US2274430A - Turning gear for internal combustion engines - Google Patents

Description

1 i v I Feb. 1942- c A. E TURNING GEAR FOR INTERNAL COMBUSTION ENGINES Filed May 10, 1939 Patented Feb. 24, 1942 TURNING GEAR FOR INTERNAL COMBUSTION ENGINES Henry Charles Alexandre Potez, Meaulte, France Application May 10, 1939; Serial No. 272,889

- In France May 1-8, 1938 A 5 Claims.

It is known that the solution of the problem of the starting of aviation engines,'and particularly of touring aeroplane engines, is 'a difficult matter, owing to the numerous and often contradictory conditions to comply with. These conditions are as follows:

An entire self-action as the only power available is'that which can be furnished by the tourist or his assistant, without excessive fatigue; a reduced size and weight; a low cost price; an easy actuation from the pilots cockpit without being obliged to leave the aeroplane; areliable working, even in cold weather, and even with an engine having already furnished a long service, in which the tightness of the valves and pistons may be imperfect for very slow speeds of the crank-shaft, even though, this tightness is quite sufficient for normal running; the greatest possible independence of the parts of the starter and of the engine during the operation of the latter.

,It is shownby experience that the conditions of entire self-action and of reduced fatigue lead to approach as closely as possible the conditions of manual turning of the propeller, at least for the engines of average power. For this purpose, it has been proposed to turn the crank-shaft by means of a hand-crank and through the medium of gear-wheels or by a lever which is connected to the crank-shaft of the engine also by gear- Wheels.

' Such devices have the drawback of obligating the operator to great efforts, which are in most cases impossible to exert from the pilots cockpit, for the reason that in order to obtain a suf ficient piston speed for the proper compression of the combustible mixture in the cylinders, it is impossible to use a great gear-reduction ratio.

The present invention has for its object to provide a turning gear for internal combustion engines, more particularly aircraft engines of small and medium power, which complies with the above-mentioned conditions and which obviates the aforesaid drawbacks, particularly in that the starting operation can be carried out from the pilots cockpit without leaving the aeroplane, with a force which is as small as may be desired, while ensuring the best conditions of turning, particularly as regards the compression and the l ignition.

.The turning gear according to the invention comprises a crank-plate, or like" device, which is connected on the one hand with means by which it can be rotated at slow speed, i. e. by using a reduced force, and on the other hand, by means of a suitable speed-reduction gear, to the crankshaft to be operated, the crank-pin of said plate being connected with an accumulator of energy" which stores up the energy during one-half of a revolution of the said plate and then restores it during the other half revolution.

According to a preferred embodiment of the invention, the said accumulator consists of one or more springs or like elastic members which are attached at one end to the crank-pin of the crank-plate, and at the other end .to a fixed vention.

Fig. 2 is a partial view of a modification of the turning gear shown in Fig. 1.

According to the embodiment shown in Fig.- l, the turninggear comprises a hand-crank I the shaft 2 of which is rotatable in the casing 3,

and carries the driving member 4 of a freewheel mechanism of any known type. The driven member 5 of said free-wheel mechanism is keyed to a shaft 6 together with a ratchetwheel 1 cooperating with a retaining pawl 8 adapted to prevent any backward rotation of the shaft 6 which would cause a backward motionof the crank I. On shaft 6 there is slidably mounted the driving member 9 of a safety friction clutch. Said driving member 9 may be urged by a spring I0 against the driven member ll of said friction clutch.

The said member H is rotatable on the shaft 6, and is connected. in rotation to a loose pinion l2. This pinion l2 meshes with a gear-wheel I 3flkeyed to a shaft [4 which is rotatable in the casing 3. plate. It carries an eccentric crank-pin I 5, to which is attached an elastic device l6 forming an accumulator of energy, which consists, in the embodiment illustrated, of spring means subject to elongation and attached to a pin ll mounted in the casing 3. l, i It will be noted that the spring means I 6 is stretched (which corresponds to an accumulation of energy) when'the'crank-pin moves from the position l5 to the position l5, both of which aresituated in the diametrical plane passing through the axes XX and YY of the shaft I4 and the attaching pin IT, but will on the contrary contract (which corresponds to a very rapid restoration of the accumulated energy) when the crank-pin moves from the position l5 to the position I5 On the shaft M of the crank-plate I3 is secured or formed the driving member l8 of a releasing device. The driven member 20 of said releasing device is normally connected in rota- ,tion to said driving member I8 by a ball l9;

which is located in two recesses formed in the The gear-wheel l3 forms a crankmembers It and and is clamped between these members by a spring 2| adapted to urge the driven part 29, which is slidably keyed to a shaft 22, towards the member I8. A pinion 23 keyed to the shaft 22 engages a gear-wheel 24 keyed to a shaft 26 extending out of the casing 3.

The unit A above described, which is preferably independent, is combined with a unit B which will be described below, the connection being made by suitable coupling devices 25 and w an intermediate shaft 26 which connects the shaft 25 of the unit A with shaft 21 of the unit B. Shaft 21, which is rotatable in the casing 28, is connected to a shaft 29 by acoupling device adapted for automatic or controlled release, which preferably provides for the complete uncoupling of the two shafts 21 and 29 when the shaft 29 tends to drive the shaft 21.

The said coupling device may, for instance, be realized as illustrated and as known per se.

In the embodiment illustrated, the shaft 21 has a threaded part 36 adapted for the longitudinal displacement thereon of a nut 3| which is impeded in its rotation by a, brake 32. The said nut carries a jaw-clutch disc 33 cooperating with a like disc 34 mounted on the shaft 29. Shaft 29 carries a pinion 35 meshing with a pinion 36 keyed to an extension of the crank-shaft 31 of the engine which is to be started.

This engine, having N cylinders, may be of the four-stroke or of the two-stroke type, operating with gasoline or with fuel oil. The gear wheels 23, 24, 35, 36 interposed between the crank-plate and the crankshaft of the engine having N cylinders are so chosen that the ratio between the angles described by the crank-plate I3 and the crank-shaft 31 during the starting will be equal to in the case of a four stroke engine, or to N in the case of a two-stroke engine, in order that the successive revolutions of the crank-plate shall correspond to the passage of the successive cylinders of the engine through the same point of the cycle, for instance to the explosion.

Moreover, the releasing device (I8, I9, 29) which provides for th momentary release of the crank-plate I3 (or like device) from the crankshaft 31 in the case of a reverse movement or return of this latter, as well as the automatic uncoupling device (33, 34), are so arranged that the relative angular positions of the said plate and of the crank-shaft will always differ by an angle which is equal to, or a multiple of 4-11 21r TV or R according to the case of a four-stroke or a twostroke engine, and. this in such a way that when the crank-pin I5 of the crank-plate (or like deyice) Passes through its dead centre opposite the The plate I3 will thus actuate through the medium of the releasing device (I8, I9, 29) the gear wheels and the automatic uncoupling device (33, 34), the crank-shaft 31 of the engine, at a very slow speed, as the reduction ratio provided by the gearings is very high for reducing the force to be exerted upon the crank I.

At the same time, the rotation of the, plate I3 causes the storing-up of a certain amount of energy in the elastic device I6, owing to the increasing tension of the" spring means, and this will take place during a time which is as long as desired, i. e., by the effect of a power which is as small as desired. When upon continuation of the rotation of the plate I3, the crank-pin I5 moves very slightly past the position corresponding to the maximum tension of the spring means I6, which will restore the accumulated energy to the crank-shaft 31 by means of the mechanical connection with said crankshaft and during a time depending only on the force of the spring means and the total load torque. During this rotation of the plate I3 under the impulse of the accumulator of energy, the hand-crank I is released, as to rotation, from the pinion I2 by the free-wheel device (4, 5). a

As the operator continues the manoeuvre, it will be noted that while the crank I turns with any circular movement, and particularly as slowly as desired and with any number of times of stopping as may be desired, the crank-shaft 31 is driven with a movement composed of a slow rotation in a given ratio to that of the hand-crank I, and of rapid angular impulses which are imparted to it by the accumulator of energy. It should be remarked that owing to the aforesaid ratio between the rotation of the plate I3 and that of the crank-shaft 31, the impulses can be transmitted to the crank-shaftfor well-defined positions of this latter, and namely in such a way that the maximum torque produced by the accumulator of energy will facilitate the passage of the pistons at the upper dead centre of the compression stroke.

In the case of a return or backfire of the engine, the clutch 9, II will slip, thus relieving the wheel 1 which is held by the pawl 8 from any abnormal stress. Moreover, the releasing device I9, I9, 29 can operat in the case in which the force is quite considerable. As long as the force does not exceed a value determined by the spring 2|, the ball l9 provides for the driving of the member 20, while in the contrary case, the said ball is forced out of its recesses and allows a relativ rotation between the members I8 and 20. (It is to be noted that this releasing device should be placed at the mostfavourable point for the protection of the parts of the starter.)

The releasing device can be replaced by a member providing for a pliable transmission of the movement, such as a shaft I4 working by torsion (Fig. 2) which, in the case of return or backfir will afford a more gradual stress upon the clutch 9, II. 3

Obviously, the invention is not limited to the embodiments herein described and represented, which are given solely by way of example.

The member for driving the pinion Il may consist of a small electric motor having the smallest power that may be desired. In this case, and in order to prevent an excessive instantaneous consumption of current, it is of advantage to still make use of a hand-crank for actuating initially the plate I3 by hand, where-,

by the plate, by means of suitable contacts with which it is provided acts, in order to supply current to the electric motor during a prede termined part of the rotation of the plate, and at well-defined intervals. It is thus possible to avoid the supply of current to the motor at the time of the maximum resistance torque of the plate, and also to take advantage of the inertia effects of a suitable flywheel mounted on the armature of the said electric motor.

The spring means It may be replaced by any other devices which will serve the same purpose, for instance by a piston compressing a fluid, or by any other device adapted to receive from the plate l3 and to store up, during a rotation 11' of this plate, a certain amount of energy, and to restore this energy as completely as possible to the said plate during the next rotation 11' which it must make in order to effect a complete evolution.

The units A and B may be closely combined in order to form a single unit.

The releasing device (l8, IE, it) may be situated at any point on the connection between the plate l3 and the shaft 31.

Having now described my invention what 1 claim as new and desire to secure by Letters Patent is:

1. A turning gear for turning the crankshaft of an internal combustion engine with a view of starting same, comprising operating means, a rotatable crank-member in the form of a circular plate carrying an eccentric crank-pin and formed with gear teeth on its periphery, a connecting means between said operating means and said crank-member for rotating same from said operating means, said connecting means including a free-wheel mechanism having a driving member connected in rotation to said operating means, and a driven member, a ratchet wheel connected in rotation to the driven member of said free wheel mechanism, apawl engaging said ratchet wheel for preventing reverse rotation thereof, a friction clutch having a driving member connected in rotation to said ratchet wheel and a driven member, a toothed pinion connected in rotation to said last-mentioned driven member and meshing with the teeth formed on v the periphery of said crank-member, a speed reducing transmission for connecting said crank member to the crankshaft to be turned and a spring means connected to and cooperating with said crank-pin and expanding during one half ofa revolution of said crank-member and contracting during the other half revolution of said crank-member thereby imparting an additional impulse to said crank shaft.

2. A turning gear as claimed in claim 1, in which said speed reducing transmission includes an automatic uncoupling device having a driving member operatively connected to said crank member and a driven member and means for operatively connecting said driven member to the crank shaft of the engine, said uncoupling device being such that the driving and driven members will be uncoupled when the driven member tends to drive the driving member whereby the turning gear is uncoupled from the engine when the latter has started.

3. A turning gear as claimed in claim 1, in which said speed reducing transmission includes an automatic releasing device having a driving member operatively connected to said crank member and a, driven member, and means for operatively connecting said driven member to the crank shaft of the engine, said automatic releasing device being such that the driving member can drive the driven member for one relative angular position only of said driving and driven members and that these members Will be uncoupled when the torque transmitted exceeds a determined value.

4. A turning gear for turning the crankshaft of a four-stroke internal combustion engine having N cylinders with a view of starting said engine, comprising operating means, a rotatable crank-member in the form of a circular gear carrying an eccentric crank-pin, a connecting means between said operating means and said crank member for-rotating same from said operating means, spring means connected to said crank-pin and expanding during one half of a revolution of said crank-member and contracting during the other half revolution of said crank-member thereby imparting an additional impulse to said crankshaft, a speed reducing transmission for connecting said crank-member to the crankshaft to be turned so that the ratio between the angles described by said crank member and said crankshaft during the starting operation will be equal to and uncoupling means inserted in said speed reducing transmission and so arranged that when these uncoupling means are operative to transmit movement the relative angular positions of said crank-member and said crankshaft will differ in all cases by an angle which is a multipl of and that when said crank-pin passes through its dead centre at the end of said one half of a revolution of the crank-member, one of the cylinders will be about to attain the end of the compression period of the cycle.

. 5. A turning gear for turning the crankshaft of a two-stroke internal combustion engine having N cylinders with a view of starting said engine, comprising operating means, a rotatable crank-member in the form of a circular gear carrying an eccentric crank-pin, a connecting means between said operating means and said crank-member for rotating same from said operating means, spring means connected to said crank-pin and expanding during one half of a revolution ofsaid crank-member and contracting during the other half revolution of said crank-member thereby imparting an additional impulse to said crankshaft, a speed reducing transmission for connecting said crank-member to the crankshaft to be turned so that the ratio between the angles described by said crank member and said crankshaft during the starting operation will be equal to N, and uncoupling means

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