Abstract:
An inspection method of the present invention performs a step of giving the electric motor an instructing for rotating a foot shaft in a reverse direction and checking whether the foot shaft is rotating in the reverse direction, and a step of checking whether hydraulic pressure acting on the hydraulic pump has reached a predetermined pressure level. By checking a rotating direction of the electric motor, it is possible to check electrical connections. By checking the hydraulic pressure, it is possible to check whether there is any trouble in a hydraulic system. Namely, the present invention can perform an electrical connection check and a hydraulic pressure check in a collective fashion.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an inspection method for inspecting hydraulic pressure etc. of an electric drive apparatus as an inspection object. 
       BACKGROUND OF THE INVENTION 
       [0002]    In four-wheel-drive vehicles, where all of front and rear wheels are drive wheels, there would occur rotating speed differences between the left and right front wheels and between the left and right rear wheels, and thus, it is important to inspect respective drive systems of the vehicles. Heretofore, there have been proposed various methods for inspecting the drive systems of the four-wheel-drive vehicles, such as one disclosed in Japanese Patent No. 4191001 (hereinafter referred to as “the relevant prior patent literature”). 
         [0003]    According to the disclosure of the relevant prior patent literature, drive power is transmitted from a front-wheel differential gear, driven directly by an engine, to a rear-wheel differential gear disposed between rear wheels, via a hydraulic clutch and two hydraulic pumps. Further, a one-way clutch for mechanically connecting the rear-wheel differential gear to the front-wheel differential gear at the time of acceleration is attached to the hydraulic clutch. 
         [0004]    Further, according to the disclosure of the relevant prior patent literature, a first connecting oil passage is provided to connect between first and second ports, and a second connecting oil passage is provided to connect between third and fourth ports. However, the first connecting oil passage may sometimes be provided to connect between the third and second ports due to an assembly mistake. Thus, there is a need to confirm that the first connecting oil passage is accurately provided to connect between the first and second ports. 
         [0005]    Whether the oil passages are connected accurately can be confirmed also by checking behavior of the rear wheels with the vehicle set in a forward traveling state by the engine. 
         [0006]    Further, because the one-way clutch is set in a connected or engaged state at the time of acceleration, the drive system including the one-way clutch can be checked by setting the vehicle in a forward traveling acceleration state. 
         [0007]    As a result of remarkable enhancement of performance of electric motors in recent years, there have been proposed four-wheel-drive vehicles in which one of the front and rear wheels are driven by an engine while the other of the front and rear wheels are driven by electric motors. One specific example of such four-wheel-drive vehicles will be described with reference to  FIG. 7 . 
         [0008]    As shown in  FIG. 7 , an electric drive apparatus  100  of the four-wheel-drive vehicle includes: a case  101 ; a left electric motor  102 L (“L” is a suffix indicating “left”); a left sun gear  104 L mounted on a left motor shaft  103 L; a left planet gear  105 L meshing with the left sun gear  104 L; a left ring gear  106 L surrounding the left planet gear  105 L; a left carrier  107 L extending from the left planet gear  105 L; and a left foot shaft  108 L connected to the left carrier  107 L and extending through the left motor shaft  103 L. The electric drive apparatus  100  also includes: a right electric motor  102 R (“R” is a suffix indicating “right”); a right sun gear  104 R mounted on a right motor shaft  103 R; a right planet gear  105 R meshing with the right sun gear  104 R; a right ring gear  106 R surrounding the right planet gear  105 R; a right carrier  107 R extending from the right planet gear  105 R; a right foot shaft  108 R connected to the right carrier  107 R and extending through the right motor shaft  103 R; brake plates  111  and  112  extending between the left and right ring gears  106 L and  106 R and the case  101 ; a hydraulic piston  113  for pressing the brake plate  112 ; a hydraulic pipe  114  for supplying hydraulic pressure to the hydraulic piston  113 ; and a hydraulic gauge  115  mounted on the hydraulic pipe  114 . 
         [0009]    The above-mentioned left sun gear  104 L, left planet gear  105 L, left ring gear  106 L and left carrier  107 L together constitute a left planet gear mechanism, an similarly, the above-mentioned right sun gear  104 R, right planet gear  105 R, right ring gear  106 R and right carrier  107 R together constitute a right planet gear mechanism. The left planet gear mechanism is a transmission mechanism that places one of the three elements, i.e. left sun gear  104 L, left ring gear  106 L and left carrier  107 L, in a non-rotating state by constraining the one element and the remaining two of the three elements in a rotatable state. Moe specifically, in the illustrated example of  FIG. 8 , the left ring gear  106 L is placed in the non-rotatable state by the hydraulic piston  113 . 
         [0010]    Once the left electric motor  102 L is activated, the left sun gear  104 L rotates, in response to which the left planet gear  105 L rotates to revolve along the left ring gear  106 L. Then, the left carrier  107 L is rotated, so that the left foot shaft  108 L is rotated. During that time, hydraulic pressure is continuously applied via the hydraulic pipe  114  to the hydraulic piston  113 . However, because a considerable amount of energy is required to generate high hydraulic pressure, continuously applying such high hydraulic pressure to the hydraulic piston  113  as above would increase energy cost. 
         [0011]    For the foregoing reason, there exists a need for a sophisticated electric drive apparatus which can reduce necessary hydraulic pressure generating energy. One specific example of such a sophisticated electric drive apparatus will be described below with reference to  FIG. 8 . As shown in  FIG. 8 , the electric drive apparatus  100 B is characterized by being constructed by adding a one-way clutch  117  to the electric drive apparatus  100  of  FIG. 7 . The other elements in the electric drive apparatus  100 B are similar to those in the electric drive apparatus  100  of  FIG. 7  and thus will not be described here to avoid unnecessary duplication. 
         [0012]    The one-way clutch  117  is mounted in a given orientation such that it is placed in an engaged state at the time of forward travel of the vehicle and in a disengaged state (free-rotating state) at the other times. When the left electric motor  102 L rotates in the forward travel direction, the left ring gear  106 L is placed in the non-rotatable state through operation of the one-way clutch  117 , and thus, the hydraulic pressure can be set at a zero (“0”) level during that time. 
         [0013]    For the electric drive apparatus  100 B of  FIG. 8 , various items are inspected during forward acceleration in the same manner as disclosed in Patent Literature 1. However, because the hydraulic pressure is at the zero (“0”) level during the forward acceleration, it is not possible to inspect the hydraulic pressure, and thus, there is a need to conduct a separate inspection of a hydraulic system by applying hydraulic pressure to the hydraulic piston  113 . Therefore, an increased inspection time would be required, which would adversely influence the productivity. 
         [0014]    Thus, even with the electric drive apparatus having the one-way clutch incorporated therein, it is required to inspect the hydraulic pressure in parallel with another inspection item, because of a demand for enhanced efficiency of the inspection. 
       SUMMARY OF THE INVENTION 
       [0015]    In view of the foregoing prior art problems, it is an object of the present invention to provide an improved inspection method which, even with an electric drive apparatus having a one-way clutch incorporated therein, can conduct inspection of hydraulic pressure in parallel with another inspection item. 
         [0016]    In order to accomplish the above-mentioned object, the present invention provides an improved inspection method for inspecting an electric drive apparatus as an inspection object, the electric drive apparatus including: an electric motor; a sun gear mounted on a motor shaft of the electric motor; a planet gear meshing with the sun gear; a carrier rotatably supporting the planet gear; a foot shaft connected to the carrier; a ring gear meshing with the planet gear and surrounding the planet gear; a brake plate provided between a case enclosing the ring gear for switching the ring gear between a rotatable state and a non-rotatable state; a hydraulic piston for pressing the brake plate; and a one-way clutch provided between the case and the ring gear and constructed to place the ring gear in the non-rotatable state when the foot shaft rotates in a forward direction but place the ring gear in the rotatable state when the foot shaft rotates in a reverse direction, the method comprises: a step of giving the electric motor an instructing for rotating the foot shaft in the reverse direction and checking whether the foot shaft is rotating in the reverse direction; and a step of checking whether hydraulic pressure acting on the hydraulic piston has reached a predetermined pressure level. 
         [0017]    The inspection method of the present invention performs the step of giving the electric motor the instructing for rotating the foot shaft in the reverse direction and checking whether the foot shaft is rotating in the reverse direction, and the step of checking whether the hydraulic pressure has reached the predetermined pressure level. By checking the rotating direction of the electric motor, it is possible to check electrical connections. By checking the hydraulic pressure, it is possible to check whether there is any trouble in a hydraulic system. Namely, the present invention can perform an electrical connection check and a hydraulic pressure check in a collective fashion. Thus, even with the electric drive apparatus having the one-way clutch incorporated therein, the present invention can provide inspection of the hydraulic pressure in parallel with another inspection item (e.g., electrical connection check). 
         [0018]    Preferably, the electric drive apparatus includes left and right electric motors, left and right sun gears, left and right planet gears, left and right ring gears and left and right carriers, and the left and right electric motors, the left and right sun gears, the left and right planet gears, the left and right ring gears, the left and right carriers, the brake plate, the hydraulic piston and the one-way clutch are accommodated together in the case. Thus, the left and right electric motors can be checked in a parallel fashion, so that an enhanced inspection efficiency can be achieved. 
         [0019]    Preferably, the electric drive apparatus is mounted on a vehicle, and a test is performed on the electric drive apparatus with the vehicle placed on a bench test machine. The bench test machine of a conventionally-known construction is used for the inspection. Namely, existing facilities of the bench test machine can be used as-is. As a result, checking inspection can be performed at low cost, and thus, an enhanced inspection efficiency can be achieved. 
         [0020]    The following will describe embodiments of the present invention, but it should be appreciated that the present invention is not limited to the described embodiments and various modifications of the invention are possible without departing from the basic principles. The scope of the present invention is therefore to be determined solely by the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Certain preferred embodiments of the present invention will hereinafter be described in detail, by way of example only, with reference to the accompanying drawings, in which: 
           [0022]      FIG. 1  is a schematic block diagram of a vehicle employing an embodiment of an electric drive apparatus the present invention; 
           [0023]      FIG. 2  is a view explanatory of basic principles of the electric drive apparatus the present invention; 
           [0024]      FIG. 3  is a view explanatory of basic principles of a planet gear mechanism in the electric drive apparatus; 
           [0025]      FIG. 4  is a sectional view taken along line  4 - 4  of  FIG. 2 , which is explanatory of basic operating principles of the electric drive apparatus the present invention; 
           [0026]      FIG. 5  is a chart showing a part of an inspection flow for checking an inner construction of electric motors in the electric drive apparatus; 
           [0027]      FIG. 6  is a chart showing the remaining part of the inspection flow for checking a hydraulic system and electrical connections in the electric drive apparatus; 
           [0028]      FIG. 7  is a view explanatory of the basic principles of a conventionally-known electric drive apparatus; and 
           [0029]      FIG. 8  is a view explanatory of the basic principles of another conventionally-known electric drive apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    Now, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, “forward rotation” or “rotation in a forward direction” of an electric motor corresponds to “forward travel” of a vehicle, and “reverse rotation” or “rotation in a reverse direction” of the electric motor corresponds to “rearward travel” of the vehicle. 
         [0031]      FIG. 1  is a schematic block diagram of a vehicle  10  employing an embodiment of an electric drive apparatus  20  of the present invention. As shown, the vehicle  10  includes a front-wheel differential gear  12  between a left front wheel  11 L and a right front wheel  11 R, and this front-wheel differential gear  12  is driven directly by an engine  13 . 
         [0032]    The electric drive apparatus  20  is disposed between a left rear wheel  14 L and a right rear wheel  14 R. The left rear wheel  14 L is driven by a left electric motor  22 L incorporated in the electric drive apparatus  20 , while the right rear wheel  14 R is driven by a right electric motor  22 R incorporated in the electric drive apparatus  20 . 
         [0033]    The left and right electric motors  22 L and  22 R are supplied with electric power from a vehicle-mounted battery  16 . The vehicle-mounted battery  16  is charged by a power generator  17  driven by the engine  13 . Rotating speed of the engine  13  is controlled by an operation of a vehicle-mounted accelerator  18 , and the front and rear wheels  11 L and  11 R are controlled by an operation of a brake pedal (vehicle-mounted brake)  19 . 
         [0034]    Because the left and right front wheels  11 L and  11 R are driven by the engine  13  while the left and right rear wheels  14 L and  14 R are driven by the left and right electric motors  22 L and  22 R, the vehicle  10  is a four-wheel-drive vehicle. During high-speed cruising travel, power supply to the left and right electric motors  22 L and  22 R is stopped, so that the vehicle  10  becomes a two-wheel-drive vehicle. 
         [0035]    Alternatively, the left and right rear wheels  14 L and  14 R may be driven by the engine  13 , and the left and right front wheels  11 L and  11 R may be driven by the left and right electric motors  22 L and  22 R. 4   
         [0036]    The following describe, with reference to  FIG. 2 , a construction of the electric drive apparatus  20  in greater detail. As shown in  FIG. 2 , the electric drive apparatus  20  includes: a case  21 ; the left electric motor  22 L; a left sun gear  24 L mounted on a left motor shaft  23 L; a left planet gear  25 L meshing with the left sun gear  24 L; a left ring gear  26 L surrounding the left planet gear  25 L; a left carrier  27 L extending from the left planet gear  25 L; and a left foot shaft  28 L connected to the left carrier  27 L and extending through the left motor shaft  23 L. 
         [0037]    The electric drive apparatus  20  also includes: the right electric motor  22 R; a right sun gear  24 R mounted on a right motor shaft  23 R; a right planet gear  25 R meshing with the right sun gear  24 R; a right ring gear  26 R surrounding the right planet gear  25 R; a right carrier  27 R extending from the right planet gear  25 R; and a right foot shaft  28 R connected to the right carrier  27 R and extending through the right motor shaft  23 R. The electric drive apparatus  20  further includes: brake plates  31  and  32  extending between the left and right ring gears  26 L and  26 R and the case  21  for switching the ring gears between a rotatable state and a non-rotatable state; a hydraulic piston  23  for pressing the brake plate  32 ; a hydraulic pipe  34  for supplying hydraulic pressure to the hydraulic piston  33 ; a hydraulic gauge  35  provided on the hydraulic pipe  34 ; and a one-way clutch  37  extending between the left and right ring gears  26 L and  26 R and the case  21  and placed in an engaged state at the time of forward rotation of the motors. 
         [0038]    A left rotation sensor  36 L is attached to the left motor shaft  23 L for constantly detecting rotating speed of the left motor shaft  23 L, i.e. the number of rotation of the left electric motor  22 L. Similarly, a right rotation sensor  36 R is attached to the right motor shaft  23 R for constantly detecting rotating speed of the right motor shaft  23 R, i.e. the number of rotation of the eight electric motor  22 R. 
         [0039]    The following describe, with reference to  FIG. 3 , basic operating principles of the one-way clutch in greater detail. As the left sun gear  24 L is rotated by the left motor shaft  23 L when the left ring gear  26 L is in the non-rotatable state by being constrained in movement as shown in  FIG. 3 , the left planet gear  25 L is rotated so that it revolves within (along the inner periphery of) the ring gear  26 L. Then, the left carrier  27 L rotates, thereby rotating the left foot shaft  28 L. Once the left ring gear  26 L becomes rotatable by being released from the constraint, no power transmission is effected any more. 
         [0040]    Further, as shown in  FIG. 4 , the one-way clutch  37  is interposed between the case  21  and the left ring gear  26 L. The one-way clutch  37  is a special clutch including, as its main component elements, a plurality of rhomboid-shaped pieces. However, because movement of such rhomboid-shaped pieces is very minute, an engaged state and a non-engaged state of the one-way clutch  37  cannot be distinguished from each other in the figure. Therefore, the operation of the one-way clutch  37  will be described in more detail with reference to  FIG. 4  using projections  38  and oscillators  39  instead of the rhomboid-shaped pieces. 
         [0041]    The case  21  is a stationary member. Even when torque is applied to rotate the left ring gear  26 L in a clockwise direction in  FIG. 4 , the left ring gear  26 L is prevented from rotating by the projections  38  being stopped by the oscillators  39 . Namely, at the time of the forward rotation of the corresponding motor, the left ring gear  26 L is placed in the non-rotatable state. 
         [0042]    When torque is applied to rotate the left ring gear  26 L in a counterclockwise direction in  FIG. 4 , on the other hand, the projections  38  pass under the oscillators  39 . Thus, at the time of the reverse rotation of the corresponding motor, the left ring gear  26 L is placed in the rotatable state. 
         [0043]    Namely, when the electric motors  22 L and  22 R are rotated in the forward direction, the left and right ring gears  26 L and  26 R are placed in the non-rotatable state by a constraining action of the one-way clutch  37 , so that the foot shafts  28 L and  28 R are rotated in the forward travel direction by the motors  22 L and  22 R. 
         [0044]    When the electric motors  22 L and  22 R are rotated in other than the forward direction, the one-way clutch  37  no longer performs the constraining action, so that the left and right ring gears  26 L and  26 R is placed in the non-rotatable state by the hydraulic piston  33  pressing the brake plate  32  against the brake plate  31 . 
         [0045]    Next, with primary reference to  FIGS. 5 and 6 , a description will be given about an inspection flow intended to check operation of the vehicle  10  and particularly operation of the electric drive apparatus  20  constructed in the aforementioned manner. 
         [0046]    First, at step ST 01 , the vehicle  10  is placed on a bench test machine of a conventionally known construction. Then, at step ST 02 , the hydraulic pressure acting on the hydraulic piston  33  is set at a “0” level, and the electric motors  22 L and  22 R are de-energized, so that the left and right foot shafts  28 L and  28 R cannot be rotated by the electric motors  22 L and  22 R. 
         [0047]    Then, a shift mode of the vehicle is set at “D” at step ST 03 , and the vehicle-mounted accelerator  18  is depressed by a human inspector at step ST 04 . Then, at step ST 05 , the front wheels  11 L and  11 R starts to be rotated in the forward travel direction by means of the vehicle-mounted engine  13   a,  and the rear wheels  14 L and  14 R are rotated in the forward travel direction by rollers of the bench test machine. 
         [0048]    Under such conditions, the respective numbers of co-rotation Nt of the left and right electric motors  22 L and  22 R are measured at step ST 06 . Even when a hydraulic clutch is OFF, the brake plate  32  may move following the brake plate  31  without the two brake plates  31  and  32  completely separating from each other. Such following movement is also called a drag phenomenon. 
         [0049]    The electric drive apparatus  20  is determined satisfactory (acceptable) if the number of co-rotation Nt of the left electric motor  22 L is a predetermined (allowable) number or below (YES determination at step ST 07 ), but determined unsatisfactory (unacceptable) if the number of co-rotation Nt of the left electric motor  22 L is over the predetermined (allowable) number (NO determination at step ST 07 ). If the electric drive apparatus  20  is determined unsatisfactory at step ST 07 , it can be considered that separation between the left foot shaft  28 L and the left electric motor  22 L has become insufficient due to a failure of the one-way clutch  37  or the like. Thus, in such a case, it is suspected that there is some trouble or problem in the interior of the electric drive apparatus  20 . 
         [0050]    Similarly, the electric drive apparatus  20  is determined satisfactory if the number of co-rotation Nt of the right electric motor  22 R is a predetermined (allowable) number or below (YES determination at step ST 08 ), but determined unsatisfactory if the number of co-rotating rotation Nt of the right electric motor  22 R is over the predetermined (allowable) number (NO determination at step ST 08 ). 
         [0051]    Then, the vehicle-mounted accelerator is returned to an initial position at step ST 09 , and the vehicle-mounted brake is depressed to stop the rotation of the front and rear wheels at step ST 10 . 
         [0052]    Connector “(A)” in  FIG. 5  connects to connector “(A)” in  FIG. 6 . At step ST 11  in  FIG. 6 , the shift mode is set at “R”. Then, at step ST 12 , an instruction for increasing the hydraulic pressure is generated on the basis of the shift mode setting at “R”. As a consequence, the brake plates contact each other into a braking state, so that the left and right ring gears  26 L and  26 R are placed in the non-rotatable state. Under such conditions, the hydraulic pressure Po is measured by the hydraulic gauge  35  of  FIG. 2  at step ST 13 . 
         [0053]    The electric drive apparatus  20  is determined satisfactory if the measured hydraulic pressure Po is a predetermined pressure level or over (YES determination at step ST 14 ), but determined unsatisfactory as having a trouble or problem with the hydraulic system if the measured hydraulic pressure Po is below the predetermined pressure level (NO determination at step ST 14 ). Such a problem with the hydraulic system is presumed to be any of a failure of the hydraulic pump, mis-connection of hydraulic piping, etc. 
         [0054]    Next, the vehicle-mounted accelerator  18  is depressed by the human inspector at step ST 15  so that the front wheels  11 L and  11 R start to be rotated in the rearward travel direction by means of the vehicle-mounted engine  13 , in parallel with which an instruction for rotating the left foot shaft  28 L in the rearward travel direction is given to the left electric motor  22 L so that the left electric motor  22 L having so far been stopped is activated, at step ST 16 . 
         [0055]    Then, the rotating direction of the left foot shaft  28 L is checked at step ST 17 . The electric drive apparatus  20  is determined satisfactory if the rotating direction of the left foot shaft  28 L is the rearward travel direction, but determined unsatisfactory if the rotating direction of the left foot shaft  28 L is not the rearward travel direction. This unsatisfactoriness is presumed to be due to an error of an electrical connection pertaining to the left electric motor  22 L, such as a connection between left and right electric components. Upon completion of the rotating direction check of the left foot shaft  28 L, the left electric motor  22 L is deactivated at step ST 18 . 
         [0056]    Then, an instruction for rotating the right foot shaft  28 R in the rearward travel direction is given to the right electric motor  22 R so that the right electric motor  22 R having so far been stopped is activated, at step ST 19 . 
         [0057]    Then, the rotating direction of the right foot shaft  28 R is checked at step ST 20 . The electric drive apparatus  20  is determined satisfactory if the rotating direction of the right foot shaft  28 R is the rearward travel direction, but determined unsatisfactory if the rotating direction of the left foot shaft  28 L is not the rearward travel direction, at step ST 20 . This unsatisfactoriness is presumed to be due to an error of an electrical connection pertaining to the right electric motor  22 R. Upon completion of the rotating direction check of the right foot shaft  28 R, the right electric motor  22 R is deactivated at step ST 21 . 
         [0058]    As described above in relation to  FIG. 6 , the check of the hydraulic system can be performed in parallel with the check of the electrical connection between the left and right electric motors  22 L and  22 R. Namely, the hydraulic system can be inspected in parallel with another inspection item without separately inspecting the hydraulic system, by just the shift mode being set at 
         [0059]    Because the inspection flow shown in  FIGS. 5 and 6  can be executed in a short time, the instant embodiment can reduce a necessary inspection time. 
         [0060]    Whereas the instant embodiment has been described above in relation to the case where the left and right electric motors  22 L and  22 R etc. are accommodated together in the single case, each of the electric motors may be accommodated in a different case. Further, the method of the present invention can be applied to the electric drive apparatus before being mounted on the vehicle, in which case the bench test machine is not required. 
         [0061]    However, in order to perform a proper final check of a completed vehicle, it is recommended that the inspection be conducted with the electric drive apparatus, having the left and right electric motors accommodated in the case, mounted on the vehicle placed on the bench test machine. 
         [0062]    The present invention is well suited for application to a final check of a completed vehicle.