Cam follower with an angled axis of rotation
Field of the invention
The invention relates to a rotary drive member comprising a longitudinal axis defining
a length direction, a curved cam contact surface forming a closed contour around the
longitudinal axis and extending in the length direction, a reciprocating member having
a carrier movable in the length direction, at least one cam follower wheel being
rotatably mounted on the carrier via a cam follower axis that extends in a direction
transverse to the length direction and that is oriented at an angle a with respect to the
transverse direction, the wheel having a wheel contact surface engaging with the cam
contact surface for rolling along the cam contact surface and driving the cam contact
surface in rotation around the longitudinal axis, wherein the cam contact surface is
oriented substantially in the transverse direction.
Background of the invention
In such a drive system, the rotating cam in combination with cam rollers transforms an
oscillating linear motion of a piston into a rotary motion of the cam surface. It is known
to apply such a drive system in a generator, a combustion engine, energy converter, or
a hybrid drive (combined generator/engine), for instance from prior art references
U.S. 1339276, U.S. 1352985, U.S.1788140 and U.S.5375567.
In EP 2 138 687 it is described that the reciprocating member comprises a piston and
the rotating cam drives a coil for generating electrical power. In these known drive
systems, a rotating cam element in combination with rollers is used to translate the
rotating movement of the cam into a translating movement to propel the pistons and
conversely. It is known that the inside edge of the rollers, which is closest to the
central, longitudinal axis, has to travel a shorter distance than the outside edge that is
situated further away from the central axis. It is known that in order to improve the
durability and performance of the rollers, these rollers are provided with a tapered
shape so that the wheels do not slip when traveling along the curved path of the cam
surface. By providing the roller wheels with a larger diameter on the outside and a
smaller diameter on the inside of the tapered rollers during rotation will effectuate the
roller wheels to run along a near perfect circular path, so that no slip occurs when the
wheels roll along the curved cam surface. In order to have a line contact rather than a
point contact between the rotating cam and the wheel contact surface of the rollers, it is
known to orient the rotating cam surface an angle that matches the tapered rollers.
It is known that if the tapered rollers of the cam follower, in combination with the
rollers axes and driver, move radially compared to cam surface (i.e. towards and away
from the central, longitudinal axis), the clearance between the rollers and the cam
surface of the rotating cam will change. Radial movement of the rollers away from the
central axis, to the outside of the cam surface causes rattle and power losses and
deterioration of the durability and performance of the rollers and cam. Movement
towards the central axis will cause too much preloading and deterioration of the
durability and performance and might result in a jam of the cam surface and rollers.
It is known that during operation the tapered wheels are mainly axially loaded against
the rotating cam surface. Because of the angle of the surface of the rotating cam, radial
forces relative to the rotating cam are generated. This causes the carrier on which the
rollers are mounted to be squeezed in a radial direction whereby the longitudinal guide
of the carrier will face an extra load that causes deterioration of the durability and
performance. This force will also create unnecessary play.
In case the wheels are being mounted on the inside off the rotating cam, the assembly
of the tapered wheel combined with the driver will be relatively difficult.
The angled axes or shafts on which the cam follower rollers are mounted on the carrier,
avoid in the event of radial movement of a roller compared to the cam surface, that
clearance between the wheels and the cam surface changes and hence undesired play or
jamming is avoided.
By applying angled shafts on which the rollers are mounted on the carrier, in the event
of axial loads on the rollers, no radial forces will be induced on the carrier and in the
event of assembly or disassemble of the drive system the roller assembly can easily be
mounted.
US patent 1,375,140 discloses an internal combustion engine in which reciprocation of
the pistons is converted into rotary motion of the shaft by cooperarion of angled rollers
carried by the pistons with a rib formed upon the periphery of a rotor. In order to
provide a true rolling motion of the rollers along the ribit is essential that the rollers are
adjusted accurately upon the cam rib. To this end, conical rollers are provided
supported on each side by a thrust-bearing that is adjustable via a screw. The thrust
bearings may be formed by ball bearings or an oil film.
It is an objective of the invention to provide a drive system of the above described type
in which the rollers move along a curved trajectory on the cam contact surface whereby
changes in play between the rollers and the cam during radial movements relative to the
rotating cam element of the rollers can be easily taken up.
It is a further objective of the invention to eliminate radial forces generated by the cam
surface while minimizing energy losses and play.
It is again an object of the invention to provide a drive system in which the
compression force of the wheel contact surface against the cam surface can be easily
adjusted.
Finally, the drive system according to the invention should allow easy construction and
disassembly and mounting of the cam and wheels for instance for maintenance or
repair.
Summary of the invention
To this end the drive system according to the invention is characterized in that a fluid
supply duct extends through the cylindrical body and connects a fluid pressure source
to a space between the transverse end part and ring-shaped wheel for axially displacing
the cylindrical body relative to the wheel.
By providing adjustability of the axial position of the rollers on their shaft driven by the
oil pressure, it is possible to easily and accurately adjust the play between the rollers
and the cam surface. This adjustment can be done during operation of the drive system
by adjusting the oil pressure in the fluid supply duct. If sufficient oil pressure is applied
the play will be always zero.
By applying a check valve situated in the cylindrical body and into the fluid duct
leading to the wheel to adjust the axial position, the oil supply pressure can be kept low
and can also create a desired amount of preload of the rollers on the cam contact
surface. During full axial loads on the roller, its axial positioning cylinder is prevented
from moving back by the check valve. The oil pressures will feed and only adjusts the
axial position cylinder when the roller is not fully loaded up until there is no play
between the roller and the cam surface.
In order to transport oil from the main support structure into the linear reciprocating
carrier on which the roller axles are mounted, an oil filled sealed slot is created on the
main support structure that is so positioned to always supply the oil intake hole of the
carrier with oil. In a likewise alternative version the slot can also be located in the
carrier and the exit hole in the main support structure.
Brief description of the drawings
A number of embodiments of a rotary drive member in accordance with the invention
will by way of non-limiting example be described in detail in relation with the enclosed
drawings. In the drawings:
Fig. 1 shows a known drive system with tapered rollers according to the prior art, the
cam follower axes of the rollers being perpendicular to the length direction,
Fig. 2 shows a partially cut-away perspective view of the drive system according to the
invention having the cam follower axis of the rollers at a non-perpendicular angle to the
length direction, the carrier assembly being situated externally from the cam surface,
Fig. 3 shows a partially cut-away perspective view of another embodiment of a drive
system according to the invention, the carrier assembly being situated within the cam
surface,
Fig 4 shows a cross-sectional view of tapered rollers,
Fig 5 shows a cross-sectional view of curved rollers,
Fig 6 shows a cross-sectional view of rollers, the cam follower surface being adjustable
in the transverse direction via a washer,
Fig 7 shows a cross-sectional of a roller, the cam follower surface being adjustable by
oil pressure,
Fig 8 shows a cross-sectional top-view of rollers assembled in their carrier, and
Fig 9 shows another direction cut-away of the main linear support structure along the
line A-A in fig 3 having 4 sets of roller assemblies.
Detailed description of the invention
Fig.l shows a known embodiment of the rotary drive system according to US 1339276,
comprising one or more cylinders 1 in which there is an intake valve 2 and a outlet
valve 3 . Inside the cylinder 1 is a piston 4 that can oscillate and to which a carrier or
driver 5 is connected. On the driver 5, two cam follower axes or roller axles 13 are
mounted. Each roller axle 13 carries a roller 7 that can rotate around the roller axle 13.
These rollers 7 are tapered and are mounted with the side of their smallest diameter r l
oriented to the center of the rotating cam axis 8 . Between the two rollers 7 a cam 9 is
placed with a cam track 10 is facing outwardly. This cam 9 is connected by bearings 11
and can rotate around the rotating cam axis 8 . On this cam 9 the cam track surface 1 is
at an angle g to the transverse direction, which angle matches the roller taper angle b in
other to have a contact line 15 between the cam track surface 12 and the roller 7 . The
cam shaft 16 can be rotationally connected to a device that is to be driven in rotation
around the axis 8 . This device can for instance comprise a generator or a gearbox. This
cam 9 is also used as flywheel. When the cam 9 rotates around the longitudinal cam
axis 8, the piston 4 will make an oscillating movement.
A fuel-air mixture is delivered to the central combustion chamber 17 via the open
Intake valve 2 when the piston 4 retracts from the cylinder 1. Following the
compression stroke, the intake valve 2 is closed and the fuel-air mixture is compressed.
Near the end of the compression stroke, the fuel-air mixture is burned causing the gas
to expand. During the expansion stoke the burned gasses propel the piston 4 . During
the exhaust stroke the combustion gases are expelled through the opened outlet valve
3 .
Fig. 2 shows the drive member according to the invention applied on a cam engine
whereby the cam track 10 is accessed on the outside of the cam 9 . The roller axels 13
are mounted at an angle a and support the tapered rollers 7 . The rollers have a roller
taper angle b. Between the two rollers 7, the cam track 10 is situated. The cam track
surface 12 is perpendicular to the longitudinal axis 8 .
Fig. 3 shows a drive member according to the invention applied on a cam engine
whereby the cam track 10 is driven from the inside. A cylinder 1 that has an inlet port
18 and an outlet port 19 is located within the closed contour of the cam 9 . Two pistons
4 can move coaxially in opposing directions within the cylinder 1. The drive rod 20 of
each piston 4 is connected to a driver 5 that is displaced in oscillation in the direction of
the longitudinal axis 8 by the drivers 5 . Each driver 5 can move in a linear fashion
between its linear displacement support structures. On the driver 5, four roller shaftsl3
are mounted in pairs at an angle a to support the tapered cam follower rollers 7 . The
tapered cam follower rollers 7 have a taper angle b. Between the two rollers 7, the cam
track 10 is placed. The rollers 7 follow the cam track 10 causing the driver 5, the drive
rod 20, and the piston 4 to move in an oscillating manner. When both pistons 4 are
traveling to their most opposite positions, the gas behind both cylinders in the back
chamber 2 1 will be compressed. Just before both pistons 4 reach their most opposite
position, the outlet port 19 will open allowing the exhaust gas to exit. Following the
intake port 18 will open, letting the compressed fresh air behind the piston into to the
cylinder 1. This compressed fresh air presses the exhaust gas out of the cylinder 1. Fuel
is being injected by the injector 22 to the intake gas. When the pistons 4 moves towards
each other, the inlet port 18 and the outlet port 19 will close and the gas will be
compressed. During the compression stroke inside the back chamber 21, a reduced
pressure will be created. This will open the reed valve 23 letting fresh outside air in.
Near the end of the compression stroke, the fuel-air mixture is ignited and burned
causing the gas inside the cylinder 1 to expand. During the expansion stroke the burned
gasses propel the pistons 4 . This cycle is repeated constantly at a frequency of for
instance between 100 and 10.000 RPM.
Fig. 4 shows a detailed partially cut-away view of driver 5 with two cylindrical bodies
15 of roller shafts 13 mounted in pairs at an angle a to support the tapered cam rollers
7 on a cam engine whereby the cam track 10 is accessed from the inside. The tapered
cam rollers 7 have a taper angle b. The tapered cam rollers 7 have a slide bearing 24.
The slide bearing is supplied with oil through the oil feed duct 25 for lubrication.
Between the two rollers 7 the cam track 10 is encased.
Fig. 5 shows a detailed view wherein the rollers 7 have a convex wheel contact surface
12.
Fig. 6 shows a detailed view wherein the play between the rollers 7 and the cam track
10 can be adjusted by placing a washer 26 between the cam roller 7 and the thrust end
of the roller shaft 13.
Fig. 7 shows a detailed view wherein the washer 26 in combination with the transverse
end 17 of the cylindrical body 15 of the roller shaft 13 creates an oil chamber 27
forming a hydraulic actuator. A sleeve 25 is placed around the cylindrical body 15 and
closes off the oil chamber 27. If oil is pressed through the oil ducts 25, 28 into the oil
chamber 27, the washer 26 will lift from the thrust end and change the axial end
position of the roller 7 . When the roller 7 is moved axially, the play between the cam
track 10 and the cam roller 7 will be adjusted to a minimum. Also a detailed view is
shown wherein a check valve 29 is mounted into the oil duct 28 in order to discourage
backflow of oil in case the oil pressure in the cylinder oil chamber 27 raises above the
011 supply pressure because of the roller load.
Fig. 8 shows a detailed view wherein the driver 5 can move linearly between its linear
displacement support structures 30. The linear displacement support 30 is fixed to the
cylinder 1 ground support structure. Oil is supplied into the oil holes 3 1 to the linear
displacement support structure 30 where it fills the oil slot 32. A part of the oil supply
is used to lubricate the linear displacement support 30. The driver 5 is provided with oil
channels 33 leading to the oil slot 32 into which the oil is pressed. The oil channels 33
are connected with the oil ducts in the roller shafts 25. A part of this oil supply
lubricates the bearing 24. A part of the oil supply feeds the hydraulic cylinder oil
chamber 27 to adjust the play.
Fig. 9 finally shows the driver 5 and its linear displacement support 30 that is combined
with the cylinder 1 and their oil intake holes 31 to supply the oil into the drive system.
Claims
1. Rotary drive member comprising a longitudinal axis (8) defining a length
direction, a curved cam contact surface (12) forming a closed contour around the
longitudinal axis and extending in the length direction, a reciprocating member (4)
having a carrier (5) movable in the length direction, at least one cam follower wheel (7)
being rotatably mounted on the carrier via a cam follower axis (6) that extends in a
direction transverse to the length direction and that is oriented at an angle a with
respect to the transverse direction , the wheel having a wheel contact surface engaging
with the cam contact surface (12) for rolling along the cam contact surface and driving
the cam contact surface in rotation around the longitudinal axis (8), wherein the cam
contact surface is oriented substantially in the transverse direction, wherein the cam
follower axis (6) comprises a cylindrical body and a transverse end part (17), the wheel
contact surface being part of a ring-shaped wheel mounted around the cylindrical body
(15) and displaceable in an axial direction of said cylindrical body, characterised in
that a fluid supply duct (25,28) extends through the cylindrical body (15) and connects
a fluid pressure source to a space between the transverse end part (17) and the ringshaped
wheel (7) for axially displacing the cylindrical body (15) relative to the wheel
(7).
2 . Rotary drive member according to claim 1, the fluid supply duct (28)
comprising a check valve (29) situated in the cylindrical body.
3 . Rotary drive member according to claim 1 or 2, wherein the carrier (5)
comprises two opposed longitudinal sides, each side supported by a slide bearing (30)
extending in the length direction, an oil supply (31) being connected to the slide
bearing and ending in a gap (32) between the slide bearing and the longitudinal side, an
oil connection path (33) being provided in the carrier (5) between the longitudinal side
and the fluid supply duct (28) in the cylindrical body (15).
4 . Rotary drive member according to claim 1,2 or 3, a sleeve being situated around
the cylindrical body (15), a thrust chamber (27) being formed in the cylindrical body,
bounded on one side by by the sleeve, the fluid supply duct (28) connecting the fluid
pressure source to the thrust chamber (27).
5 . Rotary drive member comprising a spacer ring (26) that is situated at least partly
around the cylindrical body between a top surface of the ring-shaped wheel and the
transverse end part.