Patent Publication Number: US-2019178354-A1

Title: Chain tensioning in a hybrid drive module

Description:
TECHNICAL FIELD 
     The present invention relates to a hybrid drive module, and in particular to adjustment and tensioning of a continuous member in such hybrid drive module. 
     BACKGROUND 
     Hybrid powertrains for passenger cars are gaining interest and various solutions for such applications have been proposed during the recent years. Especially it has been suggested to provide the hybrid functionality as a separate module which is added to the existing powertrain. One example of an existing hybrid drive module includes a first sprocket which is intended to be connected to the crank shaft of the internal combustion engine indirectly via a dual mass flywheel and a disconnect clutch, and an electrical motor, preferably a 48V electrical motor, being drivingly connected to a second sprocket. The sprockets are connected by means of a belt, thus forming a belt drive, in order to allow for various driving modes such as pure electrical driving, recuperation, traction mode, and boost. In this prior art system the electrical motor, the flywheel, the clutch, and the belt drive are formed as a standalone module which can be added to an existing powertrain. 
     To maintain tension in the belt drive such that torque can be transmitted via the belt, a belt drive tensioning system is generally used. These systems are normally complex hydraulic or mechanical systems and therefore a simpler device and method for tensioning is desirable. 
     SUMMARY 
     It is thus an object of the teachings herein to provide an improved hybrid drive module overcoming the disadvantages of prior art solutions. 
     According to a first aspect, a method of performing regular maintenance in a hybrid drive module is provided. The hybrid drive module comprises a housing enclosing a continuous member drive, such as a chain drive or a belt drive, and the continuous member drive comprises a chain or a belt connecting an electrical motor with a crank shaft of an associated internal combustion engine via at least one coupling. The electrical motor is fastened with respect to the crank shaft via fastening elements. The method comprises: unfastening the electric motor from said motor&#39;s fastening elements; positioning the electric motor such that the crankshaft is a distance from the electric motor and such that tension in the chain or belt is at or above a pre-specified level; and re-fastening fastening elements such that the electric motor is maintained at the distance from the crankshaft. The method allows tension to be maintained in the drive of the hybrid drive module without complex tensioning mechanisms. 
     The distance may be the straight-line distance between the rotating axes of a first sprocket arranged at a fixed position relative to the electrical motor and a second sprocket being arranged at a fixed position relative to the crank shaft. 
     In an embodiment a force is applied to the motor to position the motor and increase tension in the chain or belt. The force may be applied continuously during re-fastening. The application of the force to the motor, and not to the sprockets or to the chain/belt simplifies installation. 
     In a second aspect a hybrid drive module is provided. The hybrid drive module comprises a housing enclosing a continuous member drive which comprises a chain or belt connecting an electrical motor with a crank shaft of an associated internal combustion engine via at least one coupling. The electrical motor is fastened with respect to the crank shaft via fastening elements and the electric motor is configured to be repositionable such that tension in the chain or belt is increased. 
     In an embodiment of the hybrid drive module tension is achieved exclusively by positioning of the electrical motor with respect to the crank shaft. 
     In a third aspect a hybrid vehicle is provided. The hybrid vehicle comprises a hybrid drive module according to any of the disclosed embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the teachings herein will be described in further detail in the following with reference to the accompanying drawings which illustrate non-limiting examples on how the embodiments can be reduced into practice and in which: 
         FIG. 1  shows a schematic outline of a hybrid drive module according to an embodiment; 
         FIG. 2  is a cross-sectional view of parts of a hybrid drive module according to an embodiment; 
         FIG. 3  is a an isometric view of parts of a hybrid drive module according to an embodiment; 
         FIG. 4  is an isometric view of a cassette for closing the housing of a hybrid drive module according to an embodiment; 
         FIG. 5  is a cross-sectional view of parts of an electrical motor for use with a hybrid drive module according to an embodiment. 
         FIG. 6  is an isometric view of parts of a hybrid drive module comprising an electric motor according to an embodiment; and 
         FIG. 7  is a schematic outline of the electric motor and first and second sprockets. 
     
    
    
     DETAILED DESCRIPTION 
     Starting in  FIG. 1  a schematic layout of an engine assembly  10  of a vehicle is shown. The vehicle is typically a passenger car, and the engine assembly comprises an internal combustion engine  20  and a hybrid drive module  100  according to an embodiment. As will be explained in the following the hybrid drive module  100  is mechanically connected to a crankshaft  22  of the internal combustion engine  20  in order to provide additional drive torque to a transmission (not shown) arranged in series with the hybrid drive module  100 . Hence, the transmission is also connected to the crank shaft  22  as is evident from  FIG. 1 . 
     The hybrid drive module  100  comprises an electrical motor  110  and a continuous member drive  120 , here in the form of a chain drive, connecting the electrical motor  110  with the crank shaft  22 . The electrical motor  110  is for this purpose driving a first sprocket  122  of the chain drive  120 , whereby upon activation of the electrical motor  110  rotational movement of the first sprocket  122  is transmitted to a second sprocket  124  of the chain drive  120  via a chain  126 . 
     The second sprocket  124  is drivingly connected to the crank shaft  22  via one or more couplings. In the embodiment shown in  FIG. 1 , the second sprocket  124  is connected to the output of a disconnect clutch  130  receiving driving torque from a dual mass flywheel  140 . For parallel two-clutch systems, commonly denoted hybrid P2 systems, the disconnect clutch  130  is often referred to as the C0 clutch. The dual mass flywheel  140 , which could be replaced by another torsional damping/absorption device, receives input torque directly from the crank shaft  22 . However, for the purpose of the present embodiments either the disconnect clutch  130  and/or the dual mass flywheel  140  (or its substitute) could be omitted or replaced by another suitable coupling. 
     Also illustrated in  FIG. 1  is a further optional clutch  150 , here representing a launch clutch. Again referring to P2 systems, the launch clutch is often referred to as the C1 clutch. The launch clutch  150  is arranged downstream, i.e. on the output side of the hybrid drive module  100  upstream the transmission. It should be realized that the launch clutch  150  could be replaced by a torque converter or similar. 
     The electrical motor  110  is preferably a 48V motor/alternator which thus can be used to provide hybrid functionality to the existing powertrain of the vehicle. For other embodiments, also possible within the scope of this application, high voltage hybrid electrical motors may be utilized. More specifically, the provision of the chain drive  120  allows for modularity with high voltage hybrid electrical motors in comparison to if a belt drive would be used. A belt drive could never accommodate the much higher loads provided by a more powerful high voltage hybrid electrical motor. 
     The electric motor  110  is adjustable within the plane of the first and second sprockets  122 ,  124 . Tension can be adjusted in the chain  126  by positioning of the electrical motor  110 . In other words, tension in the chain drive  120  of the hybrid drive module  100  may be achieved exclusively by positioning of the electrical motor  110 . As opposed to belt drive systems the chain drive  120  maintains sufficient tension for driving torque transfer to the electrical motor  110  and for driving torque transfer from the electrical motor  110  without chain tensioning components. 
     The electric motor  110 , and hence first sprocket  122 , can be positioned with respect to the second sprocket  124  via at least one fastening element  111  (see  FIG. 6 ). The fastening element could, for example, be at least one bolt configured to pass through a hole in the casing of the electric motor  110 .  FIG. 6  shows a fastening element  111  for the electric motor  110  being two bolts provided in two holes provided in the casing of the electric motor  110 . In  FIG. 6  the casing of the electrical motor  110  comprising the holes extends orthogonally to the axis of rotation of the shaft of the electrical motor  110 . In  FIG. 6  the fastening elements  111  fix the motor to the engine block  10 ,  20 , however, the fastening elements could also allow the motor to be fixed to the ear structure  180  as will be later explained with reference to  FIG. 3 . In  FIG. 6 . a second set of fastening elements  112  are shown. The second set of fastening elements  112  are two slots  112  provided in the casing of the electric motor  110 . Each slot may be configured to receive a bolt or any other such means for fixing the electric motor  110  to the ear structure  180 . The form of the slots allow the motor  110  to be moved in a pre-determined range of motion during fixing of the motor  110  to the ear structure  180  and/or the engine block  10 ,  20 . 
     The first fastening elements  111  may for this purpose also comprise a slot extending in either the casing of the electric motor  110  or the engine block  10 ,  20  or the ear structure  180 . The electric motor  110  is adjustable with respect to the second sprocket  124  such the distance between the first sprocket  122  and second sprocket  124  is adjustable. This is due to the fact that the position of the first sprocket  122  is fixed relative the electrical motor  110 . 
     Through the combination of the chain drive  120  and the adjustable electric motor  110  the sprockets  122 ,  124  can remain reliably connected, even at high speeds and high torques, without the use of additional tensioning systems which are often heavy and expensive. 
     During long term operation, as is known to the person skilled in the art, the chain  126  may become elongated. A method for re-establishing tension in the elongated chain  126  is to unfasten the electric motor  110  from said motor&#39;s  110  fastening element  111 , and to subsequently applying a force to the electric motor  110  such the motor  110  is repositioned. The electric motor  110  can be repositioned at a distance such that the first sprocket  122  is a greater distance d (see  FIG. 7 ) from the second sprocket  124  and such that tension in the chain  126  is at or above a pre-specified level. After positioning, the fastening elements  111  can be re-fastened such that the electric motor  110  and first sprocket  122  are maintained at distance d from the second sprocket  124 . During re-fastening a force may be continuously applied to the electric motor  110 . 
     As shown in  FIG. 7  the distance d is the straight-line distance d between the rotating axes of the first sprocket  122  and the second sprocket  124 . When the fastening elements  111 ,  112  comprise slots the motor may be moved such that it is displaced along the length axis of the slots. An advantage of the above method and structure is that the first and second sprockets  122 ,  124 , do not need to be adjusted individually to create tension in the chain  126 . Furthermore, the chain itself  126  does not need to be adjusted. 
     The entire hybrid drive module  100  also comprises a lubrication system which according to the various embodiments presented herein is based on principle that the chain  126  will assist in circulating lubrication oil to the rotating parts of the hybrid drive module  100 , i.e. the one or more couplings  130 ,  140 . It should further be noted that in case of also utilizing a launch clutch or torque converter  150 , this component could also be arranged within the hybrid drive module  100  thus taking benefit from the same lubrication system. 
     In some embodiments the lubrication system could be supported by an oil pump  160 . 
     Lubrication oil should within the context of this disclosure be interpreted broadly to cover any automatic transmission fluid, engine oil, or other type of lubricating and cooling fluid suitable for the particular application. 
     One major advantage of the proposed solution is the small amount of package space required. Now turning to  FIG. 2  a cross-section of parts of the hybrid drive module  100  are shown, illustrating the compactness of the hybrid drive module  100 . 
     The crank shaft  22  provides input torque to a primary inertial mass  142  of the dual mass flywheel  140 . A secondary inertial mass  144  of the dual mass flywheel  140  is in turn connected to an input side of the disconnect clutch  130 , here in the form of a limited slip coupling. The output side of the disconnect clutch  130  is connected to the second sprocket  124  carrying the chain  126 . Preferably, one or more springs may be provided connecting the internal masses  142 ,  144  to each other such that the secondary inertial mass  144  may rotate relative the primary inertial mass  142  whereby the springs may deform causing a reduction of torsional vibrations being transmitted from the internal combustion engine  20 . 
     The dual mass flywheel  140  and the disconnect clutch  130  are arranged concentrically around the crank shaft  22 , thereby reducing the axial length of the hybrid drive module  100 . 
     In  FIG. 3  the engine assembly  10  is again shown. As can be seen the hybrid drive module  100  is enclosed in a housing  170 . The housing  170  is formed by an end section  24  of an engine block  26  of the internal combustion engine  20 , an ear structure  180  attached to the end section  24  and extending outwards from the engine block  26 , and a cassette (see  FIG. 5 ) sealing the housing  170 . The ear structure  180  is provided to allow space for the electrical motor  110  and the first sprocket  122  of the chain assembly  120 , while the dual mass flywheel  140 , the disconnect clutch  130 , and the second sprocket  124  are dimensioned to fit within a circular area within the end section  24 . 
     The housing  170  forms a reservoir  190  by means of an insert  200  arranged within the ear structure  180 , optionally extending into the circular area within the end section  24 . The reservoir  190  is arranged to contain oil during operation, and to provide lubrication to the chain  126  during operation. 
     The provision of the reservoir  190  allows for a completely passive lubrication system, meaning that no external oil pumps or channels are required to provide sufficient lubrication to the rotating parts of the hybrid drive module  100 . More specifically, during operation the chain  126  will throw oil at the upper end of the first sprocket  122 , so that the oil will flow into the reservoir  190 . When the oil level inside the reservoir reaches a certain height an outlet provided in the reservoir  190  will allow for oil to exit the reservoir  190  at a position where the chain  126  meets the first sprocket  122 . By such configuration the chain  126  will be lubricated by its own motion. 
     The amount of oil which is not transported to the reservoir will eventually fall downwards to the bottom of the housing  170 . Since the ear structure  180  is arranged at a vertical position slightly above the lowermost point of the circular area of the end section  26 , the oil will end up in the lowermost region of the circular area where the second sprocket  124 , the dual mass flywheel  140 , the chain  126 , and the disconnect clutch rotates. Hence, these rotating parts  124 ,  126 ,  130 ,  140 , especially the primary inertial mass  142  of the dual mass flywheel  140 , will pick up the oil and propel it around its perimeter. Optionally, the same oil may be passed through a circuit to the rotating parts for improved cooling and lubrication. Such circuit may e.g. include a heat exchanger for removing excessive heat from various components in the hybrid drive module  100 . 
     Eventually, this oil will again flow into the reservoir  190 . For this purpose the inlet of the reservoir  190  is dimensioned to receive oil primary from the chain, but also from the other rotating parts  130 ,  140 . 
     A magnet  216  is preferably arranged at the bottom of the reservoir  190  in order to attract any metal particles contained within the oil. Optionally the magnet  216  may be replaced by or in combination with a filter or other suitable means for cleaning the lubrication fluid during operation. 
     Now turning to  FIG. 4  a cassette  220  is shown. The cassette  220  forms a closure for the housing  170  and the cassette  220  is thus dimensioned to fit with the entire housing  170 , i.e. the end section  24  of the engine block  26  and the ear structure  180  attached thereto. The purpose of the cassette  220  is consequently to provide a sealed closure for the hybrid drive assembly  100 . 
     The embodiments presented above all share the same technical concept of utilizing a passive lubrication system for an entire hybrid drive module  100  using a chain drive  120  and a reservoir  190  by which lubrication oil may be circulated within the hybrid drive module  100 . 
     In  FIG. 5  an embodiment of the electrical motor  110  is shown. In this example the electrical motor  110  is configured not only to receive oil from the reservoir  190  for cooling and lubrication of the electrical motor  110 , but also to act as a pump in combination with the chain drive  120  for the entire lubrication system of the hybrid drive module  100 . 
     In particular, the rotational shaft  112  of the electrical motor  110  is provided with an axial inlet for receiving oil from the reservoir  190 . A passageway  113  inside the rotational shaft  112  transports the oil until it reaches one or more radial drillings  114 , where the oil exits and hits the rotor assembly  115 . As the rotor assembly is rotating, it will pull oil out of the shaft  112 , pass it across the rotor assembly  115 , and fling oil onto the end turns  116 . The coolant oil could optionally pass onto a heat exchanger used for the electronics to extract heat. 
     With the outlet holes  114  on the rotor assembly  115  at a radial distance from the center line of the shaft  112 , this will create a pumping action to pull the oil through. The oil could then drain back into the cassette  220  to be recirculated again. 
     An oil cooled motor  110  will allow for a much higher continuous performance level compared to a water cooled electric motor. This is due to the fact that the oil coolant is applied directly to the hot parts of the electric machine, i.e. the copper end-turns in the stator and onto the rotor assembly to cool the magnets. 
     Although the above description relates mainly to chain drives, it should be realized that the concept of adjustment and tensioning could be applied for other continuous member drives, such as belt drives. 
     It should be mentioned that the improved concept is by no means limited to the embodiments described herein, and several modifications are feasible without departing from the scope of the appended claims.