TECH N ICAL FI ELD AN D PRIOR ART

The present invention relates to a cooling system according to the preamble to the attached claim 1 .

Cooling systems of this type are principally, but not exclusively, used in wheeled working vehicles, such as lorries and buses, which may require an accessory brake in the form of a hydrody- namic retarder.

Such a hydrodynamic retarder is previously known through , for example, US 5,829,562. Oil is normally used as retardi ng mediu m. The oil will then, during braking by means of the retarder, be heated and cooled in a heat exchanger, normally a heavy-duty plate heat exchanger, by a cooling fluid that circulates around a cooling circuit according to the above. Thus, there is here an oil circuit that dampens the power developed from the retarder to the cooling fluid in the cooling circuit during retarder braking . Only one part - to be more precise, the cooling fluid cooler - in such a cooling system has a power that varies rapidly, for which reason a thermostat device should be arranged such that it is in- fluenced through a pilot line by the temperature of the cooling fluid im mediately after the cooling fluid cooler. Such a thermostat device is used to regulate the temperature of the cooling fluid in the cooling system, and normally demonstrates a temperature- dependent activation element with a wax body. Depending on the temperature of the cooling fluid , the thermostat device leads cooling fluid that flows out from the combustion engine to a cooler in order there to be cooled , before the cooling fluid is returned to the combustion engine or directly back to the combustion engine without passage through the cooler.

In a cooling system of the type defined in the introduction, where cooling fluid flowing around the cooling circuit replaces the oil as retarding medium in the retarder, the retarder wi ll also become rapid , in the sense that the power that is transferred during re- tarder braking to the cooling fluid wil l be significantly higher than it is in the case of an oil circuit, even if the amount of heat that is transferred to the cooling fluid is the same in the two cases. It follows that there are here two parts in the cooling circuit, the retarder and the cooling fluid cooler, which are rapid and for which a short feedback ti me of a thermostat arrangement is required in order to suppress temperature oscillations in the cooli ng fluid and thus the load on the components that are included in the cooling ci rcuit, principally the cooling elements in the cooling fluid cooler. The retarder and the cooling fluid cooler are, how- ever, normally located at totally different locations in the cooling fluid system, which makes the desired placement of a thermostat arrangement in such a cooling system more difficult.

SU MMARY O F TH E I NVENTION

The object of the present invention is to provide a cooling system for a motor vehicle of the type defined in the introduction through which an advantageous function is achieved with respect to rapid and appropriate response to power that is transferred to the cool- ing fl uid, not only in the cooling fluid cooler, but also in the retarder.

This object is achieved according to the invention throug h ar- ranging in a cooling system of the type defined in the introduction a thermostat arrangement that comprises a second thermostat device arranged to receive cooling fluid in the first line from the retarder and to regulate the flow of cooling fluid to the cool ing fluid cooler and to the said third li ne depending on the tempera- ture of the cooling fluid received , and through designing the second thermostat device to open for flow in the cooling circuit of cooling fluid that arrives at it onwards to the cooling fluid cooler with effect from a second temperature that is at least 5 K hig her than a first temperature of cooling fluid arriving at the first ther- mostat device in the said pilot line from wh ich this first thermostat device is designed to open for flow of cooling fluid that arrives at this thermostat device from the retarder in the first line of the cool ing circuit onwards to the cooling fluid cooler. This means that during normal operation of the motor vehicle, i.e. in the case in which braking with the involvement of the hydrody- namic retarder does not occur, only the first thermostat device of the thermostat arrangement will control the temperature of the cooling fluid , since the temperature of the cooling fluid that ar- rives at the second thermostat device after passage throug h the combustion engine will not be able to reach the said second temperature and thus the second thermostat device will remain all the ti me in a condition in which it does not lead any cooling fluid onwards to the cooling fluid cooler. During sufficiently powerful retarder braking, in contrast, the temperature of the cooling fluid that arrives at the second thermostat device from the retarder will have been increased to a temperature above the said second temperature, such that the second thermostat device will then open for flow of the cooling fluid onwards to the cooling fluid cooler. Thus, the reaction of the thermostat arrangement to the retarder braking will be very rapid, due to the arrangement of the second thermostat device. It follows that an accurate regulation of the flow of cooling fluid is achieved with the cooling system according to the invention , with a short response ti me with re- spect to not only the retarder effect but also the cooling fluid effect.

According to one embodi ment of the invention, the second thermostat device is designed to open for flow of cooling fluid to the cooler with effect from a second temperature that is 5-20 K, 5- 1 5 K, 8-1 5 K or 8-1 2 K higher than the said first temperature. It has proved to be the case that a difference between the said second temperature and the said first temperature of approximately 1 0 K is, in many cases, suitable, since this is sufficient to ensure that the temperature of the cooling fluid that arrives at the second thermostat device after passage through the combustion engine during normal driving without retarder braking will not have been able to reach the said second temperature, since the increase in temperature of the cooling fluid from its passage through the combustion engine in normally a maximu m of approxi mately 1 0 K. I n certain types of engine and cooling system, this maximal rise in temperature could be lower, and in this case a smaller difference between the first and the second temperature can be accepted. According to a further embodiment of the invention, the said first temperature is 70-90 °C or 75-85 °C. This is a suitable temperature at which cooli ng fluid in the cooling circuit of a cooling system of this type should start to be led throug h a cooling fl uid cooler in order to emit heat to it.

According to a further embodiment of the invention, the said two thermostat devices are arranged in one and the same thermostat housing , which demonstrates an inlet channel that is common to the thermostat devices and that is connected throug h a first section of line of the first li ne to an outlet of the retarder, and the thermostat housing demonstrates at least one first outlet channel connected throug h a second section of line of the first line to the cooling fluid inlet of the cooling fluid cooler, and a second outlet channel connected to the said third line. The thermostat arrangement obtains in this way one single physical position while even so obtaining with respect to regulation the two positions that are required since the rapid parts with respect to effect (the retarder and the cooling fluid cooler) are located at different loca- tions in the cooling system. By collecting the two thermostat devices in a single thermostat housing, the placement of the thermostat arrangement is si mplified , and the requirement for space that it occupies is kept at a low level. Thus, it is advantageous that the thermostat housing demonstrate a single first outlet channel that is common to the two thermostat devices, which has an advantageous effect on the requirement for space that the thermostat arrangement has.

According to a further embodi ment of the invention , the said sec- ond thermostat device demonstrates a valve body that can be displaced between different positions for the regulation of the flow of cooling fluid from the said retarder to the cooling fl uid cooler and to the said third line, a temperature-dependent activation element and a displaceable part designed such that when it is displaced it carries with it the valve body, the activation element is arranged to influence the displacement position of the said part and in this way the valve body depending on the temperature of the cooling fluid that is received from the retarder, the valve body demonstrates a valve device in the form of a first plate element that is designed such that at a first end position of the valve body it is in contact with a second plate element that forms a valve seating between an inlet in the second thermostat device from the retarder and an outlet to the cooling fluid cooler such that throug h this contact it prevents cooling fluid from flow- ing throug h this thermostat device to the cooling fluid cooler, and that the fi rst plate element is arranged such that it can be displaced under the influence of the activation element away from the said position in which it is in contact with the second plate element in order to open a connection between the inlet of the second thermostat device and the outlet to the cooling fluid cooler.

According to a further embodiment of the invention, the said first thermostat device demonstrates a valve body that can be dis- placed between different positions for the regulation of the flow of cooling fluid from the said retarder to the cooling fluid cooler and to the said third line, a temperature-dependent activation element and a displaceable part designed such that when it is displaced it carries with it the valve body, the activation element is arranged to influence the displacement position of the said part and in this way the valve body depending on the temperature of the cooling fluid that is received throug h the pilot line, the valve body demonstrates a valve device i n the form of a first plate element that is designed such that at a first end position of the valve body it is in contact with a second plate element that forms a valve seating between an inlet in the first thermostat device from the retarder and an outlet to the cooling fluid cooler such that throug h this contact it prevents cooling fluid from flowing throug h this thermostat device to the cooling fluid cooler, and that the fi rst plate element is arranged such that it can be displaced under the influence of the activation element away from the said position in which it is in contact with the second plate element in order to open a connection between the inlet of the first thermostat device and the outlet to the cooling fluid cooler.

According to a further embodiment of the invention , the said valve body comprises a second valve device that can be received when at a second end position of the valve body in a valve seating in order to prevent in this way cooling fluid that arrives at the thermostat device in question from the retarder from flowing to the said third line. In this way, it can be prevented , when intense cooling of the cooling fluid is required , in particular during intense retarder braking , that cooling fluid that arrives at the thermostat device in question flows at this thermostat device on- wards to the cooling fluid inlet of the combustion engine without passing throug h the cooling fluid cooler.

According to a further embodi ment of the invention, the valve body can be displaced from the said first end position in the di- rection away from it under the influence of the activation ele- ment, and against the influence of the spring force of a spring means that acts upon the valve body. The activation element advantageously comprises a wax body. The invention concerns also a motor vehicle according to the corresponding attached clai ms.

Other advantages and advantageous distinctive features of the invention are made clear by the description below.

B RI E F D ESCRI PTION OF DRAWI NGS

The invention will be described in more detail below with the aid of embodiments presented as examples, with reference to the attached drawings, of which :

Figure 1 is a si mplified sketch ill ustrating in principle a cooling system according to one embodi ment of the invention , Figure 2 is a si mplified and partially cut-away view of a possi ble thermostat arrangement for the cooling system in Figure 1 ,

Figure 3 is a view that corresponds to Figure 2 of an alternative design of the thermostat arrangement, and

Figure 4 is a sketch corresponding to Figure 1 illustrating in principle a cooling system according to a second embodi ment of the invention. D ETAI LE D D ESCRI PTION OF EM BO D I M ENTS O F TH E I NVENTION

Figure 1 shows extremely schematically a cooling system 1 ac- cording to the present invention , intended for a motor vehicle. This cooling system comprises a cooling circuit 2 for the cool ing of a combustion engine 3 in the vehicle and a hydrodynamic retarder 4 arranged to exert a braking influence on a driving shaft of the motor vehicle by means of a cooling fluid that flows around the cooling circuit, preferably in the form of water, possibly with the addition of additives such as glycol, to depress the freezing point. The retarder 4 is located in the cooling circuit 2 i mmediately downstream of the combustion engine 3. A cooling fluid pu mp 5 is connected into the cooling circuit in order to circulate the cooling fluid in the cooling circuit. Furthermore, a cooling fluid cooler 6 for the cooling of the cooling fluid is connected into the cooling circuit. The cooling fluid cooler 6 comprises a cool ing fluid inlet 7 connected throug h the retarder 4 with a cooling fluid outlet 8 at the combustion engine throug h a first line 9 at the cooling circuit. The cooling fluid cooler 6 demonstrates further a cooling fluid outlet 1 0 that is connected to a cooling fluid inlet 1 1 at the combustion engine 3 through a second line 1 2 of the cooling circuit. The first line 9 is connected at a point 1 3 between the retarder and the cooling fluid cooler with the second line 1 2 through a third line 1 4 of the cooling circuit in order to allow through this recirculation of the cooling fluid from the retarder to the combustion engine without passage through the cooling fl uid cooler. A thermostat arrangement 1 5 (see also now Figure 2) demonstrates a first thermostat device 1 6 arranged to regulate the flow of cooling fluid to the cooling fluid cooler 6 and to the third l ine 1 4, depending on the temperature of the cooling fluid that is led into the thermostat device from a pilot line 1 7 that is a component of the cooling circuit, which pilot li ne is connected at its upstream end to the said second li ne 1 2.

The thermostat arrangement demonstrates further a second thermostat device 1 8 arranged to receive cooling fluid in the first line 9 from the retarder 4 and to regulate the flow of cooling fl uid to the cooling fluid cooler 6 and to the said third line 1 4, depending on the temperature of the cooling fluid that has been received .

The two thermostat devices are arranged in one and the same thermostat housing 1 9 that demonstrates an inlet channel 20 that is common to the thermostat devices and that is connected through a first section of line 21 of the first line 9 to an outlet 22 at the retarder. The thermostat housing demonstrates further a first outlet channel 23 connected through a second section of l ine 24 of the first line 9 to the cooling fluid inlet 7 of the cooling fluid cooler and two further outlet channels 25, 26 connected to the said third line 1 4. The first thermostat device 1 6 demonstrates a valve body 27 that can be displaced in the thermostat housing 1 9 between different positions for the regulation of the flow of cooling fluid from the said retarder through the inlet channel 20 to the first outlet channel 23 and thus to the cooling fl uid cooler and to the said thi rd line 1 4. The thermostat device demonstrates a temperature-dependent activation element 28 that comprises a wax body 29 arranged to be met by the flow of cooling fluid in the pilot line 1 7 and a part 30 that can be displaced arranged such that during displacement thereof it takes with it the valve body. The activation element is arranged to influence the displacement position of the part 30 and thus the valve body, depending on the temperature of the cooling fluid that is received through the pilot line.

The valve body 27 demonstrates a valve means 31 in the form of a first plate element that is designed such that at a first end position of the valve body it is in contact with a second plate element 32 that forms a valve seating between an inlet in the first thermostat device connected to the inlet channel 20 and an outlet connected to the first outlet channel 23 in order through this con- tact to prevent cooling fl uid from flowing through this thermostat device to the cooling fluid cooler. The first plate element 31 is arranged such that it can be displaced under the influence of the activation element away from the said position of contact with the second plate element 32 in order to open a connection between the inlet of the first thermostat device and the outlet to the cooling fluid cooler with effect from a fi rst temperature of cooling fluid that arrives at the wax body 29 in the pilot line 1 7. It is appropriate that this first temperature be approximately +80 °C. The valve body 27 demonstrates also a second valve means 33 that can be received at a second end position of the valve body into a second valve seating 34 in order in this way to prevent cooling fluid that arrives at the first thermostat device from the retarder through the inlet channel 20 from flowing to the third line 1 4. The second thermostat device 1 8 is designed in a manner si milar to the first with respect to the valve body 35 with a valve means in the form of a first plate element 36 that is designed such that at a first end position of the valve body it is in contact with a second plate element 37 that forms a valve seating between an inlet in the second thermostat device connected to the i nlet channel 20 and an outlet connected to the first outlet channel 23. The second thermostat device demonstrates an activation element 38 arranged to influence the displacement position of the first plate element 36 depending on the temperature of the cooling fluid that is received from the retarder through the inlet channel 20 and it demonstrates for this reason a wax body 39 arranged to be met by this cooling fluid. Thus, the activation element 38 at the second thermostat device 1 8 is designed such that it influences throug h a part 42 that can be displaced the first plate element 36 away from the contact against the second plate element 37 in order to open for flow of cooling fluid that arrives there in the cooling circuit onwards to the cooling fluid cooler with effect from a second temperature that it at least 5 K hig her than the said first temperature. It is preferred that this second temperature be approxi mately 1 0 K hig her than the first temperature.

Also the second thermostat device demonstrates a second valve means 40 that can be received at a second end position of the valve body 35 into a second valve seating 41 in order in this way to prevent cooling fluid that arrives at the second thermostat device from the retarder through the inlet channel 20 from flowing to the third line 1 4. The valve bodies of the two thermostat de- vices are i nfluenced by the spring force of spring means 43, 44 towards the position that prevents flow of cooling fluid to the cooling fluid cooler 6.

The function of the cooling fluid system that has just been de- scribed is as follows: During normal driving each thermostat device will close the relevant connection between the inlet channel 20 and the outlet channel 23 to the cooling fluid cooler as long as the temperature of the cooling fluid that arrives at the first thermostat device 1 6 in the pilot line 1 7 lies under the said first tem- perature. This means that the cooling fluid will flow from the thermostat arrangement throug h the third line 1 4 to the cooling fluid inlet 1 1 of the combustion engine 1 0. When the combustion engine has heated the cooling fluid in the cooling circuit by a sufficient amount that the cooling fluid that arrives at the wax body 29 in the pilot line 1 7 has a temperature that exceeds the said first temperature, for example +80 °C, then the first thermostat device 1 6 wi ll open for flow of cooling fluid that arrives through the inlet channel 20 onwards to the outlet channel 23 and thus to the cooling fluid cooler. At the same time a part of the cooling fluid will be returned through the third line 1 4 directly to the combustion engine 3 without passing throug h the cooling fluid cooler 6. The higher the temperature of the cooling fluid in the pilot l ine 1 7 becomes, the greater will be the fraction of the cooling fl uid that arrives at the thermostat arrangement through the inlet channel 20 that is led onwards to the cooling fluid cooler. This acts, of course, in a direction to reduce the temperature of the cooling fluid in the pilot line, and this regulation wil l ensure that the temperature of the cooling fluid in the pilot line will be maintained close to the said first temperature, preferably to oscillate a maximal amount of 5 K below and above this temperature. In any case, the temperature of the cooling fluid that arrives at the thermostat arrangement throug h the inlet channel 20 will in this way not reach the said second temperature as long as the vehicle is not braked with the aid of the retarder 4.

During relatively hard retarder braking , on the other hand, the temperature of the cooling fluid that flows from the retarder will rise considerably and rapidly, and it wil l exceed the said second temperature, such that the second thermostat device will then i mmediately open a connection between the inlet channel 20 and the outlet channel 23 in order to lead cooling fluid to the cooling fluid cooler 6.

Figure 3 illustrates an alternative design of a thermostat ar- rangement arranged in a cooling circuit according to Figure 1 , which differs from the arrangement in Figure 2 in that the second thermostat device 2 does not demonstrate a second valve means and has only one outlet channel 26 to the third line 1 4 exists. The function of this thermostat arrangement is otherwise the same as that of the one illustrated in Figure 2.

Figure 4 illustrates a cooling system according to a second embodi ment of the invention that differs from the one shown in Figure 1 in that the two thermostat devices 1 6" and 1 8" are sepa- rated from each other, i.e. they are not arranged in the same thermostat housing . These thermostat devices, however, act together in the same functional manner as the thermostat devices according to Figures 2 and 3. It should , however, usually be advantageous to arrange the two thermostat devices next to each other in one and the same thermostat housing. The various com- ponents of this cooling system have the same reference numbers as the corresponding components in the cooling system according to Figure 1 , with the addition of a double pri me mark, ". The invention is, naturally, not in any way li mited to the embodiments described above: a nu mber of possibilities for modifications of it should be obvious for one skilled in the arts, without for this reason deviating from the scope of the i nvention as it has been defined in the attached clai ms.

The two thermostat devices, for example, may very well exchange places such that the first thermostat device is physically arranged in the cooling circuit somewhat closer to the retarder than the second thermostat device.