Patent Publication Number: US-2020295681-A1

Title: Voltage Boosting Fan Motor Control

Description:
FIELD 
     The present disclosure relates to fans in a vehicle, more specifically to engine cooling using fans in the vehicle. 
     BACKGROUND 
     To prevent an engine within a vehicle from overheating, a radiator fan is included within the vehicle to dissipate heat. The radiator fan blows air onto the engine to cool the engine. There are a variety of radiator fans for each vehicle size and type. The radiator fans may vary by blade size, blade numbers, blade angles, etc. Each radiator fan variable alters the cooling effect of the radiator fan, making the radiator fan more or less efficient depending on its design. 
     The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     SUMMARY 
     A system is provided and includes a temperature sensor configured to determine a temperature of an engine of a vehicle, an engine speed sensor configured to determine a vehicle speed, a switching arrangement including at least one switch, and a radiator fan control module configured to calculate a required airflow of a radiator fan of the vehicle based on the temperature, calculate a required voltage to produce the required airflow of the radiator fan based on a size of the radiator fan, in response to the required voltage exceeding a battery voltage, generate a control signal to increase a fan motor voltage of a motor of the radiator fan, and in response to the required voltage being less than the battery voltage, generate the control signal to maintain a standard fan motor voltage of the motor of the radiator fan. The system also includes a pulse-width modulation (PWM) module configured to control switching operation of the at least one switch in accordance with the control signal. 
     In other features, the radiator fan control module is further configured to: in response to the temperature exceeding a temperature threshold, generate the control signal to increase the fan motor voltage of the motor of the radiator fan; in response to the vehicle speed exceeding a maximum speed threshold, generate the control signal to increase the fan motor voltage of the motor of the radiator fan; and in response to the vehicle speed being lower than a minimum speed threshold, generate the control signal to maintain the standard fan motor voltage of the motor of the radiator fan. 
     In other features, the temperature sensor is configured to measure an engine coolant temperature. 
     In other features, the system includes an engine control module, wherein the engine control module receives a temperature signal from the temperature sensor indicating the temperature. 
     In other features, the engine control module receives an engine speed signal from the engine speed sensor indicating the vehicle speed. 
     In other features, the engine control module includes a lookup table, and wherein the lookup table includes: (i) the temperature threshold, (ii) the maximum speed threshold, (iii) the minimum speed threshold, and (iv) the size of the radiator fan. 
     In other features, the at least one switch is an n-channel metal-oxide-semiconductor field-effect transistor (MOSFET). 
     In other features, the control signal to maintain the standard fan motor voltage directs a voltage booster circuit to apply the battery voltage to the motor. 
     In other features, the control signal to increase the fan motor voltage of the motor of the radiator fan instructs the PWM module to increase a duty cycle. 
     In other features, the voltage booster circuit is coupled between the motor of the radiator fan and a battery of the vehicle. 
     A method is also provided and includes determining, with a temperature sensor, a temperature of an engine of a vehicle, determining, with an engine speed sensor, a vehicle speed of the vehicle, calculating, with a radiator fan control module, a required airflow of a radiator fan of the vehicle based on the temperature, calculating, with the radiator fan control module, a required voltage to produce the required airflow of the radiator fan based on a size of the radiator fan, in response to the required voltage exceeding a battery voltage, generating, with the radiator fan control module, a control signal to increase a fan motor voltage of a motor of the radiator fan, in response to the required voltage being less than the battery voltage, generating, with the radiator fan control module, the control signal to maintain a standard fan motor voltage of the motor of the radiator fan, and controlling, with a pulse-width modulation (PWM) module, a switching operation of at least one switch in accordance with the control signal. 
     In other features, the method further includes in response to the temperature exceeding a temperature threshold, generating, with the radiator fan control module, the control signal to increase the fan motor voltage of the motor of the radiator fan, in response to the vehicle speed exceeding a maximum speed threshold, generating, with the radiator fan control module, the control signal to increase the fan motor voltage of the motor of the radiator fan, and in response to the vehicle speed being lower than a minimum speed threshold, generating, with the radiator fan control module, the control signal to maintain the standard fan motor voltage of the motor of the radiator fan. 
     In other features, the temperature sensor is configured to measure an engine coolant temperature. 
     In other features, the method further includes receiving, with an engine control module, a temperature signal from the temperature sensor indicating the temperature. 
     In other features, the method further includes receiving, with the engine control module, an engine speed signal from the engine speed sensor indicating the vehicle speed. 
     In other features, the engine control module includes a lookup table, and wherein the lookup table includes: (i) the temperature threshold, (ii) the maximum speed threshold, (iii) the minimum speed threshold, and (iv) the size of the radiator fan. 
     In other features, the at least one switch is an n-channel metal-oxide-semiconductor field-effect transistor (MOSFET). 
     In other features, the control signal to maintain the standard fan motor voltage directs a voltage booster circuit to apply the battery voltage to the motor. 
     In other features, the control signal to increase the fan motor voltage of the motor of the radiator fan instructs the PWM module to increase a duty cycle. 
     In other features, the voltage booster circuit is coupled between the motor of the radiator fan and a battery of the vehicle. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims, and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings. 
         FIG. 1  is a functional block diagram of a radiator fan control module integrated within a vehicle; 
         FIG. 2  is a schematic of a voltage booster within a vehicle; 
         FIG. 3  is a flowchart depicting a radiator fan control module function; 
         FIG. 4  is a graph depicting a difference in airflow volume for different vehicle speeds; 
         FIG. 5  is a graph depicting changes in airflow volume and torque for different vehicle speeds and vehicle loads; and 
         FIG. 6  is a graph depicting the voltage requirements for different original equipment manufacturers (OEMs) in standard radiator fan control. 
     
    
    
     In the drawings, reference numbers may be reused to identify similar and/or identical elements. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a functional block diagram of a radiator fan control module integrated within a vehicle  100  is shown. The vehicle  100  includes an engine  104 , an engine control module (ECM)  108 , a radiator fan control module  112 , a voltage booster  116 , a motor  120 , a radiator fan  124 , a temperature sensor  128 , an engine speed sensor  132 , and a lookup table  136 . The engine  104  is controlled by the ECM  108 . The engine  104  communicates with sensors throughout the vehicle  100 , e.g., the temperature sensor  128  and the engine speed sensor  132 . The temperature sensor  128  measures the engine coolant temperature within the vehicle  100 . Alternatively, the temperature sensor  128  may measure the temperature in another area of the vehicle  100  that represents the temperature of the engine  104 . The engine speed sensor  132  is attached to a crankshaft (not shown) of the engine  104 . A vehicle speed can be calculated based on the engine speed. The engine  104  may communicate with additional sensors such as a throttle position sensor (TPS), an oxygen sensor, an air to fuel ratio (AFR) sensor, a manifold absolute pressure (MAP) sensor, an accelerator position sensor, and a mass airflow (MAF) sensor. 
     The radiator fan  124  is controlled by the radiator fan control module  112 . The ECM  108  communicates sensor information to the radiator fan control module  112 , such as through a controller area network (CAN) bus. The radiator fan control module  112  can control the motor  120  of the radiator fan  124  using the voltage booster  116 . The radiator fan control module  112  can adjust the radiator fan speed to increase an airflow volume by increasing the voltage (or boosting the voltage) delivered to the motor  120 . Alternatively, the radiator fan control module  112  can adjust the radiator fan speed to decrease airflow volume by not increasing the voltage delivered to the motor  120 . 
     By increasing the voltage delivered to the motor, the radiator fan  124  can produce a larger airflow volume, independent of its size, using a smaller input voltage. In this way, the radiator fan  124  is not limited by its size. That is, the voltage booster  116  assists smaller radiator fans produce larger airflow volumes. Further, instead of requiring different radiator fan designs for different vehicles, each vehicle can use the same radiator fan design with a fan control that increases the airflow volume produced by the radiator fan when necessary by increasing the voltage delivered to the motor  120 . 
     The radiator fan control module  112  can determine whether the voltage provided to the motor  120  should be increased in response to the engine coolant temperature exceeding a temperature threshold. The engine coolant temperature is determined from the temperature sensor  128 . The ECM  108  receives a signal from the temperature sensor  128  corresponding to the engine coolant temperature. The engine coolant temperature is communicated to the radiator fan control module  112  through the CAN bus and used to determine whether the voltage delivered to the motor  120  should be increased. In some implementations, when the voltage has been increased, the radiator fan control module  112  may also determine when to decrease the voltage delivered to the motor  120 . That is, in response to the engine coolant temperature falling below a minimum threshold, the radiator fan control module  112  can direct the voltage booster  116  to no longer increase the voltage supplied to the motor  120 . 
     The radiator fan control module  112  can calculate a required airflow volume of the radiator fan  124 . For example, the amount of heat transferred (H) can be calculated by multiplying the specific heat of the air (C p ) by the change in temperature (ΔT) by the mass heat transfer or airflow (W): 
         H=C   p   ×W×ΔT.    (Equation 1)
 
     Further, the mass heat transfer can be calculated by multiplying the amount of airflow needed to removed heat or required airflow volume (CFM) by the density (D): 
         W=CFM×D.    (Equation 2)
 
     From the above equations, the required airflow volume (CFM) can be calculated by using the following equation: 
     
       
         
           
             
               
                 
                   
                     
                       C 
                        
                       F 
                        
                       M 
                     
                     = 
                     
                       H 
                       
                         
                           C 
                           p 
                         
                         × 
                         D 
                         × 
                         Δ 
                          
                         T 
                       
                     
                   
                   . 
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     3 
                   
                   ) 
                 
               
             
           
         
       
     
     Using equation 3, the radiator fan control module  112  can determine the required airflow volume to remove the heat when the temperature or the change in temperature exceeds a maximum threshold. In response to the temperature or the change in temperature (as determined by the temperature sensor  128 ) exceeding the maximum threshold, the radiator fan control module  112  can increase the voltage delivered to the motor  120  for a predetermined time. Alternatively, the radiator fan control module  112  can increase the voltage delivered to the motor  120  until the temperature falls below a minimum threshold. That is, the voltage delivered to the motor  120  can decrease once the temperature sensor  128  determines that the engine coolant temperature is below the minimum threshold. 
     In other implementations, the radiator fan control module  112  can determine whether the voltage delivered to the motor  120  should be increased in response to the vehicle speed exceeding a predetermined speed. When the vehicle speed exceeds the predetermined speed, the engine  104  may need additional cooling. When the radiator fan control module  112  increases the voltage delivered to the motor  120 , the airflow volume increases, which cools down the engine  104 . 
     For example, the predetermined speed may be a static threshold value for all radiator fans and vehicles. Alternatively, the radiator fan control module  112  may reference the lookup table  136 , which can include different thresholds based on the size of the radiator fan  124 , the type of vehicle, and the size of the vehicle. 
     The size of the radiator fan  124  as well as the kind of vehicle  100  affects the required airflow volume of the radiator fan  124 . For example, when the radiator fan  124  is smaller in size, the airflow volume provided at a first voltage is less than the airflow volume provided by a larger fan. To determine additional airflow requirements, the radiator fan control module  112  can account for the size of the radiator fan  124  when determining whether to direct the voltage booster  116  to increase the voltage of the motor  120 . Additionally, larger vehicles can require increased heat dissipation. Therefore, the radiator fan control module  112  can further account for the type of vehicle when determining whether to deliver an increased voltage to the motor  120 . 
     The radiator fan control module  112  can adjust the voltage delivered to the motor  120  according to the size of the radiator fan  124  and the type of vehicle 100 . That is, independent of vehicle type, size, or radiator fan size, a radiator fan design may be standardized across vehicles and manufacturers using the increased voltage when necessary. Additionally, smaller radiator fan designs may be used to meet higher heat dissipation demands without needing to adjust fan blade size, the number of fan blades, or blade angle. 
     Referring to  FIG. 2 , a schematic of the voltage booster  116  within the vehicle is shown. In the present implementation, the voltage booster  116  includes a pulse-width modulation module (PWM)  200 , an inductor  204 , a transistor  208 , a diode  212 , a capacitor  216 , a first resistor  220 , and a second resistor  224 . The voltage booster  116  receives an input voltage from a battery  228 . The battery  228  may be a vehicle battery or a separate battery for the voltage booster  116 . The PWM  200  controls switching cycles of the transistor  208 . When the transistor  208  is on, the current flows through the transistor  208  causing the current to build up in the inductor  204 . When the transistor  208  is off, the current flows through the diode  212  and the capacitor  216 . The transistor  208  is switched on and off for multiple cycles, which builds up voltage in the capacitor  216 . From the voltage build up, an increased voltage is delivered to the motor  120 . 
     The PWM  200  has a duty cycle. The duty cycle determines how long the transistor  208  is switched on and how long the transistor  208  is switched off. The duty cycle controls the increase in the amount of voltage delivered to the motor  120 . That is, as the duty cycle increases, the voltage delivered to the motor  120  increases as well. When the voltage delivered to the motor  120  is increased, the speed of the radiator fan  124  increases as well as the airflow volume produced by the radiator fan  124 . When the voltage delivered to the motor  120  is not increased, the airflow volume and speed of the radiator fan  124  are not increased. 
     The radiator fan control module  112  can control the motor  120  by adjusting the duty cycle of the PWM  200 . That is, when an increased airflow volume of the radiator fan  124  is required or desired, the radiator fan control module  112  can increase the duty cycle of the PWM  200  using a control signal. The radiator fan control module  112  can generate the control signal to increase the voltage delivered to the motor  120  or generate the control signal to maintain a standard fan motor voltage, i.e., the voltage of the battery  228 . 
     Referring to  FIG. 3 , a flowchart depicting the radiator fan control module function is shown. Control starts at  300  to determine the temperature within the engine  104 . The temperature sensor  128  determines the engine coolant temperature and sends the temperature readings to the ECM  108 . Alternatively, the temperature sensor  128  may be configured to measure a different temperature within the engine  104 . The ECM  108  communicates the temperature to the radiator fan control module  112  via the CAN bus. 
     At  304 , the radiator fan control module  112  calculates the required airflow volume based on the temperature using one of the methods above. For example, the radiator fan control module  112  may determine the required airflow volume using equation 3. At  308 , the radiator fan control module  112  calculates the voltage required for the required airflow volume based on the size of the radiator fan  124 . 
     That is, the radiator fan control module  112  calculates what amount of voltage is needed for the radiator fan  124  to produce the required airflow volume needed to cool the engine  104  (i.e., reduce any increase in temperature in the engine  104 ). The size of the radiator fan is used to determine the airflow volume produced at a given voltage. 
     At  312 , the radiator fan control module  112  determines whether the voltage required is greater than the voltage of the battery  228 . If yes, the radiator fan control module  112  generates a control signal to increase the fan motor voltage. 
     The radiator fan control module  112  will generate the control signal and send the control signal to the voltage booster  116  to increase the duty cycle of the PWM  200 . In response, the voltage delivered to the motor  120  will increase, resulting in a faster rotating radiator fan  124  and faster cooling. While the increased voltage delivered to the motor  120  can create more heat, the additional heat will be dissipated due to the increased airflow volume of the radiator fan  124 . 
     Instead, if the voltage required is less than or equal to the voltage of the battery  228  at  312 , the radiator fan control module  112  generates a standard control signal at  320 . The standard control signal directs the voltage booster  116  to not increase the voltage delivered to the motor  120 . The standard control signal may do this by adjusting the duty cycle, as discussed above, resulting in the voltage of the battery  228  being delivered to the motor  120 . After the control signal is generated at  316  or  320 , control returns to  300  to monitor the temperature. 
     In other implementations, control may monitor the change in temperature. If the change in temperature exceeds a predetermined amount, the radiator fan control module  112  can generate the control signal to increase the voltage delivered to the motor  120 . 
     In alternative implementations, control may monitor the speed of the vehicle  100 . If the speed of the vehicle  100  exceeds a predetermined threshold, the radiator fan control module  112  can generate the control signal to increase the voltage delivered to the motor  120 . 
     As mentioned above, in alternative implementations, the control signal to increase the voltage can be generated until a condition met (i.e., the required voltage is equal to or below the voltage of the battery  228 , temperature falls below a threshold, etc.). Alternatively, the radiator fan control module  112  may increase the voltage delivered to the motor  120  for a predetermined period. 
     Referring to  FIG. 4 , a graph depicting a difference in airflow volume for different vehicle speeds is shown. 
     The graph depicts the airflow volume limitations of the battery  228  of the vehicle  100  based on the voltage of the battery  228 . The lowest is a six volt battery, shown at  400 . Next, an eight volt battery is shown at  404 . A ten volt battery is shown at  408 . The highest airflow volume is a twelve volt battery, shown at  412 . When the vehicle speed is 0 mph at  416 , the airflow volume needed increases for each increase in battery  228  voltage. Similarly, when the vehicle is traveling at 50 mph at  420 , the airflow volume required is higher overall and increases for higher battery  228  voltages. 
     Referring to  FIG. 5 , a graph depicting changes in airflow volume and torque for different vehicle speeds and vehicle loads is shown. The varying motor voltages  400 ,  404 ,  408 , and  412  are shown on a graph depicting motor revolutions per minute (RPM) versus torque. When the vehicle is traveling 50 mph at  500 , the load is small, requiring less torque and less airflow volume  504  as shown on the graph at  508 . When the vehicle is traveling at 0 mph at  512 , the load is large, requiring more torque and more airflow volume  504  as shown on the graph at  516 . 
     Referring to  FIG. 6 , a graph depicting the voltage requirements for different original equipment manufacturers (OEMs) in standard radiator fan control is shown. 
     The voltage of a radiator fan of OEM A can vary depending on multiple factors, including changes in pressure, vehicle speed, vehicle load, etc., as shown by line  600 . Similarly, the radiator fan for OEM B can have varying voltage requirements as well as shown by  604 . Therefore, the voltage of OEM B  604  cannot meet the high voltage requirements of OEM A  600 . However, using the radiator fan control module  112  and voltage booster  116 , the voltage requirement of both OEM A  600  and OEM B  604  can be met by increasing the voltage delivered to the motor  120  when necessary. 
     The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and/or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure. 
     Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including “connected,” “engaged,” “coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and “disposed.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.” 
     In the figures, the direction of an arrow, as indicated by the arrowhead, generally demonstrates the flow of information (such as data or instructions) that is of interest to the illustration. For example, when element A and element B exchange a variety of information but information transmitted from element A to element B is relevant to the illustration, the arrow may point from element A to element B. This unidirectional arrow does not imply that no other information is transmitted from element B to element A. Further, for information sent from element A to element B, element B may send requests for, or receipt acknowledgements of, the information to element A. 
     In this application, including the definitions below, the term “module” or the term “controller” may be replaced with the term “circuit.” The term “module” may refer to, be part of, or include: an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog/digital discrete circuit; a digital, analog, or mixed analog/digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor circuit (shared, dedicated, or group) that executes code; a memory circuit (shared, dedicated, or group) that stores code executed by the processor circuit; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip. 
     The module may include one or more interface circuits. In some examples, the interface circuits may include wired or wireless interfaces that are connected to a local area network (LAN), the Internet, a wide area network (WAN), or combinations thereof. The functionality of any given module of the present disclosure may be distributed among multiple modules that are connected via interface circuits. For example, multiple modules may allow load balancing. In a further example, a server (also known as remote, or cloud) module may accomplish some functionality on behalf of a client module. 
     Some or all hardware features of a module may be defined using a language for hardware description, such as IEEE Standard 1364-2005 (commonly called “Verilog”) and IEEE Standard 1076-2008 (commonly called “VHDL”). The hardware description language may be used to manufacture and/or program a hardware circuit. In some implementations, some or all features of a module may be defined by a language, such as IEEE 1666-2005 (commonly called “SystemC”), that encompasses both code, as described below, and hardware description. 
     The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, data structures, and/or objects. The term shared processor circuit encompasses a single processor circuit that executes some or all code from multiple modules. The term group processor circuit encompasses a processor circuit that, in combination with additional processor circuits, executes some or all code from one or more modules. References to multiple processor circuits encompass multiple processor circuits on discrete dies, multiple processor circuits on a single die, multiple cores of a single processor circuit, multiple threads of a single processor circuit, or a combination of the above. The term shared memory circuit encompasses a single memory circuit that stores some or all code from multiple modules. The term group memory circuit encompasses a memory circuit that, in combination with additional memories, stores some or all code from one or more modules. 
     The term memory circuit is a subset of the term computer-readable medium. The term computer-readable medium, as used herein, does not encompass transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); the term computer-readable medium may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory computer-readable medium are nonvolatile memory circuits (such as a flash memory circuit, an erasable programmable read-only memory circuit, or a mask read-only memory circuit), volatile memory circuits (such as a static random access memory circuit or a dynamic random access memory circuit), magnetic storage media (such as an analog or digital magnetic tape or a hard disk drive), and optical storage media (such as a CD, a DVD, or a Blu-ray Disc). 
     The apparatuses and methods described in this application may be partially or fully implemented by a special purpose computer created by configuring a general purpose computer to execute one or more particular functions embodied in computer programs. The functional blocks and flowchart elements described above serve as software specifications, which can be translated into the computer programs by the routine work of a skilled technician or programmer. 
     The computer programs include processor-executable instructions that are stored on at least one non-transitory computer-readable medium. The computer programs may also include or rely on stored data. The computer programs may encompass a basic input/output system (BIOS) that interacts with hardware of the special purpose computer, device drivers that interact with particular devices of the special purpose computer, one or more operating systems, user applications, background services, background applications, etc. 
     The computer programs may include: (i) descriptive text to be parsed, such as HTML (hypertext markup language), XML (extensible markup language), or JSON (JavaScript Object Notation) (ii) assembly code, (iii) object code generated from source code by a compiler, (iv) source code for execution by an interpreter, (v) source code for compilation and execution by a just-in-time compiler, etc. As examples only, source code may be written using syntax from languages including C, C++, C#, Objective-C, Swift, Haskell, Go, SQL, R, Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5 (Hypertext Markup Language 5th revision), Ada, ASP (Active Server Pages), PHP (PHP: Hypertext Preprocessor), Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash®, Visual Basic®, Lua, MATLAB, SIMULINK, and Python®. 
     None of the elements recited in the claims are intended to be a means-plus-function element within the meaning of 35 U.S.C. § 112(f) unless an element is expressly recited using the phrase “means for,” or in the case of a method claim using the phrases “operation for” or “step for.”