Paragraphs

Claims

Paragraph 1 : Crankcase

The crankcase [1] comprises two crankshafts [4] and [5] arranged parallel to one another, one with a long-stroke crank [4], the other with a short-stroke crank [5]; the two cylinders [2] and [3], provided respectively with pistons [6] and [8] and connecting rods [7] and [9], are respectively arranged above one of the two crankshafts [4] and [5].

The crank of the short-stroke crankshaft [5] coacts with the connecting rod [9] of the piston [8] in the smaller cylinder [3] and the crank of long-stroke crankshaft [4] coacts with the connecting rod [7] of the piston [6] in the larger cylinder [2].

The two cylinders [2] and [3] are connected one by one, from one row to the other, through a recess in the cylinder head [10], so as to form a pair of cylinders [2] and [3] in communication with each other.

In the case of an engine provided with compression ignition means, the engine comprises at least one fuel injector (not shown) in the clearance space. The fuel is injected through means known in the art (not shown) in mesh, at half speed, with the long-stroke crankshaft [4].

In the case of an engine provided with spark ignition means, the engine comprises at least one spark plug (not shown) in the clearance space [40]. The ignition is achieved through means known in the art (not shown) in synchronism, at half speed, with the long-stroke crankshaft [4]. Engine timing is achieved by means of at least one camshaft (not shown) in mesh, at half speed, with the long-stroke crankshaft [4].

The section of the cylinder head [10] overhanging the larger cylinder [2] comprises the intake and exhaust valves [13] and [14], which connect periodically the pair of cylinders [2] and [3] with the intake and exhaust pipes [11] and [12] at definite moments of the four-stroke process.

In the case of an engine with an extremely high displacement, a second camshaft (not shown) in mesh, at half speed, with the long-stroke crankshaft [4] may be arranged in the section of the cylinder head [10] overhanging the smaller cylinder [3], so as to provide a second periodic opening and closing of the intake and exhaust at the same time as the opening and closing of the intake and exhaust valves of the larger cylinder [2].

The ratio between the paired cylinders [2] and [3] is at least between 2.5 and 5, so as to permit engine accom-modation to supercharging pressure ratios ranging from 1 to 7.

The variably timed transmission comprises three superposed concentric members :

the first member is the drive shaft [17] located in the inner section,

the second member is the sleeve [28] of gear [20] located in the outer section and

the third member is the sliding tube [32] located in the intermediate section between the two aforesaid members.

Said sleeve [28] is held in a bearing plate [15] by means of a suitable double-row angular contact bearing [16] mounted between the bearing plate [15] and sleeve [28].

Said bearing plate [15] is secured to the engine unit [1] so that the variably timed transmission forms a separate assembly with respect to the shaft [18] of the short-stroke crankshaft [5].

For this purpose , the variably timed transmission and the short-stroke crankshaft [5] are designed each with their own shaft [17] and [18].

The abuting ends of shaft [17] of the variably timed transmission and of shaft [18] of the short-stroke crankshaft [5] are provided with straight male splines and corresponding female splines, so as to permit their coupling within the engine unit [1] through an axial slide movement when the bearing plate [15] in engaged in an opening of the engine unit [1].

The bearing place [15] is centred with respect to shaft [18] of the short-stroke crankshaft [5], so as to permit sel-centering of shaft [17] with respect to shaft [18] , the latter also acting as a free bearing for shaft [17] when the bearing plate [15] is applied against the engine unit [1] ; such means permits the variably timed transmission to be removed from the engine unit [1] without having to remove the short-stroke crankshaft [5].

Drive shaft [17] and sleeve [28] are advantageously held concentrically and axially with respect to each other by means of a bearing housing [22] rigidly connected to shaft [17].

The bearing housing [22] is provided with an axial and radial thrust bearing [23], so as to permit free rotation of shaft [17] independently of sleeve [28].

The bearing housing [22] is an integral part of shaft [17] at the boundary of the straight splines of the abuting ends which serve to couple shaft [17] to shaft [18] of the short-stroke crankshaft [5].

The bearing housing [22] and sleeve [28] are located inside the engine unit [1].

The bearing housing [22] is shaped as a disk which also serves as a flywheel.

The periphery of said flywheel is regularly pierced with holes [24], so as to permit a ring [25] to be bolted onto the surface of the flywheel opposite the side where the boundary of the straight splines is located.

The mounting of ring [25] on the flywheel of the bearing housing [22] serves to form a recess, so as to permit the mounting of the outer ring [26] of the axial and radial thrust bearing [23].

The inner ring [27] of bearing [23] is mounted on the sleeve [28] against a ring-shaped spacer [29] encircling sleeve [28].

The spacer [29] serves to take up the space between the inner ring [27] of bearing [23] and the inner ring of the angular contact bearing [16], the latter being held axially against a shoulder of sleeve [28] through the securing of all above parts, by means of a single nut [30] on sleeve [28].

Gear [20] of sleeve [28] is located outside the engine unit [1] and is coupled, at the same rotational speed, to the long-stroke crankshaft [4] by means of a gear [19] rigidly mounted on the latter and an intermediate gear [21] located between both aforesaid gears [19] and [20].

The drive shaft [17] comprises, on the side of the bearing housing [22] facing the bearing plate [15], helical splines [31] onto which the sliding tube [32] is engaged.

The inner surface of said sliding tube [32] comprises splines [33] mated to the helical splines [31], so as to permit the sliding tube [32] to travel helically along drive shaft [17] and provide an angular displacement between said first and third members.

The outer surface of the sliding tube [32] also comprises helical splines [34], the helix of which is contrary to that of the splines [33] on the inner surface of the sliding tube [32].

The inner surface of sleeve [28] comprises helical splines [35] mated to the outer helical splines [34] of the sliding tube [32], so as to permit the latte to travel helically in sleeve [28] and provide an angular displacement between said second and third members, at the same time as the helical travel of the sliding tube [32] along drive shaft [17].

The sleeve [28] rotates again with shaft [17] when the sliding tube [32] no longer travels axially.

The length of the sliding tube [32] is established inside sleeve [28] when the end of said sliding tube [32] is located at the stop point defined by the surface of the bearing housing [22], the other end of the sliding tube [32] is free outside sleeve [28], passes through gear [20] and emerges from the engine unit [1], so as to permit, through appropriate means, the inner ring of the double-row angular contact bearing [36] to be mounted and secured.

Said inner ring of bearing [36] rotates with the sliding tube [32], whereas the outer ring of bearing [36] does not rotate and is rigidly connected to the holding member [37].

A decision-making memory of the compression ratio programme, acting by means of a hydraulic control system, permits the holding member [37] and the sliding tube [32] to be shifted, so as to alter the lead angle between the two crankshafts [4] and [5].

The start-of-travel of the variably timed transmission is arranged so that the sliding tube [32] is at the travel-out stop position ( not shown ) of sleeve [28] ( low torque ), which corresponds to the minimum lead angle between the crank of the short-stroke crankshaft [5] and the crank of the long-stroke crankshaft [4].

The end-of-travel of the variably timed transmission is arranged so that the sliding tube [32] is at the travel-in stop position ( not shown ) of sleeve [28] ( high torque ), which corresponds to the maximum lead angle between the crank of the short-stroke crankshaft [5] and the crank of the long-stroke crankshaft [4].

According to the invention, to define and facilitate the coupling of both crankshafts [4] and [5] between the variably timed transmission, the number of teeth of gear [20] is even when the number of mated splines [34] and [35] of sliding tube [32] and sleeve [28] respectively, of mated splines [31] and [33] of shaft [17] and sliding tube [32] respectively, and of abuting splines between both shafts [17] and [18] is uneven and vice versa.

According to an alternative embodiment of the invention, the shaft [17] of the variably timed transmission comprises, on the side of the bearing housing [22] facing the bearing plate [15], straight splines [38] instead of helical splines [31], onto which the sliding tube [32] is engaged, and the inner surface of the sliding tube [32] comprises straight splines [39] instead of helical splines [33], mated to the straight splines [38] of shaft [17].

According to the invention, the minimum and maximum compression ratios selected for the type of engine to be designed, are determined based on the dimensions of the different engine members, i.e. on the one hand, the ratio between the displacements of the paired cylinders [2] and [3] and, on the other hand, the ratio between the total displacement of these cylinders [2] and [3] and the clearance space [40], these ratios being defined so that the maximum lead angle between the crank of the short-stroke crankshaft [5] and the crank of the long-stroke crankshaft [4], defined by the end-of-travel position of the variably timed transmission, determines at the end of the compression phase ( top dead center of piston [6] ), the position of piston [8] with respect to the additional volume required for the clearance space [40] to define said minimum compression ratio of the engine, with an angle of at least 90° between the connecting rod [9] and the crank of the short-stroke crankshaft [5].

The adjustment of the angle between both crankshafts, in the end-of-travel position of the variably timed transmission, in function of the appropriate dimensions of the different engine menbers, allow the engie to operate :

- in the expansion phase, with the combustion gases on the piston [8] associated at least from the maximum instantaneous torque on the crank of the short-stroke crankshaft [5] ;
- in the expansion phase, by limiting the rise of piston [8] prior to the opening of the exhaust valve [14], a source of combustion gas back pressure on said piston [8];
- at the end of the intake phase, by limiting the rise of piston [8], a cause of loss of filling volume within the cylinder [3].

This offers the advantage of maintaining the maximum specific output of the engine at full load.

The maximum compression ratio selected is achieved with the same data basis of dimensional values defined for the minimum compression ratio so that the minimum lead angle between the crank of the short-stroke crankshaft [5] and the crank of the long-stroke crankshaft [4], defined by the start-of-travel position of the variably timed transmission, determines at the end of the compression phase ( top dead center of piston [6] ), the position of piston [8] with respect to the additional volume required for the clearance space [40] to define said maximum compression ratio of the engine, with the connecting rod [9] of the crank of the short-stroke crankshaft [5] away from its top dead center, so that said connecting rod [9] forms an angle with the crank of the short-stroke crankshaft [5].

The adjustment of the angle between both crankshafts, in the start-of-travel position of the variably timed transmission, in function of the appropriate dimensions of the different engine members, allows the engine to operate :

- at the end of the compression phase, by providing a greater translational motion to piston [8] per unit degree of angular displacement between the cranks of the two crankshafts [4] and [5].

This offers the advantage of speeding up the modification process of the compression ratio of the engine at low load.

p = compression ratio

V1 = displacement of the larger cylinder of the paired cylinders.

V2 = displacement of the smaller cylinder of the paired cylinders.

V1/V2 =ratio betwwen the displacements on the paired cynlinders

α = lead angle of the crank of the short-stroke crankshaft

ve = clearance space of the paired cylinders required for gas transfer without excessive lamination.

(α minimun) = lead angle of the crank of the short-stroke crankshaft, at the start- of-travel of the variably timed transmission.

(α maximun) = lead angle of the crank of the short-stroke cranskshaft, at the end-of-travel of the variably timed transmission.

Va (α minimun) = additional volume added to the clearance space, at the start-of-travel of the variably timed transmission, defined by the minimum lead angle of the crank of the short-stroke crankshaft, when the crank of the long-stroke crankshaft is located at its top dead center, at the end of the compression phase.

Va (α maximun) = additional volume added to the clearance space, at the end-of-travel of the variably timed transmission, defined by the maximum lead angle of the crank of the short-stroke crankshaft, when the crank of the long-stroke crankshaft is located at its top dead center, at the end of the compression phase.

Vr (α minimun) = compressed air volume at the start-of-travel of the variably timed transmission, defined by the minimum lead angle of the crank of the short-stroke crankshaft, when the crank of the long-stroke crankshaft is located at its bottom dead center, at the end of the intake phase.

Vr (α maximun) = compressed air volume at the end-of-travel of the variably timed transmission, defined by the maximum lead angle of the crank of the short-stroke crankshaft, when the crank of the long-stroke crankshaft is located at its bottom dead center, at the end of the intake phase. Compression ratio characteristics and formulas of the variable volume combustion chamber engine.

( V1 + V2 ) x number of pairs of cylinders = engine displacement.

V1 + [ V2 - Vr (α) ] x number of pairs of cylinders = displacement of the engine defined by the lead angle of the variably timed transmission.

theoretic compression characteristic of the engine after definition of the compression ratios established by the lead angle of the variably timed transmission.

definition of the maximum compression ratio at the start-of-travel of the variably timed transmission. In practice, Vr (α minimum) should not be deducted from V2 as it is too negligible.

definition of the minimum compression ratio at the end-of-travel of the variably timed transmission. In practice, Vr (α maximum) should not be deducted from V2 since the air mass admitted in V1 and V2 depends on the stored calibration at the maximum supercharging pressure.

A simplified formula of the compression ratio may be assumed depending on whether Va(α) is located at any angular position between the start-of-travel and the end-of-travel of the variably timed transmission, which is :

It is possible to define a higher compression ratio between the displacements of the paired cylinders, so as to reduce the stresses on the variably timed transmission mounted on engines having lower displacements and inversely, it is possible to define a smaller compression ratio between the displacements of the paired cylinders [2] and [3], so as to increase the speed of engines having higher displacements. In practice, Vr (α maximum) should not be deducted from V2, since the mass of air admitted in V1 and V2 depends on the stored calibration between the compression ratio and the supercharging pressure. The maximum compression ratio selected is achieved on the basis of the dimensional values defined for the minimum compression ratio, so that at the start-of-travel of the variably timed transmission, the minimum lead angle between the crank of the short-stroke crankshaft [5] and the crank of the long-stroke crankshaft [4] determines, at the end of the compression phase ( top dead centre of piston [6] ), the position of piston [8] with respect to the additional volume required for the clearance space [10] to define a maximum compression ratio, with the connecting rod [9] of the crank of the short-stroke crankshaft [5] away from its top dead centre, so that said connecting rod [9] forms an angle with the crank of the short-stroke crankshaft [9]. The maximum compression ratio may thus be defined by means of the following formula :

In practice, Vr (α minimum) should not be deducted from V2, since the mass of air admitted in V1 and V2 depends on the stored calibration between the compression ratio and the atmospheric depression in the intake pipe.

The diagrams of figures 10 and 11 are based on the above formula where:

a = top dead center of smaller cylinder [3]
b = summit of smaller piston [8]
s = surface of smaller piston [8]
l = length of smaller connecting rod [9]
r = length of smaller crankshaft [5]
A = top dead center of larger cylinder [2]
B = summit of larger piston [6]
S = surface of larger piston [6]
L = length of larger connecting rod [7]
R = length of larger crankshaft [4]

Vm = clearance space [40]
α = angular rotation (0° at top dead center ) ( counterclockwise )
φ = lead angle of smaller crankshaft [5] with respect to the larger crankshaft [4].

Example to make the engine functional and performant according to one of the numerous applications:

The above formula stored in a computer computation sheet allows generation and selection of the dimensional values of the different engine members, i.e. the compression ratios between the displacements of the paired cylinders [2] and [3] and the ratio between the total volume of these cylinders [2] and [3] and the clearance space [40]; the computation sheet is defined so that the values reckoned for the maximum and minimum compression ratios of the engine coincide with the corresponding degrees of the minimum and maximum lead angles between the crank of the short-stroke crankshaft and the crank of the long-stroke crankshaft, respectively at the start-of-travel and at the end-of-travel of the variably timed transmission. The diagrams of figures 10 and 11 show examples of variation curves of the compression ratio and of the volumetric efficiency of the paired cylinders [2] [3] over 360° of angular rotation of the crank of the long-stroke crankshaft [4].

According to a particular embodiment of the invention, in the case of a high-capacity power unit, the two crankshafts [4] and [5] are each mechanically connected to a generator and the electrical circuits of the two generators are connected in parallel. The capacity of each generator is defined in function of the actual output of the corresponding crankshaft at cruise speed of the engine, so that the variably timed transmission and the corresponding couplings of the two crankshafts [4] and [5] are limited to torque compensating loads.

Advantages for a four-stroke engine with compression ignition means.

- higher volumetric efficiency ;
- higher specific output ;
- lower losses due to mechanical friction ;
- engine accommodation to the cetane number ;
- accurate definition of an ideal temperature at the end of the compression phase, so to provide suitable self-ignition of the fuel in all circumstances ( from cold starting to high supercharging pressures ) ;
- better engine performance at high altitudes ;
- lower emissions of hydrocarbons and nitrogen oxide in the exhaust gases.

Advantages for a four-stroke engine with spark ignition means.

- higher volumetric efficiency ;
- higher specific output ;
- lower losses due to mechanical friction and pumping ;
- higher partial-load effeciency of the engine, due to a higher compression ratio proportionally to the depression in the intake pipe (closing of the throttle valve) ;
- engine accomodation to the octane number ;
- better engine performance at high altitudes ;
- better air-fuel mixture homogeneity ;
- lower emmissions of carbon monoxide, nitrogen oxides and hydrocarbons in the exhaust gases.

Advantages and conditions of use of the four-stroke engine with compression ignition means and high supercharging pressure levels, mounted in road haulage tractors.

The reduction of the displacement of each cylinder of the engine, based on the mean piston speed, permits an increase in the speed of the engine and a consistent decrease in low frequencies. A higher gear reduction on the gearbox - output shaft assembly should howewer be provided up to the second engine-drive reduction. Since the mechanical friction is proportional to the displacement and less load-sensitive, the efficiency is higher. The engine brake may be kept whilst increasing the power of the engine, supported by a speed limiter on the vehicle.

Claim 1.

A four-stroke internal combustion engine having an intake phase, a compression phase,an expansion phase and an exhaust phase, said engine including :

- reciprocating pistons [6] [8], provided with self-ignition or spark ignition means ;
- two crankshafts, the first crankshaft [4] having a long-stroke crank and the second crankshaft [5] having a crank with a stroke shorter than that of the first crankshaft, said crankshafts [4] [5] being coupled at the same rotational speed via a gear train [19] [20] [21] and a variably timed transmission ;
- a number of cylinders [2] [3], arranged each above one of the two crankshafts [4] [5], said arrangement including small cylinders [3] with a displacement smaller than that of the larger cylinders [2], each larger cylinder communicating with a smaller cylinder [3] via a clearance space [40], so as to form a group of two cylinders [3] [4] in communication with each other, so as to enable gases to flow from one cylinder to the other, irrespective of the position of the pistons [6] [8] in each of said cylinders [2] [3], each piston being associated to a connecting rod [9] coacting with a crank of a crankshaft, the crank of the second crankshaft [5] coacting with the connecting rod [9] of the piston [8] in the smaller cylinder [3], and the crank of the first crankshaft [4] coacting with the connecting rod [7] of the piston [6] in the larger cylinder [2];
- a camshaft in mesh, at half speed, with the first crankshaft [4], so as to connect periodically groups of two cylinders [2] [3] with intake and exhaust pipes [11] [12] via intake and exhaust valves [13] [14], at definite moments of the four-stroke cycle, in which the variably timed transmission has a control mechanism to vary the lead angle between the crank of the second crankshaft [5] and the crank of the first crankshaft [4], by means of a hydraulic force amplifier having a controlled thrustor acting on the transmission, said transmission altering at the end of the compression phase of the piston [6] in the larger cylinder [2], the compression ratio of the engine between a minimum and a maximum, said minimum and maximum compression ratios depending on :

a ) the ratio between the displacement of the larger cylinder [2] and the displacement of the smaller cylinder [3] , and
b ) the ratio between, on the one hand, the total volume of the smaller cylinder and the larger cylinder and between , on the other hand, the volume of the clearance space [40] and an additional volume created in the smaller cylinder [3] at the end of the compression phase of the piston [6] in the larger cylinder [2], the variably timed transmission adjusting the lead angle between the crank of the second crankshaft [5] and the crank of the first crankshaft [4], so as to obtain said compression ratios, said lead angle varying between a maximun so that an angle of at least 90° is obtained between the connecting rod [9] of the piston [8] in the smaller cylinder [3] and the crank of the second crankshaft [5], at the end of the compression phase of the piston [6] in the larger cylinder [2], in order to define the minimum compression ratio, and a minimum so that the lead angle corresponds, at the end of the compression phase of the piston [6] in the larger cylinder [2], to the appropriate position of the piston [8] in the smaller cylinder [3] to create the additional volume required to obtain the maximum compression ratio, the crank of the second crankshaft [5] forming an angle with the connecting rod [9] of the piston [8] in the smaller cylinder [3].

Claim 2.

A four-stroke internal combustion engine according to claim 1, for which the crank of the first crankshaft [4] passes through a top dead center and a bottom dead center during its rotation, in which the paired cylinders [2] [3] with parallel and close positions and the two crankshafts [4] [5] are arranged to define a minimum working space of the two crankshafts, so that a minimum compression ratio between the paired cylinders [2] [3] is obtained, and in which the variably timed transmission travels between a start-of-travel position and an end-of-travel position, the minimum compression ratio of the paired cylinders [2] [3] being obtained at the end-of-travel of the variably timed transmission and calculated according to thefollowing forrmula :

Claim 3.

A four-stroke internal combustion engine according to claim 1 or 2, in which the variably timed transmission includes three superposed concentric members, i.e. an inner member constituted by a drive shaft [17], an outer member constituted by a sleeve [28] supporting a gear [20] for coupling the two crankshafts [4] [5], and an intermediate member located between said inner and outer members and constituted by a tube [32] which slides with respect to said inner and outer members, the sleeve [28] being held in a bearing plate [15] by means of a double-row angular contact bearing [16], in which the shaft [18] of the second crankshaft [5] has one end which abutes one end of the drive shaft [17], said ends having straight male splines and corresponding female splines, so as to enable their coupling and self-centering of the three members with respect to the shaft [18] of the second crankshaft [5] when the bearing plate [15] is engaged in an opening of the engine unit, and enable the transmission to be removed without having to remove the second crankshaft [5], in which a bearing [22] has a mounting ring [25] which forms the housing of the outer ring [26] of a bearing [23], the inner ring [27] of which is mounted on the sleeve [28] so as to hold the drive shaft [17], in which a spacer [29] extends between the inner ring [27] of the bearing [23] and the inner ring of the angular contact bearing [16], said spacer serving to take up the space between said rings and holding axially the ring of the angular contact bearing [16] against a shoulder of the sleeve [28], in which a single nut [30] holds the inner rings of the bearing [23] and of the angular contact bearing [16] and the spacer [29] on the sleeve [28], in which the drive shaft [17] has, on the side of the mounting ring [25] , helical or straight splines [31] onto which the sliding tube [32] is engaged, the inner surface of which has helical or straight splines [33] so as to enable said tube [32] to travel helically or linearly along the drive shaft [17], in which the inner surface of the sleeve [28] has helical splines [35], the helix of which is contrary to that of the splines of the drive shaft when the latter are helical, in which the sliding tube [32] has one end permanently free outside the sleeve [28], said end being held by an inner ring of a double-row angular contact bearing [36], the outer ring of said bearing [36] being rigidly connected to a holding member [37] of the thrustor, and in which the helical splines are arranged so that when the sliding tube [32] travels out of the sleeve, said tube reduces the lead angle between the crank of the second crankshaft [5] and the crank of the first crankshaft [4].

Claim 4.

A four-stroke internal combustion engine according to any claim 1 to 3, in which the spark ignition means includes at least one spark plug in the clearance space [40], the ignition being effected in sychronism, at half speed, with the first crankshaft [4].

Claim 5.

A four-stroke internal combustion engine according to any claim 1 to 4, in which the ratio between the displacements of the paired cylinders [2] [3] is between 2.5 and 5.

Claim 6.

A four-stroke internal combustion engine according to claim 3, in which the gear [20] supported by the sleeve [28] has respectively an even or uneven number of teeth when the number of teeth of the splines between the drive shaft [17] and the sliding tube [32] and the number of teeth of the splines at the abuting ends of the drive shaft [17] and of the shaft [18] of the second crankshaft [5] are respectively uneven or even.

Claims