Abstract:
An apparatus and method for automatic shut-off of a combustion engine driving a fluid pump of a fluid displacement unit is presented. The apparatus and method are designed to protect the fluid displacement unit form damage due to excessively high running speeds by shutting off the combustion engine and to automatically reset the combustion engine for manual restart subsequent to the combustion engine spinning down to a rest.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is the first application filed for the present invention. 
     TECHNICAL FIELD 
     The invention relates to monitoring of operating conditions and control of unattended fluid displacement equipment and, in particular apparatus and methods of monitoring an operating speed of a fluid displacement unit comprising a fluid pump powered by a combustion engine are described. 
     BACKGROUND OF THE INVENTION 
     In the field of forest fire control one colloquially uses the term “portable water pump” to refer to a fluid displacement unit. For the purpose of clear presentation of the subject matter of this application the term “fluid displacement-unit” will be used instead of the general term “water pump” and kept distinct from a “fluid pump”: a fluid displacement unit is an integral component adapted to convey water, the fluid displacement unit for forest fire control typically comprises a combustion engine driving a fluid pump. 
     In fire fighting, fluid displacement units are designed to operate unattended. The fluid displacement units typically convey water from a water store such as a lake. A fluid displacement unit conveys water from an input port such as a hose inserted in the lake to an output port such as a nozzle at and end of another hose. Operating characteristics of fluid displacement units are well established when the water supply at the input port is unlimited. 
     Water sources for forest fire fighting are sometimes limited in volume and when the water source is used up the fluid displacement units run dry. The closest water store to a forest fire is sometimes a slough or other limited store of water. Often the water in the water store is exhausted before the fire is put out or the fluid displacement unit is shut off. Typical operating characteristics of a fluid displacement unit when insufficient water is available to be drawn at the input port cannot be sustained for long periods of time without resulting damage to the fluid displacement unit. 
     The fluid pump and the combustion engine are designed to operate under load. Under load, water is conveyed through the fluid displacement unit. When insufficient water is available at the input port the load is decreased for the same torque provided by the combustion engine. The result is that the fluid pump develops a greater rotational speed and in turn the combustion engine tends to run at a higher speed. Higher running speeds induce heating in the mechanical components of the fluid pump and/or the combustion engine. Excessively high running speeds lead to excessive heating. Excessive heating results to damage to the parts of the fluid displacement unit by seizing either the fluid pump or the combustion engine. 
     It is known in the art to control rotational speed of combustion engines. There are numerous teachings of speed control enabling combustion engines to run at a predefined speed. These methods are unsuited for conveying of water since typically the cooling effects of the conveyed water onto the components of the fluid pump are taken into account in the design of fluid displacement units to minimize the production costs therefore leading to excessive heating when running dry. Other teachings call for operational speed monitoring and control allowing the fluid displacement unit to run at a lower idling speed when the water supply is insufficient at the intake port. Both of the above mentioned teachings are unsuited for the operation of a portable fluid displacement unit for forest fire control purposes since more often than not fuel resources are also limited and when water is not being pumped it is preferable that fuel resources be conserved. Current field practice utilizes methods of shutting off the combustion engine when the water supply is insufficient at the intake port. 
     Typically shutting off the engine involves a latching component which trips when an over speed condition in effect is sensed. To date, these latching components employ mechanical latching techniques and necessitate manual reset prior to restarting the combustion engine. More often than not ignorant and rookie/frustrated forest fire fighters omit resetting the latch and endlessly attempting to restart the combustion engine, often leading to flooding of the engine. Other rookie/frustrated fire fighters aware of the latching component block the action of the latching component in a position enabling operation of the fluid displacement unit under normal conditions but defeating the purpose of this protection against damage to the fluid displacement unit running at high speeds due to an insufficient supply of water at the intake port. 
     There is therefore a need for an apparatus and method for automatic shut-off of a combustion engine driving a fluid pump of a fluid displacement unit to protect the fluid displacement unit form damage and to automatically reset the combustion engine for manual restart subsequent to the combustion engine spinning down to a rest. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a fluid displacement unit having a fluid pump driven by a combustion engine, the fluid displacement unit being adapted to automatically shut-off and reset in the absence of sufficient fluid at the fluid pump&#39;s intake port. 
     It is another object of the invention to enable the fluid displacement unit to react in real-time to the absence of sufficient fluid in the fluid pump&#39;s intake port to prevent damage to the combustion engine or the fluid pump. 
     It is a further object of the invention to provide an electrical circuit for automatically shutting off a combustion engine in the absence of sufficient fluid in the fluid pump&#39;s intake port, the circuit being adapted to reset after the combustion engine spins down to a rest. 
     It is a further object of the invention to provide a portable fluid displacement unit having a fluid pump driven by a combustion engine adapted to automatically shut-off and reset for a manual restart that is operative in restrictive elemental conditions such as are encountered in forest fire fighting. 
     It is a further object of the invention to provide a low power circuit adapted to: monitor the operating speed of the fluid displacement unit, shut-off and reset the combustion engine for a manual restart after the combustion engine has spun down to a rest. 
     It is yet another object of the invention to provide a method of monitoring the operating speed of the fluid displacement unit, shut-off and reset the combustion engine for a manual restart after the combustion engine has spun down to a rest. 
     According to one aspect of the invention, a method of automatically limiting an operating speed of a fluid displacement unit is provided. The fluid displacement unit has a fluid pump powered by a combustion engine. The automatic limiting of the operating speed of the fluid displacement unit is enabled by an automatic shut-off and reset control circuit. The automatic shutoff and reset control circuit provides a frequency acceptance window and an attention electrical signal. The method teaches a sequence of steps according to which: an input electrical signal is received by the automatic shut-off and reset control circuit. The input electrical signal is representative of the operation of the fluid displacement unit. The input electrical signal is cyclical in nature having a frequency representative of a current operating speed the fluid displacement unit. The input electrical signal also provides electrical power to the automatic shut-off and reset control circuit. The automatic shut-off and reset control circuit is enabled to store electrical power to drive its constituent components. The automatic shutoff and reset control circuit generates the frequency acceptance window which represents a range of allowable frequencies the input electrical signal can have. The frequency acceptance window has a maximum cut-off frequency representative of a maximum allowable operating speed of the fluid displacement unit can have. The automatic shut-off and reset control circuit also generates the attention electrical signal. The attention electrical signal is characterized by an increasing potential. The attention electrical signal is adapted to reach a shut-off threshold level potential over a period of time at least as long as one cycle of the input electrical signal when the frequency of the input electrical signal represents the maximum allowable operating speed of the fluid displacement unit. The automatic shut-off and reset control circuit selectively decreases the potential of the attention electrical signal to a minimum potential level to prevent the attention electrical signal from reaching the shut-off threshold level potential if the frequency of the input electrical signal is within the frequency acceptance window. Fuel ignition in the combustion engine is inhibited if the potential of the attention electrical signal exceeds the shut-off threshold level potential. Manual restart of the fluid displacement unit is provided by re-enabling fuel ignition in the combustion engine after the combustion engine has spun down to rest. 
     According to another aspect of the invention, a fluid displacement unit having a fluid pump driven by a combustion engine and an automatic shut-off and reset control circuit is provided. The automatic shut-off and reset control circuit receives from an induction coil associated with the combustion engine an input electrical signal representative of the operation of the fluid displacement unit. The automatic shut-off and reset control circuit has an electrical power store, a first electrical signal generator, a second electrical signal generator, a decision circuit, a latching circuit and a biased electrical switching component. The power store is supplied with electrical power from the input electrical signal and drives the components of the automatic shut-off and reset control circuit. The first electrical signal generator is adapted to generate the first electrical signal defining a frequency acceptance window. The frequency acceptance window represents a range of allowable operating speeds of the fluid displacement unit. The frequency acceptance window has a maximum cut-off frequency which represents the maximum allowable operating speed of the fluid displacement unit. The second electrical signal generator is adapted to generate an attention electrical signal. The attention electrical signal is characterized by an increasing potential. The attention electrical signal is adapted to reach a shut-off threshold level potential over a period of time at least as long as one cycle of the input electrical signal, when the input electrical signal represents the maximum allowable operating speed of the fluid displacement unit. The decision circuit is adapted to decrease the potential of the attention electrical signal to a minimum potential level if the frequency of the input electrical signal is within the frequency acceptance window. The latching component is adapted to: compare the attention electrical signal against the shut-off threshold level potential, trip when the attention electrical signal exceeds the shut-off threshold level potential and latch once tripped in a state in which a shut-off electrical signal is generated for as long as electrical power is provided to the latching circuit. The biased electrical switching component has a default deactivated state and an activated state. The biased electrical switching component is connected such that fuel ignition in the combustion engine is inhibited when the biased electrical switching component is activated by the shut-off electrical signal. The biased electrical switching component automatically resets to the default deactivated state in the absence of the shut-off electrical signal. 
     According to yet another aspect of the invention, an automatic shut-off and reset control circuit for limiting the operating speed of a combustion engine is provided. The combustion engine has an ignition coil providing an input electrical signal representative of the operation of the combustion engine. The automatic shutoff and reset control circuit has an electrical power store, a first electrical signal generator, a second electrical signal generator, a decision circuit, a latching circuit and a biased electrical switching component. The power store is supplied with electrical power from the input electrical signal and drives the components of the automatic shut-off and reset control circuit. The first electrical signal generator is adapted to generate the first electrical signal defining a frequency acceptance window. The frequency acceptance window represents a range of allowable operating speeds of the combustion engine. The frequency acceptance window has a maximum cut-off frequency which represents the maximum allowable operating speed of the combustion engine. The second electrical signal generator is adapted to generate an attention electrical signal. The attention electrical signal is characterized by an increasing potential. The attention electrical signal is adapted to reach a shut-off threshold level potential over a period of time at least as long as one cycle of the input electrical signal, when the input electrical signal represents the maximum allowable operating speed of the combustion engine. The decision circuit is adapted to decrease the potential of the attention electrical signal to a minimum potential level if the frequency of the input electrical signal is within the frequency acceptance window. The latching component is adapted to: compare the attention electrical signal against the shut-off threshold level potential, trip when the attention electrical signal exceeds the shut-off threshold level potential and latch once tripped in a state in which a shut-off electrical signal is generated for as long as electrical power is provided to the latching circuit. The biased electrical switching component has a default deactivated state and an activated state. The biased electrical switching component is connected such that fuel ignition in the combustion engine is inhibited when the biased electrical switching component is activated by the shut-off electrical signal. The biased electrical switching component automatically resets to the default deactivated state in the absence of the shut-off electrical signal. 
     According to another aspect of the invention the biased electrical switching component is connected across an ignition rail and an ignition return rail. 
     According to yet another aspect of the invention the biased electrical switching component is a solid state switch such as a transistor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which: 
     FIG. 1 is a schematic diagram showing, according to the invention, components of a fluid displacement unit; and 
     FIG. 2 is a circuit diagram showing, according to the invention, an automatic shut-off and reset control circuit. 
    
    
     It will be noted that throughout the appended drawings, like features are identified by like reference numerals. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a schematic diagram showing, according to the invention, components of a fluid displacement unit  10 . The fluid displacement unit  10  has fluid pump  12  driven by a combustion engine  14  through a drive shaft  16 . 
     The fluid pump  12  is adapted to convey a fluid, such as water. The fluid is received at the fluid pump  12  through a hose  18  having two ends. The hose  18  is connected at an end to the fluid pump  12  and is connected at the other end to a debris filter. The debris filtered end of the hose  18  represents an intake port  20  for the fluid pump  12 . The fluid is delivered from the fluid pump  12  via another hose  22 . The hose  22  is connected at an end to the fluid pump  12  and is connected at the other end to a nozzle  24  used in forest fire fighting. 
     The combustion engine  14  is adapted to be manually started, employing for example a pull string starter (not shown) operatively connected to a crank shaft (not shown). The combustion engine  14  has spark plugs (not shown) for enabling ignition of fuel in operating the combustion engine  14  and at least one induction coil providing a spark potential to create sparks during the operation of the combustion engine  14 . To manually start the combustion engine  14 : the pull string starter is used to rotate the crank shaft, the at least one induction coil creates the necessary ignition spark potential to ignite the fuel which takes over in driving the combustion engine  14  and the combustion engine  14  continues to operate on its own. One simple way to stop the combustion engine is to remove the ignition spark potential. One way of removing the ignition spark potential is to short the ignition coil output. 
     According the embodiment shown in FIG. 1, the combustion engine  14  has an induction coil  32  used to provide an ignition spark current delivered onto an ignition rail  34 . The induction coil arrangement presented herein and with reference to this embodiment does not limit the scope of the invention and is only used for the purpose of illustrating the invention. 
     According to the preferred embodiment, the combustion engine  14  is further adapted with an automatic shut-off and reset control circuit  36 , referred to as the control circuit  36  hereinafter and shown in detail in FIG.  2 . The control circuit  36  is connected to ignition rail  34  and a current return rail  38  which is typically a chassis of the fluid displacement unit  10 . Return rail  38  is shown in FIG. 2 as chassis ground connections. The control circuit  36  receives an input electrical signal representative of the operation of the fluid displacement unit  10  extracted from rail  34 . The operation of the control circuit  36  is sustained by the current provided by the input electrical signal. The operation of the control circuit  36  is dependent on the characteristics of the potential of the input electrical signal. Specifically the potential of the input electrical signal varies cyclically in time at a temporal frequency related to the rotation of the drive shaft  16  as will be understood by persons of ordinary skill in the art. 
     According to an implementation of the preferred embodiment, the control circuit  36 , shown in FIG. 2, is adapted to derive power from the input electrical signal provided on rail  34 . The input electrical signal provided by rail  34  has an alternating current waveform whose frequency is representative of a current operating speed of the fluid displacement unit  10 . The diode  39  is used rectify the input electrical signal. 
     A rectified input electrical signal  40  is provided through a limiting resistor  42  to a voltage regulator circuit  44  comprised of a shunt resistor  46 , a voltage defining Zener diode  48  and a power storing capacitor  50 . The voltage regulator circuit  44  provides electrical power to the rest of the components of the control circuit  36 . Electrical power provision is schematically shown by the “V+” label throughout the diagram. 
     According to an implementation of the preferred embodiment, the rectified input electrical signal  40  is provided as a clock signal through another limiting resistor  52  to a first signal generator  53  comprising: an SR flip-flop  54  having a data input D tied high and a set input S tied low, a capacitor  56  and a current limiting resistor  58 . The SR flip-flop  54  is clocked on every cycle of the rectified input electrical signal  40 . The SR flip-flop  54  is clocked at the current operating speed of the combustion engine  14 . 
     On every clock cycle, the SR flip-flop  54  sets a non-inverting output Q to the logical value of the data input D. Since the data input D is tied high the Q input is set logic high on every cycle. Tied to the non-inverting output Q is the capacitor  56  drawing current from the non-inverting output Q through the limiting resistor  58 , when the output Q is high. Capacitor  56  and the limiting registor  58  control the time period in which the capacitor  56  charges. Once this time period elapses, capacitor  56  is charged to the value of the supply voltage V+ which represents logic high. The capacitor  56  is also tied to a reset input R of the SR flip-flop  54 . Once capacitor  56  charges, the reset input R is therefore driven high which resets the SR flip-flop  54  setting the non-inverting output Q to ground. As the non-inverting output Q sits at ground the capacitor  56  starts discharging through resistor  58 . On a subsequent cycle of the input electrical signal, as the SR flip-flop  54  is clocked again, some current is provided through a resistor  60  to a transistor  62  connected across the capacitor  56  to speed up the discharging process before charging of the capacitor  56  ensues again. 
     Therefore for long consecutive cycles corresponding to a low current operating speed of the combustion engine  14 , the non-inverting output  54  provides a waveform which is logic high for a fixed time period at the beginning of each cycle imposed by capacitor  56  and resistor  58 . This fixed time period is chosen to be the period of one cycle corresponding to the maximum allowable operating speed of the first electrical signal generator provides a frequency acceptance window for frequencies of the input electrical signal corresponding to operating speeds below the maximum allowable operating speed of the combustion engine  14 . 
     According to an implementation of the preferred embodiment, during the time that the non-inverting output Q of the SR flip-flop  54  is logic high, the non-inverting output Q provides a charging voltage to two capacitors  64  and  66 . As capacitor  64  charges through limiting resistors  68  and  70 , a base current is provided to transistor  74  enabling the transistor to conduct. As the capacitor  64  is charged up the base current to the transistor  74  is removed. The transistor  74  is connected across capacitor  66 . Therefore as soon as the non-inverting output Q goes high, transistor  74  discharges capacitor  66  through resistor  76 . The value of resistor  76  controls the time period in which the capacitor  66  discharges. A fast discharge of the capacitor  66  is preferred. Capacitor  64 , resistor network  68 ,  70  and transistor  74  represent a decision circuit  75  adapted to discharge capacitor  66  if the frequency of the input electrical signal is within the acceptance frequency window imposed by the first signal generator  53   
     Therefore after the non-inverting output Q goes high, after the capacitor  64  charges up and after transistor  74  no longer conducts, the capacitor  66  starts charging through the resistor network  76 ,  78 . The combined values of the resistors  76  and  78  control the time period in which the capacitor  66  charges. Compared to the time period in which the capacitor  66  discharges, a long charge time period is preferred (at least longer than one cycle of the frequency of the input electrical signal when the input electrical signal represents the maximum allowable operating speed of the combustion engine). More on the preferred length of the charge time period of capacitor  66  below. The capacitor  66  charges for as long as the non-inverting output Q of the SR flip-flop is logic high. Therefore capacitor  66  and resistor network  76 ,  78  represents a second signal generator  77 . The second signal generator  77  is adapted to provide an attention electrical signal  79 . 
     According to the invention, the characteristics of the control circuit  36  as described are such that as soon as the current operating speed of the combustion engine  14  becomes higher than the maximum allowable operating speed, perhaps due to insufficient water at the intake port  20  of fluid displacement unit  10 , transistor  62  is driven into conduction before capacitor  56  has a chance to fully charge and the capacitor  56  is discharged. The non-inverting output Q therefore is latched logic high because the capacitor  56  does not charge fully and the SR flip-flop  54  is not reset from cycle to cycle of the input electrical signal. With the non-inverting output Q of the SR flip-flop  54  kept at logic high for a period of a few cycles, capacitor  66  has time to charge up driving the attention electrical signal  79  to higher and higher potential levels from cycle to cycle. 
     According to an implementation of the preferred embodiment, the potential level of the attention electrical signal  79  developed across capacitor  66  and resistor  76  is provided to a non-inverting input of a comparator  80  of a latching circuit  81 . The comparator  80  is supplied at its inverting input with a threshold potential level provided by bleed resistor  82  and at least one series diode  84 . As long as the voltage at the non-inverting input of the comparator  80  is kept below the inverting input of comparator  80 , comparator  80  keeps an output  86  to ground. As soon as the comparator  80  is in a state in which the voltage at the non-inverting input becomes larger than the inverting input, the comparator  80  drives the output  86  logic high. As soon as the output  86  of the comparator  80  goes logic high a positive feedback resistor network made up of resistors  88  and  90  provides the necessary voltage at the non-inverting input to keep the comparator  80  latched in a state in which it provides a logic high at output  86 . The comparator  80  is latched in a state in which it provides a logic high at output  86  for as long as there is power provided to the comparator  80  from the power storing capacitor  50  of the voltage regulator circuit  44 . Driving the output  86  of the comparator  80  logic high provides a shut-off signal. 
     According to an implementation of the preferred embodiment, a biased electrical component such as a transistor  92  is driven into conduction as soon as the output  86  of the comparator  80  is driven logic high. Transistor  92 , for as long as it is driven shunts rail  34  to chassis ground  38  through a current limiting resistor  94  therefore providing automatic shut-off of the combustion engine  14  if the current operating speed of the combustion engine  14  exceeds the maximum allowable operating speed. 
     With ignition rail  34  shunted to ground, the combustion engine  14  can no longer sustain ignition and spins down to rest. As the combustion engine  14  spins down to rest, the power storing capacitor  50  is no longer provided with power and is depleted by the latched components of the control circuit  36 . The power storing capacitor is chosen such that it is depleted in a time period longer than that required for the combustion engine  14  to spin down to rest. 
     According to the invention, without power, the comparator  80  can no longer maintain output  86  at logic high. Transistor  92  is no longer provided with the necessary base current to conduct and no longer provides a shunt for the ignition rail  34  to ground therefore automatic reset is provided for the fluid displacement unit  10  after the combustion engine  14  has spun down to a rest. 
     According to the invention, a biased electrical switching component  92  is employed in effecting automatic control over the operation of the fluid displacement unit  10 . The biased electrical switching component  92  has a default deactivated state and an activated state. The biased electrical switching component is operatively connected so as to selectively inhibit fuel ignition in the combustion engine  14  when activated by the shut-off signal. The biased electrical switching component  92  is connected across the ignition rail  34  and chassis ground  38  so that when activated, the ignition rail  34  is shunted thereby preventing ignition in the combustion engine  14 . The biased feature of the biased electrical switching component  52  enables its automatic reset to the default deactivated state in the absence of the shut-off signal  50 . As examples of biased electrical switching components there are: electromechanical relays, solid state relays, power transistors, etc. 
     An electromechanical relay is not preferred in a preferred implementation of the invention because, although less expensive, the electromechanical relay is prone to mechanical failure due to repetitive use and consumes a considerable amount of electrical power decreasing the efficiency of a portable type fluid displacement unit. 
     Should the portable and self-powered requirements be a non-issue, the use of relays can be enabled by an electrical power buffer such as a battery or a large capacitative network (not shown). 
     The embodiments of the invention described above are intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.