Abstract:
A hub drive has a tubular housing suspended in a vehicle, and a motor in one, inboard end of the housing, and a gearbox in the other end. A hub is driven by the gearbox and is journalled on the housing. A gallery is defined between the motor and housing to receive lubricant from an external connector to cool the motor before delivery via a passage to a rotor of the motor, and thence to the gearbox to lubricate the gearbox. The drive is dismantleable without removal of the vehicle wheel, from the open ends of the housing. A gear change mechanism permits minimisation of the motor while still providing a wide range of torque and speed capability.

Description:
BACKGROUND OF THE INVENTION 
   1) Field of the Invention 
   The present invention relates to hub drives for vehicles, in particular a steerable land vehicle. 
   2) Description of Related Art 
   Hub drives are known in hybrid vehicles comprising four or more driven wheels each provided with an independent electric motor driving a gearbox mounted in the hub of the wheel. Power for the motors is usually provided by a battery, which is itself normally charged by a combustion engine mounted in the vehicle. Such an arrangement is efficient for vehicles operating in various conditions such as public transport. They are also effective for certain military vehicles for providing stealth operation occasionally when the combustion engine is temporarily stopped. 
   The requirements for hub drives are multifarious. They should be light since they are mounted on unsuspended parts of the vehicle, yet they need to meet respectable power expectations. Indeed, such expectations are not just in respect of peak torques that the motor and associated gearbox deliver (perhaps in the region of 20,000 Nm, with continuous torque at about half this), but also in respect of the instantaneous torques they may experience in the field. Such torques may be generated, for example, through forced acceleration due to the vehicle dropping onto a wheel from a height. Such torques that the drive might be expected to handle in some vehicles are in the region of 70,000 Nm. 
   Hub drives also need to be accessible, so that they can be serviced easily when faults develop. They require effective braking systems. Braking torque requirements are invariably much higher than required drive torques. 
   Frequently, it is desirable to employ the motor, at least partially in this respect, to assist braking and feedback power to the battery charging circuit. An efficient control system is also required to synchronise drive to each wheel to ensure efficient operation, and this may include anti-slip and anti-lock functions, yaw control and vehicle steering. 
   Hub drives should be reliable, particularly in military vehicles. Active control of tyre pressures is also desirable in such vehicles, and facilities for this impact the design of hub drives. 
   WO-A-9723363 discloses a drive having a motor in a casing forming a frame suspended in the vehicle. The motor drives a shaft forming a sun wheel for a planetary gearbox, whose planet gears drive a hub rotationally mounted on an extension of the frame around the shaft. A clutch selectively locks a planet wheel to the frame to transmit drive. 
   U.S. Pat. No. 5,163,528 and U.S. Pat. No. 5,014,800 both disclose a wheel motor having a stator fixed to a casing and a rotatable rotor and an integrated reduction gear. 
   U.S. Pat. No. 4,389,586 discloses a wheel drive having an inboard mounting frame tube incorporating planetary gears and an motor removal from an outboard side, the wheel being mounted on large diameter bearings on the frame tube. 
   U.S. Pat. No. 5,472,059 discloses a frame on the inboard side of which is mounted a motor whose drive shaft extends through the frame and on a neck of which frame is mounted a wheel hub. A planetary gearbox is on the outboard end of the frame and shaft and drives the hub. 
   U.S. Pat. No. 5,382,854 discloses a wheel drive in which a stator is fixed in a frame element, and a rotor drives the sun wheel of a planetary reduction gear disposed within the confines of the rotor and arranged to drive a hub rotationally mounted in the frame. The frame forms a sealed casing receiving oil which is circulated to both cool the motor and lubricate the planetary gear system. 
   In none of the aforementioned arrangements is substantial dismantling of the drive possible without removing the wheels of the vehicle. 
   BRIEF SUMMARY OF THE INVENTION 
   In accordance with a first aspect of the present invention, a hub drive system for a vehicle, comprising: 
   a) a tubular housing suspended by the vehicle and having an inboard and an outboard end; 
   b) a wheel hub rotationally mounted on the outboard end of the housing; 
   c) an electric motor disposed in the inboard end of housing; 
   d) a planetary gearbox, disposed in the outboard end of the housing and driven by the motor through a hollow primary shaft; 
   e) an output flange of the gearbox operatively connected to the hub, 
   f) a casing for the motor; 
   g) a stator in the casing; 
   h) a hollow rotor rotationally mounted in the casing and operatively connected to the primary shaft of the gearbox; 
   i) a gallery defined between the housing and casing and into which a lubricant for the gearbox is injectable to cool the motor; 
   j) a passage in the casing to deliver lubricant from said gallery to said hollow rotor to further cool the motor; and 
   k) said rotor being arranged to deliver said oil to the primary shaft to lubricate the gearbox. 
   The motor casing preferably has a substantially cylindrical outboard end sealed and centred in the housing by an O-ring. 
   The casing preferably is a sliding fit in the housing to permit inboard access to the motor without any need for a wheel removal. 
   In another aspect, the invention provides a hub drive system for a vehicle, comprising: 
   a) a tubular housing suspended by the vehicle and having inboard and outboard open ends; 
   b) a wheel hub rotationally mounted through hub bearings on the outboard end of the housing; 
   c) an electric motor disposed in the inboard end of the housing; 
   d) a planetary gearbox, disposed in the outboard end of the housing within the radial confines of said bearings and driven by the motor through a primary shaft; 
   e) an output flange of the gearbox detachably connected to the hub and closing the outboard end of the housing; wherein 
   f) without removing the wheel, the motor is removable inboard of the housing and the gearbox is dismantleable primarily outboard of the housing. 
   The motor preferably drives a primary shaft of the gearbox, which shaft is rotationally supported in the hub. The other, inboard end of the primary shaft is journalled in the motor. The motor preferably has a casing in which is fixed a stator and in which is rotationally journalled a rotor. In which event, the primary shaft is preferably journalled in the motor through the rotor. 
   The gearbox preferably comprises two stages of gear reduction and a gear change mechanism. 
   The gear change mechanism preferably comprises a shift gear ring for a first planet gear carrier rotationally mounted on the primary shaft and driving the hub, which shift gear ring is lockable to one of the primary shaft and the housing by a shift mechanism. 
   The planet gear carrier may drive the hub through one or two fixed ratio gear sets. 
   The shift mechanism may comprise a shift element slidable between two positions, in a first position locking the shift gear ring to a housing gear ring, and in a second position locking the shift gear ring to a primary shaft gear ring. 
   The shift element may include a ferromagnetic disc axially shiftable by solenoids mounted in the housing. 
   Alternatively, the shift element may comprise a magnetic sleeve shiftable by an induction coil mounted in the housing. 
   The gear change mechanism may further include active speed control of the motor during gear change to adjust dynamically the motor speed to the requisite speed commensurate with the desired gear ratio and when said shift element is in a neutral position intermediate said first and second positions and in which neither said housing gear ring nor said primary shaft gear ring is locked to the shift gear ring, said active speed control comprising a motor speed sensor, a hub speed sensor and a control arrangement to accelerate or decelerate the motor in dependence upon which gear is selected. The control arrangement may be in software. 
   A brake disc is preferably mounted on the hub and brake callipers mounted on the housing. 
   In another aspect, the present invention provides a hub drive system for a vehicle, comprising: 
   a) a tubular housing suspended by the vehicle and having inboard and outboard open ends; 
   b) a wheel hub rotationally mounted through hub bearings on the outboard end of the housing; 
   c) an electric motor disposed in the inboard end of the housing and comprising a stator fixed with respect the housing and a rotor journalled for rotation in the housing; 
   d) a planetary gearbox, disposed in the outboard end of the housing and driven by the motor through a primary shaft coaxial with the rotor; 
   e) an output flange of the gearbox detachably connected to the hub and closing the outboard end of the housing; and 
   f) a gear change mechanism between the rotor and a first stage gear reduction of the gearbox to provide three options:
         i) to interpose a further gear reduction stage ahead of said first stage reduction;   ii) to disconnect drive of the motor from the gearbox; and   iii) to isolate said further gear reduction stage and connect drive from the motor direct to said first stage.       

   Preferably, said shift element has a third, neutral position in which the shift ring is locked to neither the primary shaft ring nor the housing ring. Said neutral position may be between said first and second positions, said shift element moving coaxially with respect to said primary shaft. 
   Said shift element may be a ring surrounding said primary shaft, it may be provided with ferromagnetic elements and it may be disposed within the confines of a gear shift coil fixed in the housing and adapted to move the shift element by magnetic interaction. 
   Preferably, said first stage gear reduction comprises a first sun gear, driven by the motor, planets, carried by a first planet carrier and driving said output flange, and a first planet ring fixed in the housing. Said first sun ring may be formed on said intermediate planet carrier. 
   The gearbox preferably has a second stage reduction after said first stage and directly driving said output flange. In which case, said second stage may comprise a second sun gear, driven by the first stage gear reduction, planets, carried by said output flange, and a second planet ring fixed in the housing, the second sun ring preferably being formed on said first planet carrier. 
   An air tube is preferably disposed in the rotor and primary shaft to deliver air from a port in the casing to a port in the hub for controlling tyre pressure of a wheel mounted on the hub. 
   The air tube may be arranged to increase the rotor contact surface area per unit volume of lubricant flowing past the rotor at any given instant. Moreover, said air tube is preferably fixed in the output flange, passages therein communicating with a port on the output flange to permit connection of a conduit to a tyre valve of a wheel mounted on the hub. In this event, it may be rotationally mounted in an inboard end plate of the motor, passages therein communicating with a port on the end plate to permit connection of a conduit from a source of air under sufficient pressure to control inflation of the tyre, a rotary seal being disposed between said air tube and end plate. 
   Said seal may be arranged to separate said passages in the endplate that communicate the air tube with said port on the end plate from said passage in the casing that delivers lubricant from said gallery to said hollow rotor. 
   The invention provides also a hub drive system that incorporates a combination of the aforementioned aspects of the present invention. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The invention is further described hereinafter, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is a side section showing the general assembly of a hub drive in accordance with the present invention; 
       FIG. 2  is an enlarged view of the top half of the drive in  FIG. 1 ; 
       FIG. 3  is an enlarged view of the bottom half of the drive in  FIG. 1 ; 
       FIG. 4  is a perspective view of the drive of  FIG. 1  from its outboard end; and 
       FIG. 5  is a perspective view of the drive of  FIG. 1  from its inboard end. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the drawings, a hub drive  10  comprises a housing  12  mounted in a vehicle through suspension joints  14 ,  16  fixed to the housing  12 . The housing  12  is essentially tubular having an inboard open end  18  and an outboard open end  20 . 
   In the inboard end  18  is disposed a motor  22  comprising a casing  24  in three parts. The casing  24  comprises an inboard end plate  24   a , an essentially cylindrical part  24   b  and an outboard end plate  24   c . Inside the casing  24  is fixed a stator  26 . Rotationally journalled between the end plates  24   a,c  is a rotor  28 . The rotor is journalled in bearings  30   a,b  and is provided with a through-bore  32 . 
   The rotor  28  drives a primary gear shaft  34  of a gearbox  36  disposed in the outboard end  20  of the housing  12 . The gearbox  36  is described further below, but terminates in a drive or output flange  38  which is connected to a hub  40  journalled on the housing  12  through bearings  42   a,b . The hub  40  carries a wheel rim  44  through a hub flange  45 . Also formed on the hub  40  is a brake disc  46 , brake callipers  47  (see  FIGS. 4 and 5 ) being mounted on the housing  12 . The brake callipers have linkages  49  for the connection of steering or tracking arms (not shown). 
   Turning to  FIG. 2 , the rotor  28  is a permanent magnet rotor driven by a rotating magnetic fields caused by fluctuating currents in the stator coils  26  under the control of a control system (not shown). Electrical leads (not shown) supplying power and control signals to the motor, as well as sensor signals from the motor and gearbox, pass through a connector  51 . The rotor  28  is splined to the end of the primary shaft  34  so that it rotates at the same speed as the rotor  28 . A shift mechanism  50  comprises a shift element  52  which is axially slidable with respect to the primary shaft  34  by a solenoid coil  54  mounted in a housing flange  56  forming part of the housing  12 . The shift element  52  has three positions, it being shown in a neutral position in the drawings. In a first position, a planet gear ring  58 , provided with a gear ring  60 , is free with respect to a housing gear ring  62 , fixed on the flange  56  and with respect to a primary shaft gear ring  64 , fixed on the primary shaft  34 . The planet ring  58  is journalled for rotation on the shaft  34  through bearing sleeves  59 . 
   When a low gear ratio is selected, the coil  54  urges the shift element  52  rightwardly in the drawings so as to lock gear rings  60  and  64  together. Rotation of the primary shaft  34  caused by rotation of the rotor  28 , is then transmitted directly to first planet ring  58  which accordingly rotates at the speed of rotation of the primary shaft  34 . On the primary shaft  34  is locked a sun ring  66 . Between that and an internal gear  68  on the planet gear ring  58  are a plurality of planet gears  70  carried by a first planet carrier  72 . In this low ratio gear, sun ring  66  and  68  rotate at the same speed as the primary shaft  34  and consequently communicate drive directly to the planet carrier  72  which therefore also rotates at the same speed as the primary shaft  34 . 
   Carrier  72  has sun gear  73  that drives planets  74  mounted on second planet carrier  76 . Planets  74  rotates inside first housing planet ring  78  so that second carrier  76  is driven to rotate but at a reduced speed compared with primary shaft  34 . 
   Second carrier  76  itself has a second gear sun gear  77  that drives planets  80  of a third stage reduction and which rotate in a second housing planet ring  82 . Planet rings  78 ,  82  are fixed in the housing  12  by flange  84  and securing bolts  86 . That flange also locates bearings  42   a,b  and hub  40  on the housing  12 . 
   Planets  80  are mounted on drive flange  38  which rotates at a further reduced speed compared with second planet carrier  76 . In this low ratio gear position, therefore, there are two stages of gear reductions provided by stages  73 , 74 , 76 , 78  and  77 , 80 , 82 , 38 . 
   When the shift element  52  is shifted leftwardly in the drawings, however, the high ratio gear is selected in which housing ring  62  is locked to the gear ring  60  of the planet ring  58 . Accordingly, planet ring  58  becomes locked with respect to the housing  12 . Drive from shaft  34  then passes through sun gear  66  to first planet carrier  72  at reduced speed via planets  70  rotating in planet ring gear  68 . Thereafter, the drive is as obviously previously described. But in this high ratio gear there is a third stage  66 , 70 , 68 , 72  of speed reduction. 
   In accordance with the first aspect of the present invention, an annular gallery  89  is defined between casing  24  and housing  12  between O-rings  92  and  94 . Referring to  FIG. 3 , an oil inlet port  96  permits connection of a high pressure oil supply (not shown) to the housing  12  to pump oil under pressure into the gallery inlet manifold  90   a . The oil flows around casing cylindrical part  24   b  cooling the stator coils  26  in the process and evolving into gallery outlet manifold  90   b . Here, a passage  93  is formed in the end plate  24   a  delivering the oil to a central bore  25  of the end plate  24   a . The rotor  28  is journalled on one of its ends in the bore  25  through bearing  30   b . A rotary seal  31  closes the inboard end of the bore  25 . The outboard end of the bore  25  is plugged by an air tube  97  rotationally supporting one end of an air tube  98  through a bearing  100 . A seal  102  seals the air tube  98  with respect to the bore  25 . The function of air tube  98  is described further below. 
   Therefore, oil in the bore  25  from the passage  93  has only one route out, which is through annular passage  104  defined between the bore  32  of the rotor  28  and the outside of air tube  98 . In passing along this passage, the rotor  28  is cooled by the oil flow. Given the narrow dimension of the annular passage  104 , and, indeed, the annular gallery  98  effective transfer of heat from the rotor and stator to the oil can be achieved. This is due to the large ratio of surface area of the parts to be cooled to the volume of oil flowing over those parts. The rate of flow of oil is, of course, dependent upon the pressure of the oil. 
   After cooling the motor  22 , the oil flows into the confines of gear box primary shaft  34 , which, like the rotor  28 , has a through bore  35 . Periodically along the shaft  34 , passages  106  through the shaft  34  permit oil to jet into the interior of the gearbox  36 . By this mechanism, the various gears in the gearbox are lubricated. Finally, the oil collects in a sump  108  where a passage  110  returns the oil to an outlet port  111  (see  FIG. 5 ) for re-circulation to the pump (not shown). 
   Drive flange  38  is bolted to hub  40  by a plurality of bolts  112  and sealed thereto by an O-ring  114 . Hub  40  is sealed to the housing  12  by lip seal  116 . This permits further passages  118  through the side of housing  12  to transport oil to the space  120  between the hub  40  and housing  12  and lubricate the bearings  42   a,b . In combination with the hub  40 , the drive flange  38  therefore serves as a closure cap for the open end  20  of the housing  12 . 
   Primary shaft  34  rotates at a different speed to the end flange  38  and is mounted therein on bearings  122 . Thus, with respect to the housing  12 , primary shaft  34  is mounted at its outboard end through bearing  122 , and bearings  42   a,b , and its other end through the rotor  28  and its bearings  30   a,b  and the location of end plates  24   a,c  in the housing  12 . Bearings  122  are mounted in a central bore  124  of the drive flange  38 . The bore is closed by a plug  126  in which is fixed air tube  98 . The plug  126  has a central chamber  128  in communication with the bore of the air tube  98 . The plug  126  also has passages  129 , communicating the chamber  128  with passages  130  in the drive flange  38  that terminate in connectors  132 . These connect conduits (not shown) to the inlet valves of tyres mounted on the wheel rim  44 . 
   The air tube  98  passes through a nut  134  that locates the primary shaft  34  with respect to the bearing  122 . The tube  98  continues along the bore of the primary shaft  34 , through the bore  32  of the rotor  28 , and past seal  102 . The air tube is mounted in bearing  100  in plug  97  and communicates, along passages  135  formed in the plug  97  and boss  137  fixed to the end plate  24   a , with conduit connector  136 . A conduit (not shown) is connectable to connector  136  to provide air under pressure to control inflation of the tyre on the wheel rim  44 . Thus, the seal  102  not only closes the outboard end of bore  25  and prevents the escape of oil therefrom, but also it seals air tube  98  and prevents air under pressure therein from escaping into the motor and gearbox. Indeed, given the respective oil and air pressures on either side of the seal  102 , that seal does not have to be so effective that it wears rapidly against the air tube  98 . 
   As can be seen most clearly from  FIG. 1 , the arrangement of the present invention permits the motor  22  to be withdrawn from the inboard end of the housing  12  while the wheel  44  of the vehicle is on the ground. There is no necessity, assuming sufficient room is provided between the rear of the housing  12  and the vehicle body (not shown) to separately support the vehicle and remove the wheel  44 . The same is true of the gear box  36 , which can be accessed by removing the bolts  112  and removing the drive flange  38  and primary shaft  35  and the planet carrier  76  and  72  retained thereon, along with sun ring  34  and planet ring  58 . Gear change mechanism  50  is, however, left in position and must be dismantled from the motor, inboard end of the housing  12 . Nevertheless, the entire drive system can be disassembled and serviced without the necessity to remove a wheel. This renders maintenance of the wheel drive very straightforward. By providing a gear change mechanism, so that the drive ratio between the motor rotor  28  and drive flange  38  can be changed, the size of the motor can be considerably reduced, whilst still meeting the dual requirements of high low-speed torque and high cruising speed. 
   Given that a control system is necessary to drive the motor  22  at an appropriate speed in synchronisation with the drive of other motors on the vehicle, it is straightforward to provide electrical actuation of the gear change mechanism, as described above. Indeed, one of the advantages of a gear change mechanism is the provision of a neutral position, so that drive to the gearbox from the motor can be disconnected when desired, or vice-versa. The ability to select neutral may be important in a fault condition when, for example, the motor or wheel speed cannot be detected. In this event, drive to a given wheel can be terminated and that drive put in neutral to minimise the effect of the fault. Moreover, since wheel speed and motor speed are monitored by the control system (primarily for the purposes of synchronisation with other wheels) it is also straightforward to change the speed of the motor when the gear change mechanism  50  is in neutral. This enables the motor speed to be synchronised with the new gear to be entered. In this way, mechanical synchronisation elements can be avoided. 
   A further possible feature is acceleration or deceleration of the motor in the instant before a particular gear is disengaged so as to remove torque from the gear change mechanism  50  when a gear is being disengaged. 
   Another feature of the hub drive is the external mechanical brake disc ( 46 ). Although regenerative braking can be employed through the motor acting as a generator during braking (so as to save energy, as well as assisting braking of the vehicle), the provision of a mechanical brake primarily permits a small motor to be employed. 
   Accordingly, the entire drive has relatively small dimensions, particularly in the axial direction, so that there is less cantilever between suspension elements and the wheel load, despite the necessity to provide sufficient room between the inboard end of the drive housing and vehicle body parts to permit removal of the motor. 
   The reader&#39;s attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. 
   All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. 
   Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
   The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.