The engine with no crank shaft is temporarily known by a name called ‘running gearing’ engine. The technology of running gear can be applied to all formerly manufactured engines equipped with crank mechanism. This seminars deals with the arrangement and working of the engine and also its comparison with conventional type of engine. The comparison result shows that running gearing engine as much improved engine parameters than conventional crank engine.
• THE ARRANGEMENT OF THE RUNNING GEARING
• THE PRINCIPLE OF OPERATION
• COMPARISON WITH CRANK-ENGINE
• GAS DYNAMICS
• DIMENSION & MASS
• PRODUCTION COST
Running gearing is a new type of mechanism designed to transform progressive motion into rotary motion. The term “running gearing” is only a temporary name given to the mechanism and the mechanism has not yet been given its definite name.
The running gearing is developed by Mr. V.A.Vorgushin, an engineer, a M.T.S. in co-authorship with Mr. P.A. Shishkin, an engineer.
The technology of a running gearing makes it possible to withdraw from an engine its main component - a crank mechanism and to improve the engine’s parameters.
The technology of the running gear can be applied to all formerly manufactured engines, equipped with crank mechanisms. Both modernization of the available stock of engines and realization of new projects may become a very profitable business for a number of years.
THE ARRANGEMENT OF THE RUNNING GEARING
The arrangement of the engine is shown in figure-1. The running gearing is made up of toothed gear 1 seated on the engine shaft and being in constant mesh with gear frame 2. Gear frame 2 is shaped consisting of two racks of equal length and two toothed semicircles of equal radii. By this alternative the gear frame is connected to piston 3 of cylinder block 5 via a motion unit of Z axis.
For fixing of the extreme left and the extreme right positions of gear frame 2 (fixing of L dimension as per fig.) the device is equipped with a mechanism of dynamic fixing (not shown in fig.1).
A mechanism of dynamic fixing is the cam-type. It comprises a cam itself and two linear rests. The working face of the cam represents an arc of the sector of a circle. The cam and toothed gear 1 are seated on the axis of rotation of the shaft and they are stationary relative to each other. Linear rests are fixed along the gear racks; working faces of linear rests are the surfaces facing the axis of symmetry of the gear frame.
THE PRINCIPLE OF OPERATION
In the process of rotation of toothed gear 1 (arrowed line) being in mesh with the left gear rack of frame 2 as per Fig. 1 of the sketch, piston 3 with gear frame 2 is moving upwards. At the moment when toothed gear 1 is going from the section of the left gear rack to the section of the toothed semicircle of frame 2 motion velocity of piston 3 is slowing down abruptly, falling off to zero in the point, when the vertical axis of symmetry of gear frame 2 is in alignment with the diametric line of toothed gear 1. This momentum corresponds to the upper dead centre (UDC) for piston3.
Concurrently, with the transfer of toothed gear 1 from the gear rack section to the toothed semicircle section of frame 2, the fixing mechanism takes frame 2 off the rest audits displacement is initiated to the left under the effect of cross-axis component force, exerted in the engagement of toothed gear 1 with the toothed semicircle of frame 2. Completely the cross motion is finished at the moment of toothed gear 1 transfer from the section of the toothed semicircle to the section of the right gear rack of frame 2. At that very instant the teeth of gear 1 are wholly dropping out of mesh with the left gear rack and are engaging with the right one. The fixing mechanism locates the position of the frame relative to the toothed gear according to L dimension. From the above indicated UDC point the movement of piston 3 with gear frame 2 is initiated to the opposite direction, i.e. downwards accompanied by a drastic linear velocity increase from zero.
The process of further rolling of the gear over the gear rack with the change-over to the upper toothed semicircle and then from it to the left gear rack, and all the processes coming about in this case (the process of fixing and releasing of the gear frame) are similar to those described. As a result as in a crank engine, the complete double piston stroke is carried out in one complete revolution of a toothed gear.
COMPARISON WITH CRANK-ENGINE
The comparison of the running gearing engine with conventional crank engine can be done under four categories. They are
2. Gas dynamics.
3. Dimension and mass.
4. Production cost.
In spite of the fact that a piston travels one and the same way along the straight line both in a running gearing engine and in a crank mechanism engine, kinematics of these mechanisms differs fundamentally.
The motion path of a contact point and the principle of operation of a running gearing have an effect first of all on the variation of a velocity gradient of the piston and its acceleration along the angular displacement of an engine shaft.
Basically variations are clearly seen in Fig.2 and Fig.3, where velocity variations and acceleration along the angular displacement of the shaft are compared both for running gearing engines and crank mechanism engines.
At the initial part of the stroke the piston acceleration in a running gearing engine considerably exceeds the piston acceleration in a crank mechanism engine (Fig.3) and its velocity is actively increasing (Fig.2), peaking at ≈ 1/15 stroke. At that point the acceleration reduces to zero and the piston velocity remains constant over the greater part of the travel path. In the middle part of the stroke the piston velocity is considerably lower than that in a crank engine, having a favorable effect on the wear rate and on the mechanical efficiency of the engine. The mechanical efficiency of the running gearing is higher also due to the fact that sliding friction is changed by rolling friction.
Close to the end part of the stroke, at approximately 1/15 of its portion too, negative acceleration starts actively increasing and the piston velocity rapidly decay to 0.
After the dead centre the piston moves in an opposite direction. The process reiterates.
The curve of the velocity variation and acceleration in running gearing engines in its view appears to be closer to the similar curves of free piston engines. It means that the running gearing kinematics, taking up the force field of an indicated diagram, is more consistent with the free movement of translationally traveling masses.
The fact that maximum values of start acceleration and deceleration of the mechanism are twice as large as similar values of typical engines, this may be qualified as disadvantages of the scheme. However, the values of actual loads fall within permissible limits, if the material of carrying parts is well selected, design provisions have been made to decrease the mass of moving elements and geometrical parameters of the unit have been adequately selected.
The major prerequisite for the use of a running gearing in internal-combustion engines is its feature to transmit the moment from the gas pressure force at the maximum arm representing the radius of the reference circle of the shaft gear.
Due to this characteristic the shape of the curve of the shaft torque against its angular displacement is completely changed (Fig.4). Here certain interesting features can be observed:
1. As opposed to crank mechanism engines, negative and positive portion of the torque from one cylinder is changed more evenly over the stroke; actually it does not change the sign and to a large extent repeats the view of an indicated diagram of a working cylinder.
2. Through the redistribution of acceleration and deceleration inertial forces at the initial and end parts of the stroke peak loads on the shaft are cut off at the final phase of compression stroke and at the initial phase of expansion stroke.
3. With the increase in number of revolutions the growth of the degree of compression in an engine does not overload the motion mechanism as the work of compression at the end stroke is carried out by the inertial forces.
4. At the initial expansion stroke forces of inertia expend the part of the cycle work but then at the end stroke at deceleration they give up the effective work to the shaft. A flywheel receives a substantial impulse before the run of the next stroke. The evenness of revolutions in running gearing engines is noticeably higher.
The variation of the total torque of a four-cylinder engine (Fig.5) demonstrates that positive torque values occur almost within the whole range of angular displacement over the complete shaft rotation. It is indicative of the high evenness and stability of engine operation. Idling revolutions are lower than in crank mechanism engines.
The use of a running gearing in internal -combustion engines considerably reduces vibrations. It is explained both by the reduction in the amount of unevenly rotating masses of the first and second orders and by the drastic decrease in the vibration amplitude of a connecting rod. The connecting rod amplitude in a running gearing is determined by the design scheme in itself. It equals to the tooth depth in a gearing, which is by 5-8 times less than in crank mechanism engines, where the connecting rod amplitude is equal to 2 crank radii.
The use of a running gearing in diesel engines appears to be particularly topical. It is favored by the lower number of revolutions of diesels per unit time and by the feature of the running gearing kinematic scheme to unload the shaft by inertia forces at the parts of the stroke which are under high degrees of compression.
An intensive rise in the piston velocity up to the maximum value at the initial stroke creates good conditions for using the air flow inertia and for developing of a dynamic charging effect of the cylinder due to the higher discharging in front of the piston bottom moving away fastly. Since the flow rate in an inlet pipeline is proportional to the piston velocity - the degree of charging will increase with the rise of revolutions, ensuring a considerable increase in the power. On the other hand this property must improve the engine throttle characteristics by reducing the required range of turning of a throttle gate. The extent of engine throttling will decrease. The factor of dynamic charging and the factor of reduction in the degree of throttling will increase the efficiency of the unit in all modes. Gain in power in this case does not require the availability of options (a turbine and a compressor).
When estimating the velocity variations before and after the upper dead centre (Fig.2), it can be noted, that the piston velocity in an running gearing engine changes much more intensively, than in a typical engine with a crank mechanism. This condition should have a beneficial effect on antiknocking resistance of the operation process. Actually a rise in velocities near UDC means an adequate reduction of duration of the piston stay in the zone of the compression ratio limiting values and this in its turn reduces the probability of knocking and smoothes off the consequences of its manifestation. It is observed that with the decrease in a scale factor, i.е. with the reduction of time intervals of the cycle, a tendency to knocking is fastly diminishing and starting from a certain value of similarity parameters it absolutely vanishes, even for very high degrees of compression. All the foregoing arguments considered we anticipate high anti-knock properties of running gearing engines, which will allow them to burn safely the lowest octane gasoline brands.
Based on the kinematic properties of a running gearing which are manifested in redistribution of velocities over the piston stroke, a conclusion can be made that losses for the cooling system are reduced. It has been known that in other equal conditions, the amount of heat passing through the unit of the wall area is proportional to the time of the gases contact. Graphs of piston velocities (fig.2) clearly show that in the region of the highest temperatures of the cycle (the 1-st quarter of the expansion stroke) piston velocities of running gearing engines considerably exceed those of crank mechanism engines. Consequently, the contact time of gases for each elementary segment of the travel is considerably lower. It is evident from the calculations that losses for the cooling system are reduced by 1,5-1,6 times.
It is important to make a remark about a gas distribution system. If for four-stroke running gearing engines the gas distribution systems differ not at all from the standard type, but, regretfully, for two-stroke engines the use of a running gearing scheme brings about a need for increasing by 40-50% the stroke portion, being assigned for outlet and inlet ports. In this case it is caused by the negative effect of the high piston velocity near LDC on the time-section of gas distribution ports.
A need for a big portion of waste stroke for the gas distribution ports impedes the selection of optimum parameters of a running gearing as S/D cylinder ratio is increased.
The mentioned disadvantages make a four-stroke cycle be more advantageous for a running gearing engine.
A comparative calculation of parameters for crank mechanism engines and running gearing engines, are shown in table.1
A comparison of the estimated data shows that the running gearing engine exhibits the high improvement of all the main parameters of the piston engine.
Hence, specific effective fuel consumption is found to be less by 59%, net efficiency of the cycle increases by 63%, power and torque, after the obtained data are matched to a single engine displacement of 1,48 l , are increased by 59,6% and 85% accordingly.
DIMENSION & MASS
Generally, the reduction of running gearing engine dimensions is determined by 2 factors:
- the connecting rod length is decreased by 5-8 times
- the shaft rotation axis can approach a cylinder sleeve by
approximately 2/3 piston stroke
Both factors involve the considerable reduction in the dimensions of a carrying casing, and hence, in the engine dimensions. Actually the longitudinal dimension of the casing is restricted by the width of the cylinder sleeve cooling "jacket". The number of alternatives for the arrangement of auxiliary components is increased. Additional space is vacated in the car's under bonnet.
The mass of the running gearing engine decreases both due to the realization of the dimension advantages and on the basis of the lower mass of the running gearing mechanism itself.
For newly designed engines the lower mass of a flywheel can be adopted, as the smoothness of operation of running gearing engines is considerably higher.
Except the above mentioned provisions, the specific mass is furthermore determined by the specific power which increases unevenly in a running gearing engine.
For newly designed car/ automobile running gearing engines it is practicable to achieve the specific mass, equaling to 0.8-1.2 kg per a kilowatt of power.
1. First of all the use of a running gearing results in dozens per cent of qualitative improvement of the basic data of a piston engine. The cost of a rotary-to-reciprocating movement conversion device comprises 8-15% of the total value of the engine. Consequently, under the other similar conditions, the use of a running gearing reduces the production cost of a power unit as applied to the cost of the engine as a whole. This is the first and the basic factor.
2. The running gearing mechanism itself does not involve any production processes which have not been mastered in the manufacture. In essence the concept represents a new constructive combination. The totality of experience in shaft, connecting rod and gearing production can be applicable to the elements of the unit. This case defines the second factor of the decrease in the production cost of a power unit.
3. The advantages in terms of mass and dimensions resulting from the use of a running gearing reduce the metal-intensity of the structure, close down the crankshaft production lines and simplify the manufacturing process of the body parts and it can not but influence the cost reduction. This is the third factor.
4. The arrangement particulars of a running gearing are such that serially-produced engines can be easily modified to fit a standard running gearing without big investments into the change of specialization. All adjusting and preparatory operations can be carried out during the engineering support of a production process. This is the fourth factor.
5. The arrangement particulars of a running gearing allow going into full production of group-assemblies for modification of the stock of earlier produced engines, providing shortly to set up a large-scale production of the unit, considerably exceeding the requirements of the basic production of new engines. The fifth factor not only decreases the production cost of the unit and a power unit, but ensures additional profit for a plant.
6. A unique standard design of a running gearing can be used by the basic production for the models which are close in cylinder capacity and in updating of the earlier produced stock of engines. In this case expansion of production volume pays off the organization of production of the unit elements at highly specialized production belt lines, ensuring the lowest production cost. This is the sixth factor.
The obvious advantages of running gearing engines – a steep rise in torque of the shaft and a proportional growth of economical efficiency - will promote their fast and wide spread. The advancement of the process will be influenced by the fact that the current stock of combustion engines can be quite easily updated for a running gearing mechanism.
The extensive use of engines of this kind in transport and in industry can solve the problem of power (energy) resources shortage for a long period in many countries. Also, it is reasonably to speak about the essential prerequisites to the reduction of world oil prices, as the fast growth in the efficiency of generation of a power unit reduces the dependence on purchasing of power resources in the same proportion.
Taking into account the fact that fuel filling tanks of transportation facilities are invariable, it can be noted that the use of running gearing engines adequately increases the transportation range without refueling. This is especially essential for air and sea transport.
2. ‘Fundamental of Gas Dynamics’ by K.L.Yadao.
3. ‘Internal Combustion Engines-Theory and Practice’ by S.P.Sen.