SE542998C2 - A cooling system for an engine and a water retarder - Google Patents

Abstract

Cooling system for an engine (2) and a water retarder (6). The cooling system comprises a radiator (16), a radiator bypass line (14), a thermostat (13, 31), an expansion tank (18), a static line 19, an engine inlet line (10), a coolant pump (9), and an engine outlet line (11), a retarder inlet line (20) and a retarder outlet line 23. The retarder inlet line (20) and the engine inlet line (10) receive coolant from a part (17) of the cooling system in which the pressure is defined by the static line (19). Thus, the coolant pump (9) and the water retarder (6) operates in parallel. The engine outlet line (11) is provided with a first flow passage (11a) directing coolant to the thermostat (13, 31) when the water retarder (6) is disengaged and a second flow passage (lib) directing coolant to a part (14, 20) of the cooling system in which the pressure is defined by the static line (19) when the water retarder (6) is engaged.

Description

AND PRIOR ART The present invention relates to a cooling system for an engine and a Water retarder according to the preamble of claim l.

Heavy vehicles are often equipped With one or several supplementary brakes in orderto reduce Wear on the ordinary Wheel brakes. Such a supplementary brake may be ahydraulic retarder. One kind of hydraulic retarder, commonly referred to as a Waterretarder, uses coolant as cooling medium as Well as Working medium. A Water retardercomprises a stationary arranged stator unit and a rotor unit Which rotates With a speedrelated to the speed of the powertrain of the vehicle. The stator unit and rotor unitdefine a toroidal space enclosing stator vanes and rotor vanes. The supply of liquidcoolant to the toroidal space results in a braking movement of the power train and thedriving Wheel of the vehicle. Furthermore, the relative movements of the stator vanesand the rotor vanes provide a coolant floW through the retarder and the cooling system.Consequently, a Water retarder can be defined as a pump With a high pump capacity.The cooling demand is usually high When a Water retarder is engaged. It is desired touse the high coolant floW caused by the Water retarder to increase the cooling effect of the coolant When it floWs through the radiator.

EP l 702 820 shows a cooling system for a combustion engine and a hydrodynamicbrake, Which can be designed as a Water retarder. The cooling system comprises acoolant pump, a combustion engine and a circuit directing coolant to the hydrodynamicbrake. Said circuit receives coolant in a position downstream of the coolant pump.Thus, the coolant pump and the hydrodynamic brake operate in series When thehydrodynamic brake is engaged. This means that the coolant pump can be overflowedby the higher coolant floW from the hydrodynamic brake. The cooling system isprovided With a controllable throttle valve in a downstream position of thehydrodynamic brake. The existence of the controllable throttle valve eliminates the risk that the coolant pump is overflowed by the coolant floW from the hydrodynamic brake but it also elin1inates the possibility to increase the coolant floW and the cooling capacity in the cooling system When the hydrodynamic brake is engaged.

SUMMARY OF THE INVENTION The object of the present invention is to provide a cooling system for an engine and aWater retarder having a design making it possible to increase the coolant floW in thecooling system When the Water retarder is engaged at the same time as negative pressures in the engine are avoided.

These objects are achieved by the features defined in claim l. ln view of the fact thatthe Water retarder has a higher pump capacity than the coolant pump, there is a riskthat the coolant pump is overfloWed When the Water retarder is engaged. In such a case,a pressure drop is obtained over the coolant pump Which can lead to negative pressuresin the engine, backflows in parallel channel in the engine and that the Water retarderpumps coolant of a very high pressure to the radiator. HoWever, this risk is onlypresent When the coolant pump and the Water retarder operate in series in the coolingsystem. In order to avoid cavitation at a start process of the coolant pump, the inlet ofthe coolant pump is connected to a part of the cooling system in Which a static linepressure prevails Which is related to the pressure in an expansion tank and a static line.According to the invention, the retarder inlet line is also connected to the same part ofthe cooling system in Which the pressure is defined by the static line pressure. Thus,the coolant pump and the Water retarder receives coolant from common part of thecooling system With the same pressure. This means that the coolant pump and theWater retarder operates in parallel Which elin1inates the risk that the coolant pump is overflowed by the higher coolant floW from the Water retarder.

During engagement of the Water retarder, the pressure is increased in certain parts ofthe cooling system. In order to maintain a coolant floW through the engine by thecoolant pump When the Water retarder is engaged, it is necessary that the engine outletline directs coolant to a part of the cooling system Which has a relatively low pressure.

The engine outlet line comprises a second floW passage configured to direct coolant to the part of the Cooling system in Which the pressure is defined by the static linepressure. Such a design of the engine outlet line ensures that the cooling pump is ableto direct a cooling floW through the engine also When the Water retarder is engaged Which elin1inates the risk that negative pressures are created in the engine.

According to an embodiment of the invention, the second floW passage is configuredto direct coolant to the radiator bypass line When the Water retarder is engaged. Theradiator bypass line is a part of the cooling system Where static line pressure prevails.ln this case, it is possible to design a short second floW passage directing the coolantpast the therrnostat. Alternatively, the second floW passage may be configured to directcoolant to the retarder inlet line When the Water retarder is engaged. The static linepressure also prevails in the retarder inlet line. ln this case, the coolant leaving the engine circuit is directed to the retarder circuit.

According to an embodiment of the invention, the first floW passage comprises a firstend line provided With a check valve. The eXistence of first end line and the checkvalve makes it possible to direct coolant from the engine to the thermostat When theWater retarder is disengaged. Thus, it possible to control the therrnostat in aconventional manner by means of coolant from the engine When the Water retarder isdisengaged. During engagement of the Water retarder, a high coolant pressure iscreated adj acent to the thermostat. This high pressure moves the check valve to aclosed position Which prevents a backflow in the first inlet line and the engine outlet line.

According to the invention, the second floW passage comprises asecond end line provided With a relief valve. When the Water retarder is engaged, thecheck valve blocks the coolant floW in the first end line. Thus, the pressure in theengine outlet line increases and the relief valve is moved to an open position. Thismeans that the coolant floW in the engine outlet line is instead directed to the secondend line Which in its turn directs the coolant floW to the part With static line pressure.The eXistence of the second end line and the relief valve makes it possible to maintain the coolant floW through the engine outlet line and avoid negative pressures in the engine When the Water retarder is engaged. The engine outlet line m-a-yßbei_s branched into the first end line and the second end line.

According to an embodiment of the invention, the retarder outlet line is configured todirect coolant to the first end line of the engine outlet line in a position doWnstream ofa check Valve and upstream of the thermostat. Such a design makes it possible to directcoolant from the retarder outlet line to the thermostat via a part of the first end linesituated doWnstream of the check Valve. ln this case, the temperature of the coolantfrom the retarder outlet line controls the therrnostat and the cooling of the coolant in the cooling system.

According to an embodiment of the invention, the retarder outlet line is configured todirect coolant to a radiator inlet line situated doWnstream of the therrnostat andupstream of the radiator. ln case the coolant has a loWer temperature than theregulating temperature of the therrnostat, a part of the coolant floW is directed to theradiator bypass line and a remaining part of the coolant floW is directed to the radiator.ln case the coolant has a higher temperature than the regulating temperature of thethermostat, the therrnostat blocks the floW to the radiator bypass line and the entire coolant floW is directed to the radiator.

According to an embodiment of the invention, the retarder outlet line is configured todirect coolant to the therrnostat. ln this case, the entire coolant floW from the retarderoutlet line is directed to the therrnostat Which distributes the coolant floW to the radiator bypass line and the radiator in vieW of the temperature of the coolant.

According to an embodiment of the invention, the therrnostat is a design such that ithas different regulating temperatures When the Water retarder is disengaged and Whenthe Water retarder is engaged. Such a thermostat may be controlled by a control unit.Alternatively, the therrnostat comprises two Wax bodies changing phase at differenttemperatures. One Wax body Which controls the thermostat in vieW of the temperature of the coolant floW in the engine circuit When the Water retarder is disengaged and one wax body Which controls the therrnostat in view of the temperature of the coolant flow in the retarder circuit when the water retarder is engaged.

According to an embodiment of the invention, the retarder inlet line and the engineinlet line are configured to receive coolant from a n1ixing line receiving coolant fromthe radiator bypass line and the radiator. During operating conditions when there is acoolant flow through the radiator bypass line and the radiator, the existence of themixing line ensures that the coolant flow to the engine inlet line and the retarder inlet line has the same temperature.

According to an embodiment of the invention, the cooling system comprises a firstpressure release mechanism configured to prevent that the coolant pressure rises abovea maximum acceptable pressure level in the retarder outlet line. Since the waterretarder has a significantly higher pump capacity than the coolant pump, the coolantflow in the cooling system is abruptly changed when the water retarder is engaged. Inthis case, a high pressure peak may be created in the cooling system. However, theexistence of the first pressure release mechanism prevents that the coolant pressurerises above a maximum acceptable pressure level in the retarder outlet line. The firstpressure release mechanism may comprise a connection line extending between theretarder outlet line and the retarder inlet line and a relief valve configured to open andreduce the pressure in the retarder outlet line when the pressure difference between said lines exceeds a predeterrnined value.

According to an embodiment of the invention, the cooling system comprises a secondpressure release mechanism configured to prevent that the coolant pressure rises abovea maximum acceptable pressure level in the retarder inlet line. During a disengagingprocess of the water retarder, the water retarder provides an abrupt deceleration of thecoolant flow in the retarder inlet line. The abrupt deceleration of the coolant flow mayinitiate a high pressure peak in the retarder inlet line and also because several liters ofcoolant inside the retarder being pushed out into the cooling system without being ableto relief pressure through expansion tank relief valve quick enough. The second pressure release mechanism prevents a pressure peak in the retarder inlet line in a simple and effective manner. The second pressure release mechanism may comprise aconnection line eXtending between the retarder outlet line and the retarder inlet line and a check valve configured to open and equalize the difference between the pressurein the retarder inlet line and the pressure in the retarder outlet line if the pressure in the retarder inlet line eXceeds the pressure in the retarder outlet line.

The invention is also related to a vehicle comprising a cooling system according to the above.

BRIEF DESCRIPTION OF THE DRAVVINGS In the following preferred embodiments of the invention is described, as examples, with reference to the attached drawing, in which: Fig. l shows a cooling system according to a first embodiment of the invention, Fig. 2 shows a cooling system according to a second embodiment of theinvention, Fig. 3 shows a cooling system according to a third embodiment of theinvention, Fig. 4 shows a cooling system according to a fourth embodiment of theinvention and Fig. 5 shows the thermostat in Fig. 4 more in detail.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THEINVENTION Fig. l shows a schematically indicated vehicle l which may be a heavy vehicle. Thevehicle l is driven by a combustion engine 2. The combustion engine 2 may be an Ottoengine, a diesel engine or another kind of engine such as an electric engine. Thevehicle l comprises a powertrain, which in addition to the combustion engine 2,comprises a clutch mechanism 3, a gearboX 4 and a gearboX output shaft 5. The vehicle l is equipped with a water retarder 6 comprising a stator unit which is stationary arranged in the vehicle and a rotor unit Which is, via a motion transmitting mechanism7, connected to the gearboX outlet shaft 5. Thus, the rotor unit is rotated by a speeddefined by the speed of the gearboX outlet shaft 5 and the gear ratio in the motiontransmitting mechanism 7. The stator unit and the rotor unit define a toroidal spacereceiving coolant during activation of the Water retarder. The stator unit comprisesstator vanes and the rotor unit comprises rotor vanes situated in the toroidal space. Acontrol unit 8 is adapted to control the activation of the Water retarder 6 by means of aretarder valve 6a in view of information from a brake activating member 8a, Which may be a brake pedal or a lever.

A cooling system With a circulating coolant is used to supply coolant to thecombustion engine 2 and the Water retarder 6. The coolant is used as Working mediumand cooling medium in the Water retarder 6. The cooling system comprises an enginecircuit. The engine circuit comprises an engine inlet line 10 Which is provided With acoolant pump 9. The coolant pump 9 circulates coolant from the engine inlet line 10 tocooling channels in the combustion engine 2. The engine circuit comprises an engineoutlet line 11 receiving coolant from the combustion engine 2. The engine outlet line11 is branched in a first end line11a and a second end linel lb. The first end line11a comprises a check valve 12a and the second end line11b comprises a relief valve 12b.

The cooling system comprises a thermostat 13 receiving coolant from the first end linella. The thermostat 13 directs coolant to a radiator bypass 14 When the coolant has alower temperature than its regulating temperature. The radiator bypass 14 may alsoreceive coolant from the second end linel lb. The thermostat 13 directs coolant to aradiator 16, via a radiator inlet line l5a, When the coolant has a higher temperaturethan its regulating temperature. The coolant is cooled in the radiator 16 by a cooling airfloW forced through the radiator 16 by ram air and a not indicated radiator fan. Thecoolant leaves the radiator 16 via a radiator outlet line 15b. A miXing line 17 receivingcoolant from the radiator bypass line 14 and the radiator outlet line 15b. A static line19 eXtends from an expansion tank 18 to the miXing line 17. The static line 19 defines a static line pressure in the miXing line 17.

The Cooling system comprises a retarder Circuit. The retarder Circuit comprises aretarder inlet line 20. The retarder inlet line 20 receives coolant from the miXing linel7. The retarder inlet line 20 comprises a check valve 22. The retarder inlet line 20directs coolant to the water retarder 6. The retarder circuit comprises a retarder outletline 23 receiving the coolant from the water retarder 6. ln this case, the retarder outletline 23 directs the coolant to the first end linel la in a position downstream of thecheck valve l2a and upstream of the thermostat l3. The retarder circuit comprisesfurther an engine bleed passage 25 directing a continuously small coolant flow towardsthe water retarder 6. When the water retarder 6 is disengaged, the coolant flow fromthe engine bleed passage flows past the water retarder 6, via a shaft seal passage 26, tothe retarder outlet line 23. The water retarder 6 needs a small coolant flow to start andthe shaft seal passage 26 needs a small coolant flow for its function. The retardercircuit comprises further a first connection line 27 and a relief valve 28 which isdesigned to open when the difference between the coolant pressure in the retarderoutlet line 23 and the coolant pressure in the retarder inlet line 20 eXceeds a maximumacceptable value. The cooling circuit comprises a second connection line 29 providedí-and a check valve 30 which is designed to open when the pressure in the retarder inlet line 20 eXceeds the pressure in the retarder outlet line 23.

The coolant pump 9, which may be a mechanical pump, starts the circulation ofcoolant in the cooling system as soon as the combustion engine 2 starts. Duringoperating conditions when the control unit 8 receives information from the brakecontrol unit 8a indicating that the retarder 6 is not to be engaged, the control unit 8 setsthe retarder valve 6a in a closed positon such that it prevents a coolant flow, via theretarder inlet line 20, to the water retarder 6. ln this case, the retarder outlet line 23only receives the above mentioned small coolant flow from the engine bleed passage25. The coolant pump 9 directs the entire coolant flow to the combustion engine 2. Thecoolant leaving the combustion engine 2 enters the engine outlet line ll. Since there isno high pressure coolant flow from the water retarder 6 to the first end linel la, theentire coolant flow in the engine outlet line ll is directed, via the first end linel la andthe check valve l2a, to the thermostat l3. On the other hand if the coolant temperature is below the regulation temperature of the therrnostat l3, the coolant flow is directed, via the radiator bypass line 14, to the coolant pump 9. In case the coolant temperatureis above the regulation temperature of the thermostat 13, the coolant flow is directed tothe radiator 16 before it enters the coolant pump 9. Thus, the thermostat 13 and thecooling system operate in a conventional manner when the water retarder 6 is disengaged.

During operating conditions when the control unit 8 receives information from thebrake control unit 8a indicating that the water retarder 6 is to be engaged, it sets theretarder valve 6a in an open position. The water retarder 6 operates as a pump and itsucks coolant from the miXing line 17, via the retarder inlet line 20, to the waterretarder 6. Usually, the water retarder 6 has a significantly higher pump capacity thanthe coolant pump 9. In view of this fact, the water retarder 6 may initiate an abruptacceleration of the coolant flow and a high pressure peak in the cooling system when itis engaged. In case the pressure difference in the retarder outlet line 23 and the retarderinlet line 20 eXceeds a maximum acceptable value, the relief valve 28 is designed toopen. The retarder inlet line 20 is comprised in a part of the cooling system in whichthe pressure is defined by static line 19. The static line pressure is substantiallyconstant. In view of this fact, it is relatively easy to design the relief valve 28 such thatit opens when the pressure in the retarder outlet line 23 eXceeds a predeterminedmaximum pressure. Thus, the eXistence of the first connection line 27 and the reliefvalve 28 eliminates high pressure peaks in the retarder outlet line -l-lä in a simple andreliable manner. The retarder inlet line 20 is together with the radiator bypass line 14,the radiator outlet line 15b, the miXing line 17 and a portion of the engine inlet line 10situated upstream of the coolant pump 9 comprised in said part of the cooling system in which static line pressure prevails.

The coolant flow from the water retarder 6 is received in the retarder outlet line 23.The retarder outlet line 23 directs the coolant flow to the first end 1ine11a in a positionbetween the check valve 12a and the thermostat 13. The check valve 12a prevents acoolant flow in the first end line 11 in a direction towards the engine outlet line11.Thus, the entire coolant flow from the water retarder 6 is directed to the thermostat 13. In case the coolant flow from the water retarder 6 has a temperature below the regulation temperature of the thermostat 13, the thermostat 13 directs the coolant floWto the radiator bypass line 14. In case the coolant floW has a temperature above theregulation temperature of the thermostat 13, the thermostat 13 directs the coolant floWto the radiator 16. The therrnostat 13 may be a Wax thermostat With a constantregulating temperature. Altematively, the therrnostat 13 may comprise a valvecontrolled by the control unit 8. In the latter case, it is possible to have a firstregulating temperature When the Water retarder 6 is disengaged and a second regulatingtemperature, Which differs from the first regulating temperature, When the Waterretarder 6 is engaged. Due to the high pump capacity of the Water retarder 6, anincreased coolant floW is provided through the radiator 16 When the Water retarder 6 isengaged. This, means that the coolant obtains a more effective cooling in the radiator16 and the cooling system a higher cooling capacity When the Water retarder 6 is engaged.

The cooling system is designed such that the engine inlet line 10 and the retarder inletline 20 receive coolant from said part of the cooling system in Which the static linepressure prevails. Thus, the coolant pump 9 and the Water retarder 6 operate in parallelWhen the Water retarder 6 is engaged. ïlïheseïmeans that the coolant pump 9 is ableto circulate coolant through the combustion engine 2 When the Water retarder 6 isengaged despite the fact that the coolant pump has a significantly lower pump capacitythan the Water retarder 6. In view of the fact that the coolant pressure in the retarderoutlet line 23 is significantly higher than the pressure in the engine outlet line 11, thecheck valve 12a blocks the coolant floW from the engine outlet line llto the therrnostat 13 When the Water retarder 6 is engaged. This means that the pressure in the engine outlet line ll increases such that the relief valve 12b in the second end line llb is open.

The coolant floW in the engine outlet line ll is directed, via the second end linel lb, tothe radiator bypass line 14. Thus, the coolant continues to floW through the combustionengine 2 in an intended direction When the Water retarder 6 is engaged. Consequently,the above mentioned design of the cooling system elin1inates the risk that negativepressures and back flows are created in the combustion engine 2 When the Water retarder 6 is engaged. 11 The coolant flow from the combustion engine 2 is not cooled when the water retarder 6is engaged. However, during most operating conditions, this is not necessary since thecombustion engine 2 is not loaded when the water retarder 6 is engaged. Furthermore,the coolant flow through the combustion engine 2 is small in relation to the coolantflow through the water retarder 6. The small uncooled coolant flow from the radiatorbypass line l4 is mixed with the significantly larger cooled coolant flow from theradiator l6 in the miXing line l7. Thus, the small uncooled coolant flow through thecombustion engine 2 does not substantially reduce the cooling capacity of the cooling system when the water retarder 6 is engaged.

Fig. 2 shows a cooling system corresponding to the cooling system in Fig. l except fortwo differences. In this case, the retarder outlet line 23 ends in the radiator inlet linel5a. Thus, the retarder outlet line 23 ends in a downstream position of the therrnostatl3 and an upstream position of the radiator l6. Furthermore, the second end linel lbends in the retarder inlet line 20 in a position downstream of the check Valve 22.During operating conditions when the water retarder 6 is disengaged, there is sub stantially no coolant flow in the retarder inlet line 20 to the water retarder 6. Thecoolant pump 9 circulates the entire coolant flow, Via the engine inlet line l0 and thecombustion engine 2, to the engine outlet line ll. Since the relief Valve l2b requires ahigher pressure to open than the check Valve l2a, the entire coolant flow in the engineoutlet line ll is directed, via the first end linel la, to the thermostat l3. In case thecoolant temperature is below the regulation temperature of the thermostat l3, thecoolant flow is directed, via the radiator bypass line l4, to the coolant pump 9. In casethe coolant temperature is above the regulation temperature of the therrnostat l3, thecoolant flow is directed to the radiator l6 before it enters the coolant pump 9. Thus, thethermostat l3 and the cooling system operate in a conventional manner when the water retarder 6 is disengaged.

During operating conditions when the water retarder 6 is engaged, a high coolant flowis directed from the water retarder 6, Via the retarder outlet line 23, to the radiator inletline l5a. A part of the coolant flow enters the thermostat l3. ln case the temperature of the coolant in the retarder outlet line 23 is below the regulation temperature of the 12 thermostat l3, the thermostat l3 is moved to an open position and said part of thecoolant flow from the retarder outlet line 23 is directed to the radiator bypass line 14.A remaining part of the coolant flow from the retarder outlet line 23 is directed to theradiator l6. The distribution of the coolant flow in the retarder outlet line 23 to thebypass line l4 and the radiator l6 depends on the flow resistances in the respectiveflow passages. ln case the coolant temperature is above the regulation temperature ofthe thermostat l3, the thermostat l3 is moved to a closed position such that the entire coolant flow from the retarder outlet line 23 is directed to the radiator l6.

Furthermore, the coolant flow from the retarder outlet line 23 creates a high pressure inthe radiator inlet line l5a. The high pressure in the radiator inlet line l5a prevents thecoolant of the lower pressure to flow through the thermostat l3 and reach the radiatorinlet line l5a. The pressure in the engine outlet line ll increases and the relief valvel2b opens such that the coolant flow in the engine outlet line ll is directed, via thesecond end linel lb, to retarder inlet line 20. Thus, the low static line pressure in theretarder inlet line 20 makes it possible to maintain the coolant flow through the combustion engine 2 when the water retarder 6 is engaged.

Fig 3 shows a cooling system corresponding to the cooling system in Fig. 2 except forthe positioning of the check valve l2a. ln this case, the check valve l2a is positionedin the radiator inlet line l5a. The retarder outlet line 23 directs coolant to the radiatorinlet line l5a in a position downstream of the check valve l2a and upstream of theradiator l6. During operating conditions when the water retarder 6 is disengaged, thecoolant pump 9 circulates the entire coolant flow, via the combustion engine 2, to theengine outlet line ll. Since the relief valve l2b requires a predeterrnined pressure toopen, the entire coolant flow is directed, via the first end line lla, to the thermostat l3.ln case the coolant temperature is below the regulation temperature of the thermostatl3, the coolant flow is directed, via the radiator bypass line l4, to the coolant pump 9.ln case the coolant temperature is above the regulation temperature of the thermostatl3, the coolant flow is directed, via the check valve l2a and the radiator inlet line l5a,to the radiator l6. Also in this case, the thermostat l3 has a convention function when the water retarder 6 is disengaged. 13 During operating conditions when the water retarder 6 is engaged, the water retarder 6directs a high pressure coolant flow to the radiator inlet line 15a. The check Valve 12aprevents the coolant flow from the retarder outlet line 23 to reach the thermostat 13.The high pressure coolant flow to the radiator inlet line 15a prevents a coolant flowfrom the engine outlet line 11 to the radiator inlet line 15a when the water retarder 6 isengaged. In view of this fact, the coolant flow in the engine outlet line 11 is alwaysdirected, Via the second end 1ine11b, to the radiator bypass line 14 independent of the coolant temperature when the water retarder 6 is engaged.

Fig. 4 shows a cooling system corresponding to the cooling system in Fig. 1 except forsome differences. In this case, the retarder outlet line 23 ends in the therrnostat 31.Furthermore, the therrnostat 31 has a design such that it opens at different coolanttemperatures when the water retarder is disengaged and engaged. Fig. 5 shows anembodiment of such a thermostat 31. The therrnostat 31 comprises a housing 32. Thehousing 32 comprises a first inlet connected to the first end line 11a of the engineoutlet line 11, a second inlet connected to the retarder outlet line 23, and a third inletconnected to a supply line 34a of a pilot circuit 34. The housing 32 comprises further afirst outlet connected to the radiator bypass line 14, a second outlet connected to theradiator inlet line 15a, and a third outlet connected to a retum line 34b of the pilotcircuit 34. The pilot line 34 directs a small coolant flow from the engine inlet line 10 ina position downstream of the coolant pump 10, Via the supply line 34a, to thethermostat 31. The pilot line 34 return the coolant flow from the thermostat 31, Via the return line 34b, to the engine inlet line 10 in a position upstream of the coolant pump .

The thermostat 31 comprises a first thermal expansion member 35 which is in heattransfer contact with the coolant in the pilot line 34. The first thermal expansionmember 35 comprises a first capsule 35a, which encloses a first wax material, and afirst piston 35b. The first piston 35b provides a stroke from a retracted position to astroke position when the first wax material in the first capsule 35a melts and passes into liquid phase. The thermostat 31 comprises a second thermal expansion member 36 14 Which is in heat transfer contact With the coolant in the retarder outlet line 23. Thesecond thermal expansion member 36 comprises a second capsule 36a, Which enclosesa second Wax material, and a second piston 36b. The second piston 36b provides astroke from a retracted position to a stroke position When the second Wax material in the second capsule 36a melts and passes into liquid phase.

The first thermal expansion member 35 and the second thermal expansion member 36are connected to a common valve body 37. The valve body 37 has a tubular shapeWith a completely open upper portion and a partly open bottom portion. The valvebody 37 is movably arranged betWeen a first end position in Which it directs the entirecoolant floW to the radiator bypass line l4 and a second end position in Which it directsthe entire coolant floW to the radiator inlet line l5a. The valve body 37 comprises aconnecting member 38 fixedly connected to a bottom portion of the valve body 37.The first piston 35b is connected to the valve body 37 via a pushing member 39, amoment transmitting member 40, a spring seat 4l, a valve spring 42 and theconnecting member 38. A loWer contact surface of the pushing member 39 is looselyconnected to an upper contact surface of the moment transrr1itting member 40. Thismeans that the second piston 36b is able to move the valve body 37 from the first endposition to the second end position independent of the stroke of the first piston 35b.The second piston 36b is slidably arranged in a longitudinal direction in a recess theconnecting member 38. This means that the first piston 35b is able to move the valvebody 37 from the first end position to the second end position independent of thestroke of the second piston 36b. Thus, the thermal expansion member 35, 36 providing the longest stroke defines the position of the valve body 37.

During operating conditions When the Water retarder 6 is disengaged, the small coolantfloW through the engine bleed passage 25to the retarder outlet line 23 is substantiallynegligible. Thus, the second piston 36b of the second therrnal expansion member is ina retracted position. The coolant pump 9 circulates a coolant floW, via the combustionengine 2, the engine outlet line ll and the first end line lla, to the thermostat 3 l. Atthe same time, the coolant pump 9 provides a small cooling floW to the therrnostat 3l via the pilot supply line 34a. In case the coolant temperature in the pilot supply line 34a is below the regulation temperature of the first thermal expansion member 35, thefirst Wax body is in solid phase. Consequently, the first piston 35b is in the retractedposition. In case the coolant temperature in the pilot supply line 34a is above theregulation temperature of the first thermal expansion member 35, the first Wax body isin liquid phase. Consequently, the first piston 35b is in the stroke position. In this case,the temperature of the coolant in the pilot supply 34a defines the position of the valvebody 37. If the valve body 37 is in the first end position, the entire coolant floW fromthe engine outlet line ll is directed to the radiator bypass line l4. If the valve body 37is in the second end position, the entire coolant floW from the engine outlet line ll isdirected to the radiator inlet line l5a. Also in this case, the cooling system and the thermostat 3l has a conventional function When the Water retarder 6 is disengaged.

During operating conditions When the Water retarder 6 is engaged, the Water retarder 6 directs a high pressure coolant floW, via the retarder outlet line 23, to the therrnostat 3l.

The existence of the check valve l2a prevents a backflow from the therrnostat l3, viathe first end line lla, to the engine inlet line ll. The increased pressure in the first inletline lla directs the coolant floW in the engine outlet line ll, via the second end linellb, to the radiator bypass line l4. In this case, the coolant floW from the pilot supplyline 34a comes in heat transfer contact With the first therrnal expansion member 35 andthe coolant floW from the retarder outlet line 23 comes in heat transfer contact With thesecond therrnal expansion member 36. In case none of these coolant floWs have ahigher temperature than the regulating temperatures of the respective therrnalexpansion members 35, 36, both pistons are maintained in the retracted position. Thevalve member 37 is maintained in the first end position and the coolant floW from the retarder outlet line 23 is directed to the radiator bypass line l4.

In case, the coolant floW in the pilot supply line 34a has a higher temperature than theregulating temperature of the first therrnal expansion member 35 or coolant floW in theretarder outlet line 23 has a higher temperature than the regulating temperature of thesecond therrnal expansion member 36, at least one of said pistons 35b, 36b is moved to the stroke position Which means that it moves the valve member 37 to the second end 16 position. ln this case, the coolant floW from the retarder outlet line 23 is directed to the radiator inlet line l5a.

The invention is not restricted to the described embodiment but may be Varied freelyWithin the scope of the claims. The thermostat 3l can be designed in many differentWays. The first thermal extension element 35 may alternatively by controlled by thetemperature of the coolant floW in the engine outlet line ll instead of the temperature of the coolant floW in pilot circuit 34.

Claims (13)

17 Claims

1. Cooling system for an engine (2) and a Water retarder (6) Which is connected to apower train in a vehicle (1), Wherein the cooling system comprises a radiator (16), aradiator bypass line (14), a therrnostat (13, 31) configured to direct coolant to theradiator bypass line (14) and/or the radiator (16), an expansion tank (18), a static line(19) connected to the expansion tank (18) and configured to define the pressure in astatic line pressure part (14, 17, 19, 20) of the cooling system, an engine inlet line (10)configured to receive coolant from said static line pressure part (17) of the coolingsystem and to direct it to the engine (2), a coolant pump (9) arranged in the engine inletline (10), an engine outlet line (1 1) configured to receive coolant from the engine (2)and direct it, via a first flow passage (1 la) to the therrnostat (13, 31) When the Waterretarder (6) is disengaged, a retarder inlet line (20) configured to direct coolant to theWater retarder (6) and a retarder outlet line (23) configured to receive coolant from theWater retarder (6), characterized in: - that the retarder inlet line (20) is configured to receive coolant from said static linepressure part (17) of the cooling system; - that the engine outlet line (11) is configured to direct coolant, via a second floWpassage (1 lb), to said static line pressure part (14, 20) of the cooling system When theWater retarder (6) is engaged; - that the engine outlet line (11) is branched in a first end line (1 la) and a second endline (1 lb), Wherein the first floW passage comprises the first end line (1 la) and thesecond floW passage comprises the second end line (11b); - that the cooling system comprises a check valve (l2a) arranged in the first end line(1 la) or in a radiator inlet line (15a); and - that the second end line (1 lb) is provided With a relief valve (l2b).

2. Cooling system according to claim 1, characterized in that the second floW passage(1 lb) is configured to direct coolant to the radiator bypass line (14) When the Water retarder (6) is engaged. 18

3. Cooling system according to claims 1 or 2, characterized in that the second flowpassage (1 lb) is configured to direct coolant to the retarder inlet line (20) When the Water retarder (6) is engaged.

4. Cooling system according to any of the preceding claims, characterized in that theretarder outlet line (23) is configured to direct coolant to the first end line (1 la) of theengine outlet line (11) in a position doWnstream of a check valve (l2a) and upstream of the therrnostat (13).

5. Cooling system according to any one of the preceding claims 1 to 4, characterized inthat the retarder outlet line (23) is conf1gured to direct coolant to the radiator inlet line (15a) situated doWnstream of the therrnostat (13) and upstream of the radiator (16).

6. Cooling system according to any one of the preceding claims 1 to 4, characterized in that the retarder outlet line (23) is configured to direct coolant to the therrnostat (31).

7. Cooling system according to any one of the preceding claims, characterized in thatthe therrnostat (31) is a design such that it has a different regulating temperatures When the Water retarder is disengaged and When the Water retarder is engaged.

8. Cooling system according to claim 1, characterized in that the engine inlet line (10)and the retarder inlet line (20) are conf1gured to receive coolant from a mixing line (17) receiving coolant from the radiator bypass line (14) and the radiator (16).

9. Cooling system according to any one of the preceding claims, characterized in thatthe cooling system comprises a first pressure release mechanism (27, 28) configured toprevent that the coolant pressure rises above a maximum acceptable pressure level in the retarder outlet line (23).

10. Cooling system according to claim 9, characterized in that the first pressure releasemechanism comprises a connection line (27) extending between the retarder outlet line (23) and the retarder inlet line (20) and a relief valve (28) configured to open and 19 reduce the pressure in the retarder outlet line (23) When the pressure differencebetween the retarder inlet line (20) and the retarder outlet line (23) exceeds a predeterrnined value.

11. ll. Cooling system according to any one of the preceding claims, characterized in thatthe cooling system comprises a second pressure release mechanism (29, 30) configuredto prevent that the coolant pressure rises above a maximum acceptable pressure level in the retarder inlet line (20).

12. l2. Cooling system according to claim ll, characterized in that the second pressurerelease mechanism comprises a connection line (29) extending between the retarderoutlet line (23) and the retarder inlet line (20) and a check valve (30) conf1gured toopen and reduce the pressure in the retarder inlet line (23) When the pressure in the retarder inlet line (20) exceeds the pressure in the retarder outlet line (23).

13. l3. A vehicle comprising a cooling system according to any one of the preceding claims l- l 2.