between the lead and earth. By changing the potentiometer setting the operation of the sender can be simulated and the pointer on the gauge will move accordingly. When it settles in the position showing the maximum desirable temperature, measure the voltage before the potentiometer. Next, by using the variable resistor VR1, set the same voltage at pin 3 of the op amp IC1. This is the value which will trigger the alarm. The LED and buzzer may be tested by shorting the Vcomp terminal post to ground.
The circuit has been tested for more than a year now. To protect it from moisture and dust the enclosure is filled with synthetic resin.
Often, particularly when driving in a convoy, you stop, get out of the Landrover and walk to see what's going on ahead of you. Not infrequently, it is another vehicle that got stuck and needs help. You can leave the engine running, but it make take half an hour before you return to drive away, or switch it off, with the effect described above.
Two minutes are usually sufficient to reduce the temperature to the normal working level. I have designed a simple circuit that allows me to turn off the ignition key and leave the engine idling for two minutes, after which time it will switch itself off automatically.
The circuit is based on the UB6047 timer IC which is also used for controlling the rear window heater. By maitaining current supply to the injection pump fuel cut-off solenoid the engine can be kept running independently of other controls, eg. the position of the ingition key.
The system is activated by by pushing a momentary action switch on the instrument binnacle (I used a modified switch originally used for turning the radio volume down).
The circuit is housed in a 1.5 in. x 1.5 in. plastic box filled with potting compound for protection agains elements and fixed under the dashboard.
Click on the thumbnail to see the circuit diagram.
The sender is connected to a 12 mm dia large LED array fitted on the instrument binnacle and a buzzer. It would be a bit annoying to bear with yet another buzzer that goes off when the ignition is switched off, which would happen before oil pressure builds up to the working level. For this reason I designed a circuit that switches the buzzer only after the ignition key is in the on position and the vehicle has started moving.
The circuit is based on the LM2907 frequency to voltage converter, which is also used for operating the tachometer.
When power is supplied to the circuit (by switching on the ignition), it waits for the 12V/0V pulses coming from the speedo sender on the gearbox. After couting a predetermined number of pulses it activates a relay that closes the loop with the oil pressure sender. This will happen after the vehicle has moved over the distance of 20 - 30 feet. If the pressure is too low, at that moment or any time afterwards, the buzzer will sound and the LED will come on. The system stays active on as long as the ignition key is on.
The circuit is housed in a 1.5 in. x 1.5 in. plastic box filled with potting compound for protection agains elements and fixed under the dashboard. It requires no additional switches and works fully automatically.
Click on the thumbnail to see the circuit diagram.
Engine protection system
Overheating alarm system Having once cooked the engine I decided to increase my chances of avoiding a major problem next time round. Therefore I have installed a simple system which warns me visually and audibly when the engine gets hot beyond the acceptable limit.
The system is housed in a small plastic box bolted to the inside of the hinged cover below the steering wheel. The buzzer is fitted on top of the circuit enclosure and the LED on the instrument panel housing.
Circuit description:
The coolant temperature sender in the thermostat housing changes its resistance depending on the temperature. Maximum resistance is reached at the lowest coolant temperature. Voltage registered by the temperature gauge on the instrument panel causes the pointer to move up and down the scale as illustrated on the diagram. For the typical engine temperature voltage at the sender terminal should be between 5.5V and 4.5V. These values are approximate and may vary depending on the type of the sender installed in the vehicle.
An op-amp acts as a comparator between the voltage supplied from the thermostat temperature sender and the voltage preset by the R1/Rv divider. If the engine temperature rises, ie. the sender resistance drops, so does the voltage supplied to the inverting op-amp input. When the preset voltage is reached (the temp gauge is about to reach the red area) the op-amp output goes high and drives the transistor which then powers a flashing LED and a piezzo buzzer. With the LED flashing, the buzzer is switched on and off. C1 introduces a hysteresis which prevents activation by intermittent voltage fluctuations.
Click to enlarge
The circuit requires one op amp (e.g. 741 family), one transistor to drive the LED and buzzer, two capacitors, one variable resistor and a couple fixed value resistors. The choice of components and semiconductors is not critical, as long as they are automotive grade. All parts, including the blinking LED are available form the Maplin Electronics catalogue.
To test the operation of the alarm circuit you will need to disconnect the lead from the temperature sender terminal post and connect a 4.7k potentiometer between the lead and earth. By changing the potentiometer setting the operation of the sender can be simulated and the pointer on the gauge will move accordingly. When it settles in the position showing the maximum desirable temperature, measure the voltage before the potentiometer. Next, by using the variable resistor VR1, set the same voltage at pin 3 of the op amp IC1. This is the value which will trigger the alarm. The LED and buzzer may be tested by shorting the Vcomp terminal post to ground.
The circuit has been tested for more than a year now. To protect it from moisture and dust the enclosure is filled with synthetic resin.
Turbo protection system
When the engine is hot, eg. after a long drive in high revs on or a motorway, by switching it off immediately, the supply of oil to the turbo bearings is discontinued. This increases turbo wear and causes premature failures. It can be prevented by keeping the engine on idle for a short time to allow it cool down by itself. Often, particularly when driving in a convoy, you stop, get out of the Landrover and walk to see what's going on ahead of you. Not infrequently, it is another vehicle that got stuck and needs help. You can leave the engine running, but it make take half an hour before you return to drive away, or switch it off, with the effect described above.
Two minutes are usually sufficient to reduce the temperature to the normal working level. I have designed a simple circuit that allows me to turn off the ignition key and leave the engine idling for two minutes, after which time it will switch itself off automatically.
The circuit is based on the UB6047 timer IC which is also used for controlling the rear window heater. By maitaining current supply to the injection pump fuel cut-off solenoid the engine can be kept running independently of other controls, eg. the position of the ingition key.
The system is activated by by pushing a momentary action switch on the instrument binnacle (I used a modified switch originally used for turning the radio volume down).
The circuit is housed in a 1.5 in. x 1.5 in. plastic box filled with potting compound for protection agains elements and fixed under the dashboard.
Click on the thumbnail to see the circuit diagram.
Low oil pressure warning system
I have noticed that the standard oil pressure sender is not the best way to inform the driver of the condition of the engine lubricating system. The red light on the instrument panel comes on when there is virtually no oil pressure, hence the engine is near the point of getting seized. This can be remedied by fitting an additional sender that informs me of the oil pressure drop before it is too low. The sender is connected to a 12 mm dia large LED array fitted on the instrument binnacle and a buzzer. It would be a bit annoying to bear with yet another buzzer that goes off when the ignition is switched off, which would happen before oil pressure builds up to the working level. For this reason I designed a circuit that switches the buzzer only after the ignition key is in the on position and the vehicle has started moving.
When power is supplied to the circuit (by switching on the ignition), it waits for the 12V/0V pulses coming from the speedo sender on the gearbox. After couting a predetermined number of pulses it activates a relay that closes the loop with the oil pressure sender. This will happen after the vehicle has moved over the distance of 20 - 30 feet. If the pressure is too low, at that moment or any time afterwards, the buzzer will sound and the LED will come on. The system stays active on as long as the ignition key is on.
The circuit is housed in a 1.5 in. x 1.5 in. plastic box filled with potting compound for protection agains elements and fixed under the dashboard. It requires no additional switches and works fully automatically.
Click on the thumbnail to see the circuit diagram.
© Roman Gozdzikowski 1998-2003
