Patent Grant
7467739
1. Field of the Invention
The present invention relates to a combustion-powered, fastener-driving tool for driving fasteners, such as nails, rivets, or staples. The combustion-powered, fastener-driving tool includes a cylinder in the top section of which is formed a combustion chamber. The combustion-powered, fastener-driving tool generates a motive force for driving a piston in the cylinder by igniting a mixture of air and a flammable gas in the combustion chamber.
2. Description of the Related Art
Conventional combustion-powered, fastener-driving tools is disclosed, for example, in U.S. Pat. Nos. 5,197,646 and 4,522,162. Such conventional combustion-powered, fastener-driving tools typically include a housing serving as the main enclosure of the tool, a cylinder accommodated in the housing, a piston disposed in the cylinder and guided by the cylinder to move vertically in a reciprocating motion, a driving blade fixed to the piston for driving a fastener into a workpiece when the piston moves in a downward operation, a combustion chamber frame provided in the housing that slides vertically while guided by the periphery of the cylinder, the combustion chamber frame forming a combustion chamber having walls defined by the combustion chamber frame and the piston when the combustion chamber frame is moved upward, an injection opening for injecting a flammable gas from a gas cylinder accommodated in a grasping portion or a handle into the combustion chamber, a fan provided in the combustion chamber, a spark plug for igniting a mixture of air and the flammable gas injected into the combustion chamber, a trigger mounted on the handle, and an ignition system electrically connected to the trigger for producing a spark in the spark plug when the trigger is operated.
The combustion-powered, fastener-driving tool having this construction supplies a mixture of the flammable gas from the gas cylinder mounted on the housing and air to the combustion chamber. The combustion-powered, fastener-driving tool generates a spark with the spark plug in the combustion chamber when the trigger is operated to detonate the mixture in the combustion chamber. The resulting explosion generates a driving force for driving a nail or other fastener. Unlike a compressed-air, fastener-driving tool that uses compressed air as a driving source, this combustion-powered, fastener-driving tool requires no compressor and is, therefore, much easier to transport to a construction site or the like. Further, the combustion-powered, fastener-driving tool can be conveniently provided with an internal power source, such as a battery, so that the tool can be used in any environment without requiring a commercial power supply.
As shown in
However, a spark from the spark plug cannot reliably ignite a gas concentration outside of the gas concentration band, that is, when the ignition ratio is less than 100%. In fact, the gas in the combustion chamber does not ignite at all when the concentration of gas separates farther from the upper or lower limits of the gas concentration band. Hence, there is a demand to expand this gas concentration band at which the ignition ratio is 100% in order to ensure stable ignition.
However, the amount of liquid injected from the gas cylinder is easily influenced by temperature inside the faster-driving tool or external air temperature. Such changes in the amount of liquid gas injected at a low temperature or a high temperature may result in a gas concentration outside of the gas concentration band, making it impossible to ignite the mixture reliably. This unreliable ignition is likely due primarily to a flameout phenomenon in which the electrode of the spark plug robs the heat from the spark.
In view of the foregoing, it is an object of the present invention to provide a combustion-powered, fastener-driving tool capable of producing reliable sparks by preventing this flameout phenomenon and increasing the opportunities of ignition by expanding the gas concentration range in which the fuel can be stably ignited or burned.
It is another object of the present invention to obtain a gas concentration range that does not depend on temperature.
The following is a general description of representative combustion-powered, fastener-driving tools disclosed in this specification, wherein the combustion-powered, fastener-driving tool according to the present invention is assumed to be disposed in an orientation in which a fastener is fired vertically downward against a workpiece.
According to one aspect of the present invention, a combustion-powered, fastener-driving tool includes: a housing; a cylinder fixedly disposed in the housing; a combustion chamber disposed on top of the cylinder, the combustion chamber accommodating a gaseous mixture of existing air in the combustion chamber and fuel injected therein; a spark plug that is disposed in the combustion chamber and generates a spark to combust the gaseous mixture in the combustion chamber; a trigger that produces the spark in the spark plug when operated; a piston movably supported in the cylinder and driven by combustion in the combustion chamber; a driving blade coupled to the piston for driving a fastener; and a spark controller that generates a plurality of sparks in succession with the spark plug.
The combustion-powered, fastener-driving tool as defined above may further include a temperature sensor that detects a tool temperature. The tool temperature indicates the temperature of the fastener-driving tool primarily increased by heat generated in the combustion chamber. The spark controller varies the number of sparks generated in the spark plug based on the temperature detected by the temperature sensor.
The spark controller may control the spark plug to generate a first predetermined number of sparks when the tool temperature is within a predetermined range, a second predetermined number of sparks when the tool temperature is lower than lowest temperature in the predetermined range, and a third predetermined number of sparks when the tool temperature is higher than highest temperature in the predetermined range, wherein the second predetermined number and the third predetermined number are greater than the first predetermined number.
Preferably, the spark controller includes a spark capacitor charging circuit, and a spark energy accumulating capacitor connected to the spark capacitor charging circuit. The spark energy accumulating capacitor supplies energy to the spark plug to generate the spark, wherein the spark capacitor charging circuit varies a charge time for charging the spark energy accumulating capacitor based on the number of sparks to be generated.
It is also preferable that the spark controller include a combustion sensor that is disposed in the housing, detects occurrence of combustion of the gaseous mixture in the combustion chamber, and outputs a detection signal indicative of occurrence of combustion, and that the spark controller cancel the generation of sparks with the spark plug when the combustion sensor outputs the detection signal.
Since the combustion-powered, fastener-driving tool of the present invention generates a plurality of sparks in the spark plug when the trigger is operated, the combustion-powered, fastener-driving tool can expand the gas concentration range, that is, the gas concentration band at which a reliable ignition ratio is obtained. Accordingly, stable ignition or combustion can be achieved at low temperatures or high temperatures.
By reducing the number of generated sparks based on the temperature, or varying the amount of consumed energy required for generating sparks, based on the number of sparks to be generated, the combustion-powered, fastener-driving tool of the present invention can reduce unnecessary power consumption in the battery, which is mounted in the combustion-powered, fastener-driving tool.
The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which:
A combustion-powered, fastener-driving tool according to a preferred embodiment of the invention will be described with reference to the accompanying drawings. Hereinafter, the terms “upward”, “downward”, “upper”, “lower”, “above”, “below”, “beneath” and the like will be used throughout the description assuming that the combustion-powered, fastener-driving tool is disposed in an orientation in which it is used as shown in
As shown in
The magazine 13 mounted on the housing 14 includes a spark controller 24. The spark controller 24 is electrically connected to such components as the trigger 12, a push switch 23, and a temperature sensor 5 in order to receive electrical signals generated by these components for controlling the charging of a spark energy accumulating capacitor (spark capacitor) C2 described later and for controlling the generation of sparks in the spark plug 9, as well as for starting and controlling the motor 8, which drives the fan 6. The spark controller 24 is also electrically connected to a battery 25, such as a Ni—Cd battery that is mounted in a holder (not shown) provided in part of the handle 11. The battery 25 supplies power to the spark controller 24.
The cylinder 4 and the head cover 20 are internally disposed in the housing 14 and fixed thereto. However, the combustion chamber frame 15 is coupled with the push lever 21 disposed in the bottom of the cylinder 4 and is guided by the housing 14 and the cylinder 4. A spring 26 urges the combustion chamber frame 15 downward in the drawing, that is, in a direction for driving a nail 51, serving as the fastener in the preferred embodiment. Hence, the combustion chamber frame 15 is capable of moving axially with respect to the housing 14.
When the push lever 21 is pressed against a workpiece 50, such as a wood material, the push lever 21 opposes the urging force of the spring 26 and the combustion chamber frame 15 moves above the cylinder 4, forming a combustion chamber 15a. Specifically, the combustion chamber 15a is a space enclosed by the combustion chamber frame 15, the head cover 20, and the piston 10, in which a mixture of a combustion gas and air is burned. In order to form a hermetically sealed combustion chamber 15a, a seal member 22, such as an O-ring, is interposed between the upper end of the cylinder 4 and the lower end of the head cover 20.
A slidable seal member 27 is provided around the piston 10 so that the piston 10 can move vertically within the cylinder 4. Provided below the cylinder 4 are an exhaust hole 3, a check valve (not shown) for opening and closing the exhaust hole 3, and the bumper 2 against which the piston 10 collides. When the piston 10 abruptly moves to its bottom dead point to drive the nail 51 and collides with the bumper 2, the bumper 2 deforms to absorb excess energy in the piston 10.
The combustion chamber 15a accommodates the fan 6, which can be rotated by the motor 8 disposed above the head cover 20; the spark plug 9 for generating a spark when the trigger 12 is operated; and the injection opening 19 for injecting flammable gas into the combustion chamber 15a from the gas cylinder 7, which stores this flammable gas (liquid gas). Fins 16 are also provided around the inner periphery of the combustion chamber 15a as ribs that protrude radially inward.
The magazine 13 and the tail cover 1 are mounted below the housing 14. The magazine 13 is filled with a plurality of the nails 51. The tail cover 1 guides the nails 51 supplied from the magazine 13 and sequentially sets the nails 51 beneath the piston 10.
In the static state shown in
If a user grips the handle 11 and pushes the end of the push lever 21 against the workpiece 50 when the fastener-driving tool 100 is in this state, the push lever 21 moves upward against the opposing force of the spring 26, causing the combustion chamber frame 15, which is coupled to the push lever 21, to rise to the position shown in
As shown in
After pressing the push lever 21 against the workpiece 50, the user then pulls the trigger 12 provided on the handle 11 to activate the spark controller 24. At this time, the spark controller 24 controls the spark plug 9 to produce a plurality of sparks in succession for igniting and burning the gaseous mixture. The combusted gas expands to move the piston 10 downward and strike the nail 51 in the tail cover 1.
After striking the nail 51, the piston 10 contacts the bumper 2, and the combusted gas is discharged from the cylinder 4 via the exhaust hole 3. As described above, a check valve is disposed in the exhaust hole 3. This check valve is closed after the combusted gas has been discharged from the cylinder 4 and at the point that the interior of the cylinder 4 and the combustion chamber 15a have reached atmospheric pressure. While the gas remaining in the cylinder 4 and the combustion chamber frame 15 has just been combusted and is high in temperature, the heat from the combusted gas is absorbed by the inner walls of the cylinder 4 and combustion chamber frame 15 and by the fins 16 and the like, thereby rapidly cooling the gas. As a result, the pressure in the combustion chamber 15a drops to atmospheric pressure or below (thermal vacuum) and the piston 10 is drawn back to its initial top dead center.
When the user subsequently releases the trigger 12 (turns the trigger 12 off) and lifts the tool, the push lever 21 separates from the workpiece 50, allowing the push lever 21 and the combustion chamber frame 15 to move downward by the urging force of the spring 26 and return to the position shown in
In the state shown in
As described above, a feature of the present invention is that the spark controller 24 controls the spark plug 9 to generate a plurality of sparks in succession. In order to ensure stable ignition with the spark plug, the spark controller 24 according to the present invention has the structure described below.
The computation control IC 241 has an external crystal oscillator PZT1 for generating a clock signal required by the computation control IC 241 itself as a timing signal. The computation control IC 241 receives such control input signals as an ON signal from the trigger 12, an ON signal from the push switch 23, and a detection signal from the temperature sensor 5 and outputs control signals required for input stage transistors in the spark capacitor charging circuit 242, spark circuit 243, motor drive circuit 244, and motor regular operation circuit 245 to control the operations of these circuits. The computation control IC 241 is also electrically connected to a power source control circuit IC2 and halts output from this circuit when output from the power circuit 246 is less than or equal to a prescribed voltage.
The spark capacitor charging circuit 242 includes transistors Q1-Q3 forming switch circuits, a booster coil T1, a chopper switch transistor Q5, and a drive signal generating circuit (oscillator) IC4 for outputting a drive signal to the chopper switch transistor Q5. Through the switching operation of the chopper switch transistor Q5, the spark capacitor charging circuit 242 generates a voltage higher than that of the battery 25 (7.2 V) in the secondary winding of the booster coil T1. This voltage charges the spark energy accumulating capacitor C2 via a diode D2 as a voltage having a single polarity. The charge voltage of the spark energy accumulating capacitor C2 is 150 V, for example.
The spark circuit 243 includes a spark coil T2 having a primary winding connected in series to the spark energy accumulating capacitor C2, a discharge thyristor SCR1 provided for discharging the charge voltage of the spark energy accumulating capacitor C2 through the primary winding of the spark coil T2, and the drive transistor Q4 for supplying a spark signal having a prescribed pulse width to a gate of the discharge thyristor SCR1. The computation control IC 241 forms and supplies a spark signal having the prescribed pulse width for driving the transistor Q4 when the trigger 12 is turned on.
After the spark energy accumulating capacitor C2 has been charged to the prescribed voltage, such as 150 V, the computation control IC 241 supplies the spark signal (conducting pulse signal) to the gate of the discharge thyristor SCR1, so that the discharge thyristor SCR1 becomes electrically conductive. Accordingly, the charge in the spark energy accumulating capacitor C2 is discharged via the discharge thyristor SCR1 and the primary winding of the spark coil T2. As a result, a high voltage of 15 KV, for example, is induced in the secondary winding of the spark coil T2, and this high voltage generates a spark in the spark plug. A feature of the present invention is that a plurality of sparks is generated successively in the spark plug when the trigger 12 is operated. The number of sparks that are generated successively is increased if the temperature in the operating environment is low or high with respect to a predetermined temperature.
Next, a sample operation of the fastener-driving tool 100 will be described for the case of generating three sparks.
The operations for obtaining the charge waveform shown in
After the charging time T1 has elapsed, the computation control IC 241 outputs a LOW level control signal to the base of the transistor Q4 for a prescribed time (10 msec, for example). This control signal turns the transistor Q4 on, and supplies a current to the gate of the discharge thyristor SCR1 for turning the discharge thyristor SCR1 on. When the discharge thyristor SCR1 is turned on, the accumulated charge in the spark energy accumulating capacitor C2 is discharged via the discharge thyristor SCR1 and the primary winding of the spark coil T2, inducing a high voltage, such as 15 KV, in the secondary winding of the spark coil T2 and generating a spark in the spark plug 9 due to the high voltage.
When the discharge thyristor SCR1 discharges the energy accumulated in the spark energy accumulating capacitor C2, characteristics caused by a decline in anode voltage returns the discharge thyristor SCR1 to an off state. After the computation control IC 241 has output the control signal to the base of the transistor Q4 for the prescribed time (10 msec), the computation control IC 241 changes the control signal to the HIGH level, turning off the transistor Q4.
Hereafter, similar operations of the spark controller 24 are applied to the spark energy accumulating capacitor C2 for a second charging time T2 and a third charging time T3. After each of the charging times T2 and T3 elapses, the discharge thyristor SCR1 is turned on to generate a spark in the spark plug 9.
As described above, the gas concentration band is the range in which the ignition ratio is 100%. As shown in
With this type of combustion-powered, fastener-driving tool, the combustion-powered, fastener-driving tool must prevent unnecessary power consumption since the driving source is a battery. Therefore, in the preferred embodiment of the present invention, the temperature sensor 5 is preferably used to vary the number of sparks by steps. While it is more effective to position the temperature sensor 5 as near the combustion chamber 15a as possible, the temperature sensor 5 need not be placed in the area for accommodating the gas cylinder 1, but may instead be placed on the top surface of the head cover 20, a side surface of the cylinder 4, or the like. The temperature sensor 5 detects the temperature of the fastener-driving tool 100 primarily increased by heat generated in the combustion chamber 15a.
Prior to beginning the control operation, the battery 25 must be inserted in the fastener-driving tool 100 so that the fastener-driving tool 100 is operable. At the beginning of the control process in S101, the spark controller 24 determines whether the trigger 12 is on. If the trigger 12 is on (S101: YES), then the process advances to S102.
In S102 the spark controller 24 detects the battery voltage V. In S103 the temperature sensor 5 detects the temperature of the fastener-driving tool 100. In S104 the spark controller 24 determines the number of sparks to be generated based on the relationship of the temperature and the number of sparks shown in
In S105 the spark controller 24 sets charging times T1, T2, T3, and the like for charging the spark energy accumulating capacitor C2 for each spark. In S106 the spark controller 24 sets a charge number (spark number) n for charging the spark energy accumulating capacitor C2 for the first charge. In S107 the spark controller 24 begins charging the spark energy accumulating capacitor C2.
In S108 the spark controller 24 determines whether the specified charge time has elapsed. When the specified charge time has elapsed (S108: YES), then in S109 the spark controller 24 turns the discharge thyristor SCR1 on, induces a high voltage in the spark coil T2, and controls the spark plug 9 to generate a spark. In S110 the spark controller 24 increments the charge number n for charging the spark energy accumulating capacitor C2 (n=n+1). In S111 the spark controller 24 determines whether the charge number n has reached a preset number Sc.
If the spark controller 24 determines in S111 that the spark number n has not reached the preset number Sc (S111: NO), then in S113 the spark controller 24 determines whether the trigger 12 has not yet been turned off. If the trigger 12 has not yet been turned off (S113: NO), then the process returns to S107 and the spark controller 24 begins charging the spark energy accumulating capacitor C2.
However, if the spark controller 24 determines in S111 that the spark number n has reached the preset number Sc (S111: YES), then in S112 the spark controller 24 determines whether the trigger 12 has been turned off. If the trigger 12 has been turned off (S112: YES), then the spark controller 24 returns to the initial state.
In the preferred embodiment described above, the charging time for the three sparks is uniformly controlled as T1=T2=T3. However, the charging time may be varied for each spark. In the embodiment shown in
In the preferred embodiment described above, a plurality of sparks is generated in response to the operation o_ the trigger. However, if the ignition of burning of fuel gas by a spark generated in the middle of the plurality of sparks is detected, it is possible to cancel the generation of other sparks after this ignition period. For example, using the graph of temperatures and spark numbers shown in
Cancelling subsequent sparks after combustion is achieved is useful for extending the life of the battery.
While the invention has been described in detail with reference to specific embodiments thereof, it would be apparent to those skilled in the art that many modifications and variations may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims.
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