EP2150433A1

EP2150433A1 - Heating system for use in a vehicle

Info

Publication number: EP2150433A1
Application number: EP08825861A
Authority: EP
Inventors: Anders Folkesson; Christian Gravesen; Lars Overgaard
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2007-05-15
Filing date: 2008-05-14
Publication date: 2010-02-10
Also published as: WO2008147305A1; SE531113C2; SE0701183L; EP2150433A4

Abstract

The present invention relates to a heating system for a vehicle, the vehicle comprising an energy converter, a first cooling medium circuit for carrying a first cooling medium, said cooling medium of said first cooling medium circuit being arranged to absorb and/or dissipate heat to and/or from said energy converter, and a second cooling medium circuit for carrying a second cooling medium, wherein said system includes resistor means arranged to be connected to at least one source of electrical power and arranged in thermal communication with cooling medium of said first cooling circuit for, at least in a heating mode, heating the said first cooling medium by means of heat dissipated when connected to said electrical power source. The said resistor means is further being arranged to be in thermal communication with cooling medium of said second cooling medium circuit for, at least in a heating mode, heating the said second cooling medium, and wherein said cooling medium of said second cooling medium circuit is arranged to dissipate heat to a passenger compartment of said vehicle. The invention also relates to a vehicle.

Description

HEATING SYSTEM FOR USE IN A VEHICLE FIELD OF THE INVENTION

The present invention relates to a heating system for use in a vehicle, and in particular the present invention relates to a heating system wherein a resistor is used for dissipation of heat to a cooling medium in a cooling path according to the preamble of claim 1. The present invention also relates to a vehicle brake system according to claim 19 and a vehicle according to claim 20. BACKGROUND OF THE INVENTION

The current discussions regarding climate changes and the effects thereof, together with the increase in fuel costs in the past decade has stimulated the research and development of alternative fuel vehicles, as well as of hybrid vehicles. Also, there is ongoing research with an aim to improve fuel efficiency of conventional combustion engine vehicles. In particular, there is an anxiety about the effects of exhaust and noise emissions from vehicles in urban areas.

With regard to vehicles in general, and heavy vehicles in particular, vehicle use in urban areas often involves a plurality of frequent starts and stops during a journey, with corresponding fuel consuming accelerations and, from an engine point of view, kinetic energy wasting decelerations. This has as result that a great deal of energy is consumed in order to accelerate the vehicle to a "cruising" speed, only to be consumed as braking power almost immediately, or only after a short while. Such scenarios are particularly common in areas having a high traffic density, and/or a plurality of traffic lights or, with regard to city buses, frequent bus stops. Among the ongoing research projects to reduce energy (fuel) consumption according to the above, there is extensive research in the field of hybrid vehicles, aiming at relieving the negative effects of driving conditions of the above kind.

A hybrid vehicle is a vehicle that uses two or more power and/or fuel sources. A common type of hybrid vehicles is hybrid-electrical vehicles, which include a power generating source such as an internal combustion engine or fuel cells, and one or more electric motors, wherein the said one or more electric motors are used as propulsion motor (s).

The use of an electric motor as propulsion motor has the advantage that in certain operation conditions, such as when using the electric motor for braking purposes, e.g., in order to decelerate the vehicle or maintain a constant speed in a downhill grade, the electric motor cease acting as a motor and, instead, becomes an alternator which regenerates electrical energy for feed-back to the electric system of the vehicle. This is known as regenerative braking and has the advantage that, apart from being used to reduce wear of mechanical braking system components, the regenerated energy can be used to charge electric energy storage means for use in a subsequent acceleration and/or for powering other electrical equipments .

However, the storage capacity of the electric storage means are often limited, e.g. due to weight and/or space limitations, and, therefore, the electric storage means can become fully loaded during the deceleration, in particular when going downhill for a longer period of time, with the result that excess energy is produced, which can not be taken care of in a favourable manner, and thereby limiting the advantages of the regenerative braking. Consequently, although the regenerative braking is capable of storing some of the electric energy produced during braking for later use, there is still, especially during certain driving conditions, a need for an improved system for reusing energy regenerated in the system.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a system that solves the above mentioned problem. This object is achieved by a system according to the characterising portion of claim 1.

According to the present invention, it is provided a heating system for a vehicle, the vehicle comprising an energy converter, a first cooling medium circuit for carrying a first cooling medium, said cooling medium of said first cooling medium circuit being arranged to absorb and/or dissipate heat to and/or from said energy converter, and a second cooling medium circuit for carrying a second cooling medium, wherein said system includes resistor means arranged to be connected to at least one source of electrical power and arranged in thermal communication with cooling medium of said first cooling circuit for, at least in a heating mode, heating the said first cooling medium by means of heat dissipated when connected to said electrical power source. The said resistor means is further being arranged to be in thermal communication with cooling medium of said second cooling medium circuit for, at least in a heating mode, heating the said second cooling medium, and wherein said cooling medium of said second cooling medium circuit is arranged to dissipate heat to a passenger compartment of said vehicle.

This has the advantage that the energy converter can be rapidly heated to its normal working temperature. If, for example, the energy converter is an internal combustion engine, the present invention allows that the normal working temperature of the engine can be reached in a shorter period of time as compared to the prior art, which, in turn, has the advantage that emissions during cold starts can be reduced. If the energy converter is a fuel cell system, the heating of the fuel cell system to a suitable working temperature can reduce losses in the chemical reaction and increase lifetime. Further, the invention also has the advantage that high- temperature cooling medium can be circulated, simultaneously and/or sequentially through the heater element (s) in a passenger compartment, such as a driver's cabin in a lorry or passenger cabin of a bus, or a storage compartment, to allow that the passenger compartment (storage compartment) to rapidly be heated to a comfortable (suitable) temperature. In one embodiment the said first cooling medium circuit and the said second cooling medium circuit consist of a single cooling medium circuit. In one embodiment of the present invention, the electrical brake is used as secondary brake having similar to conventional secondary brakes such as retarders . This is accomplished by using a high-power resistor capable of dissipating high electrical powers as heat. This has the advantage that this "electrical" braking system can replace the secondary brake system, e.g. a retarder system, that in certain jurisdictions are required in addition to the conventional mechanical braking system (e.g., brake discs and pads) , since the mechanical brake system can be overheated, and thereby malfunction, in extreme braking conditions.

The invention also relates to a vehicle.

Further characteristics of the present invention, and advantages thereof, will be evident from the following detailed description of preferred embodiments and appended drawings, which are given by way of example only, and are not to be construed as limiting in any way.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 discloses a power train of a hybrid vehicle in which the invention advantageously can be utilized.

Fig. 2 discloses a vehicle cooling system with resistor use according to the invention. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Fig. 1 discloses a power train of a hybrid vehicle according to a first exemplary embodiment of the present invention. There are hybrid vehicles of various kinds, and the disclosed vehicle is a series hybrid vehicle. Series hybrid vehicles often comprise an energy converter in form of an internal combustion engine, which actuates a generator, which in turn supplies current to an electric motor that powers vehicle's drive wheels. Apart from series hybrid vehicles, there are parallel hybrid vehicles, which simultaneously can transmit power to the drive wheels from two separate sources, e.g., an internal combustion engine and an electric motor. There also exist series-parallel hybrids having the flexibility to operate in either series or parallel mode. Although the present invention is exemplified for a series hybrid vehicle, the invention is equally applicable in other kinds of vehicles .

The series hybrid vehicle power train in fig.l comprises an internal combustion engine 101, such as a diesel engine, which is power supplied from a fuel tank 102. Instead of being, in a conventional manner, connected to a transmission, the output shaft of the combustion engine is connected to a generator 103, which is used to generate electrical power from the mechanical power provided by the combustion engine 101. Consequently, the conventional use of gearbox and optional frictional element (clutch) is omitted. Instead, the half shafts 104, 105, which in a conventional system are propelled by a propeller shaft via an axle gear, are propelled by an electric motor 106, the outgoing shaft of which being connected to the half shafts 104, 105 by means of an axle gear 107. The axle gear can, in principle, consist of a conventional differential, which has the advantage that no intermediate gears are necessary, thereby resulting in a less complicated as well as cost and energy efficient transmission. This is possible due to the fact that an electric motor by means of suitable electronics can be speed controlled with a maintained high torque, wherein the maximum speed of the vehicle being determined by the maximum speed of the electric motor 106 and axle gear ratio.

The power supply to the electrical motor 106 can, for example, constitute a three-phase power supply, i.e., the motor being a three-phase motor. However, the speed control requires that the frequency of the AC voltage fed to the motor can be varied, since the speed of the motor is directly proportional to this frequency.

In order to provide the motor 106 with a variable frequency three-phase power supply, a power electronics arrangement 108 is used, which also is used for a plurality of other functions, as will be disclosed below. The power electronics arrangement 108 is necessary since even though the generator 103 can be used to generate a three-phase output voltage, the generated frequency will depend on the speed of the combustion engine, which, in turn, will depend on the current power demand and not the current speed of the vehicle. Also, the engine 101 can be arranged to work at a suitable working point, e.g. at a constant speed, with varying load, whereby the generator 103 will generate three-phase power supply of a constant frequency. The generator 103 generated voltage is provided to the power electronics arrangement 108 wherein it is rectified and thereby providing a direct voltage. Depending on the generator used, this voltage can have a rather high amplitude, e.g., 500-700 V, which then is used by an inverter arrangement, for example consisting of a plurality of IGBT (Insulated Gate Bipolar Transistor) transistors, which by appropriate switching, can provide a three-phase voltage of a desired and variable frequency for driving the electric motor 106 and thereby drive wheels. In this way, the vehicle speed can be controlled from zero to top speed by controlling the frequency supplied to the motor 106 from 0 Hz to a frequency resulting in the top speed of the vehicle. Further, since a vehicle usually comprises a plurality of direct current applications and, furthermore, electrical energy storage means generally are of a direct-current voltage type, the rectified voltage can be used, with down conversion where appropriate, for power supplying such functions. For example, the direct- current voltage generated in the power electronics arrangement 108 can be converted to, e.g., 24 V (or 12 V or 48V) for conventional 24 V (12V, 48V) applications, such as cooling fans or conventional vehicle electronics in general. Furthermore, the direct-current voltage is used to charge electric energy storage means which, in the disclosed example, can consist of, e.g., 24V batteries for conventional use, but also a high voltage supercapacitor module 109. As is appreciated by a person skilled in the art, a supercapacitor module 109 could, instead, consist of one or more high voltage batteries. The supercapacitor module 109 is preferably charged directly by the rectified voltage without down conversion, and has such high voltage that the motor 106, even if only for a short period of time, can be solely power supplied by the supercapacitor module. Conversely, if the vehicle is braking, e.g. in order to decelerate or to maintain constant speed when going downhill, the motor 106 will act as a generator, that is, the back electromotive force generated by the motor 106 when applying a braking force on the half shafts 104, 105 will induce a three-phase voltage in the stator windings of the motor 106, and thereby regenerate electrical power, which, in turn, also can be rectified to the intermediate voltage of the power electronics arrangement 108 in a manner known per se and thereby charge the supercapacitor module (or, when used, batteries) 109 with the regenerated power. By means of suitable down conversion, this regenerated power can, of course, also be used to charge, e.g., 24 V batteries of the vehicle. Advantageously, the supercapacitor module is prioritized as power supply to the motor 106, since as soon as the capacitor module has been drained from energy, it is capable of being recharged by, and thereby reuse regenerated energy from the electric motor 106. This means that the hybrid system shows most to advantage when the vehicle frequently is performing alternating acceleration and deceleration (braking) manoeuvres, since in such situations the difference between using regenerated energy as power source instead of a conventional internal combustion engine system is the largest. Apart from the above fuel-saving advantages of a hybrid vehicle of the kind disclosed in fig. 1, the invention according to one embodiment has the advantage that due to the fact that the electric motor 106 can be used to apply high braking power, use of a high-power resistor according to the present invention enables that the combination of electric motor and resistor can be used as a braking system capable of dissipating high powers. This has the advantage that this "electrical" braking system can replace other kinds of secondary braking systems that often are required with regard to heavy vehicles. For example, in some jurisdictions there exist governmental requirements stating that heavy vehicles must comprise at least one secondary braking system in addition to the conventional mechanical braking system (e.g., brake discs and pads) . Furthermore, this secondary braking system is often required to have such capacity that the vehicle by means of the secondary brake system only can be kept at a predetermined maximum speed for a predetermined period of time in a downhill stretch having a predetermined slope. Consequently, the secondary brake system, which often consists of a retarder, can, according to one embodiment of the invention, be replaced by the electrical brake, with savings in system complexity, weight and cost as result. If a hybrid system, such as the one disclosed in fig. 1, is used as secondary braking system, the braking power generated by the electric motor 106, and thereby the generated electric power induced in the stator windings of the motor 106, can, as mentioned, reach rather high powers, for example in the order of 50-60 KW. This, in turn, means that if the vehicle is in a downhill slope of some length, the supercapacitor module 109 will rather quickly be fully charged, which means that the regenerated energy must somehow be dissipated in other ways. This is accomplished by a resistor unit 110 having a high power capacity, which simply converts the generated electric power to heat, which, for example, can be cooled off by a radiator .

Previously, such resistor units 110 have been used to dissipate power generated during braking, but only to a limited extent, and therefore not as in the inventive concept of the invention.

According to the present invention, however, the resistor unit 110 is, in addition, or alternatively, used for other applications, and one exemplary embodiment will be described with reference to fig. 2, in which a part of a vehicle cooling system 200 is disclosed, and wherein the use of a resistor unit 110 according to the invention will be described more in detail.

In the figure the resistor 110, which is a high voltage resistor and preferably adapted to the rectified intermediate voltage of the power electronics arrangement 108, is arranged in a heat dissipation relationship with cooling medium in a cooling medium circuit 201. For example, the resistor 110 can be in the shape of a coil which is simply immersed into the cooling medium for allowing an efficient heat exchange. The circulation of the cooling medium in the cooling medium circuit is controlled by means of a circulation pump 202, such as an electric water pump, and when the cooling medium is circulated past the resistor, a controllable amount of heat can be dissipated to the cooling medium. The amount of heat dissipated to the cooling medium can, for example, be controlled by the flow of the cooling medium past the resistor, which, e.g., can be controlled by means of the circulation pump 202 and/or a by-pass valve 203, which is capable of diverting a portion of the flow for by-passing the resistor, and also the voltage applied to the resistor and thereby the current and amount of heat generated by the resistor 110. If the resistor 110 is used for dissipating excess energy generated during, for example, braking, this excess energy is normally dissipated by applying a high voltage to the resistor 110, which thereby generates a larger amount of heat, which, in turn, is dissipated to the cooling medium, whereafter the cooling medium is circulated through a radiator 204 that preferably is arranged in the front of the vehicle . The cooling effect of the radiator can, in a conventional manner, be enhanced by utilizing a fan 205 for increasing the air flow passing the radiator 204. As was mentioned above, the resistor 110 can be of such dimension that powers in the order of 50 - 60 KW or more is converted to heat by means of the resistor and dissipated to the cooling medium, which then, in turn, dissipates this heat to ambient air by means of the radiator.

Such situations are common, for example, when the vehicle is going downhill with applied electric brake as described above. Consequently, there are situations wherein large amounts of heat energy simply are dissipated for no purpose. According to the invention, this heat is, at least in operating conditions that so allow, used according to the following. For example, in the disclosed embodiment the resistor is arranged in a cooling medium circuit that passes through the internal combustion engine for providing cooling of the internal combustion engine in a conventional manner. This arrangement has the advantage that the resistor can be used to facilitate a rapid heating of the cooling medium, and thereby internal combustion engine, at cold starts of the vehicle to enable the internal combustion engine to reach normal operation temperature faster, and thereby reduce engine wear and reduce cold start emissions.

In a system such as the one disclosed in fig. 1, the generator 103 (engine 101) can, in such situations, be controlled to produce more electric power than what currently is consumed by the electric propulsion motor, wherein the generated excess energy can be used for heating the cooling medium by means of generating heat by the resistor 110. Due to the high power capabilities of the resistor, the cooling medium can, in a shorter period of time as compared to conventional heating by the combustion engine, be heated to a high temperature, and by circulating this high-temperature cooling medium through the internal combustion engine, the internal combustion engine can be rapidly heated to its normal working temperature. In these situations, the radiator 204 is preferably bypassed by means of bypass pipe 206 (the bypass being controlled by a valve 207) in order to ensure that the cooling medium reaching the engine still has a high temperature. Further, the invention allows that the cooling medium in these situations can be heated to a higher temperature than the temperature that is reached when normally heated by the engine. This has the advantage that the engine heating process is increased even further, so that the normal working temperature of the engine is reached even faster.

According to the invention, however, the heat generated by the resistor is also used for heating of a passenger compartment and/or a storage compartment.

With regard to, in particular, heavy vehicles, these are mostly used as working vehicles, and thereby are also often subject to working environment related regulations. For example, there may be restrictions regarding the temperature in the passenger compartment, such as, with regard to a lorry, the driver' s cabin, and in particular with regard to minimum temperatures. Such regulations are also overcome by the present invention by the embodiment disclosed in fig. 2.

As can be seen in the figure, the cooling medium can be circulated through an additional circuit 210, which passes through the heater element (s) 208 of the driver's cabin. In this way, in a similar manner to the above, circulation of high-temperature cooling medium through the heater element (s) 208 of the driver's cabin, allow that the driver's cabin can rapidly be heated to a comfortable temperature. Similar to the above, the radiator 204 is preferably bypassed by means of bypass pipe 206 in order to ensure that a sufficient amount of high-temperature cooling medium reaches the heater element (s) 208. This embodiment is even more to advantage with regard to buses, since the passenger compartment in a bus often is large, and usually has large window portions having an unfavourable coefficient of heat passage. When such buses are parked overnight in cold areas and/or weather, the bus usually must be parked indoors, or be provided with additional (fuel powered or electrical powered) heaters to allow the passenger compartment to be heated to a comfortable temperature in a reasonable time. Such additional heaters are usually installed in buses in Nordic and other cold countries to provide faster cabin heat-up during cold starts as well as providing extra heat during vehicle operation in cold weather.

According to the invention, however, the requirements regarding such overnight parking can be substantially alleviated, and the additional heaters can be omitted which thereby reduces the system complexity, vehicle weight and costs and eliminate the maintenance need of the heater system. In such a vehicle, the heaters 208 of fig. 2 represent the heater elements of the passenger compartment, and due to the heat power that the resistor is capable of delivering, a rapid cabin warm-up can be obtained by heating up the cooling medium faster than normal and/or to a higher temperature. Consequently, the invention allows the bus to be parked in colder areas, or allow a shorter time from start-up to when the vehicle can be put into service.

The invention also has the advantage that the resistor can be used to keep the cooling medium warm during operation (service) in cold weather by means of excess energy from regenerated energy, and thereby secure proper cabin heating. Further, when the vehicle is parked overnight it can be connected to an external electrical system, and by means of energy from the external electrical system heat the vehicle and the engine cooling medium in a simple manner.

Further, since the hybrid system according to the invention replaces the normal retarder as a secondary brake, the resistor system can be used to dissipate electric brake energy into the cooling system as heat and then be distributed as appropriate, disposed by the radiator even when the energy storage system is fully charged or of other reasons cannot accept more energy. Even further, since the resistor is also used to dispose excess energy, the high-voltage system can be kept well balanced in a simple manner by means of the resistor, i.e., to keep the high-voltage power electronics within desired levels by dissipating energy as heat when appropriate so as to ensure that the voltage does not rise uncontrollable with possible component damage as result.

So far, the same cooling medium has been used for heating both engine and cabin/passenger compartment. In an alternative embodiment, the engine cooling system and the cabin cooling system can consist of separate circuits, in which case the resistor unit either can consist of a separate resistors for each cooling medium circuit, or be arranged such that the cooling medium circuits can be arranged to be simultaneously heated by the resistor, or alternatively set in a heat exchanging relation with the resistor, e.g., by suitable operation of, e.g., valves.

In an alternative embodiment, the cooling medium is arranged to alternatively circulate through the energy converter (engine) and passenger compartment heater, respectively.

Claims

1. A heating system for a vehicle, the vehicle comprising an energy converter, and a first cooling medium circuit for carrying a first cooling medium, said cooling medium of said first cooling medium circuit being arranged to absorb and/or dissipate heat to and/or from said energy converter, and wherein said systerα includes resistor means arranged to be connected to at least one source of electrical power and arranged in thermal communication with cooling medium of said first cooling circuit for, at least in a heating mode, heating the said first cooling medium by means of heat dissipated when connected to said electrical power source, - said vehicle comprising a second cooling medium circuit for carrying a second cooling medium, said resistor means further being arranged to be in thermal communication with cooling medium, of said second cooling medium circuit for, at least in a heating mode, heating the said second cooling medium, and wherein said cooling medium of said second cooling medium circuit is arranged to dissipate heat to a passenger and/or storage compartment of said vehicle, characterised in that said resistor means is arranged to control the voltage of a high-voltage system of the vehicle by dissipating energy as heat when the voltage exceeds a threshold.

2. System according to claim 1, characterised is that said energy converter is a motor for propulsion of the vehicle, or a motor for supplying power to a propulsion motor, or a fuel ceil system for providing power to a propulsion motor of said vehicle.

3. System according to claim 1 or 2, characterised in. that said motor is an internal combustion engine or an electric motor,

4. System according to claim 1, characterised that said vehicle comprises one or more electric motors for regenerative braking, and that the at least one source of electrical power, at least in a regenerative braking mode, comprises electrical power generated from regenerative braking of the. vehicle,

5. System according to claim 4,. characterised in that one or more motors for propulsion of the vehicle is also the motor (s) for regenerative braking the vehicle.

6. System according to claim 4, characterised is that, in a heating mode, at least part of said regenerated electrical power is dissipated as heat by means of said resistor.

7. System according to claim 1, characterised in that said electric power supply at least partially consists of any from the group; an electrical energy storage means, a fuel cell system, a vehicle external power source, energy regenerated by means of an electric motor.

8, System according to claim 7, characterised in that said electrical energy storage means consist of one or more from the group: capacitor,- supercapacitor, battery,

9. System according to any of the preceding claims , characterised, in that said resistor means is immersed in said cooling medium.

10. System according to any of the preceding claims, characterised in that said resistor means consists of two or more resistor means, wherein said first resistor means is arranged to dissipate heat to said first cooling medium circuit and that a second resistor means is arranged to dissipate heat to said second cooling medium circuit,

11. System according to claim 1, characterised ia that one of said first and second cooling medium circuits is drawn off from the other cooling medium circuits

12. System according to claim 1, characterised in that the cooling medium is arranged to alternatively circulate through the energy converter and passenger (and/or storage) compartment heater, respectively.

13. System according to any of the preceding claims, characterised in that said first cooling medium, circuit and said second cooling medium circuit are arranged to pass said resistor means as a single circuit.

14. System according to any of the preceding claims, characterised in that said energy storage is arranged to provide electrical power for dissipation by said resistor means.

15. System according to any of the preceding claims, characterised in that the vehicle comprises an electrical brake system, wherein energy regenerated by applying a decelerating torque on one or more wheels of said vehicle by means of said electric brake system is arranged to be dissipated as heat by said resistor means,

16. Braking system for a vehicle, the vehicle comprising:

- a hydraulically operated friction service brake system, in which a friction element is arranged for frictional engagement with a rotating element for providing a vehicle decelerating torque, said rotating element being arranged to rotate with a wheel of said vehicle, and

- a second brake system, wherein said second brake system is capable of providing a brake power constituting a substantial amount of the brake power obtainable by said service brake system to reduce wear and/or avoid overheating of said service brake system, characterised is that said second brake system is an electrical brake system, wherein energy regenerated by applying a decelerating torque on one or more wheels of said vehicle by means of said electric brake system is arranged to be dissipated as heat by a resistor means capable of dissipating a main part of said brake power, wherein said resistor means is arranged to control the voltage of a high-voltage system of the vehicle by dissipating energy as heat when the voltage exceeds a threshold.

17. Vehicle, characterised in that it comprises a system according to any of the claims 1-16.