Abstract:
Engine accessory drives are used with internal combustion engines to drive one or more accessories and are conventionally driven off a front end drive assembly. However, driving the accessories off the front end drive assembly has implications in respect of both increased engine noise and extended engine length. An engine accessory drive in accordance with this invention reduces engine noise and engine length. An engine accessory drive for transmitting a force between a first end ( 2 ) and a second end ( 3 ) of an engine ( 1 ) comprises a primary drive ( 18 ) locatable at the first end ( 2 ) of the engine.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to a drive for one or more engine accessories and, in particular, to a drive for transmitting force between the ends of an engine and to an engine including the drive.  
         BACKGROUND  
         [0002]    In internal combustion engines of certain configurations, for example engines with four in-line cylinders, excitations are created from engine out-of-balance forces and couples or moments generated by the rotating and reciprocating engine component masses. These excitations may be undesirable, particularly in mobile vehicles into which the engines may be fitted.  
           [0003]    The transmission of engine excitations into a vehicle may be reduced by means of flexible engine mountings, although it is desirable in some vehicles, such as frameless tractors, to incorporate balance shafts driven by the engine to counteract such excitations.  
           [0004]    Balance shafts are typically driven by a dedicated drive from a gear located at the front end of a crankshaft, and thus it is usual for the balance shaft assemblies to be installed within the sump of an engine, to be closely adjacent to the crankshaft. The balance shaft assembly will thus take up space that could beneficially be used for oil containment. A balance shaft assembly located in a sump may also cause aeration of the engine lubricating oil and may further be difficult to access for servicing.  
           [0005]    Engines are typically provided with front end accessories in the form of alternators, fans, power steering pumps, air conditioning pumps and the like. A front end accessory drive is typically provided by a pulley in communication with the engine crankshaft nose (i.e. externally of the engine). However, direct communication between the pulley and the crankshaft nose results in significant engine noise. More particularly the pulley, being typically disc or bell-like in construction, acts like a loud speaker to transmit engine noise from the engine.  
           [0006]    Further, the crankshaft pulley is generally located at an end of the engine that is frequently relatively exposed to the radiator air intake opening of the vehicle, thus the engine noise emitted via a crankshaft pulley may add significantly to the vehicle&#39;s ‘drive-by’ noise.  
           [0007]    Moreover, a seal must be provided at the front end of the engine at the crankshaft to prevent oil leakage and dirt ingress. However, such a seal is vulnerable to damage due to shaft rotation and dirt contamination.  
           [0008]    The present invention sets out to overcome these and other disadvantages of the prior art.  
         SUMMARY OF THE INVENTION  
         [0009]    According to the invention there is provided an engine accessory drive comprising a primary drive locatable at a first end of the engine; a first balance shaft externally mountable of the engine and drivable by said primary drive; a secondary drive locatable at a second end of the engine and drivable by said first balance shaft; a second balance shaft externally mountable of the engine and drivable by said secondary drive; and an engine accessory drivable by said secondary drive. The invention also encompasses an engine including such an engine accessory drive. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    Embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which:  
         [0011]    [0011]FIG. 1 is an isometric view from the rear of an engine provided with a drive for one or more front end accessories according to the invention, and  
         [0012]    [0012]FIG. 2 is an isometric view from the front of the engine of FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0013]    [0013]FIGS. 1 and 2 show an engine  1 , having a first end  2  and a second end  3 , provided with a drive  4  of the invention. In the present embodiment the first end  2  of the engine  1  is a rear end  2  of the engine  1 . The second end  3  of the engine  1  is a front end  3  of the engine  1 . The drive  4  is located at the rear end  2  of the engine  1  and is therefore a rear end drive  4 .  
         [0014]    The engine  1  is provided with a first balance shaft assembly  7  and a second balance shaft assembly  8 . The first and second balance shaft assemblies  7 ,  8  include, respectively, first and second balance shafts  9 ,  10  mounted in respective first and second tubular housings  12 ,  13 . A balance shaft design that may be used with this invention is illustrated in commonly-owned British Patent Application No 0106852.7 filed on 20 Mar. 2001.  
         [0015]    The first and second balance shaft assemblies  7 ,  8  are mounted on opposite first and second sides  14 ,  15  respectively of the engine  1  in a diametrically opposed configuration about a centreline  16  of a crankshaft  17  of the engine  1  and are offset vertically with respect to the centreline  16 .  
         [0016]    The first shaft  9  is in communication with a primary drive  18  in the form of a rear end drive assembly  18  of the drive  4  at the rear end  2 . The rear end drive assembly  18  is located at the rear end  2  of the engine  1  between the engine and a flywheel (not shown). More particularly, the first shaft  9  is provided with a toothed drive gear  19  at a rear end thereof which meshes with an idler gear  20 . The idler gear  20  in turn meshes with a crankshaft gear  21  mounted on a flywheel end of the crankshaft  17 .  
         [0017]    It will be appreciated that the primary drive  18  could take other forms. In particular the drive gear  19  could be driven directly from the crankshaft gear  21 , or via any other gear train that is driven by the crankshaft  17  and located at or near the rear end  2  of the engine  1 . For example, the drive gear  19  could mesh with a gear that is provided on a side  14  or  15  of the engine  1  at or near the rear end  2 , the gear at the side  14  or  15  of the engine  1  typically being driven by the crankshaft  17  via appropriate internal or external gearing. The primary drive  18  could alternatively comprise or include a belt drive or a chain drive.  
         [0018]    Thus the first balance shaft  9  is drivable by the rear end drive  4 .  
         [0019]    The first shaft  9  of the first balance shaft assembly  7  extends from the rear end  2  of the engine  1  to the front end  3  of the engine  1 . Similarly, the second shaft  10  of the second balance shaft assembly  8  extends from the rear end  2  of the engine  1  to the front end  3  of the engine  1 .  
         [0020]    In use, as the crankshaft  17  is rotated in known manner, the crankshaft gear  21  drives the idler gear  20 , which in turn drives the first balance shaft drive gear  19  to rotate the first balance shaft  9  of the first balance shaft assembly  7 . The first balance shaft  9  transfers the torque imparted to it from the crankshaft gear  21  and idler gear  20  to the front end  3  of the engine  1 . Thus, the first balance shaft  9  takes a driving force from the rear end  2  of the engine  1  and transmits or transfers the force to the front end  3  of the engine  1 . As described further below, the driving force can be exploited at the front end  3  of the engine  1  to drive one or more engine accessories.  
         [0021]    The first balance shaft  9  is provided with a toothed pulley  22  at a front end  23  thereof. A secondary drive  24  in the form of a synchronous toothed belt  24  extends between the toothed pulley  22  and a second toothed pulley  25  at a front end  26  of the second balance shaft  10  on the opposite side of the engine  1 . The secondary drive  24  is therefore drivable by the first balance shaft  9 , while the second balance shaft  10  is not driven directly by the rear end drive assembly  18  but by the toothed belt  24 . As the balance shaft  9  is driven by the primary drive  18  of the engine  1 , the drive is transferred to the front end  3  of the engine  1  via the balance shaft  9  and is used to drive the second balance shaft  10  via the synchronous belt  24 . Thus the second balance shaft  10  is drivable by the secondary drive  24 .  
         [0022]    An engine accessory  30  in the form of an alternator  31  is located at the front end  3  of the engine over the first balance shaft assembly  7 . The alternator  31  is provided with an alternator pulley  32  for engaging the belt  24 , so that the alternator  31  is drivable by the secondary drive  24 . A lower idler pulley  33  is mounted at the front end  3  of the engine  1  below the first balance shaft assembly  7 . The lower idler pulley  33  may alternatively be an accessory drive pulley.  
         [0023]    The front end  3  of the engine  1  is further provided with a water pump pulley  34  which facilitates passage of the synchronous belt  24  between the first balance shaft toothed pulley  22  and the alternator pulley  32 . The water pump pulley  34  and the alternator pulley  32  are in communication with, respectively, a water pump  35  and the alternator  31  to drive the water pump and the alternator.  
         [0024]    It will be appreciated that, in an alternative embodiment of the invention, the second balance shaft  10  could be directly driven by the rear end drive assembly  18 .  
         [0025]    The belt  24  is provided with teeth  27  on a top face  28  and a bottom face  29  thereof so that the first and second balance shafts  9 ,  10  of the first and second balance shaft assemblies  7 ,  8  can be contra-rotated.  
         [0026]    It will be appreciated by those skilled in the art that the drive of the invention can drive other accessories  30  such as a fan, power steering pump, air conditioning pump, oil pump or the like.  
         [0027]    The rear end drive assembly  18  of the engine  1  including the first balance shaft drive pulley  19 , the idler pulley  20  and the crankshaft pulley  21  is configured so that the first shaft  9  of the first balance shaft assembly  7  is driven at twice engine speed.  
         [0028]    As the first and second balance shafts  7 ,  8  are driven from the rear end  2  of the engine  1 , there is no requirement to have a conventional crankshaft pulley at the front end  2 . Thus, the front end of the engine  1  can be sealed more easily. Also, as no drive is being taken off the front end of the crankshaft  17 , the conventional rotary seal that is typically used to seal the front end of the crankshaft  17  is not required.  
         [0029]    As this conventional seal is not required, and the conventional front end drive assembly is also not required, the engine can be made shorter. This is a particular advantage as engine manufacturers are being pressed to provide smaller engines whilst maintaining power output.  
       INDUSTRIAL APPLICABILITY  
       [0030]    The drive of the invention finds application in engines where it is desired to eliminate a conventional front end drive assembly to reduce engine noise and to reduce engine length.  
         [0031]    The invention finds particular application in engines employing balance shafts where the balance shafts can be driven from the rear of the engine yet transfer power between the rear of the engine and the front of the engine. In an in-line four-cylinder engine, the balance shafts are required to rotate at twice engine speed, hence the load transmitted by pulley  22  to the synchronous belt  24  at any given point in time will be less than if the pulley  22  were rotating at a lower relative speed.  
         [0032]    The drive of the invention also releases the front end of the engine to make the crankshaft available as a power take-off point for accessories such as a gearbox, pump or the like if desired. However, this would entail the introduction of a crankshaft oil seal, thus negating some of the advantage of the invention.  
         [0033]    Modifications and improvements may be made to the foregoing without departing from the scope of the present invention.