Abstract:
A drive mechanism for accessory assemblies of a reciprocating internal combustion engine having a switchable planetary transmission which is positioned concentrically to the crankshaft and is driven by the latter. To prevent the noise- and wear-producing vibrations of the free end of the crankshaft from reaching the planetary transmission, a vibration isolator which functions as a cross-recess coupling is provided between the crankshaft and the planetary transmission.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a drive mechanism for accessory assemblies of a reciprocating internal combustion engine. 
     BACKGROUND INFORMATION 
     French Unexamined Patent Application No. 2 644 866 discloses a drive mechanism for accessory assemblies of a reciprocating internal combustion engine having a switchable planetary transmission. The planetary transmission is positioned concentrically to the crankshaft and includes a planetary gear carrier attached to the crankshaft, planet gears, a ring gear that can be locked against an end shield using a braking device and a sun gear that is connected to a belt pulley. The sun gear is positioned in the end shield and can be connected to the planetary gear carrier via a one-way clutch. 
     Switchable planetary transmissions of this type are intended to provide adequate power to accessory assemblies, such as an air conditioner compressor and electric generator, at engine idling speeds without causing those assemblies to race at high engine speeds, which may cause damage. This makes it possible to guarantee the operation of the vehicle electrical system even if the accessory assembly size might be reduced. This is so even if an electrically heated windshield and an electrically heated (pre)-catalytic converter are needed in addition to the equipment now present. The latter is an important prerequisite in reducing pollutant emissions during a cold start. 
     However, the switchable planetary transmission described in French Unexamined Patent Application 2 644 866 has a large volume and poor efficiency, since it is difficult to lubricate. Because it is connected rigidly to the free end of the crankshaft, this planetary transmission is subjected to the latter&#39;s vibratory load, making it susceptible to failures and producing noise emissions. 
     A switchable planetary transmission whose drive provides damping of the torsional vibrations stemming from the crankshaft is known from German Patent Application No. 1 526 560. This damping is achieved by a combination of compression springs and rubber cushions that are arranged in the planetary gear carrier. However, this has no effect on radial or axial vibrations of the crankshaft end, but only on its tangential vibrations which, unlike radial and axial vibrations, can be corrected by torsional vibration isolators and vibration dampers. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a switchable planetary transmission which is reliable, compact, and quiet and has a high level of efficiency and a long service life. 
     The present invention provides a drive mechanism for accessory assemblies of a reciprocating internal combustion engine comprising a switchable planetary transmission ( 1 ) which is positioned concentrically to the crankshaft ( 2 ) and which has a planetary gear carrier ( 12 ) connected to the crankshaft ( 2 ) with planet gears ( 15 ), as well as a ring gear ( 17 ) that can be locked against an end shield ( 19 ) by a braking device and a sun gear ( 16 ) that is connected to a belt pulley ( 21 ). The sun gear is positioned in the end shield ( 19 ) and can be connected to the planetary gear carrier ( 12 ) via a one-way clutch ( 22 ). The present invention is characterized in that the planetary gear carrier ( 12 ) is connected to the crankshaft ( 2 ) by a vibration isolator ( 8 ). 
     To prevent the vibrations produced by the crankshaft end from being transmitted to the planetary transmission, a vibration isolator is connected between the units. The vibration isolator is connected to the crankshaft end and the planetary gear carrier, but does not allow passage of the vibrations produced by the crankshaft end, due to its elasticity or its geometry. 
     Isolating the vibrations produced by the crankshaft end makes it possible to design a much more light-weight and thus more compact planetary transmission. This also reduces its susceptibility to failures and its noise emissions, in particular the belt pulley noise emissions. 
     In principle, it is conceivable to connect the crankshaft and planetary gear carrier to the vibration isolator by screwing, riveting, or gluing, etc. An especially simple mounting method, however, is to provide both parts with axial claws which need only to be inserted into corresponding slots in the vibration isolator. An identical number of claws produces a more symmetrical, and thus smaller, load and allows the vibration isolator to be centered before it is mounted. The number of claws is not specified. Two or three per part are usual. 
     If the vibration isolator is made of an elastic material (such as polyurethane), it is capable of filtering out tangential and axial vibrations as well as radial vibrations. 
     The tangential vibrations produced by the crankshaft end can be eliminated on the latter by torsional vibration isolators or vibration dampers. It is therefore also possible to use vibration isolators made of an inelastic material. Although their torsional rigidity prevents them from filtering out torsional vibrations, the radial and axial clearance of the claws allows the latter to move radially and axially within the slots, thus eliminating radial and axial vibrations. 
     Similarly, the vibration isolator can also be designed in the shape of a square or hexagon, with the claws being tangential to its circumferential sides. A vibration isolator known as a cross-recess coupling is characterized by an especially simple design, since it has only four radial slots distributed evenly across its circumference, each accepting two claws. 
     According to one preferred embodiment of the present invention, the ring gear is mounted on the planet gears so that it can move in an axial direction, and the brake disc is integrally molded onto the ring gear. The one-piece design of the ring gear and brake disk, the floating attachment of the ring gear onto the planet gears, and the ability of corresponding brake pads to move within a retaining ring with an integrated axial stop give the brake a simple design. 
     A cylindrical piston actuated by oil pressure ensures that the brake pads apply a uniform pressure on the brake disk, thus allowing the latter to operate with little wear and tear. Positioning the cylindrical piston between an outer and an inner guide ring also allows the latter to be operated with little wear and tear and offers freedom in selecting the material for the end shield. The linear contact between a rounded torus of the cylindrical piston and the brake pad facing it avoids twisting and thus wear and tear. 
     An electronic controller inhibits switching pressure or a variation in engine speed when the planetary transmission is switched on and off. 
     Because it is placed in the timing box, the planetary transmission is reliably lubricated with motor oil, thereby achieving a high level of efficiency and reducing wear and tear. This solves one problem that could never be controlled by positioning the planetary transmission on the free crankshaft end outside the engine housing. In addition, arranging the planetary transmission in this manner requires only one dynamic gear oil sealing ring, just like in a standard engine. This ring does not have to provide a seal against differential oil pressure, but must merely withstand the vacuum in the crankcase. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One embodiment of the present invention is explained in greater detail in the description below on the basis of the drawings, in which: 
     FIG. 1 shows a cross section of a switchable planetary transmission with a parking or setting brake for a ring gear; and 
     FIG. 2 shows an actuating element for the setting brake. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a planetary transmission  1  which is positioned coaxially to a crankshaft  2  and is driven by the latter. It is driven by a sprocket wheel combination  3 , which is screwed against free end  2   a  of crankshaft  2  by an anti-torque socket-head screw  4 . Sprocket wheel combination  3  is also used to drive the gas exchange control mechanism of the engine and is therefore arranged conformally to crankshaft  2  with spring groove  5  and spring  6 . 
     A flange  7  of sprocket wheel combination  3 , located at free crankshaft end  2   a , has facing claws  11  perpendicular to plane  2  of the drawing which each fit with a limited amount of tangential clearance and a greater amount of radial clearance into a slot  10  on the circumference of a ring-shaped vibration isolator  8 . If necessary, a vibration damper  9  can also be mounted on flange  7  and used to dampen the torsional vibration resonance of crankshaft  2 . 
     On its lateral surface, vibration isolator  8  has two additional facing slots  10  on the plane of the drawing into which two corresponding claws  11  of a planetary gear carrier  12  fit with a limited amount of tangential clearance and a greater amount of radial clearance. Mounted on the side of planetary gear carrier  12  facing away from crankshaft  2  are at least three evenly distributed bolts or axles  13  on which planet gears  15  are mounted in bearing bushes  14 . Planet gears  15  engage with an inner sun gear  16  and an outer ring gear  17 . 
     Sun gear  16  is an integral component of a sleeve  17   a , with a ball bearing  18  mounted in an end shield or housing part  19  being positioned at its end farthest away from the crankshaft. An end shield  19  closes an opening in a timing box  36  which surrounds planetary transmission  1  and whose lower end is closed by an oil pan  37 . Upstream from ball bearing  18 , a fine-toothed gearing  20  is provided on the circumference of sleeve  17   a  for attaching a belt pulley  21  so that it transmits torque. The accessory assemblies are driven by this belt pulley. A one-way clutch  22 , which is used to couple planetary gear carrier  12  with sleeve  1   7   a , is provided in the area of sleeve  17   a  close to the crankshaft. 
     A radial-lip-type oil seal  26  is provided between end shield  19  and belt pulley  21 . To relieve the latter of all oil pressure, oil holes  38  are provided around its circumference in end shield  19 . 
     Ring gear  17  is mounted on planet gears  15  in a floating and thus self-centering manner. Ring gear  17  has an integrated brake disk  23 , designed like a radial flange, on its outer circumference. A mounting device or retaining ring  25  for brake pads  24  provided on both sides of brake disk  23  is located on end shield  19 , with an axial stop  35  being assigned to one of brake pads  24 . The end face of sleeve  17   a  is closed by a plastic cover  27 . 
     FIG. 2 shows an example of a hydraulic brake actuator  28  having an air vent  29 , a hydraulic oil chamber  33 , and a cylindrical piston  30 . This cylindrical piston  30  is mounted between an outer and an inner guide ring  31 ,  31   a  in end shield  19  so that it can move in an axial direction, and is sealed by sealing rings  32 . Guide rings  31 ,  31   a  are made of a wear-resistant material. This makes it possible to select any material for the end shield. 
     Cylindrical piston  30  has a rounded torus  34  that interacts with one of brake pads  24 . The compressive force exerted by cylindrical piston  30  on one brake pad  24  causes brake disk  23  to be clamped between brake pads  24  due to the axial motion, since axial stop  35  prevents second brake pad  24  from moving out of the way. The linear contact between torus  34  and disk-shaped brake pad  24  preferably takes place along the line of gravity of the latter, thus ensuring that the brake pad is applied evenly and without being forced. 
     The mechanism according to the present invention operates as follows: crankshaft  2  drives planetary gear carrier  12  via sprocket wheel combination  3  and vibration isolator  8 . The latter functions like a cross-recess coupling in combination with its four slots  10 , which are arranged in pairs facing each other and are offset from one another by 90°, and with claws  11  of sprocket wheel combination  3  and planetary gear carrier  12  fitting into the slots with a limited amount of tangential clearance and a greater amount of radial clearance. This arrangement does not allow the transmission of radial or axial vibrations produced by free crankshaft end  2   a  to planetary gear carrier  12 . The transmission path from planetary gear carrier  12  to sleeve  17   a  via one-way clutch  22  is therefore also free of radial and axial vibrations produced by crankshaft  2 , which has a positive effect on the noise level and service life of all components of planetary transmission  1 . 
     At a low engine speed, the application of hydraulic oil to cylindrical piston  30  in hydraulic oil chamber  33  presses brake pads  24  against brake disk  23  of floating ring gear  17  and against axial stop  35  of mounting device  25 . This holds ring gear  17  in place above mounting device  25  on end shield  19  so that planet gears  15  rest on or roll off of ring gear  17 . While rolling, planet gears  15  rotate around their bolts  13  and drive sun gear  16  in the rotational direction of planetary gear carrier  12 . The mechanism thus gears up to a higher speed according to the ratio between the number of teeth in ring gear  17  and the number of teeth in sun gear  16 . 
     As the engine speeds up from a certain speed, brake disk  23  and brake pads  24  disengage from one another. Because there is no torque support on ring gear  17 , planetary gear carrier  12  engages with one-way clutch  22 , thereby coupling sleeve  17   a  or belt pulley  21  with crankshaft  2  via vibration isolator  8  in a 1:1 ratio. Planetary transmission  1  now rotates with ring gear  17 , planetary gear carrier  12 , planet gears  15 , and sun gear  16  as a single unit without performing any efficiency-reducing relative movements. Since belt pulley  21  is driven directly, the accessory assemblies are prevented from racing, since the rotational speed of belt pulley  21  equals the rotational speed of crankshaft  2 . Because coupling with belt pulley  21  takes place via vibration isolator  8 , the torque of crankshaft  2 , but not its radial or axial vibrations, is transmitted to sleeve  17   a  with belt pulley  21 . In both modes of operation, the drive mechanism is therefore free of wear- and noise-promoting vibrations of the crankshaft. Because it is positioned in the timing box, planetary transmission  1  is always well lubricated, which has a positive effect on its efficiency and service life.