Abstract:
A suspension mechanism for a motor of a combustion chamber fan in a combustion powered hand tool constructed and arranged for driving a driver blade to drive a fastener into a work piece, the tool generating an upward axial acceleration of the motor upon a combustion in the chamber, a subsequent reciprocal axial acceleration of the motor when the piston bottoms out on a bumper, at least one of the accelerations causing the motor to oscillate relative to the tool, the suspension mechanism includes a suspending portion configured for providing progressive dampening to the motor upon the generation of the axial accelerations.

Description:
RELATED APPLICATION 
     The present application is related to copending U.S. patent application Ser. No. 08/996,284, filed Dec. 22, 1997 for “Combustion Powered Tool with Improved Combustion Chamber Fan Motor Suspension”, which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to improvements in portable combustion powered fastener driving tools, particularly to improvements relating to the suspension of a motor for a combustion chamber fan for decreasing the operationally-induced axial acceleration and oscillation of the motor to decrease wear and tear on the motor, and specifically in applications where low-cost, iron core fan motors are employed to power the combustion chamber fan motor. 
     Portable combustion powered, or so-called IMPULSE® brand tools for use in driving fasteners into workpieces are described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722, 5,197,646 and 5,263,439, all of which are incorporated by reference herein. Similar combustion powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill. under the IMPULSE® brand. 
     Such tools incorporate a generally pistol-shaped tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces the spark for ignition, and a fan located in the combustion chamber provides for both an efficient combustion within the chamber, and facilitates scavenging, including the exhaust of combustion by-products. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a cylinder body. 
     A valve sleeve is axially reciprocable about the cylinder and, through a linkage, moves to close the combustion chamber when a work contact element at the end of the linkage is pressed against a workpiece. This pressing action also triggers a fuel metering valve to introduce a specified volume of fuel into the closed combustion chamber. 
     Upon the pulling of a trigger switch, which causes the ignition of a charge of gas in the combustion chamber of the engine, the piston and driver blade are shot downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original, or “ready” position, through differential gas pressures within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade. 
     Upon ignition of the combustible fuel/air mixture, the combustion in the chamber causes the acceleration of the piston/driver blade assembly and the penetration of the fastener into the workpiece if the fastener is present. This combined downward movement causes a reactive force or recoil of the tool body. Hence, the fan motor, which is suspended in the tool body, is subjected to an acceleration opposite the power stroke of the piston/driver blade and fastener. 
     Then, within milliseconds, the momentum of the piston/driver blade assembly is stopped by the bumper at the opposite end of the cylinder and the tool body is accelerated toward the workpiece. Therefore, the motor and shaft are subjected to an acceleration force which is opposite the direction of the first acceleration. These reciprocal accelerations cause the motor to oscillate with respect to the tool. The magnitude of the accelerations, if left unmanaged, are detrimental to the life and reliability of the motor. 
     Conventional combustion powered tools of the IMPULSE® type require specially designed motors to withstand these reciprocal accelerations of the shaft and motor, and the resulting motor oscillations. Among other things, the motors are preferably of the ironless core type, and are equipped with internal shock absorbing bushings, thrust and wear surfaces, and overall heavier duty construction. Such custom modifications result in relatively expensive motors which increase the production cost of the tools. 
     Thus, there is a need for a motor suspension mechanism for a combustion powered tool which reduces operating demands on the motor, increases reliability of the motor, and allows the use of closer to standard production fan motors to reduce the tool&#39;s production cost. In an ongoing attempt to reduce manufacturing costs, it is desirable to use the lowest cost fan motor possible for this application. At this time, such a motor is a conventional iron core motor, also known as permanent magnet, brushed DC motor of the type produced by Canon and Nidec Copal of Japan, as well as many other known motor manufacturers. When iron core motors were employed as combustion tool fan motors, the conventional suspension was found to result in an underdampened condition, wherein the motor oscillated excessively and out of tune relative to the operational oscillation of the combustion tool, as described above. In other words, there is a mechanical impedance mismatch between the combustion tool and the combustion chamber fan motor. This is due in large part to the greatly reduced weight of the iron core motors as compared to conventional motors. The iron core motors weigh only about ⅓ as much as conventional ironless core combustion chamber fan motors. The iron core motors are less durable, and are incapable of withstanding the degree of 50 g forces or higher which are generated through combustion. 
     As a result, in operation, the conventional combustion tool motor suspensions underdampen the iron core motor. This underdampening significantly reduces the effectiveness of the suspension, and subjects the motor to damaging axial forces. Instead, the goal is to achieve critical dampening, in which there is just enough dampening to receive the combustion-generated motion and prevent oscillation past equilibrium. 
     One way to achieve critical dampening between the fan motor and the combustion tool is to increase its flexibility, as by reducing the mass of the resilient suspension member which circumscribes and projects radially from the motor and the motor container to fasten those components to the combustion head of the tool. It has been found that increasing the flexibility in this way, to a degree which will satisfactorily suspend the iron core motor, also results in the unsatisfactory situation wherein the suspension member loses its resiliency and, upon the generation of the forces initiated by combustion, is unable to return the motor to the designated start position. 
     Another design parameter of combustion tools is that, while capacitors are known for reducing voltage spikes and transients for brushed motors, and it is advantageous to place the capacitor closer to the source of the spikes and transients, capacitors were not able to survive the impact forces generated in a combustion tool at the fan motor. Thus, such noise suppression capacitors had to be mounted in more remote, and less effective locations on the tool. 
     Thus, there is a need for a combustion tool fan motor suspension which can accommodate an iron core motor and provide sufficient dampening to protect the motor from combustion-generated impact forces. There is also a need for a combustion tool fan motor suspension which allows the mounting of a noise suppression capacitor on or near the fan motor. 
     Accordingly, it is an object of the present invention to provide an improved combustion powered tool with an improved suspension mechanism for an iron core combustion chamber fan motor, in which the suspension reduces operationally-induced reciprocal accelerations of the motor while keeping the oscillations of the motor within an acceptable range. 
     Another object of the present invention is to provide an improved combustion powered tool which features a mechanism for dampening operationally-induced oscillation of the combustion chamber fan motor, especially when the motor is of the iron core type. 
     It is a further object of the present invention to provide an improved combustion powered tool having a suspension which is mounted to the tool to “float” relative to the combustion chamber and thus dampen combustion induced vibrations. 
     It is yet another object of the present invention to provide an improved combustion powered tool having a suspension mechanism for a combustion chamber fan motor which increases the life of the motor. 
     It is still another object of the present invention to provide an improved combustion powered tool having a suspension mechanism for a combustion chamber fan motor which can accommodate the mounting of a noise suppression capacitor on or near the fan motor. 
     BRIEF SUMMARY OF THE INVENTION 
     The above-listed objects are met or exceeded by the present improved combustion powered fastener tool, which features a mechanism for suspending a combustion chamber fan motor that reduces the effects of the reciprocal axial acceleration of the motor, and the resulting oscillation of the motor, during operation of the tool. In the preferred embodiment, the assembly includes a flexible rubber web vulcanized to a motor retaining ring. The web is also vulcanized to a cylinder head mounting bracket so that only the web secures the ring to the bracket. In addition, the bracket is mounted via threaded fasteners and bushings to the cylinder head so that it will “float” relative to the movement of the combustion chamber. To this end, the bracket features resilient standoffs located at the cylinder head mounting points which provide progressive dampening. As the motor changes position, dampening increases. As such, the present motor suspension mechanism provides more accurately tuned dampening to iron core fan motors than conventional suspensions. Another feature of the present motor suspension is that it permits the mounting of a noise suppression capacitor on the fan motor. 
     More specifically, the present invention provides a suspension mechanism for a motor of a combustion chamber fan in a combustion powered hand tool constructed and arranged for driving a driver blade to drive a fastener into a work piece, the tool generating an upward axial acceleration of the motor upon combustion in the chamber, a subsequent reciprocal axial acceleration of the motor when the piston bottoms out on a bumper, at least one of the accelerations causing the motor to oscillate relative to the tool, the suspension mechanism includes a suspending portion configured for providing progressive dampening to the motor upon the generation of the axial accelerations. 
     In another embodiment, the present invention provides a suspension mechanism for a motor of a combustion chamber fan in a combustion powered hand tool constructed and arranged for driving a driver blade to drive a fastener into a work piece, the suspension mechanism comprising a motor mounting bracket which, upon fastening to a cylinder head of the tool, is configured to be movable relative to the cylinder head. 
     In yet another embodiment, the present invention provides a suspension mechanism for a motor of a combustion chamber fan in a combustion powered hand tool constructed and arranged for driving a driver blade to drive a fastener into a work piece, the suspension mechanism including a rigid motor retaining ring defining a cup for accepting the motor, the motor having an armature shaft end, said motor retaining ring being configured so that the motor is secured thereto only at the armature shaft end. 
     In addition, the present invention also provides a combustion powered hand tool constructed and arranged for driving a driver blade to drive a fastener into a work piece. The tool includes a combustion chamber defined in part by a cylinder head, a combustion chamber fan, a motor connected to said fan and a suspension mechanism for the motor configured for regulating the relative axial movement of the motor relative to the cylinder head. The suspension mechanism includes a suspending portion configured for providing progressive dampening to the motor upon the initiation of axial acceleration of the cylinder head. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a fragmentary side view of a combustion powered fastener tool in accordance with the present invention, the tool being partially cut away and in vertical section for purposes of clarity; 
     FIG. 2 is an exploded perspective view of the cylinder head of the tool depicted in FIG. 1, with the suspension mechanism and combustion chamber fan motor according to the present invention; 
     FIG. 2A is a section taken along the line  2 A of FIG.  2  and in the direction generally indicated; 
     FIG. 3 is a cross-section of the cylinder head and suspension mechanism of the present invention taken along the line  3 — 3  of FIG.  2  and in the direction generally indicated; 
     FIG. 4 is an overhead plan view of the present suspension mechanism, with portions omitted for clarity; 
     FIG. 5 is an enlarged fragmentary view of the mechanism depicted in FIG. 4; 
     FIG. 6 is a cross-section taken along the line  6 — 6  of FIG.  4  and in the direction generally indicated; 
     FIG. 7 is an overhead plan view of a circuit board configured for mounting to the present combustion fan motor; 
     FIG. 8 is a graph showing the operationally-induced acceleration and oscillation of a conventionally-suspended combustion chamber iron core fan motor in a combustion powered hand tool. The X-axis represents time in milliseconds and the Y-axis represents accelerations in g&#39;s measured by an accelerometer; and 
     FIG. 9 is a graph of the type in FIG. 8 showing the performance of an iron core fan motor in a combustion powered hand tool equipped with the improved motor suspension of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, a combustion powered tool of the type suitable for use with the present invention is generally designated  10 . The tool  10  has a housing  12  including a main power source chamber  14  dimensioned to enclose a self-contained internal combustion power source  16 , a fuel cell chamber  18  generally parallel with and adjacent to the main chamber  14 , and a handle portion  20  extending from one side of the fuel cell chamber and opposite the main chamber. 
     In addition, a fastener magazine  22  is positioned to extend generally parallel to the handle portion  20  from an engagement point with a nosepiece  26  depending from a lower end  28  of the main chamber  14 . A battery (not shown) is provided for providing electrical power to the tool  10 , and is releasably housed in a compartment (not shown) located on the opposite side of the housing  12  from the fastener magazine  22 . Opposite the lower end  28  of the main chamber is an upper end  30 . A cap  32  covers the upper end  30  and is releasably fastened to the housing  12  to protect the fan motor and spark plug. As used herein, “lower” and “upper” are used to refer to the tool  10  in its operational orientation as depicted in FIG. 1; however it will be understood that this invention may be used in a variety of orientations depending on the application. 
     A mechanically linked fuel metering valve (not shown), such as that shown in U.S. Pat. No. 4,483,474 may be used. Alternatively, an electromagnetic, solenoid type fuel metering valve (not shown) or an injector valve of the type described in commonly assigned U.S. Pat. No. 5,263,439 is provided to introduce fuel into the combustion chamber as is known in the art. A pressurized liquid hydrocarbon fuel, such as MAPP, is contained within a fuel cell located in the fuel cell chamber  18  and pressurized by a propellant as is known in the art. 
     Referring now to FIGS. 1,  2 , and  3 , a cylinder head  34 , disposed at the upper end  30  of the main chamber  14 , defines an upper end of a combustion chamber  36 , and provides a spark plug port (not shown) for a spark plug  38  (FIG. 4 only), an electric fan motor  40 , and a sealing O-ring  41 . In the present invention, the fan motor  40  is a conventional iron core motor, also known as permanent magnet, brushed DC motor of the type produced by Nidec Copal of Tokyo, Japan, Canon of Japan, as well as many other known motor manufacturers. The motor  40  has an armature shaft end  42  with an armature (not shown), an armature shaft  43 , and at least one mounting aperture  44 , which may be threaded depending on the application. 
     Referring to FIGS. 2,  2 A and  3 , the motor  40  includes a brush end  45  opposite the armature shaft end  42 . As is known in the art, the armature shaft  43  (and the armature, not shown) is supported in the motor by bearings. A bearing  46  at the brush end  45 , and similarly at the armature shaft end  42 , axially supports the armature shaft  43  and the armature. A feature of the present motor  40  is that the bearing  46  has a flange  47  which is located inside a motor housing  48 , rather than outside, as in many conventional motors. This disposition of the bearing  46  and the flange  47  has been found to prevent unwanted unseating of conventional bushings after exposure to repeated reciprocal forces of the type generated by combustion tools and described above. Aside from the modifications recited above, a conventional iron core motor is preferably beefed up to better withstand the challenging environment of a combustion tool. For example, the commutator is preferably provided with plastic tabs to prevent it from rotating relative to the armature shaft  43 , additional adhesive is applied to the commutator to increase axial and rotational load capacities and the wire ends of the armature windings are wrapped around the insulator additional times to prevent their unwinding. 
     The fan motor  40  is slidingly suspended by a fan motor suspension mechanism, generally designated  50 , within a depending cavity  52  in the center of the cylinder head  34  to allow for some longitudinal movement of the motor. As is best seen in FIG. 3, the motor  40  is preferably retained in the cavity  52  so that an air gap  54  is created between the lower or armature shaft end  42  of the motor (enclosed by a protective cap as will be described below) and a floor  56  of the cavity  52 . The function of the air gap  54  is to provide operating dynamic clearance, i.e., to provide clearance for the motor during oscillations occurring in the course of operation. 
     Referring now to FIGS. 2,  3  and  6 , in a preferred embodiment, the mechanism  50  includes a rigid, circular motor retaining cup  58  having an outer annular lip  59 , a generally cylindrical sidewall  60  and a floor  62 . In the preferred embodiment, the motor retaining cup  58  is made by drawing a flat disk of sheet metal or equivalent material, and is dimensioned to circumscribe and enclose the motor  40 , however it can be appreciated that other shapes for the cup  58  may be used in tools having different combustion chamber head shapes. l An advantage of this structure of the cup  58  is that it provides a heat and dirt barrier for protecting the motor  40 . Further, the cup  58  provides the attachment point for the motor  40 , since the floor  62  is provided with a central armature shaft aperture  64  (FIG. 6.) for accommodating the armature shaft  43 , and apertures  65  through which fasteners  66  secure the armature shaft end  42  to the floor  62 . 
     Thus, a feature of the present suspension  50  is that the motor  40  is secured to the cup  58  only at the armature shaft end  42 . Yet another feature of the motor retaining cup  58  is that once the motor  40  is secured thereto, it serves as a linear bearing journal for axial movement of the motor relative to the cavity  52  in the cylinder head  34 . 
     The suspension mechanism  50  also includes a mounting bracket  68  which is secured to the cylinder head  34  with a plurality of, and preferably three openings  70  through which are passed threaded fasteners  71 . As best seen in FIGS. 3 and 6, the bracket  68  includes an inner radiused shoulder  72  and a depending sidewall  74 . The shoulder  72  and the sidewall  74  of the bracket  68  are concentric with, and radially spaced from, a radial lip  76  of the motor retaining cup  58 . In the preferred embodiment, the motor retaining cup  58  is provided with a resilient “C”-shaped bumper  75  (FIG. 4) vulcanized or bonded to the outer annular lip  59  of the cup  58 . The bumper  75  prevents the motor retaining cup  58  from contacting a circuit board  116  if the tool is dropped. 
     Between and integrally secured to the depending sidewall  74  and the radial lip  76  is a resilient web  78  having an inner portion  80  secured to the sidewall lip  76 , a middle portion  82 , and an outer portion  84  secured to the sidewall  74  (best seen in FIG.  6 ). In the preferred embodiment, the web  78  is a neoprene rubber with a durometer of 25-30 hardness which is vulcanized both to the cup  58  and the bracket  68 . However, it is contemplated that other materials and bonding methods as are known in the art will provide the necessary adhesion and flexibility properties similar to those of rubber. 
     As best shown in FIG. 6, the web  78  is secured to the sidewall  74  and the lip  76  such that an upper surface  86  of the web forms an annular dish-like groove or recessed area. It will be seen that the web  78  is the only structure provided for securing the head mounting bracket  68  to the motor retaining cup  58 . Also, in the preferred embodiment, the upper surface  86  preferably has a plurality of equidistantly spaced, descending bores  88  extending at least partially through the middle portion  82 . In the preferred embodiment, the bores  88  are blind, in that they do not extend entirely through the middle portion  82 . This construction is preferred as a manufacturing technique to prevent rubber flashings created by molding throughbores from becoming detached from the web  78  and falling into the engine. A lower surface  90  of the web  78  has an annular groove  92  which is configured such that the groove does not communicate with the bores  88 . As shown in FIG. 4, the web  78  and a part of the mounting bracket  68  are interrupted, and do not form complete circles, to allow for a space for installing the spark plug  38 . 
     The web  78  provides a shock absorbing and isolating system to minimize the operational dynamics of the main chamber  14  caused by the combustion on the motor and also to protect the motor from axial acceleration and large oscillations. Although the preferred embodiment includes the bores  88  in the upper surface  86  and the annular groove  92  in the lower surface  90 , it is contemplated that the bores and the groove could be in either surface  86 ,  90 , and that the depth of the groove  92  may vary. The depth and orientation of the bores  88  may vary with the application. For example, a second set of bores may also be provided to the web  78  so that they open toward the lower surface  90 . Also, the depth of the groove  92  may vary with the application. Further, it is contemplated that several other patterns or other durometers for the rubber for the web  78  would provide similar shock absorbing characteristics. Therefore, the bores  88 , and the groove  92  do not necessarily need to be present, and if present, do not necessarily need to be round, nor the grooves or recessed areas  86 ,  92  annular, nor do all of the bores need to be in the upper surface  86  characterized by rounded corners to prevent tearing. It is contemplated that one of ordinary skill in the art will be able to vary the number, spacing, disposition and/or configuration of the bores  88  and/or the groove  92  to suit a particular application. 
     Referring now to FIGS. 4-6, an important feature of the present suspension mechanism  50  is that it provides progressive dampening to the motor  40  upon the generation of impact forces by combustion in the tool  10 . In the present application, “progressive dampening” means that the suspension mechanism  50  provides increased energy absorption as the motor  40  moves axially relative to the cylinder head  34 . This progressive dampening reduces operationally-induced acceleration and oscillation of the motor  40  and allows the use of more conventional motors to drive the fan. 
     One aspect of the present suspension mechanism  50  which provides this advantage is that the mounting bracket  68  is partially de-coupled relative to the cylinder head  34 . Rather than being rigidly secured to the cylinder head  34 , the mounting bracket  68  is fastened to the cylinder head with a plurality (preferably three) of the threaded fasteners  71  and plurality of bushings described below, but is retained in an axially spaced relationship relative to the cylinder head by a like plurality of resilient spacer members  94  at each attachment point. Each of the spacer members  94  has a base  96  which, in the preferred embodiment is generally circular, however other shapes are contemplated. A central aperture  98  is provided for accommodating the bushing and the fastener  71 . In addition, each spacer member  94  has a plurality, and preferably three, peripherally spaced rubber or otherwise resilient standoffs  100  projecting generally axially from the base  96 . 
     When viewed from the side, the rubber standoffs  100  are tapered and form a generally pointed upper end or tip  102  as they extend from a lower end  104  adjoining the base  96 . It is this tapered or triangular configuration which provides the progressive dampening. It is also contemplated that the number and precise configuration of the standoffs  100  may vary to suit the application. It should be noted that the spacer members  94  are preferably made of the same rubber-like material which forms the resilient web  78 , and are preferably vulcanized to the mounting bracket  68  when the web  78  is formed. 
     Referring now to FIGS. 2 and 6, the upward travel of the mounting bracket  68  and the spacer members  94  is restrained by a rigid mounting bushing  106  associated with each spacer member. Each of the mounting bushings  106  is configured for matingly engaging the resilient spacer member  94  and has a radially projecting lip  108  for providing a stop to axial movement of the head mounting bracket  68 . The lip  108  is provided with a diameter sufficient to engage the standoffs  100 . In addition, the bushings  106  engage the cylinder head  34  a(their lower ends, and are provided with a sufficient axial length to accommodate vertical travel of the mounting bracket  68  during operation. At their upper ends  110 , the bushings  106  have a nipple  112  dimensioned to matingly engage a corresponding opening  114  in a circuit board  116  (FIG.  6 ). At each attachment point, once the fastener  71 , with the assistance of a lockwasher  118 , secures the circuit board  116  and the bushing  106  to the cylinder head  34 , the mounting bracket  68 , and the suspension  50 , actually “float”, or are movable independently of, and relative to the cylinder head. 
     Due to the construction of the standoffs  100 , when operational forces cause the suspension  50  to move upward relative to the cylinder head  34 , the standoffs  100  compress, and their tapered configuration provides progressively more dampening with increased axial movement of the mounting bracket  68 . Accordingly, with more axial travel of the mounting bracket  68 , there will be more energy absorbed by the resilient spacer members  94  to decelerate the motor  40 . The dampening is limited by the radial lip  108  and the circuit board  116 . If necessary, additional energy is absorbed by the resilient web  78 , which allows the motor retaining cup  58  to move relative to the mounting bracket  68 . 
     Referring now to FIGS. 2 and 7, another feature of the present tool  10  is that the increased effectiveness of the suspension mechanism  50  allows for the mounting of a noise suppression capacitor  120  directly upon the motor  40 . As indicated above, noise suppression capacitors are known for the purpose of reducing voltage spikes and transients. In conventional combustion tools of the type sold under the IMPULSE® brand, the relatively heavy duty ironless core motors did not generate voltage spikes to the extent where a noise suppression capacitor was needed. However, the present tool  10  employs the typically lighter duty iron core motors  40  with which such suppression is advisable, especially to protect the electronic control unit (ECU) which generates the signal for the spark plug  38 . By the same token, these types of capacitors cannot normally survive the significant “g” forces generated in a combustion tool. Thus, the present suspension mechanism  50  provides another benefit in that the capacitor  120  can be mounted directly on the motor  40 , for increased suppressive qualities. 
     More specifically, the capacitor  120 , which is preferably of the 1 uf size, although other sizes are contemplated depending on the application, is connected to a circuit board  122  having a conventional noise suppression circuit  124 , as is known in the art. The circuit board  122  and the capacitor  120  are mounted adjacent the brush end  45  of the motor  40 . To withstand the impacts experienced by the motor  40 , the circuit board  122  is secured by chemical adhesive to the brush end  45  of the motor, in addition to solder points  126 . A protective cap  128  covers the circuit board  122  and snapingly engages the edge of circuit board  122 . 
     Referring now to FIG. 1, the generally cylindrical combustion chamber  36  opens and closes by sliding motion valve member  130  which is moved within the main chamber  14  by a workpiece contacting element  132  on the nosepiece  26  using a linkage in a known manner. The valve member  130  serves as a gas control device in the combustion chamber  36 , and sidewalls of the combustion chamber are defined by the valve member  130 , the upper end of which sealingly engages an O-ring  41  to seal the upper end of the combustion chamber. A lower portion  136  of the valve member  130  circumscribes a generally cylindrical cylinder body or cylinder  138 . An upper end of the cylinder body  138  is provided with an exterior O-ring (not shown) which engages a corresponding portion of the valve member  130  to seal a lower end of the combustion chamber  36 . 
     Within the cylinder body  138  is a reciprocally disposed piston  144  to which is attached a rigid, elongate driver blade  146  used to drive fasteners (not shown), suitably positioned in the nosepiece  26 , into a workpiece (not shown). A lower end of the cylinder body defines a seat  148  for a bumper  150  which defines the lower limit of travel of the piston  144 . At the opposite end of the cylinder body  138 , a piston stop retaining ring  152  is affixed to limit the upward travel of the piston  144 . 
     Located in the handle portion  20  of the housing  12  are the controls for operating the tool  10 . A trigger switch assembly  154  includes a trigger switch  156 , a trigger  158  and a biased trigger return member  160 . The ECU  162  under the control of the trigger switch  156  activates the spark plug  38 . 
     As the trigger  158  is pulled, a signal is generated from the ECU  160  to cause a discharge at the spark gap of the spark plug  38 , which ignites the fuel which has been injected into the combustion chamber  36  and vaporized or fragmented by a fan  164 . The fan  164  is driven by the armature shaft  43 , and is located within the combustion chamber  36  to enhance the combustion process and to facilitate cooling and scavenging. The fan motor  40  is preferably controlled by a head switch and/or the trigger switch  156 , as disclosed in more detail in the prior patents incorporated by reference. 
     The ignition forces the piston  144  and the driver blade  146  down the cylinder body  138 , until the driver blade contacts a fastener and drives it into the substrate as is well known in the art. The piston then returns to its original, or “ready” position through differential gas pressures within the cylinder, which are maintained in part by the sealed condition of the combustion chamber  36 . 
     The fan motor  40  experiences two primary accelerations during this cycle. First, when the ignition of combustible gases in the chamber  36  forces the piston  144  downwardly toward the workpiece, and preferably a fastener into the workpiece, the tool  10  experiences an opposing upward force, or a recoil force, in the opposite direction. The fan motor  40 , which is suspended by the mechanism  50  in the tool, is accelerated upwardly in the direction of the recoil of the tool by a force transmitted through the suspension mechanism. Further, the armature shaft  43  is accelerated in the same direction by having constrained movement relative to the motor within limits of axial play. Then, in less than approximately  10  milliseconds, the piston  144  bottoms-out in the cylinder  138  against the bumper  150 . This action changes the acceleration of the tool  10  towards the workpiece. Therefore, the motor and shaft are now accelerated in this new, opposite direction. 
     These reciprocal accelerations are repeatable and the suspension mechanism  50  must be tuned so that the motor does not oscillate excessively with respect to the tool and either bottom out or top out as discussed earlier. By “tuned” it is meant that the resilience of the suspension mechanism is adjusted to prevent a particular motor from excessive oscillation within predetermined, application-specific limits, depending on the combustion-induced force generated by the particular power source  16 . The present tuned suspension mechanism  50  anticipates the two opposite accelerations separated by a predetermined fairly repeatable time and resiliently constrains the motor within the bounds of the cap and the floor of the cavity to minimize the acceleration force of “g&#39;s” witnessed by the motor. 
     FIGS. 8 and 9 show the acceleration and oscillation experienced by the motor during operation of the tool. The results shown in FIG. 8 are from a tool having a suspension incorporating the resilient web  78  disposed between the cup  58  and the bracket  68 , and incorporating an iron core motor  40 , which is lighter than the motor for which the suspension was designed. As shown, at about 4 milliseconds after ignition (which occurs at about the 5 millisecond point on the graph), shown at  170 ,  5  the motor experienced an acceleration force of about or 40 g from the acceleration of the tool due to the recoil force which was immediately transmitted to the motor through the suspension mechanism. At about 9 milliseconds after ignition, shown at  172 , the motor experienced an acceleration in the opposite direction of about 135 g following when the piston  144  bottomed-out in the cylinder  138  which was again transmitted to the motor. Thereafter, the motor experienced an oscillation of approximately two additional accelerations greater, labeled as  174  (40 g&#39;s) and  176  (25 g&#39;s) caused by its lack of tuning of the suspension mechanism. Note that this suspension did not have the present “floating” mounting bracket  68  and the standoffs  100 . 
     FIG. 9 shows the acceleration and oscillation experienced by the motor  40  in a tool  10  equipped with the present improved fan motor suspension mechanism  50 . After ignition, the first acceleration  170  of the motor  40  was about 30 g and the reciprocal acceleration  172  was only about 35 g. Thereafter, the motor  40  experienced no additional accelerations above 30 g&#39;s. The “floating” progressive dampening provided by the present suspension mechanism  50  causes less immediately transmitted acceleration, while also not allowing excessive amplitude of oscillation so there is no bottoming out or topping out. 
     The result of the present invention is that the improved fan motor suspension mechanism  50  not only decreases acceleration of the motor  40 , but also decreases the overall travel or displacement of the motor and the amount of oscillation of the motor. As shown in FIGS. 8 and 9, due to proper tuning, the improved motor suspension mechanism  50  decreases acceleration and also dampens oscillation and dynamically operates without detrimental contact within the positive constraints of the tool  10  (bottoming or topping out). A major benefit of this discovery is that the motor  40  may be of the inexpensive, lightweight iron core type and may still accommodate the severe acceleration forces generated by the tool  10 . 
     While a particular embodiment of the combustion tool suspension for iron core fan motor of the invention has been shown and described, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the invention in its broader aspects and as set forth in the following claims.