GB2518670A

GB2518670A - An apparatus and system for detecting a cooling system leak

Info

Publication number: GB2518670A
Application number: GB1317236.6A
Authority: GB
Inventors: Benjamin Macdonald; Christopher James Leck
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2013-09-30
Filing date: 2013-09-30
Publication date: 2015-04-01
Anticipated expiration: 2033-09-30
Also published as: GB2518670B; CN104514614B; DE102014219642A1; GB201317236D0; CN104514614A

Abstract

The pressure cap 21 is particularly for a degas tank 20 or radiator of a vehicle engine cooling system and has a deformable, pressure-sensitive membrane 28 and an electrical contact switch 27. When a pressure inside the degas tank is equal to or greater than a predetermined pressure limit, e.g. 0.5-0.7 bar, the membrane causes the switch to obtain a first operating state. Otherwise, the switch is in a second operating state. The switch preferably comprises first 29 and second 30 electrically conductive contact surfaces whereby deforming of a resilient portion 31 of the membrane upwards urges the second contact surface into connection with the first, placing the switch in the first state. The cap may include an aperture 33 to introduce air at atmospheric pressure into the cap and a releasable fastener for connection to a neck 20n of the degas tank. An engine system comprising the pressure cap is also claimed whereby a processor preferably compares the operating state of the switch with an expected state based on sensed engine speed and coolant temperature to determine whether there is a coolant leak. A method of preventing a vehicle engine from overheating is also claimed (figure 3).

Description

An Apparatus and System for Detecting a Cooling System Leak This invention relates to an internal combustion engine cooling system and, in particular, to an apparatus for detecting the loss of engine coolant pressure due to a poorly fitted degas tank cap or failed hose oonnection at the tank.

Liguid cooled internal combustion engines are critically dependent on their coolant systems. As fuel economy regulations increase and customer preference shifts to smaller, higher power density engines it is more important to prevent coolant loss to avoid damage to the engine. For larger engines such as are used for heavy trucks, the loss of engine coolant can result in engine running too hot resulting in engine shutdown. Also, if the vehicle has a poorly fitted degas tank cap or failed hose connection at the tank, the coolant can come into contact with the hot exhaust system and potentially cause a fire.

Most modern automobile engines use a closed pressurised type of cooling system operating at a system pressure of approximately lOOkPa (1 bar) so as to raise the boiling point of the coolant to approximately 12000. Such pressurised systems normally include a degas tank that is physically separated from the radiator and is closed by a pressure cap.

The degas tank operate under the same pressure of approximately 1 bar as the other components of the cooling system and is connected to the engine and the radiator so that the coolant can circulate through the degas tank.

One purpose for the degas tank is to allow entrained air and gas in the coolant to be separated from the coolant as the coolant flows through the degas tank to improve heat transfer efficiency.

When the engine is running, a coolant pump pumps liguid coolant and any air in the coolant through an inlet hose to the degas tank and returns it to the engine via an outlet hose to a low pressure side of the pump and then to a water jacket of the engine.

The pressure cap of the degas tank is similar tc the type of cap located on a radiator and removal of the pressure cap permits the coolant level of the cooling system to be periodically topped up.

Current vehicles are at risk of ooolant loss with possible overheating and safety concerns if the pressure cap is not fitted properly on the degas tank because the coolant will then boil at a lower temperature than when it is pressurised to the correct level. For example with the degas cap removed the coolant will boil at approximately 100°C rather than the expected 120°C. If the ooolant boils due to an ill-fitted degas cap then coolant will be lost via the leakage path past the degas cap and this can ultimately lead to engine failure or damage occurring to the engine.

US Patent 5,656,771 discloses a system for monitoring the state of a cooling system that includes a pressure sensor to detect internal pressure inside the cooling system. However, such a system is complex in construction and includes a pressure sensor that has to be oalibrated.

The inventors have realized that there is a need for a simple, cost effective engine protection system to indicate when a pressure cap such as a degas tank cap is not fitted properly.

It is an objeot of the invention to provide such a simple, cost effective engine protection system to indicate when a pressure cap is not fitted properly.

[STATEMENTS OF INVENTION REPEATTNG THE CLATMS WILL BE INSERTED HERE IN THE FINAL VERSION. THESE HAVE BEEN OMITTED

TO SAVE TIME WHEN REVIEWING THIS SPECIFICATION]

The invention will now be described by way of example with reference to the acoompanying drawing of which: Fig.1 is a schematic view of an engine system according to a second aspect of the invention having a degas tank cap according to a first aspect of the invention; Fig.2 is a schematic cross-section through a degas tank cap in accordance with the first aspect of the invention; Fig.3 is a flowchart of a method for detecting cooling system pressure loss according to a third aspect of the invention.

With reference to the Fig.1 there is shown an engine system 10 for a motor vehicle having an engine 41, a powertrain 42, an electronic controller 24 and a cooling system 15. The cooling system 15 is conventional in arrangement (See for example and without limitation the cooling circuit shown in Fig.1 of GB Patent 2437064) and comprises one or more radiators (not shown), a thermostat (not shown) a coolant pump 40 and a degas tank 20. The degas tank 20 is connected to the engine 41 through coolant inlet and outlet lines 22 and 23 respectively.

The engine 41 is a conventional liquid cooled engine including a water jacket through which liquid coolant is pumped. The engine 41 is arranged to drive a powertrain 42.

Liquid coolant in the cooling system is pumped in this case by a conventional engine driven pump 40 to cause the liquid coolant to flow through the cooling system and the water jacket of the engine 41. When the engine 41 is running, the coolant pump 40 pumps the liquid coolant and any entrained air in the liquid coolant through inlet hose 22 into the degas tank 20 where the entrained gas is separated from the liquid coolant which then flows back via the outlet hose 23 to the pump 40.

With reference to Fig.2, there is shown one embodiment of a degas tank cap in accordance with the invention.

The degas tank 20 includes a removable degas tank cap 21 that is remcvably attached tc the degas tank 20 and, in this case, the releasable attachment means used is a screw thread for threaded engagement with a complementary thread formed on a neck 20n of the degas tank 20.

The removable degas tank cap 21 has a pressure actuated switch 27 located inside the cap 21. The switch 27 is operated by a deformable membrane 28 sensitive to pressure.

The degas tank cap 21 further comprises an electrical connecting member 32 mounted on the degas tank cap 21 to provide a wiring connection to the switch 27. An aperture 33 in the degas tank cap 21 permits air at atmospheric pressure to enter to one side of the deformable membrane 28.

Therefore, one side of the deformable membrane 28 is exposed to atmospheric pressure and the other side is exposed to the pressure subsisting within the degas tank 20.

The deformable membrane 28 includes a resilient portion 31 which deforms responsive to varying pressure within the degas tank 20.

A first contact 29 of the switch 27 is fixedly mounted on the cap 20 and a second contact 30 of the switch 27 is arranged for movement in response to deflection of the deformable membrane 28.

The first and second contacts 29 and 30 are spaced apart a set distance such that, when the pressure within the degas tank 20 reaches a predetermined limit, the deflection of the deformable membrane 28 will push the second contact into engagement with the first contact 29 to close the switch 27 and place the switch in an ON' state.

When the pressure inside the degas tank 20 is below the predetermined limit, the second contact 30 will move with the deformable membrane 28 away from the first contact 29 to open the switch 27 and place the switch in an OFF' state.

The resilience of the resilient portion 31 of deformable membrane 28 and the spacing between the two contacts 29, 30 are chosen so as to activate the switch 27 into the ON' state only when the pressure is at or above the predetermined pressure level and to deactivate the switch 27 below the predetermined pressure level.

The predetermined pressure level is the minimum pressure level acceptable in the degas tank 20 under normal engine operating conditions with the degas cap 20 correctly in place such as, for example and without limitation 50 to 70 kPa (0.5 to 0.7 Bar).

An electronic processor such as a powertrain control module (PCM) 24 is connected to the switch 27 of degas tank cap 21 and to an engine speed sensor 25 and an engine coolant temperature sensor 26.

Operation of the engine system 10 is as follows with reference to Figs. 1 and 2.

When the pressure inside the degas tank 20 exceeds the predetermined level during normal engine running conditions, the pressure inside the degas tank 20 acts against the deformable membrane 28 which pushes the switch 27 cn the cap 21 to the ON state and a signal is sent to the POM 24 which is indicative of the ON' state of the switch 27. When the pressure inside the degas tank 20 drops below the predetermined value, the pressure acting against the deformable membrane 28 is reduced, thereby releasing the switch 27 to an OFF state and a signal is sent to the PCM 24 indicative of the OFF' state of the switch 27. Thus, the deformable membrane 28 controls the switch 27 to change its state based upon whether the pressure inside the degas tank exoeeds the predetermined value.

The Powertrain Control Module (PCM) 24 also receives signals from the engine coolant temperature (ECT) sensor 26 and the engine speed (RPM) sensor 25. The PCM 24 uses the signals from the speed and temperature sensors 25 and 25 to determine whether the pressure within the degas tank 20 should be at or above the predetermined pressure level.

The PCM 24 is programmed to check the signal from the switch 27 in the degas tank cap 21, when it is expected that the predetermined pressure level should have been reached in the degas tank 20 under the current engine operating conditions received from the speed and temperature sensors 25 and 26. It would for example be expected for the switch 27 to be in the ON' state when the engine speed is above a predefined speed limit and the coolant temperature is above a predefined temperature limit.

If the switch 27 indicates an ON' state corresponding to the current operating conditions and the current operating conditions are such that the predetermined pressure level should have been reached in the degas tank 20, then the PCM 24 allows normal functioning of the engine.

When the degas tank cap 21 is not fitted properly, the pressure inside the degas tank 20 will not build up to the expected pressure level during normal engine operating conditions because of leakage through the poorly fitted degas tank cap 21. Due to the insufficient pressure build up inside the degas tank 20, the pressure sensitive deformable membrane 28 will not activate the switch 27 to change its state from OFF' to ON', even though the PCM 24 expects the switch 27 to be in the ON state based upon the current engine operating conditions as deduced from the FOT sensor 26 and RPM sensor 27. Therefore, if the switch 27 has not changed its state from OFF' to ON', when the engine operating conditions infer that there should have been a state change then this is indicative of poorly fitted degas cap 21. The PCM 24 will then operate the engine 41 in an overheating failsafe mode for safety until the cooling system 15 can be further investigated. For example, the power output from the engine 41 may be limited to prevent excessive heat generation while the engine 41 is operated in the overheating failsafe mode. At the same time, the driver is also provided with a warning of a cooling system fault.

This is because, even if no great loss of coolant has occurred due to a poorly fitted or missing degas tank cap, it is important to signal the fact that a cooling system designed to operate under pressure is not being correctly pressurized so that remedial action can be taken.

Fig.3 shows a method 100 for preventing the overheating of the engine 41 of a vehicle having a liguid cooling system 15.

The method comprises in box 105 of an initial step of providing a pressure cap for a component of the cooling system having a pressure sensitive switch the state of which is determined by deformation of a membrane supported by the pressure cap due to variations in pressure of coolant stored in the component of the cooling system, the switch being operable such that, if the pressure of the coolant in the component of the cooling system is one of egual to and greater than a predetermined pressure limit, the switch attains a first state and, if the pressure of the coolant in the component of the cooling system is less than the predetermined pressure limit, the switch attains a second state.

The method proper starts in box 110 when the engine is switched on.

Then in box 120 an electronic processor such as the PCF4 24 receives signals indicative of engine speed and coolant temperature.

Then in box 130 it is determined, based upon the current engine speed and coolant temperature, if the pressure of the coolant in the component of the cooling system should be at least equal to the predetermined pressure limit and if it is not the method advances through box 135 back to box 120 without checking the state of the pressure sensitive switch. However, if the pressure should be at least equal to the predetermined pressure limit then the method advances to box 140 where the state of the pressure sensitive switch is checked. If the output from the switch indicates that the switch is in the second state when the pressure in the coolant stored in the component of the cooling system should be at least equal to the predetermined pressure limit then the method advances to box 150 and the engine is then operated in an engine overheating failsafe mode to prevent overheating of the engine 41 and a warning signal is provided to a user of the engine 41. The method then returns to box 120. However, if in box 140 the output from the switch indicates that the switch is in the first state, the method advances to box 145 and normal operation of the engine is continued and the method then returns to box 120.

Therefore, by placing a pressure activated switch on the degas tank cap and monitoring its state using an electronic processor under certain engine operating conditions, coolant loss leading to engine overheat and safety concerns due to poorly fitted degas cap can be avoided. One advantage of the invention is that there is no need to actually measure the magnitude of the pressure within the degas tank. Therefore calibration of the leakage detection part of the system is not reguired as the switch output is binary in nature. Furthermore complexity of the system is reduced because a simple binary output is used to determine when certain engine operating conditions subsist whether the degas cap is correctly fitted and is not leaking.

Although the invention has been described with reference to its use on a component of the cooling system in the form of a degas tank cap of a vehicle, it will be appreciated by those skilled in the art that it could be applied with similar advantageous effect to a radiator cap of a vehicle in which case the component of the cooling system would be a radiator.

Although the invention is described with respect to a swItch the state of which is "ON" when the coolant pressure is egual to or greater than a predefined pressure limit and "OFF" when the pressure is below the predefined pressure limit, it will be appreciated that the opposite logic could be used so that the switch is "OFF" when the coolant pressure is egual to or greater than a predefined pressure limit and "ON" when the pressure is below the predefined pressure limit.

It will be further appreciated that there need not be a mechanical linkage between the membrane and the switch, the switch could, for example be a magnetic proximity switch.

-10 -It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to one or more embodiments it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

-11 -Claims 1. A pressure cap for a cooling system of a motor vehicle, the pressure cap comprising a releasable attachment means for mounting the pressure cap on a component of the cooling system, an electrical switch located inside said pressure cap, a pressure sensitive membrane having a deformable surface portion operatively connected to the switch so as to change the state of the switch in response to variations in pressure within the component of the cooling system wherein, when the pressure in the component of the cooling system is one of equal to and greater than a predetermined pressure limit, deformation of the pressure sensitive membrane causes the switch to attain a first operating state and, when the pressure in the component of the cooling system is below the predetermined pressure limit, the pressure sensitive membrane causes the switch to attain a second operating state.
2. A pressure cap as claimed in claim 1 wherein the first state is an ON state and the second state is an OFF state.
3. A pressure cap as claimed in claim 1 or in claim 2 wherein the switch has first and second electrically conductive surfaces, the deformable surface portion of the pressure sensitive membrane is operatively connected to a respective one of the first and second electrically conductive surfaces of the switch, so as to move the respective one surface towards and away from the other electrically conductive surface in response to variations in pressure within the component of the cooling system so as to effect changes in the state of the switch.
4. A pressure cap as claimed in claim 3 wherein said first electrically conductive surface is normally disengaged from said second electrically conductive surface when the -12 -pressure in the component of the cooling system is below the predetermined limit.
5. A pressure cap as claimed in claim 3 or in claim 4 wherein said second electrically conductive surface engages said first electrically conductive surface when the pressure within the component of the cooling system is one of egual to or greater than the predetermined pressure limit.
6. A pressure cap as claimed in any of claims 1 to 5 wherein the component of the cooling system is a degas tank and the pressure cap is a degas tank cap.
7. An engine system comprising an engine, a cooling system for the engine including a pressure cap as claimed in any of claims 1 to 6 and an electronic processor wherein the switch is operatively connected to the electronic processor and the electronic processor uses the state of the switch to determine whether there is a leak between the pressure cap and the component of the cooling system to which it is attached.
8. A system as claimed in claim 7 wherein the electronic processor is further connected to an engine speed sensor and a coolant temperature sensor and is operable to check the state of the switch when the outputs from the engine speed and coolant temperature sensors indicate that the pressure within the component of the cooling system should be at least equal to the predetermined pressure limit.
9. A system as claimed in claim 8 wherein, if the state of the switch indicates that the pressure in the component of the cooling system is below the predetermined pressure limit, the electronic processor is operable to provide a warning that a cooling system leak has been detected.

-13 -
10. A system as claimed in claim 8 or in claim 9 wherein, if the state of the switch indicates that the pressure in the component of the cooling system is below the predetermined pressure limit, the electronic processor is operable to operate the engine in an overheating failsafe mode of operation.
11. A system as claimed in any of claims 7 to 10 wherein the electronic processor is a Powertrain Control Module electrically connected to the switch.
12. A method for preventing the overheating of an engine of a vehicle having a liquid cooling system wherein the method comprises: providing a pressure cap for a component of the cooling system having a switch the state of which is determined by deformation of a membrane supported by the pressure cap due to variations in pressure of coolant stored in the component of the cooling system, the switch being operable such that, if the pressure of the coolant in the component of the cooling system is one of equal to and greater than a predetermined pressure limit, the switch attains a first state and, if the pressure of the coolant in the component of the cooling system is less than the predetermined pressure limit, the switch attains a second state; determining, based upon engine speed and coolant temperature, if the pressure of the coolant in the component of the cooling system should be at least equal to the predetermined pressure limit and if the output from the switch indicates that the switch is in the second state when the pressure in the coolant stored in the component of the cooling system should be at least equal to the predetermined pressure limit; operating the engine in an engine overheating failsafe mode to prevent overheating of the engine.

-14 -
13. A method as oiaimed in olairn 12 wherein the component of the cooling system is a degas tank and the pressure cap is a degas tank cap.
14. A pressure cap for a cooling system of a motor vehicle substantially as described herein with reference to the accompanying drawing.
15. An engine system substantially as described herein 13 with reference to the accompanying drawing.
16. A methcd fcr preventing the overheating of an engine cf a vehicle having a liquid ocoling system substantially as described herein with reference to the accompanying drawing.