The present disclosure relates to balancing an internal combustion engine.
An opposed-piston, opposed-cylinder (OPOC) engine 10, as disclosed in U.S. Pat. No. 6,170,443, and incorporated herein in its entirety, is an asymmetrical configuration. Such an OPOC engine 10 is shown isometrically in
The movement of the intake pistons is displaced from the movement of the exhaust pistons such that the exhaust pistons precede the intake pistons in attaining their respective extreme positions by about 20 degrees. This is accomplished by asymmetrically orienting the eccentric journals on crankshaft 20 to which the pistons couple. By asymmetrically orientating the journals on crankshaft 20, the scavenging events are asymmetrically timed. The inertia forces, at a given engine speed, arising in the direction of reciprocation, X, is illustrated in
Although the balancing is nearly perfect for the engine of
To at least partially overcome imbalance in an opposed-piston engine, an engine is disclosed that has a first cylinder having a central axis, a second cylinder having a central axis parallel to the central axis of the first cylinder, a unitary crankshaft situated between the two cylinders and having at least five journals and four webs: a front main journal having a central axis collinear with an axis of rotation of the crankshaft; a rear main journal having a central axis collinear with the axis of rotation of the crankshaft; a central eccentric journal; a front eccentric journal between the front main journal and the central eccentric journal; a rear eccentric journal between the rear main journal and the central eccentric journal; a front outer web located between the front main journal and the front eccentric journal; a front inner web located between the front eccentric journal and the central eccentric journal; a rear inner web located between the central eccentric journal and the rear eccentric journal; a rear outer web located between the rear eccentric journal and the rear main journal. A central axis of the front and rear eccentric journals is offset from the axis of rotation by an outer crank throw. A central axis of the central journal is offset from the axis of rotation by an inner crank throw. The front and rear eccentric journals are substantially equally phased. The central eccentric journal is asymmetrically phased with respect to the front. A first piston is disposed in the first cylinder and coupled to the central eccentric journal via a first pushrod. A second piston is disposed in the second cylinder and coupled to the central eccentric journal via a second pushrod. A third piston is disposed in the first cylinder and coupled to the front eccentric journal via a first pullrod and coupled to the rear eccentric journal via a second pullrod. A fourth piston is disposed in the second cylinder and coupled to the front eccentric journal via a third pullrod and coupled to the rear eccentric journal via a fourth pullrod. Reciprocation of the pistons, the pushrods, and the pullrods generates an unbalanced inertia. The front inner web includes a first counterweight. The rear inner web includes a second counterweight. The first and second counterweights cause the center of gravity to be displaced from the axis of rotation of the crankshaft to at least partially counteract the unbalanced inertia force. The first and second counterweights are situated to provide clearance between the counterweights and the first and second pistons at all crankshaft positions.
In some embodiments, the first and second counterweights counteract approximately half of the unbalanced inertia force. In other embodiments, the front outer web includes a third counterweight and the rear outer web includes a fourth counterweight. The center of gravity of the crankshaft is displaced from the central axis due to the first, second, third, and fourth counterweights; the displacement of the center of gravity is situated to overcome approximately half of the inertia force.
Each of the first and second cylinders has a plurality of intake ports and a plurality of exhaust ports. The first and second pistons are exhaust pistons arranged to reciprocate when the crankshaft rotates thereby covering and uncovering the exhaust ports. The third and fourth pistons are intake pistons arranged to reciprocate when the crankshaft rotates thereby covering and uncovering the intake ports. The first and second pistons weigh less than the third and fourth pistons. The outer crank throw is shorter than the inner crank throw such that (the mass of first piston plus a translatory component of the mass of the pushrod) times the outer crank throw is substantially equal to (the mass of the third piston plus a translatory component of the mass of the first and second pullrods) times the inner crank throw.
In some embodiments, the first and second cylinder central axes are substantially collinear and the center of gravity of the crankshaft is located substantially on a plane perpendicular to the axis of rotation of the crankshaft that includes the central axes of the two cylinders. Such embodiments have pairs of pushrods and pairs of pullrods with each pair coupling to a single journal. Alternatively, the pushrod pair or the pullrod pairs couple to the crankshaft adjacent to each other. In such embodiments, the central axes of the first and second cylinders are displaced from each other.
The inner eccentric journal is eccentric from the axis of the axis of rotation of the crankshaft by an inner crank throw; and the outer eccentric journal is eccentric from the axis of the axis of rotation of the crankshaft by an outer crank throw. An inner reciprocating mass is a mass of the first piston plus a translatory component of mass attributable to the first pushrod; an outer reciprocating mass is a mass of the third piston plus a translatory component of mass attributable to the first pullrod plus a translatory component of mass attributable to the second pullrod. The inner reciprocating mass times the inner crank throw is roughly equal to the outer reciprocating mass times the outer crank throw. A first-order unbalanced inertia force during rotation of the engine is due to asymmetric phasing of the pistons which is due to asymmetric phasing between the inner journal and the outer journal. The displacement of the center of gravity of the crankshaft due to the counterweights is determined to cancel approximately half of the first-order unbalanced inertia force.
In some embodiments, the engine has at least one accessory coupled to the engine with a shaft of the accessory parallel to the crankshaft and the shaft of the accessory rotating in an opposite direction with respect to the crankshaft at the same rotational speed as the crankshaft. The accessory has at least one counterweight coupled to the accessory. The counterweight on the accessory has a mass and a location with respect to the axis of rotation of the accessory canceling a portion of the unbalanced inertia force due to the pistons.
The engine, in some alternatives, has crankshaft pulley coupled to the crankshaft, an accessory pulley counter rotating at the same speed as the crankshaft pulley with the crankshaft pulley and the accessory pulley engaged via a flexible member, an accessory shaft and an accessory coupled to and rotating with the accessory pulley; and a counterweight coupled to the accessory shaft. A serpentine member couples with the crankshaft and a pulley coupled to the accessory. The serpentine member is one of a toothed belt and a chain. The accessory may be an oil pump, a water pump, an alternator, a fuel pump, an air conditioning compressor, and an air pump.
Also disclosed is an engine system having a crankshaft with at least five journals and four webs: a front main journal having a central axis collinear with an axis of rotation of the crankshaft, a rear main journal having a central axis collinear with the axis of rotation of the crankshaft, a central eccentric journal, a front eccentric journal between the front main journal and the central eccentric journal, a rear eccentric journal between the rear main journal and the central eccentric journal, a front outer web located between the front main journal and the front eccentric journal, a front inner web located between the front eccentric journal and the central eccentric journal, a rear inner web located between the central eccentric journal and the rear eccentric journal, and a rear outer web located between the rear eccentric journal and the rear main journal. The engine has a first cylinder having a first piston reciprocating therein with the first piston coupled to the crankshaft via a first connecting rod and a second cylinder having a second piston reciprocating therein with the second piston coupled to the crankshaft via a second connecting rod. The engine further includes a third piston reciprocating in the first cylinder with the third piston coupled to the crankshaft via third and fourth connecting rods and a fourth piston reciprocating in the second cylinder with the fourth piston coupled to the crankshaft via fifth and sixth connecting rods. The crankshaft further includes a first counterweight applied to the front inner web and a second counterweight applied to the rear inner web.
Reciprocation of the pistons leads to unbalanced inertia forces perpendicular to the axis of rotation of the crankshaft. The first and second counterweights cause the center of gravity of the crankshaft to be displaced in such a manner to counteract at least a portion of the unbalanced inertia forces. A primary accessory counter rotating at crankshaft speed and coupled to the engine has a third counterweight coupled thereto. The third counterweight causes center of gravity of the primary accessory to be displaced from an axis of rotation of the primary accessory. The engine may also have a secondary accessory coupled to the engine with the secondary accessory counter rotating at crankshaft speed and having a fourth counterweight associated with the secondary accessory. The fourth counterweight causes center of gravity of the secondary accessory to be displaced from an axis of rotation of the secondary accessory. The first and second counterweights counteract about half of the unbalanced force. The first and second counterweights, however, lead to an imbalance in a direction perpendicular to both the axis of the first cylinder and the axis of rotation of the crankshaft. The third and fourth counterweights counteract about half of the unbalanced force due to the pistons and the translatory component of the connecting rods as well as counteracting the imbalance created by the first and second counterweights.
The engine system may further include a crankshaft pulley coupled to the crankshaft, a serpentine member wrapped around a portion of the crankshaft pulley, a first rotating accessory having an axis of rotation parallel to an axis of rotation of the crankshaft and a first accessory pulley engaged with the serpentine member, a second rotating accessory having an axis of rotation parallel to the axis of rotation of the crankshaft and a second accessory pulley engaged with the serpentine member, a third counterweight coupled to the first rotating accessory, and a fourth counterweight coupled to the second rotating accessory.
The engine system includes a cylinder block housing first and second cylinders in which first and second pistons reciprocate, a driving gear associated with the crankshaft, a driven gear engaging with the driving gear with the driven gear having the same number of teeth as the driving gear, an accessory shaft and an accessory coupled to and rotating with the driven gear, and a third counterweight coupled to the accessory shaft. The accessory shaft associated with the accessory is supported on a first end by a first bearing in a first side of the cylinder block and is supported on a second end by a second bearing in a second side of the cylinder block. The third counterweight is located between the two bearings.
In some embodiments, central axes of the first and second cylinders are displaced from each other. The first and second connecting rods are pushrods that couple to the crankshaft adjacent to each other. The third and fourth connecting rods are pullrods that couple to the crankshaft adjacent to each other. The fifth and sixth connecting rods are pullrods that couple to the crankshaft adjacent to each other. The central eccentric journal has two journal portions: one to which the first connecting rod couples and one to which the second connecting rod couples. The front eccentric journal includes two journal portions: one to which the third connecting rod couples and one to which the fourth connecting rod couples. The rear eccentric journal has two journal portions: one to which the fifth connecting rod couples and one to which the sixth connecting rod couples.
In some embodiments, a crankshaft pulley is coupled to the crankshaft. An accessory pulley counter rotating at the same speed as the crankshaft pulley with the accessory pulley driven by the crankshaft accessory pulley via a flexible member. An accessory shaft and an accessory are coupled to and rotating with the accessory pulley. A second counterweight is further coupled to the accessory shaft.
A method to balance an OPOC engine is also disclosed that includes: determining the mass of pistons disposed in engine cylinders and the translatory component of the connecting rods associated with the pistons, determining the unbalanced piston inertia force, F, along the cylinder axis at a predetermined engine speed, and specifying a counterweight force, F_CS, associated with the crankshaft to counteract a fraction of the unbalanced piston inertia forces. The fraction that the crankshaft counterweight(s) overcome is approximately one-half, is one embodiment. The engine system also may have rotating accessories associated with the engine. The method also includes determining offsets (x_1, x_2, y_1, y_2, z_1, and z_2) at which first and second counterweights may be provided on engine accessories, such offsets being those that prevent collision between the counterweights and other engine components. The forces of the first and second counterweights, F_1 and F_2, provided on accessories at least partially based on force balances on the crankshaft. Once F_1 and F_2 are known, the masses can be backed out via the offset that have already been defined.
As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated.
In
Due to the offset timing of the exhaust and intake pistons, for a short duration of crank rotation, in any of the cylinders in
The inertia force in the X direction due to the pistons' reciprocal movement in engine 50 is shown in
Although the resultant inertia forces 104 of engine 50 (
There is no corresponding unbalanced inertia force in the Y direction for the unbalanced OPOC, as indicated by 108 in
Referring now to
An OPOC engine having offset cylinders, such as shown in
The counterweights react against the unbalanced inertia force in the X direction as shown in
To overcome the inertial force in the Y direction that is introduced by the counterweight(s) on the crankshaft, counterweights may be added to accessories that rotate in the opposite direction, but as the same speed, as crankshaft 60. Not only do such counterweights on the accessories overcome the Y-direction imbalance introduced by the counterweight(s) on the crankshaft, but the accessory counterweights also overcomes the remaining inertial imbalance in the X direction as shown in
Referring to
In
Crankshaft 150 rotates counter clockwise in
The counterweight(s) applied to crankshaft 150 overcomes about one-half of the inertia force imbalance of the pistons in the X direction but introduces an inertia force imbalance in the Y direction. Counterweight 156 on gear 154 is sized to overcome about one-quarter of the inertia force imbalance due to reciprocation of the pistons in the X direction. And, because gear 154 rotates in an opposite direction from crankshaft 150, it overcomes about one-half of the Y direction imbalance introduced by a counterweight on crankshaft 150. Counterweights 168 and 170 on pulleys 162 and 164, respectively, are sized to overcome about one-eighth of the inertia force imbalance due to reciprocation of the pistons. Again, because pulleys 162 and 164 rotate in the opposite sense of crankshaft 150, they collectively overcome about one-half of the Y direction imbalance introduced by a counterweight on crankshaft 1150. The engine is balanced with the set of counterweights as described.
An alternative to putting counterweights on two accessories is shown in
A crankshaft 300 that rotates about axis 302 according to an embodiment of the disclosure is shown in
As described above, the present disclosure also applies to an engine in which the connecting rods couple to the crankshaft adjacent to each other, such as the engine in
An isometric view of crankshaft 300 is shown in
An alternative embodiment of a crankshaft 450 rotating about axis 452 is shown isometrically in
In
By performing force balances on the free body diagrams in
−F_CS+F—1+F—2=0;
z—1*F1+z—2*F—2+z_CS*F_CS=T—y;
−z1*F1−z—2*F—2+z_CS*F_CS=T—x;
z—1*F—1+z—2*F—2=T—z90; and
−x—1*F—1−x—2*F—2+T_zBDC.
Also assume that T_x=T_y.
Setting F_CS=F/2, the other variables are found to be:
F—1=(F_CS/(z—1−z—2))*z—2;
F—2=(F_CS/(z—1−z—2))*z—1;
T—y=F_CS*z_CS;
T—x=F_CS*z_CS;
T—z90 =(F_CS/(z—1−z—2))*(z—1*y—2−z—2*y—1); and
T—zBDC=(F_CS/(z—1−z—2))*(x—1*z—2−x—2*z—1).
By selecting values for the offsets for the counterweights, counterweight masses can be determined so that the OPOC engine can be fully balanced for some situations and nearly fully balanced for other situations.
In
In one special case: y_CS=0; x_1=−x_2; y_1=−y_2; z_1=−z_2; and F_CS=F/2. In this case, P_1=P_2=F/4. The remaining torques are all zero. In a first sample case: y_CS=0; x_1=x_2=0; z_2=−1.9*z_1; y_1=−1.4*z_1; y_2=(z_2/z_1) *y_1; and F_CS=F/2. In this case, the results are approximately, P_1=F/3 and P_2=F/6 with the remaining torques all zero. And in yet another sample case with the values the same as in the first sample case except that x_1=x_2=0.839*y_1. The results for P_1 and P_2 are approximately the same: P_1=F/3 and P_2=F/6, but there is a remaining torque, T_zBDC which acts in the direction of the peak torque from the gas forces due to combustion in the cylinder.
While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.
The present application claims priority benefit from U.S. provisional patent application 61/549,678 filed 20 Oct. 2011.
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