Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
  • B27L—REMOVING BARK OR VESTIGES OF BRANCHES; SPLITTING WOOD; MANUFACTURE OF VENEER, WOODEN STICKS, WOOD SHAVINGS, WOOD FIBRES OR WOOD POWDER
  • B27L7/00—Arrangements for splitting wood

Definitions

• the present invention relates to a hydraulically opera ⁇ ted tool of the kind which includes two working members which are intended to move towards one another when effecting a working stroke, so as to work a workpiece located therebetween, wherein at least one of the working members ' is operated by a piston-cylinder device, such as a wood splitter comprising a fixed splitting wedge and a pressure plate which is driven by a piston-cylinder device and which functions to feed the wooden workpiece towards the wedge, and also of the kind with which hy ⁇ draulic fluid under pressure is delivered to the piston- cylinder device through an adjustable valve with each working stroke, so as to move the associated tool member towards the other tool member, and said tool further comprising spring means for returning said working compo ⁇ nent when the hydraulic pressure is again lowered, and in which tool the piston is provided with a normally closed channel between its high pressure and low pressure side and include means which means are provided for opening said channel when the piston approaches its end position in the cylinder.
• a piston-cylinder device such as a wood splitter comprising
• this pressure impulse can cause the motor to begin to rotate in the reverse direc ⁇ tion, in which case it is necessary to switch-off the motor and restart the same prior to commencing a follow ⁇ ing working operation.
• This phenomenon can also occur when the piston during its working stroke meets an unex ⁇ pectedly high resistance which is strong enough to stop the piston immediately.
• the main object of the present invention is to provide a hydraulically operated tool which will eliminate these drawbacks among other things, and with which the requi ⁇ site working pressure is only generated when required.
• the invention is based on the realization that the afore ⁇ said problems, among other things with regard to the occurrence of pressure impulses at the end of the working stroke of the piston, can be eliminated by equalizing the pressure between the different sides of the piston in a very simple fashion. This can be achieved without the use of drive motor braking means, latching mechanisms or intricate systems for leading away pressure oil.
• a hydraulically driven tool of the kind defined in the first paragraph of the document is, in accordance with the invention, particularly characterized in that the aforesaid channel extends in the piston wall inwardly of a piston seal which surrounds said piston and has a generally radially directed inlet and outlet which connect the channel with a space between the piston rod and the cylinder on different sides of the piston seal; in that the channel includes a displaceable slide which normally closes said channel; and in that a mechanical actuator is provided for displacing the slide upon con ⁇ tact with a part of the cylinder housing or an element projecting therefrom.
• An arrangement of this kind enables the piston to be braked gently at the end of its working stroke in a very simple and reliable manner.
• the displaceable slide is suitably mounted in the channel so as to normally close the generally radially directed inlet thereof.
• the pressurized hydraulic fluid will thereby have no appreciable affect on the slide opening movement as the pressure acts radially on the slide.
• the aforesaid actuator will preferably have the form of a slide activating rod which is connected with the slide and arranged to coact with the cylinder end-closure when the piston approaches its end position, said slide being displaceable against the action of a return spring.
• a check valve is conveniently mounted in the hydraulic piston-cylinder supply line.
• the check valve is mount ⁇ ed very close to the pump means of the hydraulic pump, so that the amount of hydraulic fluid present between the check valve and said pump means will be smaller than the amount required to drive the pump in a reverse direction through one revolution, and preferably smaller than the amount required to drive the pump in a reverse direction through three-quarters of a revolution.
• the check valve will suitably include a ball which is spring-biased against a valve seat, and means will be provided which function to re ⁇ strict movement of the ball away from said seat so as to minimize the distance that the ball must travel in order to close the valve.
• the ar ⁇ rangement includes a hydraulic pump which is driven continuously by an electric motor or a combustion engine, and a manually adjustable valve means for initiating each working stroke of the tool.
• the hydraulic fluid circulates in a circuit between the pump and the fluid tank when the tool is idle, such that the hydraulic fluid is only temporarily placed under pressure in conjunction with each working stroke.
• the valve is constructed to connect the outlet of the hydraulic pump to both the tank and the piston-cylinder unit when the tool is idle and so that when the valve setting is adjusted the valve will successively close the connection to the tank while maintaining the connection to the piston-cylinder unit.
• the valve suitably includes a valve slide which is rota- table in a housing and has one axial inlet and at least one radial outlet, the position of said valve slide being adjusted against the action of a return spring which is able to return the slide to its rest position.
• Figure 1 is a perspective view of an inventive wood splitter
• Figure 2 is a side view, partly in section, of the ar- rangement shown in Figure 1;
• Figure 3 illustrates part of the arrangement in Figure 2 in larger scale, with the piston in its outer end posi ⁇ tion;
• Figure 4 is an exploded view of a valve arrangement forming part of the wood splitter shown in Figure 1;
• Figure 5 is a side view, partly in section, of the valve arrangement shown in Figure 4;
• Figures 6 and 7 are cross-sectional views of the valve arrangement shown in Figure 4, and show the valve ar ⁇ rangement in two different working positions; and
• Figure 8 illustrates, partly in section, a check valve included in the arrangement illustrated in Figure 1.
• the wood splitter shown in Figure 1 includes a stand part in the form of a box beam 1, and a sharp-edged splitting wedge 2 mounted on the forward end of the stand part.
• the upper surface of the box beam 1 functions as a feed table for wood pieces 3. These wood pieces are advanced in a known manner, with the aid of a pressure plate 4 which is fitted to the tubular piston rod 5 of a piston 7 mounted for reciprocating movement in a cylinder 6, see Figure 2.
• the piston 7 is a single-acting piston and is driven by hydraulic oil delivered from a hydraulic pump 9 through a hydraulic line 8 and a valve arrangement 10.
• the pump 9 is driven by a con ⁇ tinuously operating electric motor 11 which is connected directly to the pump 9.
• another drive source may be used such as a combustion engine for in ⁇ stance.
• the pump 9 takes hydraulic oil from the box beam 1 through a suction line 12, said box beam also function ⁇ ing as an oil tank.
• the valve arrangement 10 further includes a port 16 which is connected to a pressure line 15 extending from the pump 9 and which is also connected to an axial inlet in a rotatable valve slide 17 included in the valve arrange ⁇ ment 10.
• the slide 17 has a slot-like radial opening 18 which when in an idle position connects the axial channel of the slide with both the port 13 and a port 19 connec ⁇ ted with the line 8, as shown in Figures 5 and 6.
• the slide may alternatively be provided with two separate radial openings, one for the port 13 and one for the port 19. It is important, how-ever, that the ports 13 and 19 can be opened to the port 16 simul ⁇ taneously, and that the port 13 can be closed selectively and successively while the port 19 remains open, see Figure 7.
• the port 13 is closed by turning the valve slide 17 with the aid of a valve operating lever 20, see Figure 4, which in the idling position rests against a stop 21 with the opening 18 taking the position shown in Figure 5 and Figure 6.
• the arrangement When using a hydraulic pump which is driven by a contin ⁇ uously operating motor, the arrangement will operate in the following manner. It will observed here that the electric motor and pump used with the illustrated em ⁇ bodiment have been shown in the form of a separate unit, although this has been done solely in order to simplify illustration of the arrangement. In practice, the pump/motor unit is fixed to the cylinder 6 or the stand 1, in which case the pressure hose 15 may optionally be excluded and replaced with a fixed screw connection between the pump and the valve.
• the piston is provided, in accordance with the invention, with means which cause the pressure between the two sides of the piston to be equalized before the piston is stopped mechanically by said parts 24.
• the piston 7 is provided to this end with a channel 25 inwardly of the piston seal 26.
• the channel 25 has a generally radial inlet 27 on the high pressure side of the piston seal and a corresponding outlet on the pressureless side thereof.
• a displaceable slide 28 which normally closes the radial inlet 27, see Figure 2.
• the slide can be displaced against the action of a return spring 29 such as to open the inlet 27, as illustrated in Figure 3.
• the slide is provided to this end with a rod 30 which projects out forwardly of the piston 7 and coacts with the cylinder end-closure 24 before the piston contacts said end-clo ⁇ sure.
• the aforedescribed arrangement functions to essen- tially equalize the high pressure acting on the piston 7 via the channel 25 before the piston strikes the end stop, therewith obtaining a gentle braking effect.
• This will avoid, among other things, harmful retrocessive pressure surges in the hydraulic system which would otherwise be liable to damage both the hydraulic pump and the drive motor.
• This soft braking effect has particular significance in manually handled, motor-driven tools with which a full working stroke is normally used. Because in the case of this embodiment the hydraulic pressure acts on the slide 28 solely in a radial direction, its axial movement is not negatively affected to any appreciable extent.
• the solution is based on the realization that the amount of oil enclosed between the check valve and the working member of the hydraulic pump should not be so large as to cause the hydraulic pump to rotate in reverse such as to reverse the direction of rotation of the electric motor.
• Tests have shown that the amount of oil enclosed between the check valve and the hydraulic pump should not be so large as to enable the motor to be rotated through a full revolution in the reverse direction at prevailing pres ⁇ sures in the enclosed oil volume.
• this quan ⁇ tity of oil will be much smaller than that just en- tioned, such that the motor cannot even be rotated through three-quarters of a revolution and, in the case of certain types of motors, the possibility of reverse rotation should be fully eliminated.
• the check valve is placed in the immediate vicinity of the working members of the hydraulic pump 9 , as illus ⁇ trated in Figure 8.
• the pump working members have been referenced 31 and may, for instance, take the form of teeth on a gearwheel.
• the check valve 32 is fastened directly to the pump casing 9.
• TJie illustrated check valve includes a ball 33 and a spring 34 which urges the ball against a valve seat 36.
• a fixed rod 35 which limits the distance to which the ball 33 can be moved away from the valve seat 36, so as to shorten travel of the ball when closing the valve and therewith also the time taken to close the valve.
• the spring 34 should also be somewhat stronger than springs that may normally be used, so as to achieve the quickest possible valve clo- sing time.
• an inventive wood splitter to be made very light in weight and given small dimensions and manufactured at a low cost.
• the wood splitter can be driven by a constant speed electric motor or, alterna ⁇ tively, by a combustion engine.
• the tool is handled readily and can be easily transported by car between its different places of use.
• Another important advantage is that a high hydraulic pressure is only generated when required, namely during each working stroke.
• the invention has been described above with reference to the exemplifying embodiment illustrated in the drawings.
• the described hydraulic drive can be used with other hand-operated instruments in addition to wood splitters, for instance with pruning shears and like tools.
• the illustrated embodiment can also be modified in several respects within the scope of the invention.
• the arrangement of the pressure equalizing slide and its guide means can be varied while retaining the desired function, or may be replaced with some other openable element.
• the pressure equalizing ar ⁇ rangement has been described with reference to a single- acting device, it will be understood that the same prin ⁇ ciple can be applied with a double-acting device, wherein a corresponding equalization of pressure will take place in the other end position of the piston.
• the check valve may also be modified.
• the rod may be re ⁇ placed with some other mechanical stop means.

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Cited By (5)

Citations (7)

• 1992
  • 1992-02-18 SE SE9200484A patent/SE9200484L/sv not_active Application Discontinuation
• 1993
  • 1993-02-11 AU AU35798/93A patent/AU3579893A/en not_active Abandoned
  • 1993-02-11 WO PCT/SE1993/000105 patent/WO1993015886A1/en active Application Filing

Patent Citations (7)

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