Patent Description:
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be exemplified with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as cars.

The vehicle industry is striving to reduce CO<NUM> emissions. Various alternatives to diesel and gasoline have been developed for energizing the vehicles. One such alternative is battery electric vehicles. Another alternative is the use of hydrogen gas. The chemical energy of the hydrogen may, for example, be converted into mechanical energy in an internal combustion engine or into electric energy in fuel cells, in order to propel the vehicle.

Fuel cell electric vehicles (FCEVs) such as fuel cell trucks have a very high cooling requirement compared to conventional diesel engine powered trucks. A circulating flowing coolant is used for cooling the fuel cells. The heat deposited from the fuel cells to the coolant is usually dissipated into the ambient through a heat exchanger. A fan may be placed behind the heat exchanger to increase the cooling capacity of the heat exchanger by driving ambient air through the heat exchanger. The cooling power provided is proportional to the fan power and the vehicle speed. The cooling power is also limited by the size of the heat exchanger and the temperature of the ambient air. The energy required to dissipate the heat energy increases and the arrangement is less efficient at higher heat loads due to the properties of the fan. The maximum cooling power is limited by the design power of the fan. In view of the above, it would be desirable to increase the cooling capacity of existing arrangements as well as to reduce parasitic load due to the fan to improve the energy efficiency of the vehicle.

An object of the invention is to provide a system and a method, which at least partly mitigate the drawbacks of the prior art. The object is achieved by a system and by a method according to the accompanying independent claims.

The general inventive concept is based on the realization that a cooling buffer may advantageously be provided to cater for situations when the normal cooling capacity of a heat exchanger and fan is not enough. In particular, the inventors have realized that such a cooling buffer may be charged when the ratio of the cooling power vs. fan power is above a predefined value or value range (typically when the cooling capacity is considered to be in excess of what is needed to cool the fuel cells), and when the cooling power vs. fan power is below said predefined value or value range (i.e. not enough cooling capacity to cool the fuel cells) then the cooling buffer may be discharged. An advantage of providing a "hot buffer" is that, when the cooling power vs. fan power is above the predefined value or value range, i.e. when the cooling capacity of the heat exchanger and fan is in excess, thermal energy may advantageously be provided from the hot buffer to make better use of the cooling capacity, and at least some of this additional cooling may be used to charge the cooling buffer.

Thus, according to a first aspect of the present disclosure, there is provided a cooling system in a fuel cell electric vehicle (FCEV), wherein the cooling system comprises:.

By the provision of a cooling system which comprises a first ("hot") chamber and a second ("cold") chamber that can thermally affect the coolant in the coolant circuit in a controlled manner, an improved cooling capacity and energy efficiency is achieved.

The positive displacement device may for instance be, or comprise, a fan. However, it may be any other device that moves an external fluid (typically air) to assist the heat exchanger in dissipating heat to the environment. For example, the positive displacement device may be, or comprise, a compressor. It should be understood that when using the term "fan power" in this disclosure, it does not necessarily mean that the positive displacement device is a fan. Rather this term is used consistently for simplicity, regardless of the specific type of positive displacement device. Similarly, the abbreviation COPfan will be introduced below, and it should be understood that this likewise is not limited to the positive displacement device being a fan.

The fan power of the positive displacement device is a measure of the energy supplied to the positive displacement device. The cooling power is a measure of how much heat can be rejected to the environment under current operating conditions of the vehicle. The cooling power may thus be affected by the outside air temperature, the vehicle speed (air speed) and the speed of the positive displacement device. For example, the cooling power may be expressed as: <MAT> where.

The control unite may thus determine the present ratio of cooling power/fan power of the positive displacement device, e.g. based on sensor inputs, such as including speed sensor, temperature sensors, etc..

The ratio of cooling power provided for a given fan power is thus the Coefficient of Performance of the fan (COPfan). The inventive concept provides a strategy to harvest cooling power available at operating points where COPfan is very high and deploy that in operating points where cooling power is insufficient or COPfan is very low. Thus, the inventive concept increases cooling capacity and enables a reduction in power required to operate the cooling system.

The ratio, COPfan, may thus be compared to a predefined value or to a predefined value range. A predefined value range may be advantageous as it allows for tolerances and errors of margin which might occur from for example sensor inputs. Furthermore, it may be desirable to have a first value to be exceeded for charging the cooling system (i.e. the ratio COPfan is above such a first value) and to be below a different second value for discharging the cooling system (i.e. the ratio COPfan is below such second value). The first and second values may together define a value range.

As explained above, the first chamber is configured to contain relatively hot fluid, i.e. it functions as a hot buffer, while the second chamber is configured to contain relatively cold fluid, i.e. it functions as a cooling buffer. The temperature of the relatively hot fluid will normally be above the average temperature of the coolant in the coolant circuit. In other words, the thermal potential energy of the fluid in first chamber is normally positive relative to the thermal energy of the coolant in the coolant circuit. Conversely, the temperature of the relatively cold fluid will normally be below the average temperature of the coolant in the coolant circuit. In other words, the thermal potential energy of the fluid in second chamber is normally negative relative to the thermal energy of the coolant in the coolant circuit.

The control unit may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The control unit 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 it 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.

The transferring of thermal energy between the coolant in the coolant circuit and the chambers may accomplished in various manners. For instance, the thermal energy may be transferred via fluid connections or via thermal connections. Thus, it should be understood that the thermal energy may in some embodiments be transferred by passing a fluid to/from thee coolant circuit, and in some embodiments by providing an interface the temperature of which may be controlled and by which the coolant can pass to pick up or release heat.

Thus, according to at least one exemplary embodiment, the cooling system comprises fluid connections for providing said first and second chambers in fluid communication with said coolant circuit, wherein thermal energy is provided to said chambers by passing coolant into said chambers, and wherein thermal energy is released from said chambers by passing coolant away from the chambers.

Fluid connections provide a simple and practical way of transferring thermal energy. Suitably, the fluid that flows through the fluid connections is some of the coolant in the coolant circuit. When the coolant has passed through the fuel cell arrangement, its temperature has been raised. Some of that coolant having raised temperature may suitably be diverted to the first chamber and stored. Later, when COPfan is high, the hot coolant may be returned to the coolant circuit. Similarly, when the coolant has passed through the heat exchanger and lowered its temperature, the cooled coolant may be diverted into the second chamber and stored. Later, when COPfan is low, the cooled coolant may be returned to the coolant circuit.

In some exemplary embodiments, at least one of the first and second chamber may be in fluid communication with the coolant circuit by means of a single fluid connection in which fluid may be passed both ways, e.g. using a bi-directional pump. In other exemplary embodiments, at least one of the first and second chamber may be in fluid communication with the coolant circuit by means of two fluid connections, one for leading fluid into the chamber (e.g. via a valve that can be selectively opened and closed) and one for returning fluid to the coolant circuit (e.g. via a pump).

As understood from above, according to at least one exemplary embodiment, the cooling system comprises valves for regulating flow of coolant to and from said chambers, wherein the control unit is configured to control said valves based on the value of said ratio. Valves provide a simple and effective way to control the fluid flow and thus thermal energy transfer. For example, when the ratio, COPfan, is above the predefined value or value range, then a valve at the first chamber may be closed preventing coolant to pass into the first chamber while a valve at the second chamber may be opened allowing coolant to pass into the second chamber. Hereby, cold thermal energy is stored in the first chamber for future cooling of the coolant. When the ratio, COPfan, is below the predefined value or value range, i.e. the cooling efficiency is not enough, then a valve at the second chamber may be closed preventing the relatively cool fluid from entering the second chamber (all the cooled fluid is needed to the be supplied to the fuel cells) and the stored cold thermal energy may be released from the second chamber as a supplement to aid in cooling the fuel cells. In the meantime, the a valve at the first chamber is suitably open to allow the coolant heated by the fuel cells to the be stored in the first chamber as a hot buffer for future use when the cooling efficiency is once again in excess.

As already understood from above, according to at least one exemplary embodiment, the cooling system comprises a first pump for pumping coolant from the first chamber to the coolant circuit and a second pump for pumping coolant from the second chamber to the coolant circuit, wherein the control unit is configured to activate the first pump when said ratio is above said pre-defined value or value range, wherein the control unit is configured to activate the second pump when said ratio is below said pre-defined value or value range. This is advantageous as a pump is a well-controllable component for transferring fluid from the chambers to the coolant circuit.

According to at least one exemplary embodiment, the first and second chambers are variable volume chambers located in a common vessel, the chambers being separated by a movable separation member, such as a diaphragm or a plunger, wherein the pressure difference across the movable separation member is used for driving the coolant out from the respective chamber when the control unit controls said valves based on said ratio.

This is advantageous as the pumps in the previously discussed exemplary embodiments may be omitted. The control unit only needs to control the opening and closing of the valves, and the pressure difference across the movable separation member will after opening of a valve cause the movable separation member to move and thus push the fluid out of the relevant chamber. Thus, the force of the movable separation member, which has been built up by the creating the pressure difference, may replace the force exerted by the pumps in the previous examples.

According to at least one exemplary embodiment, the cooling system comprises a heat exchanging device in thermal connection to the first chamber and the second chamber, wherein thermal energy is transferred between the coolant circuit and the first and second chambers via said heat exchanging device. Since there is no exchange of fluids between the coolant circuit and the chambers, the first and second chambers may advantageously contain a different fluid than the coolant in the coolant circuit. For example, a less expensive fluid may be used in the chambers.

According to at least one exemplary embodiment, the control unit is configured to monitor the state of charge of an electrical storage system (ESS) of the FCEV, and upon determination of a certain surplus of energy in the ESS the control unit controls at least a part of said surplus of energy to be supplied to the positive displacement device to increase the thermal energy removed from the heat exchanger, wherein thermal energy from the first chamber is provided to the coolant of the coolant circuit and is passed into the heat exchanger, after which part of the thermal energy of the cooled coolant leaving the heat exchanger is provided to and stored in the second chamber. This is advantageous as excess electrical energy may be used to boost the performance of the positive displacement device. Put differently, at least some of the excess electrical energy may converted and stored as coo thermal energy in the second chamber. The excess electrical energy may for example be produced during braking events and may for example be available at vehicle idle operation.

According to at least one exemplary embodiment, the control unit is configured to increase the fan power of the positive displacement device when the FCEV is operating at a point when said ratio is above said pre-defined value or value range. This is particularly advantageous in combination with surplus of energy in the ESS being supplied to the positive displacement device.

According to a second aspect of the present disclosure, there is provided a vehicle comprising a cooling system according to the first aspect, including any embodiment thereof. The advantages of the vehicle of the second aspect are largely analogous to the advantages of the cooling system of the first aspect, including any embodiment thereof.

According to a third aspect of the present disclosure, there is provided a method of controlling a cooling system in a fuel cell electric vehicle (FCEV), wherein the cooling system comprises a coolant circuit circulating a coolant, a heat exchanger for cooling the circulating coolant and a positive displacement device for removing thermal energy from the heat exchanger to the environment, the method comprising:.

The advantages of the method of the third aspect are largely analogous to the advantages of the control system of the first aspect and the vehicle of the second aspect, including any embodiments thereof.

Some exemplary embodiments of the method of the third aspect are listed below.

According to at least one exemplary embodiment, said providing of thermal energy to/from either one of the first and second chambers comprises transferring coolant between the coolant circuit and the first and second chambers, respectively.

According to at least one exemplary embodiment, the cooling system further comprises a heat exchanging device in thermal connection with the first and second chambers, wherein said providing of thermal energy to/from either one of the first and second chambers comprises transferring thermal energy between the coolant of the coolant circuit and the first and second chambers, respectively via said heat exchanging device.

According to at least one exemplary embodiment, the method comprises:.

According to at least one exemplary embodiment, the method comprises increasing the fan power of the positive displacement device when the FCEV is operating at a point when said ratio is above said pre-defined value or value range.

According to a fourth aspect of the present disclosure, there is provided a computer program comprising program code means for performing the steps of the method of the third aspect, including any embodiment thereof, when said program is run on a computer. The advantages of the computer program of the fourth aspect are largely analogous to the advantages of the method of the third aspect, including any embodiment thereof.

According to a fifth aspect of the present disclosure, there is provided a computer readable medium carrying a computer program comprising program code means for performing the steps of the method of the third aspect, including any embodiment thereof, when said program product is run on a computer. The advantages of the computer readable medium is largely analogous to the advantages of the method of the third aspect, including any embodiment thereof.

According to a sixth aspect of the present disclosure, there is provided a control unit for controlling a cooling system of a fuel cell electric vehicle (FCEV), the control unit being configured to perform the steps of the method according to the third aspect, including any embodiment thereof. The advantages of the control unit of the sixth aspect are largely analogous to the advantages of the method of the third aspect.

<FIG> illustrates schematically a vehicle <NUM> (in particular a fuel cell electric vehicle, FCEV) on which at least some exemplary embodiments of the invention may be implemented. Although the vehicle <NUM> is illustrated in the form of a truck, other types of vehicles, such as busses, construction equipment, trailers, passenger cars or even boats may be provided in accordance with the invention. The truck (vehicle <NUM>) comprises a cab <NUM> in which a driver may operate the vehicle <NUM>. The vehicle <NUM> comprises an energy conversion system <NUM> which includes a stack of fuel cells. The illustration is made relative to a schematic outline of certain parts of a truck, however, it should be understood that the specific location of the components may be placed differently than in the exemplary illustration. In the illustration the cab <NUM> of the truck, a connector <NUM> for towing a trailer and a pair of rear wheels <NUM> of the truck have been schematically indicated. The fuel cells <NUM> may be provided at the cab <NUM>, for example under the cab <NUM>. Behind the cab <NUM>, there are provided hydrogen tanks <NUM> for storing hydrogen gas which may be supplied to the fuel cells <NUM>. The hydrogen tanks <NUM> are merely illustrated schematically and only two are shown. However, it should be understood that the vehicle <NUM> may have more hydrogen tanks, or fewer. Although not illustrated, the hydrogen tanks <NUM> may suitably be held by a rack attached to the chassis, or by any other suitable support structure.

The vehicle <NUM> further comprises a heat exchanger <NUM> and a cooling passage <NUM> for circulating a coolant, i.e. a cooling fluid, such as a liquid, for example glycol-based. The cooling passage <NUM> extends from the heat exchanger <NUM> and passes along the stack of fuel cells <NUM> for transporting heat away from the stack of fuel cells <NUM>.

A pump <NUM> is provided to pump coolant that has taken up heat from the stack of fuel cells <NUM>. Downstream of the pump <NUM> there may be provided a thermostat <NUM> which senses the temperature of the coolant in the conduit and if the temperature is above a predefined value the coolant may be led back to the heat exchanger <NUM> to be cooled down before returning to the stack of fuel cells <NUM>. If the thermostat <NUM> determines that the temperature of the coolant is still low enough, it may be returned to the stack of fuel cells <NUM> without being led through the heat exchanger <NUM>.

The vehicle <NUM> illustrated in <FIG> may suitably be modified by implementing a cooling system in accordance with the following exemplary embodiments that will now be discussed.

<FIG> illustrates very schematically a cooling system <NUM> according to at least one exemplary embodiment of the invention. Similarly to <FIG> there are provided fuel cells <NUM>, in some type of fuel cell arrangement, for example in the form of a stack of fuel cells. The fuel cells <NUM> need to be cooled and a coolant pump <NUM> is provided to pump the coolant around a coolant passage or coolant circuit <NUM>. The coolant pump <NUM> pumps the coolant from the fuel cells <NUM> to and through a heat exchanger <NUM> and back to the fuel cells <NUM>. Although not illustrated in <FIG>, there may similarly to the illustration of <FIG> optionally be provided a thermostat to determine if the temperature of the coolant is still low enough for it to be returned to the fuel cells <NUM> without being led through the heat exchanger <NUM>.

As illustrated in <FIG>, there is provided a positive displacement device <NUM>, here illustrated in the form of a fan, for blowing air onto the heat exchanger <NUM> to improve dissipation of heat from the heat exchanger <NUM>. The dissipation of heat is not only dependent on the flow of air from the positive displacement device <NUM>, but may also be dependent on other factors such as the exterior relative air flow caused by the vehicle speed, the air temperature, the type of coolant, the mass of coolant, etc..

The cooling system <NUM> also comprises a first chamber <NUM>, such as in a tank, and a second chamber <NUM>, such as in another tank. Each one of the first chamber <NUM> and second chamber <NUM> is operatively connected to the coolant circuit <NUM>. More specifically, there are provided fluid connections <NUM>, <NUM>, <NUM>, <NUM> for enabling communication of fluid between the coolant circuit <NUM> on the one hand and the first and second chambers <NUM>, <NUM> on the other hand. Although the communication for each one of the first and second chambers <NUM>, <NUM> may be established by a single bi-directional conduit, in the present illustration the communication is established by means of an inlet conduit <NUM>, <NUM> and an outlet conduit <NUM>, <NUM>. Each inlet conduit <NUM>, <NUM> allows fluid in the form of coolant to be diverted from the coolant circuit <NUM> and into the respective first and second chamber <NUM>, <NUM>. A valve <NUM>, <NUM> is provided in each inlet conduit <NUM>, <NUM> to enable or disable transfer of coolant from the coolant circuit <NUM> to the first and second chambers <NUM>, <NUM>. Each outlet conduit <NUM>, <NUM> allows fluid to be passed from the first and second chambers <NUM>, <NUM>, respectively, to the coolant circuit <NUM>. Thus, coolant that has once been diverted and stored in the first and second chambers <NUM>, <NUM> may at a later point in time be returned to the coolant circuit <NUM>. A pump <NUM>, <NUM> is provided in each outlet conduit <NUM>, <NUM> to enable transfer of coolant from the respective chamber <NUM>, <NUM> to the coolant circuit <NUM>. In some exemplary embodiments, it may be conceivable to have a bi-directional conduit for one of the first and second chambers <NUM>, <NUM>, while the other one is associated with separate inlet and outlet conduits.

The cooling system <NUM> further comprises a control unit <NUM>. The control unit <NUM> may communicate with other components wirelessly or by wire. The control unit <NUM> is configured to monitor the ratio of cooling power/fan power (COPfan) of the positive displacement device <NUM>. The control unit <NUM> is also configured to control thermal energy transfer between the coolant and said chambers <NUM>, <NUM> based on said ratio. As can be understood from <FIG>, since the first chamber <NUM> is located downstream of the fuel cells <NUM> (which raise the temperature of the coolant) but upstream of the heat exchanger <NUM> (which lowers the temperature of the coolant), the first chamber <NUM> is configured to contain relatively hot fluid. Conversely, since the second chamber <NUM> is located downstream of the heat exchanger <NUM> but upstream of the fuel cells <NUM>, the second chamber <NUM> is configured to contain relatively cold fluid.

As will be discussed in more detail below, when the vehicle is operating at a point where said ratio (COPfan) is above a pre-defined value or value range, then the control unit <NUM> is configured to cause thermal energy from the first chamber <NUM> to be provided to the coolant in the coolant circuit <NUM> and passed into the heat exchanger <NUM>, after which part of the thermal energy of the cooled coolant leaving the heat exchanger <NUM> is provided to and stored in the second chamber <NUM>. Conversely, when the vehicle is operating at a point where said ratio (COPfan) is below said pre-defined value or value range, then the control unit <NUM> is configured to provide stored cold thermal energy from the second chamber <NUM> to the coolant in the coolant circuit to reduce the temperature of the coolant before it is passed to the fuel cells <NUM>, after which part of the thermal energy of the heated coolant leaving the fuel cells <NUM> is provided to and stored in the first chamber <NUM>.

It should be understood that although a schematic control unit <NUM> is only illustrated in <FIG>, such a control unit is, in practice, also included in the other exemplary embodiments (that will be discussed below) for controlling the operation of the cooling system and performing the method of controlling the cooling system of those exemplary embodiments.

<FIG> illustrate, in accordance with at least one exemplary embodiment, a method of operating the cooling system <NUM> of <FIG>. <FIG> illustrates the operation of the cooling system <NUM> during a charge mode of the cooling system <NUM>. <FIG> illustrates the operation of the cooling system <NUM> during a discharge mode of the cooling system <NUM>. For explanatory purposes only the active conduits are shown in <FIG>. Thus, when a valve is closed, the corresponding conduit is not illustrated.

<FIG> illustrates that if the vehicle is operating at a point where the ratio (COPfan) is above a predefined value or value range, the fluid from the first chamber <NUM> is pumped into the coolant circuit <NUM> and is passed into the heat exchanger <NUM>. In other words thermal energy from the first chamber <NUM> is provided to the coolant in the coolant circuit <NUM> and is passed into the heat exchanger <NUM>. The fan power of the positive displacement device <NUM> may be increased to achieve the required coolant outlet temperature from the heat exchanger <NUM>. The valve <NUM> at the inlet conduit <NUM> of the second chamber <NUM> is open and part of the cooled fluid enters the second chamber <NUM>. In other words, part of the thermal energy of the cooled coolant leaving the heat exchanger <NUM> is provided to and stored in the second chamber <NUM>.

<FIG> illustrates that if the vehicle is operating at a point where the ratio (COPfan) is below the predefined value or value range, the fluid from the second chamber <NUM> is pumped (by means of the pump <NUM> in outlet conduit <NUM>, controlled by the control unit) into the coolant circuit <NUM> and flows through the fuel cells <NUM>. In other words, the stored cold thermal energy from the second chamber <NUM> is provided to the coolant in the coolant circuit <NUM> to reduce the temperature of the coolant before it is passed to the fuel cells <NUM> of the vehicle. Part of the fluid heated by the fuel cells <NUM> is then diverted into the first chamber <NUM> via the open valve <NUM> in the inlet conduit <NUM> to the first chamber <NUM>. Thus, part of the thermal energy of the heated coolant leaving the fuel cells <NUM> is provided to and stored in the first chamber <NUM>.

From the above it can be understood that during charge mode (<FIG>), the high performance of the heat exchanger <NUM> and positive displacement device <NUM> is used for storing energy in the form of cold coolant in the second chamber <NUM>. Next, during the discharge mode (<FIG>), the stored cold thermal energy is used for reducing the energy demand of the positive displacement device <NUM> to maintain the temperature requirements.

<FIG> illustrates a cooling system <NUM>' according to at least another exemplary embodiment of the invention. Similarly to <FIG>, each one of the first chamber <NUM>' and the second chamber <NUM>' can be arranged in fluid communication with the coolant circuit <NUM>. However, instead of using dedicated pumps at outlet conduits for moving the coolant from the chambers <NUM>', <NUM>', the moving force is achieved by means of a diaphragm <NUM> subjected to a differential pressure. The first and the second chambers <NUM>', <NUM>' may be provided in a common vessel, but are separated by the intermediate diaphragm <NUM> extending across the vessel. In other words, the first and second chambers <NUM>', <NUM>' are variable volume chambers, wherein the volume is varied based on the movement of the diaphragm <NUM>. It should be understood that any other appropriate movable separation member may be used instead of a diaphragm, such as for instance a plunger. Similarly to <FIG>, in <FIG> each chamber <NUM>', <NUM>' is associated with an inlet conduit <NUM>', <NUM>' and an outlet conduit <NUM>', <NUM>'. The inlet conduits <NUM>', <NUM>' as well as the outlet conduits <NUM>', <NUM>' are provided with valves <NUM>', <NUM>', <NUM>, <NUM>. When the valve <NUM>', <NUM>' of an inlet conduit <NUM>', <NUM>' is open, coolant from the coolant circuit <NUM> is allowed to pass into the chamber which is interconnected with the coolant circuit by means of the inlet conduit. When the valve <NUM>, <NUM> of one of the outlet conduits <NUM>', <NUM>' is open, coolant is allowed to pass out from the associated chamber to the coolant circuit <NUM>.

<FIG> illustrate, in accordance with at least one exemplary embodiment, a method of operating the cooling system <NUM>' of <FIG>. <FIG> illustrates the operation of the cooling system <NUM>' during a charge mode of the cooling system <NUM>'. <FIG> illustrates the operation of the cooling system <NUM>' during a discharge mode of the cooling system <NUM>'. For explanatory purposes only the active conduits are shown in <FIG>. Thus, when a valve is closed, the corresponding conduit is not illustrated.

<FIG> illustrates that if the vehicle is at a point where the ratio (COPfan) is above a predefined value or value range, the fluid from the first chamber <NUM>' is pressed into the coolant circuit <NUM> and is passed into the heat exchanger <NUM>. The valve <NUM>' at the inlet conduit <NUM>' to the second chamber <NUM>' has been opened and the valve <NUM> at the outlet conduit <NUM>' from the first chamber <NUM>' is open. Since the coolant pump <NUM> displaces the coolant in the coolant circuit <NUM>, the coolant enters the second chamber <NUM>' creating a higher pressure than in the first chamber <NUM>' (pressure difference indicated by the pair of arrows pointing left in the figure). This causes the diaphragm <NUM> to push coolant out from the first chamber <NUM>'. Thus, similarly to the example in <FIG>, here in <FIG>, thermal energy from the first chamber <NUM>' is provided to the coolant in the coolant circuit <NUM> and is passed into the heat exchanger <NUM>, and part of the thermal energy of the cooled coolant leaving the heat exchanger <NUM> is provided to and stored in the second chamber <NUM>'.

<FIG> illustrates that if the vehicle is operating at a point where the ratio (COPfan) is below the predefined value or value range, the opening and closing of the valves are switched. Now, in contrast to <FIG>, the valve <NUM>' at the inlet conduit <NUM>' to the first chamber <NUM>' is opened and the valve <NUM> at the outlet conduit <NUM>' from the second chamber <NUM>' is opened. The pressure difference is reversed (indicated by the pair of arrows point to the right in the figure) and the diaphragm <NUM> will cause fluid from the second chamber <NUM>' to be pushed into the coolant circuit <NUM> and to flow through the fuel cells <NUM>. In other words, the stored cold thermal energy from the second chamber <NUM>' is provided to the coolant in the coolant circuit <NUM> to reduce the temperature of the coolant before it is passed to the fuel cells <NUM> of the vehicle, and part of the thermal energy of the heated coolant leaving the fuel cells <NUM> is diverted to and stored in the first chamber <NUM>'.

<FIG> illustrates a cooling system <NUM>" according to at least yet another exemplary embodiment of the invention. Unlike the exemplary embodiments shown in <FIG> and <FIG>, the embodiment in <FIG> does not allow fluid communication between the coolant circuit <NUM> and the first and second chambers <NUM>", <NUM>". Instead, thermal energy is transferred through a thermal connection. <FIG> illustrates that the cooling system <NUM>" comprises a heat exchanging device <NUM> which is in thermal connection with the first chamber <NUM>" and the second chamber <NUM>" (illustrated by the dotted lines). Thermal energy is transferred between the coolant circuit <NUM> and the first and second chambers <NUM>", <NUM>" via said heat exchanging device <NUM>. Thus, fluid may pass through the heat exchanging device <NUM> between the first and second chambers <NUM>", <NUM>". The fluid may be a different fluid than the coolant fluid. <FIG> also shows that the cooling system <NUM>" has a first passage <NUM> and a second passage <NUM>, each one having a valve <NUM>, <NUM>. The heat exchanging device <NUM> is located in a bypass portion <NUM> to the coolant circuit <NUM>.

<FIG> illustrate, in accordance with at least one exemplary embodiment, a method of operating the cooling system <NUM>" of <FIG>. <FIG> illustrates the operation of the cooling system <NUM>" during a charge mode of the cooling system <NUM>". <FIG> illustrates the operation of the cooling system <NUM>" during a discharge mode of the cooling system <NUM>". For explanatory purposes only the active conduits are shown in <FIG>. Thus, when a valve is closed, the corresponding conduit is not illustrated.

<FIG> illustrates that if the vehicle is at a point where the ratio (COPfan) is above a predefined value or value range, part of the coolant that has exited the heat exchanger <NUM> is diverted into the bypass portion <NUM> to be led through the heat exchanging device <NUM>. At the same time, the separate fluid from the first chamber <NUM>" is moved through the heat exchanging device <NUM> (e.g. by means of a pump). As the fluid moves through the heat exchanging device <NUM> it will transfers thermal energy to the coolant. Thus, the coolant will be heated, while the fluid will be cooled. The cooled fluid enters and is stored in the second chamber <NUM>". Thus, in the illustrated charge mode, part of the cooled coolant that exits the heat exchanger <NUM> is guided to the fuel cells <NUM>, but another part is guided through the heat exchanging device <NUM> in the bypass portion <NUM>. The heated coolant leaves the heat exchanging device <NUM> and is guided via the first passage and its opened valve <NUM> to a location downstream of the fuel cells <NUM> but upstream of the heat exchanger <NUM>. Thus, similarly to the examples in <FIG> and <FIG>, here in <FIG>, thermal energy from the first chamber <NUM>" is provided to the coolant, however, here via the heat exchanging device <NUM>, and is passed into the heat exchanger <NUM>, and part of the thermal energy of the cooled coolant leaving the heat exchanger <NUM> is provided to and stored in the second chamber <NUM>" as stored cold thermal energy.

<FIG> illustrates that if the vehicle is operating at a point where the ratio (COPfan) is below the predefined value or value range, the fluid from the second chamber <NUM>" is moved through the heat exchanging device <NUM> (e.g. by means of a pump). Simultaneously, some of the coolant is diverted to pass through the heat exchanging device <NUM> via the now operand valve <NUM> of the second passage <NUM>, and thermal energy will be transferred from the coolant to the other fluid in the heat exchanging device <NUM>. Thus, the chamber fluid will take up heat and then be passed to the first chamber <NUM>", while the coolant will lose heat and be cooled and then passed via the bypass portion <NUM> (in reverse direction) back to the coolant circuit <NUM> and the fuel cells <NUM>. Thus, as in the previous example, the stored cold thermal energy from the second chamber <NUM>" is provided to the coolant in the coolant circuit to reduce the temperature of the coolant before it is passed to the fuel cells <NUM> of the vehicle, and part of the thermal energy of the heated coolant leaving the fuel cells <NUM> is passed to and stored in the first chamber <NUM>".

<FIG> illustrates a cooling system <NUM>‴ according to at least a further exemplary embodiment of the invention. The cooling system <NUM>‴ substantially corresponds to the cooling system of <FIG>. However, <FIG> illustrates that the vehicle has an electrical storage system (EES) <NUM>. The control unit <NUM> is configured to monitor the state of charge of the EES <NUM>. When the control unit <NUM> determines that the EES <NUM> has a certain surplus of energy, then the control unit <NUM> controls at least part of said surplus of energy to be supplied to the positive displacement device <NUM> to increase the thermal energy removed from the heat exchanger <NUM>. This may in particular be done in a charge mode, i.e. when thermal energy from the first chamber <NUM> is controlled to be provided to the coolant of the coolant circuit <NUM> and passed into the heat exchanger <NUM>, after which part of the thermal energy of the cooled coolant leaving the heat exchanger <NUM> is provided to and stored in the second chamber <NUM> as stored cold thermal energy. The control unit <NUM> may thus suitably be configured to increase the fan power of the positive displacement device <NUM> when the vehicle is operating at a point when said ratio (COPfan) is above said pre-defined value or value range.

Claim 1:
A fuel cell electric vehicle (FCEV) (<NUM>) comprising a cooling system (<NUM>, <NUM>', <NUM>", <NUM>‴), wherein the cooling system comprises:
- a coolant circuit (<NUM>) circulating a coolant,
- a heat exchanger (<NUM>) for cooling the circulating coolant,
- a positive displacement device (<NUM>) for removing thermal energy from the heat exchanger to the environment,
- a first chamber (<NUM>, <NUM>', <NUM>") configured to contain relatively hot fluid,
- a second chamber (<NUM>, <NUM>', <NUM>") configured to contain relatively cold fluid,
- characterized in that the FCEV comprises a control unit (<NUM>) configured to monitor the ratio of cooling power/fan power of the positive displacement device and configured to control thermal energy transfer between the coolant and said chambers based on said ratio, wherein
when the FCEV is operating at a point where said ratio is above a pre-defined value or value range, then thermal energy from the first chamber is provided to the coolant in the coolant circuit and is passed into the heat exchanger, after which part of the thermal energy of the cooled coolant leaving the heat exchanger is provided to and stored in the second chamber, and
when the FCEV is operating at a point where said ratio is below said pre-defined value or value range, then stored cold thermal energy from the second chamber is provided to the coolant in the coolant circuit to reduce the temperature of the coolant before it is passed to the fuel cells (<NUM>) of the FCEV, after which part of the thermal energy of the heated coolant leaving the fuel cells is provided to and stored in the first chamber.