Patent Publication Number: US-8970396-B1

Title: Hourmeter system and method

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The following application claims priority to co-pending U.S. Nonprovisional patent application Ser. No. 13/957,034 filed Aug. 1, 2013 entitled HOURMETER SYSTEM AND METHOD, which claims priority to U.S. Provisional Patent Application Ser. No. 61/678,841 filed Aug. 2, 2012 entitled HOURMETER SYSTEM AND METHOD. The above-identified applications from which priority is claimed are incorporated herein by reference in their entireties for all purposes. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an hourmeter system and method of operation, and more particularly, an hourmeter system for monitoring and measuring engine operation time in outdoor power equipment. 
     BACKGROUND 
     Engine operating time hourmeters are frequently used in outdoor power equipment. Outdoor power equipment includes, but is not limited to, riding lawn mowers, lawn and agricultural tractors, snowmobiles, snowblowers, jet skis, boats, all terrain vehicles, bulldozers, generators, and the like. Hourmeters among other things, let the owner and/or manufacturer of the power equipment monitor how long the engine has been operated, when the equipment is due for repair/maintenance service, and whether the equipment is still under warranty. 
     Further discussion relating to developments in the hourmeter are discussed in U.S. Pat. Nos. 7,154,814 and 7,034,674 (collectively “Patents”). The Patents are owned by the assignee of the present application and are incorporated herein by reference in their entirety. 
     SUMMARY 
     One example embodiment of the present disclosure includes an hourmeter system and method for monitoring engine operation in power equipment. A programmable controller monitors and updates an indication of the running times of an engine. An interface circuit coupled to the programmable controller and also coupled to a power source for starting the engine. The interface circuit includes a detector circuit for detecting presence of a periodic noise signal whose presence is indicative of operation of the engine. The programmable controller is programmed to accumulate times of engine operation in a memory and communicate those times of engine operation for display. 
     In one embodiment, the hourmeter system comprises a power line coupled to a power source of the power equipment, a first lead line having a first state, the first lead line comprising ignition detection circuitry coupled to the power line and a microcontroller, a second lead line having a second state, the second lead line comprising noise detection circuitry coupled to the power line and the microcontroller, a third lead line having battery voltage detection circuitry coupled to the power line and the microcontroller, and an hourmeter coupled to the microcontroller that is enabled when the first, second, and third states are activated, indicating engine operation in power equipment. 
     Another example embodiment of the present disclosure includes a method of measuring engine operation time for power equipment. The method comprises the steps of monitoring a power line for changes in voltage with a voltage monitoring circuit to provide a first signal to a microcontroller at a first input and monitoring the power line for signal noise with a signal noise circuit to provide a second signal to the microcontroller at a second input. These two inputs provide enough information for a microcontroller implemented hourmeter to measure engine operation time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages of the present disclosure will become apparent to one skilled in the art to which the present invention relates upon consideration of the following description of the invention with reference to the accompanying drawings, wherein like reference numerals refer to like parts unless described otherwise throughout the drawings and in which: 
         FIG. 1  illustrates one form of power equipment using an hourmeter system in accordance with one example embodiment of the present disclosure; 
         FIG. 2  is a block diagram illustrating the electrical construction of the hourmeter system in accordance with one example embodiment of the present disclosure; 
         FIG. 3  is a flow diagram illustrating the operation of the hourmeter system in accordance with one example embodiment of the present disclosure; 
         FIG. 4  is a state diagram of operating states of a controller used in implementing a second example embodiment of the present disclosure; 
         FIG. 5  is a block diagram of the electrical construction of an hourmeter system in accordance with a second example embodiment of the present disclosure; 
         FIGS. 6-11  are more detailed schematics of a noise detector that forms part of the  FIG. 5  block diagram; 
         FIG. 12  is a voltage versus time depiction of the sensed battery voltage during starting of an engine. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the figures generally wherein like numbered features shown therein refer to like elements throughout unless otherwise noted. The present disclosure relates to an hourmeter system and method of operation, and more particularly, an hourmeter system for monitoring and measuring engine operation time in outdoor power equipment. 
       FIGS. 1 and 2 , and particularly  FIG. 2  illustrate the electrical construction of an hourmeter system  10  in accordance with one example embodiment of the present disclosure. The hourmeter system  10  measures and displays power equipment engine operating time. A physical hourmeter  12  is typically located on the external profile of the power equipment  14 , such as a dash panel  16  as seen in  FIG. 1 . 
     The hourmeter  12  displays, via a liquid crystal display an accumulated amount of time the engine  17  has been operated. Typically, the hour meter  12  is mounted on the dashboard  16  of outdoor power equipment  14  such as a tractor, snowmobile, riding lawn mower, personal water craft, or boat to inform the owner of the number of operation hours of the engine  17 , since the power equipment was manufactured. However, it should be appreciated that the hourmeter system  10  of the present disclosure can be utilized with any type of internal combustion engine and is not limited to any particular type of equipment or vehicle. 
     For ease of installation and compactness, circuitry and the liquid crystal display of the hourmeter  12  is mounted to a printed circuit board  18 . The circuit board  18 , in turn, is conveniently plugged into a socket (not shown) disposed beneath the dashboard of the power equipment  14  and coupled to a power line  20  of a power source  22  of the power equipment. 
     The hourmeter system  10  of the present disclosure employs novel power supply signal analysis “PSSA” to advantageously assure accurate measurement and monitoring of the engine operation time. That is, the PSSA determines the engine state (ON/OFF) by monitoring and processing simultaneously in one example embodiment three distinguishable states of the power source  22 . In the illustrated example embodiment, the power source  22  is a 12V battery. 
     The first state, or state 1 is a key-on state that is active, present, or in a first enabling condition when the power line  20  ranges between 12.6 VDC at full charge to 11.7 VDC at full discharge for an open-circuit. The second state or state 2 is a charging voltage state that is active, present, or in a second enabling condition when power line  20  rises to a voltage level between 13.8 VDC and 14.1V, because of the charge provided by a charging system, such as a generator. The third state or state 3 is an ignition impulse and/or generator noise state that is active, present, or in a third enabling condition when the power line  20  carries a superimposed noise signal. 
     As further discussed below, the three distinguishable states prevent the occurrence of false negative enabling of the hourmeter without the engine running. That is, state 1 could be present with the power equipment key in an “ON” position, but without the engine running. State 2 could be present with remote or a wall power battery charger charging the equipment battery without the engine running. 
     The PSSA advantageously discriminates, separates, compares, and analyzes each signal from all three states separately before determining the current engine state, and whether or not time measurement of the hourmeter  12  should begin, continue, or stop. In one example embodiment, a microcontroller  30  is used to collect and process the PSSA output signals and states, determining whether or not the engine is running and time should be accumulated on the hourmeter  12 . In another example embodiment, an application specific integrated circuit “ASIC” is used to collect and process the PSSA output signals and states, determining whether or not the engine is running and time should be accumulated on the hourmeter  12 . 
     Referring specifically to  FIG. 2 , a hourmeter system  10  is shown in accordance with one example embodiment of the present disclosure. The hourmeter system  10  comprises a power line  20  coupled to power source  22  that in the illustrated example embodiment comprises a battery. The hourmeter system  10  further comprises first  32 , second  34 , and third  36  lead lines, and a microcontroller  30 . The leads lines  32 ,  34 , and  36  are constructed in parallel and are coupled at a first end to the power line  20  and at a second end to an input/output pin of the microcontroller  30 . The first, second, and third states are measured by first  32 , second  34 , and third  36  lead lines, respectively. 
     An input  38  of the microcontroller  30  monitors the first state, or state 1, which is a key-on state that is active or in a first enabling condition when the power line  20  ranges between 12.6 VDC at full charge to 11.7 VDC at full discharge for an open-circuit. The software or firmware  60  within the microcontroller  30  is programmed to a prescribed range  40  for monitoring state 1 at input  38 . It should be appreciated by those skilled in the art that the prescribed range  40  could be modified as necessary based on, for example, load requirements and power source  22  size. 
     An input  48  of the microcontroller  30  monitors the second state or state 2, which is a charging voltage state that is active or in a second enabling condition when power line  20  rises to a prescribed voltage level  50 , which in the illustrated example embodiment is between 13.8 VDC and 14.1V, because of the charge provided by a charging system, such as a generator. The software or firmware  60  within the microcontroller  30  is programmed to a prescribed range  50  for monitoring state 2 at input  48 . It should be appreciated by those skilled in the art that the prescribed range  50  could be modified as necessary based on, for example, the size of the generator used with the power equipment. 
     Inputs  42  and  44  of the microcontroller  30  monitor the third state or state 3, which is an ignition impulse and generator noise state that is active or in a third enabling condition when the power line  20  carries a superimposed ignition or impulse noise. The software or firmware  60  within the microcontroller  30  is programmed to a prescribed frequency ranges  46  and  47  for the known frequency characteristics of the noise at respective inputs  42  and  44 , respectively. It should be appreciated by those skilled in the art that the prescribed frequency ranges  46 ,  47  could be modified as necessary based on the electrical noise characteristic of the specific type of power equipment. 
     Lead line  32  further comprises a low-pass filter  62  for signal conditioning input  38  to the microcontroller  30 . In one example embodiment, the low-pass filter  62  is an RC analog circuit. 
     Lead line  36  further comprises a low-pass filter  64  for signal conditioning input  48  to the microcontroller  30 . In one example embodiment, the low-pass filter  64  is an RC analog circuit. Lead line  36  also comprises power source  22  state of charge and charging voltage comparator. 
     Lead line  34  further comprises a DC block  68 , limiter  70 , low-pass filter  72 , and amplifier  74  in series for signal conditioning inputs  42  and  44  to the microcontroller  30 . In one example embodiment, the low-pass filter  72  is an RC analog circuit. Lead line  34  also comprises peak detector  76  and impulse detector  78  in parallel, coupled to inputs  42  and  44 , respectively. The peak detector  76  is condition to detect operation of generator noise. 
     If the inputs  38 ,  48 , and at least one of  42  and  44  receive a signal that the states are enabled or active, then the engine  17  is operating and an output signal at output  80  of the microcontroller  30  is generated, enabling operation of the hourmeter  12 . This advantageously prevents false operation of the hourmeter  12 . That is, the hourmeter  12  will not operate if state 1 alone is enabled, that is the key is left in the ON position. Similarly, the hourmeter  12  will not operate if the state 2 alone enabled, preventing the hourmeter from running if the battery is being charge or remote noise is detected. 
       FIG. 3  illustrates a flow diagram illustrating an operation  100  of the hourmeter system  10  in accordance with one example embodiment of the present disclosure. In one example embodiment, the flow diagram represents the logic process of software or firmware located in the microcontroller  30 . The operation  100  is initiated at  110  in which a plurality of states are monitored. In one example embodiment, the plurality of states are processed and monitored at  120  simultaneously. 
     A first state  130  represents a key-on state that is monitored from power line  20 . The first state  130  is active or in a first enabling condition at determination step  160  when a power line  20  ranges between a prescribed voltage range at full discharge for an open-circuit. The prescribed voltage range is programmed into the firmware or software of the microcontroller  30 . 
     A second state  140  is a charging voltage state that is monitored from power line  20 . The second state  120  is active or in a second enabling condition at determination step  170  when power line  20  rises to a prescribed voltage level range that is above the power source  22  voltage. The prescribed voltage level range rises above the power source voltage because of the charging system voltage provided by a charging system, such as a generator. The prescribed voltage level range is programmed into the firmware or software of the microcontroller  30 . 
     A third state  150  is an ignition impulse and/or generator noise state that is monitored from power line  20 . The third state is active or in a third enabling condition at determination step  180  when the power line  20  carries a superimposed noise. Such noise frequency or frequency range once isolated is captured as a prescribed frequency or prescribed frequency range that is programmed into the firmware or software of the microcontroller  30 . 
     If the hourmeter system  10  operation  100  at the determination steps  160 ,  170 , and  180  are active, i.e. in the affirmative, the digital hourmeter  12  is enabled at  190 / 200  to count or track the engine operation time. If the hourmeter system  10  operation  100  at any one of the determination steps  160 ,  170 , and  180  are negative, the process  100  returns to the operation initiation  110 . The signal in determination steps  160 ,  170 , and  180  need to be enabled to activate the tracking or counting of engine operation time. 
     Advantageously, the process  100  only requires coupling or monitoring of the power source  22  power line  20 , which is the same terminal (connection) needed to provide power to the power apparatus  14 . Hence, no extra installation, interface, terminal, or connection is needed for the hourmeter  12  or hourmeter system  10  to function and operate. 
     Second Alternate Example Embodiment 
     A second alternate example embodiment of a system  200  for monitoring operation of an engine in power equipment is described in reference to  FIGS. 4-12 . This second alternate example embodiment includes a programmable controller  210  for monitoring a status of the engine  17  such as the engine of a riding lawn mower depicted in  FIG. 1  and storing an indication and/or communication of the running times of the engine. An interface circuit  220  is coupled to the programmable controller  210  and also coupled to a power source, such as the battery  22  of  FIG. 5  for starting the engine  17 . The interface circuit  220  includes a detector circuit  222  for detecting presence of a periodic noise signal whose presence is indicative of operation of the engine. The representative programmable controller  210  is a Model STM8 commercially available from STmicroelectronics and includes a memory for accumulating times of engine operation and also communicating these accumulated times for display on a visual display  224  of the hourmeter  12 . 
     As depicted in  FIG. 5 , A power conversion circuit  226  is used to power the programmable controller. This circuit  226  drops the battery voltage from the battery  22  to a value for powering the controller. The rest of the system has a separate power source similar to the circuit  226 . A battery voltage monitor  228  is also coupled to the battery  22  and includes an input  229  to the controller for monitoring battery voltage. In the exemplary embodiment, the voltage at the input  229  is one fifth the voltage appearing at the high (+) side of the battery. As seen below, the battery voltage is used by the controller to detect an operating state of the system  200  and more particularly is used in transitioning from a state in which the engine is deemed to be “not running” to a state in which the engine is running and therefore the accumulated run time of the engine should be updated. 
       FIG. 4  depicts a state diagram for program instructions executing on the controller  210  in characterizing the system  200  and more particularly in determining when the engine is running. The controller  210  categorizes the system  200  into a sequence of operating states based on monitored conditions. 
     An initial operating state  230  ( FIG. 4 ) is a state in which the controller  210  is powered by the battery  22  and is waiting for an event to occur which would cause the controller  210  to transition to another state depicted in the state diagram of  FIG. 4 . In the exemplary embodiment, a transition path  232  from the initial power up state  230  to a so called pre-crank state  234  is made in response to receipt by the controller of a starter enabled signal. This starter enabled signal can originate from either an ignition switch or from an additional controller communicating with the controller  210 . 
     The pre-crank state  234  is entered upon receipt of a starter enabled signal. The term “crank” originates from a time in which motor vehicles were hand cranked by a motorist with a handle turned at right angles to a shaft. In more modern equipment the cranking for initiating combustion within an internal combustion chamber is performed by a starter motor (not shown).  FIG. 12  is a depiction of time versus voltage on the high side (+) of the battery  22  depicting an interval  236  before a crank state is entered, an interval  238  while the engine is cranked by the starter motor, and an interval  240  after the engine is started and hence, as the battery  22  begins charging due to the presence of a generator output voltage and periodic noise signal from a generator  242  which in combination with the battery power the circuit  220  (see  FIG. 5 ). The controller  210  maintains its characterization of the system  200  in the pre-crank state  234  so long as the battery voltage as sensed at the input  229  is greater than a threshold Vcrank and the starter enabled signal is still present. 
     Two paths  250 ,  252  cause the controller  200  to exit the pre-crank state  234 . One path  250  leads to a starting or crank state  254  which the, controller  210  transitions to as the engine is starting. A second path  252  leads back to the intial or power up state  230 , if the starter enabled signal is removed before engine cranking begins. The controller  210  transitions to the crank state  254  by a transition path  250  traversed on a decision that is based on sensed battery voltage. More particularly, the crank state  254  can be entered only when the battery voltage as sensed at the input  229  is less than a “Vcrank” threshold which is a constant programmed into the controller operating system. This constant is dependent on the system characteristics, but for one riding lawn mower system Vcrank is about 10 volts. 
     A crank timer variable Tcrank is started when the controller enters the crank state  254  and is updated while in that state. This timer variable is compared to a fixed or constant value of TcrankMIN programmed into the controller when the battery voltage rises above VcrankMin. The comparison between Tcrank and TcrankMIN is to avoid false passage through the crank state  254  due to transitory conditions within the system which might trigger entry to the crank state if this state were based on battery voltage alone. Such transitory drops in sensed battery voltage might be due to use and presence of accessories&#39; noise in the system not related to starting of the engine. As an example, assume the battery voltage drops below the threshold Vcrank but for only a short time. When the battery voltage drops, the controller sets the crank timer Tcrank to zero and the controller enters the crank state  254 . However, the drop in battery voltage is due to a transitory condition and immediately the battery voltage rises. Since the crank timer Tcrank just started, conditions are appropriate (Vbat&gt;Vcrank &amp;&amp; Tcrank&lt;TcrankMin) for the controller to exit the crank state  254  along the exit path  256  and return to the pre-crank state  234 . 
     The controller  210  enters a post crank state  260  based on sensed battery voltage at the input  229  to the controller and the value of the timer Tcrank that the controller initiated when the path  250  was traversed to the crank state  254 . As seen in the  FIG. 12  depiction, once the engine starts the battery voltage will again rise above the Vcrank value. However, this battery voltage comparison must also be accompanied by the timer Tcrank reaching a value greater than or equal to TcrankMIN. If both conditions are satisfied, the controller exits the crank state along the path  258  and enters the post crank state  260  after starting a post crank timer. Hopefully, the engine cranking by the starter motor has caused the engine to start, but the controller must account for the possibility that the engine does not start. The post crank timer counts to an upper limit or expiration value while the controller monitors an input  223  coupled to the battery through the detector circuit  222 . 
     Evaluation of signals on the high side of the battery has resulted in a better understanding of a signature of the electrical signals on the high side when the engine is running. The detection circuit  222  provides an analysis of noise on the high (+) battery terminal that is referred to herein as power system spectrum analysis or PSSA. In brief, the PSSA implemented by the detection circuit allows the controller  210  to detect an engine running condition by monitoring the electrical noise produced by the running engine in the 12 volt power system of the device. This noise is produced and comprises a signature of the combination of the engine stator, voltage generator, and voltage regulator for example of the riding lawn mower depicted in  FIG. 1 . 
     Returning to the state diagram of  FIG. 4 , a engine running state  262  is entered by the controller along a path  264  from the post crank state  260 , if a noise signal representative of a running engine is sensed at the input  223 . While in the engine running state, the controller updates a variable indicating engine run time since an initial or first start up of the engine. This variable is typically stored in non-volatile memory so that in the event the controller is disconnected from the battery, the run time of the engine is maintained. Most commonly, the controller exits the engine running state  262  when the operator turns an ignition switch to an off position and the engine stops. When this occurs the signature of a running engine is no longer present at the input  223  and the state  262  is exited along the transition path  266 . 
     The controller enters an engine stall state  270  for a brief period of one to two seconds. If during that short interval the signature of a running engine is again sensed at the input  223  the controller transitions along the path  272  back to the engine running state  262 . This sequence occurs when the engine briefly stalls and is hopefully not a frequent occurrence. In the disclosed example embodiment, the controller continues to increment the engine run time variable during the time spent in the engine stall state  270 . If the stall period timer of one to two seconds expires without reappearance of a noise signature at the input  223  the controller returns via the transition path  274  to its initial or the power up state  230 . 
     Returning to the block diagram of  FIG. 5 , additional details of the detector circuit  222  are described. The detector is connected to the battery by means of a blocking circuit  310  that impedes a direct current component of a battery signal from passing through the detector. An output  312  from the blocking circuit  310  is coupled to a first frequency attenuating filter  314  that attenuates signals passing through the blocking circuit having a frequency higher than a first threshold from passing through the detector. In accordance with the exemplary embodiment the threshold is 3000 hertz (3 khz) and the filter is also referred to as a low band pass filter since frequencies above 3 khz are blocked and attenuated. 
     A variable attenuator  320  is coupled to the first frequency attenuating filter  314  for attenuating signals from the first frequency attenuating filter  314  in a manner that is dependent on or based on the magnitude of signals from the first frequency attenuating filter. At low engine speeds (low rpm), the signals subsequent to the filter  314  tend to be relatively small in value. As the engine speeds increase (higher rpm) the size of the signals is larger. The variable attenuator  320  makes these signals more uniform in size due to operation of a feedback loop  321 , which implements automatic gain control. An output from the variable attenuator  320  passes through a constant gain amplifier  322  to a second frequency attenuating filter  324 . This second frequency attenuating filter impedes signals of a frequency greater than the first filter threshold (approx. 3 khz) passing through the detector from reaching the controller. Although higher frequency signals are attenuated by the first low pass filter  314 , some higher frequency signals bypass this filter and the second frequency attenuating filter  324  blocks these unwanted signals. An output from the second filter is level shifted by a dc restoration circuit  330  so that an A/D converter within the controller only receives positive voltage signals at the input  223 . 
     The combination of the two filters  314 ,  324 , variable attenuator  320  and constant gain amplifier  322  constitute the forward path. The feedback loop portion of the detector  222  includes a half wave voltage doubler  332 , which rectifies and shapes the signal output from the filter  324 . Next, a voltage delay circuit  334  only acts on signals greater than 2.4 volts and for signals less than this threshold, the feedback loop acts like a open circuit and prevents the automatic gain control from engaging signals less than 2.4 volt at the output. A loop filter  336  reduces noise in the feedback loop  321  and the bias circuit  338  is a standard circuit for biasing the attenuator.  FIGS. 6-11  depict circuit components that make up the detector  222  in greater detail. 
     A signal at the input to the controller has a well defined and discernable signature when the engine is running. A sequence of positive pulses appear at the input  223  and the controller receives those pulses which are analyzed after being converted to a digital number by the A/D converter internal to the controller. The controller continuously compares the received pulses&#39; amplitude and period to a present voltage (about 0.85 volts or more) and time (about 200 microseconds or lower) thresholds. In the absence of the noise from a running or operating engine, the input signal at the controller input  223  is a very small noise level below the preset voltage threshold. 
     What have been described above are examples of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.