WO2019151920A1

WO2019151920A1 - A thermostat arrangement for a cooling system for a combustion engine

Info

Publication number: WO2019151920A1
Application number: PCT/SE2019/050042
Authority: WO
Inventors: Zoltan Kardos; Svante Johansson; Ola Hall
Original assignee: Scania Cv Ab
Priority date: 2018-01-31
Filing date: 2019-01-23
Publication date: 2019-08-08
Also published as: SE542068C2; DE112019000278T5; SE1850110A1; DE112019000278B4

Abstract

The present invention relates to a thermostat arrangement for a cooling system for a combustion engine (2). The thermostat arrangement comprises an electrically controlled valve (12) configured to distribute a coolant flow rate between a radiator (9) and a radiator bypass line (10) in the cooling system, an actuator (13) configured to move the electrically controlled valve (12) to different valve positions in which it distributes different coolant flow rates in a stepless manner to the radiator (9) and the radiator bypass line (10), and a control unit (14) configured to determine a desired valve position of the electrically controlled valve (12) and to control the actuator (13) such that it moves the electrically controlled valve (12) to said desired valve position. The electrically controlled valve (12) is dimensioned to provide an adjustable coolant flow rate to the radiator (9) up to a certain flow rate limit. The thermostat arrangement comprises two additional valves (15, 18) which are arranged in parallel and designed to be automatically moved to an open position and provide an additional coolant flow rate to the radiator (9) when a respective threshold parameter value of the coolant is exceeded.

Description

A thermostat arrangement for a cooling system for a combustion engine

BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates to a thermostat arrangement for a cooling system for a combustion engine according to the preamble of claim 1.

Especially in heavy vehicles, it can be wise to use electrically controlled thermostats in order to provide an increased accuracy of the coolant temperature during substantially all operating conditions. An electrically controlled thermostat may comprise a valve which distributes the coolant flow from the combustion engine to a radiator and a radiator bypass line, an electric motor which moves the valve to different valve positions in a stepless manner and a control unit which controls the electric motor such that it moves the valve to a determined valve position. The electrically controlled thermostat may be provided with an integrated fail-safe mechanism. In case the cooling system is used to cool further components or mediums than the combustion engine, the electrically controlled thermostat may include multiple inlets and outlets allowing separate coolant flows to and from said components. However, electrically controlled thermostats are large and expensive.

US 2014/0150738 shows a cooling system for an engine comprising a thermostat provided with a temperature-sensitive material such as a wax material and a shock reducing valve arranged in parallel to the thermostat. The thermostat is configured to selectively direct coolant from the engine to a heat exchanger when the temperature of the coolant is greater than a temperature threshold of the thermostat. The shock reducing valve may be configured to minimize and/or substantially eliminate thermal shock caused by a sudden flow of relatively high temperature coolant from engine to heat exchanger via the thermostat.

JP 3859307 shows a cooling system with a circulating coolant for cooling of an engine. The cooling system comprises a control valve unit disposed between an engine and a radiator. The control valve unit comprises a thermo stat-type control valve provided with a temperature sensing portion which comprises a wax material and a solenoid valve which is controlled by an electronic control unit. The cooling system enables flow rate control employing the characteristics of both the control valves efficiently to thus realize ideal regulation of the temperature of the coolant, and also prevent the engine from overheating even upon fault in either of those control valves.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an inexpensive thermostat

arrangement for a cooling system for a combustion engine which has capacity to maintain a desired operating temperature of the combustion engine and the coolant with a high accuracy during substantially all operating conditions.

The above mentioned object is achieved by the arrangement defined in claim 1. The thermostat arrangement comprises an electrically controlled valve configured to distribute a coolant flow rate to a radiator and a radiator bypass line, a control unit determining a desired position of the electrically controlled valve at which it distributes a desired coolant flow rate to the radiator and an actuator which moves the electrically controlled valve in a stepless manner to desired positions. The above mentioned components may be included in an electrically controlled thermostat.

During most operating conditions of a cooling system, it is sufficient to provide a relatively low coolant flow rate to the radiator in order to maintain a desired operating temperature of the combustion engine. In view of this fact, it is possible to use a relatively small electrically controlled valve and a small actuator for directing a required coolant flow rate to the radiator and maintaining a desired operating temperature of the combustion engine with a high accuracy during a large part of the operating time of the cooling system. The cost for such a small electrically controlled valve and small actuator is significantly lower than the cost for a corresponding valve and actuator of a conventional size enabling control of the entire flow range.

According to the invention, the thermostat arrangement comprises two additional valves designed to be automatically moved to the open position and provide an additional coolant flow rate to the radiator when a respective threshold parameter value of the coolant is exceeded, wherein the additional valves are arranged in parallel with each other and in parallel with the electrically controlled valve.

It is possible to use such an additional valve and provide an increased coolant flow rate to the radiator during operating conditions when the electrically controlled valve is not able to direct a sufficient coolant flow rate to the radiator. The small electrically controlled valve and the additional valves are together able to maintain a desired operating temperature of the combustion engine and the circulating coolant with a high accuracy during substantially all operating conditions. Each additional valve may be a simple and inexpensive valve. The total cost for the small electrically controlled valve and the additional valves is significantly lower than the cost for a corresponding valve of a conventional size.

According to the invention, a first additional valve is automatically moved to the open position when a threshold temperature of the coolant is exceeded. The temperature of the coolant is a parameter related to the cooling need required for cooling of the combustion engine. It is relatively easy to determine a suitable threshold temperature of the coolant at which the first additional valve is to open and provide an increased coolant flow rate to the radiator. The threshold temperature of the coolant may be about l00°C. Thus, the threshold temperature of the coolant may be somewhat higher than the regulating temperature of a conventional thermostat in a cooling system.

According to the invention, a second additional valve is automatically moved to the open position when a threshold pressure of the coolant is exceeded. The pressure of the coolant in a cooling system is related to the coolant flow rate provided by the pump in the cooling system. The pump is usually a mechanical pump driven by the combustion engine. In case the cooling system includes a retarder cooler, the cooling system is heavily loaded when the retarder is activated. During activation of the retarder, the combustion engine and the pump are beneficial to achieve a high speed which increases the pressure of the coolant in the cooling system. It is possible to define a threshold pressure of the coolant indicating that the retarder has been activated. The threshold pressure of the coolant may be related to a predetermined engine speed of the combustion engine or the pump. When the retarder is activated, the second additional valve is automatically moved to the open position in which it provides an increased coolant flow rate to the radiator. Such an additional valve may also be a fail-safe valve which is open if the function of the electrically controlled valve fails. Such a pressure activated valve may have a simple design and be inexpensive.

According to an embodiment of the invention, each additional valve is dimensioned to provide a larger coolant flow rate to the radiator than the electrically controlled valve. Since the electrically controlled valve is not able to provide a coolant flow rate above a relatively small flow rate limit, it is necessary that each additional valve has capacity to provide a significantly higher coolant flow rate to the radiator in order to prevent overheating of the combustion engine during operating conditions when the combustion engine is heavily loaded. Each additional valve may be dimensioned to provide a coolant flow rate to the radiator which is at least three times larger than the flow rate limit of the electrically controlled valve.

According to an embodiment of the invention, the first additional valve comprises a thermal expansion element arranged in thermal contact with coolant in the cooling system and which comprises a material changing phase at a threshold temperature of the coolant. The material may be a wax material. In this case, the first additional valve may be a simple and inexpensive wax thermostat. The thermal expansion element may be arranged in thermal contact with a continuous coolant flow in a suitable position of the cooling system. Advantageously, the thermal expansion element is in contact with the coolant flow in a pilot line. The pilot line may direct coolant from an engine outlet line to the radiator bypass line. In this case, the thermal expansion element senses the temperature of the coolant in the engine outlet line.

According to an embodiment of the invention, the actuator is an electric motor. The use of an electric motor makes it uncomplicated to provide movements of the electrically controlled valve to desired valve positions with a high accuracy.

Alternatively, the actuator may be a pneumatically or hydraulically activated cylinder.

According to an embodiment of the invention, the control unit is configured to determine the position of the electrically controlled valve by means of information about a parameter related to the temperature of the combustion engine. The main object of the cooling system is to maintain a desired regulating temperature of the combustion engine. The coolant in the engine outlet line has a temperature

corresponding to the temperature of the combustion engine. Thus, the control unit may control the electrically controlled valve by information from a temperature sensor sensing the temperature of the coolant in the engine outlet line. Alternatively, the control unit may receive information from a temperature sensor sensing the temperature of engine oil which lubricates and cools the combustion engine or any other parameter which is related to the temperature of the combustion engine. According to an embodiment of the invention, the control unit is configured to determine a suitable valve position of the electrically controlled valve by means of information about a parameter related to the total coolant flow rate in the cooling system. The coolant flow rate in the cooling is provided by a pump which may be driven by the combustion engine. In this case, the coolant flow rate in the cooling system varies with the speed of the pump and the combustion engine. In order to provide a correct distribution of the coolant flow to the radiator and the radiator bypass line, it is many times necessary to take the actual coolant flow rate into consideration.

According to an embodiment of the invention, the threshold temperature and the threshold pressure of the coolant are determined such that at least one of the additional valves is moved to the open position when the electrically controlled valve is unable to provide a required coolant flow rate to the radiator. It is usually possible to determine a threshold temperature and a threshold pressure of the coolant at which the electrically controlled valve is unable to provide a required coolant flow rate to the radiator. This means that at least one of the additional valves can be moved to the open position and supply an increased coolant flow rate to the radiator substantially immediately as the required coolant flow rate to the radiator exceeds the flow rate limit of the electrically controlled valve.

BRIEF DESCRIPTION OF THE DRAWING

In the following a preferred embodiment of the invention is described, as an example, with reference to the attached drawing, in which:

Fig. 1 shows a cooling system provided with a thermostat arrangement

according to an embodiment of the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Fig. 1 shows a schematically disclosed vehicle 1 powered by a combustion engine 2. The vehicle 1 may be a heavy vehicle and the combustion engine 2 may be a diesel engine. The vehicle 1 comprises a cooling system comprising a pump 3 circulating a coolant through the cooling system. The pump 3 is arranged in an engine inlet line 4 of the cooling system. The pump may be a mechanical pump 3 driven by the combustion engine 2. Thus, the pump 3 circulates a coolant flow rate in the cooling system related to the engine speed of the combustion engine. The coolant leaving the combustion engine 2 is received in an engine outlet line 5. The engine outlet line 5 comprises a retarder cooler 6. A thermostat arrangement is arranged at an end of the engine outlet line 5. The purpose of the thermostat arrangement is to provide a coolant temperature in the engine inlet line 4 which makes it possible to maintain a desired operating temperature of the combustion engine 2. The thermostat arrangement distributes coolant flow from the engine outlet line 5, via a radiator inlet line 8, to a radiator 9 and to a radiator bypass line 10. The radiator bypass line 10 directs coolant to the engine inlet line 4. A radiator outlet line 11 directs coolant from the radiator 9 to the engine inlet line 4. Thus, the engine inlet line 4 receives a mixture of cooled coolant from the radiator 9 and uncooled coolant from the bypass line 10 which is adapted to provide a cooling of the combustion engine 2 such that it achieves a desired operating temperature.

The thermostat arrangement comprises an electrically controlled valve 12 configured to distribute coolant from the engine outlet line 5 to the radiator 9 and the radiator bypass line 10. An actuator 13 is configured to move the valve 12 to different valve positions. The actuator 13 may be an electric motor. A control unit 14 is configured to control the actuator 13 such that it moves the electrically controlled valve 12 to a desired valve position in which it distributes the coolant flow from the engine outlet line 5, via a first outlet line 12a, to the radiator 9 and, via a second outlet line 12b, to the radiator bypass line 10. The electrically controlled valve 12 is designed to distribute the coolant in a stepless manner. Thus, the coolant entering the combustion engine 2 has a desired temperature with a high accuracy. The electrically controlled valve 12, the actuator 13 and the control unit 14 can be defined as an electrically controlled thermostat. However, the electrically controlled valve 12 is dimensioned such that it is relatively small. Due to this fact, it is unable to provide a coolant flow rate to the radiator 9 above a certain flow rate limit.

The thermostat arrangement comprises a first additional valve 15 which is arranged in parallel with the electrically controlled valve 12. The first additional valve 15 is arranged in a first connection line 15a having an extension between the engine outlet line 5 and the radiator inlet line 8. The first additional valve 15 comprises a thermal expansion element 16 to be in thermal contact with a coolant flow in a pilot line 17. The pilot line 17 receives coolant from the engine outlet line 5 and directs it to the radiator bypass line 10. It is a continuous coolant flow through the pilot line 17. The thermal expansion element 16 senses a coolant temperature in the pilot line 17 which corresponds to the actual coolant temperature in the engine outlet line 5. The thermal expansion element 16 may comprise a capsule enclosing a material body changing phase at a regulation temperature of the first additional valve 15. The thermal expansion element 16 comprise a movement transmitting mechanism which moves the first additional valve 15 to a closed position when the material body is in a solid phase and to an open position when the material body is in a liquid phase. The material body may be a wax body. When the first additional valve 15 is in the closed position, it prevents a coolant flow from the engine outlet line 5, via the first connection line l5a, to the radiator 9. When the first additional valve 15 is in an open position, it allows a coolant flow from the engine outlet line 5, via the first connection line l5a, to the radiator 9. The first addition valve 15 is dimensioned such that it is able to provide a considerably larger coolant flow rate to the radiator 9 than the electrically controlled valve 12.

The thermostat arrangement comprises a second additional valve 18 which is arranged in parallel with the electrically controlled valve 12 and the first additional valve 15.

The second additional valve 18 is arranged in a second connection line 18a having an extension between the engine outlet line 5 and the radiator inlet line 8. The second additional valve 18 is designed to be in a closed position during operating conditions when the coolant pressure in the engine outlet line 5 is below a predetermined threshold pressure and in an open position during operating conditions when the coolant pressure in the engine outlet line 5 is above said predetermined threshold pressure. The second additional valve 18 may comprise a valve body which is kept in a closed position by means of a mechanical spring. The valve body may be moved to an open position against the action of the spring when the coolant pressure exceeds the predetermined threshold pressure. When the second additional valve 18 is in a closed position, it prevents a coolant flow from the engine outlet line 5, via the second connection line 18a, to the radiator 9. When the second additional valve 18 is in an open position, it allows a coolant flow from the engine outlet line 5, via the second connection line 18 a, to the radiator 9.

The control unit 14 receives substantially continuously information about a parameter related to the temperature of the combustion engine 2. In this case, the control unit 14 receives information from a temperature sensor 20 sensing the temperature of the coolant in the engine outlet line 5, which is a parameter related to the temperature of the combustion engine 2. The control unit 14 also receives information about a parameter related to the coolant flow rate in the cooling system. In this case, the cooling unit 14 receives information from, for example, an engine control unit 21 about the engine speed of the combustion engine 2, which is related to the speed of the pump 3 and the coolant flow rate in the cooling system.

During operation of the combustion engine 2, the pump 3 circulates a coolant flow rate through the cooling system. The control unit 14 receives substantially continuously information about the coolant temperature in the engine outlet line 5 from the sensor 20 and information from the motor control unit 21 about the engine speed of the combustion engine, which is a parameter related to the coolant flow rate in the cooling system. In view of this information, the control unit 14 determines how the coolant flow rate in the cooling system is to be distributed between the radiator 9 and the radiator bypass line 10 in order to provide a desired operating temperature of the combustion engine 2. The control unit 14 initiates a movement of the actuator 13 such that it moves the electrically controlled valve 12 to a valve position in which the determined distribution of the coolant flow rate to the radiator 9 and the radiator bypass line 10 is achieved.

As indicated above, the electrically controlled valve 12 is relatively small such that it is unable to direct a coolant flow rate to the radiator 9 above a certain flow rate limit. However, it is possible to cool the combustion engine to a desired operating temperature during at least a main part of the operating time of the combustion engine 2 with a relatively small coolant flow rate. The electrically controlled valve 12 may be dimensioned to provide a flow rate to the radiator 9 up to a certain flow rate limit making it possible to provide a sufficient cooling during about 70-80% of the operating time of the combustion engine 2. During the remaining 20-30 % of the operating time, when, for example, the combustion engine 2 is heavily loaded, the electrically controlled valve 12 is not able to provide the required coolant flow rate to the radiator 9 for cooling the combustion engine 2 to a desired operating temperature.

The first additional valve 15 has a regulating temperature which may be some degrees higher than the desired temperature of the combustion engine 2. When the coolant temperature in the pilot line 17 reaches the regulation temperature of the first additional valve 15, the material body of the thermal expansion element 16 melts and the first additional valve 15 is automatically moved to the open position. The first additional valve 15 and the connecting line l5a are dimensioned to provide a significantly larger coolant flow rate to the radiator 9 than the electrically controlled valve 12. Thus, the cooling capacity of the cooling system increases significantly when the first additional valve 15 is open. The high coolant flow rate, via the first connection line 15a, to the radiator 9 results in an effective cooling of the combustion engine 2. The material body of the thermal expansion element 16 solidifies and the first additional valve 15 is moved back to the closed position when the coolant temperature drops to a lower temperature than the regulation temperature of the first additional valve 15.

During operating conditions when the retarder is activated, the coolant is heated in the retarder cooler 6. During an activating process of the retarder, it is not likely that the electrically controlled valve 12 is able to provide a required coolant flow rate to the radiator 9 for maintaining a suitable coolant temperature in the cooling system. During the activating process of the retarder, a low gear is put into a gear box connected to combustion engine 2 such that the combustion engine 2 and the pump 3 achieve a high speed. Thus, the pump 3 provides a high coolant flow rate in the cooling system during operating conditions when the retarder is activated. Since the coolant flow rate is related to the coolant pressure in the cooling system, the pressure in the cooling system is mostly high when the retarder is activated.

The second additional valve 18 has a regulating pressure which is higher than a regular operating pressure in the cooling system and lower than the pressure which occurs during activation of the retarder. The regulating pressure of the second additional valve 18 may be related to a certain engine speed. When the pressure in the cooling system reaches the regulation pressure of the second additional valve 18, the second additional valve is automatically moved to an open position. The second additional valve 18 and the connecting line 18a are also dimensioned to provide a significantly larger coolant flow rate to the radiator 9 than the electrically controlled valve 12. Thus, the cooling capacity of the cooling system increases significantly when the second additional valve 18 is open. The open second addition valve 18 results in a very effective cooling of the coolant in the radiator 9 such that the coolant temperature is at an acceptable level during the entire period of time at which the retarder is activated. In case the coolant temperature exceeds the regulation temperature of the first additional valve 15 during activation of the retarder, the first additional valve 15 is also moved to an open position. In this case, the cooling flow rate to the radiator 9 increases further. When the activation of the retarder ends, the pressure in the cooling system drops to a normal level and the second additional valve 18 is automatically moved to the closed position. The first additional valve 15 is maintained in the open position until the coolant temperature drops to a temperature below the regulating temperature of the first additional valve 15.

The invention is not restricted to the described embodiment but may be varied freely within the scope of the claims.

Claims

1. A thermostat arrangement for a cooling system for a combustion engine (2), wherein the thermostat arrangement comprises an electrically controlled valve (12) configured to distribute a coolant flow rate to a radiator (9) and a radiator bypass line (10) in the cooling system, an actuator (13) configured to move the electrically controlled valve (12) to different valve positions in which it distributes different coolant flow rates in a stepless manner to the radiator (9) and the radiator bypass line (10), and a control unit (14) configured to determine a desired valve position of the electrically controlled valve (12) and to control the actuator (13) such that it moves the electrically controlled valve (12) to said desired valve position, wherein the electrically controlled valve (12) is dimensioned to provide an adjustable coolant flow rate to the radiator (9) up to a certain flow rate limit and wherein the thermostat arrangement comprises a first additional valve (15), which is arranged in parallel with the electrically controlled valve (12) and is designed to be automatically moved to an open position and provide an additional coolant flow rate to the radiator (9) when a threshold temperature of the coolant in the cooling system is exceeded, characterized in that the thermostat arrangement comprises a second additional valve (18), which is arranged in parallel with the electrically controlled valve (12) and the first additional valve (15), wherein the second additional valve (18) is designed to be automatically moved to an open position and provide an additional coolant flow rate to the radiator (9) when a threshold pressure of the coolant in the cooling system is exceeded.

2. A thermostat arrangement according to claim 1, characterized in that each additional valve (15, 18) is dimensioned to provide a larger coolant flow rate to the radiator (9) than the electrically controlled valve (12).

3. A thermostat arrangement according to claim 2, characterized in that each additional valve (15, 18) is dimensioned to provide a coolant flow rate to the radiator (9) which is at least three times larger than the flow rate limit of the electrically controlled valve (12).

4. A thermostat arrangement according to any one of the preceding claims,

characterized in that the first additional valve (15) comprises a thermal expansion element (16) which comprises a material which changes phase at the threshold temperature of the coolant.

5. A thermostat arrangement according to claim 4, characterized in that thermal expansion element (16) is in thermal contact with a continuous coolant flow in a pilot line (17) which directs coolant from an engine outlet line (5) to the radiator bypass line (10).

6. A thermostat arrangement according to any one of the preceding claims,

characterized in that the threshold pressure of the coolant is related to a certain engine speed of the combustion engine (2).

7. A thermostat arrangement according to any one of the preceding claims,

characterized in that the actuator is an electric motor (13).

8. A thermostat arrangement according to any one of the preceding claims,

characterized in that the control unit (14) is configured to determine the position of the electrically controlled valve (12) by means of information about a parameter (20) related to the temperature of the combustion engine (2).

9. A thermostat arrangement according to any one of the preceding claims,

characterized in that the control unit (14) is configured to determine the position of the electrically controlled valve (12) by means of information about a parameter (20) related to the total coolant flow rate in the cooling system.

10. A thermostat arrangement according to any one of the preceding claims,

characterized in that the threshold temperature and the threshold pressure of the coolant are determined such that at least one of the additional valves (15, 18) is moved to the open position when the electrically controlled valve (12) is unable to provide a required coolant flow rate to the radiator (9).

11. A vehicle comprising a thermostat arrangement according to any one of the preceding claims 1-10.