Patent Publication Number: US-6712157-B2

Title: Portable power tool with rotation motor and grease lubricated angle drive

Description:
The invention relates to a portable power tool having a housing with a rotation motor and a grease lubricated angle drive including a pinion and a bevel gear located in a gear chamber and coupling the output shaft to the motor. 
     This type of tool is commonly used as grinding machines, power wrenches, drilling machines etc. where a good accessibility in cramped working areas and/or a good torque reaction control have high priority. However, a problem concerned with this type of tool relates to a limited service life of the angle drive. This is mainly due to a poor lubrication of the gear teeth of the pinion and bevel gear. Several attempts have been made to cure this problem with more or less discouraging results. 
     Angle drives for the above mentioned applications are lubricated with grease, supplied at the assembly of the angle drive and/or added at certain operation intervals. What always happens during tool operation is that the grease in the angle drive gear chamber is thrown off the gear teeth and is deposited on the walls of the gear chamber. The result is that after a while no grease is left on the gear teeth and there will be a dry gear teeth engagement. This is detrimental to the service life of the angle drive. 
     One way of obtaining a satisfactory lubrication is to add a certain amount of grease to the gear chamber at short intervals, either manually via a grease nipple or automatically by a grease dispensing device originally filled with a larger amount of grease. Even a dispensing device has to be refilled at some intervals, though. When the gear chamber eventually after repeated supply has been filled up with grease to a certain extent the angle drive has to be dismantled for emptying and/or replacing the grease. Introducing extra service intervals just for ensuring a good angle drive lubrication is undesirable since it decrease the efficiency of the tool. 
     Another way of controlling grease application on the gear teeth is to accomplish relocation of the grease already present in the angle drive gear chamber from areas of deposition toward the gear teeth, continuously or at certain operation intervals. 
     Still another way of accomplishing an acceptable grease supply to the gear teeth would be to fill up the gear chamber with grease to a very large extent, which would avoid the need for repeated replenishing of grease for the angle drive lubrication. Instead, another problem would occur in that a great part of the grease volume would be in a continuous contact with the gear teeth and be agitated to high temperatures due to viscous friction. That would result in a destruction of the grease where lighter constituents would be separated from heavier constituents, and the lubricating effect of the grease would be severely impaired. 
     The main object of the invention is to provide a power tool with an angle drive in which extra service intervals are avoided in that the gear chamber is originally filled with grease to a large extent, and in which the grease is protected from being unnecessarily agitated to high temperature levels by the gear teeth. 
     Another object of the invention is to protect the grease in the gear chamber from a continuous gear teeth agitation by providing a screen device in a close vicinity to the bevel gear, thereby covering a substantial part of the bevel gear teeth and preventing a great part of the grease volume from getting into contact with and replenishing continuously the bevel gear teeth with grease. This avoids hot agitating of the grease. 
     Further objects and advantages of the invention will appear from the following specification and claims. 
    
    
     A preferred embodiment of the invention is below described in detail with reference to the accompanying drawings. 
     In the Drawings: 
     FIG. 1 shows a longitudinal section through the forward end a power tool according to the invention. 
     FIG. 2 shows a side view of the angle drive and output shaft. 
     FIG. 3 shows a horizontal view illustrating a grease screen device with a lateral opening for the angle drive pinion. 
     FIG. 4 shows a horizontal view illustrating the underside of the bevel gear and a leaf spring element coupling for activating the grease relocating device. 
     FIG. 5 shows a horizontal view of the forward end wall of the angle drive gear chamber including a grease relocating device. 
    
    
     The power tool illustrated in the drawings is of the angle drive type and comprises a housing  10 , a rotation motor  11 , an output shaft  12  arranged in a certain angle relative to the rotation axis of the motor  11 , and an angle drive  13  coupling the output shaft  12  to the motor  11 . The angle drive  13  comprises a pinion  16  connected to the motor  11  and a bevel gear  17  secured to the output shaft  12 . The pinion  16  engages gear teeth on the upside of the bevel gear  17 . The output shaft  12  is journalled relative to the housing  10  in two roller bearings  18 , 19  and carries at its forward end a combined ball-type balancing unit and a mounting device  20  for attaching a working implement (not shown) to the output shaft  12 . For supporting and securing the working implement there is also provided a support disc  21  having a central splined opening  22  for receiving a matching clamping piece (not shown) for engaging the working implement. 
     In a close vicinity to the upper end surface of the bevel gear  17  there is mounted a stationary disc shaped wall element  24  forming a grease screen device. This wall element  24  is secured to the housing  10  by two screws  25  and is formed with a central opening  26  for receiving the output shaft  12  and a sleeve  27  with a hexagonal opening for the output shaft  12 , and a lateral opening  28  for the pinion  16 . See FIG.  4 . 
     The angle drive  13  comprises a gear chamber  30  having a forward end wall  31  supporting the forward output shaft bearing  18  and having a circular groove  32  concentrically disposed relative to the output shaft  12 . The groove  32  has a rounded V-shape and forms a circular movement path for a grease relocating element  33 . A coupling device  34  is mounted on the underside of the bevel gear  13  for activating and moving the grease relocating element  33  along the groove  32  at rotational movement of the output shaft  12  and the bevel gear  17 . This coupling device  34  comprises a leaf spring element  35  having a free end portion  36  which is pre-formed to reach axially below the upper edge of the grease relocating element  33  (see FIG. 2) so as to positively engage by its free end portion  36  the grease relocating element  33  and move the latter along the groove  32  at reverse rotation of the output shaft  12 . The leaf spring element  35  is secured to the underside of the bevel gear  17 . See FIG.  4 . 
     Before use of the power tool, the gear chamber  30  is filled up to a large extent, for instance to 70-90% of its volume, with lubricating grease, and because of the grease screen forming wall element  24  a great part of the grease volume is prevented from getting into contact with the teeth of the bevel gear  17  and is, thereby, prevented from getting into the engagement zone between the pinion  16  and the bevel gear  17 . This means that despite a high degree of grease filling in the gear chamber  30  a small part only of the grease volume will be exposed to agitation by the pinion and bevel gear teeth, and the temperature of the grease could be maintained at an acceptably low level. This is of great importance in order to avoid the grease from being destructed due to hot agitation and, thereby, loosing its lubricating properties. 
     Despite the above described grease screen arrangement a lot of grease will successively end up beneath the bevel gear  17 , i.e. at a location where it can not contribute to the lubrication of the angle drive gear teeth. This means that the circular groove  32  in the lower gear chamber end wall  31  is filled with grease. At reverse rotation movements of the output shaft  12 , normally occurring at change of working implement, the free end portion  36  of the leaf spring element  35  will engage the grease relocation element  33  and move the latter a certain distance along the groove  33 , thereby forcing some grease out of the groove  32  and up along the side walls of the gear chamber  30 . This means that some grease is returned from the deposition area underneath the bevel gear  17  to the active gear teeth contact zone. 
     Also at forward rotation of the output shaft  12  during normal operation of the tool the leaf spring  35  will accomplish some slow movement of the grease relocation element  33 , because at forward rotation the leaf spring element  35  sweeps over the grease relocation element  35  yielding axially elastically under a certain contact force and exerts a certain frictional drive force onto the grease relocation element  35 . This drive force is transferred via viscous friction in the grease layer inevitably present between the two parts and is repeated at the rotation frequency of the output shaft  12 . 
     In order to enhance the driving force between the leaf spring element  35  and the grease relocation element  33  during normal forward rotation of the output shaft  12  the grease relocation element  33  could at least partly be formed of a magnetic material, whereas the leaf spring element  35  comprises a ferro-magnetic material. Thereby is accomplished a magnetic pulling force on the grease relocation element  35  each time the leaf spring element  35  passes the latter. Since the rotation speed of the output shaft  12  is high there is a high frequency of pulling force pulses, caused by friction or friction/magnetic action, acting on the grease relocation element  35  resulting in a successive advancement of the grease relocation element  35  in the groove  32  and, hence, a successive relocation of grease from underneath the bevel gear  17  to active lubricating areas. 
     The invention is not limited to the above described example but may be varied within the scope of the invention as recited in the claims.