Abstract:
A motorcycle ( 1 ) having a frame ( 2 ) mounted on a front wheel ( 3 ) and on a rear wheel ( 4 ), each wheel ( 3, 4 ) operationally cooperating with a corresponding suspension unit ( 5, 6 ) connected to the frame ( 2 ), the wheels ( 3, 4 ) resting on a support surface (S); the rear suspension unit ( 6 ) including a reaction rod ( 15 ) selectively yieldable along a longitudinal axis (W) and having two opposing ends ( 15 A,  15 B), the ends ( 15 A,  15 B) being selectively approachable to each other when the vehicle ( 1 ) is braked in order to obtain lowering of the barycenter of the motorcycle ( 1 ) towards the support surface (S) to enable greater braking of the vehicle ( 1 ) and greater vehicle stability during this braking.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a motorcycle and in particular to a motorcycle of the type having a frame mounted on a front wheel and on a rear wheel, each wheel operationally cooperarting with a corresponding suspension unit connected to the frame.  
         BACKGROUND OF THE INVENTION  
         [0002]    In a motorcycle, in particular in a sports motorcycle, two main factors are known to limit the obtainable deceleration: the first is the friction between the wheel tire and the surface (for example of asphalt) on which the vehicle moves, and the second is the tendency of the vehicle to tilt forwards. In high-performance motorcycles, tilting represents the main limit. This tilting occurs when the resultant of the forces acting on the motorcycle barycentre during braking (i.e. the braking force and that deriving from the weight of the vehicle plus driver) encounters the support surface (or ground) at a point to the front of the point of contact of the front wheel with this surface. Tilting does not occur if this resultant encounters said surface between the points at which the front and rear wheels make contact with the ground.  
           [0003]    With the known “geometries” of known motorcycle suspension units, in which the wheels are connected to the frame via usual elastic damper members (with the front unit comprising a reaction rod and possibly a rocker or similar member), during braking there is progressive transfer of the combined weight of the vehicle plus driver towards the front wheel. There is hence a front “sinking” effect of the motorcycle and a simultaneous extension of the rear suspension unit. The movement of each suspension causes the vehicle barycentre to shift, however the sum of these movements results in a substantial immovability of the barycentre; consequently if the resultant of the aforesaid forces when applied to this barycentre encounters the surface or ground to the front of the point of contact of the front wheel with this ground (which can happen during very intense braking, so-called “to the limit”), the rear wheel rises from the ground with consequent considerable motorcycle instability.  
         SUMMARY AND OBJECTS OF THE INVENTION  
         [0004]    An object of the present invention is to provide a motorcycle of high stability during braking, in which very sudden vehicle braking even at high speed can be obtained without risk of raising its rear wheel.  
           [0005]    Another object is to provide a motorcycle of the aforesaid type which is reliable in use under all conditions.  
           [0006]    These and further objects which will be apparent to one skilled in the art.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The present invention will be better understood from the accompanying drawing, which is provided by way of non-limiting example and in which:  
         [0008]    [0008]FIG. 1 is a schematic illustration of the motorcycle according to the invention;  
         [0009]    [0009]FIG. 2 is a diagram of a rear suspension unit of the motorcycle of FIG. 1 shown during normal unbraked use of the vehicle;  
         [0010]    [0010]FIG. 3 is a diagram of the suspension unit of FIG. 2 shown during braking of the motorcycle of FIG. 1;  
         [0011]    [0011]FIG. 4 is a schematic illustration of the hydraulic circuit associated with the suspension unit of FIGS. 2 and 3; and  
         [0012]    [0012]FIG. 5 is a schematic illustration of the control circuit of the suspension unit of FIGS. 2 and 3. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    With reference to said figures, a motorcycle  1  (shown very schematically) comprises a streamlined frame  2 , supported by a rear wheel  3  and a front wheel  4 . A usual front suspension unit  5  is associated with the wheel  3 , and a rear suspension unit  6  is associated with the wheel  4 . The rear wheel  4  is associated with the frame  2  via one or more arms  8  (only one is shown in FIG. 1). The rear suspension unit  6  is positioned between the arm  8  and the frame  2 , for example a lattice frame. The arm  8  is secured at one end  9  to the hub  10  of the wheel  4  and at its opposite end is hinged at  12  to the frame  2 .  
         [0014]    In the described embodiment, the suspension unit  6  comprises a rocker  13  pivoted to a projection  14  rigid with the frame  2 ; to the opposite ends  13 A and  13 B of the rocker  13 , there are pivoted respectively a hydraulic actuator  15  (replacing a usual rigid reaction rod) and an elastic damper member (or simply “damper”)  16 . The actuator  15  presents a longitudinal axis W, a first end  15 A pivoted to the rocker  13  and a second end  15 B pivoted on a pin  17  which secures it to the arm  8 . One end  16 A of the damper  16  is also pivoted on this pin. The actuator  15  is of the hydraulic type and comprises a cylinder  20  within which a piston  21  slides, the cylinder being fixed to the rocker  13  and the piston being associated with a rod  22  connected to the pin  17 . The position of the piston  21  within the cylinder  20  (of double acting type) defines in this latter two variable volume chambers  20 A and  20 B connected to conduits  23  and  24  respectively. The conduit  23  is connected to a valve member or unit  27 , preferably comprising at least one solenoid valve, connected to a reservoir  30  via a conduit  28 . A further conduit  31  originating from the reservoir  30  is also connected to the solenoid valve via a filter  32 , a pump  33  and unidirectional valves  34  and  35 . An accumulator  37  is connected to the conduit  31  between the two valves. A fluid, for example oil, is present in the reservoir  30  and in the entire system  40  defined by the conduits  23 ,  28  and  31  and by the members connected to them; this system is totally independent of the other hydraulic systems of the vehicle. However the oil of said system can also be oil from the engine lubrication circuit (of which in this case the reservoir  30  would form part and to which the system  40  would be connected).  
         [0015]    The pump  33  draws oil from the reservoir and feeds it to the accumulator  37 , which is able to supply high flow rates (substantially instantaneously) to the actuator  15  when this is necessary. The valve member or solenoid valve  27  is controlled by a control unit  41  able to modify the height of the motorcycle barycentre from the ground S only during particular braking situations in which, in the absence of the invention, the vehicle could raise the rear wheel  4  from the ground and, in the limit, tilt forwards. Such situations are in particular those involving prolonged braking. To be able to operate effectively, the unit  41  receives information from several sensors positioned on the motorcycle, and which can include: a sensor  42  for measuring the pressure of the front wheel  3  on the brake  43  (for example via a pressure sensor positioned in the braking circuit connected to the brake  43 ), a sensor  45  for determining the position of the fork  46  of the front suspension unit  5 , a sensor  47  for determining the position of the rear wheel  4  relative to the ground by monitoring the rear suspension unit  6 , a movement speed sensor  48 , a sensor  49  measuring the position of the piston  21  within the cylinder  20  and a sensor  50  for measuring the degree of opening of the throttle valve (or measuring the degree of throttling of the engine intake duct). From the data originating from all or at least a part of these sensors (or measurement members), the unit  41  senses when the invention can be activated, or for how long the actuator  15  is to be operated and at what rate.  
         [0016]    Various logics can be used on which the unit  41  bases its decision to activate the system; these include the following logics, causing the unit  41  to operate when:  
         [0017]    a) the pressure of the front brake (measured by the sensor  42 ) exceeds a predetermined threshold pressure;  
         [0018]    b) the front fork sinks more than a certain predetermined value (this measured by the sensor  45 );  
         [0019]    c) the case in which both the aforesaid conditions under points a) and b) occur,  
         [0020]    d) the aforedescribed combinations in combination with a determination that the vehicle speed is greater than a predetermined value;  
         [0021]    e) closing the throttle from accelerator fully open to fully closed within a time less than a certain predetermined value, possibly in combination with one or more of the aforedescribed conditions.  
         [0022]    Various logics can be used on which the unit  41  bases its decision to extend the actuator  15  (to return to its normal position), including those based on the following measurements:  
         [0023]    I) the pressure of the front brake (measured by the sensor  42 ) falls below a predetermined threshold pressure;  
         [0024]    II) the amplitude sensor of the rear damper measures a compression thereof greater than a predetermined value;  
         [0025]    III) the load on the rear wheel is greater than a predetermined value, measured by a sensor which measures the load acting on the actuator  15 ;  
         [0026]    IV) the occurrence of two or more of the aforedescribed conditions;  
         [0027]    V) the passing of a predetermined system intervention time.  
         [0028]    The aim of all this is to achieve a lowering of the vehicle barycentre only simultaneously with the sinking of the fork  46 , whereas when the vehicle is not under braking, or if the conditions for intervention of the unit  41  do not exist, the actuator  15  must remain in a completely extended and rigid position so as to behave as the usual reaction rod of a rear suspension unit of the state of the art. It will now be assumed that the motorcycle  1  is to be used in accordance with one of the aforedescribed operating logics. It will also be assumed that it is in a position perpendicular to the ground S and that the driver is about to apply prolonged braking (for example because the vehicle, at high speed, is to confront a bend, for example during a competition). Under these conditions, the driver presses the usual brake lever to activate the vehicle front brake. Following this pressing action the sensor  42  feeds a signal to the unit  41  denoting that the driver is braking.  
         [0029]    As a result of this action on the brake lever, the vehicle begins to brake and simultaneously the fork  46  begins to “sink”. At the same time, the unit  41  (totally automatically) monitors the position of the suspension  5  via the sensor  45 , and the vehicle speed. If (at the commencement of braking) the unit  41  senses that the braking pressure exceeds a predetermined threshold value and that the front suspension has compressed beyond a predefined threshold value, this unit instantaneously acts on the valve unit or solenoid valve  27  to enable the pressure of the oil of the circuit  40  to be released from the chamber  20 A, whereas the chamber  20 B remains under pressure. Following this, the actuator  15  yields along its longitudinal axis W so that its opposing ends  15 A and  15 B approach each other. In other words, the piston  21  of the actuator  15  moves from the position of FIG. 2 to that of FIG. 3, with the result that in the initial stage of braking, the residual weight on the rear wheel does not discharge to the ground via the rear tire, but accelerates its movement downwards with consequent lowering of the motorcycle barycentre towards the ground S. As a result of this lowering, the resultant of the braking force and the weight force (vehicle weight plus driver weight) applied to the barycentre encounters the ground S between the points of contact of the wheels  3  and  4  with the ground, meaning that a braking force can be achieved which is higher than that which can be generated in those motorcycles without the present invention.  
         [0030]    It should be noted that the lowering movement of the barycentre deriving from the movement of the piston  21  within the cylinder  20  is very fast (also because the vehicle moves its vertical position while along a straight portion of the ground S, hence the driver does not risk falling), whereas the opposite movement when the piston moves from the position of FIG. 3 to that of FIG. 2 (movement controlled by the unit  41  via the sensor  49  and obtained by suitable activation of the valve unit  27 ) is slow, said opposite movement being actuated when the motorcycle enters a bend or immediately before. The slow movement is provided in order not to alter the equilibrium of the vehicle.  
         [0031]    Hence by virtue of the invention, high stability of a braking motorcycle can be achieved and the braking force acting on the vehicle front wheel be also increased without risk of tilting the motorcycle.  
         [0032]    A preferred embodiment of the invention has been described. Others are however possible, such as one in which the form of the circuit  40  is different from that of FIG. 4. Other variants are also to be considered as falling within the scope of the present invention.