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CPC Definition - Subclass F01B

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Last Updated Version: 2026.08
F01B
MACHINES OR ENGINES, IN GENERAL OR OF POSITIVE-DISPLACEMENT TYPE, e.g. STEAM ENGINES (of rotary-piston or oscillating-piston type F01C; of non-positive-displacement type F01D; internal-combustion engines F02B; combustion-product engine plants F02G; machines or engines, other than of positive-displacement type, for liquids F03B; positive-displacement engines driven by liquids F03C; wind motors F03D; positive-displacement machines for liquids F04B; rotary-piston, or oscillating-piston, positive-displacement machines for liquids F04C)
Definition statement

This place covers:

Machines or engines, in general or of positive-displacement type.

References
Limiting references

This place does not cover:

Rotary-piston or oscillating-piston machines or engines

F01C

Non-positive-displacement machines or engines, e.g. steam turbines

F01D

Internal-combustion engines

F02B

Combustion-product engine plants

F02G

Machines or engines, other than of positive-displacement type, for liquids

F03B

Positive-displacement engines driven by liquids

F03C

Wind motors

F03D

Positive-displacement machines for liquids

F04B

Rotary-piston, or oscillating-piston, positive-displacement machines for liquids

F04C

Informative references

Attention is drawn to the following places, which may be of interest for search:

Steam engine plants

F01K

Cyclically operating valves for machines or engines

F01L

Lubricating of machines or engines in general

F01M

Pumps for liquids or elastic fluids

F04

Crankshafts, crossheads or connecting-rods

F16C

Flywheels

F16F

Gearings for interconverting rotary motion and reciprocating motion in general

F16H

Pistons, piston rods or cylinders, for engines in general

F16J

Glossary of terms

In this place, the following terms or expressions are used with the meaning indicated:

engine

a device for continuously converting fluid energy into mechanical power, thus, this term includes, for example, steam piston engines or steam turbines, per se, or internal-combustion piston engines, but it excludes single-stroke devices.

machine

a device which could equally be an engine and a pump, and not a device which is restricted to an engine or one which is restricted to a pump.

pump

a device for continuously raising, forcing, compressing, or exhausting fluid by mechanical or other means. Thus, this term includes fans or blowers.

positive displacement

the way the energy of a working fluid is transformed into mechanical energy, in which variations of volume created by the working fluid in a working chamber produce equivalent displacements of the mechanical member transmitting the energy, the dynamic effect of the fluid being of minor importance, and vice versa.

non-positive displacement

the way the energy of a working fluid is transformed into mechanical energy, by transformation of the energy of the working fluid into kinetic energy, and vice versa.

oscillating-piston machine

a positive-displacement machine in which a fluid-engaging work-transmitting member oscillates. This definition applies also to engines and pumps.

rotary-piston machine

a positive-displacement machine in which a fluid-engaging work-transmitting member rotates about a fixed axis or about an axis moving along a circular or similar orbit. This definition applies also to engines and pumps.

rotary piston

the work-transmitting member of a rotary-piston machine and may be of any suitable form, e.g., like a toothed gear.

free piston

a piston of which the length of stroke is not defined by any member driven thereby.

cylinders

positive-displacement working chambers in general. Thus, this term is not restricted to cylinders of circular cross-section.

main shaft

the shaft which converts reciprocating piston motion into rotary motion or vice versa.

plant

an engine together with such additional apparatus as is necessary to run the engine. For example, a steam engine plant includes a steam engine and means for generating the steam.

working fluid

the driven fluid in a pump or the driving fluid in an engine. The working fluid can be in a compressible, gaseous state, called elastic fluid, e.g. steam; in a liquid state; or in a state where there is coexistence of an elastic fluid and liquid phase.

Reciprocating-piston machines or engines characterised by number or relative disposition of cylinders or by being built-up from separate cylinder-crankcase elements (F01B 3/00, F01B 5/00 take precedence)
References
Limiting references

This place does not cover:

Reciprocating-piston machines or engines with cylinder axes coaxial with, or parallel or inclined to, main shaft

F01B 3/00

Reciprocating-piston machines or engines with cylinder axes arranged substantially tangentially to a circle centred on main shaft axis

F01B 5/00

{the connection of the pistons with an element being at the outer ends of the cylinders}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

1a.

media86.png

1b.

media87.png

{the connection of the pistons with an actuating or actuated element being at the inner ends of the cylinders}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

1a.

media88.png

1b.

media89.png

{Disconnecting the pistons from the actuating or actuated cam}
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Disengagement of connections between pistons and main shafts

F01B 31/24

with more than one main shaft, e.g. coupled to common output shaft
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Combinations of two or more machines or engines

F01B 21/00

Reciprocating-piston machines or engines with cylinder axes coaxial with, or parallel or inclined to, main shaft axis
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media90.png

{having stationary cylinders}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media91.png

{having two or more sets of cylinders or pistons}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media92.png

{having self-acting distribution members, e.g. actuated by working fluid}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

1a. Engine with coaxial pistons

media93.png

1b. Power distribution member of coaxial piston engine actuated by a working fluid

media94.png

1c. Graph of working characteristics of coaxial piston engine

media95.png

Figure 1c illustrates the operation of the coaxial piston engine. Curve A indicates the motion of the reciprocating piston (10) relative to the cylinder head with respect from bottom dead center [BDC)] to top dead center [TDC]. Curve B indicates the lift of inlet valve (17) from its seat. Curve C indicates the motion of the push rod (41) relative to the face of the swash plate (35) thus depicting a cam profile.

{Cylindrical distribution members}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

1a.

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1b.

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{Conical distribution members}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media98.png

{having rotary cylinder block}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media99.png

{inclined to main shaft axis}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media100.png

{Arrangements for pressing the cylinder barrel against the valve plate, e.g. fluid pressure}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media101.png

{Particularities in the contacting area between cylinder barrel and valve plate}
Definition statement

This place covers:

Illustrative examples of subject matter classified in this place:

1. Cylinder barrel openings for valve plate

media102.png

2. Cylinder barrel openings for valve plate

media103.png

3. Cylinder barrel openings for valve plate

media104.png

4. Cylinder barrel openings for valve plate

media105.png

{Bearing arrangements}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media106.png

{Cylinder barrel}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media107.png

{Conical valve means}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media108.png

{Swash plate}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media109.png

{Connection between cylinder barrel and inclined swash plate}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media110.png

{having pistons with rotary and reciprocating motion, i.e. spinning pistons}
Definition statement

This place covers:

Reciprocating-piston machines or engines with cylinder axes coaxial with, or parallel or inclined to, main shaft axis, wherein the pistons rotate (spin) about their longitudinal axis as they reciprocate.

Illustrative example of subject matter classified in this place:

media72.jpg

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Piston motion being transmitted by curved surfaces

F01B 3/04

with wobble-plate
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media111.png

the piston motion being transmitted by curved surfaces
Definition statement

This place covers:

Piston motion being transmitted by curved surfaces, e.g. by cams or grooves.

Illustrative example of subject matter classified in this place:

media73.png

{by two or more curved surfaces, e.g. for two or more pistons in one cylinder}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media112.png

by multi-turn helical surfaces and automatic reversal
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media113.png

the helices being arranged on the pistons
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media114.png

Control of working-fluid admission or discharge peculiar thereto
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Cyclically operating valves for machines or engines in general

F01L

{for machines with rotary cylinder block}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media115.png

{by turning the valve plate}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media116.png

{by changing the inclination of the swash plate}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media117.png

{by turning the swash plate (with fixed inclination)}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media118.png

{by changing the inclination of the axis of the cylinder barrel relative to the swash plate}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media74.png

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Control of working-fluid admission or discharge by changing inclination of the swash plate

F01B 3/106

Reciprocating-piston machines or engines with cylinder axes arranged substantially tangentially to a circle centred on main shaft axis
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media119.png

{the connection of the pistons with an actuated or actuating element being at the outer ends of the cylinders}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media120.png

{the connection of the pistons with an actuated or actuating element being at the inner ends of the cylinders}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

1a.

media121.png

1b.

media122.png

Machines or engines with two or more pistons reciprocating within same cylinder or within essentially coaxial cylinders (in opposite arrangement relative to main shaft F01B 1/08)
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media123.png

References
Limiting references

This place does not cover:

Coaxial cylinders in opposite arrangement relative to main shaft

F01B 1/08

with oppositely reciprocating pistons
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

1a.

media124.png

1b.

media125.png

1c.

media126.png

using only connecting-rods for conversion of reciprocatory into rotary motion or vice versa
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media127.png

with side rods
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

1a.

media129.png

1b.

media128.png

having piston-rod of one piston passed through other piston
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media130.png

using rockers and connecting-rods
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media131.png

acting on different main shafts
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media132.png

with pistons synchronously moving in tandem arrangement
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media133.png

with differential piston (F01B 7/20 takes precedence)
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media134.png

References
Limiting references

This place does not cover:

Machines or engines with two or more pistons reciprocating one within another

F01B 7/20

with two or more pistons reciprocating one within another, e.g. one piston forming cylinder of the other
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media135.png

Reciprocating-piston machines or engines characterised by connections between pistons and main shafts, not specific to groups F01B 1/00 - F01B 7/00
Definition statement

This place covers:

Reciprocating-piston machines or engines characterised by connections between pistons and main shafts and not specific to groups F01B 1/00 - F01B 7/00, e.g. when no recognisable crank shaft is present or the main shaft is a cam shaft.

Illustrative example of subject matter classified in this place:

media75.png

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Connections disengageable during idling

F01B 31/24

with crankshaft
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media136.png

{of Bourke-type or Scotch yoke}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media137.png

with rotary main shaft other than crankshaft
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media138.png

{the connections comprising gear transmissions}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media139.png

{with rack and pinion}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media140.png

the piston motion being transmitted by curved surfaces
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

1a.

media141.png

1b.

media142.png

with ratchet and pawl
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media143.png

{in which the movement in the two directions is obtained by one double acting piston motor}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media144.png

{one side of the double acting piston motor being always under the influence of the fluid under pressure}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

1a.

media145.png

1b.

media146.png

{the fluid under pressure being continuously delivered to one motor chamber and reacting the other chamber through a valve located in the piston, to bring the piston back in its start-position}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media147.png

{in which the movement in the two directions is obtained by two single acting piston motors, each acting in one direction}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media148.png

{one single acting piston motor being always under the influence of the fluid under pressure}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media149.png

{in which the movement in only one direction is obtained by a single acting piston motor, e.g. with actuation in the other direction by spring means}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media150.png

{with actuation in the other direction by gravity}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media151.png

{in which the movement in two directions is obtained by two or more double acting piston motors}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

1a.

media152.png

1b.

media153.png

1c.

media154.png

Equalising or cushioning devices
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

1a.

media155.png

1b.

media156.png

Engines combined with reciprocatory driven devices, e.g. hammers
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media76.png

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Engines combined with pumps

F01B 23/08

for generating vibration only
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

1a. Engine for producing vibrations on a conveying line

media157.png

1b. Engine in first position

media158.png

1c. Engine in second position

media159.png

with direct fluid transmission link
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media77.png

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Equalising or cushioning devices

F01B 11/02

Reciprocating-piston machines or engines with rotating cylinders in order to obtain the reciprocating-piston motion
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Machines or engines of flexible-wall type

F01B 19/00

with one cylinder only
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media160.png

with more than one cylinder
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media85.png

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Reciprocating-piston machines or engines with cylinder axes coaxial with, or parallel or inclined to, main shaft axis having rotary cylinder block

F01B 3/0032

{with cylinder axes arranged substantially tangentially to a circle centred on main shaft axis}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media161.png

{the connection of the pistons with the actuated or actuating element being at the outer ends of the cylinders}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media162.png

{the connection of the pistons with an actuated or actuating element being at the inner ends of the cylinders}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media163.png

Reciprocating-piston machines or engines with movable cylinders other than provided for in group F01B 13/00
Definition statement

This place covers:

Reciprocating-piston machines or engines with movable cylinders other than provided for in group F01B 13/00, e.g. reciprocating-piston machines or engines having reciprocating cylinders or pivoting and oscillating cylinders.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Slide-valve gear or valve arrangements, with cylindrical, sleeve or part-annularly-shaped valves, surrounding working cylinder or piston

F01L 5/06

Reciprocating-piston machines or engines characterised by use of uniflow principle
Definition statement

This place covers:

Reciprocating-piston machines or engines characterised by use of uniflow principle, e.g. compressed gas engines where the working fluid enters a working cylinder, expands and then exits the cylinder.

Illustrative example of subject matter classified in this place:

media164.png

Glossary of terms

In this place, the following terms or expressions are used with the meaning indicated:

In patent documents, the word "uniflow" is often used with the meaning "open circuit where a gas enters a cylinder, expands and is then released."

Engines
Definition statement

This place covers:

Compressed gas engines.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Arrangement or mounting of steam or gaseous-pressure propulsion units of the piston type in vehicles

B60K 3/02

Arrangement or mounting of plural diverse prime-movers for mutual or common propulsion, prime movers comprising combustion engines and a chargeable fluidic accumulator for storing fluid energy

B60K 6/12

{with fluid heating}
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media165.png

The Figure illustrates a burner (k) heating fluid supplied to a uniflow engine.

{using separators}
Definition statement

This place covers:

Separators for separating liquid or oil from compressed gas for gas engines.

Steam engines
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Toys

A63H

Steam engine plants

F01K

Positive-displacement machines or engines of flexible-wall type
Definition statement

This place covers:

Positive-displacement machines or engines of flexible-wall type, e.g. where the piston is made of a diaphragm or bellows.

Illustrative example of subject matter classified in this place:

media166.png

with plate-like flexible members
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

1a.

media167.png

1b.

media168.png

with tubular flexible members
Definition statement

This place covers:

Illustrative example of subject matter classified in this place:

media169.png

Combinations of two or more machines or engines (F01B 23/00 takes precedence)
Definition statement

This place covers:

Combinations of two or more machines or engines, e.g. a combined internal combustion engine and steam engine.

References
Limiting references

This place does not cover:

Adaptations of machines or engines for special use; Combinations of engines with devices driven thereby

F01B 23/00

Informative references

Attention is drawn to the following places, which may be of interest for search:

Combinations of two or more positive-displacement pumps in pumping installations or systems specially adapted for elastic fluids

F04B 41/06

Combinations of two or more machines or pumps, each being of rotary-piston or oscillating-piston type; Pumping installations

F04C 11/00

Combinations of two or more pumps, each being of rotary-piston or oscillating-piston type, specially adapted for elastic fluids; Pumping installations specially adapted for elastic fluids; Multi-stage pumps specially adapted for elastic fluids

F04C 23/00

Combinations of two or more non-positive-displacement pumps in pumping installations or systems

F04D 13/12

Combinations of two or more non-positive-displacement pumps in pumping installations or systems specially adapted for elastic fluids

F04D 25/16

Rotary fluid gearing using pumps and motors of the volumetric type, i.e. passing a predetermined volume of fluid per revolution

F16H 39/00

Rotary fluid gearing of the hydrokinetic type

F16H 41/00

Other fluid gearing, e.g. with oscillating input or output

F16H 43/00

Combinations of fluid gearings for conveying rotary motion with couplings or clutches

F16H 45/00

Adaptations of machines or engines for special use; Combinations of engines with devices driven thereby
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Reciprocating-piston machines or engines without rotary main shaft, e.g. of free-piston type

F01B 11/00

Rotary fluid gearing using pumps and motors of the volumetric type, i.e. passing a predetermined volume of fluid per revolution

F16H 39/00

Rotary fluid gearing of the hydrokinetic type

F16H 41/00

Other fluid gearing, e.g. with oscillating input or output

F16H 43/00

Combinations of fluid gearings for conveying rotary motion with couplings or clutches

F16H 45/00

Regulating, controlling or safety means (controlling combustion engines F02D)
References
Limiting references

This place does not cover:

Controlling combustion engines

F02D

Informative references

Attention is drawn to the following places, which may be of interest for search:

Regulating or controlling in general

G05

Regulating or controlling by varying working-fluid admission or exhaust, e.g. by varying pressure or quantity
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Distributing or expansion valve gear

F01L

Arrangements or adaptations of working-fluid admission or discharge valves
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Valves in general

F16K

Starting of machines or engines (starting combustion engines F02N)
References
Limiting references

This place does not cover:

Starting combustion engines

F02N

Means for moving crank off dead-centre
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Turning-gear in general

F16H

Engines
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Refrigeration machines

F25B

Component parts, details or accessories not provided for in, or of interest apart from, other groups
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Machine or engine casings, other than those peculiar to steam engines

F16M

Means for equalising torque in reciprocating-piston machines or engines
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Suppression of vibrations in systems; Means or arrangements for avoiding or reducing out-of-balance forces, e.g. due to motion

F16F 15/00

Cooling of steam engines; Heating; Heat insulation
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Cooling of fluid machines or engines in general

F01P

Heat insulation in general

F16L 59/00

Lubricating arrangements of steam engines
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Lubricating arrangements of fluid machines or engines in general

F01M

Arrangements of measuring or indicating devices
References
References out of a residual place

Examples of places in relation to which this place is residual:

Warning devices

F01B 25/26

Informative references

Attention is drawn to the following places, which may be of interest for search:

Measuring instruments or the like per se

G01

Silencers specially adapted for steam engines
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Arrangements of exhaust pipes or tubes on steam engines

F01B 31/30

Gas-flow silencers or exhaust silencers for machines or engines in general

F01N

Safety means against water hammer or against the penetration of water
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Steam traps

F16T