SE543762C2 - A cooling system for an engine and a water retarder - Google Patents

Abstract

Cooling system for a combustion engine (2) and a water retarder (6). The cooling system comprises a retarder circuit (13) comprising a radiator bypass (13a), a radiator passage (13b) including the water retarder (6), and a valve device (12) which in a retarder on position directs the entire coolant flow to the water retarder (6) at the same time as it prevents a coolant flow through the retarder bypass (13a). Such a design makes it possible to use the entire pump capacity of the water retarder (6) to circulate coolant through the coolant system. Furthermore, the cooling system comprises a pressure release mechanism preventing high pressure peaks above a maximum acceptable pressure level in the cooling system which may occur during an engaging process and a disengaging process of the water retarder (6).

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 pumping capacity.

US 2010/0147641 shows a cooling system comprising a coolant pump, a combustionengine and a retarder circuit comprising a hydrodynamic retarder. The retarder circuitcomprises a switching valve directing the entire coolant flow to the hydrodynamicretarder when the hydrodynamic retarder is engaged at the same time as coolant flowthrough a retarder bypass is prevented. Such a design of the retarder circuit makes itpossible to increase the coolant flow in the cooling system significantly by means ofthe hydrodynamic retarder which usually has a higher pumping capacity than theordinary coolant pump. However, the engagement of hydrodynamic retarder results inan abrupt acceleration of the coolant flow in the cooling system and the disengagementof the hydrodynamic retarder results in an abrupt deceleration of the coolant flow inthe cooling system. Abrupt coolant flow changes result in temporarily pressure peaks in the cooling system which may shorten the lifetime of the components in the cooling system. Furthermore, there is an obvious risk that negative pressures are created in the combustion engine when the hydrodynamic retarder is engaged.

EP 1 251 050 shows a Cooling system comprising a coolant pump, a combustionengine and a retarder circuit. The retarder circuit comprises a retarder passage directingcoolant to a hydrodynamic retarder, a retarder bypass, and a switching valve allowing acoolant flow to the retarder passage when the hydrodynamic retarder is to be engaged.However, the retarder bypass is not blocked when the hydrodynamic retarder isengaged. In view of this fact, a large part of the coolant flow provided by thehydrodynamic retarder is directed back in a reversed direction through the retarderbypass when the hydrodynamic retarder is engaged. Consequently, it is not possible toincrease the coolant flow in the cooling system when the hydrodynamic retarder is engaged.

SUMMARY OF THE INVENTION The object of the present invention is to provide a cooling system for a combustionengine and a water retarder having a design making it possible to increase the coolantflow in the cooling system when the water retarder is engaged at the same time as undesired pressures in the cooling system are eliminated.

These objects are achieved by the features defined in claim l. The engine may be anarbitrary engine which has to be cooled during operation. The engine may be acombustion engine, an electric engine etc. The cooling system comprises a valvedevice preventing a coolant flow through a retarder bypass when the water retarder isengaged. Thus, no part of the coolant flow provided by the water retarder can bedirected back via the retarder bypass. Consequently, the entire pump capacity of thewater retarder can be used to circulate the coolant in the cooling system. Usually, awater retarder has a significantly higher pump capacity than a coolant pump.Consequently, it is possible to increases the coolant flow in the cooling system significantly and the heat exchange in the radiator when the water retarder is activated.

Since the water retarder has a significantly higher pump capacity than the coolantpump, the coolant flow in the cooling system is abruptly changed when the waterretarder is engaged and disengaged. Thus, there is a great risk that high pressure peaksare created in the cooling system when the water retarder is engaged and disengagedby the valve device. In order to prevent such high pressure peaks, the cooling systemcomprises a pressure release mechanism configured to prevent that the coolantpressure rises above a maximum acceptable pressure level in a specific point in thecooling system. The existence of the pressure release mechanism secures that thecoolant pressures will not increase above a maximum acceptable level in a simple andeffective manner in said specific point of the cooling system. By arranging the pressurerelease mechanism in a suitable specific point, the risk that high pressure peaks are propagated to sensitive components in the cooling system is eliminated.

According to the invention, the pressure release mechanism comprises a connectionline extending between the specific point and a reference point in the cooling systemand a relief valve configured to open and allow a coolant flow from the specific pointto the reference point via the connection line when the pressure difference between thespecific point and the reference point exceeds a predetermined value. The relief valveopens when a certain pressure difference prevails between the specific point and thereference point. In view of this fact, it is suitable to choose a reference point in thecooling system having relatively constant pressure. In such a case, it is easy todimension the relief valve such that it opens when the pressure in the specific pointexceeds a maximum acceptable pressure level. The relief valve may have a simpledesign and be relatively inexpensive. It is to be noted that said high pressure peakshave a short duration. In view of this fact, the coolant flow directed from the pressure release point, via the connection line, to the reference point is small. .åceffirtíing to the imfeniitln, the etimísustitvn engine is arranved in a position títf-yvnstreatat of the. attßtixlant pump and utïsstreatn of tlte Water retarder in the coolingsystem. En view of the fact that the :water retarder a liigliei' pump capacity' than thecoolant nunte. th ere is a risk th at ne “fative nresstires are created in the eorttlaustion ensßixie vvhen the water retarder is aftïttzaf mi. ln order to eíiniinzzte this nrtgfblein, the cooling svfstiïin coinnrises a line connecting the static, line to a first iïsoint in tiie tfooliiiš:systern situated. dovaristi'ea1r1 aíxftlie enfiine and tinstreani :ifthe water retarder such that a nressiire related to the ipiressure in the expaiisiori tank is' created doinfristrearn oftlie engine. Since stuch a nc-sitivff: pressure prewfails doiafnstreztni of the enfßine. tlie risk tiiat iie-øaiivfe tiresstires are created in the engine is eliiniiiated. ßtccfirdiiig to the imfeiitifin, said. line is an engine lwtiziss liite coníiaiireii to :lirect tfooif-iiit to said first point dovafnstriëani of the eniiiiie froiïo a second point in the cooling systern situated in a. position iinstreaii: otftlie ciíiolaiit nurim and the engine. Thepressure :ii-fin in the engine Eixfnass line is iouif. Tlius tlie existence otthe eivfine hvfnass creates a pressiire .relateei to the positive iïiressiire in the exnaiision tank in the :above defiiied igioints on :siffnosite siiies ofthe engine. The coolinv system :nav ccunnrise a check *valve ailiíixifiiig a cooiaiit flow in onlv :ine tlirectifni tlir-ouefli the engine hvoass line. Thus. the clieck »falve allšrrwfs a coolant iioiæf tlirougli the en gina byfiçsass liite to 'the *water retarder sit-hen fin: iifater retztrdei' is engaged and it nrewfents a cooiaiïit flow' in. the onnfisite direction throiußli the engine bvnass lirie »sfheri the »water retarder is tfíisengzigfed.

According to an embodiment of the invention, the specific point is arranged in aretarder outlet line receiving coolant from the retarder circuit. During an engagingprocess of the Water retarder, the Water retarder provides an abrupt acceleration of thecoolant floW received in the retarder outlet line. The abrupt acceleration of the coolantfloW may initiate a high pressure peak propagating in the intended flow direction fromthe retarder circuit to downstream situated parts of the cooling system. Since thespecific point is arranged in the retarder outlet line, such high pressure peaks aresubstantially immediately reduced to an acceptable pressure level before they reach downstream situated parts in the cooling system.

According to an embodiment of the invention, the specific point is arranged in aretarder inlet line directing coolant to the retarder circuit. During a disengaging processof the Water retarder, the Water retarder provides an abrupt deceleration of the coolant floW in the retarder inlet line. The abrupt deceleration of the coolant flow may initiate a high pressure peak propagating in an opposite direction to the intended floW directionin the Cooling system. Since the specific point is arranged in the retarder inlet line,such high pressure peaks are substantially immediately reduced to an acceptablepressure level before they reach upstream situated components in the in the cooling system.

According to an embodiment of the invention, said reference point is positioneddoWnstream of the coolant pump and upstream of the combustion engine in the coolingsystem. The coolant pump is usually arranged closed to the combustion engine. In thiscase, the connection line is able to direct a small quantity of coolant of a high pressurefrom the specific point to a reference point situated between the coolant pump and thecombustion engine. In this case, the reference point is situated on the pressure side of the coolant pump.

According to an embodiment of the invention, the reference point is pressureconnected to a static line in the cooling system. In this case, the reference point issituated on the suction side of the coolant pump. The pressure in this reference point isrelatively constant Which makes it easy to define an opening pressure of the reliefvalve such that it opens When the pressure in the specific point exceeds a not acceptable level.

According to an embodiment of the invention, the reference point is situated in theretarder inlet line in the cooling system. The retarder inlet line and the retarder outletline are usually arranged at a small distance from each other. In case the specific pointis arranged in the retarder outlet line, it is possible to connect it to a reference point inthe retarder inlet line by means of a short connection line. Alternatively, the referencepoint is situated in the retarder outlet line in the cooling system. In this case, the reference point can be connected to a specific point in the retarder inlet line With short connection line.

According to an alternative embodiment, the valve device is a directional valve movably arranged between a retarder on position and a retarder off position. Such adirectional valve may be a solenoid valve arranged in a connection point between theretarder bypass and the retarder passage. However, it is possible to design the valvedevice in other ways. The valve device may, for example, comprise a valve member in the retarder bypass and a valve member in the retarder passage.

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

BRIEF DESCRIPTION OF THE DRAWINGS In the following preferred embodiments of the invention is described, as examples, with reference to the attached drawing, in which: Fig. 1 shows a cooling system according to a first and a second embodiment ofthe inventiomggi Fig. 2 shows a cooling system according to a third embodiment of the invention»iæ-iveaæ-E-iiäiæ-aaz-ë ”E a e.. .Jing igyzït' L; acccrdlzig f: íiššliš: *nal . ššnQní zrií.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THEINVENTION Fig. 1 shows a schematically indicated vehicle 1 which may be a heavy vehicle. Thevehicle 1 is driven by a combustion engine 2. The combustion engine 2 may be an Ottoengine or a diesel engine. The vehicle 1 comprises a powertrain, which in addition tothe combustion engine 2, comprises a clutch mechanism 3, a gearbox 4 and a gearboxoutput shaft 5. The vehicle 1 is equipped with a water retarder 6 comprising a statorunit which is stationary arranged in the vehicle and a rotor unit which is, via a motiontransmitting mechanism 7, connected to the gearbox output shaft 5. Thus, the rotor unitis rotated by a speed defined by the speed of the gearbox output shaft 5 and the gearratio in the motion transmitting mechanism 7. The stator unit and the rotor unit definea toroidal space for receiving coolant during activation of the water retarder. The statorunit comprises stator vanes and the rotor unit comprises rotor vanes situated in thetoroidal space. A control unit 8 is adapted to control the activation of the water retarder6 by means of information from a brake activating member 8a, which may be a brake pedal.

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 a coolantpump 9 circulating the coolant in the cooling system. The coolant pump 9 is arrangedin an engine inlet line 10 from which it circulates coolant to cooling channels in thecombustion engine 2. The coolant leaving the combustion engine 2 enters a retarderinlet line 11. The retarder inlet line 11 is connected to a valve device in the form of adirectional valve 12. The directional valve 12 is switchable between two positionsnamely a retarder off position and a retarder on position. In the retarder off position,the directional valve 12 directs the coolant past the retarder 6 via a retarder bypass l3a.In the retarder on position, the directional valve 12 directs the entire coolant flow tothe retarder passage 13b and the water retarder 6. The directional valve 12 is arrangedin a connection point between the retarder bypass 13a and the retarder passage 13b. Inview of that fact, the directional valve 12 prevents a coolant flow through the retarderbypass 13a in the retarder on position. The retarder passage 13b comprises a pressurecontrol valve 15 and a check valve 16 which are arranged in a downstream position of the retarder 6. The coolant leaving the retarder circuit 13 enters a retarder outlet line 17 via the bypass 13a or the retarder passage 13b. The retarder outlet line 17 directs the coolant to a thermostat 18.

The thermostat 18 directs the coolant to a radiator bypass 19 when the coolant has alower temperature than a regulating temperature of the thermostat 18. The radiatorbypass 19 directs the coolant to the engine inlet line 10. When the coolant has a highertemperature than the regulating temperature, the thermostat 18 directs the coolant to aradiator line 20 comprising a radiator 21. The coolant is cooled in the radiator 21 by acooling air flow forced through the radiator 21 by ram air and a not indicated radiatorfan. When the coolant has been cooled in the radiator 21, it is directed to the engineinlet line 10. An expansion tank 22 for the coolant is, via a static line 23, connected to the engine inlet line 10 in a position upstream of the coolant pump 9.

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 is engaged. Duringoperating conditions when the control unit 8 receives information from the brakecontrol unit 8a indicating that the retarder 6 is not to be engaged, it initiates amovement of the directional valve 12 to the retarder off position. In this position, thecoolant flow in the retarder inlet line 11 is directed, via the retarder bypass l3a and the retarder outlet line 17, to the thermostat 18.

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 initiates amovement of the directional valve 12 to the retarder on position, which means thatcoolant is directed to the retarder passage 13b and the retarder 6. The water retarder 6operates as a pump and it sucks coolant from the retarder inlet line 11. In the retarderon position, the directional valve 12 prevents a coolant flow through the retarderbypass 13a. This measure prevents a back flow of the coolant through the retarderbypass 13a when the water retarder is engaged. Thus, the entire coolant flow providedby the water retarder 6 is directed to the retarder outlet line 17. Consequently, theentire pumping capacity of the water retarder 6 can be used to circulate coolant in the cooling system.

Usually, the water retarder 6 has a significantly higher pump capacity than the coolantpump 9. In view of this fact, the Water retarder 6 initiates an abrupt acceleration of thecoolant flow in the retarder outlet line 17 during an engaging process of the waterretarder when the directional valve just has been switched to the retarder on position.In this case, a high pressure peak can be initiated in the retarder outlet line 17 in thecooling system. Furthermore, the coolant flow receives an abrupt deceleration during adisengaging process of the water retarder when the directional valve 12 just has beenswitched to the retarder off position. In this case, a high pressure peak can be initiatedin the retarder inlet line 11 in the cooling system. In case the directional valve 12 isfrequently switched between the retarder off position and the retarder on position, thereis a risk that such high pressure peaks shorten the lifetime of pressure sensitive components in the cooling system.

In order to avoid high pressure peaks during the engaging process of the water retarder,the cooling system shown in Fig 1 comprises a first connection line 24a extendingbetween a specific point ps in the retarder outlet line 17 and a reference point prsf in theengine inlet line 10 situated between the coolant pump 9 and the combustion engine 2.The first connection line 24a comprises a first relief valve 25a. The first relief valve25a is designed to open when the pressure difference between the specific point ps andthe reference point pfsf exceeds a predetermined value. It is possible to estimate thepressure in the reference point prsf with a relative high accuracy during an engagingprocess of the water retarder 6. In view of that fact, it is possible to design the reliefvalve 25a such that it opens when the pressure exceeds a maximum acceptablepressure level in the specific point ps in the retarder outlet line 17. In such a case, a partof the coolant flow in the retarder outlet line 17 is directed to the engine inlet line 10.This measure reduces the magnitude of a high pressure peak in the retarder outlet line17 during an engaging process of the water retarder 6. Thus, the existence of the firstconnection line 24a and the relief valve 25a eliminates high pressure peaks in the retarder outlet line 17 in a simple and reliable manner. 11 Fig. 1 also shows a second alternative connection line 24b extending between a high-pressure point ps in the retarder outlet line 17 and a reference point pfef in the engineinlet line 10 situated upstream of the coolant pump 9. The pressure in this referencepoint pfef is related to the pressure in the static line 23 and the expansion tank 22. Thepressure in this reference point is relatively constant. Thus, it is relatively easy todesign the second relief valve 25b such that it opens when the pressure in the specificpoint ps exceeds a maximum acceptable pressure level. The second connection line 24bis an alternative to the first connection line 24a, which eliminates pressure peaks abovea predetermined level in retarder outlet line 17 in the cooling system. Thus, it is enough to use one of said connection lines 24a, 24b.

In case the coolant flows in series through the coolant pump 9, the combustion engine2 and the water retarder 6 during engagement of the water retarder 6, there is anobvious risk that negative pressures are created in the combustion engine 2. Negativepressures may reverse the coolant flow in parallel cooling channels in the combustionengine 2. In order to eliminate this problem, the cooling system comprises an enginebypass line 28 provided with a check valve 29. The engine bypass line 28 is connectedto a first point p1 in a position downstream of the combustion engine 2 and a secondpoint pz in a position upstream the coolant pump 9 and the combustion engine 2. Thepressure drop in the engine bypass line 28 is negligible. Thus, there is substantially nopressure difference between the first point p1 and the second point pz. Since the enginebypass line 28 ensures a positive pressure, which is defined by the static line 23 andthe expansion tank 22, in a position downstream of the combustion engine 2, negativepressures in the combustion engine 2 is avoided. Thus, the existence of the enginebypass line 28 eliminates the risk that negative pressures are created in the combustionengine 2 when the water retarder 6 is engaged. When the water retarder is disengaged, the check valve 29 prevents a reversed coolant flow through the engine bypass line 28.

Fig. 2 shows a cooling system corresponding to the cooling system in Fig. 1 except forthe positioning of the connection lines 24c, 24d. In this case, the cooling systemcomprises a third connection line 24c extending between a specific point ps in the retarder outlet line 17 and a reference point pfef in the retarder inlet line 11. A third 12 relief valve 25c in the third connection line 24c is designed to open when the pressureexceeds a maximum acceptable pressure level in the specific point ps in the retarder outlet line 17. The existence of the third connection line 24c and the third relief valve25c eliminates high pressure peaks in the retarder outlet line 17 in the cooling system Which can occur during the engaging process of the Water retarder 6.

A fourth connection line 24d is used in combination With the third connection line 24c.The fourth connection line 24d extends between a specific point ps in the retarder inletline ll and a reference point pfef in the retarder outlet line l7. The fourth connectionline 24d comprises a fourth relief valve 25d Which is designed to open When apredetermined pressure difference is created between the specific point ps in theretarder inlet line ll and the reference point pfef in the retarder outlet line l7. It ispossible to design the fourth relief valve 25d such that it opens When the pressure inthe specific point ps in the retarder inlet line ll exceeds a maximum acceptablepressure level. The existence of the fourth connection line 24d and the fourth reliefvalve 25d eliminates high pressure peaks in the cooling system Which can occur duringthe disengaging process of the Water retarder 6. Thus, the existence of the thirdconnection line 24c and the fourth connection line 24d reduces the magnitude of pressure peaks created during engaging processes of the Water retarder 6 as Well as during disengaging processes of the Water retarder 6. 13 s-ystefa--e-efrfifsrises-ifre--e-i-zgê-iæ-e-åäygëass--š-í-fae--š-S-r-Ira--view-eíf-tia-at-ašïí-iefi--ëh-e--avaêer--reiaráef-á The invention is not restricted to the described embodiment but may be varied freely Within the scope of the claims. It is not necessary that the engine is a combustionengine. The engine may be an arbitrary engine Which has to be cooled during operation.

Claims (9)

Claims

1. Cooling system for a combustion engine (2) and a Water retarder (6) which isconnected to a power train in a vehicle (1), wherein the cooling system comprises acoolant pump (9) configured to circulate coolant in the cooling system, an expansiontank (22), a static line (23) connected to an inlet of the coolant pump (9), a radiator(21) configured to cool the coolant, a retarder circuit (13), a retarder inlet line (11)configured to direct coolant to the retarder circuit (13) and a retarder outlet line (17)configured to receive coolant from the retarder circuit (13) and wherein the retardercircuit (13) comprises a retarder bypass (13a) configured to direct coolant past thewater retarder (6), a retarder passage (13b) configured to direct coolant through thewater retarder (6), and a valve device (12) configured to be moved to a retarder onposition when the water retarder (6) is to be activated in which it directs the entirecoolant flow from the retarder inlet line (11) to the water retarder passage (13b) at thesame time as it prevents a coolant flow through the retarder bypass (13a), wherein thecooling system comprises a pressure release mechanism (24a-d, 25a-d) configured toprevent that the coolant pressure rises above a maximum acceptable pressure level in aspecific point (ps) in the cooling system, the pressure release mechanism comprising aconnection line (24a-d) extending between the specific point (ps) and a reference point(pssf) in the cooling system, and wherein: - the pressure release mechanism comprises a relief valve (25 a-d) configured to openand allow a coolant flow from the specific point (ps) to the reference point (pssf) via theconnection line (24a-d) when the pressure difference between the specific point (ps)and the reference point (pfsf) exceeds a predeterrnined value; - the combustion engine (2) is arranged in a position downstream of the coolant pump(9) and upstream of the water retarder (6) in the cooling system; and - the cooling system comprises a line (28) connecting the static line (23) to a first point(pi) situated downstream of the engine (2) and upstream of the water retarder (6) suchthat a pressure related to the pressure in the expansion tank (22) is created in the first point (pi) downstream the engine (2), characterized in that said line is an engine bypass line (28) conf1gured to direct coolantto said first point (p1) doWnstream of the engine (2) from a second point (pg) situated in a position upstream of the coolant pump (9) and the engine (2).

2. Cooling system according to claim 1, characterized in that said specific point (ps) is arranged in the retarder outlet line (17) receiving coolant from the retarder circuit (13).

3. Cooling system according to claim 1, characterized in that said specific point (ps) is arranged in the retarder inlet line (11) directing coolant to the retarder circuit (13).

4. Cooling system according to any one of the preceding claims, characterized in thatthe reference point (pmf) is situated doWnstream of the coolant pump (9) and upstream of the combustion engine (2) in the cooling system.

5. Cooling system according to any one of the preceding claims 1 to 3, characterized inthat the reference point (pmf) is pressure connected to a static line in the cooling system.

6. Cooling system according to claim 1 or 2, characterized in that the reference point (pfef) is situated in the retarder inlet line (11) in the cooling system.

7. Cooling system according to claim 1 or 3, characterized in that the reference point (pfef) is situated in the a retarder outlet line (17) in the cooling system.

8. Cooling system according to any one of the preceding claims, characterized in thatthe Valve device is a directional Valve (12) movably arranged between a retarder on position and a retarder off position.

9. A Vehicle comprising a cooling system according to any one of the preceding claims 1-8.