Oil pump for hand rail chain saw machines

The invention relates to an oil pump for hand rail chain saw machines in which a pump plunger has an annular groove at its end remote from the drive and which is connected via a duct to the pump oil pressure channel, so that the sucking in of secondary air, high wear and an undefined lubrication are avoided.

BACKGROUND OF THE INVENTION 
The invention relates to an oil pump with a pump plunger arranged in a pump 
casing and able to perform lifting movements by means of a drive for hand 
rail chain saw machines. 
Valveless-controlled plunger pumps have been mainly used for the 
lubrication of the cutting chain in motor saws of the aforementioned type. 
The pumps are driven by a worm drive or a combined worm-toothed gear 
drive. As a particularly lightweight, compact construction is required for 
motor saws, this requirement also applies to the oil pump, although its 
function must not be impaired. 
In connection with this requirement, the sealing of the pump plunger shaft 
is particularly difficult, because it is very short due to the compact 
construction and consequently sucks in air via the plunger shaft during 
the suction phase accompanied by increased suction resistance, either due 
to cold, i.e. viscous oil or due to contamination of the suction filter. 
This is prejudicial to the operation of the pump and the contact surface 
of the plunger and the drive in general becomes generally free from 
lubricant and is consequently exposed to increased wear. 
In the case of the known oil pumps for motor saws, this problem is either 
unsolved or only partly solved. Known solutions are accurate cylinder fits 
or seals by O-rings or long plungers. 
All these solutions have the disadvantage that they are not free from wear 
and do not ensure an adequate lubrication of the drive. 
BRIEF SUMMARY OF THE INVENTION 
The problem of the present invention is to provide an oil pump for hand 
rail chain saw machines, which obviates the aforementioned deficiencies 
with respect to such machines such as the sucking in of secondary air, 
wear and not precisely defined lubrication. 
According to the invention, this problem is solved by a pump of the 
aforementioned type constructed in such a way that at its end remote from 
the drive the pump plunger has an annular groove connected to the pump oil 
pressure channel via a duct. 
As the annular groove provided on the plunger shaft is subject to the 
action of the medium from the pressure side and is sealed with the medium 
supplied, an adequate lubrication for the drive is ensured and wear to its 
most important parts is prevented. As the annular groove is under system 
pressure, by means of the clearance between the pump plunger and the pump 
cylinder a clearly defined waste oil quantity is supplied which is used 
for lubricating the drive. 
The advantages resulting from the novel construction of the oil pump are in 
particular that the pump can be kept small without its function being 
impaired. A further advantage is that a clearly defined lubrication of the 
drive, i.e. the defined waste oil quantity can be ensured. The invention 
also provides the advantage that in operation the pump plunger is 
continuously wetted with an oil film and forced lubrication takes place 
with rising operating pressure. It is also extremely advantageous that no 
moving parts, i.e. parts subject to wear, are required for sealing and 
lubrication.

DESCRIPTION OF THE DRAWING AND PREFERRED EMBODIMENT 
The invention is described in greater detail hereinafter relative to a 
non-limitative embodiment and the attached drawing which shows a 
cross-section through an oil pump with a pressure seal. 
In the drawing, 10 is a pump casing in which a pump plunger 12 performs a 
lifting movement. In the case of the embodiment shown in the drawing, the 
lifting movement is produced by a worm gear 15 and a lifting cam 16. 
To prevent a penetration of secondary air during the suction phase from 
chamber 1 via cylinder faces 12a and 12b into cylinder chamber II, an 
annular groove 13 is formed in the pump plunger 12 connected via a 
cross-bore 14 with the oil pressure channel D. The oil suction channel is 
indicated at S.