Abstract:
A utility vehicle, in particular a firefighting vehicle, comprising an extendable aerial apparatus like a turnable ladder and/or an aerial rescue platform, a jacking system with lateral ground supports for jacking the vehicle body, and a stabilization mechanism for preventing tilting of the vehicle body in its jacked state. The stabilization mechanism includes a hydraulically operable rear axle blocking device for blocking the rear axle suspension of the vehicle. The stabilization mechanism further includes at least one hydraulically lockable shock absorber integrated into the front axle suspension of the vehicle. The rear axle blocking device and the hydraulically lockable shock absorber are controlled by a common hydraulic control to lock the hydraulically lockable shock absorber at the same time or with a delay after activating the rear axle blocking device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a utility vehicle, in particular a fire fighting vehicle, comprising an extendable areal apparatus like a turnable ladder and/or an areal rescue platform and a jacking system. 
         [0003]    2. Description of the Related Art 
         [0004]    When the areal apparatus of a utility vehicle, such as a fire fighting vehicle, is extended, it is important to secure the vehicle against a tilting movement in the lateral direction. For this purpose, jacking systems are provided that comprise lateral ground supports for jacking a vehicle body. These supports can be extracted from the vehicle body into an operating position in which the ends of the supports rest on the ground, so that the weight load of the vehicle rests on the supports, and the vehicle axles and their suspensions are relieved. In some cases the vehicle is lifted from the ground completely, so that the wheels do not have contact with the ground anymore. However, in other cases it is completely sufficient to lift the vehicle body from the axle in a way that the wheels keep a minimum of ground contact. 
         [0005]    To perform this deflection of the vehicle load to the lateral ground supports, the jacking system comprises stabilization means with a rear axle blocking device for blocking the rear axle suspension of the vehicle. This rear axle blocking device can be operated hydraulically and may comprise, for example, a pulling means for pulling the rear axle in an upward direction against the vehicle body, i.e. against the spring force of the rear axle suspension. In its activated state, with the rear axle pulled against the vehicle body, the rear axle suspension is blocked completely to prevent any relative movement of the axle against the vehicle body. In a simple and common construction, the pulling operation of the rear axle blocking device is performed by a steel rope connecting the rear axle with the end of a hydraulic cylinder and being guided over a deflection pulley. If the hydraulic cylinder is retracted, the rear axle is pulled in an upward direction, as described above. 
         [0006]    However, even if the rear axle is blocked, the stabilization means cannot prevent a tilting movement of the vehicle body completely in some operation states of the areal apparatus. This is due to the arrangement of the lateral ground supports at the length position of the vehicle. While the rear pair of ground supports can be arranged at the rear end of the vehicle, the front pair of ground supports is usually arranged between the front and rear axles. When the areal apparatus is extended in the front direction (i.e. the driving direction) of the vehicle, extending over the driver&#39;s cabin, the center of gravity of the vehicle shifts in this direction. Consequently the load of the vehicle is deflected towards its front axle, and the vehicle tends to perform a tilting movement around the front pair of ground supports, slightly lifting the rear end of the vehicle and lowering the driver&#39;s cabin against a spring force of the front suspension of the front axle. In another operating state of the areal apparatus, when it is extended in the opposite direction over the rear end of the vehicle, the spring force of the front axle suspension tends to promote a lifting of the driver&#39;s cabin, so that a tilting movement of the vehicle in the opposite direction over a rear pair of ground supports is promoted. 
         [0007]    It is clear from the above that the usual spring dampening function of the front axle suspension promotes tilting movements in such operating conditions of the areal apparatus in an undesired way. However, there is no known way to deactivate the front suspension system. In particular it is impossible to block the front axle in the same way as with the hydraulically operable rear axle blocking device described above, because of the limited construction space in the front axle area and the increased complexity of the construction of the front axle, for example, by the limitations of the steering system. It must also be considered that a complete unloading of the front axle by pulling up the axle against the vehicle body, as with the rear axle blocking device, would even promote the front tilting of the vehicle when the areal apparatus is extended over the driver&#39;s cabin, so that the desired effect cannot be achieved. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore an object of the present invention to further develop the stabilization means of the checking system of the utility vehicle in question to even prevent tilting movements in an operating condition which the areal apparatus is largely extended in the front direction as well as in the rear direction of the vehicle, without increasing the complexity of the front axle suspension system to a large extend. 
         [0009]    This object is achieved by a utility vehicle comprising the features of claim  1 . 
         [0010]    The stabilization means of the jacking system of the utility vehicle according to the present invention comprises at least one hydraulically lockable shock absorber integrated into the front axle suspension of the vehicle. It serves as a blocking means for deactivating the front axle suspension, i.e. to prevent any lifting or lowering movement of the front portion of the vehicle body with or against the spring force of the front suspension. Unlike the rear axle blocking device, the front axle is not lifted to be pulled against the vehicle body but keeps its position. If the hydraulically lockable shock absorber is locked, the front suspension with the front axle serves as an additional stabilizing means to prevent a tilting or lowering movement of the driver&#39;s cabin when the areal apparatus is extended in the front direction. If it is extended in the opposite direction over the rear portion of the vehicle, the spring force of the front suspension is blocked, and a tilting movement in the opposite direction is not further promoted. 
         [0011]    This hydraulically lockable shock absorber can replace the usual shock absorber integrated into conventional front axle suspensions, and it is not necessary to integrate a large number of additional parts into the construction space of the front axle suspension. It is another advantage that the conventional rear axle blocking device, as described above, and the front axle blocking device represented by the lockable shock absorber are both hydraulically operable, so that they are both controlled by one hydraulic control means, like, for example, a control valve. This hydraulic control means can block the hydraulically lockable shock absorber at the same time or with a delay after activating the rear axle blocking device. This secures that the hydraulically lockable shock absorber is locked, i. e. the blocking of the front axle suspension is activated, only in case the rear axle blocking device is in its activated state. 
         [0012]    According to a preferred embodiment of the present invention, the hydraulic control means comprise a control valve when an inlet port communicating with a hydraulic pressure source and with a first outlet port communicating with the rear axle blocking device and at least one second outlet port communicating with the hydraulically lockable shock absorber. 
         [0013]    These and other aspects of the present invention will be apparent from and elucidated with the reference to a preferred embodiment described hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0014]    The only figure is a schematic view of a firefighting vehicle as one embodiment of a utility vehicle according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The firefighting vehicle  10  in the figure is one example of a utility vehicle according to the present invention. The firefighting vehicle is equipped with a turnable ladder  12  on its top that is turnable around a vertical axis and comprises a number of ladder segments (not shown) that are slidably supported on each other so that the ladder  12  is extractable. In the turning position of the ladder  12  shown in the figure, the ladder  12  can be extracted to extend partially over the driver&#39;s cabin  14  of the vehicle  10 . When turned into the opposite direction, the ladder  12  can be extracted into the rear direction of the vehicle. 
         [0016]    The vehicle  10  further comprises, as usual, a pair of front wheels  16  and a pair of rear wheels  18 , the wheels of each pair  16 ,  18  being provided at the ends of a front axle  20  and rear axle  22 , respectively. The front axle  20  and the rear axle  22  are mounted at a front axle suspension  24  and a rear axle suspension  26 , respectively. Each of the front axle suspension  24  and a rear axle suspension  26  allow the vehicle body  30  resting on the suspensions  24 ,  26  to be lowered or lifted against or promoted by the spring force of the respective suspension  24 ,  26 , so that a load impact acting from the ground during the driving operation of the vehicle  10  is dampened, and its transmission to the vehicle body  30  is restricted. This suspension function is well known with conventional vehicles  10  of any different kinds, and it shall not be described near further. Its representation in the figure is also simplified to a large extent. 
         [0017]    The vehicle  10  is further provided with a jacking system to give the vehicle  10  a safe stand when the turnable ladder  12  is operated. The jacking system comprises lateral ground supports  32 ,  34  for jacking the vehicle body  30 . In the meaning of the present description, the term “jacking” shall designate a relocation of the weight load of the vehicle body  30  from the front end rear axle suspensions  24 ,  26  towards the lateral ground supports  32 ,  34 , i. e. the front and rear axles  20 ,  22  are unloaded, and the load is taken by the ground supports  32 ,  34 . In the present case this does not necessarily mean that the wheels  16 ,  18  loose their ground contact completely, but it is rather preferred that the wheels  16 ,  18  keep a minimum of ground contact. 
         [0018]    There are two pairs of lateral ground supports  32 ,  34 , namely one front pair of ground supports  32  located between the front axle  20  and the rear axle  22  and positioned nearer to the front axle  20  than to the rear axle  22 , and a rear pair of ground support  34  positioned at the rear end of the vehicle  10  behind the rear axle  22 . These ground supports  32 ,  34  are moveable between retracted positions at or within the vehicle body  30  and extracted operating positions in which the ends of the supports  32 ,  34  rest on the ground to jack the vehicle body  30 . By this extracting and jacking operation the support area of the vehicle  10  is largely widened, giving the vehicle  10  a secure stand during a rescue operation. 
         [0019]    The jacking system further comprises stabilization means for preventing tilting or rolling movements of the vehicle body  30  when the turnable ladder  12  is extracted. These stabilization means comprise a rear axle blocking device  36  for blocking the rear axle suspension  26  of the vehicle  10 . This rear axle blocking device  36  can be operated hydraulically and comprises a hydraulic cylinder  38 . At the end of the hydraulic cylinder  38 , a steel rope  40  is attached with one end, while its other end is attached to the rear axle  26 . The steel rope  40  is deflected over a deflection pulley  42 . When the hydraulic cylinder  38  is retracted, the steel rope  40  is pulled to lift the rear axle  26  attached to the steel rope  40  upward direction to draw it against the vehicle body  30 . This drawing action is performed against the spring force of the rear axle suspension  26  in the state in which the vehicle body is jacked by the lateral ground supports  32 ,  34 . This has the effect that the rear axle  22  is unloaded, and the weight load of the vehicle body  30  is transferred to the lateral ground supports  32 ,  34 . It is noted that in this blocking operation of the rear axle blocking device  36 , the rear wheels  18  are not lifted from the ground completely but keep ground contact to a certain degree, as described above. However, the elastic suspension function of the rear axle suspension  26  is blocked in such a way that any tilting or rolling movement of the rear portion of the vehicle body  30  is prevented. 
         [0020]    According to the present invention, the stabilization means further comprises a hydraulically lockable shock absorber  44  integrated into the front axle suspension  24  of the vehicle  10 . This hydraulically lockable shock absorber  44  may replace a conventional shock absorber as one element of the front axle suspension  24 , to dampen a load impact acting on the front axle  20 . However, by locking this shock absorber  44 , this dampening suspension function is blocked, so that the front axle  20  keeps a fixed position relative to the vehicle body  30 . With other words, the hydraulically lockable shock absorber  44  represents a front axle blocking device. However, unlike the rear axle blocking device  36 , no large and bulky additional construction elements (like, for example, the hydraulic cylinder  38  and the additional deflection pulley  42 ) are necessary at the front axle suspension  24 , because the hydraulically lockable shock absorber  44  merely replaces the conventional shock absorber, without taking significantly more space. 
         [0021]    The stabilization means further comprise hydraulic control means that allow a common control of the hydraulically lockable shock absorber  44  and the rear axle blocking device  36 , i. e. its hydraulic cylinder  38 . These hydraulic control means comprise a hydraulic control valve  46  to control the distribution of a hydraulic pressure of a hydraulic pressure source to both the hydraulic cylinder  38  of the rear axle blocking device  36  as well as to the hydraulically lockable shock absorber  44 . In particular it is possible to control the hydraulic pressure to the respective elements such that the hydraulically lockable shock absorber  44  is locked at the same time or with a delay after activating the rear axle blocking device  36 , to make sure that the front axle suspension  24  is locked only in case the rear axle blocking device  36  is activated. In more detail, the pressure originating from the hydraulic pressure source is distributed by the control valve  46  such that the hydraulic cylinder  38  is provided with an operation and/or control pressure to be retracted, and at the same time or with a predetermined delay, the hydraulically lockable shock absorber  44  is provided with a hydraulic control pressure to be operated such that the shock absorber  44  is locked. For this purpose the control valve  46  is provided with an inlet port communicating with a hydraulic pressure source  48  via an inlet line  50 , with a first outlet port communicating with the rear axle blocking device  36  via a first outlet line  52 , and with a second outlet port communicating with the hydraulically lockable shock absorber  44  via a second outlet line  54 . It is noted that usually the vehicle  10  will be equipped with a pair of two hydraulically lockable shock absorber  44  at both lateral sides of the vehicle  10 , i. e. at each front wheel  16 , as usual, and each of these shock absorber  44  will be provided with a control pressure via a respective second outlet line. 
         [0022]    In a state in which the rear axle blocking device  36  is activated and the hydraulically lockable shock absorber  44  is locked, both front and rear axle suspensions  24 ,  26  are deactivated. At its front portion, the vehicle  10  is additionally stabilized by the deactivated front axle suspension  24 , because no lowering or lifting movement of the driver&#39;s cabin  14  with respect to the front axle  20  is possible. Consequently a tilting of the vehicle body  30  to the front direction is prevented when the turnable ladder  12  is extracted in the front direction. On the contrary, if the turnable ladder  12  is extracted to the opposite direction, because of the deactivation of the front axle suspension  24 , a tilting movement of the vehicle body  30  in the opposite direction is not further promoted by the spring force of the front suspension  24 .