Hitachi DH 40MRY Technical Data And Service Manual page 17

Structure of the Neidhardt spring
The main body (back cover) is connected to the
lower handle through four cylindrical rubbers
(handle dampers). The shaft fixed to the handle is
turned in conjunction with the handle movement
and the rubbers are rolled and compressed to
absorb vibration. The Neidhardt spring prevents
the handle from moving horizontally. Thus the
Model DH 40MRY can provide high vibration-
proofing effect without hindering the operability by
twisting. In addition, the handle is prevented from
being pulled out (Fig. 6).
Striking operation
The rotation of the armature is transferred to the crank shaft and connecting rod, which in turn cause the
piston to reciprocate inside the cylinder. As the piston reciprocates, the changing air pressure inside the air
chamber between the piston and the striker causes the striker to continuously strike against the end of the
second hammer. At the same time, the air-cushion effect within the air chamber absorbs the impact of the
striker. Should the air escape from the air chamber, the air-cushion effect would cease, and the impact energy
would not be absorbed. Accordingly, the O-rings mounted on the striker and the piston play an extremely
important role in sealing the air within the air chamber.
Mechanism to prevent idle hammering
The mechanism against idle hammering of the Model DH 40MRY is about the same as the Model DH 40MR in
which, when the drill bit or the bull point is not pressed against a concrete or similar material, the second
hammer moves to a position as shown in Fig. 7 so that the striker is displaced from its hammering position.
Thus the air hole is opened and no change is caused in the air pressure chamber by the piston movement,
then the hammering action is stopped.
Second hammer, striker movement distance
Second hammer
Fig. 7
--- 14 ---
Compressed by turning
Rebound
Fig. 6
Striker
Air chamber
Air hole
Turning direction
of the handle