Abstract:
A hydraulic disc coupling ( 4 ) for an AWD vehicle has means for supplying cooling and lubricating oil to the disc package ( 12 ) of the coupling, said means including a shut-off valve ( 32 ) for shutting-off said supply at will. The shut-off valve ( 32 ) comprises an axially movable valve slide ( 42 ), provided with a transverse valve flange ( 44 ) for cooperation with a valve seat ( 45 ) in the coupling housing, the slide being actuatable in a closing direction by spring force and in an opening direction by a hydraulically operated ball ( 47 ), having an actuation end position in a sealing ball seat ( 51 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a shut-off valve in a hydraulic disc coupling for an AWD vehicle, the coupling having means for supplying cooling and lubricating oil to the disc package of the coupling, said means including the shut-off valve for shutting-off said supply at will. 
       BACKGROUND OF THE INVENTION 
       [0002]    As is well known in the art, an AWD (All Wheel Drive) vehicle can be provided with at least one hydraulic disc coupling for distributing the driving torque from the vehicle engine to all of the vehicle wheels. Especially, such a coupling may be provided in the drive line between the front axle and the wheels of the rear axle, most often in the vicinity of the rear axle differential. 
         [0003]    Sometimes, it may be desirable to use the AWD vehicle in a FWD (Forward Wheel Drive) mode. In this case the coupling is disconnected, i e its discs are separated from each other. 
         [0004]    By operating the vehicle with the coupling in a disconnect mode, rotating masses in the vehicle are reduced, leading to a lower fuel consumption. 
         [0005]    In a practical case a propeller shaft of the vehicle, possibly including one or two bevel gear transmissions, has a hydraulic disc coupling at one end and a simple coupling, for example a dog clutch, at the other end. In the disconnect mode both these couplings must be disconnected for obtaining the desired effect. 
         [0006]    A pump actuator system is disclosed in WO 2011/043722. In such a system the supply of hydraulic oil to the coupling piston is governed by the rotative speed of a pump. 
         [0007]    For obtaining the desired result in a disconnect mode, it may be of importance to reduce the drag torque within the disc package of the coupling by removing cooling and lubricating oil, that is supplied to the package in the connect mode. 
         [0008]    A gravity lubrication system may be used. Such a system may comprise a side reservoir for cooling and lubricating oil, which is supplied by gravity to the disc package and returned to the side reservoir by forces created by rotating disc coupling parts. 
         [0009]    A shut-off valve is provided to shut off the supply of oil in the disconnect mode and to reestablish the supply in the connect mode. The reestablishment is activated by hydraulic pressure controlling the coupling. 
         [0010]    The use of a normal slide valve as the shut-off valve has certain disadvantages. These disadvantages also apply in a second use of a shut-off valve, namely in a normal AWD coupling system without any disconnect/connect function. In a stand-by mode of such a coupling it may be advantageous to reduce or eliminate drag losses due to oil splashes from rotating parts in the coupling. 
         [0011]    A normal slide valve has a certain stroke and area. This means that a certain oil volume has to be branched-off to the shut-off valve from the control oil flow to the coupling, which negatively influences the coupling reaction time at the shift-over from disconnect to connect mode or from stand-by mode to torque transfer mode. 
         [0012]    A certain hydraulic pressure must be reached to activate and move a normal slide valve against the forces from sealings and a return spring. In a slide valve the sealing is primarily used for preventing oil leakage at intermediate and high pressure ranges (where response times in the AWD mode can be influenced). The friction of the sealing necessitates a higher return spring force, which means that the minimum pressure rises for two reasons. A high minimum pressure level will restrict the lowest possible torque transfer of the coupling in a negative way. 
         [0013]    Due to difficulties at the sealing manufacturing the diameter of the slide cannot be too small, as the friction then will be proportionally too high. This will be a disadvantage for the oil consumption mentioned above. 
       THE INVENTION 
       [0014]    It is accordingly a main object of the invention to provide a shut-off valve without the mentioned and other disadvantages. 
         [0015]    This is according to the invention accomplished in that the shut-off valve comprises an axially movable valve slide, provided with a transverse valve flange for cooperation with a fixed valve seat, the slide being actuatable in a closing direction by spring force and in an opening direction by a hydraulically operated ball, having an actuation end position in a sealing ball seat. 
         [0016]    In a practical embodiment the valve slide may have a control pin for engagement with the ball. 
         [0017]    A compression spring may be arranged to act on the valve slide in its axial direction. 
         [0018]    The ball seat may preferably be arranged in a ball cage, threadingly engaged in a housing bore, in which the valve slide is arranged. The control pin may extend into the ball cage. The ball cage may be provided with a stop ring for holding the ball in the ball cage. 
         [0019]    The ball can opposite the control pin be acted on by hydraulic pressure supplied through a housing bore. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The invention will be described in further detail below under reference to the accompanying drawings, in which 
           [0021]      FIG. 1  is a schematic view of a first embodiment of a rear axle architecture with a disconnect coupling of an AWD vehicle, 
           [0022]      FIG. 2  is a corresponding view of a second embodiment, 
           [0023]      FIG. 3  shows a hydraulic scheme for the coupling provided with a shut-off valve, 
           [0024]      FIG. 4  is a cross section through a portion of an AWD coupling with a shut-off valve according to the invention in a closed position, and 
           [0025]      FIG. 5  is the same cross section with the valve in an open position. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    A drive system of an AWD (All Wheel Drive) vehicle is well known in the art. Typical examples are shown in WO 2011/043722. Such a system has an engine, a front axle with a differential, an intermediate shaft or cardan shaft, and a rear axle with a differential. In order to distribute the torque not only to the front axle but also to the rear axle in accordance with the driving conditions, an electronically controlled wet disc coupling is arranged in the driveline to the rear axle, often in the intermediate shaft or otherwise close to the rear differential. This wet disc coupling will be further described below. 
         [0027]    Two embodiments of rear axle architectures for an AWD vehicle are shown in  FIGS. 1 and 2 . 
         [0028]    The first embodiment shown in  FIG. 1  has the intermediate shaft  1 , the rear axle  2  (axle halves  2 A and  2 B), the rear differential  3 , and the wet disc coupling  4 . The coupling  4  is arranged around the first rear axle half  2 A functionally between a ring gear  3 A and the housing of the differential  3 . 
         [0029]    The second embodiment shown in  FIG. 2  contains the same members  1 - 4 , but here the coupling  4  is situated in the first rear axle half  2 A, providing the same result as the first embodiment. 
         [0030]    Other embodiments are of course possible in an AWD vehicle. 
         [0031]    The function of the coupling  4  when driving the vehicle in an AWD mode is described elsewhere, for example in the mentioned WO 2011/043722. 
         [0032]    When it is desired to drive the AWD vehicle in an FWD (Forward Wheel Drive) mode, the disc coupling  4  is disconnected, i e its discs are separated for preventing them from transmitting any torque. The coupling  4  may be said to be in a disconnect mode. For enhancing this separation effect, the oil normally provided in the coupling  4  for lubricating and cooling its discs can be removed from the coupling. In order to reduce the acceleration of the rotating mass of the intermediate propelling shaft  1  and to eliminate the drag torque in bearings and sealings therefor, clutch means, preferably close to the front axle differential, may be provided to bring the intermediate shaft  1  to a standstill in FWD mode of the vehicle. 
         [0033]    When the AWD mode of the vehicle is to be resumed, the requirement may be that the disc coupling  4  is fully operable within a time of 0.4-0.5 s or even less, i e that the discs of the coupling are brought into engagement with each other. 
         [0034]      FIG. 3  is an overall illustration of the hydraulic means for actuating or controlling the disc coupling  4 . Reference is made to WO 2011/043722 for a full description of the actuating means. 
         [0035]    The coupling  4  comprises a disc package  12  actuated by means of a piston  13  received in a cylinder  14 . The piston  13  has a piston rod  13 ′. When the piston  13  is actuated by means of hydraulic pressure, the discs of the disc package  12  will get into contact with each other and establish driving contact between the two shafts to which they are connected. There is a return spring  15  of the compression type to bring the piston  13  back to its initial position, when the hydraulic pressure on the piston decreases. 
         [0036]    An electric actuator motor  16  drives an actuator pump  17  via a drive shaft  18 , which also drives a centrifugal regulator  19 . The position of the centrifugal regulator  19  controls the position of and flow through a pressure overflow valve  20 . 
         [0037]    Hydraulic oil for the hydraulic actuator system is contained in a reservoir  21 . It is sucked into the pump  17  through a hydraulic line  22  and is delivered therefrom towards the cylinder  14  through a main hydraulic line  23 . Depending on the position of the centrifugal regulator  19  and thus the pressure overflow valve  20 , a portion of and sometimes all of the hydraulic flow is diverted through a hydraulic line  24 , through the overflow valve  20  and back to the reservoir  21 . The result is that the hydraulic actuator pressure delivered to the cylinder  14  is governed by the centrifugal regulator  19 . 
         [0038]    By the provision of the pressure overflow valve  20 , creating an overflow of excess oil back into the reservoir  21 , the actuator motor  16  may be constantly running and will hereby have a very short reaction time to build up pressure in the system when needed, as it is already running, and thus less energy will be spent for accelerating rotating parts. 
         [0039]    Under normal operation conditions, when there is no need to have the coupling  4  engaged, the actuator motor  16  is running at a rotational speed below that at which the pressure overflow valve  20  closes. When there is a demand for engaging the coupling  4 , i e for actuating the piston  13 , a high current/voltage is supplied to the actuator motor  16 . The speed of the drive shaft  18  will go up, whereby the overflow valve  20  will be closed by the centrifugal regulator  19 . Conversely, if the rotational speed of the motor drive shaft  18  is lowered, the overflow valve  20  will be opened. 
         [0040]    This system may be called a pump actuator system, as opposed to an accumulator system. In this system the controlled actuator pressure is created and delivered by a pump, whereas in an accumulator system the controlled actuator pressure is delivered from an accumulator charged by a pump. 
         [0041]    When the FWD mode for the vehicle is to be accomplished, either at will by the driver or by software in the vehicle, the hydraulic pressure in the cylinder  14  is decreased, so that the return spring  15  disconnects the coupling  4  by separating its discs  12 . 
         [0042]    As already stated, the operational condition of the coupling  4  shall be resumed very quickly after a disconnection as described, say within 0.4-0.5 s or less. 
         [0043]    In a normal pump actuator system as described it would be difficult to reach the desired connect times after a disconnection, even if the pump displacement is increased several times in comparison with the needs at normal operation. 
         [0044]    The problem with the low connect times can be solved by reducing the effective piston area during the connect phase as is described below. 
         [0045]    A 3/2 directional solenoid valve  25  is arranged in a hydraulic line  23 A from the main hydraulic line  23  to a closed compartment of the cylinder  14  behind the piston  13 . The valve  25  has a solenoid  26  for its operational movement to the left in the drawing and a compression spring  27  for its return movement. In the drawing the valve  25  is in its normal or idle position assumed at AWD operation of the coupling  4 , and the solenoid  26  is energized for obtaining the connect mode after a disconnect mode. In this position, hydraulic oil is submitted through line  23  to the front side of the piston  13  but also through line  23 A to the back side of the piston  13 . By the presence of the piston rod  13 ′ at the back side of the piston  13  the result will be an effective piston area of some 15% in comparison with the area of the piston  13  in normal AWD operation. With a smaller area the required amount of hydraulic oil in the connect mode will be greatly reduced, and the piston travel will be faster to the “kiss point” between the discs  12  in the coupling  4 . Also, the regulating pressure will be higher, say 30-80% of maximum pressure, and accordingly the percentage pressure/torque accuracy will be much higher, as desired. 
         [0046]    During the movement of the piston  13  to the right in the drawing in the connect mode hydraulic oil will have to be transferred from the back side to the front side of the piston. This is illustrated in  FIG. 3  by a check valve  28  between the lines  23  and  23 A. However, for obtaining a minimal restriction of the oil flow, it is preferred to arrange one or more check valves in the piston  13  itself. 
         [0047]    In the valve position shown in  FIG. 3  the back side of the piston  13  is drained to the reservoir  21  through the valve  25 . 
         [0048]    The illustrated coupling  4  may be provided with a gravity lubrication system. For cooling and lubricating the discs  12  of the coupling  4 , hydraulic oil may be submitted by gravity from a hydraulic side reservoir  29  through a line  30  during operation. By forces created by rotating parts in the coupling  4 , the oil will be forced back to the side reservoir  29  through a line  31 . A shut-off valve  32  may be arranged in the line  30  for cutting off the supply of oil through the line  30  in the disconnect mode of the coupling  4  in order to reduce drag torque from the oil in the coupling. This valve  32  is operated by the hydraulic pressure in the line  23  through a line  33  and by a return spring  34 . 
         [0049]    The present invention is concerned with the design of the shut-off valve  32 . Reference is first made to  FIG. 4 , showing the valve in the same position as in  FIG. 3 , namely closed by spring force, corresponding to a disconnect mode of the coupling  4 . 
         [0050]    The cross section of  FIG. 4  is from a lower part of the housing for the coupling  4  with the disc package  12  in the upper part to the right. 
         [0051]    A housing compartment  40  is in contact with the side reservoir  29  ( FIG. 3 ) and thus contains hydraulic oil. A bore  41  connects the compartment  40  with the disc package  12  for the supply of cooling and lubricating oil. The bore  41  can be closed-off from the compartment  40  by means of the valve according to the invention, corresponding to the valve  32  in  FIG. 3 . 
         [0052]    The valve has a valve member in the form of a slide  42 , axially movable in a valve bore  43  in the housing. The slide  42  has a transverse valve flange  44  to be applied against a valve seat  45  in the housing around the bore  41 . The application force is provided by spring force, preferably by a compression spring  46  supported by the housing. This spring  46  corresponds to spring  34  in  FIG. 3 . 
         [0053]    The valve opening movement of the slide  42  to the left in the drawing against the force of the spring  46  is actuated by a ball  47 . This ball  47  is movably arranged in a ball cage  48 , threadingly and sealingly received in the bore  43 . The ball cage  48  has a center hole for a control pin  49  of the slide  42  in contact with the ball  47 . For keeping the ball  47  within the ball cage  48 , the latter is to the right in the drawing provided with a stop ring  50 . 
         [0054]    The ball  47  has a slightly smaller diameter than the cross-sectional diameter in the ball cage  48  and is—when moving to the left in the drawing—applied against a ball seat  51  in the ball cage  48 . 
         [0055]    The movement of the ball to the left in the drawing is controlled by oil pressure supplied through a housing bore  52 , corresponding to the hydraulic line  33  in  FIG. 3 . 
         [0056]      FIG. 5  corresponds to  FIG. 4  but shows the shut-off valve in an open position with the ball  47  engaging the ball seat  51  under the hydraulic pressure supplied through the housing bore  52 . The ball  47  has pushed the slide  42  to the left in the drawing against the force of the spring  46 , so that the valve flange  44  has been lifted from the valve seat  45  establishing connection between the housing compartment  40  and the housing bore  41  to the disc package  12 . 
         [0057]    The shut-off valve according to the invention provides a number of advantages: 
         [0058]    There are no sealing frictions, which means that the return spring  46  may be weaker and provide less counter-force and that the minimum pressure level will go down. 
         [0059]    By using a ball a leakage system will be obtained, when the valve I opened and the ball has reached its ball seat. 
         [0060]    The diameter of the ball can be kept small, leading to a much reduced consumed control volume, in practice without relevance. 
         [0061]    Modifications are possible within the scope of the appended claims, for example that the shut-off valve is arranged as a separate entity outside the coupling itself. 
         [0062]    Although the shut-off valve has been shown and described in its use in a hydraulic disc coupling for an AWD coupling, other similar uses for supplying cooling and lubricating oil in units in the drive line of a vehicle may be envisaged and are to be seen as included in the scope of the appended claims. Examples of such other units are transfer cases and final drives.