Internal-combustion engines – Vibration compensating device – Balancing arrangement
Reexamination Certificate
1999-02-09
2001-10-02
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Vibration compensating device
Balancing arrangement
C074S590000, C074S603000
Reexamination Certificate
active
06295962
ABSTRACT:
The invention relates to a crankshaft and piston arrangement for a combustion engine. In particular, the invention relates to means for balancing such an arrangement especially in a single cylinder or parallel twin cylinder engine.
GB 2057061 teaches the use of a balancing link pivotally connected to a crankshaft at a point diametrically opposed to the big end of the connecting rod to a piston. The balancing link is pivotally connected at its end opposite to the crankshaft to a guide link which is pivotally connected at a fixed point on the engine. GB 2057061 teaches that certain relationships between the length of the connecting rod, the separation of the big end thereof and the centre of rotation of the crankshaft, the separation of the crankshaft pivot point of the balancing link and the centre of the crankshaft, and the separation of the pivots on the balancing link must be met. In particular, that patent specification states that the mutual pivot point of the balancing link and guide link should be positioned at the centre of percussion of the balancing link, which pivot point therefore has a fixed position in relation to the centre of gravity of the balancing link as described in the earlier patent. However, the cost of manufacture of the engine described in GB 2057061 is relatively expensive due to the construction of the additional pivot link and guide link. Moreover, it is not found to provide sufficient reduction in engine vibration to enable high speed of revolution of the crankshaft and/or relatively smooth operation thereof at moderate speeds of revolution.
Accordingly, an object of the invention is to avoid or at least mitigate the problems of the prior art. An object is therefore to provide a well balanced engine. A first aspect of the invention provides a crankshaft and piston arrangement for a combustion engine, comprising a piston pivotally connected to a crankshaft by a connecting rod, and balance means comprising a connecting rod and a balance arm pivotally connected thereto, the balance arm being connectable at an end remote from the connection rod to the engine and wherein the balance arm provides a balance mass. Preferably this mass is substantially provided in the region of the balance means connecting rod thus to produce a force substantially equal in magnitude to the force generated by the motion of the piston. The balance means is preferably substantially diametrically opposed to the piston and connecting rod in one preferred form, or provided on the same side of the crankshaft as the piston in another.
Beneficially, the connecting rod for the balance means can be substantially identical to the connecting rod for the piston.
Beneficially, the balance arm can provide a force equal in magnitude but opposite in direction to the force generated by the accelerations and decelerations of the piston.
Preferably, the balance arm comprises a relatively massive end which end is pivotally connected to the balance means connecting rod. The massive end of the balance arm can be separated into two regions (or forked) such that the end of the balance means connecting rod is engaged between the massive forked end of the balance arm. Further, the centre of rotation of the pivot between the balance arm and balance means connecting rod can be centrally disposed in the massive end of the connecting arm.
In a preferred form, the arrangement comprises two parallel pistons each connected by a connecting rod and bearing to the crankshaft. Preferably, a balance arm is provided for each piston. More preferably, the balance arms extend in substantially opposite directions to one another away from their respective connecting rods.
In one form, the connecting rods of the balance means for a twin piston engine share a co-axial axis of rotation on the crankshaft. Also, the connecting rods can be angularly displaced with respect to one another. The degree of angular displacement is preferably less than or equal to 10° and more preferably in the order of 3° when the pistons are radially outermost.
In another form a single piston arrangement is provided having two balance means each having a balance arm, which arms extend in substantially opposite directions to one another away from the crankshaft. In such an arrangement, preferably a series of four crankshaft webs are used to enable connection in series of a balance means, a piston connection rod and a second balance means to the crankshaft.
In a further preferred form, when the piston is radially outermost an angle is presented between the central axis of the piston and the longitudinal axis of the balance arm which is preferably in the order of or less than 90°. More preferably, the angle is greater than 45° and can be in the order of 50 to 75°. When the piston is in a central position of the overall stroke of the piston, preferably the balance arm or arms are horizontal, or present substantially a right angle between the longitudinal axis of the balance arm and the axis between the balance arm pivot with the connecting rod and the centre of rotation of the crankshaft.
The balance means and pistons can be in any order along the crankshaft. However, in a further preferred form of the invention, the crankshaft comprises in axial order a first piston, two balance means and a second piston arranged along the crankshaft. Preferably, each of the pistons and balance means is separated from its neighbour by a crank web to which each is pivotally connected by a bearing. Preferably, a central main bearing is disposed centrally along the axis of the crankshaft symmetrically between two pairs each comprising one of the pistons and one of the balance means.
In another preferred arrangement the balance means is provided on the same side of the crankshaft as the piston, this provides the benefit of a reduction in the overall size of the crankshaft and piston arrangement. The length of the balance means connecting rod is preferably shorter in this arrangement than the piston connecting rod in order to allow for movement of the piston. Accordingly, the connecting rod lengths and the stroke of the piston and balance means can be adjusted in order to maintain an equal L/R ratio for the balance means and piston connecting rod, or to achieve the desired L/R for the balance means. Where L is the length of the connecting rod and R (the throw) is half the stroke of the piston or balance means.
According to a second aspect of the invention there is provided a crankshaft and piston arrangement for combustion engines comprising two pistons each pivotally connected to a crankshaft by an associated connecting rod, and a pair of balance means comprising a guided balance mass to reduce the vibrations created by movement of the pistons in use, the arrangement further comprising a central main bearing. Beneficially this inhibits crankshaft bending and so avoids out of balance forces. Preferably the balance means are connected on opposite sides of the central main bearing which in turn are connected to crankshaft webs connected to the piston connecting rods.
In this arrangement, the balance means can comprise a balance mass pivotally connected to the crankshaft wherein the balance mass is guided by a relatively less massive link pivotally attachable to a fixed point in an engine in use. Alternatively the arrangement of the first aspect of the invention can be used each having a central main bearing.
According to a third aspect of the invention, there is provided an engine having a crankshaft and piston arrangement for combustion engines comprising a piston pivotally connected to a crankshaft by a connecting rod and balance means comprising a balance mass pivotally connected to the crankshaft and a guide link pivotally connected to the balance mass and connectable at an end remote from the balance mass to a fixed point on the engine, wherein the guide link for the balance means is connected to the engine on the same side of the crankshaft as the piston. Beneficially the balance means is therefore clear of the engine oil sump and a reduced overall engine size can b
Kamen Noah P.
Naxsym Engine Technology Ltd.
Wood Phillips VanSanten Clark & Mortimer
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