SPECIFICATIONSafety Devices for Internal CombustionEnginesThis invention relates to safety devices for internal combustion engines including those running on petrol or diesel fuel. With petrol engines the fuel enters the cylinders in gaseous form and is ignited by spark plugs energised in sequence through a distributor switch device from the engine ignition circuit. With diesel engines the fuel is injected in liquid form into the cylinder in sequence by an injector pump or pumps actuated by a solenoid device energised from the engine ignition circuit.The ignition circuit is energised when starting the engine from any suitable supply such as an electric battery and in vehicles powered by such engines includes the starter motor but as soon as the engine is running normally it drives an electric generator which takes over the energising of the ignition circuit, cuts out the battery and where used the starter motor and recharges the battery.
Most internal combustion engines are cooled by water in a radiator connected by water joints of tubing to a cooling jacket in the engine block.
Over long periods including long runs in hot weather the water level falls and eventually the engine overheats sometimes with severe damage to it and the same can occur with a sudden loss of water or drop in the oil pressure. Similarly if the oil level drops below a safe level in the sump from which lubricating oil is forced round the moving parts of the engine, the friction losses during engine running can cause siezure and serious damage to the engine.
Devices are known which are sensitive to such overheating or siezure and initiate a signal to a cut out device in the fuel supply system thereby stopping the engine when the fuel in the pipeline, including the carburetter in petrol engines, is used up. Such devices however have a delay while the fuel is being used up and often the damage is done to the engine before that occurs.
The main object of the present invention is to provide an improved safety device in which the aforesaid disadvantages are minimised or overcome.
According to the present invention a safety device for an internal combustion engine comprises an ignition system providing supply of electric current to the engine firing device, a first switch responsive to the pressure in the engine lubrication system and a second switch responsive to the liquid coolant level in the engine cooling system, such that should the oil pressure and/or coolant level fall below predetermined safe values the ignition circuit will be broken automatically and the engine stopped.
In a preferred construction the first switch comprises a relay normally in the closed position in the ignition circuit but movable into the open position by the device influenced by a signal from a device responsive to low pressure in the oil supply system of the engine. Preferably the second switch is normally urged into the closed position but is movable into the open position by a device influenced by a signal from a device responsive to low coolant level in the cooling system of the engine.
Where the engine is started by an electric motor initially energised by a source of electric supply on closing the ignition switch the safety device will allow current to flow to the engine firing device until the engine is running and then one or other or both of the oil and coolant switches will close to cause the ignition circuit to take over the current supply and break the ignition circuit should oil pressure and/or coolant level fall below the predetermined safety value.
In order that the invention may be more fully understood one construction in accordance therewith will now be described by way of example with reference to the accompanying diagrammatic electric circuit diagrams, in which Fig. 1 shows the ignition circuit of an internal combustion engine running on petrol or diesel oil, the circuit being shown in the engine start position, but with no oil pressure in the engine lubricating system and with a safe level of coolant in the engine cooling system;Fig. 2 shows a similar circuit to Fig. 1 with the engine stopped, the oil pressure below a safe value and the coolant level high; andFig. 3 shows a similar circuit to Figs. 1 and 2 but with the engine stopped, the oil pressure satisfactorily high and the coolant level below the safe limit;Fig. 4 shows a similar circuit to Figs. 1 to 3 with the engine running and the oil pressure and coolant level at safe values.
The circuit diagrams of Figs. 1 to 4 show an ignition system for a conventional petrol or diesel oil fired internal combustion engine. The engine may be a stationary engine as used in marine craft for driving the propeller shaft, or in a factory for driving machinery or electric generator or in a self propelled vehicle acting as the prime mover. The engine is not shown but the relevant parts of the lubricating system and its cooling system are shown. The coolant is normally water but it may be a different coolant such as diluted anti-freeze liquid. The diagrams in addition show a battery, starter motor and starter motor switch in the ignition circuit to show how the safety device operates when they are employed as in a stationary or in a self-propelled vehicle.
In Figs. 1 to 4, the circuit shows a lead 1 from the concentional ignition switch 18 through an oil pressure relay 2 and a coolant level, relay 3 to the engine firing system (not shown).
The oil pressure relay 2 comprises a movable contact 4 normally urged into the operative position (Figs. 3 and 4) where it engages a contact 6 in the lead 7 of the circuit to the relay 3.
The relay 2 has an electro-magnetic device 8 such as a solenoid connected to the ignition circuit and to earth through an oil pressure switch 9 when energised as will be described, it will open the relay by moving the contact 4 into the inoperative position. The switch 9 is in a circuit 25 containing an oil warning device 26 such as a light which is connected to lead 1 through a lead 27. In Fig. 1 the relay 2 is open, there is no oil pressure and the device 26 is in the "on" position. A further contact 10 is provided which the contact 4 engages in the open position to close a circuit 23 of the engine stop solenoid or stop motor if fitted.
This circuit 23 may include a relay (not shown) which when the engine stops breaks this circuit.
The relay 3 is similar to the construction of the relay 2 but its electro-magnetic device 11 is in circuit with a coolant low level switch 12, its contact 14 ieads through circuit 13 to the engine firing mechanism. A lead 28 connects the switch 12 to the lead 27 through a warning device 29 e.g. a light In Fig. 1 the water level is satisfactory so switch 12 is open and the device 29 is in the "off" position. A further contact 1 5 is provided which the contact 24 engages in the open position to close the circuit 23. The coolent level indicator such as a float or magnetic switch is provided in the header tank of the radiator of the cooling system where the coolant is hottest so that the earliest warning of overheating is given.
The operation of the device is as follows, assuming the oil level in the engine lubricating system is sufficient when the engine is running to provide safe lubrication of the engine and assuming the coolant level in the cooling system is sufficient adequately to cool the engine when running.
If the engine ignition switch 1 8 is placed in the operative or "on" position the lead 1 is energised.
Since the oil level is safe but the engine not running the contact 4 is open and the switch 9 is closed so that the device 26 is "on" and the contact 10 energises the circuit 23. If the engine is now started the oil pressure in the lubricating system will rise and in the conventional manner opens the switch 9. The device 8 is deenergised and the contact 4 engages the contact 6 to energise the lead 7. Since the coolant level is safe the switch 1 2 is open, the device 11 deenergised, the contact 4 in engagement with the contact 14 so that the line 13 to the engine firing mechanism is energised and the engine will continue to run under safe conditions.
Should the oil pressure fall below the predetermined value (Fig. 2) the switch 9 will close, the device 8 will be energised, thereby opening the contact 4, the engine will stop at once due to breaking the ignition circuit, and the oil warning light 26 will come on indicating to the operator the cause of the engine stoppage.
If the oil pressure remains of satisfactory value but the coolant level falls below a safe limit (Fig.
3) the switch 12 will close, the device 11 will close and the engine will stop immediately while the warning device 29 will come on indicating the cause of the stoppage.
Where the engine is provided with a selfstarter electric motor, this is shown in Figs. 1 to 4 at 1 7 and is connected through a conventional ignition and starter switch 18 of the ignition circuit which includes a starter solenoid 21 and an electric battery 20. The lead 19 is connected in circuit with the starter solenoid switch 21, a conventional diode 22 and the engine firing mechanism.
In operation when the ignition circuit is turned on the switch 18 is closed and when the starter switch 30 is turned on the starter solenoid 21 closes and the battery 20 energised the motor to start the engine which is temporarily supplied through the diode 22 and the engine firing mechanism is energised. When the engine starts and is running the starter switch 30 is turned off, the switch 21 opens and the starter motor is deenergised and stops. The ignition switch then allows the current supply to pass to the engine firing mechanism through the line 1 as already described.
Thus by means of the safety device of this invention the engine is automatically and immediately stopped should the oil pressure in the lubricating system and/or the coolant level in the cooling system reach predetermined unsafe levels and damage to the engine will be prevented. At the same time the warning devices will indicate to the operator the cause of the stoppage.
Moreover the safety device of the present invention may be fitted to an existing engine or vehicle at low cost, as well as being easily fitted to a new vehicle or engine.
In this specification the devices of the circuits are described as being earthed but it will be understood that such earthing may be positive or negative to suit the vehicles and for machines in which they are incorporated.