EP3444461B1

EP3444461B1 - Thermostat for cooling system of an internal combustion engine for vehicles

Info

Publication number: EP3444461B1
Application number: EP18188319.0A
Authority: EP
Inventors: Massimiliano Borasso; Ignazio CATALANO; Stefano VITTORINI
Original assignee: Sei Servizi Per L'economia E Per L'ingegneria Srl; Meccanotecnica Umbra SpA
Current assignee: SEI - SERVIZI PER L'ECONOMIA E PER L'INGEGNERIA Srl; Meccanotecnica Umbra SpA
Priority date: 2017-08-18
Filing date: 2018-08-09
Publication date: 2020-03-11
Anticipated expiration: 2038-08-09
Also published as: EP3444461A1

Description

The present patent application for industrial invention relates to a thermostat for the cooling system of an internal combustion engine for vehicles.
Alternative internal combustion engines are known, which are used as propulsion system for vehicles. Today the evolution of these engines is dominated by the attempt to reduce the CO2 emissions, with a reduction of fuel consumption. In fact, the production of CO2 in the discharge gases depends on the quantity of burnt fuel and, consequently, on the absolute or specific consumption of the propulsion systems.
The sector related with the improvement of the heating (faster warm up) and with the control and management of the engine (thermal management) is undoubtedly characterized by very low implementation costs for saved CO2 unit (fuel consumption). Several technologies are available also in the thermal management sector:

electrical or mechanical actuation of circulation pumps of the coolant independently from the rotational speed of the engine,
use of high-efficiency pumps,
control of oil circulation (and its thermal stabilization),
control of engine cooling according to several thermal levels, etc.

These new technologies have been already tested and approved and many of them are already available on the market.
It must be considered that:

a) in light duty vehicles (vehicles for transportation of single passengers), the most important aspect refers to the reduction of the warm up time of the engine, both for metal masses and for engine oil; for this type of engines, also the possibility of fixing a desired temperature level of the coolant accordingly to the engine operation may be important;
b) In heavy-duty engines (buses, transportation of goods, engines for off-road vehicles, etc.) the problems related to the warm up are not important; on the contrary, it is more important to define a thermal operation of the engine according to the load (power or torque).

In both cases, the possibility to change the thermal operation of the engine according to the load (power generated by the engine) is extremely important. The modification of the thermal operation of the engine depends on the modification of the temperature of the water of the cooling circuit.
Such a modification of the thermal operation is defined by the opening of a valve provided in a thermostat disposed in a conduit in communication with the radiator. The opening of such a valve permits a flow of coolant from the radiator to the engine. The valve of the thermostat has a shutter that is kept in normally closed position by means of a spring connected to the shutter. A wax capsule is mounted inside the spring. When the temperature of the coolant reaches a preset value, the wax capsule is expanded, moving the shutter of the valve against the contrast force of the spring. Consequently, the shutter is moved to the opening position and permits the flow of coolant from the radiator towards the engine. The complete expansion of the wax capsule is obtained in a temperature range from 85°C to 95°C. The complete expansion of the wax capsule corresponds to a force that pushes the shutter of the valve and lets the coolant circulate from the radiator towards the engine.
In such a way, the heat acquired by the coolant during the cooling of the engine is exchanged in the radiator and the temperature of the coolant remains constant. If the way from the radiator to the engine was closed, the coolant would recirculate inside the engine and would be progressively heated. When the way from the radiator to the engine is open, the radiator adjusts the temperature of the coolant, which is maintained in a range defined by the complete opening of the thermostat valve.
In modern thermostats (electrically-assisted thermostats), a thermal resistance is housed inside the wax capsule, which causes the expansion of the wax capsule when it is crossed by the electrical current, before the preset temperature range is reached by the coolant. So, the opening of the thermostat valve is anticipated. Because of the anticipated opening of the way from the radiator to the engine, the coolant is stabilized at a lower temperature and this is a larger operational margin of the cooling circuit compared to the situation without electrical command. For example, in sports engines, the engine must be stabilized at a lower thermal level in order to avoid local overheating, localized vaporization, etc.
From an electrical viewpoint, an electrically-assisted thermostat has a higher level of freedom compared to traditional thermostats because it permits to modify the temperature of the coolant "downwards", thus bringing the parts assisted by the coolant to a lower thermal level. These parts can be metal masses of the engine, the lubrication oil, the overpowering air, the recirculated discharge gases and any other functions related with the coolant.
However, this type of electrically-assisted thermostat is impaired by the fact that the temperature of the coolant cannot be modified "upwards". In other words, the heating resistance permits the anticipation of opening of the thermostat valve, but not its delay. In fact, when the temperature of the coolant reaches the preset range (85°C-95 °C), the thermostat valve opens inevitably, permitting the coolant to flow from the radiator to the engine. Being the radiator capable of exchanging the thermal power acquired by the coolant while flowing, said exchange corresponds to the maintenance of a thermal level of the coolant at the complete opening value of the thermostat. Upwards variations are possible, but they are temporary and related to limited periods and, in any case, defined by the temperature of the complete opening of the thermostat. On the contrary for some applications, it may be desirable to delay the opening of the thermostat valve in order to have a coolant stabilized at a higher temperature than the traditional range (85°C-95 Such arrangements are disclosed in the documents: JP H04 73473 and DE 10 2010 018998 .
The purpose of the present invention is to eliminate the drawbacks of the prior art by disclosing a thermostat for cooling system of an internal combustion engine that is versatile and suitable for operating with different levels of freedom, being a better control element of the temperature of the coolant compared to the thermostats of the prior art.
Another purpose of the present invention is to disclose such a thermostat that is efficient, effective, reliable, inexpensive and easy to make.
These purposes are achieved according to the invention with the characteristics of the independent claim 1.
Advantageous embodiments of the invention appear from the dependent claims.
The thermostat of the invention is defined by the independent claims 1 and 4.
The cooling means of the thermostat provide the thermal control of the engine at different temperature values. This involves several advantages that are reflected on the output of the internal combustion engine, with special reference to heavy duty engines with very long mileage.
In fact, a higher average temperature of the engine corresponds to:

a reduction of specific consumption because the warmer surfaces of the engine generate a reduction of the power dissipated by friction between the rubbing and support elements of the drive shaft, as well as a better propagation of the combustion phenomenon;
a reduction of the thermal power exchanged with the exterior and, consequently, a higher output of the engine; and
an optimization of the operation of the engine auxiliary parts.

These advantages may result in considerable operating savings (fuel costs) in heavy duty engines. In this type of engines, it may be also possible to experimentally adjust the operating temperature of the engine according to the load. For each load, the thermostat may bring the temperature of the coolant to a value defined as "optimal". These advantages are also obtained in light duty engines used for passengers transportation, although less evidently, in view of the temporary operation of light duty engines.
The connection of the Peltier cell to electrical power cables permits to use the same power system of the electrical resistance to power the Peltier cell.
Alternatively, instead of the Peltier cell, the cooling means may comprise a cooling system that feeds a coolant used to cool the sensitive element by means of conduits.
Additional features of the invention will appear clearer from the detailed description below, which refers to merely illustrative, not limiting embodiments, wherein:

Fig. 1 is a diagrammatic view of a cooling system of an internal combustion engine;
Fig. 2 is a sectional view of a first embodiment of the thermostat according to the invention, with the shutter in closed position from the radiator to the engine;
Fig. 3 is the same view as Fig. 2, with the shutter in open position from the radiator to the engine;
Fig. 4 is a sectional view of the sensitive element of the thermostat of Fig. 2;
Fig. 2 is a sectional view of a second embodiment of the thermostat according to the invention, with the shutter in closed position from the radiator to the engine;
Fig. 6 is the same view as Fig. 5, with the shutter in open position from the radiator to the engine;
Fig. 7 is a sectional view of the sensitive element of the thermostat of Fig. 5; and
Fig. 8 is a block diagram of a control system of the temperature of the coolant of the engine, which uses the thermostat of the invention.

With reference to Fig. 1, an internal combustion engine (100) is illustrated, it being provided with a cooling system. The cooling system comprises a supply tank (101) that contains a coolant that circulates in a cooling circuit (102). The cooling circuit (102) is connected to:

a heat exchanger (103) of water-oil type, to cool the engine (100);
a radiator (104) to cool the coolant that circulates in the cooling circuit;
a heater (105) to heat the interior of the vehicle.

A pump (106) permits the circulation of coolant in the cooling circuit (102). The radiator (104) comprises electrical fans (107).
A temperature sensor (108) is disposed in the cooling circuit (102) to detect the temperature of the coolant that circulates in the cooling circuit.
A thermostat (1) is disposed in the cooling circuit (102) in communication with the engine (100) and with the radiator (104).
With reference to Fig. 2, the thermostat (1) is a three-way valve with a body (10) that comprises:

a first inlet (11) connected to the engine (100);
a second inlet (12) connected to the radiator (104) and
an outlet (13) connected to the engine (100);

A shutter (3) is disposed in the body (10) of the thermostat in such a way as to close and open the flow of coolant on the second inlet (12) connected to the radiator (104) or on the first inlet (11) connected to the engine (100).
In particular, the body (10) comprises:

a first chamber (20) in communication with the first inlet (11) and the outlet (13); and
a second chamber (21) in communication with the first chamber (20) and with the second inlet (12).

The shutter (3) is a cylinder that is mounted with possibility of sliding in axial direction on a cylindrical shank (15) integral with the body (10) of the thermostat.
The shutter comprises:

a first flange (30) suitable for closing the communication between the first chamber (20) and the second chamber (21); and
a second flange (31) suitable for closing the communication between the first chamber (20) and the first inlet (11).

A spring (25) is disposed around the shutter (3). The spring has a first end (25a) fixed to the body (10) and a second end (25b) fixed to the first flange (30), in such a way as to push the first flange (30) in a closing position of the second inlet (12) from the radiator.
The thermostat (1) is a thermostat valve of the normally closed type, which opens when the temperature of the coolant reaches a preset threshold value, generally comprised in the range of 85°C-95°C.
In view of the above, when the temperature of the coolant that circulates n the cooling circuit (102) is lower than the threshold value, the thermostat (1) is closed, i.e. the shutter (3) closes the flow from the radiator to the engine. Therefore the radiator (104) is bypassed and the coolant exchanges heat in the heat exchanger (103) of the engine (100), cooling down the engine (100) without passing through the radiator (104), and increasing its temperature. When the temperature of the coolant reaches the threshold value, the thermostat (1) opens, i.e. the shutter (3) opens the flow from the radiator to the engine; therefore the coolant passes through the radiator (104) wherein it is cooled, and flows towards the engine (100), in such a way as to maintain a substantially constant temperature of the coolant.
In Fig. 2 the thermostat (1) is closed, i.e. the shutter closes the flow from the radiator to the engine.
In Fig. 3 the thermostat (1) is open, i.e. the shutter opens the flow from the radiator to the engine.
The thermostat (1) comprises a sensitive element (4) disposed inside the cylindrical body of the shutter (3).
With reference to Fig. 4, the sensitive element (4) comprises a capsule (40) fixed to the cylindrical shank (15) of the body of the thermostat.
The capsule (40) is internally empty. A sensitive material (5) is disposed inside the capsule (40) and changes its volume when its temperature reaches the threshold value. The sensitive material (5) is generally composed of a wax mixture that melts and increases its volume at a temperature of approximately 85°C -95°C. Other types of sensitive materials, including liquid and gaseous materials, can be provided.
The wax (5) is held by a flexible membrane (6) composed of a seal that surrounds and holds an actuation stem (8) and prevents the wax (5) from coming out of the capsule (40).
The actuation stem (8) has a point (80) in contact with the membrane (6). The actuation stem (8) is mounted with possibility of sliding in axial direction inside a guide (41) integral with the capsule (40) of the sensitive element.
The actuation stem (8) has a back portion (82) that comes out of the capsule (40) and is connected to the shutter (3) (Fig. 2). In particular, the back portion (82) of the actuation stem is connected to the second flange (31) of the shutter.
The coolant is in contact with the cylindrical body of the shutter (3) that transfers the heat to the sensitive element (4) by conduction. Therefore, when the temperature of the coolant reaches the threshold value, the sensitive material (5) melts and increases its value. Consequently, the actuation stem (8) is pushed downwards by the sensitive material (5), overcoming the force of the thrust (25). Therefore the shutter (3) is moved to the opening position, permitting the flow of the coolant from the radiator.
An electrical heating resistance (7) is disposed in the sensitive material (5). The electrical heating resistance (7) is connected to power supply cables (70) that come out of the sensitive element to be connected to a power supply system (75).
The electrical heating resistance (7) increases its temperature when it is crossed by the electrical current.
If the radiator (104) is not to be bypassed when the temperature of the coolant is lower than the threshold value, the electrical heating resistance (7) is powered in order to heat the sensitive material (5) in such a way that the sensitive material (5) reaches the threshold value where the volume increases and actuates the actuation stem (8) opening the flow from the radiator (104) towards the engine (100).
According to the invention, cooling means (R) are coupled with the sensitive element (4) to cool the sensitive material (5) of the sensitive element (4).
According to a first embodiment, the cooling means (R) comprise a Peltier cell (9) disposed around the capsule (40) of the sensitive element. When it is crossed by the electrical current, the Peltier cell (9) has a cold side (9a) in contact with the capsule (40) of the sensitive element to absorb heat and cool the sensitive element, and a warm side (9b) facing outwards to dissipate the heat. A heat sink (not shown in Fig. 4) can be provided outside the Peltier cell.
The Peltier cell (9) is connected to power supply cables (90) that come out of the sensitive element to be connected to a power supply system (75). In such a case, the same power supply system of the electrical heating element (7) can be used to power the Peltier cell (9).
If the capsule (40) of the cylindrical element is cylindrical, also the Peltier cell (17) is cylindrical and internally empty, with the cold surface (17) facing inwards, in such a way as to be inserted on the capsule (40) of the sensitive element.
The electrical heating element (7) is disposed inside the capsule (40) of the sensitive element, in an upper portion of the capsule (40). Instead, the Peltier cell (17) is disposed outside the capsule (40) of the sensitive element, in a lower portion of the capsule (40).
If the radiator (104) is to be bypassed, also when the temperature of the coolant has reached the threshold value, the Peltier cell (9) is powered in order to take the heat from the sensitive element (4), cooling the sensitive material (5), in such a way that the sensitive material (5) does not reach the threshold value where it increases its volume and actuates the actuation stem (8). In view of the above, the shutter (3) remains in closed position, also when the temperature of the coolant has reached the threshold value.
Figs. 5, 6 and 7 show a second embodiment, wherein instead of the Peltier cell, the cooling means (R) comprise a cooling system (209) that feeds a coolant used to cool the sensitive element (4) by means of conduits (290).
The coolant coming from the cooling system (209) is directly introduced inside the cylindrical body of the shutter (3) to come in contact with the external surface of the capsule (40) that contains the sensitive material (5).
A cylindrical chamber (35) is disposed between the external surface of the capsule (40) and the internal surface of the cylindrical body of the shutter (3), surrounding the capsule (40). The coolant can circulate in the cylindrical chamber (35).
Advantageously, the conduits (290) of the coolant are obtained in the shank (15) of the body of the thermostat and communicate with the chamber (35).
Although it is not shown in the Figures, the conduits (290) of the cooling fluid can communicate with a heat exchanger disposed in the chamber (35) around the capsule (40) of the sensitive element. In such a case, the heat exchanger is an optional element because the flow of coolant removes the heat. The heat exchanger is connected to the cooling system (209) in such a way to form a cooling circuit where the coolant is fed.
The cooling system (209) can comprise the refrigeration unit of the vehicle used as air conditioner of the vehicle to cool the coolant or another dedicated refrigeration unit.
The cooling system (209) of the thermostat can use the coolant that comes out of the radiator (104), which eventually passes in the cooling unit represented by the air conditioner of the vehicle or by another dedicated cooling unit.
Because of the cooling means (R), the thermostat (1) has an additional level of freedom that permits to change the temperature of the coolant "upwards", delaying the opening of the thermostat (1) in such a way to have a coolant that is stabilized to a higher temperature than the temperature of the traditional range (85°C-95 °C). This result can be obtained without dramatically changing the technology of the thermostat (1), cooling the sensitive element (4) in such a way that the temperature of the coolant can reach higher values, until the way to the radiator (104) is opened. The cooling of the sensitive element (4) can be obtained:

a) by means of the Peltier cell (9) which is powered with electrical current and operates as a static refrigerator, taking thermal energy from a warmer capsule (the sensitive element (4)) and exchanging it with a means with higher temperature;
b) by means of a coolant that may come from the air conditioning system in the interior of the vehicle or from an air conditioning system that is specifically designed for this application;
c) by means of a coolant that my come from the same cooling circuit of the engine (102), taking it downstream the radiator (104) and cooling it in the refrigeration unit that is used for the air conditioning of the vehicle or in another micro refrigeration unit that is dedicated for the specific application.

In the three aforementioned cases, the cooling power that is necessary for cooling the sensitive element (4) must be such to keep the sensitive material (5) contracted, in such a way not to expand, exerting the force that, by opposing the force of the spring (251), open the shutter (3) towards the way of the radiator (104).
The electrical power to be absorbed by the sensitive element (4) depends on several factors. For illustrative purposes:

Amount of wax inside the capsule: 25 g
Specific heat of the wax: 2 kJ kg/°C
Cooling of the capsule: 20 °C

In such a case, the cooling energy is 200 J. If such energy is supplied in 10/20 seconds, the necessary cooling power is 10-20 W.
The following "versions" may be provided:

a) The capsule (40) is coated by a cylindrical crown that contains several Peltier cells (9) with suitable cooling power to cool the capsule and keep the sensitive element (5) contracted; if the output of said Peltier cells is known (for example, 5 %), the electrical power is 200-400 W, which can be technologically obtained. By dosing said electrical power, it is also possible to control the thermostat (1) with a variable opening of the shutter (3) towards the radiator (104), acquiring an additional level of freedom compared to an on/off configuration. The conduit that connects the radiator (104) to the thermostat (1) may remain partially closed (or open) in such a way to define a correlation between the opening of the thermostat (1) and the thermal operation of the engine (100) (balance temperature of the coolant of the engine). Such a solution is not invasive with respect to the traditional construction of the thermostat and benefits from the fact that, in any case, electrical energy is already available for the thermostat and no major changes are necessary.
b) The capsule (40) is externally crossed (between the cylindrical body of the shutter (3) and the capsule (40)) by a low temperature fluid. Said fluid may be air (if taken from the outside the temperatures will never exceed 40°C), and also a low temperature thermal carrier produced by the air conditioning system or by a micro refrigeration system that is especially designed to cool the thermostat. Such a solution is justified for heavy duty engines (with mileage of 5-6 hundred thousands of kilometers per year, medium-high operation of the engine and generally not very variable during the emission), where the fuel saving that can be obtained by adjusting the thermal operation of the engine with the power generated by the engine are considerable;
c) The coolant of the capsule (40) may also be the coolant of the engine (100) taken downstream the radiator (104) and cooled in the air conditioning system or in a dedicated micro refrigeration system.

In the cases b) and c), considering an average performance coefficient of the air conditioning system (or of the micro refrigeration system) equal to 1, the electrical absorption would be equal to 10- 20 W, which is lower than the value absorbed in the case of Peltier cells. Therefore, one of these two solutions ((b) or (c)) would be considerably more convenient from an energy viewpoint.
Because of the cooling means (R) the thermostat (1) is opened when the coolant has a higher temperature than the convention range (85°C-95 °C), in such a way as to have a coolant stabilized at a higher temperature.
With reference to Fig. 8, the opening temperature value of the thermostat (1) from the radiator (104) to the engine (100) may be related to the engine parameters declared by the engine manufacturer and, by means of a temperature map (111) with the operation temperatures of the engine that are obtained either experimentally or theoretically or from on board processing by means of semi-empirical mathematical models. Said temperature map (111) is stored in a memory of an electronic control unit (110).
The temperature sensor (108) detects the temperature of the coolant that comes out of the engine (100). The temperature detected by the sensor (108) is compared with the temperature values of the temperature map (111). According to the temperature control, the electronic control unit (110) sends a command signal (S1) to control the operation of the cooling means (R) of the thermostat and consequently the movement of the shutter (3) of the thermostat to adjust the opening/closing level of the flow from the radiator to the engine according to the temperature values of the temperature map (111).
With such an aid, the temperature of the coolant acts as control variable of an operation status of the engine, which is specifically controlled for the thermal aspects of the engine (metal masses, engine oil, thermal services provided on board, etc.) according to the reduction of consumption, polluting emissions and CO2 emission.
Numerous equivalent variations and modifications can be made to the present embodiments of the invention, which are within the reach of an expert of the field, falling in any case within the scope of the invention, as it is defined in the following claims.

Claims

Thermostat (1) for the cooling system of an internal combustion motor (100) for vehicles, wherein the cooling system comprises a radiator (104) and a cooling circuit (102),
said thermostat (1) comprising:
- a sensitive element (4) comprising a capsule (40) containing a sensitive material (5) that changes its volume when it reaches a threshold temperature,

- an actuation rod (8) associated with the sensitive material (5) and connected to a shutter (3) intended to close/open a flow of coolant from the radiator (104) to the motor (100), said shutter (3) being in closed position when the sensitive material (5) has a lower temperature than the threshold temperature and being moved to open position when the sensitive material reaches and exceeds the threshold temperature,

- cooling means (R) coupled with said sensitive element (4) to cool the sensitive material (5), delaying the opening (3) of the thermostat (1), in such a way as to have a flow of coolant that is stabilized at a temperature higher than the threshold temperature of the sensitive material; said cooling means (R) comprising at least one Peltier cell (9) disposed on said capsule (40) of the sensitive element;
characterized in that it comprises

- an electrical heating resistance (7) disposed inside said capsule (40) to heat said sensitive material (5), and

- a power supply system (75) connected to the electrical resistance (7) to power said heating electrical resistance (15),
wherein said power supply system (75) is connected to said Peltier cell (9) to power said Peltier cell (9).
The thermostat (1) of claim 1, wherein said Peltier cell (9) surrounds said capsule (40).
The thermostat (1) of claim 1 or 2, comprising a heat sink coupled outside said Peltier cell (9).
The thermostat (1) for cooling system of an internal combustion motor (100) for vehicle, wherein the cooling system comprises a radiator (104) and a cooling circuit (102),
said thermostat (1) comprising:
- a sensitive element (4) comprising a capsule (40) containing a sensitive material (5) that changes its volume when it reaches a threshold temperature,

- an actuation rod (8) associated with the sensitive material (5) and connected to a shutter (3) intended to close/open a flow of coolant from the radiator (104) to the motor (100), said shutter (3) being in closed position when the sensitive material (5) has a lower temperature than the threshold temperature and being moved to open position when the sensitive material reaches and exceeds the threshold temperature,

- cooling means (R) coupled with said sensitive element (4) to cool the sensitive material (5), delaying the opening (3) of the thermostat (1), in such a way to stabilize the coolant at a temperature higher than the threshold temperature of the sensitive material;
wherein said cooling means (R) comprise a cooling system (209) of the sensitive element that feeds a coolant on the sensitive element (4), in such a way to cool the sensitive element (4),
characterized in that
said capsule (40) of the sensitive element is disposed inside a cylindrical body of the shutter (3) and said cooling means (R) comprise conduits (290) connected to the cooling system (209) of the sensitive element and in communication with the inside of the shutter (3) wherein said capsule is disposed (40) to introduce the coolant inside the shutter in contact with the capsule (40) that contains the sensitive material.
The thermostat (1) of claim 4, wherein said cooling system (209) of the sensitive element comprises an air conditioner that is the vehicle air conditioner.
The thermostat (1) of claim 4 or 5, wherein said cooling system (209) of the sensitive element takes the coolant from said cooling circuit (102) of the internal combustion motor (100) of the vehicle, downstream the radiator (104).
Coolant control system of an internal combustion motor (100) comprising:
- a thermostat (1) according to any one of the preceding claims;

- a temperature sensor (108) intended to detect the temperature of the coolant at the output of the internal combustion motor (100),

- a temperature map (111) stored in a memory and containing operating temperatures of the internal combustion motor (100),

- a control unit (110) connected to the temperature sensor (108), to the temperature map (111) and to the cooling means (R) of the thermostat to control the cooling means (R) according to the temperature values of the temperature map (111).