Braking system, fuel cell system, and vehicle comprising fuel cell system

Abstract

The present invention relates to a braking system for a vehicle at least partially propelled by an electric traction motor, the braking system comprising an electric machine electrically connected to an electric source; an air flow producing unit mechanically connected to, and operated by, the electric machine; and an electrical brake resistor arrangement positioned in fluid communication between the air flow producing unit and an ambient environment, the electrical brake resistor arrangement being electrically connected to the electric source and arranged to heat air supplied from the air flow producing unit by electrical power received from the electric source, and to supply heated air to the ambient environment.

Claims

1. A braking system for a vehicle at least partially propelled by an electric traction motor, the braking system comprising: an electric machine electrically connected to an electric source; an air flow producing unit arranged in an air flow line of the braking system, the air flow producing unit being mechanically connected to, and operated by, the electric machine; and an electrical brake resistor arrangement positioned in the air flow line in fluid communication between the air flow producing unit and an ambient environment, the electrical brake resistor arrangement being electrically connected to the electric source and arranged to heat air supplied from the air flow producing unit by electrical power received from the electric source, and to supply heated air to the ambient environment.

2. The braking system of claim 1, wherein the air flow producing unit is an air compressor arranged to compress the received air and transmit the compressed air to the electrical brake resistor arrangement.

3. The braking system of claim 1, wherein the braking system further comprises an air heating arrangement positioned in fluid communication with, and upstream from, the air flow producing unit for heating the air supplied to the air flow producing unit.

4. The braking system of claim 3, wherein the air heating arrangement is formed by the electric machine, wherein air is received and heated by the electric machine and supplied to the air flow producing unit.

5. The braking system of claim 3, wherein the air heating arrangement is formed by a heat exchanger connected to a liquid cooling system.

6. The braking system of claim 1, wherein the braking system further comprises an air flow restriction arrangement positioned downstream from the electrical brake resistor arrangement.

7. The braking system of claim 6, wherein the electrical brake resistor arrangement is integrally formed with the air flow restriction arrangement.

8. The braking system of claim 1, wherein the braking system further comprises a control unit connected to the electric source and the electric machine, the control unit being configured to: receive a signal indicative of a current energy dissipation request from the electric source, and when the electric source requests dissipation of energy: control the electric machine to propel the air flow producing unit for producing a flow of air to the electrical brake resistor arrangement; and control the electric source to supply electric power to the electrical brake resistor arrangement for heating the air received by the electrical brake resistor.

9. The braking system of claim 8, wherein the current energy dissipation request is based on a desired energy level of the electric source at an upcoming driving position for the vehicle, wherein, before the vehicle arrives at the upcoming driving position, the control unit is configured to: control the electric machine to propel the air flow producing unit for producing a flow of air to the electrical brake resistor arrangement; and control the electric source to supply electric power to the electrical brake resistor arrangement for heating the air received by the electrical brake resistor.

10. The braking system of claim 8, wherein the control unit is further configured to: determine, based on the current energy dissipation request, an amount of energy to dissipate; determine a first maximum operational power level of the air flow producing unit; determine a second maximum operational power level of the electrical brake resistor arrangement; and control the electric machine and the electrical brake resistor arrangement to dissipate the amount of energy without exceeding the first and second maximum operational power levels.

11. The braking system of claim 8, wherein the control unit is further configured to: receive a signal indicative of a braking request for the vehicle; and control the electric machine to propel the air flow producing unit and the electric source to supply electric power to the electrical brake resistor arrangement when the vehicle requests braking.

12. A fuel cell system, comprising: a fuel cell stack arrangement comprising an air inlet side for receiving air to the fuel cell stack arrangement via an air inlet conduit; and the braking system of claim 1, wherein the air flow producing unit is connected to the air inlet conduit at a position upstream from the fuel cell stack arrangement.

13. The fuel cell system of claim 12, further comprising: a fuel cell air flow producing unit connected to the air inlet conduit upstream from the fuel cell stack arrangement; and a fuel cell electric motor mechanically connected to the fuel cell air flow producing unit; wherein the air flow producing unit is connected to the air inlet conduit at a position downstream from the fuel cell air flow producing unit.

14. The fuel cell system of claim 13, wherein the electrical brake resistor arrangement is arranged in downstream fluid communication with the fuel cell air flow producing unit.

15. An electrically propelled vehicle comprising the fuel cell system of claim 12, wherein the electrically propelled vehicle is arranged to receive electric power from the fuel cell system.

16. A braking system for a vehicle at least partially propelled by an electric traction motor, the braking system comprising: an air flow producing unit configured to generate a flow of air; and an electrical brake resistor arrangement positioned downstream from the air flow producing unit and arranged to receive the flow of air generated by the flow producing unit, the electrical brake resistor arrangement being electrically connected to an electric source; wherein the electric source is configured to supply electric power to the electrical brake resistor arrangement to heat the air received by the electrical brake resistor arrangement from the air flow producing unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above, as well as additional objects, features, and advantages, will be better understood through the following illustrative and non-limiting detailed description of exemplary embodiments, wherein:

(2) FIG. 1 is a lateral side view illustrating an example embodiment of a vehicle in the form of a truck;

(3) FIG. 2 is a schematic illustration of a braking system according to an example embodiment;

(4) FIG. 3 is a schematic illustration of a braking system according to another example embodiment;

(5) FIG. 4 is a schematic illustration of a fuel cell system according to an example embodiment; and

(6) FIG. 5 is a schematic illustration of a braking system according to a still further example embodiment.

DETAILED DESCRIPTION

(7) The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness. Like reference character refer to like elements throughout the description.

(8) With particular reference to FIG. 1, there is depicted a vehicle 10 in the form of a truck. The vehicle comprises a traction motor 101 for propelling the wheels of the vehicle. The traction motor 101 is in the example embodiment an electric machine arranged to receive electric power from a battery or directly from a fuel cell system which is described in further detail below. The vehicle 10 also comprises a control unit 114 for controlling various operations as will also be described in further detail below, and a braking system (not shown in detail in FIG. 1) arranged to dissipate electric energy for obtaining an auxiliary braking action for the vehicle.

(9) In order to describe the braking system in further detail, reference is made to FIG. 2 which is a schematic illustration of a braking system according to an example embodiment. The braking system 100 depicted in FIG. 2 comprises an electric machine 102 arranged to receive electric power 103 from an electric source 104. The electric source 104 can be, for example, a vehicle battery or a fuel cell system as is described in further detail below with reference to FIG. 4. The electric source 104 can, as another option, be formed by an electric inverter, or other electric machine, etc. Thus, the purpose of the electric source is to supply electric power to the electric machine. The electric source can, according to an example, also be arranged to receive electric power from the traction motor 101 of the vehicle. Moreover, the electric machine 102 can also be connected to a cooling system 105 of the vehicle 10. The cooling system 105 may either be a liquid cooling system or an air cooling system.

(10) The braking system 100 further comprises an air flow producing unit 106 mechanically connected to, and operated by, the electric machine 102. Preferably, the air flow producing unit 106 is mechanically connected to the electric machine 102 by a shaft 107. The air flow producing unit 106 serves, amongst other things, the purpose of supplying a flow of air 113. The air flow producing unit 106 can thus be formed by various arrangements to serve such purpose. The air flow producing unit 106 is thus preferably arranged to also significantly increase the pressure level of the air, as well as to increase the temperature level and flow velocity of the air. According to examples, the air flow producing unit 106 can be an air fan or a compressor. For simplifying the description of the various example embodiments of the present invention, the air flow producing unit 106 will in the following be referred to as a compressor 106 or a brake compressor 106.

(11) The brake compressor 106 is arranged in an air flow line 111 of the braking system 100. The braking system 100 further comprises an electrical brake resistor arrangement 108 in the air flow line 111. The electrical brake resistor arrangement 108 is arranged in downstream fluid communication with the brake compressor 106 and thus receives the air flow from the brake compressor 106. The electrical brake resistor arrangement 108 comprises an electrical brake resistor and is electrically connected to the above described electric source 104. In FIG. 2, the electric source 104 is thus depicted as two components for simplicity of understanding. It should be readily understood that the electric source could be either a single component or separate components. The electrical brake resistor arrangement 108 thus receives the air from the brake compressor, whereby the air is heated by in the electrical brake resistor by the electric power received from the electric source 104. The air is thereafter supplied to the ambient environment. According to the example embodiment depicted in FIG. 2, the braking system 100 may also comprise an air flow restriction arrangement 112 between the electrical brake resistor arrangement 108 and the ambient environment for maintaining a suitable pressure level within the braking system. The air flow restriction arrangement 112 may comprise a muffler.

(12) Still further, the braking system 100 exemplified in FIG. 2 comprises an air heating arrangement 110 arranged in upstream fluid communication with the brake compressor 106. The air heating arrangement 110 is in FIG. 2 arranged by a heat exchanger connected to the cooling system of the vehicle 10. Thus, the heat exchanger receives liquid fluid from the cooling system and pre-heats the air before it is delivered to the brake compressor 106. The heat exchanger 110 is thus preferably an air-to-liquid heat exchanger but may, as an alternative, be an air-to-air heat exchanger which uses relatively warm air to heat the air that is supplied to the brake compressor 106.

(13) The braking system 100 also comprises the above described control unit 114. The control unit 114 is preferably connected to the electric machine 102 and the electrical brake resistor arrangement 108. Hereby, the control unit 114 can control operation of these components. The control unit 114 should however be construed as being connected/connectable to other components of the braking system, such as to the electric source 104 and to the brake compressor 106. The control unit 114 and functional operations thereof will be described in further detail below.

(14) The control unit 114 preferably comprises processing circuitry including a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The processing circuitry may also, or instead, include an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. Where the processing circuitry includes a programmable device such as the microprocessor, microcontroller or programmable digital signal processor mentioned above, the processor may further include computer executable code that controls operation of the programmable device. It should be understood that all or some parts of the functionality provided by means of the processing circuitry may be at least partly integrated with a e.g. a primary vehicle control unit, or other control units of the vehicle, which is/are arranged to detect an upcoming traffic situation, road topology, etc. The information from the primary vehicle control unit can thus be transmitted to the above described control unit 114 for decision making of the control unit 114.

(15) By means of the braking system 100 depicted in FIG. 2 and described above, electric power from the electric source 104 is dissipated by electrifying the brake compressor 106 and the electrical brake resistor arrangement 108, whereby the electric power for the brake compressor 106 as well as for the electrical brake resistor arrangement 108 heats is used for heating the air. The electric power is thus dissipated into the air which is released to the ambient environment.

(16) In order to describe another example embodiment, reference is made to FIG. 3 which is a schematic illustration of a braking system according to another example embodiment. The example embodiment depicted in FIG. 3 contains features similar to the example embodiment depicted in FIG. 2. As such, only features that are different from FIG. 2 will be described unless specified otherwise.

(17) As can be seen, the example embodiment depicted in FIG. 3 does not contain the above described heat exchanger. Instead, the air heating arrangement 110 is formed by the electric machine 102. Hereby, air is received, and heated, by the electric machine 102 before delivery to the brake compressor 106. The electric machine 102 can also be a battery inverter motor. An inverter can thus be arranged between the battery and the motor. The inverter can be incorporated in the motor. It should be readily understood that a combination of FIG. 2 and FIG. 3 is also conceivable, where a heat exchanger is positioned in either upstream or downstream fluid communication with the electric machine 102 when the electric machine 102 is positioned as illustrated in FIG. 3.

(18) By means of the control unit 114 depicted in FIGS. 2 and 3, the braking system can be operated in a number of manners for dissipating electric power into heated air which is released into the ambient environment. For example, the control unit can be arranged to receive a signal indicative of a current energy dissipation request from the electric source. For example, a current energy dissipation request may be based on e.g., a battery having a SOC-level above a maximum predetermined limit, whereby the battery is in need of dissipating energy. For example, the control unit may receive a signal indicative of an upcoming downhill slope where the vehicle will need to use the battery for braking and energy recuperation. In such case, the battery should preferably have a relatively low SOC-level for being able to receive electric power.

(19) When the electric source requests dissipation of energy, the control unit 114 is arranged to control the electric machine to energize the brake compressor for compressing air and producing a flow of compressed air to the electrical brake resistor arrangement 108. The control unit 114 also controls the electrical brake resistor arrangement 108 to be energized by electric power to further heat the received compressed air. Hereby, the electric source 104 reduces its electric power level by heating the air.

(20) The brake compressor 106 as well as the electrical brake resistor arrangement 108 may be controlled to not exceed their respective operational power level. Thus, an optimization can be controlled by the control unit for utilizing the brake compressor and the electrical brake resistor arrangement at their preferred operational points.

(21) According to an example embodiment, the control unit 114 may be configured to receive a signal indicative of an upcoming driving situation. The control unit 114 may also receive a signal indicative of a current operational status of external systems, such as batteries and cooling system, as well as a signal indicative of a current operational status of the brake compressor 106 and the electrical brake resistor arrangement 108. The control unit may thereafter control the electric machine 102 and the electrical brake resistor arrangement 108 based on a combination of the current operational status of the external systems and the current operational status of the brake compressor 106 and the electrical brake resistor arrangement 108. Hereby, an optimization of the entire system is performed such that all components can substantially operate at their preferred operational points. Thus, the cooling system will not overheat, the battery will maintain a desired SOC-level, the brake compressor will not overspeed, and the electrical brake resistor arrangement will not overheat.

(22) The control unit 114 thus controls the electric machine to operate the brake compressor 106, as well as controls the electrical brake resistor arrangement 108 for optimization thereof. According to another example and as also indicated above, the control unit 114 can be arranged to receive a signal indicative of a braking request for the vehicle 10. When a braking request is indicated, the control unit 114 controls the electric machine 102 to propel the brake compressor 106 and controls the electric source 104 to supply electric power to the electrical brake resistor arrangement 108.

(23) The above described braking system 100 can be advantageously incorporated in a fuel cell system. Reference is therefore made to FIG. 4 which is a schematic illustration of a fuel cell system 200 according to an example embodiment. As can be seen in FIG. 4, the fuel cell system 200 comprises the above described braking system 100. In particular, the fuel cell system 200 comprises a fuel cell stack arrangement 202 comprising an air inlet side 204 for receiving air to the fuel cell stack arrangement via an air inlet conduit 206. The fuel cell stack arrangement 202 is thus arranged to generate electric power indicated by arrows 300. The fuel cell system 200 further comprises an air outlet conduit 207 arranged to receive air from the fuel cell stack arrangement 202. A fuel cell air flow producing unit 208, in the following referred to as a fuel cell compressor 208 is arranged in the air inlet conduit 206. A fuel cell turbine 210 is preferably arranged in the air outlet conduit 207, wherein the fuel cell compressor 208 and the fuel cell turbine 210 are mechanically connected to a fuel cell electric motor 214. The fuel cell electric motor 214 could be the traction motor of the vehicle 10, or it can be merely used for operating the fuel cell compressor 208 and the fuel cell turbine 210. It should however be readily understood that the fuel cell stack arrangement 202 can also be connected to a battery for storing the electric power generated by the fuel cell stack arrangement before delivery of electric power to the traction motor.

(24) Air is thus received by the fuel cell compressor 208, in FIG. 4 depicted as flowing into the fuel cell compressor 208 via an air filter 230. The compressed air from the fuel cell compressor 208 is delivered into the fuel cell stack arrangement 202 where the air is used for in the electrochemical reactions in the fuel cell stack to produce electricity.

(25) As depicted in the example embodiment of FIG. 4, the brake compressor 106 is connected to the air inlet conduit 206 at a position upstream the fuel cell stack arrangement 202. The fuel cell system 200 further comprises valves 220, 222 for controlling the flow direction of the air in the fuel cell system. As can be seen by FIG. 4, the air compressed in the brake compressor can, by controlling the valve 220 be directed to the inlet side 204 of the fuel cell stack arrangement 202. Also, the valve 222 can be arranged in a closed position to prevent air from being supplied from the fuel cell compressor 208 to the inlet side of the fuel cell stack arrangement.

(26) The fuel cell electric motor 214 and/or the fuel cell stack arrangement 202 may thus form the above described electric source, whereby electric power is dissipated from at least one of these electric sources by using the braking system as described above. The fuel cell system may, although not depicted in FIG. 4, comprise a single valve replacing the valves 220, 222. In detail, a three-way valve may be used instead of the two valves 220, 222.

(27) Reference is now made to FIG. 5, which illustrates a further example embodiment of the braking system 100. The main difference between the embodiment depicted in FIG. 5 and the embodiment depicted in FIG. 3 is that the embodiment in FIG. 5 does not comprise the electrical brake resistor arrangement. Conversely, the braking system 100 in FIG. 5 uses solely the brake compressor 106 for dissipating electric power 103 from the electric source 104. The example embodiment in FIG. 5 thus comprises the electric machine 102, which is electrically connected to the electric source, and the brake compressor 106 which is mechanically connected to the electric machine 102. As an option, and as indicated in FIG. 5, the braking system may also comprise the above described heat exchanger 110 and the flow restriction arrangement 112. The heat exchanger can be an air-to-liquid heat exchanger, an air-to-air heat exchanger, etc. As an alternative, and as depicted in FIG. 3, the heat exchanging process can also for the FIG. 5 embodiment be provided by using the electric machine 102 as a heat source. Air is hereby directly removing heat from the contact with the electric machine as air flows over the electric machine. Thus, in a similar manner as described above in relation to FIG. 3, the braking system 100 may use the electric machine 102 instead of the heat exchanger for increasing the temperature level of the air before the air is supplied to the brake compressor 106. The FIG. 5 embodiment hereby provides an advantageous cooling power increase for the braking system.

(28) It is to be understood that the present disclosure is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.