Abstract:
Spring characteristics are switched in response to running conditions or use requirements of a bicycle in order to improve riding comfort and vehicle performance. A rod  2  is connected to a piston  3  which slides in a cylinder  1,  a piston-side chamber (A) and a rod-side chamber (B) are partitioned in the cylinder  1  by the piston  3  and compressed air fills the two chambers, a passage  4  which connects the two chambers is opened and closed by a switch valve  5,  the cylinder  1  is connected to the vehicle wheels and the piston rod  2  is connected to the vehicle body, the piston  3  displaces in response to vibration applied to the vehicle body in order to absorb vibrations.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to an air spring which is disposed between a vehicle wheel and the body of a two-wheeled vehicle in order to absorb vibration.  
         BACKGROUND OF THE INVENTION  
         [0002]    The provision of an air spring between a vehicle wheel and vehicle body in modern bicycles improves riding comfort by absorbing road surface vibrations when the bicycle is running.  
           [0003]    Various types of air springs have been proposed and an example thereof is shown in FIG. 9.  
           [0004]    This type of air spring comprises an air chamber A which is partitioned by a piston  103  in a cylinder  101  and an air chamber B in a tank  110  which is separated from a cylinder  1 . The air chambers A and B which are filled with pressurized air connected by a passage  108 . The air chambers A, B are connected and disconnected as a result of switching operations performed by a switch valve  109  which is provided in the passage  108  connecting the chambers.  
           [0005]    When the air chambers A, B are connected, the effective volume of the air spring is increased with the result that a low spring force is applied. When the air chambers A, B are disconnected, a small effective volume corresponding to only the air chamber A results in a high spring force.  
           [0006]    For example, a piston rod  102  is connected to the vehicle wheel and the cylinder  101  is connected to the vehicle body in this air spring. An air chamber C disposed opposite the piston  103  is at atmospheric pressure.  
           [0007]    A bicycle comprising an air spring allows the rider to switch the switch valve  109  in order to select a hard ride based on a high spring force or a soft ride based on a low spring force when riding the bicycle.  
           [0008]    However a tank  110  which is separate from the cylinder  101  is required in the air spring in order to switch between a high and low spring force. Moreover the capacity of this tank  110  must be large in order to increase the differential variation (width thereof of the spring force resulting from switching.  
           [0009]    As a result, the problem has arisen that the overall size of the spring is increased.  
         SUMMARY OF THE INVENTION  
         [0010]    The object of the present invention is to provide an air spring enabling two clearly distinct spring characteristics in a compact unit.  
           [0011]    In order to achieve above the object, the invention provides an air spring for a two-wheeled vehicle, the air spring being disposed between a vehicle body and a vehicle wheel. The air spring comprises a piston which slides in a cylinder member, a rod member which is engaged with the piston, a rod-side air chamber and a piston-side air chamber which are partitioned in the cylinder member by the piston and are filled with compressed air, a passage which connects the two air chambers, and a switch valve which opens and closes the passage. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 shows the principle of an air spring according to the present invention.  
         [0013]    [0013]FIG. 2 compares the spring characteristics of a conventional air spring with an air spring according to the present invention.  
         [0014]    [0014]FIG. 3 shows the relationship of a sensor and a drive chain in a bicycle.  
         [0015]    [0015]FIG. 4 shows another example of the relationship of a sensor and a drive chain in a bicycle.  
         [0016]    [0016]FIG. 5 shows yet another example of the relationship of a sensor and a drive chain in a bicycle.  
         [0017]    [0017]FIG. 6 is a cross sectional view of an embodiment applying an air suspension for a bicycle according to the present invention.  
         [0018]    [0018]FIG. 7 is a cross sectional view of an embodiment applying a front fork for a bicycle according to the present invention.  
         [0019]    [0019]FIG. 8 is an enlarged cross sectional view of a section of FIG. 7.  
         [0020]    [0020]FIG. 9 shows a conventional air spring. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    An embodiment as shown in FIG. 1 will be described below.  
         [0022]    An air spring according to the present invention is housed in a bicycle (not shown).  
         [0023]    A cylinder  1  for the air spring is connected to a vehicle wheel and a rod  2  which expands and contracts from within the cylinder  1  is connected to the vehicle body.  
         [0024]    A piston  3  which is connected to the rod  2  slides in the cylinder  1 . An air chamber A and an air chamber B are partitioned on both sides of the piston  3  and the air chambers A, B are filled with pressurized air. Hereafter the air chamber A below the piston  3  will be termed the piston-side air chamber and the air chamber above the piston  3  will be termed the rod-side air chamber.  
         [0025]    A connecting passage  4  is provided in order to connect the two air chambers A, B. A switch valve  5  which opens and closes the connecting passage  4  and a throttle (orifice)  6  which is disposed in series with the switch valve  5  are provided along the connecting passage  4 .  
         [0026]    The switch valve  5  is switched by an external operating input between a connecting position  5   a  which opens the connecting passage  4  and a cut-off position  5   b  which closes the connecting passage  4  when the operating input above is released. The cut-off position  5   b  comprises a check valve  5   c  which prevents the entry of air from the air chamber A to the air chamber B and which allows reverse flow in the reverse direction. As a result however, air flow from air chamber B to air chamber A occurs even in the cut-off position  5   b  when the pressure of the air chamber B is higher than the air pressure in the air chamber A.  
         [0027]    The check valve  5   c  may be disposed along a bypass passage which bypasses the switch valve  5  switched between an ON and OFF position.  
         [0028]    Thus when the rod  2  enters the cylinder  1  as a result of a compressive force, the air spring displays distinct high and low spring forces as described hereafter.  
         [0029]    Firstly when the switch valve  5  of the connecting passage  4  is maintained at the cut-off position  5   b  as shown, only the air chamber A is compressed by the piston  3  descending in the cylinder  1  and a spring force is generated by a repulsive force with respect to air compression.  
         [0030]    The amount of air compression is proportional to the pressured surface area and the stroke amount of the piston  3 . Since the effective volume at this time is small since only the air chamber A is compressed, the spring force is rapidly increased by increases in the stroke amount.  
         [0031]    The spring force characteristics are shown in FIG. 2 at “a”.  
         [0032]    In contrast when the switch valve  5  is switched to the connecting position  5   a , a section of the air in the air chamber A also flows into the air chamber B due to the piston  3  descending in the cylinder  1 . As a result, the effective volume of the air spring becomes the total of the capacity of the air chamber A and the air chamber B.  
         [0033]    Moreover in the air chambers A and B, only a volume of air is compressed which corresponds to the entry of the piston rod  2  in the cylinder  1 .  
         [0034]    As a result, in comparison to the cut-off position above, the compression amount of air resulting from the same piston stroke is clearly smaller.  
         [0035]    Thus the spring force at this time is a low spring force as shown in FIG. 2 at “b”.  
         [0036]    When these high and low spring forces are compared with the spring characteristics of the conventional air spring as shown in FIG. 9, firstly the high spring force at “c” displays approximately the same high spring characteristics if the cross sectional surface area of the piston and the volume of the compressed volume are equal.  
         [0037]    However in the present invention, when compression is initiated, although the pressure of the air chamber B is the same as the pressure of the air chamber A, since one air chamber in the conventional example is at atmospheric pressure, the initial compressive pressure is lower to a corresponding degree at “a” in the present invention.  
         [0038]    At the low spring force shown at “d”, in contrast to the conventional example in which both air chambers A and B are compressed by the pressured cross sectional face of the piston, the chambers A and B are compressed in the present invention in response to the cross sectional area of the piston rod which has a pressured surface area is smaller than the piston. As a result, even when the effective volume is the same, increases in compressive pressure by the same piston stroke are clearly smaller in the present invention and the generated spring force is therefore lower.  
         [0039]    Thus in the present invention, when the spring characteristics are switched, it is possible to clearly increase the differential variation (width thereof) of the spring force in comparison to the conventional example. However in the conventional example, the capacity of the tank and the size of the air spring must be greatly increased in order to achieve this type of large differential variation. In the present invention, since the air chamber A and the air chamber B are formed in the cylinder  1 , it is not required to provide the tank separately which allows reductions in space required for components.  
         [0040]    In the expansion stroke during which the piston rod undergoes maximum expansion, the air chamber B is compressed. If the pressure in the air chamber B at this time is higher than the pressure in the air chamber A, since the check valve  5   c  is opened even when the switch valve  5  is at the cut-off position, the pressure in the air chamber A equals the pressure of the air chamber B. As a result, when the switch valve  5  is either connected or cut-off, the compressive force is the same at an initial stroke position when the air spring undergoes maximum expansion.  
         [0041]    Thus when running off-road, a preferred spring force can be obtained in a bicycle housing an air spring by closing the switch valve  5  to create a high spring force and, when running on-road, a low spring force is created by opening the switch valve  5 .  
         [0042]    It is often the case that the switch valve  5  is set to be normally closed (normally-closed type) when the bicycle provided with an air spring is set to off-road use. The switch valve  5  is set to be normally open (normally-open type) when the bicycle provided with an air spring is set to on-road use.  
         [0043]    When the switch valve  5  is in the connecting position  5   a , the throttle  6  which is provided in the connecting passage  4  applies a throttle resistance to the flow of air passing between the air chamber A and the air chamber B. When in the cut-off position  5   b , the throttle  6  applied a throttle resistance to the flow of air from the air chamber B to the air chamber A. Therefore a damping force is generated with respect to the repulsive force of the air spring.  
         [0044]    As a result, when the switch valve  5  is in the connecting position  5   a  for a low spring force, that is to say, when set to a soft ride, the throttle  6  displays a large damping force when the air spring undergoes a high speed compression with a large stroke on landing after a bicycle jump for example. Thus it is possible to avoid bottoming of the piston  3  in the air spring.  
         [0045]    The air spring has a full rebound spring  7  on the rear face of the piston  3  in FIG. 1, that is to say, on the outer peripheral side of the rod  2  in the air chamber B. When the air spring extends nearly up to maximum extension, the full rebound spring  7  damps the shock of maximum extension on the piston  3 .  
         [0046]    Although the input of the switch valve  5  may be manually operated by the driver, as shown in the embodiment in FIG. 3 to FIG. 5, the valve  5  is adapted to be switched in response to operational conditions by an external electrical signal.  
         [0047]    [0047]FIG. 3 shows automatic control of the switch valve  5  based on a detection signal from a sensor  10  which detects strain on a drive chain  9  in the bicycle.  
         [0048]    When the air spring is housed by support on the rear wheel side of the bicycle, it is preferred that the air spring generates a high spring force when the rider strongly depresses the pedal during acceleration or start motion of the bicycle,.  
         [0049]    A sensor  10  which detects strain (shown by the solid line in the figure) on the drive chain  9  which revolves between the gear  8  of the rear wheel and the crank gear  11  connected to the pedal. The switch valve  5  is switched by input electrical signals as a result of the detection signals from the sensor  10 . The spring force of the air spring is increased by the switching operation of the switch valve  5 .  
         [0050]    When the spring force of the air spring is loose during start motion or acceleration, a supporting force is not easily obtained when strongly depressing the pedal and thus desirable acceleration characteristics are not obtained. However the tension resulting from the downward pressure exerted by the rider is efficiently transmitted to the crank gear  11  and the drive wheels are rotated with high efficiency by increasing the spring force of the air spring in this manner.  
         [0051]    When the drive chain  9  is not in under strain, for example when a large drive force is not required during downhill coasting, the drive chain  9  is loose. Thus a detection signal from the sensor  10  is not output and the switch valve  5  is placed in a connection state which results in a low spring force in the air spring. Therefore a setting for a soft ride is possible at this time.  
         [0052]    In the arrangement as shown in FIG. 3, an idler pulley  10   a  comes into the contact for example with the drive chain  9  and when the pulley  10   a  is shifted by strain on the drive chain  9 , this operation is detected by the sensor  10 .  
         [0053]    In contrast, as shown in FIG. 4, it is possible to adapt the device so that a sensor  10  detects the pulley  10   a  moving through a stroke via a link  10   b.    
         [0054]    The embodiment as shown in FIG. 3 can be applied to the situation in which there is sufficient space to dispose the sensor  10  in a orientation which is roughly orthogonal to the drive chain  9 . Furthermore the embodiment as shown in FIG. 4 can be applied to the situation in which there is not sufficient space roughly orthogonal to the drive chain  9 .  
         [0055]    In the embodiment as shown in FIG. 5, the signal from the sensor shown in FIG. 3 or FIG. 4 is input to a controller  13  and is converted to an electrical drive signal therein. The converted signal is output to the switch valve  5 .  
         [0056]    The air spring in FIG. 1 shows the principle of operation. The detailed structure of the air spring will be described below based on FIG. 6 .  
         [0057]    The air spring in FIG. 6 is shown as supporting the rear wheel of the bicycle as a suspension spring. The air spring has a piston  3  which is inserted to slide freely in a cylinder  1  which acts as a member connected on the vehicle wheel. A hollow rod  2  which acts as a member connected to the vehicle body is connected to the piston  3 .  
         [0058]    An air chamber A and an air chamber B are partitioned in the cylinder  1  by the piston  3 . The air chamber B is normally connected with the hollow chamber B′ in the rod  2  by a passage  15 .  
         [0059]    A passage  16  is formed in the piston  3  to connect the air chamber A and the air chamber B with a switch valve  5  is interposed therein. The passage  16  also functions as the orifice  6  in FIG. 1.  
         [0060]    The switch valve  5  comprises a check valve  17 . A poppet  17   a  is biased towards closure by the spring  17   b . In contrast, an actuator  18  is provided opposite the poppet  17   a . When the push rod  18   a  of the actuator  18  is depressed by the poppet  17   a , the check valve  17  is opened as shown in the figure.  
         [0061]    When the check valve  17  is opened, the air chamber A and the air chamber B are connected and the spring force of the air spring is low. When the check valve  17  is closed, only the air chamber A is operated which results in a reduction in the effective volume of the air spring. Therefore the spring force of the air spring can be increased.  
         [0062]    An electrical signal is supplied to the actuator  18  from an external controller. In this manner, when the actuator  18  which comprises a motor for example is operated, the push rod  18   a  is extended and the poppet  17   a  is depressed.  
         [0063]    In this state, the spring force characteristics of the air spring are switched to a low state.  
         [0064]    In contrast, when the actuator  18  is not operated, since the poppet  17   a  is pressed upwardly by the spring  17   b  and closed, the spring force of the air spring is increased.  
         [0065]    When the pressure in the air chamber B is higher than the pressure in the air chamber A such as when the rod  2  has extended, the poppet  17   a  compresses the spring  17   b  and the check value  1  opens and allows air flow.  
         [0066]    The actuator  18  is disposed in the rod  2 . Since the rod  2  acts as a member with respect to the vehicle body, even when the air spring is expanded, component durability is increased irrespective of vibration or drag from the actuator  18  on the harness  19   a  or the connector  19   b  which are connected to the external member (the controller near the vehicle body) from the actuator  18 .  
         [0067]    An annular bump cushion  20   a  is provided on an end face near the air chamber A, that is to say, near the pressured face of the piston  3  which comprises the lower end face in the figure. An annular bump cushion  20   b  is provided which corresponds to a full rebound spring  7  as described above (Refer to FIG. 1) on the end face near the air chamber B, that is to say, on the rear face of the piston  3  which is the upper end face in the figure.  
         [0068]    The piston  3  can be prevented from colliding with the cylinder  1  during maximum compression or expansion of the air spring by the provision of the bump cushion  20   a  and the bump cushion  20   b.    
         [0069]    Although the air spring according to the present invention was described with reference to use in a bicycle, the air spring may be used in a motor bike. Of course in this event, the effect of the invention is the same as that described above.  
         [0070]    The air spring may be housed in the front of the bicycle with the same effect being obtained as that described above.  
         [0071]    This embodiment is described with reference to FIG. 7 and FIG. 8.  
         [0072]    [0072]FIG. 7 shows an expandable support shaft  31  which acts as a front fork for supporting the front wheel and which can be used when applying the present invention to a bicycle or the like. The expandable support shaft  31  may correspond to a combination of left and right shafts used as the expandable support shaft for supporting the front wheel which is used in a normal motor bike. Alternatively a single expandable support shaft  31  may be used as a cantilevered type.  
         [0073]    The lower end of the expandable support shaft  31  for supporting the front wheels is provided with an outer tube  32  which supports the front wheels of a bicycle for example. An inner tube  35  is inserted to slide freely through bearings  33 ,  34  into the interior from an upper end of the outer tube  32 . The inner tube  35  is connected to the vehicle body.  
         [0074]    A section of the upper end of the inner tube  35  is sealed by a cap  37  which is provided with an air-sealing valve  36 . Thus it is possible to input pressurized air into the interior of the expandable support shaft  31  which comprises an outer tube  32  and an inner tube  35  through the air input valve  36 .  
         [0075]    A piston  38  is mounted which slides on an inner wall of the outer tube  32  on a lower end of the inner tube  35 . As shown in FIG. 8, a seal  39  and a piston ring  40  are provided on an outer peripheral face of the piston  38 . Although the air sealing characteristics are maintained by the piston ring  40  and the seal  39 , the interior of the expandable support shaft  31  partitions an air chamber  41  in the outer tube  32 , an air chamber  42  in the inner tube  35  and an air chamber  43  near the inner tube  35 .  
         [0076]    The air chamber  42  in the inner tube  35  is normally in communication with the air chamber  43  in the inner tube  35  via the through holes  46 ,  47  provided on the boss  45  which acts as a mounting member for the piston  38  corresponding to the inner tube  35 .  
         [0077]    A connecting passage  48  is provided in the piston  38  and the boss  45 . The connecting passage  48  branches from the through hole  47  and communicates with the air chamber  41  in the outer tube  32 . A check valve mechanism  49  is disposed in series with the throttle  55  along the connecting passage  48  and allows airflow only from the air chamber  42  to the air chamber  41  near the outer tube  32 .  
         [0078]    The check valve mechanism  49  is closed by a return spring  51  which is interposed with the cap  50  which is fitted with the piston  38 . The air chambers  42 ,  43  in the inner tube  35  and near the inner tube  35  are placed in communication with the air chamber  41  in the outer tube  32  by pressing the valve body  56  of the check valve mechanism  49  into an open position against the return spring  51 .  
         [0079]    An electrical actuator  53  is provided in the interior of the air chamber  43  of the inner tube  35  in order to perform opening and closing operations on the valve body  56  of the check valve mechanism  49  with an externally supplied signal.  
         [0080]    The electrical actuator  53  is fixed between a boss  45  of the piston  38  and the support seat  57  which is fixed by a snap ring  52  on the inside of the inner tube  35 .  
         [0081]    When the electrical actuator  53  is operated, the push rod  54  extends and depresses the valve body  56  of the check valve mechanism  49  in order to forcibly open the valve  56 .  
         [0082]    When the bicycle is running with the check valve mechanism  49  closed, when a large external force such as the inertia of the load or the upward thrust from the road surface is applied, the extendable support shaft  31  for supporting the front wheels is operated in a compressing direction. Thus the effective volume is comprised by only the air chamber  41  in the outer tube  32 . Since the cross sectional volume of the piston  38  comes under pressure, the expandable support shaft  31  generates a large air spring repulsive force and effectively absorbs the inertia or the upward thrust.  
         [0083]    When the electrical actuator  53  is operated in response to an external signal, the air chamber  42  and the air chamber  43  in the inner tube  35  increases the overall air chamber capacity by coming into communication with the air chamber  41  in the outer tube  35  since the push rod  54  forcibly presses the check valve mechanism  49  open.  
         [0084]    In this state, air in the air chambers  41 ,  42 ,  43  is compressed by a pressured surface corresponding to the cross sectional volume of the inner tube  35 . As a result, the air spring repulsive force is smaller in comparison to a compression operation with the check valve mechanism  49  closed.  
         [0085]    Even when the vehicle is running with the check valve mechanism  49  closed, the air chambers  42 ,  43  in the inner tube  35  are compressed as the expandable support shaft  31  expands. When the air pressure is greater than the air pressure of the air chamber  41  in the outer tube, the check valve mechanism  49  is opened. As a result, the pressure relationship of the air chamber  41  and the air chambers  42 ,  43  can be returned automatically to an initial state which thus ensures reliable functioning of the air spring.  
         [0086]    Although this has not been described in particular above, when the front wheels are supported by a pair of left and right expandable support shafts  31 , one of the expandable support shafts  31  comprises an air spring as described above and the other expandable support shaft is supported by a metallic coil spring. Alternatively a hydraulic oil damping mechanism may be combined with an air pressure support.  
         [0087]    The present invention is not limited to the above embodiments and various changes may be made within the technical scope of the invention as understood by a person skilled in the art without departing from the spirit and scope thereof.