[0001] This invention relates to a log splitting machines in which the log splitting action
is provided by a single-acting hydraulic cylinder-piston unit with spring return.
[0002] Such log splitting machines normally comprise a virtually horizontal operating seat
in which the log to be split is positioned between two mutually movable members, known
as the log pusher and the blade.
[0003] The log pusher is normally fixed, while the blade is operated by a hydraulic cylinder-piston
unit, which can either be single or double acting and is connected to a motor-driven
pump by way of a suitable interposed distributor.
[0004] Log splitting machine are known from WO 93/15886, comprising a single acting hydraulic
cylinder-piston unit with its return controlled by an elastic means such as a spring,
a motor-driven pump and an hydraulic distributor arranged to selectively connect the
piston chamber of said cylinder-piston unit to the pump delivery or to discharge.
[0005] In such log splitting machines, to increase productivity the respective cylinder-piston
unit can be operated in two modes, usually known as normal and regenerative, to which
two different lengthening speeds of the cylinder-piston unit correspond.
[0006] For correctly defining said operative modes, the basic characteristics of usual single
and double acting cylinder-piston units can be summarized as follows.
[0007] A usual single acting cylinder-piston unit comprises an outer cylinder and a slidable
inner piston which divides the volume of the cylinder into two parts usually known
as the piston chamber and the piston rod chamber, this latter housing at least one
elastic return means, typically a helical spring.
[0008] When operating in the normal operative mode a single acting cylinder-piston unit
is elongated by feeding oil into the piston chamber, with consequent loading of the
at least one spring, the same cylinder-piston unit being shortened by the thrust of
the spring after connecting the piston rod chamber to discharge.
[0009] A usual double acting cylinder-piston unit comprises an outer cylinder and a slidable
inner piston which divides the volume of the cylinder into two parts again known as
the piston chamber and the piston rod chamber, these two chambers being both constantly
filled with oil.
[0010] When operating in the normal operative mode a double acting cylinder-piston unit
is elongated by feeding oil into the piston chamber and connecting the piston rod
chamber to discharge, the same cylinder-piston unit being shortened by the reverse
operation.
[0011] When a double acting cylinder-piston unit operates in said regenerative mode, during
lengthening of the cylinder-piston unit the oil leaving the piston rod chamber is
recovered and added to that directed to the piston chamber. This is achieved by connecting
the pump delivery to both chambers of the cylinder-piston unit.
[0012] In this manner the outward speed of the piston increases, for equal oil pressure
and throughput, relative to the speed which the same piston can achieve during operation
in normal mode, said increase being directly proportional to the ratio of cylinder
cross-section to piston rod cross-section.
[0013] If, for example, the cross-section through the piston rod is one half that through
the cylinder, as is often the case in such log splitting machines, the outward speed
of the piston when in regenerative mode is exactly twice its outward speed when in
normal mode.
[0014] In the known art, and again with reference to double acting cylinder-piston units,
switching between the regenerative and the normal mode can be done manually by operating
the oil distribution valve positioned downstream of the pump, or automatically by
providing a conduit which short-circuits the oil between the two chambers of the cylinder-piston
unit by the controlled operation of a valve sensitive to the pressure in the piston
chamber.
[0015] In both cases, on commencing a log splitting phase the service hydraulic unit of
the log splitting machine is set in the regenerative mode, which in order to achieve
maximum log splitting speed with minimum force is maintained if the log does not offer
excessive resistance, i.e. such as to raise the pressure of the oil in the piston
chamber above a predetermined value.
[0016] If instead the log offers particularly high resistance, measurable for example by
a pressure transducer associated with the hydraulic circuit, and such that the pressure
in the piston chamber exceeds said predetermined value, the machine is switched between
the regenerative and the normal mode, in one of the aforesaid ways.
[0017] The detailed description of the relative hydraulic circuits and distribution valves
is omitted, as these are wall known to an expert of the art.
[0018] The result of said automatic or manual switching is minimum lengthening speed with
maximum available force.
[0019] The facility to operate both in regenerative mode and normal mode, typical of double
acting cylinder-piston units, becomes extremely problematic in the case of single
acting cylinder-piston units, because of the fact that in these latter the piston
chamber does not contain oil.
[0020] In the aforedescribed log splitting machines the use of double acting hydraulic units
involves costs incompatible with market requirements, hence in this sector it is preferred
to use units with single acting cylinder-piston units and so renounce the advantages
of the regenerative mode operating system.
[0021] Some circuit arrangements which enable single acting cylinder-piston units to operate
in regenerative mode are known, but these are not utilized in practice for two reasons.
[0022] Firstly, these arrangements involve complicated hydraulic circuits, which are very
similar to those typical of double acting cylinder-piston units because of the need
to also ensure filling of the piston chamber of the cylinder-piston unit.
[0023] Secondly, said circuits do not allow automatic switching between the regenerative
and the normal operating mode.
[0024] Consequently in this sector there is a deeply felt need for log splitting machines,
operated by single acting cylinder-piston units which can operate in regenerative
mode and in normal mode, with automatic switch-over.
[0025] The main object of the present invention is precisely to satisfy said requirement.
[0026] A further object is to satisfy said requirement within the context of a simple, rational,
reliable, durable and low-cost construction comprising a relatively small number of
component parts.
[0027] Said objects are attained by a log splitting machine presenting the characteristics
indicated in the claims.
[0028] It is of the type essentially comprising a hydraulic circuit with a motor-driven
pump for supplying pressurized oil to a hydraulic distributor by means of which the
lengthening and shortening strokes of the cylinder-piston unit can be selected.
[0029] This latter comprises a piston chamber and a piston rod chamber which are both filled
with oil, and a transfer path through which, during lengthening of the cylinder-piston
unit, the oil present in the piston rod chamber can either flow into the piston chamber
or be discharged into the pump reservoir, depending on the state of a preset pressure-sensitive
valve present in the piston chamber.
[0030] The piston rod chamber is directly connected to the reservoir by an independent conduit
provided with a directional valve which prevents the oil discharging into the reservoir
but enables it to rise from the reservoir to the piston rod chamber.
[0031] According to the teachings of the invention, a transfer conduit is provided which
bypasses the distributor and is intercepted by a first unidirectional valve which
prevents transfer of oil from the piston chamber to the piston rod chamber but not
vice versa.
[0032] Upstream of the first directional valve there is a suction conduit which dips into
the oil reservoir and is intercepted by a second directional valve which enables the
oil to pass only towards the piston rod chamber.
[0033] Between the suction conduit and the piston rod chamber there branches the discharge
conduit of the piston rod chamber, which is intercepted by the preset overpressure
valve sensitive to the pressure in the piston chamber.
[0034] By virtue of the aforedescribed solution, and as will be apparent hereinafter, during
lengthening of the cylinder-piston unit the oil leaving the piston rod chamber enters
the piston chamber when the pressure in this latter is less than the preset pressure
of the overpressure valve, and discharges to the reservoir when said pressure exceeds
said preset value. Hence all the objects of the invention are attained in that on
the one hand the switching between the regenerative and normal operating modes is
automatic, and on the other hand the hydraulic unit is simple overall and of low cost,
inter alia because its activation and deactivation can be achieved by a distributor
with only two operative positions.
[0035] The characteristics and constructional and functional merits of the invention will
be apparent from the ensuing detailed description given with reference to the single
accompanying figure which shows by way of example a hydraulic scheme of the log splitting
machine according to the invention.
[0036] It comprises a hydraulic pump 1 driven by a motor unit 2 and presenting a suction
conduit 10 which dips into an oil-containing reservoir 3, and a delivery conduit 4
connected to a hydraulic distributor 5 of sliding type.
[0037] The distributor comprises a first position in which the pump is connected directly
to the piston chamber of the cylinder-piston unit, and a second position in which
the pump and piston chamber of the cylinder-piston unit are both connected to discharge.
[0038] From the delivery conduit 4 there branches a recirculation conduit 6 which leads
to the reservoir 3 and is intercepted by a maximum pressure valve 60.
[0039] The distributor 5 presents an extremely simple constructional form in that it comprises
only two operative positions, to be selected by the user, for example in operating
a log splitting machine.
[0040] The position illustrated corresponds to the passive or return stroke of the log splitting
blade, the other position corresponding to the active or outward stroke of the blade.
[0041] The single acting cylinder-piston unit 9 associated with the blade presents a first
chamber 90 between the piston 8 and the cylinder rear end, hereinafter known as the
piston chamber, and a second chamber 91 between the piston 8 and the cylinder front
end, hereinafter known as the piston rod chamber, in which a compression spring 99
is housed for the return of the piston.
[0042] Both said chambers 90, 91 are constantly filled with oil.
[0043] The piston chamber 90 is connected to the casing of the distributor 5 by the conduit
7, whereas the piston rod chamber 91 is connected to the reservoir 3 by the conduit
indicated by 12.
[0044] The conduit 12 is intercepted by an overpressure valve 120 of presetting type as
shown, which is operationally connected to the conduit 7 as shown in the figure by
a dashed line, and is sensitive to the pressure in the conduit 7.
[0045] A transfer conduit 13 connects the conduit 12 upstream of the valve 120 to the conduit
7.
[0046] The transfer conduit 113 could evidently be directly connected to the chambers 90
and 91 of the cylinder-piston unit 9.
[0047] The transfer conduit 13 is intercepted by a unidirectional valve 130, which in the
illustrated example is a non-return valve of ball type, and when in its closed position
prevents passage of oil from the conduit 7 to the conduit 12.
[0048] An oil suction conduit 14 is also provided, which connects that branch of the conduit
13 upstream of the valve 130 to the reservoir 3 and is intercepted by a non-return
valve 140, which in the illustrated example is a ball valve preventing flow of oil
towards the reservoir.
[0049] Finally, a discharge conduit 15 branches from the casing of the distributor 5 and
is connected at its other end into the conduit 12 upstream of the respective overpressure
valve 120.
[0050] The discharge conduit 15 could evidently be directly connected to the reservoir 3.
[0051] The described unit operates in the following manner.
[0052] When the distributor 5 is in its first operative position shown in the figure, with
the pump 1 operating and the piston 8 completely retracted, the valves 120, 130 and
140 are closed and the pumped oil returns to the reservoir 3 through the conduit 15
connected into the conduit 12.
[0053] When the operator switches the distributor 5 to its second position (not shown),
the pumped oil enters the piston chamber 90 through the conduit 7, the valves 120
and 140 remain closed, the valve 130 is opened by the pressurized oil flowing from
the piston rod chamber 91 and entering the piston chamber 90, and the blade of the
log splitting machine advances at maximum speed to act on the log with minimum force.
[0054] If the log splitting blade encounters a resistance such that along the conduit 7
the oil exceeds the preset pressure of the overpressure valve 120, the hydraulic unit
automatically switches from regenerative mode to normal mode, by which the log splitting
blade advances at minimum speed to act on the log with maximum force.
[0055] Specifically, on attaining said preset pressure the valve 140 remains closed, whereas
the valve 120 opens with simultaneous closure of the valve 130, with the result that
only the pumped oil enters the piston chamber 90, whereas the oil leaving the piston
rod chamber 91 is discharged to the reservoir 3 through the valve 120.
[0056] As soon as the resistance which caused said switching disappears, the valve 120 recloses
and the valve 130 automatically returns to the previously occupied position, the system
then returning to its regenerative configuration.
[0057] When the log splitting blade has reached the end of its advancement travel, if the
distributor 5 is not switched to its first operative position the pumped oil returns
to the reservoir through the recirculation conduit 6.
[0058] On resetting the distributor 5 to the same configuration as Figure 1, with the pump
1 in operation, the piston 8 retracts by the effect of the thrust of the spring 99,
the oil leaving the piston chamber 90 discharges to the reservoir 3 together with
the pumped oil, the valves 120 and 130 remain closed, and the valve 140 opens by the
effect of the vacuum created in the piston rod chamber 91 by the piston 8 during its
retraction, with the result that said piston rod chamber 91 completely fills with
oil, ready to operate the cylinder-piston unit 9 in the regenerative mode.
[0059] Both the regenerative and normal modes of operation are determined by the second
operative position of the distributor 5, in which it connects together the two conduits
4 and 7, and closes the discharge conduit 15. The merits and advantages of the invention
are apparent from the aforegoing and from an examination of the accompanying figure.
1. Blockspaltmaschine, die eine einfach wirkende hydraulische Zylinder-Kolbeneinheit
(9) aufweist, deren Rückführung durch eine elastische Einrichtung, wie zum Beispiel
eine Feder, eine motorgetriebene Pumpe (1) und einen Hydraulikverteiler (5) gesteuert
wird, der dafür vorgesehen ist, die Kolbenkammer (90) der Zylinder-Kolbeneinheit (9)
wahlweise mit der Pumpenzuleitung oder der Ausleitung zu verbinden,
dadurch gekennzeichnet, dass
die Kolbenstangenkammer (91) der Zylinder-Kolbeneinheit (9) mit der Kolbenkammer (90)
mittels einer Rohrleitung verbunden ist, die ein Unidirektionalventil (130) aufweist,
welches die Ölübertragung in Richtung der Kolbenstangenkammer und zu dem Öltank (3)
durch eine Ausleitungsrohrleitung verhindert, die durch ein voreingestelltes Überdruckventil
(120) verschlossen ist, welches für den Pumpenzuleitungsdruck empfindlich ist, und
durch eine separate Saugrohrleitung, die mit einem Unidirektionalventil (140) versehen
ist, welches den Ölfluss in Richtung des Tankes (3) verhindert.
2. Blockspaltmaschine nach Anspruch 1,
dadurch gekennzeichnet, dass
die Unidirektionalventile (13,140) Kugelventile sind.
3. Blockspaltmaschine nach Anspruch 1,
dadurch gekennzeichnet, dass
der Hydraulikverteiler (5) ein Verteiler mit zwei Betriebspositionen ist, die jeweils
der Verkürzung und der Verlängerung der Zylinder-Kolbeneinheit (9) entsprechen, wobei
er in der ersten davon die Zuleitung der Pumpe (1) und die Kolbenkammer (90) mit dem
Tank und in der anderen davon die Pumpe mit der Kolbenkammer verbindet.
4. Blockspaltmaschine nach Anspruch 3,
dadurch gekennzeichnet, dass
der Verteiler (5) ein Schiebeverteiler ist.