Abstract:
An all-wheel drive vehicle with two steered vehicle axles. Each having a main steering cylinder with piston rods actively connected with the wheels. The main steering cylinders each have first and second chambers ( 30, 31 ) delimited by at least one piston element ( 34, 35 ) which moves longitudinally in the cylinder and is connected to the piston rod ( 28 ), such that adjusting pressure in the cylinder with an electric control unit, biases the piston elements and the piston rods to achieve specified wheel steering angles. Furthermore, a third chamber ( 32 ), which can be pressurized, is provided between a first and a second piston element ( 34, 35 ) of a main steering cylinder ( 26 ), which respectively delimit the first and second chamber ( 30, 31 ). The piston rods are sectioned, such that a first section is connected to the first piston element and a second section is connected to the second piston element.

Description:
[0001]    This application claims priority from German Application Serial No. 10 2006 030 143.9 filed Jun. 29, 2006. 
       FIELD OF THE INVENTION 
       [0002]    The invention concerns a vehicle, in particular an all-wheel drive vehicle, with a first steered vehicle axle and a second steered vehicle axle. 
       BACKGROUND OF THE INVENTION 
       [0003]    In practice, vehicles and in particular all-wheel drive vehicles are known, for example so-termed telescopic loaders or telemanipulators, which are preferably used as construction vehicles. Because there is often only restricted room available on building sites, such vehicles have to be able to maneuver within very small spaces. 
         [0004]    Accordingly, it is sought to make such vehicles with as small a turning radius as possible. For this purpose the vehicles are fitted with two vehicle axles that can both be steered, for example by way of an axle-pivot or a pivoted bogie steering system, but large wheel steering angles are needed in order to achieve the required maneuverability. 
         [0005]    Unfortunately, the steering angle error in construction vehicles made with a short: wheelbase increases with increasing wheel steering angle. However, an increase of the steering angle error is undesired because, if the wheels are affected by steering angle error, sliding movements occur, which result in high tire wear. Particularly in the case of construction vehicles, this is a great disadvantage because tire replacement entails very high costs. 
         [0006]    Accordingly, the purpose of the present invention is to provide a vehicle of the type described above, which is characterized by a very small turning radius and, at the same time, by lower tire wear. 
       SUMMARY OF THE INVENTION 
       [0007]    A vehicle, in particular an all-wheel drive vehicle, with a first steered vehicle axle and a second steered vehicle axle is proposed. The axles each comprise a main steering cylinder, whose piston rods are in active connection with wheels of the vehicle axles; the main steering cylinders, being formed in each case with a first chamber, and a second chamber, which are delimited by at least one piston element arranged to be able to move longitudinally in a cylinder device and connected to one of the piston rods, which can be acted upon by a control pressure that can be adjusted by an electric control unit to produce the required wheel steering lock angle. According to the invention, in each case, between a piston element that delimits the first chamber and one that delimits the second chamber of a main steering cylinder, a third chamber is formed that can be acted upon by control pressure. The piston rods are made in more than one section and, in each case, a first section being connected to a first piston element that delimits the first chamber and a second section is connected to a second piston element that delimits the second chamber of a main steering cylinder. 
         [0008]    In a vehicle designed, according to the invention, it is advantageously possible to move the first piston element, relative to the second piston element with the first and second sections of the piston rod, respectively, attached thereto so that, in the area of the two wheels on a vehicle axle, a different wheel steering angle can be set. By virtue of this ability to adjust, the wheel steering angles of the wheels of a vehicle axle independently of one another, by way of the control pressure, a steering angle error that occurs, for example while driving around a turn, can be compensated in an advantageous manner. 
         [0009]    Furthermore, in a vehicle with the inventive design including two vehicle axles made as described above, the steering angles of all the wheels can be made in such a manner that the extensions of the center lines of the axle steering knuckles meet at least approximately at a point in the middle of the vehicle and a steering angle error is minimal. With such control of the wheel steering angles, if it is possible to turn the wheels of an all-wheel drive vehicle arranged on one side of the vehicle in the opposite direction of the wheels on the other side of the vehicle, then the vehicle will advantageously spin around the vehicle mid-point. A vehicle made in this way has a very small turning circle, which is particularly advantageous for construction vehicles. 
         [0010]    Construction vehicles known from current practice are made, among other things, with superstructures, such as cranes, rotating turrets or the like, which are, in each case, equipped in the area between the superstructure and the supporting structures of the vehicle with mechanisms for rotating the superstructures relative to the supporting structures. In a vehicle with the inventive system design, no such device for rotating a vehicle superstructure, relative to its supporting structure, is needed since the superstructure can be rotated by turning the vehicle as a whole relative to its surroundings, even within a small maneuvering area. Consequently, a construction vehicle, built in accordance with the invention, can be produced considerably more cheaply. 
         [0011]    In a further development of the vehicle, according to the invention, a third chamber of the main steering cylinder can be pressurized with control pressure by way of a switching control valve device preferably made as a 3/3 magnetic control valve. This constitutes a particularly simple, compact and inexpensive design in which, preferably other control valve devices associated with the first chamber and the second chamber of the main steering cylinder can be used together with the control valve device associated with the third chamber to set or adjust the wheel steering angles of the individual wheels. 
         [0012]    Particularly accurate adjustment of the steering angle of the wheels can be achieved by providing sensors that determine the steering angles of the wheels, which are in active connection with an electric control device for adjusting the control pressure for the third chamber of the main steering cylinder, by which the control valve device associated with the third chamber is actuated, such that the electric control device receives feedback signals from the sensors concerning the realization of specified values and can, if necessary, adapt the wheel steering angles with reference to differences between the actual and intended values thereof. 
         [0013]    In addition, the electric control device can be in active connection with an electric control unit that feeds control pressure to the first and second chambers of the main steering cylinder, by way of the valve devices associated with the first and second chambers are actuated to be able to match the control pressures in the various chambers of the main steering cylinder to one another to an extent that minimizes steering angle errors. Thus, in the area of the electric control device and/or in the area of the control unit, it is preferably possible to advantageously verify whether the desired wheel positions have been reached. 
         [0014]    In a further embodiment of the inventive vehicle, the sensors that determine the wheel steering angles are in direct active connection with the electric control unit. In this case, both of the control valve devices, associated with the first and second chambers, and the control valve devices, associated with the third chambers, can be actuated by the control unit since the function of the electric control device is implemented in the control unit. In this connection, at the discretion of those with knowledge of the field, the chambers of the main steering cylinder can be controlled, in each case, either by both the electric control unit and the electric control device or by the electric control unit alone, depending on the respective application, and with regard to the structural space available and the line lengths required for the connection of the various elements. It can also be provided that each vehicle axle is associated with an electric control device of its own or that both vehicle axles are subject to the control of a common electric control device. 
         [0015]    To establish the steering angles of the wheels, the sensors can also be associated directly with the main steering cylinders so that the steering angles are determined from the positions of the piston elements. 
         [0016]    If both the first section of the piston rods and the second section of one piston rod are, in turn, made in two parts and articulated with respect to one another by way of a hinge joint, mechanical stresses, resulting from movements of the vehicle axle elements that occur while driving round a curve, can be reduced or completely avoided in a simple manner, which advantageously increases the life of the vehicle axles. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The invention will now be described, by way of example, with reference to the accompanying drawings. For the sake of clarity in the description of the various example embodiments, the same indices are used for components having the same structure and function. The drawings show: 
           [0018]      FIG. 1  is a simplified schematic diagram of a first embodiment of a vehicle according to the invention; 
           [0019]      FIG. 2  is a simplified schematic diagram of a second embodiment of a vehicle according to the invention, and 
           [0020]      FIG. 3  is another schematic representation of a vehicle according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIG. 1  shows a schematic representation of a vehicle  1 , in the present case, made as an all-wheel drive vehicle. The vehicle  1  has a drive engine  3  which produces a drive torque. In a known manner, the drive torque is transmitted by a gearbox  4  and a distributor gear system  5  to two drive shafts, represented in the Figure by heavy broken lines, of which a first drive shaft  7  is associated with a first vehicle axle  10  and a second drive shaft  8  is associated with a second transverse vehicle axle (not shown) which is structurally the same as the first vehicle axle  10 . 
         [0022]    By way of a first differential unit  13 , associated with the first vehicle axle  10 , and a second differential unit, associated with the second transverse vehicle axle, the drive torque is transmitted to wheels  16 ,  17  connected to the respective vehicle axle  10  and the second vehicle axle (not shown). 
         [0023]      FIG. 2  illustrates the schematic diagram of a second embodiment of the vehicle  1  in which, from the distributor gear system  5 , two drive shafts  21 ,  22  extend to the wheels  16 ,  17  connected to the first vehicle axle  10 , such that the first drive shaft  21  drives the wheel  16  and the second drive shaft  22  drives the wheel  17 . In a manner equivalent to the drive shafts  21  and  22  associated with the wheels  16  and  17 , two more drive shafts  23 ,  24  extend from the distributor gear system  5  to the wheels associated with the second vehicle axle and shown in  FIG. 3 , the third drive shaft  23  driving a wheel  18  and the fourth drive shaft  24  driving a wheel  19 . 
         [0024]    In the vehicles  1 , according to  FIGS. 1 and 2 , both the first vehicle axle  10  and the second vehicle axle can be steered. Since the steering mechanisms of both axles have the same structure, in what follows only a steering mechanism  27 , associated with the first transverse vehicle axle  10 , will be described. 
         [0025]    The steering mechanism  27  of the first vehicle axle  10 , shown in  FIGS. 1 and 2 , in the present case, is made with a main steering cylinder  26  formed as a synchronous cylinder with a piston rod  28 , the main steering cylinder  26  being orientated in the transverse direction of the vehicle parallel to the vehicle axle  10  which, in a known way, extends between the wheels  16 ,  17 . Besides a first chamber  30 , used in conventional steering systems, and a second chamber  31 , the main steering cylinder also has a third chamber  32  located in the transverse direction of the vehicle between the first chamber  30  and the second chamber  31 . 
         [0026]    The piston rod  28  is made in two parts, relative to the middle of the vehicle, and the parts, associated with each side of the vehicle, are each also made in two sections and consist of a first section  28 A of the piston rod  28  and a track rod  38 A on one side of the vehicle, and a second section  28 B of the piston rod  28  and a track rod  38 B on the other side of the vehicle. 
         [0027]    The chambers  30 ,  31  and  32  are separated from one another by a first piston element  34 , which is arranged between the first chamber  30  and the third chamber  32  and is connected to the first section  28 A of the piston rod  28 , and a second piston element  35 , which is arranged between the second chamber  31  and the third chamber  32  and is connected to the second section  28 B of the piston rod  28 . Thus, the first section  28 A and the second section  28 B of the piston rod  28  can move relative to one another in the transverse direction of the vehicle, depending on the volume of fluid in the third chamber  32  of the main steering cylinder  26 . 
         [0028]    The respective ends of the first section  28 A and the second section  28 B of the piston rod  28 , facing away from the main steering cylinder  26 , are articulated, in each case, by piston rod links  37 A,  378  formed as a ball joint to the respective track rods  38 A and  38 B. In turn, at their ends, facing away from the piston rod  28 , the track rods  38 A and  38 B are, in each case, articulated by respective track rod links  39 A,  39 B, also made as ball joints, to wheel supports  40 A,  40 B. The wheel supports  40 A,  40 B are fixed on wheel hubs  41 A,  41 B of the wheels  16  and  17 , which are, in turn, made so that together with the wheels  16  and  17 , they can swivel relative to the vehicle axle  10  about steering rotation axes  42 A,  42 B. 
         [0029]    In a known way, the first chamber  30  and the second chamber  31  of the main steering cylinder  26  are connected, via pressure lines  50 ,  51  to a fluid circuit by way of which a fluid can flow either into the respective chamber  30  or  31  or out of the respective chamber  30  or  31 . An electric control unit (not shown) controls the fluid pressure in the first chamber  30  and the second chamber  31  of the main steering cylinder  26 , via control valve devices associated with the chambers. 
         [0030]    The third chamber  32  of the main steering cylinder  26  is also connected into a fluid circuit, in such a manner that the fluid flow into and out of the third chamber  32  is controlled by a control valve device  46 , in this case, made as a 3/3 magnetic control valve. The 3/3 magnetic control valve  46  is actuated by an electric control device  48  which, depending on the wheel steering angle of the wheels  16  and  17  and by interaction with the electric control unit, either fills the third chamber  32  of the main steering cylinder  26  with fluid or drains fluid out of it. The electric control device  48  obtains information about the steering angle of the wheels  16  and  17  from sensors  44 A,  44 B, which determine the wheel steering angles by measuring the angle between the respective wheel hubs  41 A and  41 B and the transverse direction of the vehicle and which are in active connection with the electric control device  48 . 
         [0031]    In a vehicle of alternative design, a person with knowledge of the subject can also arrange sensors directly on the main steering cylinders, these sensors measure the position of the first piston element and the second piston element within the main steering cylinder. From the position of the piston elements, the electric control device can calculate the position of the wheels. 
         [0032]    Likewise, a person with knowledge of the field can arrange for the function of the electric control device to be integrated in the electric control unit and, in that case, the electric control unit is in active connection with the wheel position determining sensors and the same electric control unit actuates the control valve device associated with the fluid chamber. 
         [0033]    When the fluid chamber  32  of the main steering cylinder  26  of the first vehicle axle  10  is filled, the piston elements  34  and  35  in the main steering cylinder  26 , connected to the piston rods  28 , move away from one another in a direction parallel to the vehicle axle  10 , such that the track rods  38 A,  38 B are also moved apart by the track rod links  39 A,  39 B. The wheel supports  40 A and  40 B and the wheel hubs  41 A and  41 B in a fixed angular relation with one another relative to the track rod links  39 A,  39 B are, therefore, rotated about the track rod links  39 A and  39 B by the movement of the track rods  38 A,  38 B. When the third chambers  32  of the two vehicle axles are drained, the wheels  16 ,  17 ,  18 ,  19  are swiveled away from their current positions about the steering rotation axes  42 A,  42 B in an analogous manner. 
         [0034]    Accordingly, in an advantageous way, during normal forward or reverse driving, the wheel steering angles can be influenced by the electric control device  48  as a function of the positions of the wheels  16 ,  17  calculated from the data provided by the angle sensors  44 A,  44 B in such a manner that the extensions of the wheel hubs  41 A,  41 B meet at any time, while the vehicle is rounding a curve at a common point located outside the vehicle  1 . This ensures that the vehicle  1  is operated with exceptionally low wear in the area of the wheels  16 ,  17 , since, in that case, no stressful lateral sliding movements occur in the area of the wheels  16 ,  17 . 
         [0035]    Of course, it can also be that only one vehicle axle is fitted with a main steering cylinder having three chambers, particularly when only one steered vehicle axle is used. Furthermore, depending on the driving situation, low-wear operation can also be achieved by providing that only one of the two main steering cylinders of the vehicle axles is actuated by the electric control device, for example when the other, also steerable axle does not undergo any steering movement in the driving situation. 
         [0036]    If the third chambers  32  of the main steering cylinders  26  are filled with fluid in such a manner that the extension of the center lines of the wheel hubs  41 A,  41 B of the wheels meet at a point in the middle of the vehicle as shown, the vehicle can be spun about the point in the middle of the vehicle by reversing the rotation direction of the wheels  16  and  18 , and  17  and  19 , respectively. By way of the electric control device, such a condition called for by a driver&#39;s wish can only be realized when the vehicle is at rest. 
         [0037]    In the vehicle  1 , represented in  FIG. 1 , the rotation direction reversal of the wheels  16  and  18 , relative to the wheels  17  and  19 , is carried out in the first differential unit  13  and the second differential unit  14 , where the wheels  16 ,  17  or  18 ,  19  of a vehicle axle  10  or  11 , respectively, are driven in different directions. 
         [0038]    In a vehicle of alternative design, the wheel rotational direction on one side of the vehicle is reversed with the help of two planetary gearsets, one planetary gearset being arranged on one side of a vehicle axle in each case, between the differential unit and one of the wheels. 
         [0039]    In the vehicle  1 , represented in  FIG. 2 , the rotation direction of the wheels  16  and  18 , relative to the wheels  17  and  19 , is reversed in the distributor gear system  5  in particular by way of a planetary gearset and, in this case, too, the rotation direction of either the first drive shaft  21  and the third drive shaft  23  or the rotation direction of the second drive shaft  22  and the fourth drive shaft  24  is reversed when compared with normal driving. 
       REFERENCE NUMERALS 
       [0000]    
       
           1  vehicle 
           3  drive engine 
           4  transmission gearbox 
           5  distributor gear system 
           7  first drive shaft 
           8  second drive shaft 
           10  first vehicle axle 
           13  first differential unit 
           16  wheel 
           17  wheel 
           18  wheel 
           19  wheel 
           21  first drive shaft 
           22  second drive shaft 
           23  third drive shaft 
           24  fourth drive shaft 
           26  main steering cylinder 
           27  steering mechanism 
           28  piston rod 
           28 A first section of the piston rod 
           28 B second section of the piston rod 
           30  first chamber of the main steering cylinder 
           31  second chamber of the main steering cylinder 
           32  third chamber of the main steering cylinder 
           34  first piston element 
           35  second piston element 
           37 A piston rod link 
           37 B piston rod link 
           38 A track rod 
           38 B track rod 
           39 A track rod link 
           39 B track rod link 
           40 A wheel support 
           40 B wheel support 
           41 A wheel hub 
           41 B wheel hub 
           42 A angle sensor 
           42 B angle sensor 
           46  control valve device 
           48  electric control device 
           50  pressure line 
           51  pressure line