Power control system for a double-acting hot gas engine

The invention relates to a power control system for a hot gas engine in which the power depends on the mean working gas pressure in the engine. Said engine is of the type having an even number of working gas charges separated by pistons each having two axially displaced piston rings. Said piston rings and their piston ring grooves are shaped to act as check valves and so that in each other piston the space between the piston rings will contain gas of maximum working cycle pressure whereas in the remaining pistons it will be minimum working cycle pressure.

This invention relates to a power control system for a double-acting hot 
gas engine. 
BACKGROUND OF THE INVENTION 
Double-acting hot gas engines generally comprises three or more working gas 
charges each of which are cyclically compressed at low temperature, 
heated, expanded at high temperature and cooled. The work performed during 
a working cycle is almost proportional to the amount of working gas in the 
charge. 
Therefore, it is common practise to vary the amount of working gas in each 
working gas charge in order to govern the power output--e.g. in case the 
engine speed and the engine temperatures should be kept nearly constant. 
The U.S. Pat. No. 3,927,529 shows a power control system of this known 
type. In order to avoid interconnections between the various working gas 
charges of the engine while being able to perform a simultaneous gas 
supply or gas removal by means common to all working gas charges, the gas 
supply system should comprise two check valves at each connection to a 
part of the working gas charge limiting device--e.g. the cold gas 
connection duct between the low temperature part of the cylinder and an 
adjacent cooler. 
It is also known from the U.S. Pat. No. 3,927,529 to provide each piston 
with two piston rings each of which allowing flow of gas in one direction 
only across the piston ring. A minimum working cycle gas pressure will 
prevail in the space between the two piston rings in case both piston 
rings allow gas flow only away from said space. The two piston rings act 
as check valves and the purpose is to maintain an equal mean pressure in 
all working gas cycles of the engine. 
The U.S. Pat. No. 4,417,444 shows a double-acting hot gas engine having 
axially spaced piston rings at each piston. The axial distance is greater 
than the piston stroke and a connection is established between the space 
between the piston rings and a source of gas having minimum or maximum 
pressure. Again the purpose is to maintain equal pressures in working gas 
charges. 
OBJECT AND SUMMARY OF THE INVENTION 
The object of the present invention is to provide a power control system 
which is based upon varying the amount of working gas in the working gas 
charges, but in which the check valves in the gas supply and dump system 
may be dispensed with. Said check valves contribute to the number of 
moving parts in the engine and require maintenance and represents a risk 
of leakage and performance losses. 
According to the present invention a power control system for a 
double-acting hot gas engine having an even number of working gas charges 
each of which being limited by reciprocating pistons in two cylinders and 
each of said pistons being provided with two axially spaced piston rings 
allowing flow of gas to pass each ring in one direction only is according 
to the invention characterised in that a first one of two piston limiting 
a working gas charge is provided with piston rings adapted to provide 
maximum working gas pressure between them, whereas the other one of said 
two pistons is provided with piston rings adapted to provide minimum 
working gas pressure between them, a controllable connection being 
established from a high pressure gas source to the space between the 
piston rings of said other one of said two pistons, whereas another 
controllable connection is established from the space between the piston 
rings of said first one of said two pistons to a low pressure gas source.

DETAILED DESCRIPTION 
The working gas system shown in FIG. 1 comprises a conduit 1 connected to a 
gas source of minimum gas pressure (not shown). Said source may be e.g. 
the suction side of a compressor. 
Another conduit 2 is connected to a gas source of maximum pressure (not 
shown). Said source may be a storage tank connected to the delivery side 
of a gas compressor. The gas referred to above should be suitable as 
working gas in a hot gas engine and as is commonly known in the art said 
gas should have small molecules in case the engine should have a high 
specific power output. Usually hydrogen or helium are used. 
The tubes 1 and 2 are provided with adjusting valves 3 and 4 respectively. 
The relevant parts of the hot gas engine are four cylinders 5-8 each 
containing a piston 9-12 respectively. Each piston comprises a generally 
cylindrical part 13 carrying a dome 14 at one end and a piston rod 15 at 
the other end. 
The pistons in two neighbouring cylinders influence a charge of working 
gas. E.g. the lower side of the piston part 13 in the cylinder 1 acts upon 
a working gas charge located in the cylinder 5 below the piston part 13 
and in the cylinder 6 above the dome 14 of the piston 10 as well as in 
connecting ducts 16-19. Said ducts represent the following elements as is 
well known in the art: A cold gas connecting duct 16, a cooler 17, a 
regenerator 18 and a heater 19. 
The piston rods 15 and connected to a crank shaft mechanism (not shown) in 
which the cranks are 90 degrees angularly spaced. 
It will be understood that due to the angular displacement of the cranks 
each piston of the four cylinders will move cyclically with 90 degrees 
displacement relative its neighbouring pistons. This will cause one 
compression and one expansion of each working gas charge during each 
revolution of the engine. The direction of rotation is such that each 
working gas charge mainly is located in the high temperature engine 
parts--i.e. the heater 19 and the space above the dome 14--during 
expansion, whereas each charge of working gas is located in the low 
temperature engine parts--i.e. the cooler 17 and the space below the 
piston part 13--during the compression. 
As each working gas charge is compressed at low temperature and expanded at 
high temperature the engine will produce power. 
The power output is nearly proportional to amount of working gas in the 
four working gas charges. 
The pistons in the cyclinders 6 and 8 (which an 180 degrees cyclically 
spaced) are provided with piston parts 13 having piston ring grooves as 
shown in FIG. 2. The two grooves are designated by the reference numerals 
20 and 21. They are axially spaced through a distance greater than the 
piston stroke. This makes it possible to maintain a connection between an 
opening 22 in the cylinder wall and the space 23 between the cylinder wall 
and the piston limited by two piston rings 24 and 25 in the grooves 20 and 
21 respectively. 
The piston rings 24 and 25 are loosely fitted in the grooves in the axial 
direction. The grooves 20, 21 are also provided with radially extending 
channels 26 and 27 respectively outside the piston rings 24, 25. Piston 
having such grooves and such piston rings have been described e.g. in the 
U.S. Pat. No. 3,927,529. 
Working gas may therefore always pass to the space above the piston part 13 
through the channels 26 via the inner part of the groove 20 behind the 
ring 24. 
Working gas may also always pass to the space below the piston part 13 
through the channels 27 via the inner part of the groove 21 behind the 
ring 25. 
Consequently the gas pressure in the space 23 will correspond to the 
minimum pressure of the cyclically varying pressures of the two working 
gas charges separated by the piston part 13. 
The opening 22 is connected via the conduit 2 to a maximum gas pressure 
source. Therefore, if the valve 4 is opened, gas till pass to the space 23 
and into the working gas charges separated by the piston part 13. 
FIG. 3 depicts the pistons of the cylinders 5 and 7. The piston part 13 is 
provided with grooves 30 and 31 adapted to receive piston rings 34, 35 
leaving a spaced 33 between them. Said space 33 is always in connection 
with an opening 32 in the cylinder wall and said opening 32 is connected 
to the conduit 1 having gas draining ability. The grooves 30 and 31 are 
provided with radially extending channels 36 and 37 respectively allowing 
gas to pass from the working gas charges separated by the piston to the 
space in each groove 30, 31 behind the piston ring 34, 35 and into the 
space 33. 
Therefore, the space 33 will always contain gas of maximum working gas 
pressure. 
If the pressure in the space 33 is lowered by opening the valve 3 of FIG. 1 
the maximum pressure of the cycling working gas pressure will thus be 
lowered corresponding to a decreasing amount of working gas in the engine. 
FIG. 4 shows how the axial length of the piston parts 13 may be decreased 
by decreasing the axial distance between the piston rings 40 and 41. The 
space between the piston rings 40, 41 is connected to a chamber 42 in the 
piston part 13. Said chamber 42 is in turn connected to an axial, central 
bore 43 which at radial bores 44 is connected to a chamber 45 having an 
axial length greater than the piston stroke. Said chamber 45 is provided 
with an opening 46 corresponding to the openings 22 and 32 of FIGS. 2 and 
3. Piston rod seals 47 and 48 are surrounding the piston rod and are 
axially spaced and located to ensure that the bores 44 always will be 
located between the seals 47 and 48 regardless of the position of the 
piston rod. It will be understood that the design of FIG. 4 allows a 
shorter piston and cylinder design.