Abstract:
A lifting vehicle comprising: a frame carrying a front axle and a rear axle; carrying a pair of front wheels and a pair of rear wheels, respectively; a lifting boom articulated in a rear section of the frame; and a stability control system configured to control the conditions of operational stability of the vehicle, wherein said stability control system comprises: a first and a second load sensor configured to provide information about the loads acting on the front right wheel and on the front left wheel and an electronic control unit programmed for: calculating a transverse dimension of the position of the center of gravity of the vehicle according to the values provided by said first load sensor and said second load sensor; comparing the transverse dimension of the position of the center of gravity of the vehicle with reference values and; reporting conditions of transversal instability of the vehicle when said calculated value of the transverse dimension exceeds a corresponding reference value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of Italian patent application number TO2015A000108, filed Feb. 18, 2015, which is herein incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a lifting vehicle comprising:
       a frame carrying a front axle and a rear axle, carrying a pair of front wheels and a pair of rear wheels, respectively;   a lifting arm articulated in a rear section of the frame; and   a stability control system configured to control the conditions of operational stability of the vehicle.       
 
         [0007]    2. Description of Prior Art 
         [0008]    The reference legislation for stability control systems of lifting vehicles is the regulation EN15000. One of the main security features provided by the regulation EN15000 for vehicles with lifting arms is the control function of the risk of longitudinal rollover. To perform this safety function, micro-switches arranged on the rear axle are used, which detect when the rear axle load falls below a predetermined threshold. An electronic control unit alerts the operator to a situation of the risk of rollover and blocks the movements that aggravate the rollover risk. 
         [0009]    The document EP-A-2520536 by the same Applicant describes a lifting vehicle equipped with a stability control system including an electronic control unit that receives information provided by: a length sensor, which detects the length of extension of the arm; an angle sensor, which detects the inclination angle of the telescopic arm, and by sensors that provide information on the type of equipment applied to the arm. The electronic control unit is programmed to act on a limiting valve in order to limit the maximum speed of lowering the arm depending on the type of equipment, the value of the load applied to the arm, and the length and angle of inclination of the arm. 
         [0010]    The information on the type of equipment mounted on the arm, together with the information gathered from the various control sensors of the arm geometry and load weighing sensors carried by the arm allow the correct stability diagram to be provided to the operator, along with continuous information in real time on the instantaneous stability conditions of the vehicle. 
         [0011]    However, this stability control system and those of lifting vehicles currently available on the market are configured to check only the longitudinal stability of the vehicle, or rather, the degree of stability against the risk of longitudinal rollover. 
         [0012]    On the other hand, for the operational safety of lifting vehicles, transverse stability is also very important, especially in the case of vehicles that can also operate on uneven and rough terrains, such as some vehicles with lifting arms that are also usable as agricultural tractors. In fact, the transverse rollover is one of the most serious accidents with respect to agricultural vehicles. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention aims to provide a lifting vehicle equipped with an improved stability control system, which also controls the transverse stability of the vehicle. 
         [0014]    According to the present invention, this object is achieved by a lifting vehicle having the characteristics forming the subject of claim  1 . 
         [0015]    The stability control system according to the present invention comprises a first and a second load sensor, configured to provide information about the loads acting on the front left wheel and on the front right wheel of the vehicle. An electronic control unit is programmed: to calculate a transverse dimension of the position of the center of gravity of the vehicle as a function of the values provided by the first and the second load sensors; to compare the transverse dimension of the position of the center of gravity of the vehicle with reference values, and to report conditions of transverse instability of the vehicle when the calculated value of the transverse dimension of the center of gravity exceeds a corresponding reference value. 
         [0016]    The transverse stability control system according to the present invention can be fully integrated with control systems of longitudinal stability already currently present on the current lifting vehicles. Therefore, thanks to the present invention, the lifting vehicles can be equipped with an integrated system of longitudinal and transverse stability control, which ensures total operational safety of lifting vehicles, by integrating the longitudinal (front and back) stability control with the transverse stability control. 
         [0017]    The stability control system according to the present invention can use the signaling devices already present on normal production machines, such as, for example, a graphic display that shows the stability diagram of the vehicle, a signal light with three lights indicating the stability state of the vehicle and an acoustic warning. Thanks to these tools, the operator is informed in real time about the state of longitudinal and transverse stability of the vehicle, so as to be able to operate in complete safety up to the limit of the capacity of the vehicle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The present invention will now be described in detail with reference to the attached drawings, given purely by way of non-limiting example, wherein: 
           [0019]      FIG. 1  is a perspective view of a lifting vehicle according to the present invention. 
           [0020]      FIG. 2  is a perspective view of the part indicated by the arrow II in  FIG. 1  of a vehicle with a fixed front axle. 
           [0021]      FIG. 3  is an enlarged perspective view of the detail indicated by the arrow III in  FIG. 2 , illustrating a first arrangement of the front axle load sensors. 
           [0022]      FIG. 4  is a partially sectioned view of the part indicated by the arrow IV in  FIG. 3  illustrating a second arrangement of the front axle load sensors. 
           [0023]      FIG. 5  is a perspective view illustrating the front part of a vehicle with oscillating front axle. 
           [0024]      FIG. 6  is a perspective view of the part indicated by the arrow VI in  FIG. 5  illustrating the arrangement of the load sensors in a vehicle with an oscillating axle. 
           [0025]      FIG. 7  is a schematic view of a stability control system according to the present invention. 
           [0026]      FIGS. 8 and 9  are front and side views of a lifting vehicle illustrating the distribution of loads in the transverse direction and in the longitudinal direction . 
           [0027]      FIGS. 10, 11 and 12  are schematic views illustrating the stability diagram of the vehicle in three different operating situations. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    With reference to  FIG. 1 , numeral  10  indicates a lifting vehicle comprising a frame  12  including a robust central longitudinal beam to which a control and driving cab  14  and a motor unit are fixed (schematically represented by  15  in  FIG. 7 ). The motor unit and the control and driving cab are arranged on opposite sides of the frame  12 . A lifting boom  16  is articulated to a rear section  18  of the frame  12 . 
         [0029]    The frame  12  carries a front axle  20  and a rear axle  22 , carrying a pair of front wheels  24   d,    24   s  and a pair of rear wheels  25   d,    25   s,  respectively. 
         [0030]    The vehicle  10  according to the present invention comprises a stability control system, which controls both the longitudinal stability and the transverse stability. To control the stability, the vehicle is provided with two load sensors  26   d ,  26   s  configured to detect the load on the front right wheel  24   d  and on the front left wheel  24   s.    
         [0031]    The lifting vehicles  10  can have a fixed or oscillating front axle  20 . The load sensors  26   d,    26   s  associated with the front wheels  24   d  and  24   s  can be of different types and can be arranged differently according to whether the front axle  20  is fixed or oscillating. 
         [0032]      FIG. 2  illustrates the case in which the front axle  20  is fixed with respect to the frame  12 . In this case, the front axle  20  is essentially formed by a transverse beam fixed to the front end of the longitudinal beam  12  forming the frame of the vehicle. In this case, as shown in  FIG. 3 , the load sensors  26   d,    26   s  can be formed by strain gauges  28  applied to the front axle  20  in the vicinity of the wheels  24   d,    24   s . The strain gauges  28  detect the deformation of the front axle  20  and provide a measure of the load that has generated this deformation. 
         [0033]    Alternatively, as shown in  FIG. 4 , the load sensors  26   d,    26   s  may be formed of respective load cells  30  mounted on the support of the reducer of the respective front wheel  24   d,    24   s.    
         [0034]      FIG. 5  illustrates an example in which the vehicle comprises an oscillating front axle  20 . In this case, the front axle  20  is connected to the frame  12  of the vehicle by means of two hydraulic cylinders  32   s,    32   d  arranged alongside the respective front wheels  24   s,    24   d.  Each hydraulic cylinder  32   s,    32   d  has an upper end fixed to the frame  12  and a lower end fixed to the front axle  20 . In this case, the load sensors  26   d,    26   s,  which detect the loads acting on the front wheels  24   d,    24   s  can be formed by load cells  34  fixed to the respective cylinders  32   d,    32   s.  For example, each load cell  34  can be fixed between the body of the cylinder  32   s,    32   d,  and the upper fixing flange of the cylinder. 
         [0035]    Whatever type of sensors used and their arrangement, the load sensors  26   d,    26   s  are arranged to provide respective electrical signals indicative of the loads acting on the respective front wheels  26   d,    26   s.    
         [0036]      FIG. 7  schematically illustrates a stability control system  36  according to the present invention. The stability control system  36  comprises an electronic control unit  38 , which receives the signals coming from the load sensors  26   d,    26   s  associated with the front wheels  24   d,    24   s.  The electronic control unit  38  also receives signals coming from the two micro-switches  40  arranged on the rear axle  22  level with the rear wheels  25   s,    25   d.    
         [0037]    The stability control system  36  comprises an absolute inclination sensor associated with the vehicle frame, which detects the absolute angle of longitudinal inclination of the vehicle relative to the ground. A relative angle sensor  44  is also provided, which detects the inclination angle of the boom  16  with respect to the vehicle frame. A sensor  46  is also provided, which detects the length of extension of the telescopic lifting boom  16  and a boom load sensor  48 , which detects the load applied to the boom  16 . The stability control system  36  also comprises a display  50 , a signal light  52  and a selector  54  settable by the operator to select different operating modes of the stability control system  36 . 
         [0038]    The electronic control unit  38  carries out the control of the longitudinal stability of the vehicle  10  according to signals coming from the micro-switches  40  associated with the rear axle  22 . When the micro-switches  40  indicate a condition of load on the rear axle  22  that is lower than a predetermined threshold, the electronic control unit  38  alerts the operator to a situation of danger of longitudinal rollover and blocks the movements that aggravate the risk of longitudinal rollover. 
         [0039]    To control the transverse stability, the electronic control unit  38  calculates the transverse and longitudinal dimensions of the position of the center of gravity G of the vehicle  10  according to the signals coming from the load sensors  26   d,    26   s  of the front wheels  24   d,    24   s  of the boom load sensor  48 . 
         [0040]    With reference to  FIGS. 8 and 9 , the transverse dimension Y of the position of the center of gravity G of the vehicle  10  is calculated by the following expression: 
         [0000]    
       
         
           
             Y 
             = 
             
               
                 V 
                 d 
               
               
                 
                   V 
                   d 
                 
                 + 
                 
                   V 
                   s 
                 
               
             
           
         
       
     
         [0041]    wherein: 
         [0042]    Y is the distance of the center of gravity G from the center of the right wheel  24   d;    
         [0043]    V d  is the vertical load acting on the right wheel  24   d,  measured by the load sensor  26   d;  and 
         [0044]    V s  is the vertical load acting on the left wheel  24   s,  measured by the load sensor  26   s.    
         [0045]    With reference to  FIG. 9 , the longitudinal dimension X of the position of the center of gravity G of the vehicle is calculated according to the load on the front axle V a  and of the load on the rear axle V d . 
         [0046]    The load on the front axle V a  is given by the following expression: 
         [0000]    
       
      
       V 
       a 
       =V 
       d 
       +V 
       s  
      
     
         [0047]    wherein V d  and V s  are the load values on the front wheels  24   d,    24   s  measured by the load sensors  26   d,    26   s.    
         [0048]    The load on the rear axle V p  is calculated by the following expression: 
         [0000]        V   p   =P   m  cos α+ P   c   −V   a  
 
         [0049]    wherein: 
         [0050]    V p  is the load on the rear axle; 
         [0051]    P m  is the weight of the unloaded machine, which must be evaluated by a preliminary calibration; 
         [0052]    α is the absolute inclination angle of the vehicle with respect to the ground; 
         [0053]    P c  is the weight of the load applied to the boom  16  detected by the boom load sensor  48 ; and 
         [0054]    V a  is the load on the front axle calculated as previously indicated. 
         [0055]    Note that in the case in which the machine is inclined, the load sensors  26   d,    26   s  and  48  detect the load perpendicular to the support plane, while the weight of the machine for the correct balance of the forces must be multiplied by cos α, where a is the angle detected by the sensor of absolute longitudinal inclination of the vehicle  10 . 
         [0056]    The relationship that provides the longitudinal dimension of the position of the center of gravity G of the vehicle is the following: 
         [0000]    
       
         
           
             X 
             = 
             
               
                 V 
                 a 
               
               
                 
                   V 
                   a 
                 
                 + 
                 
                   V 
                   p 
                 
               
             
           
         
       
     
         [0057]    The preliminary calibration for determining the weight of the machine P m  is carried out in the following way:
       a sample load of known weight is chosen;   the machine is loaded with the sample weight;   the boom  16  is extended until the micro-switches  40  of the rear axle  22  are engaged; and   at this point V d  and V s  are measured and the weight of the machine is calculated with the expression: P m =V d +V s −P c .       
 
         [0062]    The weight of the machine P m , determined in this way, is not exactly equal to the actual weight of the machine. However, using this value, the system is calibrated so that the indicator on the display is in the emergency zone of front rollover at the exact moment in which the antirollover micro-switches  40  of the rear axle  22  are activated. 
         [0063]    With reference to  FIGS. 10, 11 and 12 , the electronic control unit  38  shows the position of the center of gravity G of the vehicle on the display  50 , calculated as previously indicated. The position of the center of gravity G is represented on a stability diagram of the vehicle. The stability diagram has the shape of an isosceles triangle with its vertex at the center of the rear axle  22  and the base parallel to the front axle  20 . 
         [0064]    The inclined sides of the triangle represent, for each longitudinal dimension X of the position of the center of gravity G, the limit values of the transverse dimension Y above which the vehicle is at risk of transverse rollover. 
         [0065]    The areas within the area indicated with  54  represent operational conditions of full safety of the vehicle. These operating conditions are indicated by a green signal light  52 . 
         [0066]    On the stability diagram of the vehicle a perimetral band  56  that surrounds the triangle  54  is reported. When the calculated position of the center of gravity G is located in the band  56 , the vehicle is in working conditions at the limit of transverse rollover. These conditions are indicated by a yellow light of the signal light  52 . Finally,  FIG. 12  represents the case in which the calculated position of the center of gravity G is outside of the band  56 . In these conditions, the vehicle is in a critical working condition, at a high risk of longitudinal or transverse rollover. This condition is indicated by a red signal light  52 . 
         [0067]    Thanks to the stability control system according to the present invention, the operator is able to prevent the vehicle rollover in all directions, also due to external causes to the use of the vehicle. In fact, the loss of stability, especially lateral, is due to the conditions in which the vehicle is operating, regardless of the load diagram prepared in accordance with existing standards. For example, an inappropriate inflation of the tires, an uneven or yielding terrain, the lifting of an unbalanced load, etc. may be the cause of side rollover, even within the operating limits provided by the load diagrams. The stability control system according to the present invention is able to recognize these dangerous situations and to inform the operator about the real state of the vehicle stability. 
         [0068]    Of course, without prejudice to the principle of the invention, the details of construction and the embodiments can be widely varied with respect to those described and illustrated, without thereby departing from the scope of the invention as defined by the claims that follow.