Patent Publication Number: US-11396342-B2

Title: Front suspension of the telescopic type with anti-dive effect

Description:
FIELD OF APPLICATION 
     The present invention relates to a front suspension of the telescopic type with anti-dive effect for vehicles. The present invention applies to both vehicles with endothermic, electrical engine and hybrid solutions, and to human traction vehicles, such as cycles. 
     PRIOR ART 
     As is known, a front suspension of the telescopic type, be it traditional or with upside down stems, consists of a fork having stems that telescopically slide with respect to the respective sheaths, in which they are at least partially housed and guided. The fork may be either single-arm or double-arm. 
     During braking, due to the transfer of load on the front axle of the vehicle, due to deceleration, the telescopic front fork tends to compress and thus ‘dive’ more than would happen for just the static weight of the vehicle with pilot and any other suspended loads (such as passenger, luggage and the like). 
     The dive of the front axle, possibly constrained to reaching the end of stroke in compression of the fork stems, has as a direct consequence a significant change in the vehicle balance. 
     In fact, if one thinks for example of a two-wheel motorcycle, but the same phenomenon also applies to different types of vehicles with more wheels, the trail of the vehicle is reduced, in particular, in the compression step of the telescopic fork. The modification of the trail changes the sensitivity and responsiveness of the handlebar perceived by the pilot. Also, as a result of a poorly controlled and/or excessive dive of the fork, an extension of the rear suspension which is in turn poorly controlled is generally obtained, resulting in the lightening of the rear axle, until the limit condition of detachment of the rear wheel from the ground is achieved, which could result in loss of control of the trajectory set by the pilot. 
     It should be noted that changing the balance during the dive does not necessarily have negative effects. In other words, on the one hand an excessive dive is certainly negative, since it involves a change in the dynamic balance that can undermine the vehicle and the driver, especially if the end of stroke is reached with relative risk of rebound of the front wheel; on the other hand, a controlled dive of the fork may even facilitate and improve drivability and riding feeling. 
     In fact, due to the extent of the fork dive, the pilot is able to perceive the dynamic behavior of the vehicle in addition to perceiving, in advance, the achievement of the grip limit of the tire. In addition, a controlled dive of front axle provides better descent to to set a curve both because it facilitates the descent of the front axle and because reducing the trail increases the pilot&#39;s responsiveness and thus sensitivity. 
     As can be inferred from the above, the fork dive causes, depending on its extent, a substantial modification of the dynamic balance of the vehicle. A controlled dive is not only not harmful but improves driveability and manoeuvrability of the vehicle. 
     Front suspension solutions exist in the art aimed to reduce or control the dive effect in braking. 
     In the present discussion, the term “antidive” refers to a purely mechanical system acting on a telescopic front suspension whereby, taking advantage of the torque generated by the front brake system (irrespective of the type), the dive that would normally be present in this type of suspension generated by the same braking torque can be managed, more or less perceptibly. Managing the dive basically means reducing it but, as seen, nothing prevents one from canceling or amplifying it (the latter case is referred to as “prodive”). The system may be present on one side only of a dual-arm front suspension (which then has a traditional telescopic fork on one side and a telescopic fork with antidive system on the other side) or on both (which then has two telescopic forks with antidive system). In the case of a single-arm suspension, the antidive system is not necessarily present only on the side where the fork itself is. 
     Antidive solutions used in the past in case of telescopic front suspension consisted of articulated quadrilateral systems or even simpler ones (direct return); without going into detail, an antidive effect was obtained with these systems tied only to the braking torque and little manageable as a function of the stroke of the front suspension, and thus indirectly a dive with narrow margin of control, with reference to the above. 
     Due to these limitations, the known quadrilateral type systems were abandoned over the years and currently are no longer used. 
     The problem of excessive dive under heavy braking thus remains unresolved or rather, such a problem is addressed by further stiffening the suspension to prevent an excessive dive thereof or, worse still, reaching the end of stroke in compression. 
     The drawback of this strategy is to have an always very rigid suspension (even when not required) so that it can sustain high deceleration and load transfers, but this inevitably leads to easy loss of grip of the front tire; in fact the latter, in the case of very stiff suspension, struggles to follow the roughness of the road surface and basically tends to bounce thereon, thus sensibly reducing the contact forces and thus adherence, with the road surface itself. 
     DISCLOSURE OF THE INVENTION 
     The need of solving the drawbacks and limitations mentioned with reference to the prior art is therefore felt. 
     Such a need is met by a front suspension of the telescopic type with anti-dive effect according to claim  1 . 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the present invention will appear more clearly from the following description of preferred non-limiting embodiments thereof, in which: 
         FIG. 1  shows a perspective view of a front suspension  4  according to an embodiment of the present invention; 
         FIG. 2  shows a schematic side view of a motorcycle comprising the suspension in  FIG. 1  in a non-dive configuration or maximum extension of the suspension; 
         FIG. 3  shows the enlargement of detail III in  FIG. 2 ; 
         FIG. 4  shows a sectional view along the sectional plane IV-IV in  FIG. 2 ; 
         FIG. 5  shows a schematic side view of the motorcycle in  FIG. 2  in a partial dive configuration of the suspension; 
         FIG. 6  shows the enlargement of detail VI in  FIG. 5 ; 
         FIG. 7  shows a schematic side view of the motorcycle in  FIG. 2  in a maximum dive configuration of the suspension; 
         FIG. 8  shows the enlargement of detail VIII in  FIG. 7 ; 
         FIG. 9  shows a schematic view of a force scheme of a suspension according to the present invention; 
         FIGS. 10-12  show side views of suspensions according to embodiment variants of the present invention; 
         FIG. 13  shows a diagram of the anti-dive force variation of a suspension according to the present invention. 
     
    
    
     Elements or parts of elements in common between the embodiments described below are referred to with the same reference numerals. 
     DETAILED DESCRIPTION 
     With reference to the above figures, reference numeral  4  globally indicates an overall schematic view of a front suspension of the telescopic type with anti-dive effect according to the present invention. 
     For the purposes of the present invention, it should be noted that the front suspension may be applied to any type of vehicle  8 , be it preferably a motor vehicle, such as a motor cycle, or a human traction vehicle. 
     The term motorcycle should be considered in a broad sense, encompassing any motor cycle having at least two wheels, i.e. one front wheel  12  and one rear wheel  16 . Therefore, this definition also includes three-wheel motorcycles, such as two paired and steering wheels on the front end and one driving wheel at the rear, but also motorcycles that include only one wheel, steering, on the front end and two driving wheels at the rear. Finally, the definition of motorcycle also includes the so-called quads, with two wheels at the front end and two wheels at the rear end. 
     With the term kinematic connection, each connection must be considered to allow the reciprocal distance of the connected elements to vary over time. The mechanical connection, unlike the kinematic connection, keeps the distance between two constant connection points over time. 
     The present invention focuses on the front axle  20  of vehicle  8  without discussing the type of frame  24  of the vehicle or the rear axle  28 . 
     For the purposes of the present invention, frames  24  of any shape and size may be used: they may be, for example, trellis type frames, box-shaped, die-cast, and so on. 
     The front suspension  4  of the telescopic type with anti-dive effect comprises at least one sheath  32  and at least one stem  36 , housed and guided telescopically inside said sheath  32  according to a direction of the fork axis Z-Z, in a known manner. 
     The distance between the positions of maximum approach and maximum mutual distancing between sheath  32  and stem  36  defines the suspension stroke. 
     Sheath  32  and stem  36  typically, but not exclusively, have circular section. 
     In a known manner, between stem  36  and sheath  32  there are arranged the suspensions comprising at least one spring and a shock absorber (not shown); typically, said suspensions are at least partially housed into sheath  32  and/or stem  36 . 
     For the purposes of the present invention, the front suspension  4  may be both of traditional type, having sheath  32  positioned at the bottom, connected to the front wheel  12  and stem  36  positioned at the top, kinematically connected to handlebar  40 , and of the type with reversed or ‘upside down’ stems, having stem  36  positioned at the bottom, connected to the front wheel  12  and stem  32  positioned at the top, kinematically connected to handlebar  40 . 
     Moreover, the suspension may be either single-arm or two-arm type. 
     The front suspension  4  comprises a foot  44  associated to sheath  32  or to stem  36  that rotatably supports a wheel spindle  48  of an associable front wheel  12  defining a rotation axis X-X. 
     Foot  44  will be associated to sheath  32  in the case of traditional suspension, while it will be associated to stem  36  in the case of suspension with upside down stems. 
     A braking device  52  is further provided for the associable front wheel  12  which comprises a support  56  rotatably mounted with respect to the wheel spindle  44  so as to be able to oscillate about the rotation axis X-X, as better described hereinafter. 
     The braking device  52  typically is a calliper for disc brake adapted to exert a braking action on a brake disc  60  integral in rotation with the front wheel  12 . 
     Advantageously, between support  56  of the braking device  52  and foot  44  of suspension  4  are interposed transfer means  64  of the braking force, exerted by the braking device  52 , on a portion of the suspension integral to element  32 ,  36  between sheath  32  and stem  36  that does not support foot  44 . 
     In other words, in case of conventional fork, where foot  44  is associated to sheath  32 , the transfer means  64  release the braking force on stem  36  or on a portion of the suspension integral to stem  36 . In case of fork with upside down stems, where foot  44  is associated to stem  36 , the transfer means  64  release the braking force on sheath  32  or on a portion of the suspension integral to sheath  32 . 
     In general, the transfer means release, in the direction of the fork axis Z-Z, a part of the braking force on a suspended mass of the vehicle, so as to facilitate the extension of the fork. The suspended mass will be integral with sheath  32  in the case of fork with upside down stems while it will be integral with stem  36  in the case of traditional fork. In general, suspended mass means both a mass of the actual fork, suspended with respect to the wheel, and a mass of the frame that supports the fork and which is in turn suspended with respect to the wheel. Therefore, for the protection scope of the present invention, suspended mass means both a suspended mass of the fork and a suspended mass of frame  24  that supports the fork. 
     The transfer means  64  comprise a cam  68  hinged to foot  44  in a first hinge point  72 . 
     Therefore, foot  44  of the front suspension  4  supports the front wheel spindle  48  (as in a traditional fork) and also acts as a fulcrum to cam  68 . 
     Moreover, cam  68  is kinematically connected to the braking device  52 , and is mechanically connected to a portion of the suspension integral with element  32 ,  36  between sheath  32  and stem  36  that does not support foot  44  so as to transfer to said element  32 ,  36 , in the direction of the fork axis Z-Z, a part of the braking force. 
     In other words, in the case of conventional fork, in which foot  44  is associated to sheath  32 , cam  68  is mechanically connected to stem  36  or to a portion of the suspension integral to stem  36  so as to transfer thereto, in the direction of the fork axis Z-Z, at least a part of the braking force: such a transfer of force opposes the compression of the suspension. 
     In case of fork with upside down stems, in which foot  44  is associated to stem  36 , cam  68  is mechanically connected to sheath  32  or to a portion of the suspension integral to sheath  32  so as to transfer thereto, in the direction of the fork axis Z-Z, at least a part of the braking force. 
     According to an embodiment, cam  68  is mechanically connected to a portion of the suspension integral with element  32 ,  36 , between sheath  32  and stem  36 , which does not support foot  44 , by means of a connecting rod  73  hinged, at opposite ends, to cam  68  and to said portion of the suspension integral to element  32 ,  36  that does not support foot  44 . 
     According to an embodiment, the connecting rod  73  is hinged to cam  68  and to collar  74  integral with said element  32 ,  36  so as to transfer to this, in the direction of the fork axis Z-Z, a part of the braking force. 
     Therefore, if cam  68  is hinged to a foot  44  integral to sheath  32 , the connecting rod  73  will be hinged to cam  68  and to collar  36  or to a portion of the suspension integral to stem  36 ; 
     conversely, if cam  68  is hinged to a foot  44  integral to stem  36 , the connecting rod will be hinged to cam  68  and to collar  74  integral to sheath  32 , or to a portion of the suspension integral to sheath  32 . 
     In general, as seen, the reaction force generated by the antidive mechanism and due to the braking force, instead of being released on collar  74  can also be released on other components of the suspension rigidly constrained to sheath  32  in the case of a fork with upside down stems, or rigidly constrained to stem  36  in the case of a conventional fork. Such components may for example be a steering plate  75 , typically the bottom plate, or any further suspended mass. 
     Therefore, the use of a collar  74  should be considered as one of the embodiments of the antidive suspension proposed and not binding. What matters is in fact that the reaction to the braking force is released by the antidive suspension on the suspended mass of the vehicle with a component along the fork axis Z-Z such as to control the dive of the suspension itself. 
     According to an embodiment, cam  68  comprises a curvilinear guide profile  76  that slidably houses a roller  80  in turn hinged at a second hinge point  84  integral with support  56  of the braking device  52  and movable with this, so that said roller  80  transmits to cam  68  only perpendicular forces at a contact point P with the guide profile  76  of cam  68  itself. In particular, roller rotates in an axial-symmetric manner around the second hinge point  84 . 
     In other words, since roller  80  rotates around the second hinge point  84 , it is not able to transmit forces to the guide profile  76  that are not passing by the hinge point and perpendicular to the contact point P with the guide profile  76 . 
     According to an embodiment, the guide profile  76  of cam  68  has a centre of curvature C variable along its extension, said centre of curvature C determining a relative eccentricity d variable with respect to the first hinge point  72 , the eccentricity d being the distance between the first hinge point  72  and a straight line perpendicular to a contact point P mutual between the guide profile  76  of cam  68  and said roller  80 . 
     Preferably, the guide profile  72  of cam  68  is shaped so as to present at least one portion of no eccentricity d. 
     As better described below, canceling the eccentricity d involves no transfer of the braking force, in the direction of the fork axis Z-Z, to element  32 ,  36 , between sheath  32  and stem  36 , which does not support foot  44 . In other words, when eccentricity d is canceled, the antidive effect is canceled irrespective of the extent of the same braking force. 
     According to an embodiment, the curvilinear guide profile  76  comprises a first curvilinear portion  88  having a first centre of curvature C′ eccentric with respect to the first hinge point  72 , i.e. having non zero eccentricity d, and a second curvilinear portion  92 , tangent and contiguous to the first curvilinear portion (C′), having a second centre of curvature (C″) aligned with the first hinge point ( 72 ), i.e. having no eccentricity d. 
     According to further embodiments, the curvilinear guide profile  76  comprises a number of curvilinear portions greater than or equal to 2, said curvilinear portions being tangent to each other in respective connecting portions. 
     Instead, the guide profile  76  comprises at least one stretch curved as a circumference arc, and, even more preferably, it comprises a plurality of circumference arcs joined together. 
     The curvilinear guide profile  76  has a slot shape that extends between a first and a second abutment  96 ,  98 , defining the ends-of-stroke in rotation of cam  68 . 
     According to a possible embodiment ( FIG. 10 ), there is provided a preloaded traction spring  100  between foot  44  and support  56  of the braking device  52 . 
     For example ( FIG. 11 ), said traction spring  100  connects together a roller fixing screw  80  with the first hinge point  72  of cam  68 . 
     According to a further embodiment ( FIG. 12 ), there is provided a preloaded torsion spring  104  between support  56  of the braking device  52  and the wheel spindle  48 . 
     The purpose of the traction spring  100  and of the torsion spring  104  which may be provided independently of each other or may also coexist in the same embodiment, is to cancel or otherwise limit the clearances and/or the vibrations between the movable parts of the front suspension  4 . 
     To achieve the same purpose, according to a possible embodiment, support  56  of the braking device  52  comprises two oblique bearings  108 ,  110  arranged in an “X” mounting scheme in correspondence of opposite axial ends of foot  44 . 
     It should be noted that, on the one hand, the braking device  52 , typically the calliper for disc brake, must be able to rotate freely around the wheel spindle  48 , and on the other hand the assembly clearances should be minimized. The cited ‘X’ mounting scheme that uses two oblique bearings  108 ,  110  fulfils this task; preferably, said oblique bearings  108 ,  100  are preloaded by lock nuts. 
     This ‘X’ mounting scheme of the bearings is not binding; the oblique bearings may for example be arranged as an “O”, or possibly replaced with ball bearings, roller cages, etc. while still ensuring the free rotation between foot  44  and the braking device  52 . 
     The bearings are preferably dust-shielded. 
     The operation of a front suspension of the telescopic type with anti-dive effect according to the invention will now be described. 
     In particular, in order to better understand the operation of the suspension described, it is useful to adopt a mathematical discussion of the forces exchanged between the parts. 
     With reference to  FIG. 9 , the forces at play should first be defined as follows:
         F: longitudinal ground force generated by the braking torque,   K: normal force to the guide profile  76  of cam  68 ; i.e. this represents the force that support  56  of the braking device  52  exerts on cam  68 ;   B: cam  68  reaction on the connecting rod  73 ;   S: force generated by the antidive system in the direction of the fork axis Z-Z, such as to extend the fork, that is, distance stem  36  from sheath  32 ; in other words, it is the useful component of B that actually generates the antidive effect.       

     In addition the following magnitudes of the suspension are defined:
         a: distance between the contact point with the ground of the front wheel  12  and the axis of rotation X-X; in other words, ‘a’ represents the rolling radius of the front wheel  12 ;   b: distance between the axis of rotation X-X and the straight line normal to the point of contact P between cam  64  and the guide profile  76 ;   d: eccentricity value, described above;   e: distance between the first hinge point  72  of cam  68  and the straight line of extension of the connecting rod  73  (the distance between a point and a straight line obviously is intended to be measured perpendicular to the straight line itself).       

     The mathematical model applicable to the suspension provides the balance of moments as follows:
         Balance of moments for support  56  of the braking device  52 :
 
 F*a=K*b  whereby  K=F*a/b;  
   Balance of moments for cam  68 :
 
 K*d=B*e  whereby  B=K*d/e=F *( a/b )*( d/e )
   Thrust S
 
 S=B *cos(α)= F *( a/b )*( d/e )*cos(α)
       

     Wherein α is the inclination angle of the fork axis Z-Z with respect to the connecting rod  73 . As a result, the ratio S/F is defined as follows:
 
 S/F =( a/b )*( d/e )*cos(α)
 
     The ratio S/F obtained with the present invention is essential to understand the operation of the suspension. 
     In particular:
         “d”, that is, the eccentricity, the magnitude of considerable interest is tied to the guide profile  76  of cam  68 : if as a function of the fork stroke, i.e. of sheath  32  with respect to stem  36 , this magnitude goes to 0, the ratio S/F goes to 0; that is, in this case, the anidive effect goes to 0 irrespective of the braking force F present (as mentioned above). In the case in the figure (example), we have have a “cam” profile consisting of two arcs of circles, namely the two curvilinear stretches  88 ,  92  tangent to each other, of which one with a center of curvature C′ eccentric with respect to the first hinge point  72  of cam  68  and one aligned with the first hinge point  72  of cam  68 . When, at a given stroke of stem  36  or sheath  32 , roller  80  of cam  68  goes from the first curvilinear stretch  88  to the second curvilinear stretch  92 , eccentricity “d” goes to 0 and thus indirectly, also S, i.e. the antidive thrust goes to 0. The geometry of the guide profile  76  of cam  68  obviously can be any, and the proposed solution is not binding (‘n’ circle arcs with n&gt;=2 may be used, for example, properly defined spline, etc.);   angle “α” may be managed to vary the S component with equal B; at the same time, one must avoid that by increasing angle “α”, an excessive thrust value normal to the fork axis Z-Z is achieved (which could become critical for the fork itself);   “a” varies depending on the roll angle of the vehicle and depends on the geometry of the tire. It is therefore not a parameter on which there is particular flexibility.       

     The other magnitudes “b” and “e” are more related to geometry (i.e. to overall dimensions) and indirectly to the loads to which the individual components of the antidive system are subjected. 
     As described above, in general the system uses the torque generated by the front brake to create an axial thrust on the fork which tends to extend it, thus reducing the stroke and dive speed of the same, especially in the first braking phase. The object of controlling the dive of the front suspension during braking has thus been achieved. 
     The weight that will then have the “braking point” when establishing the adjustments of the front suspension (stiffness, spring preload and hydraulics) will be reduced as part of the support given by the suspension at this stage will be replaced by the contribution of the anidive system. 
     The proposed system has the peculiarity of using a “cam” profile: using the variation of eccentricity between the guide profile of the cam and the rotation spindle of the same it is possible to:
         decide at what point of the fork stroke end the antidive effect irrespective of the braking force present;   deciding the percentage of axial force generated on the fork with respect to the braking force on the ground.       

     An example of variation of the antidive force of a suspension according to the present invention is shown in  FIG. 13 , where cam  68  is calibrated so as to have the cancellation of the dive force, or the cancellation of the antidive effect for a dive stroke of the suspension greater than or equal to 80 mm. The abscissa shows the dive stroke, while the ordinate shows the percentage of the antidive force S with respect to a unit braking force F. 
     As can be understood from the description, the suspension according to the invention allows overcoming the drawbacks of the prior art. 
     In particular, the suspension according to the present invention establishes, in a very flexible and completely arbitrary manner, and depending on the stroke of the fork (from all compressed to all extended), the ratio of F to S (i.e. between the braking force on the ground and the antidive thrust that opposes the yield or dive of the suspension). One can for example and actually cancel the antidive effect S from a certain dive stroke of the fork on, irrespective of the value of the braking force F using a suitable cam profile. This flexibility is useful for example if one wants, in a cornering maneuver, a concrete antidive effect in the first part of the brake (motorcycle straight and need for support in order to curb more decisively) which then tends to cancel itself towards the curve center (prior to the brake release step), where the conditions of adhesion for the front tire are considerably reduced and the presence of “residual” forces given by the antidive, or simply their cancellation given by the release of the same brake could further limit worsen them. 
     Therefore, the present invention allows setting the vehicle so as to have the preferred dynamic behavior in order to obtain an antidive effect which is calibrated as a function of the dive stroke and of the extent of braking. 
     A man skilled in the art may make several changes and adjustments to the suspensions described above in order to meet specific and incidental needs, all falling within the scope of protection defined in the following claims.