200858
2/MAR/2007
FORM 2
THE PATENTS ACT 1970 (39 of 1970)
COMPLETE SPECIFICATION (SECTION 10)
TITLE
A compact drive mechanism of a reciprocating machine
APPLICANTS
IIT Bombay, Indian Institute of Technology, Powai, Mumbai - 400076, Maharashtra, India, an Indian institute
INVENTOR
Under Section 28(2)
Prof Shridhar Laxman Bapat, IIT Bombay, Department of Mechanical Engineering, Powai, Mumbai 400076, Maharashtra, India, an Indian national
The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed :


ORIGINAL
480/MUMNP/2000
25/5/2000

GRANTED
10-3-2004

This invention relates to a compact drive mechanism of a reciprocating machine.
Reciprocating machines are generally power corisurning type or power generating type. Power consuming reciprocating machines include gas compressors, liquid pumps, Stirling cycle based coolers, pulse tube coolers or machine tools such as lathes. Power generating reciprocating machines include generators, expanders, prime movers such as internal combustion engines or Stirling cycle based engines. Drive to the above machines is given through a drive mechanism comprising crank shaft and connecting rod arrangement(s) connected to piston(s) reciprocating in cylinders). Each connecting rod is connected to the respective piston and crank shaft using gudgeon pin and crank pin respectively. Because of the crank shaft and connecting rod, the size of the drive mechanism increases lengthwise thereby rendering it heavy and bulky. The efficiency of the drive mechanism depends on the mass flow rate and pressure ratio of the working fluid of the drive mechanism. The mass flow rate and pressure ratio of the working fluid in turn depends on the piston stroke for a given diameter of the cylinder. The larger the piston stroke, the higher the mass flow rate and

pressure ratio of the working fluid and the higher the efficiency of the drive mechanism. The piston stroke is determined by the crank length. The larger the crank length, the longer the piston stroke. The connecting rod length is dictated by the ratio of piston stroke and cylinder diameter. Ideally the ratio is 2. If the ratio exceeds 2, the connecting rod length increases thereby further increasing the size of the drive mechanism lengthwise and rendering it further bulky and heavy. Also, if the connecting rod length is increased beyond certain limit it may buckle and may not function properly. During reciprocating motion of the piston in the cylinder, the connecting rod exerts a force component perpendicular to the piston called side force or side thrust because of which the piston rubs more against the corresponding side of the cylinder causing uneven and non-uniform wear and tear to both the piston and cylinder. This may lead to leakage of the working fluid and malfunctioning of the machine. In order to rectify the problem reconditioning/replacement of the piston and/or cylinder liner may be required. Balancing of side force is done by attaching balancing weights to the crank to reduce the vibrations. However, in a single cylinder drive mechanism it is not possible to balance the side force completely and hence some vibrations are unavoidable. Wear and tear to the gudgeon pin

and crank pin are unavoidable calling for the periodic replacement thereof. Breakage of the above pins may also occur at times.
An object of the invention is to provide a compact drive mechanism of a reciprocating mechine.
Another object of the invention is to provide a compact drive mechanism of a reciprocating machine which is efficient in performance.
Another object of the invention is to provide a compact drive mechanism of a reciprocating mechanism which allows the piston to reciprocate in the cylinder linearly thereby eliminating side thrist.
The term piston(s), wherever used in this specification, includes plunger(s) and displacer(s).
According to the invention there is provided a compact drive mechanism of a reciprocating machine comprising a rotary disc and a stationary disc disposed spacedly parallel to each other, a driven disc disposed between the rotary disc and stationary disc perpendicularly

rotatably engaged thereto and rotatable around the periphery of the rotary disc and stationary disc and at least one reciprocating L-shaped member comprising a piston limb and a load bearing limb, the piston limb eccentrically passing through the stationary disc in sliding contact therewith and adapted to act as a piston reciprocating in a cylinder rigidly fitted to the stationary disc, the piston limb being rotatable in the stationary disc and cylinder, the load bearing limb eccentrically passing through the driven disc in sliding contact therewith and disposed in a guide sleeve rigidly fitted to the driven disc, the piston limb and load bearing limb defining the same radial distances from the centres of the respective discs equal to half the stroke of the piston in the cylinder.
The following is a detailed description of the invention with reference to the accompanying schematic drawings, in which :
Figs 1 and 2 are crosssections of a compact single cylinder drive mechanism of a reciprocating machine according to an embodiment of the invention at different positions of the piston; and

Figs 3 and 4 are crosssections of a compact four cylinder drive mechanism of a reciprocating machine according to another embodiment of the invention at different positions of the pistons.
Referring to Figs 1 and 2 of the accompanying drawings, the compact drive mechanism 1A comprises a rotary disc 2 (whose hub is marked 3) and a stationary disc 4 disposed spacedly parallel to each other. 5 is a driven disc provided with a tapered extension 6 at the periphery thereof and disposed between the rotary disc and stationary disc perpendicularly. The tapered extension at the periphery of the driven disc is rotatably engaged in matching tapered grooves 7 and 8 provided at the confronting faces of the rotary disc and stationary disc, respectively. The driven disc is rotatable in the grooves 7 and 8 around the periphery of the rotary disc and stationary disc. 9 is a reciprocating L-shaped member comprising a piston limb 10 and a load bearing limb 11. The piston limb eccentrically passes through the stationary disc in sliding contact therewith and is adapted to act as a piston in a cylinder 12 rigidly fitted to the stationary disc. The piston limb is rotatable in the stationary disc and cylinder. The suction valve and discharge valve of the cylinder are marked 13 and 14, respectively. The load bearing limb 11

eccentrically passes through the driven disc in sliding contact therewith and is disposed in a guide sleeve 15 rigidly fitted to the driven disc. The piston limb and load bearing limb define the same radial distances R from the centres of the respective rotary discs equal to half the stroke of the piston in the cylinder.
In the case of a power consuming machine such as gas compressor or liquid pump the rotary disc is given rotary motion by connecting the hub thereof, for instance, to a prime mover such as electric motor shaft. In the case of a power generating machine such as expander or internal combustion engine, energy output of expander by way of high pressure fluid or heat output of internal combustion engine due to combustion of fuel air mixture is used to give rotary motion to the hub of the rotary disc. The rotary disc rotates about its own axis and transmits drive to the driven disc which in turn describes guided rotary motion around the peripheries of the rotary disc and stationary disc in the respective grooves 7 and 8 thereof. Rotary motion of the driven disc causes reciprocation of the piston limb and load bearing limb in the cylinder and guide respectively and the rotary motion gets converted into reciprocating linear motion. Fig 1

shows the position of the piston limb and load bearing limb in the respective cylinder and guide at the end of a suction stroke. This may be considered to be at 0° of rotation. The suction valve is open and the piston limb is at the bottom of the cylinder at its lowest position and is held in the stationary disc. The load bearing limb is outside the guide at its outer most position and is disposed in the driven disc. The pressure of the working fluid during suction stroke is minimum. Therefore, the force on the piston limb during the suction stroke is minimum and is borne by the load bearing limb against the driven disc. As the driven disc rotates in the clockwise direction, the piston limb moves up in the cylinder and the discharge stroke begins. The working fluid pressure builds up in the cylinder and causes the suction valve to close. The working fluid pressure continues to build up in the cylinder until it reaches the set pressure required to open the discharge valve. On reaching the set pressure the discharge valve opens and the working fluid is discharged from the cylinder at the set pressure. Thus, the mechanism is utilised for driving a gas compressor or liquid pump or such other power consuming reciprocating machine. Alternatively, the mechanism is utihsed for driving a power generating reciprocating machine such as generator, expander or internal combustion engine. As the piston limb moves up in the

cylinder, the working fluid gets compressed and the force on the piston limb increases. Simultaneously, the load bearing limb progressively moves into the guide sleeve and bears the increased load on the piston limb against the guide sleeve. By the time the discharge stroke is completed the driven disc would have rotated 180° around the periphery of the rotary disc and stationary disc and the piston limb and the load bearing limb would have moved maximum into the cylinder and guide sleeve respectively and taken the positions shown in Fig 2. During the discharge stroke the stroke of the piston limb in the cylinder is 2R, where R is the radial distance from the centre of the stationary disc to the centre of the piston limb or from the centre of the driven disc to the centre of the load bearing limb. During further rotation of the driven disc in the clockwise direction the piston limb moves down in the cylinder to its lowest position and the load bearing limb moves out of the guide to its outermost position. Due to downward movement of the piston limb in the cylinder, pressure drops in the cylinder and discharge valve closes and suction valve opens. The working fluid is sucked into the cylinder through the suction valve. During suction stroke the force on the piston limb decreases and is borne by the load bearing limb sliding out against the guide sleeve. By the time the driven disc has rotated by 360°

around the peripheries of the rotary disc and stationary disc, the piston limb and the load bearing limb would have moved out of the cylinder and guide sleeve to the maximum, respectively and taken the positions as shown in Fig 1. During the suction stroke also, the stroke of the piston in the cylinder is 2R. The radial distance R decides the stroke of the piston limb and may be varied depending upon the pressure ratio required. The mass flow rate of the working fluid depends on the diameter of the piston limb which may be varied to achieve required mass flow rate. The suction stroke and discharge stroke are thus repeated. As the tapered extension 6 of the driven disc 5 is rotating in the grooves 7 and 8 the contact between the tapered extension and surfaces of the grooves is a rolling contact. Therefore, friction between the contact surfaces is minimum thereby minimising frictional power loss and resulting in a high drive efficiency of the mechanism.
Referring to Figs 3 and 4 of the accompanying drawings, the drive mechanism 1B thereof comprises four reciprocating L-shaped members, namely member 16 (whose piston limb and load bearing limb are marked 17 and 18 respectively), member 19 (whose piston limb and load bearing limb are marked 20 and 21, respectively), member 22 (whose piston

limb and load bearing limb are marked 23 and 24, respectively) and member 25 (whose piston limb and load bearing limb are marked 26 and 27 respectively). Member 25 and its limbs are hidden by member 19 and its limbs. The L-shaped members are disposed in the stationary disc and driven disc at equal angular distances from one another and also at the same radial distances R from the centres of the respective rotary and stationary discs. The cylinders are marked 28, 29, 30 and 31 respectively. Cylinder 31 is hidden by cylinder 29. The guide sleeves are marked 32, 33, 34 and 35 respectively. Guide sleeve 35 is hidden by guide sleeve 33. The suction valve and discharge valve of the cylinders 28, 29, 30 and 31 are marked 36 and 37, 38 and 39, 40 and 41 and 42 and 43, respectively. At the instant as shown in Fig 3 at 0° rotation the piston limb 17 in cylinder 28 has moved down to its lowest position and completed the suction stroke, the piston limb 20 in cylinder 29 has moved up and completed half the discharge stroke, the piston limb 23 in cylinder 30 has moved up to its topmost position and completed the discharge stroke and piston limb 26 in cylinder 31 has moved down and completed half the suction stroke. As the driven disc rotates in the clockwise direction, piston limb 17 in cylinder 28 moves up to its top most position and completes the discharge stroke, piston limb 20 in cylinder 29

moves up further and completes the discharge stroke and moves down and completes half the suction stroke, the piston limb 23 in cylinder 30 moves down to its lowest position and completes the suction stroke and piston limb 26 in cylinder 31 moves further down and completes the suction stroke and moves up and completes half the discharge stroke as shown in Fig 4 by which time the driven disc has rotated by 180°. During further rotation of the driven disc in the clockwise direction, piston 17 in cylinder 28 moves down to its lowest position and completes the suction stroke, piston limb 20 in cylinder 29 moves further down and completes the suction stroke and moves up and completes half the discharge stroke, piston limb 23 in cylinder 30 moves up to its extreme top position and completes the discharge stroke and piston limb 26 in cylinder 31 moves further up and completes the discharge stroke and moves down and completes half the suction stroke as shown in Fig 3. The sequence of strokes is thus repeated. The maximum power and hence torque is required for each cylinder only when the desired compression ratio is still to be achieved during compression stroke. Also during the suction stroke power requirement is negligible. Therefore, with multicylinder mechanism the power requirement almost averages out and the torque to be provided by the mechanism will have less fluctuations and will

be more or less the same. Thus, a multi cylinder system ensures smooth operation of the machine.
The angular distances of the L-shaped members from one another are selected depending upon the phase differences required in the reciprocating movements of the piston limbs ie the differences in the positions of the piston limbs during rotation of the driven disc.
According to the invention the crank shaft and connecting rod and balancing weights have been eliminated thereby eliminating drawbacks associated therewith. The piston stroke may be increased to realise increased mass flow rate and pressure ratio of the working fluid and thus increased efficiency of the drive mechanism by shifting the position of the L-shaped member radially outwardly in the driven disc and stationary disc. Increase in piston stroke does not increase the size of the drive mechanism lengthwise. On the contrary, it only results in increase in the diameters of the rotary and stationery discs which is uniform and symmetrical. Therefore, the drive mechanism is compact and symmetrical. There is also size reduction of the drive mechanism as the cylinder is directly mounted on the stationary disc.

The mass flow rate also may be increased by increasing the diameter of the piston without increasing the size of the drive mechanism length wise. The L-shaped member reciprocates linearly in the driven disc and stationary disc. Therefore, the piston reciprocates in the cylinder linearly eliminating side thrust on piston and vibrations thereof and uneven and non-uniform wear and tear to the piston and cylinder and resulting reconditioning/replacement thereof. The drive mechanism has improved drive efficiency due to the contact of the driven disc with the rotary disc and stationary disc is rolling contact and frictional power loss at the contact surfaces is minimal.
The above embodiments are by way of illustrative examples and should not be construed to be limitative of the scope of the invention. Several variations of the invention are possible without deviating from the scope thereof. For instance, the piston limb of the L-shaped member may be provided with a piston. Instead of tapered extension of the driven disc at the periphery thereof and tapered grooves in the rotary disc and stationary disc, the corresponding surfaces may be provided with gears to facilitate smooth rotation of the rotary disc and driven disc. The number of

We Claim :
1) A compact drive mechanism (1A) of a reciprocating machine
comprising a rotary disc (2) and a stationary disc (4) disposed spacedly
parallel to each other, a driven disc (5) disposed between the rotary disc and
stationary disc perpendicularly rotatably engaged thereto and rotatable
around the periphery of the rotary disc and stationary disc and at least one
reciprocating L-shaped member (9) comprising a piston limb (10) and a load
bearing limb (11), the piston limb eccentrically passing through the
stationary disc in sliding contact therewith and adapted to act as a piston
reciprocating in a cylinder (12) rigidly fitted to the stationary disc, the
piston limb being rotatable in the stationary disc and cylinder, the load
bearing limb eccentrically passing through the driven disc in sliding contact
therewith and disposed in a guide sleeve (15) rigidly fitted to the driven
disc, the piston limb and load bearing limb defining the same radial
distances from the centres of the respective discs equal to half the stroke of
the piston in the cylinder.
2) A compact drive mechanism as claimed in claim 1, comprising
two or more L-shaped members and corresponding number of cylinders, the

angular distances between the L-shaped members corresponding to the phase differences in the reciprocating movements thereof.
3) A compact drive mechanism as claimed in claim 1 or 2, wherein the driven disc is provided with a tapered extension at the periphery thereof adapted to be engaged in matching tapered grooves provided at the confronting faces of the rotary disc and stationary disc to provide rolling contact therebetween and minimise friction between the contact surfaces thereof.
4) A compact drive mechanism of a reciprocating machine substantially as herein described particularly with reference to the accompanying drawings.
Dated this 23rd day of May 2000.
(Arindam Paul)
of DePENNING & DePENNING Agent for the Applicants