Abstract:
The invention relates to a road-milling machine which has a ladder  11  to allow the driver&#39;s position  7  of the civil engineering machine to be climbed to easily. The ladder is mounted on one  1 B of the two longitudinal sides of the frame  1  of the machine to be pivotable about an axis of pivot  27  extending substantially at right angles to the direction of travel. The ladder can thus be folded upwards to widen the working range of the machine. However, should the ladder not be in a state where it is folded upwards while the machine is being used to do work, the ladder cannot be damaged against obstacles which suddenly make an appearance in the working range. Should the ladder hit against an obstacle, the ladder is able to move out of the way of the obstacle by pivoting out of the vertical position in the opposite direction to the direction of travel. A further advantage of the ladder lies in the fact that the ladder can easily be folded upwards or downwards not only from the ground but also from the driver&#39;s position.

Description:
This application claims benefit of German Patent Application DE 20 2008 013 393.9, filed Oct. 9, 2008. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a road-milling machine. 
     2. Description of the Prior Art 
     Civil engineering machines of different designs are known for underground and above-ground construction. What are used for the construction of roads are self-propelled road-building machines, which include for example known road-milling machines. Known road-milling machines have a driver&#39;s position for the driver of the machine. 
     Because of the relatively large dimensions of road-milling machines, the driver&#39;s position is arranged at a relatively great height above the ground. For climbing to the driver&#39;s position, road-milling machines therefore have a ladder which is arranged on one side of the frame of the machine below the driver&#39;s position. To make the climb to the driver&#39;s position easier, the ladder should reach to a point which is as close as possible to the ground. The ladder should also be spaced sufficiently far away from the frame of the machine to ensure that when the driver of the machine is climbing to the driver&#39;s position there is no danger of his coming into contact with parts of the machine which may possibly even be moving. 
     Basically, a ladder is disadvantageous in that it increases the width of the machine for transport. This is particularly the case when, for reasons of safety, the ladder is arranged at a sufficiently large spacing from the frame of the machine. 
     It is also a disadvantage that the ladder arranged on the side of the frame of the machine is a fundamental restriction on the working range of the machine. Even when the machine is kept sufficiently far away from lateral boundaries such for example as a wall or the like, there is still the further danger of the ladder colliding with obstacles which suddenly make an appearance within the working range. If this happens, the ladder may be ripped from its anchorage or even destroyed. 
     There are known road-milling machines in which the problem of reducing the width for transport is solved by fastening the ladder to the frame of the machine with a parallelogram linkage. The parallelogram linkage allows the ladder to be folded in against the frame of the machine, thus reducing the width for transport. It is however a disadvantage that the parallelogram linkage calls for a relatively complicated structure. 
     As well as this, what are also known are road-milling machines which have a foldable ladder which comprises two sub-sections which are connected together by joints. The two stiles of the bottom sub-section of the ladder are fastened to the stiles of the top sub-section of the ladder by rotary joints, thus enabling the bottom sub-section to be pivoted about an axis which extends in the direction of travel. When the ladder is folded upwards, there is no restriction on the working range of the machine, nor is there any danger of the ladder colliding with obstacles. However, when the driver of the machine is at the driver&#39;s position it is not easy for him to fold the ladder upwards, even though the bottom sub-section of the ladder could still be folded upwards without any problems from the ground. However, if the ladder is not folded upwards, there is still a risk of the ladder suffering damage against obstacles which suddenly make an appearance. 
     SUMMARY OF THE INVENTION 
     An object underlying the invention is to provide a road-milling machine which has a ladder for the driver&#39;s position which can be produced inexpensively and which is particularly easy to deal with. 
     This object is achieved in accordance with the invention by virtue of the features of the independent claims. Advantageous embodiments of the invention form the subject matter of the dependent claims. 
     In the case of the road-milling machine according to the invention, the ladder is mounted on one or both longitudinal sides of the frame of the machine to be pivotable about an axis of pivot extending substantially at right angles to the direction of travel. The ladder can thus be folded upwards to widen the working range of the machine. However, should the ladder not be in a state where it is folded upwards while the machine is being used to do work, the ladder cannot be damaged against obstacles which suddenly make an appearance in the working range. Should the ladder hit against an obstacle, the ladder is able to move out of the way of the obstacle by pivoting out of the vertical position. When this happens, the portion of the ladder which is situated below the axis of pivot is pivoted out of the vertical position in the opposite direction to the direction of travel. 
     A further advantage of the pivotable ladder of the road-milling machine according to the invention lies in the fact that the ladder can easily be folded upwards or downwards not only from the ground but also from the driver&#39;s position. 
     The ladder may comprise one or more sub-sections. The ladder itself may even be a ladder which can be folded together. It is preferred that the ladder is mounted on the frame of the machine to be pivotable about an axis extending substantially at right angles to the direction of travel. 
     In a preferred embodiment, provision is made for the axis of pivot extending substantially at right angles to the direction of travel to be tilted from the horizontal relative to the vertical longitudinal side in such a way that the ladder is at a slope relative to the longitudinal side of the frame of the machine, i.e. that the ladder is leant against the side-wall of the frame of the machine. The axis of pivot of the ladder may stand in an orthogonal position on the plane which is defined by the ladder in this case. On the one hand, what is achieved in this way is that in the vertical position the ladder is sloped forward in the direction of ascent relative to the vertical frame of the machine, which makes climbing aboard easier from the ergonomic point of view. What on the other hand is achieved in this way is that in the vertical position the ladder is spaced sufficiently far away from the parts of the machine which are arranged in the bottom region along the longitudinal side of the machine, which are generally moving. There is no need for a parallelogram linkage of complicated construction to increase the distance between the ladder and the frame of the machine. Consequently, there is relatively little structural complication. 
     In an alternative embodiment, provision is made not for the axis of pivot extending substantially at right angles to the direction of travel to be tilted relative to the vertical longitudinal side of the frame of the machine but for the ladder which is pivotable about the axis of pivot to be so arranged that the axis of pivot does not stand in an orthogonal position on the plane defined by the ladder and instead the axis of pivot is in an oblique position to the plane of the ladder in such a way that in the vertical position the ladder is at a slope relative to the longitudinal side of the frame of the machine. 
     In a further embodiment which is a particular preference, there is provided, for fastening the ladder to the longitudinal side of the frame of the machine, a connecting joint which has two parts which are rotatable about an axis of rotation extending substantially at right angles to the direction of travel, the frame of the machine having one part of the joint and the ladder having the other part. 
     The axis of rotation of the connecting joint may, in this case, once again be tilted relative to a longitudinal side of the frame of the machine, thus causing the ladder to be at a slope relative to the longitudinal side of the machine. Once again, it is also possible for the connecting joint to be so arranged that the axis of rotation is perpendicular to the frame of the machine, though the ladder then has to be arranged on the part of the joint which the ladder has in such a way that the ladder is at a slope relative to the frame of the machine. 
     Basically, a tilted position for the ladder relative to the frame of the machine when in the vertical position has the disadvantage that when being pivoted the ladder does not move in a plane which extends parallel to the longitudinal side of the frame of the machine. There is therefore in principle a risk of the ladder colliding with parts of the frame of the machine when it is being pivoted. In a further embodiment which is a particular preference, provision is therefore made for the axis of rotation of the connecting joint to be tilted relative to the longitudinal side of the frame of the machine, the part of the joint which the ladder has being arranged on the ladder in such a way that the axis of pivot stands in an oblique position on the plane defined by the ladder. What is achieved by this means is that the ladder has adequate clearance to move when being pivoted but on the other hand does not project too far from the frame of the machine, thus maintaining the maximum permitted width for transport of the machine. 
     The ladder is preferably mounted on a longitudinal side of the machine to be rotatable through a right angle from the vertical position, thus allowing the ladder to be pivoted from the vertical position to a horizontal position. However, in practice it may be enough for the ladder to be mounted on the frame of the machine to be pivotable through a smaller angle to enable it to move out of the way of obstacles which make an appearance in the working range. 
     The ladder is preferably resiliently preloaded to the horizontal position and/or the vertical position, thus making it easier for the ladder to move by pivoting to one position, to the other position or to both positions. The ladder is preferably resiliently preloaded to the horizontal position and/or the vertical position by a pneumatic strut which assists a pivoting movement in both directions, in which case the dead-centre point of the pneumatic strut may be selected in such a way that the ladder is more strongly preloaded in one of the two directions, or in other words that the pivoting movement is assisted at an earlier point in time in one of the two directions. 
     In a further preferred embodiment at least one sub-section of the ladder has a stile which is at the front in the direction of travel and a stile which is to the rear in the direction of travel, to which stiles rungs are fastened. Basically however the ladder may also take the form of a single-stiled ladder. 
     In a further preferred embodiment, provision is made for that stile of the ladder which is at the front in the direction of travel to be pivotably fastened to a longitudinal side of the frame of the machine whereas that stile of the ladder which is to the rear in the direction of travel has a stop member which, when the ladder is in the vertical position, is supported on a supporting member which is fastened to the longitudinal side of the machine. What is achieved in this way is that the ladder is securely locked to the frame of the machine when being climbed, but is at any time able to pivot about an axis extending at right angles to the direction of travel if it hits against an obstacle during forward travel. 
     In a further embodiment which is a particular preference, the ladder comprises a top and a bottom sub-section, with the bottom sub-section being fastened to the top sub-section to be pivotable, in the same plane as the top sub-section, about an axis which extends substantially at right angles to the direction of travel. In this way the ladder can be folded together easily without the ladder projecting outwards. 
     The top sub-section of the ladder preferably takes the form of a two-stiled ladder having a stile which is at the front in the direction of travel and a stile which is to the rear, to which stiles rungs are fastened. It is advantageous in this case for the axis of pivot of the bottom sub-section of the ladder to be arranged at that stile of the top sub-section of the ladder which is to the rear in the direction of travel, meaning that the bottom sub-section of the ladder is pivoted if it hits against an obstacle during backward travel. 
     The bottom sub-section of the ladder preferably takes the form of a single-stiled ladder having one rung fastened to one stile. The stile of the bottom sub-section of the ladder can preferably be pivoted from a folded out position to a position in which it is folded in against the top sub-section and in which the rung of the bottom sub-section rests against the other of the two stiles of the top sub-section. 
     A particular compact structure can be obtained by having the bottom portion of that stile of the top sub-section of the ladder against which the rung of the bottom sub-section rests in the folded-in position extend obliquely to the other stile of the top sub-section, thus causing the rung of the bottom sub-section not to project laterally when folded against the stile of the top sub-section. 
     In the folded-out position, the bottom sub-section of the ladder is securely held by a stop member which is supported against the top sub-section of the ladder. In the folded-in position, the bottom sub-section of the ladder can preferably be locked to the top sub-section by a fastening member. The fastening member may be a fastening member which locks the bottom sub-section in the folded-in position by a snap or latching action and which can easily be released to allow the bottom sub-section to be folded out. 
     To make the climb to the driver&#39;s position easier, the ladder preferably has a hand-hold member which projects upwards beyond the ladder in the vertical position and which the driver of the machine can use to hold himself secure when climbing the ladder. The hand-hold member may be of different forms. It may also act as a safeguard against falling-off sideways. As well as performing its safety function, the hand-hold member may also serve as a lever for pivoting the ladder from the vertical position to the horizontal position or vice versa. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the invention is explained in detail below by reference to the drawings. In the drawings: 
         FIG. 1  is a simplified view of an embodiment of road-milling machine, 
         FIG. 2  is a view from the front of an embodiment of ladder according to the invention for the road-milling machine, showing the bottom sub-section of the ladder folded out, 
         FIG. 3  is a view from the front of the ladder, showing the bottom sub-section folded against the top sub-section, 
         FIG. 4  is a view of the ladder from the side, showing the bottom sub-section of the ladder folded in, 
         FIG. 5  is a plan view of the ladder, showing the bottom sub-section of the ladder folded in, 
         FIG. 6  is a view of the ladder from the side, showing the ladder folded upwards and the bottom sub-section of the ladder folded in, 
         FIG. 7  is a plan view of the ladder, showing the ladder folded upwards and the bottom sub-section of the ladder folded in. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows the principal components of a road-milling machine which has a driver&#39;s position. The road-milling machine has a frame  1  and running gear  2 . The running gear  2  of the milling machine comprises four track-laying units  2 A,  2 B which are arranged at the front and rear ends on the two sides of the frame  1  of the machine. The frame  1  of the machine and the running gear  2  are connected together by means of piston-and-cylinder arrangements  3 A,  3 B, thus allowing each track-laying unit to be adjusted in the heightwise direction. The track-laying units  2 A,  2 B may also be referred to simply as tracks. The road-milling machine may also use wheels instead of tracks. The tracks or wheels may generally be referred to as ground engaging supports. 
     The frame  1  of the milling machine carries a milling arrangement  5  which is arranged below the frame of the machine and a feeding arrangement  6  for the milled-away material which is arranged at the front end of the frame of the machine. Milling arrangement  5  may also be referred to as a milling drum. Feeding arrangement  6  may also be referred to as a conveyor. 
     The driver&#39;s position  7  on the milling machine is situated above the surface being worked on, in the centre of the frame  1  of the machine. At the driver&#39;s position, the driver of the machine sits in front of the controls  9  on a driver&#39;s seat  8 . 
     The frame  1  of the machine has an end  1 A which is at the front in the direction of travel  10 , a rear end  1 B and two longitudinal sides  1 C,  1 D. Fastened to at least one of the two longitudinal sides  1 C or  1 D of the frame  1  of the machine, below the driver&#39;s position  7 , is a ladder  11  to enable the driver of the machine to climb to the driver&#39;s position easily.  FIG. 1  shows an embodiment in which the ladder  11 , which is only shown in a general form, is situated on the side which is on the left in the direction of travel  10 . The ladder  11  will be described in detail below by reference to  FIGS. 2 to 7 . 
       FIG. 2  is a view from the front of the ladder  11  which is mounted on the longitudinal side  1 D of the frame  1  of the machine. The ladder  11  extends from the entrance to the driver&#39;s position  7  to a point close to the ground.  FIG. 1  shows the ladder in the vertical position. The driver of the machine is able to pivot the ladder from the vertical position through 90° to a horizontal position regardless of whether he is standing on the ground next to the machine or is at the driver&#39;s position  7 . 
     The driver of the machine will pivot the ladder to the horizontal position when the working range of the machine is to be extended in the sideways direction, such for example as when milling is to be done to a point close to an adjoining wall, or when transportation is imminent. The driver of the machine will also pivot the ladder to the horizontal position when obstacles are expected. However, even if the driver of the machine has not pivoted the ladder to the horizontal position, the ladder can move out of the way of an obstacle which suddenly makes its appearance by pivoting out of the vertical position in the opposite direction to the direction of travel when it hits against the obstacle. 
     The ladder  11  has a top sub-section  11 A and a bottom sub-section  11 B. The top sub-section  11 A of the ladder  11  has a stile  12  which is at the front in the direction of travel  10  and a stile  13  which is to the rear in the direction of travel, to which stiles  12 ,  13  four rungs  14 ,  15 ,  16 ,  17  are fastened, the bottom sub-section  11 B of the ladder  11  having only one stile  18 , which is to the rear in the direction of travel, and only one rung  19 . 
     The bottom sub-section  11 B of the ladder can be pivoted upwards from the position shown in  FIG. 2  to the position shown in  FIG. 3 . The driver of the machine will fold the bottom sub-section  11 B of the ladder  11  upwards when for example milling is to be done close to a kerb. There is thus no need for the entire ladder  11  to be folded upwards. Only the bottom sub-section  11 B will also be folded upwards when the obstacles expected are only small. However, should the bottom sub-section not be folded upwards, the said bottom sub-section alone of the ladder can be pivoted during backward travel if the ladder hits against an obstacle by its bottom sub-section. 
     At the bottom end of the rear stile  13  of the top sub-section  11 A of the ladder  11 , the top end of the stile  18  of the bottom sub-section  11 B of the ladder  11  is mounted to be pivotable about a pin (and axis)  21  which extends perpendicularly to a plane in which the stiles and rungs of the ladder  11  lie. In the folded-out position, the bottom sub-section  11 B is supported laterally against the bottom portion of the rear stile  11  of the top sub-section  11 A by a stop member  22 . 
     When the bottom sub-section  11 B of the ladder  11  is folded upwards, the stile  18  of the bottom sub-section  11 B comes to rest against the bottom rung  17  of the top sub-section  11 A and the rung  19  of the bottom sub-section  11 B comes to rest against the bottom portion of the front stile  12  of the top sub-section  11 A of the ladder  11  ( FIG. 3 ). In the folded-in position, the bottom sub-section  11 B of the ladder  11  can be fastened to the top sub-section  11 A by a fastening member  23  which is arranged on the bottom portion  12 A of the front stile  12  of the top sub-section  11 A. The bottom sub-section  11 B of the ladder  11  latches home automatically in this case when folded upwards. The latched connection can be released again by operating a lever  23 A on the fastening member  23 , thus causing the bottom sub-section  11 B to drop back to the starting position under its own weight. 
     The bottom portion  12 A of the front stile  12  of the top sub-section  11 A extends obliquely downwards towards the rear stile  13  of the top sub-section  11 A, which means that the rung  19  of the bottom sub-section  11 A rests tightly against the bottom portion  12 A of the front stile  12  or is received into it. 
     The ladder  11  is fastened, at a distance from the frame  1  of the machine, to a horizontal bracket  24  and a vertical bracket  25  on the frame of the machine by a connecting joint  26 . The connecting joint  26  has two parts  26 A and  26 B which are rotatable relative to one another about an axis of rotation  27  and of which one,  26 A, is fastened to the vertical bracket  25  on the frame  1  of the machine and the other,  26 B, is fastened to the top end of the front stile  12  of the top sub-section  11 A of the ladder  11 . 
     The axis of rotation  27  of the connecting joint  26  forms the axis of pivot about which the ladder can be pivoted on the frame of the machine from the vertical position to the horizontal position. The axis of pivot  27  makes a right angle α with the vertical side-wall ID of the frame  1  of the machine, i.e. the axis of pivot extends at right angles to the direction of travel  10 . At the same time, the axis of pivot  27  is tilted relative to the vertical side-wall ID of the frame  1  of the machine at an angle β which is less than 90°, which means that in the vertical position the ladder is at a slope relative to the frame of the machine ( FIG. 3 ,  FIG. 4 ). This ensures that ergonomic climbing aboard is possible and that there is an adequate spacing from the frame of the machine. 
     In principle, the tilted position of the axis of pivot  27  relative to the frame  1  of the machine at the angle β results in the ladder  11  not extending parallel to the side-wall ID when it is pivoted from the vertical position to the horizontal position and in its not resting close to the frame  1  of the machine but in its resting more closely to the side-wall at its top side than at its bottom side. There is therefore a risk of the ladder hitting against the frame of the machine when it is pivoted. Also, the tilted position of the ladder when folded upwards is found to be a nuisance in practice. 
     This problem is solved in the case of the ladder according to the invention by causing the axis of pivot  27  to be in an oblique position on the plane in which the stiles and rungs of the ladder  11  lie. The angle γ made by the axis of pivot  27  and the reference plane mentioned is more than 90°, because the stiles and rungs of the ladder  11  are rotated slightly relative to the side-wall ID of the frame  1  of the machine ( FIG. 5 ), i.e. the plane of the ladder is inclined slightly inwards in the direction of travel  10 . In constructional terms, this is achieved by fastening that part  26 A of the connecting joint  26  which is connected to the ladder to the top end of the front stile  12  of the top sub-section  11 A of the ladder  11  in a slightly oblique position. If the ladder  11  is then pivoted from the vertical position to the horizontal position, the ladder rests close to the side-wall ID of the frame  1  of the machine in the horizontal position ( FIG. 7 ). The angles β and γ are so sized in this case that the ladder extends parallel to the longitudinal side of the frame of the machine in the horizontal position, i.e. points in the direction of travel  10 . 
     Alternatively, in a kind of kinematic reversal, the angle β may equally well be set at 90° and that part  26 A of the connecting joint  26  which is connected to the ladder may be fastened to the top end of the front stile  12  of the top sub-section  11 A of the ladder  11  in an oblique position such that in the vertical position the ladder is sloped forward in the direction of ascent relative to the side-wall ID of the frame  1  of the machine. The angle a then has to be selected to be suitably larger than 90°, in such a way that the ladder rests close to the longitudinal side ID of the frame  1  of the machine in the horizontal position. 
     The ladder  11  which is pivotably mounted on the frame of the machine at one end is held in the vertical position by virtue of the fact that the ladder is supported on the horizontal bracket  24  on the frame  1  of the machine by a stop member  28 . The stop member  28  is fastened to the top end of the rear stile  13  of the top sub-section  11 A of the ladder  11 . It takes the form of a hook and engages in a recess  29  in the horizontal bracket  24  on the frame  1  of the machine. If the ladder  11  encounters an obstacle during forward travel, it can easily pivot back, the hook-shaped stop member  28  then lifting away from the bracket  24 . In the vertical position however, the stop member  28  fits behind the front edge of the bracket  24 , which means that the ladder  11  is adequately secured. 
     The ladder is held in the horizontal position in a similar way in that it is supported, in a hole  33  in the horizontal bracket  24  on the frame  1  of the machine, by a damping stop  32 . The damping stop  32  is fastened to the front stile  12  of the top sub-section  11 A of the ladder  11 . It takes the form of a parabolic buffer and engages in a hole  33  in the horizontal bracket  24  on the frame  1  of the machine. The ladder is thereby held in place with elastic damping in five of six possible directions. To rule out the possibility of mis-operation and misuse, the ladder  11  may also be locked in this position by suitable means. 
     Fastened to the longitudinal side of the rear stile  13  of the top sub-section  11 A of the ladder  11  is an elongated hand-hold member  30  which in the vertical position extends beyond the top end of the ladder to a point above the driver&#39;s position  7 . The hand-hold member  30  serves on the one hand as an aid to climbing aboard and on the other hand as a lever for pivoting the ladder between the vertical and horizontal positions. When the driver of the machine has climbed to the driver&#39;s position, he is able to pivot the ladder between the vertical and horizontal positions from the driver&#39;s position by taking hold of the hand-hold member  30 . It goes without saying that the ladder can also be pivoted from the ground, e.g. to get the machine ready to be transported. For this purpose, the operator simply takes hold of the ladder  11  itself. 
     The pivoting movement of the ladder  11  between the vertical and horizontal positions and vice versa is assisted by a pneumatic strut  31  whose piston  31 A is fastened to hinge to the front stile  12  of the top sub-section  11 A above the axis of rotation  27  of the connecting joint  26  and whose cylinder  31 B is fastened to hinge to the horizontal bracket  24  on the frame  1  of the machine below the axis of rotation  27  of the connecting joint  26 .