Coffee machine

A coffee machine comprises a boiling chamber, two pistons adjustable independently of each other and adapted to be pushed into the boiling chamber from opposite sides and defining between them a boiling space to hold and boil a predetermined quantity of powdered coffee, a source of boiling water having a through-flow heater and a boiling water pressure generator, and a hydraulic actuating device for the pistons having a pressurized medium circuit including a pressurized medium pump. The boiling water pressure generator is constituted by a media converter, of which one side is incorporated into the water supply to the boiling chamber while its other side is connectible to the pressurized medium pump.

BACKGROUND TO THE INVENTION 
The invention relates to a coffee machine comprising a boiling chamber, two 
pistons adjustable independently of each other and adapted to be pushed 
into the boiling chamber from opposite sides and defining between them a 
boiling space to hold and boil a predetermined quantity of powdered 
coffee, a source of boiling water with a through-flow heater and a boiling 
water pressure generator and a hydraulic actuating device for the pistons 
with a pressurised medium circuit comprising a pressurised medium pump. 
Conventional coffee machines of this type use their own boiling water pump 
as a means of generating boiling water pressure. This solution is 
relatively complicated both in terms of prime cost of the coffee machine 
and also in terms of the space required. Furthermore, such pumps are 
subject to a certain wear and tear, particularly if the water contains a 
high level of lime. 
OBJECT OF THE INVENTION 
An object of the invention is to provide a coffee machine of the type 
mentioned at the outset, which affords a keenly priced, space-saving and 
as far as possible maintenance-free arrangement for generating the boiling 
water pressure. 
SUMMARY OF THE INVENTION 
According to the invention, this problem is resolved in that the boiling 
water pressure generator is constituted by a media converter, one side of 
which is incorporated into the water supply flow to the boiling chamber 
while its other side is adapted to be connected to the pressurised medium 
pump. 
Such a media converter can be of extremely simple construction which means 
that it can be produced at a low price. In addition, it is virtually 
maintenance-free and operates over long periods of time without any 
breakdown. In the coffee machine, therefore, only one pump is required, 
namely the pressurised medium pump of the hydraulic operating means, which 
is provided in any case for the pistons of the boiling chamber and, if 
need be, for ejection of the extracted powdered coffee. 
Preferably, the media converter is disposed at a point along the water 
supply line which is upstream of the through-flow heater, so that it is 
only subject to the action of the cold inflowing water. This reduces the 
risk of calcification of the media converter if the water has a very high 
lime content. In addition, it is not absolutely necessary for the media 
converter to consist of materials suitable for temperatures close to the 
boiling point of water. 
Preferably, the media converter consists of a container with a water 
chamber and a chamber to hold pressurised medium, the chambers being 
separated from each other by a pressure-transmitting element. In the case 
of an embodiment which is particularly simple in construction and 
manufacture, the pressure transmitting element is a resilient diaphragm. 
Currently, materials are known which comply with the severe requirements 
of the foodstuffs law and which also exhibit neutral response to hydraulic 
pressurised media. 
Preferably, the media converter is so constructed that at least the part of 
the container wall which defines the pressurised medium chamber tapers 
towards the aperture provided for inlet of pressurised medium, the 
diaphragm being so shaped that when the pressurised medium chamber is in a 
pressureless state, it bears on its inside face. This is a particular 
advantage of the solution according to the invention since as the 
pressurised medium flows in, it is firstly only the surface corresponding 
to the cross-section of the inlet aperture for pressurised medium which is 
effective. As the diaphragm lifts away from the inside face of the 
container wall which surrounds the chamber provided for pressurised 
medium, the effective pressure area increases progressively until, in the 
end, it corresponds to the entire area of the diaphragm which is subject 
to the action of the pressurised medium. Consequently, the boiling water 
does not enter the boiling chamber abruptly at the maximum possible 
pressure but at a gradually increasing pressure. It has been demonstrated 
that the quality of the coffee brewed can be achieved if the pressure of 
the boiling water rises gradually. A corresponding control of a boiling 
water pump would necessitate an unevenly greater cost. 
In the case of a preferred embodiment of media converter, the container 
consists of two hemispherical shells between which the diaphragm is 
clamped. 
Emptying of the pressurised medium chamber and controlling of the supply of 
water and the discharge of water to and/or from the water chamber of the 
media converter can easily be achieved in that the water chamber is 
connected to a portion of the water supply line which is disposed between 
two non-return valves, these latter being so located that when the 
pressurised medium chamber of the media converter is subjected to the 
action of pressurised media, the non-return valve which is disposed 
upstream of the water chamber is closed while that which is disposed 
downstream is opened. 
According to a further feature of the invention, disposed in the 
pressurised medium tank of the pressurised medium circuit are the 
pressurised medium pump and a heat exchanger through which passes the 
water supplying to the through-flow heater. In this way, on the one hand 
the pressurised medium pump or pressurised medium will be cooled while on 
the other the water flowing to the through-flow heater will be pre-heated. 
Consequently, it is possible to achieve a not inconsiderable saving on 
energy.

DESCRIPTION OF PREFERRED EMBODIMENTS 
In FIG. 1, reference numeral 10 generally denotes an automatic piston 
device of a coffee machine such as is described for example in Swiss 
Patent Specification No. 641 030. This automatic piston device is 
indicated in FIG. 2 in a very simplified view. It comprises a cylindrical 
boiling chamber 12 into the oppositely disposed axial ends of which it is 
possible to insert in each case a piston 14, 16, these pistons 14 and 16 
being adjustable independently of each other by a working cylinder 18, 20. 
The piston 14 and the piston 16 enclose between them a boiling space into 
which the piston 14 introduces the boiling water and out of which the 
piston 16 discharges the coffee. 
FIG. 2 also shows another working cylinder which actuates a pivot arm, not 
shown, which withdraws from the boiling chamber and feeds to a waste 
container the coffee filling which has been pressed into a tablet and 
exhausted. All these functions are described in detail in Swiss Patent 
Specification No. 641 030 so that they do not need to be explained in 
greater detail here. All three working cylinders 18, 20 and 22 are adapted 
to be connected to the pressure side of a pressurised medium pump 30 or 
pressurised medium tank 32 in each case via a separably operable multi-way 
valve 24, 26 and 28. The pressurised medium pump 30 is disposed inside the 
pressurised medium tank 32 and is driven by an electric motor 34. 
The valve assembly which comprises the valves 24 to 28 also contains a 
further optionally operable multi-way valve 36 through which the pressure 
side of the pump 30 can be connected to the pressurised medium side 38 of 
a spherical media converter 40. This media converter consists according to 
FIG. 3 of two hemispherical shells 42 and 44 of which the encircling 
radial flanges 46, 48 are bolted to each other and between which there is 
stretched a resilient diaphragm 50 which, in the unladen state, bears 
against the inside face of the hemispherical shell 42 defining the 
pressurised medium chamber, as is shown in FIG. 3. The hemispherical shell 
42 of the media converter 40 has a pressurised medium inlet 52 which is 
connected to the multi-way valve 36 through a line 54 and a pressure 
reducing valve 56 which is intended for adjustment of the boiling 
pressure. 
The water chamber of the media converter 40, which is bounded by the 
diaphragm 50 and the hemispherical shell 44 of the media converter, is 
connected by a throughflow passage 58 to a portion 60 of the line leading 
from the water mains to the boiling chamber 12, this portion being located 
between two non-return valves 62 and 64 which are connected in the same 
sense so that when the boiling pressure is generated, the non-return valve 
64 is closed in the direction of the mains while the non-return valve 62 
is opened in the direction of the boiling chamber 12. As FIG. 1 shows, the 
boiling water flows through and is pre-heated in a heat exchanger 66 which 
is disposed in the pressurised medium tank 32. In this way, it disperses 
the heat generated by the various working processes and in particular by 
the pressurised medium pump 30 disposed in the pressurised medium tank 32. 
After it leaves the heat exchanger 66, the boiling water flows through a 
volume counter 68 before entering a throw-flow heater 70 from which it 
flows to a multi-way valve 72. From here, the boiling water passes through 
a restriction or orifice plate 74 to determine the throughflow resistance 
in the automatic piston device 10. The throughflow heater 70 is connected 
to a discharge 78 via a pressure limiting valve 76. Furthermore, the 
multi-way valve 72 permits of a connection between the automatic piston 
device 10 and the discharge 78 when the residual humidity is forced out of 
the exhausted powdered coffee so that it can be ejected into the waste 
container with the lowest possible moisture content. 
Finally, FIG. 1 shows a container 8 for a cleaning agent with which the 
automatic piston device 10 can be cleaned at certain intervals. 
If it is desired to use the coffee machine according to the invention in 
order to prepare coffee, then first of all in per se known manner a 
specific quantity of coffee is ground and placed in the brewing chamber. 
When the brewing chamber is closed by the pistons 14 and 16, the piston 14 
supplies boiling water. To this end, the valve 36 is opened so the 
pressurised medium flows through the pressurised medium inlet 52 into the 
pressurised medium chamber of the media converter 40. As FIG. 3 shows, 
initially all that acts on the diaphragm 50 is a force corresponding to 
the cross-section of the pressurised medium inlet 52 at the diaphragm 50. 
Only when the diaphragm 50 lifts off the inner wall of the hemispherical 
shell 52 does the effective pressure area increase, finally occupying the 
complete cross-sectional area of the free portion of the diaphragm 50 
which is held firmly in place. In this way, the boiling water in the media 
converter is not abruptly and at full pressure forced into the brewing 
chamber 12 of the automatic piston device 10 but gradually and with a 
progressively increasing pressure. When this happens, the check valve 64 
disposed upstream of the media converter 40 is closed while the check 
valve 62 disposed downstream of the media converter 40 is opened. When the 
media converter is completely emptied and the pressurised medium chamber 
of the media converter 40 is connected to the pressurised medium tank 32, 
then water flows out of the water mains into the water chamber of the 
media converter 40 and presses the diaphragm 50 back into the position 
shown in FIG. 3. The check valve 62 is closed. 
The solution according to the invention is less expensive to manufacture, 
more economical in operation and requires less maintenance than the 
conventional solutions.