ARRANGEMENT IN A FLUID HEATING SYSTEM FOR VEHICLES

Abstract: The present invention relates to an arrangement in a closed, pressurised, fluid heating system (1) for vehicles with an onboard heat source (2). A feed-line (3) and a return-line (4) are connected to the onboard heat source (2). At least two climate-circuits (5, 6) with heat-exchanger means are arranged for heating of different parts of the vehicle interior. A bypass-line and valve means are arranged to selectively permit fluid flow between the feed-line (3) and the return-line (4). An inlet side of each respective climate-circuit (5, 6) is connected to a first output of a respective three-way valve (7, 8), whose input is connected to the feed-line (3). An inlet side of a respective bypass-line (10, 11) is connected to a second output of the same three-way valve. An outlet side of each climate-circuit (5, 6) and each bypass-line (10, 11) is connected to the return-line (4). Each respective three-way valve (7, 8) is arranged to selectively apportion the fluid flow between the respective climate-circuit (5, 6) and the respective bypass-line (10, 11) connected thereto.

Description: Arrangement in a fluid heating system for vehicles The present invention relates to an arrangement in a closed, pressurised, fluid heating system for vehicles, preferably buses, comprising an onboard heat source, a feed-line and a return-line connected to the onboard heat source and at least two climate- circuits with heat-exchanger means arranged for heating of different parts of the vehicle interior, a bypass-line and valve means arranged to selectively permit fluid flow between the feed-line and the return-line through the climate circuits and/or through the bypass-line, in accordance with the preamble of claim 1. In known fluid heating systems, e.g. in a bus comprising an internal combustion engine, the cooling system of which is used as the onboard heat source, it is usual to arrange a single bypass-line for the whole heating system. This bypass-line is usually installed in one of the climate-circuits by way of a three-way valve so that either the bypass-line or the climate-circuit receives the fluid flow. With such a bypass-line closed, all the pressure and resulting fluid flow in the system is supplied to the open climate-circuits. When only one bypass-line is used, it must be capable of passing a system specific minimum required fluid flow, for example as required by an auxiliary heater. As a consequence thereof the other climate-circuits will, when open, only operate at a reduced pressure when the bypass-line is open. This pressure drop will be considerable as the resistance to fluid flow through the bypass-line should be kept low. A system of the aforementioned kind is also prone to so called water-hammer, which can occur when the full fluid flow is halted and re-routed via the single bypass-line. As mentioned above, it is also known to use fluid heating systems in buses, which are equipped with an auxiliary fluid heater, often a combustion type heater. Such auxiliary fluid heaters are used in order to preheat the engine and in order to supply supplementary heat when the engine alone cannot fulfil the required heating capacity. Already today most buses and coaches for cold climates are equipped with auxiliary fluid heaters. Auxiliary fluid heaters will probably be even more common in the future, as today there is a tendency towards engines with higher efficiency .and resulting lower coolant temperatures in winter conditions. Auxiliary fluid heaters render an increased fluid temperature and thereby sufficient heating in winter conditions when the engine alone gives up less heat than required for the heating system. Vehicle fluid heating systems always contain gases. These gases may be combustion gas entering the system through un-tight seals in the internal combustion engine as well as outside air, infiltrating through connections and hoses within the system. With known systems the problem of gas accumulation in so called air pockets is often encountered, leading to a restriction or an obstruction of the fluid flow and hence affecting the overall performance of the heating system. In addition it is not unusual that so called thermo-syphone occurs in the known heating systems. Thermo-syphone can cause unwanted fluid flows through the system and thereby locally result in hot spots, disturbing the heat balance, resulting in an uneven appreciation of the interior climate in for example a passenger space of a vehicle, such as a bus. The object of the present invention is to provide an arrangement, which can eliminate or at least reduce the explained disadvantages of the known fluid heating systems. This object is achieved according to the invention in that said fluid heating system comprises the characterising features according to claim 1. Preferred embodiments of the present invention also comprise one or more of the characterising features according to the dependent claims. The inventive fluid heating system always provides for a system specific minimum required fluid flow, without such considerable pressure drops in the climate-circuits as is common in the state of the art heating systems using one single bypass-line. This minimum required fluid flow constitutes an hydraulic protection of one or more elements in the system, which requires a maintained guaranteed minimum fluid flow. The inventive system always provides for a minimum of at least two open circuits/lines. Therefore, each bypass-line of the inventive fluid heating system need only to be capable of receiving part of the specific minimum required fluid flow and can thus have higher resistance to fluid flow than the single prior art bypass-line. Also, due to the avoidance of the considerable pressure drops associated with the single bypass of the prior art systems, the inventive system provides for higher water speeds, which can better carry gas-bubbles towards areas where gas can be extracted. As in the inventive system the full fluid flow is split over at least two circuits/lines, the full fluid flow will under no conditions flow over one circuit. This results in a reduced risk for so called water-hammer, as only a limited fluid flow is re-routed when a valve changes its position. The physical arrangement of the elements of the inventive system also helps in avoiding accumulation of air in the components of the heating system and in avoiding the occurrence of thermo-syphone. Preferred embodiments of the invention will be further explained below with reference to the enclosed drawings, in which: Fig 1 shows a fluid heating system according to a first embodiment of the present invention. Fig 2 shows a fluid heating system with an auxiliary fluid heater according to a second embodiment of the present invention. Fig 3 schematically, in perspective, shows the physical arrangement of the valves and the connections thereto. With reference to fig 1 , 1 denotes a closed, pressurised, fluid heating system for vehicles in accordance with a first embodiment of the present invention. The fluid heating system is connected to an onboard heat source 2, in this example described as the cooling system of an internal combustion engine of the vehicle. In order to render the description of the present invention more clear, elements normally associated with these kinds of fluid heating systems and the engine cooling system such as filters, air-extractors, actuators of valves, expansion-tanks, etc. are left out. It will however be clear to the person skilled in the art that such elements can be included in the fluid heating system and engine cooling system according to this description. The inventive fluid heating system 1 also comprises a feed-line 3 and a return-line 4 connected to the engine cooling system 2. Further, the fluid heating system 1 includes two climate-circuits 5, 6 with heat-exchanger means arranged for heating of different parts of the vehicle interior, one of which 6, through the physical arrangement of its supply lines, can be arranged to have a higher priority than the other. This is achieved through connecting the input of the three-way valve 7 of the climate-circuit 6 with higher priority directly in-line with the feed-line 3 and the input of the three-way valve 8 of the other climate-circuit 5 to the feed-line 3 via a branch-line 9, which is connected to the feed-line 3 at an angle, making it harder for the fluid flow to pass through the branch-line 9 than straight through the feed-line 3 and on to the three-way valve 7 of the climate-circuit 6 with higher priority. Each climate-circuit 5, 6 can contain one heating element only or a combination of heating elements, such as heating elements with blowers, and so called heating plinths. An inlet side of each respective climate-circuit 5, 6 is connected to a first output of a respective three-way valve 7, 8, whose input is connected to the feed-line 3. Between the input of each respective three-way valve 7, 8 and the corresponding feed-line 3, 9 as well as between the first output and the corresponding respective climate-circuit 5, 6 is connected a pipe section which slope downwards with a system specific vertical height difference Δh before continuing to whichever height position is used for the respective lines and circuits (see fig. 3). An inlet side of a respective bypass-line 10, 11 is connected to a second output of the same three-way valve 7, 8. Each respective bypass-linelO, 11 contains a throttle 12, 13, either integral with the three-way valve or at an arbitrary position between the three-way valve and the return-line 4. The permitted flow through each respective bypass-line 10, 11 is reduced in comparison to a system specific minimum required fluid flow, so that the sum of the permitted fluid flows through all bypass-lines at least corresponds to the system specific minimum required fluid flow. An outlet side of each respective climate-circuit and each respective bypass-line is connected to the return-line 4 thus closing the system. The connections between the return-line 4 and the outlet side of each respective climate-circuit are carried out with pipe sections which slope downwards with a system specific vertical height difference Δh, of the previously mentioned type (see fig. 3). The connection of the respective pipe section to the return- line being located above the connection of the same pipe section to the climate-circuit, when the vehicle is in its normal essentially horizontal position. Each respective three-way valve 7, 8 is arranged to selectively apportion the fluid flow between the respective climate-circuit 5, 6 and the respective bypass-line 10, 11 connected thereto. This can be realised through permitting fluid flow through either the respective climate-circuit 5, 6 or the respective bypass-line 10, 11 connected thereto or through modulating the portions of the fluid flow allowed to pass through the climate-circuit and the bypass-line. The increased demand with respect to temperature stability within vehicles has led to the application of short cycling valves. Each valve is then controlled by means of a control-device (not shown) producing a pulsating control signal in accordance with the desired fluid flow through the respective climate-circuit connected thereto. However, modulating valves can also be used in the proposed system. Each respective modulating three-way valve is then controlled to apportion the fluid flow through the respective climate-circuit and the respective bypass-line connected thereto by means of a control-device producing a modulating control signal in accordance with the desired fluid flow through the climate-circuit connected thereto. Fig 2 shows a fluid heating system 1 according to a second embodiment of the present invention. The onboard heat source, delimited by the dotted broken line, in addition to the elements of the fluid heating system according to the first embodiment, in accordance with fig 1, also includes an auxiliary fluid heater 14, e.g. auxiliary water heater, and the engine 19 and some of the elements of the engine cooling system, such as the engine water pump 15, the thermostat valve 16, the engine coolant bypass-line 17 and the engine coolant radiator 18. The thermostat valve 16 opens the engine coolant bypass-line 17, which guarantees the minimum required coolant flow over the engine 19 when the engine is relatively cold, and the engine coolant radiator 18 is not in use. The feed-line 3 for the pressurised fluid passes the auxiliary fluid heater 14 where, if required, the fluid temperature and thereby the heating capacity can be raised in a per se known manner. The auxiliary fluid heater can be a combustion type heater, an electrical heater or any other kind of suitable heater. The auxiliary fluid heater 14 co- operates with a circulation pump 20. In an auxiliary fluid heater, during burning time and some minutes afters shut down, a considerable minimum fluid flow must be maintained in order to cool down the burner. Therefore, when the thermostatic controls of the control-device shuts down the climate-circuits 5, 6, the bypass-lines 10, 1 lwill maintain the required fluid flow. It is also possible to use the inventive heating system to guarantee the minimum required coolant flow over the engine 19. As the inventive heating system 1 always has at least two open circuits, where the prior art systems has only one, and the inventive heating system is less sensitive to water-hammer caused by re-routing of important fluid flows, the heating system 1 may be designed to allow for less resistance to fluid flow over the heating system. Less resistance to fluid flow in the inventive heating system makes it possible to reduce the dimensions of the engine coolant bypass-line 17, and possibly in certain applications also to eliminate the engine coolant bypass-line 17. This would result in higher fluid flows into the heating system during winter conditions when the thermostat valve 16 is normally closed. Fig 3 schematically shows how the valves 7, 8 and the connections thereto should be arranged in order to provide the advantageous properties of the proposed system, especially with regard to air extraction and the prevention of thermo-syphone. Through arranging the three-way valves 7, 8 so that the first output of each respective three-way valve is connected to the respective climate-circuit 5, 6 via pipe sections 21, 22 which slope downwards with a system specific vertical height difference Δh,, Δh 2 before allowing the lines to the respective climate-circuit 5, 6 to continue to whichever height position is used for them, the occurrence of thermo-syphone can be avoided. In the same way, the return-line 4 is connected to the respective climate- circuit 5, 6 via pipe sections 23, 24 which slope downwards with a system specific vertical height difference Δh 3 , Δh 4 . Ah,, Δh 2 Δh 3 and Δh 4 are system specific and need not be the same. The particular height difference Δh can for instance be about 10 times the diameter of the associated tube in order to provide the desired properties. Further, by this arrangement, when the vehicle is in its normally essentially horizontal position, air or gas in the system will automatically find its way to the bypass-lines 10, 11 and the return-line 4, where it will be carried to areas where air can be extracted and routed to an expansion tank. Although the invention has been described in relation to buses comprising an internal combustion engine, it can also equally advantageously be applied to heating systems for other vehicles, where there is a need for fluid heating systems with two or more climate-circuits, e.g. in trolley buses, motorcars with two-zones front heater and/or motor-homes. It is also obvious to the person skilled in the art that the inventive heating system 1 can be used for the most divers applications, such as in ships, trains and other transport means. The invention is obviously not limited to the embodiments described above by way of examples, but lends its self to modifications within the scope of the idea of the invention defined in the appended claims.

Claims: Claims 1. Arrangement in a closed, pressurised, fluid heating system (1) for vehicles, preferably buses, comprising an onboard heat source (2), a feed-line (3) and a return-line (4) connected to the onboard heat source (2) and at least two climate-circuits (5, 6) with heat-exchanger means arranged for heating of different parts of the vehicle interior, a bypass-line and valve means arranged to selectively permit fluid flow between the feed-line (3) and the return-line (4) through the climate circuits and/or through the bypass-line, characterised in that an inlet side of each respective climate-circuit (5, 6) is connected to a first output of a respective three-way valve (7, 8), whose input is connected to the feed-line (3), and in that an inlet side of a respective bypass-line (10, 11) is connected to a second output of the same three-way valve, and in that an outlet side of each respective climate-circuit (5, 6) and each respective bypass-line (10, 11) is connected to the return-line (4), and in that each respective three- way valve (7, 8) is arranged to selectively apportion the fluid flow between the respective climate-circuit and the respective bypass-line connected thereto. 2. Arrangement according to claim 1, characterised in that each respective bypass-line (10,11) contains a throttle (12, 13) either integral with the three- way valve (7, 8) or at an arbitrary position between the three-way valve and the return-line (4). 3. Arrangement according to claim 2, characterised in that the permitted fluid flow through each respective bypass-line is reduced in comparison to a system specific minimum required fluid flow so that the sum of the permitted fluid flows through all bypass-lines (10, 11) at least corresponds to the system specific minimum required fluid flow. 4. Arrangement according to any of the preceding claims, characterised in that between the first output of each respective three-way valve (7, 8) and the corresponding respective climate-circuit (5, 6) and between the return-line (4) and each respective climate-circuit (5, 6) is connected a pipe section which slope downwards with a system specific vertical height difference Δh before continuing to whichever height position is used for the respective lines and circuits. 8 5. Arrangement according to any of the preceding claims, characterised in that the second output of each respective three-way valve (7, 8) is located above the input and the first output of the same three-way valve, when the vehicle is in its normally essentially horizontal position. 6. Arrangement according to any of the preceding claims, characterised in that at least one of the respective three-way valves (7, 8) is arranged to selectively permit fluid flow through either the respective climate-circuit (5, 6) or the respective bypass-line (10, 11) connected thereto. 7. Arrangement according to claim 6, characterised in that at least one of the respective three-way valves (7, 8) is arranged to be controlled to selectively permit fluid flow through either the climate-circuit (5, 6) or the bypass-line (10, 11) connected thereto by means of a control-device producing a pulsating control signal in accordance with the desired fluid flow through the climate- circuit connected thereto. 8. Arrangement according to any of claims 1 to 5, characterised in that at least one of the respective three-way valves (7, 8) is arranged to be controlled to apportion the fluid flow through the respective climate-circuit (5, 6) and the respective bypass-line (10, 11) connected thereto by means of a control-device producing a modulating control signal in accordance with the desired fluid flow through the climate-circuit connected thereto. 9. Arrangement according to any of the preceding claims, characterised in that the feed-line (3) for the pressurised fluid passes an auxiliary fluid heater (14) by which, if required, the fluid temperature and thereby the heating capacity can be raised in a per se known manner. 10. Arrangement according to any of the preceding claims, characterised in that the input of the three-way valve (7) of one climate-circuit (6) is connected directly in-line with the feed- line (3) and the input of the three-way valve (8) of each other respective climate-circuit (5) is connected to the feed-line (3) via a branch-line (9), which is connected to the feed-line (3) at an angle.

Inventors: KARLSSON TOMAS, KARLSSON, TOMAS
Applicants: KARLSSON TOMAS, UWE VERKEN AB, KARLSSON, TOMAS
Application year: 1999
Main classification: B60H1
IPC codes: B60H1