Additional Cooling Pack with Fans to Handle and Peak Shave Fuel Cell Transients and High Ambient Temperatures

A work machine cooling system for cooling primary power source cooling fluid for a primary power source may include a primary power source cooling unit and a second power source cooling unit fluidly connected so that primary power source cooling fluid flows from the primary power source through the primary and secondary power source cooling units is discharged back to the primary power source. The work machine cooling system may further include a primary cooling fan disposed proximate the primary fuel cell cooling unit to discharge airflow onto the primary fuel cell cooling unit, and a secondary cooling fan disposed proximate the secondary fuel cell cooling unit to discharge airflow onto the secondary fuel cell cooling unit. The secondary cooling fan may be turned off until the primary cooling fluid temperature is greater than a transient event threshold temperature indicating the occurrence of a transient thermal event.

TECHNICAL FIELD

The present disclosure relates generally to fuel cell powered work machines and, more particularly, to fuel cell powered work machines having additional cooling packs for managing fuel cell transients and high ambient temperatures.

BACKGROUND

Fuel cell systems enable electrical power to be generated with low emissions and high efficiency. For this reason, efforts are being made to apply fuel cell systems in various mobile applications, including work machines such as electric drive dozers. In these work machines, internal combustion engines are replaced by fuel cells to provide electrical power to drive motors in the power train systems as well as replace generators currently used for on-board electrical power supply.

In addition to generating electrical energy, fuel cells, when in operation, generate thermal energy that must be removed from the fuel cell with the aid of a cooling system to prevent overheating that can cause damage to the fuel cells. In the case of work machines, fuel cells have a high capacity in respect of generating electrical energy and, correspondingly, also generates a large quantity of thermal energy that has a high cooling requirement. In some implementations, fuel cells are cooled by causing coolant to flow past and around and thereby draw heat from the fuel cells. The coolant then flows through a cooling unit such as a radiator or other type of heat exchanger where heat may be dissipated to the ambient environment in the same way that heat is dissipated from work machines with internal combustion engines. Heat from other systems of the work machine may be dissipated in a similar manner. Heat dissipation is increased by airflow over the cooling unit that is created naturally by movement of the work machine and/or artificially by a fan or other device for creating airflow.

An example of a cooling system for a vehicle powered by a fuel cell is provided by U.S. Pat. No. 8,822,093, entitled “Cooling System for Fuel Cell Vehicle” issued to Kim et al. on Sep. 2, 2014. The Kim et al. patent discloses a cooling system for a fuel cell vehicle that employs a single integrated radiator disposed on a front side of the vehicle and is configured to cool cooling fluid by exchanging heat using exterior air to integrally manage a fuel cell stack and an electrical power apparatus. The integrated radiator is divided into a first high temperature region and a second low temperature region according to a flow requirements so that the fuel cell stack is cooled with cooling fluid flowing through the high temperature region and the electrical power apparatus is cooled with cooling fluid flowing through the low temperature region.

Cooling requirements for fuel cell powered work machines can be challenging to achieve with traditional air-cooled heat exchangers. For example, work machines such as dozers operate at low speeds that result in relatively low natural air flow. Work machines also work in environments that are subjected to high ambient temperatures resulting in reduced temperature gradients between the ambient air and the cooling fluid in the cooling unit. Additionally, the fuel cells of the work machines provide power to operate implements of the work machine when the work machine is moving or stationary that create transient thermal event with increased power demands on the fuel cells and corresponding increased heat generation that are not experienced by the other machine systems.

SUMMARY OF THE DISCLOSURE

In one aspect of the present disclosure, a work machine cooling system for cooling fuel cell cooling fluid for fuel cells of a work machine is disclosed. The work machine cooling system may include a primary fuel cell cooling unit having a primary unit inlet port and a primary unit outlet port, wherein the primary unit inlet port may be fluidly connected to receive the fuel cell cooling fluid from the fuel cells, and a secondary fuel cell cooling unit having a secondary unit inlet port and a secondary unit outlet port. The secondary unit inlet port may be fluidly connected to the primary unit outlet port to receive the fuel cell cooling fluid from the primary fuel cell cooling unit, and the secondary unit outlet port may be fluidly connected to discharge the fuel cell cooling fluid to the fuel cells. The work machine cooling system may further include a primary cooling fan disposed proximate the primary fuel cell cooling unit to discharge a primary airflow onto the primary fuel cell cooling unit, and a secondary cooling fan disposed proximate the secondary fuel cell cooling unit to discharge a secondary airflow onto the secondary fuel cell cooling unit.

In another aspect of the present disclosure, a method for cooling fluid temperature control of primary power source cooling fluid for a primary power source of a work machine is disclosed. The work machine may include a primary power source cooling unit having a primary unit inlet port fluidly connected to receive the primary power source cooling fluid from the primary power source, and a primary unit outlet port. The work machine may further include a secondary power source cooling unit fluidly connected to the primary unit outlet port to receive the f primary power source cooling fluid from the primary power source cooling unit, and a secondary unit outlet port fluidly connected to discharge the primary power source cooling fluid to the power source. The method may include comparing a primary cooling fluid temperature TPCFof the primary power source cooling fluid at the primary power source cooling unit to a transient event threshold temperature TTET. In response to determining that the primary cooling fluid temperature TPCFis not greater than the transient event threshold temperature TTET, the method may include setting a primary cooling fan to a first primary cooling fan speed vPFcorresponding to the primary cooling fluid temperature TPCFto discharge a first airflow onto the primary power source cooling unit, and setting a secondary cooling fan to a first secondary cooling fan speed vSFequal to zero to prevent discharge of a second airflow onto the secondary power source cooling unit. In response to determining that the primary cooling fluid temperature TPCFis greater than the transient event threshold temperature TTET, the method may include setting the primary cooling fan to a second primary cooling fan speed vPFcorresponding to the transient event threshold temperature TTETto discharge the first airflow onto the primary power source cooling unit, and setting the secondary cooling fan to a second secondary cooling fan speed vSFcorresponding to a secondary cooling fluid temperature TSCFof the primary power source cooling fluid at the secondary power source cooling unit to discharge the second airflow onto the secondary power source cooling unit.

In a further aspect of the present disclosure, a work machine is disclosed. The work machine may include a primary fuel cell cooling unit having a primary unit inlet port and a primary unit outlet port, wherein the primary unit inlet port may be fluidly connected to receive the fuel cell cooling fluid from the fuel cells, and a secondary fuel cell cooling unit having a secondary unit inlet port and a secondary unit outlet port, wherein the secondary unit inlet port may be fluidly connected to the primary unit outlet port to receive the fuel cell cooling fluid from the primary fuel cell cooling unit, and the secondary unit outlet port may be fluidly connected to discharge the fuel cell cooling fluid to the fuel cells. The work machine may further include a primary cooling fan disposed proximate the primary fuel cell cooling unit to discharge a primary airflow onto the primary fuel cell cooling unit, a secondary cooling fan disposed proximate the secondary fuel cell cooling unit to discharge a secondary airflow onto the secondary fuel cell cooling unit, a primary cooling unit temperature sensor operatively coupled to the primary fuel cell cooling unit to sense a primary cooling fluid temperature TPCFof the fuel cell cooling fluid at the primary fuel cell cooling unit, and a secondary cooling unit temperature sensor operatively coupled to the secondary fuel cell cooling unit to sense a secondary cooling fluid temperature TSCFof the fuel cell cooling fluid at the secondary primary fuel cell cooling unit. The work machine may also include a work machine controller operatively connected to the primary cooling fan, the secondary cooling fan, the primary cooling unit temperature sensor and the secondary cooling unit temperature sensor. The work machine controller may be programmed to receive primary temperature sensor signals from the primary cooling unit temperature sensor, determine a primary cooling fluid temperature TPCFof the fuel cell cooling fluid at the primary fuel cell cooling unit based on the primary temperature sensor signals, receive secondary temperature sensor signals from the secondary cooling unit temperature sensor, determine a secondary cooling fluid temperature TSCFof the fuel cell cooling fluid at the secondary fuel cell cooling unit based on the secondary temperature sensor signals, and compare the primary cooling fluid temperature TPCFto a transient event threshold temperature TTET. In response to determining that the primary cooling fluid temperature TPCFis not greater than the transient event threshold temperature TTET, the work machine controller may be programmed to transmit primary fan control signals to the primary cooling fan to set the primary cooling fan to a first primary cooling fan speed vPFcorresponding to the primary cooling fluid temperature TPCFto discharge the primary airflow onto the primary fuel cell cooling unit, and transmit secondary fan control signals to the secondary cooling fan to set the secondary cooling fan to a first secondary cooling fan speed vSFequal to zero to prevent discharge of the secondary airflow onto the secondary fuel cell cooling unit. In response to determining that the primary cooling fluid temperature TPCFis greater than the transient event threshold temperature TTET, the work machine controller may be programmed to transmit the primary fan control signals to the primary cooling fan to set the primary cooling fan to a second primary cooling fan speed vPFcorresponding to the transient event threshold temperature TTETto discharge the primary airflow onto the primary fuel cell cooling unit, and transmit the secondary fan control signals to the secondary cooling fan to set a second secondary cooling fan to the secondary cooling fan speed vSFcorresponding to the secondary cooling fluid temperature TSCFto discharge the secondary airflow onto the secondary fuel cell cooling unit.

Additional aspects are defined by the claims of this patent.

DETAILED DESCRIPTION

FIG.1illustrates an exemplary work machine10that may be powered by primary power source that generates heat, such as fuel cells, a diesel engine, a gas-power engine or other type of internal combustion engines and the like, and cooled by cooling systems in accordance with the present disclosure. While the work machine10is depicted as a dozer, those skilled in the art will understand that the work machine10may be of any suitable type, such as those used in construction, farming, mining, transportation, or the like that may be subjected to heat transients and high ambient temperatures. In other examples, the work machine10may be any suitable work machine10, such as a loader, an excavator, a tank, a backhoe, a drilling machine, a trencher, a combine, or any other on-highway or off-highway vehicle.

In the exemplary work machine10illustrated and described herein, the primary power source is fuel cells. However, those skilled in the art will understand that cooling systems in accordance with the present disclosure may be implemented in work machines10to cool other types of primary power sources that generate heat during operation of the work machine10such as those discussed above. The implementation of the cooling systems in accordance with the present disclosure in such work machines10is contemplated by the inventors.

The machine10may include a frame12on which other elements of the work machine10are mounted. The work machine10includes a propulsion system14, such as a track chain assembly as shown. Alternatively, the work machine10may have any other suitable type of propulsion system14, such as wheels and tires. The work machine10may be an electrically powered machine that includes fuel cells16to provide electrical power to drive the propulsion system14as well as the other systems of the work machine10. The work machine10may further include a first work implement18at a front end of the frame12that may be manipulated by actuation of a first hydraulic system20that is powered by the fuel cells16to perform work functions. The work machine10may also include a transmission system (not shown) that mechanically couples a drive motor (not shown) powered by the fuel cells16to the propulsion system14to propel the work machine10over a work surface. A second work implement22mounted at a rear end of the frame12may be manipulated by a second hydraulic system24that is also powered by the fuel cells16to perform other work functions. While the first work implement18is illustrated as a blade and the second work implement22is illustrated as a hydraulic hammer, those skilled in the art will understand that the work machine10may be outfitted with more or fewer implements, and with alternative implements, to perform the necessary work functions for which the work machine10is designed.

FIGS.2and3illustrate a work machine cooling system30in accordance with the present disclosure that is configured to cool the various heat generating systems of the work machine10. The cooling system30may be particularly useful in cooling the fuel cells16during low speed operation, high ambient conditions, and fuel cell transient conditions. Referring toFIG.2, the cooling system30may include a mechanical system cooling unit32that may be in the form of a radiator or other heat exchanger that will facilitate heat transfer from cooling fluid from various mechanical systems (not shown) to the ambient atmosphere. The mechanical system cooling fluid may enter the mechanical system cooling unit32through a mechanical unit inlet port34, circulate through the mechanical system cooling unit32, and exit the mechanical system cooling unit32through a mechanical unit outlet port36. The cooling fluid exiting the mechanical unit outlet port36may circulate back to the mechanical systems to dissipate heat from those systems and return to the mechanical unit inlet port34.

The work machine cooling system30may further include a primary fuel cell cooling unit40that similarly may be in the form of a radiator or other heat exchanger that will facilitate heat transfer from cooling fluid from the fuel cells16to the ambient atmosphere. The fuel cell cooling fluid may enter the primary fuel cell cooling unit40through a primary unit inlet port42, circulate through the primary fuel cell cooling unit40, and exit the primary fuel cell cooling unit40through a primary unit outlet port44. Instead of returning directly to the fuel cells16, the fuel cell cooling fluid may pass through a secondary fuel cell cooling unit50where additional heat may be removed from the fuel cell cooling fluid. The secondary fuel cell cooling unit50may have a secondary unit inlet port52that is fluidly connected to the primary unit outlet port44to receive the fuel cell cooling fluid. The fuel cell cooling fluid may then circulate through the secondary fuel cell cooling unit50and exit the secondary fuel cell cooling unit50through a secondary unit outlet port54. The cooling fluid exiting the secondary unit outlet port54may circulate back to the fuel cells16to dissipate heat from the fuel cells16and return to primary unit inlet port42.

The work machine cooling system30may be installed within the frame12proximate the front end of the work machine10. The frame12may include a cooling system opening (not shown) at the front end, with the work machine cooling system30being oriented with the surfaces shown inFIG.2facing forward at the opening so that airflow caused by travel of the work machine10flows over those surfaces to dissipate heat.FIG.3illustrates the rearward facing side of the work machine cooling system30and the corresponding components. The work machine cooling system30may include a primary cooling fan60mounted on a primary fan bracket62that is directly or indirectly mounted to the frame12. The primary cooling fan60is positioned to discharge airflow on the rear surfaces of the mechanical system cooling unit32and the primary fuel cell cooling unit40when the primary cooling fan60is operating. The work machine cooling system30further includes one or more secondary cooling fans64mounted on a secondary fan frame66that is directly or indirectly mounted to the frame12. The secondary cooling fans64are positioned to discharge airflow on the rear surface of the secondary fuel cell cooling unit50when the secondary cooling fans64are operating.

The fans60,64may be electric fans, hydraulic fans, mechanically-driven fans or the like. The primary cooling fan60may be larger than the secondary cooling fans64as illustrated inFIGS.2and3, or the secondary cooling fans64may be the same size or larger than the primary cooling fan60. Additionally, the fans60,64may be power by the same source or different sources depending on the requirements or limitations of a particular implementation. Regardless of the relative configurations of the fans60,64, the secondary cooling fans64may be utilized to peak shave for the whole system during transient thermal events where the primary cooling fan60operating alone may require more energy or be slower to react to the transient thermal events.

The additional airflow provided by the cooling fans60,64over the cooling units32,40,50serves to regulate the heat dissipation provided by the work machine cooling system30in accordance with the present disclosure. During normal operating conditions (i.e., work machine10operating and traveling through a worksite, moderate ambient temperatures and no fuel cell transient temperature peaks), the primary cooling fan60may be operated as necessary to cool the mechanical systems and the fuel cells16without engaging the secondary cooling fans64. As the work machine10is operating, a primary cooling fluid temperature TPCFat the primary fuel cell cooling unit50may be monitored to detect when the demand for power on the fuel cells16causes a transient thermal event that increases the temperature of the fuel cells16and the heat transfer to the fuel cell cooling fluid, thereby raising the temperature of the fuel cell cooling fluid. A primary cooling fan speed vPFmay be adjusted as the primary cooling fluid temperature TPCFrises to increase heat transfer at the primary fuel cell cooling unit40to maintain the temperature TCFPbelow a transient event threshold temperature TTET. When the primary cooling fluid temperature TPCFreaches the transient event threshold temperature TTET, the secondary cooling fans64may be activated to increase the heat dissipation from the fuel cell cooling fluid as it flows through the secondary fuel cell cooling unit50.

During this time, the primary cooling fan60may be maintained at a constant speed as the primary cooling fluid temperature TPCFat the primary fuel cell cooling unit40continues to rise because the secondary fuel cell cooling unit50provides additional cooling. If the transient thermal event is temporary and the primary cooling fluid temperature TPCFat the primary fuel cell cooling unit40drops below the transient event threshold temperature TTET, the secondary cooling fans64may be stopped, and the primary cooling fan60may again be used exclusively to control the temperature of the fuel cell cooling fluid. If the transient thermal event persists or increases, or the power demand on the fuel cells16is more than a temporary transient thermal event, the additional cooling provided by the secondary fuel cell cooling unit50may not sufficiently cool the fuel cell cooling fluid. At some point, a secondary cooling fluid temperature TSCFof fuel cell cooling fluid at the secondary fuel cell cooling unit50may exceed a transient event maximum temperature TTEMwhere it becomes necessary to increase the primary cooling fan speed vPFabove the transient event threshold speed vTETto cool the fuel cell cooling fluid sufficiently to prevent damage to the fuel cells16. The primary cooling fan60may continue to run at the increased speed until the secondary cooling fluid temperature TSCFat the secondary fuel cell cooling unit50falls below the transient event maximum temperature TTEM, at which time the primary cooling fan60may return to the transient event threshold speed vTET. This cycle of adjusting the speed of the primary cooling fan60and starting and stopping the secondary cooling fans64may continue as the work machine10operates to control the temperature of the fuel cell cooling fluid and protect the fuel cells16.

Referring now toFIG.4, exemplary control system components of the work machine10pertaining to the work machine cooling system30in accordance with the present disclosure are illustrated. The control system components may include a work machine controller70that may include a microprocessor72for executing specified programs to control and monitor various systems and functions associated with the work machine10, including the work machine cooling system30. The work machine controller70may further include a memory74, such as read only memory (ROM)74, for storing a program or programs, and a random access memory (RAM)76which serves as a working memory area for use in executing the program(s) stored in the memory74. For example, the memory74may store a cooling system control program that is executed by the microprocessor72to control the operation of the cooling fans60,64based at least in part on the fuel cell cooling fluid temperatures TCFP, TCFS. Although the work machine controller70is shown, it is also possible and contemplated to use other electronic components such as a microcontroller, an ASIC (application specific integrated circuit) chip, or any other integrated circuit device. The work machine controller70may be the sole controller for the work machine10, or may be one of a number of controllers of the work machine10across which control and monitoring of the systems and functions of the work machine10are distributed.

The work machine controller70may be operatively connected to output devices, including the primary cooling fan60and the secondary cooling fans64. The work machine controller70may communicate fan control signals to motors of the cooling fans60,64to regulate their speeds to execute a fuel cell cooling fluid temperature control strategy in accordance with the present disclosure. The work machine controller70may also be operatively connected to various input devices. The input devices may include a primary cooling unit temperature sensor80that may be any appropriate temperature sensor, such as a thermistor, thermocouple, resistance thermometer or the like, that can sense a temperature and transmit primary temperature sensor signals having values indicative of the sensed temperature. The primary cooling unit temperature sensor80may be installed at the primary fuel cell cooling unit40to detect the primary cooling fluid temperature TPCFat a relevant location of the primary fuel cell cooling unit40. In one embodiment, the primary cooling unit temperature sensor80may be installed at the primary unit outlet port44to sense the primary cooling fluid temperature TPCFafter the fuel cell cooling fluid has passed through the primary fuel cell cooling unit40and dissipated heat to the ambient environment. Sensing the primary cooling fluid temperature TPCFat this location may provide an indication of whether a transient thermal event is occurring and too much heat is being transferred from the fuel cells16for the primary fuel cell cooling unit40to cool the fuel cell cooling fluid down to the transient event threshold temperature TTET.

The input devices may further include a second cooling unit temperature sensor82that may be any appropriate temperature sensor such as those mentioned above. The secondary cooling unit temperature sensor82may be installed at the secondary fuel cell cooling unit50to detect the secondary cooling fluid temperature TSCFat a relevant location of the secondary fuel cell cooling unit50. In one embodiment, the secondary cooling unit temperature sensor82may be installed at the secondary unit outlet port54to sense the secondary cooling fluid temperature TSCFafter the fuel cell cooling fluid has passed through both the primary fuel cell cooling unit40and the secondary fuel cell cooling unit50and dissipated heat to the ambient environment. Sensing the secondary cooling fluid temperature TSCFat this location may provide an indication of whether a transient thermal event or the overall power demand on the fuel cells16is causing too much heat to be transferred from the fuel cells16for the work machine cooling system30to cool the fuel cell cooling fluid down to the transient event maximum temperature TTEMwithout increasing the primary cooling fan speed vPF.

INDUSTRIAL APPLICABILITY

As discussed, the control system components ofFIG.4may control the operation of the work machine cooling system30to cool the fuel cell cooling fluid.FIG.5illustrates an exemplary cooling fluid temperature control routine100for controlling the cooling fans60,64in response to the fuel cell cooling fluid temperatures TCFP, TCFSmeasured by the cooling unit temperature sensors80,82to manage the temperature of the fuel cell cooling fluid as the thermal output of the fuel cells16changes during operation of the work machine10. The routine100may begin at a block102when the work machine10is started to set the primary fan speed vPFto an initial primary fan speed vPFI. The work machine controller70may transmit primary fan control signals to the primary cooling fan60to cause the primary cooling fan60to operate at the initial primary fan speed vPFI. The initial primary fan speed vPFImay be zero or any other fan speed to create airflow to achieve desired heat transfer at the mechanical system cooling unit32and the primary fuel cell cooling unit40. The initial primary fan speed vPFImay be a predetermined fan speed, or may be based on the primary cooling fluid temperature TPCFmeasured by the primary cooling unit temperature sensor80. After the initial primary fan speed vPFIis set at the block102, or contemporaneously therewith, control may pass to a block104to set the secondary fan speed vSFto zero under the assumption that a transient thermal event is not occurring at machine startup. The work machine controller70may transmit secondary fan control signals to the secondary cooling fans64to set the secondary fan speed vSFto zero, or merely omit sending secondary fan control signals so the secondary cooling fans64remain idle.

After the fan speeds vPF, vSFare set at the blocks102,104, control may pass to a block106where the fuel cell cooling temperature TCFPat the primary fuel cell cooling unit40is sensed. The primary cooling unit temperature sensor80may sense the fuel cell cooling temperature TCFPat the primary unit outlet port44and transmit corresponding primary temperature sensor signals to the work machine controller70. Upon receiving the primary temperature sensor signals at the block106, control may pass to a block108where the work machine controller70compares the primary cooling fluid temperature TPCFfrom the primary temperature sensor signals from the primary cooling unit temperature sensor80to the transient event threshold temperature TTET. If the primary cooling fluid temperature TPCFis not greater than the transient event threshold temperature TTETat the block108, control passes to a block110where the work machine controller70transmits primary fan control signals to set the primary cooling fan60to operate at a primary cooling fan speed vPFthat corresponds to the sensed primary cooling fluid temperature TPCF. The program for the routine100may store, or access on the memory74, a lookup table, formula or other method for determining a primary cooling fan speed vPFat which to operate to create sufficient airflow to cool the fuel cell cooling fluid based on the current primary cooling fluid temperature TPCFafter the fuel cell cooling fluid has passed through the primary fuel cell cooling unit40. After the primary cooling fan speed vPF is set at the block110, control may pass back to the block104to ensure the secondary cooling fans64are stopped before reevaluating the primary cooling fluid temperature TPCFat the blocks106,108.

If the primary cooling fluid temperature TPCFfrom the primary temperature sensor signals is greater than the transient event threshold temperature TTETat the block108, then a transient thermal event may be occurring for which the secondary cooling fans64should be started. Control may pass to a block112where the work machine controller70transmits primary fan control signals to the primary cooling fan60to operate at a primary cooling fan speed vPFcorresponding to the thermal event threshold temperature TTETin the cooling strategy for the work machine cooling system30. After the primary cooling fan speed vPFis set at the block112, control may pass to a block114where the fuel cell cooling temperature TCFS at the secondary fuel cell cooling unit50is sensed. The secondary cooling unit temperature sensor82may sense the fuel cell cooling temperature TCFS at the secondary unit outlet port54and transmit corresponding secondary temperature sensor signals to the work machine controller70. Upon receiving the secondary temperature sensor signals at the block114, control may pass to a block116where the work machine controller70compares the secondary cooling fluid temperature TSCFfrom the secondary temperature sensor signals from the secondary cooling unit temperature sensor82to the transient event maximum temperature TTEM. If the secondary cooling fluid temperature TSCFis not greater than the transient event maximum temperature TTEMat the block116, control passes to a block118where the work machine controller70transmits secondary fan control signals to set the secondary cooling fans64to operate at a secondary cooling fan speed vSFthat corresponds to the sensed secondary cooling fluid temperature TSCF. The program for the routine100may store, or access on the memory74, a lookup table, formula or other method for determining a secondary cooling fan speed vSFat which to operate to create sufficient airflow to further cool the fuel cell cooling fluid based on the current secondary cooling fluid temperature TSCFafter the fuel cell cooling fluid has passed through the work machine cooling system30. After the secondary cooling fan speed vSFis set, control may pass back to the block106to continue monitoring the cooling fluid temperatures TPCF, TSCF.

If the secondary cooling fluid temperature TSCFfrom the secondary temperature sensor signals is greater than the transient event maximum temperature TTEMat the block116, the work machine cooling system30is not generating sufficient heat transfer to cool the fuel cell cooling fluid during the transient thermal event or other power demands on the fuel cells16without additional assistance from the primary cooling fan60. Control may pass to a block120where the work machine controller70transmits primary fan control signals to the primary cooling fan60to operate at a primary cooling fan speed vPFcorresponding to the secondary cooling fluid temperature TSCF, and then to the block118to set the secondary cooling fan speed vSFbased on the secondary cooling fluid temperature TSCFbefore returning to the block106to continue evaluating the cooling fluid temperatures TPCF, TSCF. Execution of the routine100may continue in this manner until the work machine10is shut down.

The work machine cooling system30and cooling fluid temperature control routine100in accordance with the present disclosure are capable of cooling all the mechanical and electrical systems of the work machine10while having the flexibility to cool the fuel cells16during transient thermal events that are particular to electric drive work machines10. The addition of the secondary fuel cell cooling unit50increases the heat exchange area that can be utilized to cool the fuel cell cooling fluid. In normal ambient conditions, the primary fuel cell cooling unit40is sufficient to cool all of the machine systems. During fuel cell heat rejection transient events, the secondary fuel cell cooling unit50can peak shave the additional heat dissipation requirement instead of increasing the primary cooling fan speed vPFwhen it is not required to increase the airflow on the mechanical system cooling unit32, thereby increasing the efficiency of the work machine cooling system30. During warm ambient conditions, both cooling fans60,64can be running to meet the overall heat dissipation requirements for the work machine10. Those skilled in the art will understand that the work machine cooling system30in accordance with the present disclosure offers a higher cooling capacity and additional total airflow, better handling of transient thermal events with less power draw, and reduced fan noise during normal operations.