Abstract:
An improved fluid damping unit of the piston cylinder type that provides substantially equal damping in each direction and improved damping by displacing the full cross sectional area of the piston in each direction and quicker response upon reversal between jounce and rebound.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to a hydraulic damper for damping both the contraction and expansion of a vehicle ground supporting element such as, by way of example a wheel.  
         [0002]     Generally the type of hydraulic damper utilized for this purpose is not sufficiently responsive to changes from compression damping as occurs during “jounce” and expansion damping as occurs during “rebound”. In addition because of the types of construction normally employed, insufficient damping from that desired must be accepted.  
         [0003]     For example, a conventional prior art type damper is shown in  FIGS. 1 and 2 . For example, a hydraulic damper for the rear wheel of motorcycles is disclosed in Japanese Published Patent Document JP-A-Hei 6-127453.  
         [0004]      FIG. 1  is a sectional view of a prior art hydraulic dampers indicated generally by the reference numeral  21  for the rear wheel of motorcycles. The damper  21  is comprised of an outer cylinder  22  in which a piston  23  is fitted to divide the interior of the outer cylinder  22  into a contraction side oil chamber C and an extension side oil chamber D. The piston  23  is fixed to a piston rod  24  that extends outwardly of the outer cylinder  22  for connection to a component of the vehicle suspension system, for example to body portion of the associated vehicle, which connection component is indicated by the reference numeral  25 . In a similar manner, the outer cylinder is provided with a connection component  26  for connection to a component of the vehicle suspension system, for example to suspension arm for the wheel of the associated vehicle.  
         [0005]     The contraction side oil chamber C receives compressive action in contraction or jounce stroke, while the extension side oil chamber D receives compressive action in extension or rebound stroke. First and second passages  27  and  28 , respectively are formed in the piston for providing fluid communication between the contraction side oil chamber C and the extension side oil chamber D. At the extension chamber side opening  27   a  of the first passage  27  is provided a contraction time valve  29  capable of opening during contraction stroke of the piston rod  24 . In a similar manner, at the contraction chamber side opening  28   a  of the second passage  28  is provided an extension time valve  31  capable of opening during extension stroke.  
         [0006]     An in-shaft passage  24   a  is axially formed in the piston rod  24 , to provide fluid communication with the contraction side oil chamber C. In addition a communication passage  24   b  is formed to provide fluid communication between the in-shaft passage  24   a  and the extension side oil chamber D. Thus, the contraction side oil chamber C and the extension side oil chamber D are interconnected with each other via the in-shaft passage  24   a  and the communication passage  24   b.    
         [0007]     A damping force regulating valve  24   c  is inserted, to be axially movable, into the piston rod  24 . At the tip of the damping force regulating valve  24   c , a conical needle  24   d  is formed to be located within the in-shaft passage  24   a . By moving the position of the needle  24   d  back and forth, the amount of oil flowing from the needle  24   d  to the communication hole  24   d  is regulated, so as to adjust damping force in particular in low speed range during both the contraction stroke and the extension stroke.  
         [0008]     A passage  22   a  positioned below the lowermost position of the piston  23  communicates with an inlet of a base valve  32 . The base valve  32  is, in turn, in fluid communication with a sub tank  33 .  
         [0009]     With such a prior art type of hydraulic damper  21 , damping force is produced when the piston  23  relatively moves in the axial direction within the cylinder  22  in response to the irregularities on the road surface. Damping force characteristics are set to realize maneuverability and ride comfort the user desires and to obtain damping force matching the road surface conditions. These conditions are illustrated in  FIGS. 2A and 2B  which are enlarged views of the area encompassed by the circle  2  in  FIG. 1  and the flow directions are indicated by the arrows.  
         [0010]      FIG. 10 (A) shows the contraction or jounce stroke. As the piston  23  is pushed down, the pressure in the contraction side oil chamber C rises, while pressure in the extension side oil chamber D decreases. As a result, oil in the pressure in the contraction side oil chamber C pushes the contraction time valve  28  open the flow passes through the first passage  27  into the extension side oil chamber D. The flow passes through the in-shaft passage  24   a  and the communication hole  24   b  of the piston rod  24  into the extension side oil chamber D.  
         [0011]      FIG. 10 (B) shows the extension or rebound stroke. As the piston  23  is pulled up in this figure, pressure in the extension side oil chamber D rises and the pressure in the contraction side oil chamber C lowers. As a result, oil in the extension side oil chamber D pushes open the extension time valve  31  and moves through the second passage  28  into the contraction side oil chamber C, and also moves from the communication hole  24   b  of the piston rod  24  through the in-shaft passage  24   a  into the contraction side oil chamber C.  
         [0012]     The flow through the base valve  32  during these respective conditions is shown respectively in  FIGS. 3A and 3B , again by the directional arrows. Referring first to  FIG. 3A  this again shows the contraction or jounce stroke. As the piston rod  24  is inserted into the cylinder  22 , an amount of oil corresponding to the volume of the piston rod  24  flows from the cylinder  22  to the base valve  32  and is sent to the sub tank  33 . At this time, contraction side damping force is controlled by the base valve  32 .  
         [0013]     The total flows during the compression and expansion (jounce and rebound) are shown in  FIGS. 4A and 4B , respectively. Referring first to the compression stroke ( FIG. 4A ), as the piston rod  24  is pushed into the cylinder  22 , an amount of oil corresponding to the volume of the piston rod  24  flows to the base valve  32 , so that damping force on the contraction side is obtained by the control of the base valve  32 . However, since the oil acting to produce contraction side damping force is used only in the amount corresponding to the cross-sectional area of the piston rod  24 , the flow rate is small and the damping force on the contraction side cannot be obtained efficiently relative to the total cross-sectional area of the cylinder  22 .  
         [0014]     If, with the intention of increasing the damping force, the oil flow to the extension side oil chamber D is restricted by additionally throttling the contraction time valve  29  of the piston  23 , the pressure in the extension side oil chamber D tends to be negative and if so cavitation occurs. Accordingly, the damping force on the contraction operation is reduced.  
         [0015]     Now referring to  FIG. 4B  and the rebound or expansion stroke, pressure in the contraction side oil chamber C lowers, and an amount of oil corresponding to the amount of displacement of the piston rod  24  is supplied, through the base valve  32 , into the cylinder  22 . In the area of the piston  23  portion, as the piston rod  24  is drawn out, an amount of oil corresponding to the cross-sectional area of the cylinder  22  minus the cross-sectional area of the piston rod  24  flows. Thus again the amount of fluid flowing is reduced.  
         [0016]     In addition, under reversing conditions oil flows in opposite directions, a delay may occur before damping force is produced when switching from one mode to the other. The total effect of these conditions is illustrated in  FIG. 5  which is a graph showing conventional and current performance requirements of the hydraulic damper for the damping forces on extension and contraction sides plotted against the piston speed. The upper side of the vertical axis, where the damping force (N) is above 0, represents the extension side, while the lower side, the contraction side. The curves of broken lines show conventional performance while solid lines depict the desired requirements. In other words, conventionally, the contraction side damping force is less than desired, while the extension side damping force is greater than desired.  
         [0017]     It has been recognized by the inventors hereof that vehicles of light weight and high output such as sports models, require high stability and maneuverability than that obtained by the prior art units. They have understood that these vehicles require increased contraction side damping force and improved responsiveness of the extension side damping force. In other words, it is required to increase the contraction side damping force in comparison with the past, while on the extension side, the same performance as the contraction side is required. It is further required to obtain damping forces in both contraction and extension strokes while quickly responding to switching from one stroke to the other.  
         [0018]     It is a principal object of this invention to provide a vehicle suspension system that employs a greater volume of fluid for damping the jounce or compression forces than merely the effective area of piston rod displacement.  
         [0019]     It is a further object of the invention to improve the response to changes between jounce and rebound operations.  
         [0020]     It is a yet further object of the invention to provide a suspension system wherein the damping is more equal between jounce and rebound. Such requirements of the current time cannot be fully met by means of the conventional constitution in which the damping force in particular during the contraction stroke is controlled with only the limited amount of oil corresponding to the inserted volume of the piston rod.  
       SUMMARY OF THE INVENTION  
       [0021]     This invention is adapted to be embodied in a suspension system for a vehicle supporting element for movement in jounce (compression) and rebound (expansion) that provides a greater amount of fluid displacement and more equal damping while at the same time being quicker to respond to reversals in direction of movement. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]      FIG. 1  is a side elevational view, with parts broken away and shown in section of a prior art type of vehicle suspension damper.  
         [0023]      FIG. 2A  is an enlarged cross sectional view of the area encompassed by the circle  2  in  FIG. 1  showing the fluid flow during jounce (compression).  
         [0024]      FIG. 2B  is a view in part similar to  FIG. 2A , but showing the fluid flow during rebound (expansion).  
         [0025]      FIG. 3A  is an enlarged cross sectional view showing the flow through the prior art base valve during jounce (compression).  
         [0026]      FIG. 3B  is a view in part similar to  FIG. 3A , but showing the fluid flow during rebound (expansion).  
         [0027]      FIG. 4A  is a view in part similar to  FIG. 11  but shows the amount of fluid displacement during jounce (compression).  
         [0028]      FIG. 4B  is a view in part similar to  FIG. 1 , but shows the amount of fluid displacement during rebound (expansion).  
         [0029]      FIG. 5  is a graphical view showing a comparison of the actual and desired damping characteristics between those desired and those obtained by the prior art.  
         [0030]      FIG. 6  is a side elevational view, with parts broken away and shown in section, in part similar to  FIG. 1  but showing a vehicle suspension damper embodying the invention.  
         [0031]      FIG. 7A  is an enlarged cross sectional view of the area encompassed by the circle  7  in  FIG. 6  showing the fluid flow during jounce (compression).  
         [0032]      FIG. 7B  is a view in part similar to  FIG. 7A , but showing the fluid flow during rebound (expansion).  
         [0033]      FIG. 8A  is an enlarged cross sectional view of the area encompassed by the circle  8  in  FIG. 6  showing the fluid flow during jounce (compression).  
         [0034]      FIG. 813  is a view in part similar to  FIG. 5A , but showing the fluid flow during rebound (expansion).  
         [0035]      FIG. 9A  is an enlarged cross sectional view of the area encompassed by the circle  9  in  FIG. 6  showing the fluid flow during jounce (compression).  
         [0036]      FIG. 9B  is a view in part similar to  FIG. 7A , but showing the fluid flow during rebound (expansion).  
         [0037]      FIG. 10A  is an enlarged cross sectional view, in part similar to  FIG. 6 , showing the fluid flow during jounce (compression).  
         [0038]      FIG. 10B  is an enlarged cross sectional view, in part similar to  FIG. 6 , showing the fluid flow during rebound (expansion).  
         [0039]      FIG. 11  is a graph of damping forces when the piston of the hydraulic damper of the invention is displaced toward contraction and extension sides respectively in a sine wave motion.  
         [0040]      FIG. 12  is a graph made by differentiating the displacement plotted as abscissa on the graph of  FIG. 11 , with the horizontal axis representing vibration speed of the piston; and the vertical axis, damping force.  
         [0041]      FIG. 13  is a graphical view comparing the damping action of a conventional hydraulic damper and one embodying the invention. 
     
    
     DETAILED DESCRIPTION  
       [0042]     Referring now in detail to the drawings and initially to  FIG. 6 , a hydraulic damper embodying the invention is indicated generally by the reference numeral  51 . The damper  51  includes an outer housing comprised of coaxially disposed inner and outer cylinders  52  and  53  of different diameters. A piston rod  54  is inserted to be axially movable in the inner cylinder  53 .  
         [0043]     A piston  55  is fixed to the lower end of the piston rod  54  to divide the interior of the inner cylinder  53  into a contraction side oil chamber C oil the lower end side of the piston  55  and an expansion side oil chamber D on the back side of the piston  55 . The fore-end portion of the hydraulic damper  51  has a portion  56  configured for connection to a vehicle supporting component for example a wheel support member (not shown). The upper end portion  57  of the piston rod  54  is connected to a vehicle body (not shown).  
         [0044]     A base member  58  is inserted in the base end side of the outer cylinder  52  and fixed in position by means of a retaining ring  59  or the like. The outer cylinder  52  and the inner cylinder  53  are fixed to each other for example through the base member  58 . An elastic member  61  of rubber, coil spring, or the like that absorbs impact forces at the time of longest extension is attached to the base end side of the inner cylinder  53 . On the axes of the base member  58  and the elastic member  61  are respectively formed shaft holes through which the piston rod  54  is inserted.  
         [0045]     A passage  62  for providing fluid communication between the contraction side oil chamber C and the extension side oil chamber D is bored through the piston  55 . A contraction time valve  63  for opening an extension side opening  62   a  of the passage  62  in contraction stroke is provided on the end face of the passage  62  facing the extension side oil chamber D. The contraction time valve  63  is comprised of either a single or plural reed valves made from for example, annular, thin plate springs, to be pushed open by the oil flow. An in-shaft passage  64  in fluid communication with the contraction side oil chamber C is formed coaxially with the piston  55 .  
         [0046]     An axially movable damping force regulating valve  65  is inserted in an opening coaxially with the piston rod  54 . The fore-end of the damping force regulating valve  65  is formed with a conical needle  66 . The needle  66  is placed to be movable axially back and forth between a position for fully closing the base end side opening of the in-shaft passage  64  and a position for fully opening it. Oil entering the in-shaft passage  64  in contraction stroke is controlled with the needle  66  and flows into the extension side oil chamber D. The damping force regulating valve  65  moves back and forth with an regulating member  67  to regulate damping force in contraction stroke particularly in the low speed range.  
         [0047]     As with the prior art construction, on the fore-end side of the outer cylinder  52  are provided a base valve  32  and a reservoir tank  33  connected to the base valve  32 . The base valve  32  for regulating damping force during extension. The entire fore-end portion of the outer cylinder  52  is made to be in fluid communication with the inlet of the base valve  32 .  
         [0048]     A one-way valve  68  is provided at the fore-end of the inner cylinder  53 . The one-way valve  68  is opened up toward the inside of the inner cylinder  53  on an extension stroke or when the contraction side oil chamber C comes to a negative pressure.  
         [0049]     A passage hole  69  leading to the outer cylinder  52  is formed in part of the inner cylinder  53  on the back side of the piston  55 . When the piston rod  54  is inserted into the inner cylinder  53 , an amount of oil corresponding to the inserted volume of the piston rod  54  flows through the passage hole  69  into the outer cylinder  52 . The space defined between the outer cylinder  52  and the inner cylinder  53  serves as a passage  71  to the base valve  32 , so that oil flows through the passage  71  and the base valve  32  into the reservoir tank  33 .  
         [0050]     While the cylinder of the illustrated embodiment of a double structure the communication with the base valve  32  may be provided by an external passage made of a tube or the like provided between the passage hole  69  and the inlet of the base valve  32 .  
         [0051]     Now the operation of the above hydraulic damper  51  will be described, first by reference to  FIGS. 7A and 7B .  
         [0052]     These figures show the state of the portion ( 7 ), around the piston  55 , of the hydraulic damper  51  shown in  FIG. 6 .  FIG. 7A  shows contraction (jounce) stroke and with  FIG. 7B  shows the extension stroke. The arrows indicate the directions of oil flow.  
         [0053]     When the wheel is pushed up by road surface irregularities and the hydraulic damper  51  comes to the compressed state, the cylinders  52  and  53  move toward the base end side, or upward in  FIG. 7A . As a result, the piston  55  is relatively pushed down in as seen. At this time, as the pressure in the contraction side oil chamber C rises, oil flows up in the figure to open up the contraction time valve  63 .  
         [0054]     When the contraction time valve  63  opens as shown in  FIG. 7A , oil flows through the passage  62  into the extension side oil chamber D, and damping force is produced. When the pressure in the contraction side oil chamber C rises, part of oil flows from the in-shaft passage  64  through the needle  66 , and a second passage  72  bored in the piston  55  into the extension side oil chamber D. A valve  73  capable of opening in one direction toward the extension side oil chamber D is provided at the outlet of the second passage  62 . As oil flows while pushing open the valve  73 , pre-adjusted damping force is produced. At normal low speeds, oil flows through the in-shaft passage  64  into the extension side oil chamber D. Along with the increase in speed, oil pushes open the contraction time valve  63  to produce greater damping force.  
         [0055]     As the piston rod  54  is inserted into the inner cylinder  53  during the contraction stroke (See  FIGS. 6, 7   a  and  7   b ), the amount of oil corresponding to the inserted volume of the piston rod  54  becomes a surplus. This surplus oil flows, through the passage hole  69 , into the outer cylinder  52 . Thus, the pressure in the extension side oil chamber D is prevented from rising, and oil flow through the contraction time valve  63  becomes smooth to produce sufficient damping force during contraction.  
         [0056]     During an extension (rebound) stroke in which the piston  55  moves in the opposite direction, the pressure in the extension side oil chamber D rises. During this time, as shown in  FIG. 7 (B), the contraction time valve  63  and the damping force regulating valve  65  are in closed state, and oil flows, through the passage hole  69 , into the outer cylinder  52 .  
         [0057]     The operation of the one way valve  68  during the suspension travel will now be described by reference to  FIGS. 8   a  and  8   b . Again these two views show respectively the contraction (jounce) and expansion (rebound) operations with the fluid flow directions indicated by the arrows.  
         [0058]     As the pressure in the contraction side oil chamber C rises during contraction stroke, as shown in  FIG. 8   a , the one-way valve  68  remains in closed state and no oil flow occurs through the one-way valve  68 . However when the pressure in the contraction side oil chamber C lowers during extension stroke, a spring  74  deflects to open up the one-way valve  68  as shown in  FIG. 8   b . As a result, oil in the reservoir sub tank  33  flows, through the base valve  32  and the one-way valve  68 , into the inner cylinder  53 .  
         [0059]     Referring now to  FIGS. 9   a  and  9   b , these show the flow conditions respectively through the base valve  32  during the contraction (jounce) and expansion (rebound) operations with the fluid flow directions again indicated by the arrows. During the contraction stroke as shown in  FIG. 9   a , the amount of oil corresponding to the inserted volume of the piston rod  54  flows through the passage hole  69  into the outer cylinder  52 . This surplus amount of oil then flows through the base valve  32  and into the reservoir sub-tank  33 . During the extension stroke, the oil flow as shown in  FIG. 9   b , reaches the base valve  32  to push up the valve in the base valve  32  and flows into the reservoir tank  33 .  
         [0060]      FIGS. 10   a  and  10   b  show the combined oil flow shown in  FIGS. 7   a  and  7   b ,  8   a  and  8   b  and  9   a  and  9   b  in the contraction (jounce) and expansion (rebound) strokes, respectively. Again, arrows indicate the directions of oil flow.  
         [0061]     During the contraction stroke, the amount of oil corresponding to the inserted volume of the piston rod  54  flows into the reservoir tank  33 . The one-way valve  68  at the fore-end of the inner cylinder  53  remains closed by the internal pressure. Therefore, as shown in  FIG. 59   a , the amount of oil corresponding to the entire cross-sectional area of the inner cylinder  53  of the contraction side oil chamber C contributes to producing damping force during the contraction stroke. Therefore, sufficient damping force during contraction can be produced efficiently.  
         [0062]     Furthermore, because the amount of oil corresponding to the inserted volume of the piston rod  54  flows into the reservoir tank  33  which controls damping force during extension stroke, it is possible to cause oil to flow instantaneously into the contraction side oil chamber C when the stroke switches from contraction to extension. Thus, responsiveness during stroke switching is improved.  
         [0063]     During the extension stroke as shown in  FIG. 10   b , the amount of oil iii the extension side oil chamber D corresponding to the cross-sectional area of the inner cylinder  53  minus the cross-sectional area of the extended piston rod  54  flows through the passage hole  69  into the base valve  32  which serves as an extension damping force producing section. In addition, the amount of oil corresponding to the extended piston rod  54  is sent, as described above into the reservoir tank  33  during the contraction stroke. Therefore, when the one-way valve  68  of the inner cylinder  53  opens up, an amount of oil corresponding to the whole cross-sectional area of the inner cylinder  53  flows into the contraction side oil chamber C to contribute to producing extension damping force. Thus, sufficient extension damping force is produced efficiently.  
         [0064]     Furthermore, with the simple constitution as described above, the directions of oil flow during both contraction and extension stroke become the same. Therefore, it is possible to produce damping force in opposite direction smoothly without delay when switching from one stroke to the other.  
         [0065]     The performance of the hydraulic damper  51  embodying the invention in a dynamic condition may be understood by reference to  FIG. 1  which is a graph of damping forces when the piston  55  of the hydraulic damper  51  of the invention is displaced toward contraction and extension sides respectively in sine wave motion. The horizontal axis represents displacement, and the vertical axis represents damping force. The portion above 0 (N) of the vertical axis represents extension (jounce) side load, and the side below it represents contraction (rebound) side load. As an example, tracing the curve from 0 (N) upward represents the state of acceleration on the extension side; from top domes toward 0(N), deceleration on the extension side. Tracing from 0(N) downward, represents acceleration on the contraction side; up toward 0(N), deceleration on the contraction side.  
         [0066]     This graph visually shows the relationship between displacement and damping force, or change in damping force with respect to displacement, due to reciprocal motion of the piston  55 . However, it is hard to determine from this graph if performance required of a hydraulic damper is met.  
         [0067]      FIG. 12  is a graph made by differentiating the displacement plotted as abscissa on the graph of  FIG. 11 , with the horizontal axis representing vibration speed of the piston; and the vertical axis, damping force. Like  FIG. 11 , the side above 0 (N) on the vertical axis represents extension side load; the side below it, contraction side load. Tracing the curve from 0 (N) upward represents the state of acceleration on the extension side; from top down toward 0(N), deceleration on the extension side. Tracing from 0(N) downward, represents acceleration on the contraction side; up toward 0(N), deceleration on the contraction side.  
         [0068]     This graph shows that the curves of acceleration and deceleration are closer to each other. Thus more similar damping forces to each other the obtained if the curves of acceleration and deceleration are superimposed That is substantially the same damping forces are obtained in both acceleration and deceleration. It is also easy to determine if damping force responds appropriately without delay to changes in vibration speed and to switching of oscillation between the contraction side and the extension side  
         [0069]     From this graph, it is possible to determine the performance of the hydraulic damper of the invention by comparing damping force values on acceleration and deceleration at a vibration speed that is half the peak value of the vibration speed. For example, in case the performance on the contraction side of the example of  FIG. 12  is determined, the difference between acceleration side and deceleration side at 0.05 m/s, half the vibration speed of 0.1 m/s, is indicated as a rate of decrease in damping force.  
         [0070]     Referring now to  FIG. 13 , this is a graph of comparison by the method of  FIG. 12  between the inventive hydraulic damper shown in  FIG. 6  and the conventional hydraulic damper shown in  FIG. 1  for the contraction side damping force.  
         [0071]     As seen in this graph, a difference between damping forces on acceleration and deceleration sides is determined at a vibration speed of −0.15 m/s, half the peak value of −0.3 m/s. The conventional damper showed −162 N in acceleration and −668 N in deceleration, which means a rate of decrease of −76% on the acceleration side from the deceleration side. The hydraulic damper of the invention showed −800 N in acceleration and −860 N in deceleration, with a rate of decrease of −7%. Thus, the hydraulic damper of the invention showed great improvement in damping force response.  
         [0072]     Of course those skilled in the art will recognize that the foregoing example is only one specific form the invention may take. Those skilled in the art will readily realize that various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.