Hammer having a protective cover

A motor-driven hammer having an impact mechanism that is driven by the motor via a crank drive. The hammer has a protective cover that is provided with handgrips and is cushioned relative to the housing of the hammer. When viewed in the upright position of operation of the hammer, the cover is spaced from, and covers, the top, both sides, and the front of the motor and crank drive, at least relative to an operator. Two pairs of swing arms extend on both sides between the housing and the cover for positively guiding the cover parallel to the longitudinal axis of the hammer. The swing arms of a given pair of arms are disposed parallel to one another, and are spaced apart one above the other. Each arm has two ends, one of which is pivotably mounted on the cover, and the other of which is pivotably mounted on the housing. This pivotable mounting is effected by pivot mechanisms, at least some of which are embodied in the form of soft torsion springs. The swing arms have a pivot range that is free except for the torsion spring effect. Stops are provided for elastically delimiting the free pivot range of the arms. These stops cooperate in a cushioned manner and are disposed on the housing and on the cover. The stops have a spring force that increases progressively outwardly from the free pivot range of the swing arms.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a motor-driven hammer having an impact 
mechanism that is driven by the motor via a crank drive. The hammer has a 
protective cover that is provided with handgrips and is cushioned relative 
to the housing of the hammer. When viewed in the upright position of 
operation of the hammer, the cover covers, and is spaced from, the top, 
both sides, and the front of the motor and the crank drive, at least 
relative to an operator. With hammers of this general type, the task of 
the cover is to protect the operator from heat radiating from the hot 
motor parts, and from direct contact with these parts. The cover is also 
intended for muffling radiation of noise from the motor into the 
environment, and especially to the operator. In addition, the cover 
protects the operator from current pulses, which with apparatus of this 
type can be caused, for example, by striking an underground cable with the 
bit during breaking-up operations, or, with electric hammers, by 
carelessly damaging the actual electrical lead on the motor, thus 
conveying dangerous voltage to the motor parts of the hammer. Furthermore, 
by disposing the handgrips for guiding the hammer on the protective cover, 
the latter fulfills the additional task of cushioning the grip, and hence 
of avoiding damaging the health of the operator and of increasing the 
operating comfort for the latter. 
2. Description of the Prior Art 
With the heretofore known hammers of the aforementioned general type 
(German Offenlegungsschrift No. 30 35 351), the protective cover is 
supported at a number of locations on the hammer housing via simple 
springs. As a result, under certain operating conditions, the cover can 
twist or tilt relative to the housing. The cover is then in direct contact 
with the housing, and to a large extent loses its ability to fulfill the 
aforementioned tasks. With the heretofore known hammers, the ability of 
the protective cover to function is also extensively impaired as the 
operating pressure exerted upon the handgrips by the operator increases. 
The same is true for pulling upon the handgrips, which is done by the 
operator when he tries, with the hammer, to again pull out a bit that has 
become jammed, for example in working in concrete. In these cases, the 
cause for the reduction of the ability of the cover to function is the 
spring force of the simple springs between the cover and the housing which 
spring force increases very sharply and linearly already with 
comparatively small relative movements between the cover and the housing. 
These simple springs must be very strong so that contact between the motor 
housing and the protective cover cannot already occur under normal 
operating conditions. If the springs are too weak, or even if extreme 
pressure or pulling is exerted upon the cover via the handgrips, the known 
dangerous jarring blows can occur even without direct contact between the 
cover and the housing. These jarring blows are transmitted from the 
hammer, via the completely compressed springs, to the protective cover as 
spring block shocks. 
An object of the present invention therefore is to provide a hammer of the 
aforementioned general type that is designed in such a way that the 
protective cover has no possibility of coming into contact with the hammer 
housing, that both the left and the right handgrip are always uniformly 
cushioned independent of the size of the operator, that jarring blows of 
the cushioned cover with the housing are precluded even under high 
pressures and pulling forces exerted by the operator upon the handgrips, 
and that nevertheless the cushioning of the handgrips is very soft in the 
normal operating range during customary applications, so that the operator 
can hardly feel any vibration.

SUMMARY OF THE INVENTION 
The hammer of the present invention is characterized primarily by two pairs 
of swing arms that extend on both sides between the hammer housing and the 
protective cover for positively guiding the latter parallel to the 
longitudinal axis of the hammer. The swing arms of a given pair of arms 
are disposed parallel to one another, and are spaced apart one above the 
other. Each arm has two ends, one of which is pivotably mounted on the 
cover, and the other of which is pivotably mounted on the housing. This 
pivotable mounting is effected by pivot means, at least some of which are 
embodied in the form of soft torsion springs. The swing arms have a pivot 
range that is free except for the torsion spring effect. The inventive 
hammer is also characterized by stops for elastically delimiting this free 
pivot range of the swing arms. The stops cooperate in a cushioned manner, 
and are disposed on the housing and on the cover. The stops have a spring 
force that increases progressively outwardly from the free pivot range of 
the swing arms. 
The inventively provided and disposed swing arms, which are mounted on the 
protective cover and on the motor housing, effect a permanent and positive 
parallel guidance of the cover relative to the housing, and reliably 
prevent any twisting or tilting of the cover. The cushioning of the swing 
arms via torsional sleeves enables a very flat and extensively linear 
spring characteristic in the normal operating range. The delimiting of 
this normal operating range via elastic stops having a progressively 
increasing spring characteristic permits high pulling forces and pressure 
to be exerted upon the handgrips beyond this normal operating range 
without the danger of jarring blows. In this way, the inventive protective 
cover provides an optimum operability of hammers that up to now could not 
be achieved. This applies to hammers driven by a gasoline engine, as well 
as to hammers driven by an electric motor or other motors. 
Specific features of the present invention will be described subsequently. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to the drawings in detail, the hammer of FIGS. 1 to 3 is 
provided with a housing 1 that also includes the motor parts, on which 
other parts can be secured. The non-illustrated motor, which is arranged 
at the top, can be a gasoline engine or an electric motor, and in 
principle could also be a different type of energy source, such as a 
hydraulic or a pneumatic motor. In the illustrated embodiment, the top of 
the hammer housing 1 is enclosed on all sides by a protective cover 2 that 
extends at least around the motor region, but can also extend over at 
least a portion of the hammer shaft 3, in which is disposed the impact 
mechanism. The cover 2 is positively guided parallel to the longitudinal 
axis 4 of the hammer, and supports the customary handgrips 5 that are 
disposed on both sides. The cover 2 also supports the supplemental 
handgrip 6 that is required by the operator for reversing the unit and 
directing the hammer. 
The parallel guidance between the hammer 1,3 and the protective cover 2 is 
effected by two pairs of swing arms 7a, 7b and 8a, 8b, with each of said 
pairs being disposed on a different side. The arms of a given pair are 
disposed parallel to one another and one above the other. One end of each 
of the arms is pivotably connected to the cover 2, and the other end is 
pivotably connected to the housing 1. To effect this pivotable mounting, 
each of the arms 7a, 7b, 8a and 8b is provided with a shaft stub 9; these 
shaft stubs extend from the arms at right angles to the respective cover 
or housing. In the embodiment illustrated in FIGS. 1-3, the shaft stubs 9 
on the corresponding end of said arms merely extend into bores in bearing 
blocks 10 disposed on the protective cover 2. The shaft stubs 9 on the 
corresponding opposite end of the swing arms are rigidly connected with 
torsional sleeves 11 that are secured in the hammer housing 1; the 
periphery of these sleeves may be rigidly secured to the housing 1. The 
torsional sleeves 11 have a relatively great elasticity, so that they 
produce a soft shock absorption of the swing arms 7a, 7b, 8a, and 8b 
relative to the hammer housing 1, with the elasticity changing only 
slightly over a relatively large range of the reciprocal parallel 
displacement of the hammer housing 1 and the protective cover 2. 
The aforementioned range of movement, with soft shock absorption between 
the hammer housing 1 and the protective cover 2, in other words the 
corresponding pivot range of the swing arms, is elastically delimited by 
stops 12, 13 and 14, 15 that are disposed between the cover 2 and the 
housing 1 and cooperate in a cushioned manner. The stops 12, 13 delimit 
movement in one direction, and the stops 14, 15 delimit movement in the 
opposite direction. The two pairs of cooperating stops 12,13 on the one 
hand and 14, 15 on the other hand, each comprise a rigid stop 12 or 14 
that is disposed on the inside of the cover 2, and a cooperating stop 13 
or 15 that is made of resilient material and is disposed on the hammer 
housing 1. The shape and material of these resilient stops 13 and 15 are 
such that there results for the cooperating stops 12, 13 and 14, 15 a 
progressive spring characteristic, such as the one illustrated by the 
curve in FIG. 7. An example of the material that is particularly suitable 
for providing such a spring characteristic is elastic, foamed 
polyurethane. Elastic polyurethane is also a particularly good material 
for the torsional sleeves 11, although in this case the polyurethane is 
not foamed. Both of the upper swing arms 7a, 8a, as well as both of the 
lower swing arms 7b, 8b, are respectively rigidly interconnected by 
connecting members 16 that form respective swivel brackets with the swing 
arms. Such a rigid interconnection of the swing arms is particularly 
suitable where the cover 2 does not have sufficient inherent rigidity to 
itself force a synchronous movement of the swing arms. 
The protective cover 2 is high enough so that even when the greatest 
pressure or pulling is exerted upon the handgrips 5, the top of the cover 
2 does not come into contact with the hammer housing 1. 
To allow for differences in pulling and pressure, the cooperating stops 12, 
13 on the one hand, and 14, 15 on the other hand, can be provided with 
different progressive spring characteristics. It is also advisable to make 
the cooperating stops adjustable (not illustrated) in order to be able to 
adapt the spring characteristic to varying applications of the hammer. 
The embodiment illustrated in FIGS. 4-6 coincides to a large extent to that 
illustrated in FIGS. 1-3. The difference is merely in the arrangement of 
the pivot and spring points for the swing arms 7a, 7b, 8a, 8b. 
In the embodiment of FIGS. 4-6, the shaft stubs 9' of both ends of the 
respective swing arms, as opposed to the shaft stubs 9 of only one end of 
the swing arms, engage torsional sleeves 11'. At one end, these torsional 
sleeves are disposed in the hammer housing, and at the other end the 
sleeves are disposed in bearing blocks 10' provided on that wall of the 
cover 2 that faces the operator. With regard to the shaft stubs 9' that 
are supported on the cover 2, both the upper and lower shaft stubs 9' are 
respectively interconnected to form continuous rods; these rods then 
effect the rigid interconnection between the swing arms 7a, 8a on the one 
hand, and 7b, 8b on the other hand. Although it is more expensive to 
divide the torsional elasticity among all eight shaft stubs or pivot 
points, an even more favorable spring characteristic results for the 
normal operating range. 
The present invention is, of course, in no way restricted to the specific 
disclosure of the specification and drawings, but also encompasses any 
modifications within the scope of the appended claims.