POWER UNIT

Abstract

The invention relates to a power unit, in particular for a hybrid vehicle, having a two-cylinder reciprocating piston engine which comprises two pistons guided in two cylinders in a tandem arrangement and two counter-rotating crankshafts connected to the pistons by connecting rods and having an alternator that can rotate in the opposite direction to the first crankshaft and in the same direction as the second crankshaft. The invention is characterized in that the alternator is in driving engagement with at least the first crankshaft via a traction mechanism and comprises a counterbalance, wherein the first crankshaft is connected via a timing chain or a timing belt to a balancing shaft which carries a further balancing mass. The invention also relates to a vehicle, in particular a hybrid vehicle, having such a power unit.

Claims

1. Power unit, in particular for a hybrid vehicle, having a two-cylinder reciprocating piston engine which comprises two pistons guided in two cylinders in a tandem arrangement and two counter-rotating crankshafts connected to the pistons by connecting rods, and having a alternator that can rotate in the opposite direction to the first crankshaft and in the same direction as the second crankshaft, characterized in that the alternator is in driving engagement with at least the first crankshaft via a traction mechanism and comprises a counterbalance, wherein the first crankshaft is connected via a timing chain or a timing belt to a balancing shaft carrying a further balancing mass, the traction mechanism being a toothed chain having teeth on both sides and an outer side of the toothed chain engaging with a sprocket of the first crankshaft and an inner side engaging with a sprocket of the second crankshaft.

2. (canceled)

3. (canceled)

4. (canceled)

5. Power unit according to claim 1, characterized in that the first crankshaft or the balancing shaft carries a flywheel mass.

6. Power unit according to claim 1, characterized in that a translation ratio of the crankshafts to the alternator and/or to the balancing shaft is 2:1.

7. Power unit according to claim 1, characterized in that the first crankshaft comprises a timing gear, which is coupled via the timing chain or the timing belt to an idler gear of a timing drive, the diameter of which is twice the diameter of the timing gear.

8. Power unit according to claim 1, characterized in that a single alternator is provided.

9. Motor vehicle, in particular hybrid vehicle, having a power unit according to claim 1.

Description

[0016] The invention is described hereafter in greater detail on the basis of an exemplary embodiment and by reference to the attached drawing. The single figure shows a schematic side view of a power unit according to the invention, wherein components that are inessential to the invention are hidden.

[0017] The power unit shown in the figure comprises a reciprocating piston engine with two cylinders 1, 2 (two-cylinder reciprocating piston engine), in which pistons 3, 4 are guided. The pistons 3, 4 are connected to crankshafts 7, 8 by means of connecting rods 5, 6. Each piston 3, 4 is assigned to one crankshaft 7, 8 each. The reciprocating piston engine therefore comprises two crankshafts 7, 8, arranged next to one another in parallel. The crankshafts 7, 8 rotate in opposite directions. This means that the two-cylinder reciprocating piston engine is implemented in a tandem design.

[0018] The crankshafts 7, 8 each carry sprockets 9, 10. The sprockets 9, 10 are spaced apart from one another and coupled together by a toothed chain 15. The toothed chain 15 is toothed on both sides, wherein an outer side 15a of the toothed chain 15 is in engagement with the sprocket 9 of the first crankshaft 7. An inner side 15b of the toothed chain 15 is in engagement with the sprocket 10 of the second crankshaft 8. The toothed chain 15 also passes to an alternator 11, the inner side 15b of the toothed chain 15 engaging in a gear wheel of the alternator 11. The alternator 11 is therefore coupled to the crankshafts 7, 8 by means of the toothed chain 15 and is driven by the crankshafts 7, 8. The alternator 11 in this case rotates in the opposite direction with respect to the first crankshaft 7 and in the same direction with respect to the second crankshaft 8.

[0019] In some sections the toothed chain 15 passes between the sprockets 9, 10 in a straight line, the straight section of the toothed chain 15 between the sprockets 9, 10 being preferably at least 30 mm long, in order to ensure an exact engagement of the individual teeth of the toothed chain 15 in the sprockets 9, 10.

[0020] As is clearly visible in the figure, a driving side 16 of the toothed chain 15 runs between the alternator 11 and the first crankshaft 7, or sprocket 9 of the first crankshaft 7. A slack side 17 of the toothed chain 15 runs between the second crankshaft 8 or sprocket 10 of the second crankshaft 8 and the alternator 11. Since the distance between the sprocket 10 of the second crankshaft 8 and the alternator 11 is comparatively large, it is advantageous to provide a chain guide 23 between the alternator 11 and the second crankshaft 8. The chain guide 23 substantially prevents any sagging of the slack side 17 and thus contributes to the smooth running of the power unit.

[0021] On a shaft journal of the first crankshaft 7, a timing gear 21 is arranged. The timing gear 21 can be rigidly connected to the sprocket 10 of the first crankshaft 7. In any event, it is provided that a connection between the timing gear 21 and the sprocket 10 of the first crankshaft 7 is rotationally fixed. The timing gear 21 engages with a timing chain 18 that couples the timing gear 21 to a balancing shaft 12 and a timing drive 19. In particular, the timing chain 18 passes from the timing gear 21 to the balancing shaft 12 and further to an idler gear 20 that is seated on the front face of the timing drive 19. The idler gear 20 is preferably designed twice as large as the timing gear 21, so that a translation ratio of 2:1 is set between the timing drive 19 and the crankshafts 7, 8. The timing drive 19 can be advantageously designed as a deep-lying timing drive. Specifically, the timing drive 19 is preferably arranged below the level of the cylinder seal. This reduces the overall height of the power unit.

[0022] To balance out the second-order inertial forces, i.e. to provide the so-called Lanchester compensation, balancing masses 13, 14 are provided. One of these balancing masses 13 is arranged on the alternator 11. Rotating in phase with this but in the opposite direction, a further balancing mass 14 is arranged on the balancing shaft 12. Between the balancing shaft 12 or the alternator 11 and the crankshafts 7, 8 there exists a translation ratio of 1:2. In other words, both the alternator 11 and the balancing shaft 12 rotate twice as fast as the crankshafts 7, 8. The rotation of the balancing shaft 12 and the alternator 11 are each in opposite directions to one another, so as to ensure an efficient balancing of the second-order inertial forces.

[0023] To compensate for the alternating torques, which occur due to the ignition order of the reciprocating piston engine in 4-cycle operation, a flywheel mass 22 is provided, which is connected to the first crankshaft 7. The flywheel mass 22 is preferably arranged on a reverse side of the reciprocating piston engine. In other words, at its longitudinal ends the first crankshaft 7 comprises a shaft journal, wherein the sprocket 9 and the timing gear 21 are located on a first, frontal shaft journal. On a second shaft journal, opposite to the first, the flywheel mass 22 is rotationally fixed. A further flywheel mass 24 can be connected to the second crankshaft 8. The flywheel mass 24 which is assigned to the second crankshaft 8 is preferably smaller than the flywheel mass 22 of the first crankshaft 7.

LIST OF REFERENCE NUMERALS

[0024] 1, 2 cylinder [0025] 3, 4 piston [0026] 5, 6 connecting rod [0027] 7 first crankshaft [0028] 8 second crankshaft [0029] 9, 10 sprockets [0030] 11 alternator [0031] 12 balancing shaft [0032] 13, 14 balancing masses [0033] 15 toothed chain [0034] 15a outer side [0035] 15b inner side [0036] 16 driving side [0037] 17 slack side [0038] 18 timing chain [0039] 19 timing drive [0040] 20 idler wheel [0041] 21 timing gear [0042] 22, 24 flywheel masses [0043] 23 chain guide