SELF-PROPELLED CONSTRUCTION MACHINE AND METHOD FOR OPERATING A SELF-PROPELLED CONSTRUCTION MACHINE

Abstract

The invention relates to a self-propelled construction machine, comprising a machine frame supported by a chassis having wheels or crawler tracks. The basic principle of the invention involves determining a variable Δ which is characteristic of the milling profile on the basis of a functional relationship between the variable which is characteristic of the milling profile and the advance speed v and/or milling drum rotational speed n. The variable Δ which is characteristic of the milling profile is a correction variable for adjusting the height of the milling drum with respect to the surface of the ground.

Claims

1-16. (canceled)

17. A method for operating a self-propelled construction machine having a milling drum for machining the ground, the height of which drum is adjustable with respect to a surface of the ground to be machined such that material is removed from the ground, the method comprising: when an advance speed of the construction machine is zero, lowering the milling drum to a first position wherein a lower edge of a cutting circle of the milling drum is at a level of the surface of the ground, wherein a milling depth of the milling drum is calibrated to zero; while the advance speed of the construction machine is still zero, lowering the milling drum from the first position into a second position wherein the lower edge of the cutting circle of the milling drum is at a distance from the level of the surface of the ground corresponding to an initial specified milling depth; machining the ground at an advance speed above zero; and when the construction machine returns to an advance speed of zero, raising the milling drum to at least a third position wherein the lower edge of the cutting circle of the milling drum is at a distance from the level of the surface of the ground corresponding to a current specified milling depth.

18. The method of claim 17, wherein: when the construction machine returns to an advance speed of zero, the milling drum is raised to the first position.

19. The method of claim 17, wherein a difference between the second position and the third position accounts for changes made by a driver of the construction machine to the specified milling depth during an advance of the construction machine.

20. The method of claim 17, wherein a difference between the second position and the third position accounts for changes in the specified milling depth based on a current wear state of the milling drum.

21. The method of claim 17, further comprising, during an advance of the construction machine, wherein the advance speed is above zero, correcting the specified milling depth to correspond to a desired milling profile, said correction based at least in part on the advance speed and/or a milling drum rotational speed

22. The method of claim 17, wherein correcting the specified milling depth to correspond to a desired milling profile comprises: determining a variable which is characteristic of a milling profile, based at least in part on the advance speed and/or the milling drum rotational speed, determining a correction variable for the specified milling depth, based at least in part on the variable which is characteristic of the milling profile, and instead of the specified milling depth, a value that is corrected using the correction value is continuously set for the milling depth.

23. The method of claim 22, wherein the correction variable is a vertical distance between a point on the milling profile at which the milling depth is a minimum and a point on the milling profile at which the milling depth is a maximum.

24. The method of claim 23, wherein: the value that is corrected using the correction value is a deviation of a value between the minimum milling depth and the maximum milling depth from the maximum milling depth.

25. The method of claim 22, wherein the variable which is characteristic of the milling profile is determined on the basis of a functional relationship between the variable which is characteristic of the milling profile and a ratio of the advance speed to the milling drum rotational speed.

26. The method of claim 22, comprising: continuously measuring values for at least the milling depth of the milling drum and the advance speed of the construction machine; determining a volume of material removed from the ground, based at least on the measured values for the milling depth of the milling drum and a distance travelled by the construction machine; and applying a correction variable for the determined volume of material removed from the ground, based on the determined variable which is characteristic of the milling profile.

27. A self-propelled construction machine comprising: a machine frame supported by a chassis having wheels or crawler tracks; a milling drum arranged on the machine frame for machining the ground; a drive device for driving the wheels or crawler tracks and the milling drum; a lifting device for adjusting a height of the milling drum with respect to a surface of the ground to be machined; and a control and processing unit configured: when an advance speed of the construction machine is zero, to lower the milling drum to a first position wherein a lower edge of a cutting circle of the milling drum is at a level of the surface of the ground, wherein a milling depth of the milling drum is calibrated to zero; while the advance speed of the construction machine is still zero, to lower the milling drum from the first position into a second position wherein the lower edge of the cutting circle of the milling drum is at a distance from the level of the surface of the ground corresponding to a specified milling depth; and when the construction machine returns to an advance speed of zero, to raise the milling drum to at least a third position wherein the lower edge of the cutting circle of the milling drum is at a distance from the level of the surface of the ground corresponding to a current specified milling depth.

28. The self-propelled construction machine of claim 27, wherein: when the construction machine returns to an advance speed of zero, the milling drum is raised to the first position.

29. The self-propelled construction machine of claim 27, wherein a difference between the second position and the third position accounts for changes made by a driver of the construction machine to the specified milling depth during an advance of the construction machine.

30. The self-propelled construction machine of claim 27, wherein a difference between the second position and the third position accounts for changes in the specified milling depth based on a current wear state of the milling drum.

31. The self-propelled construction machine of claim 27, wherein the control and processing unit is further configured, during an advance of the construction machine wherein the advance speed is above zero, to correct the specified milling depth to correspond to a desired milling profile, said correction based at least in part on the advance speed and/or a milling drum rotational speed.

32. The self-propelled construction machine of claim 27, wherein the correction of the specified milling depth to correspond to a desired milling profile comprises: determining a variable which is characteristic of a milling profile, based at least in part on the advance speed and/or the milling drum rotational speed, determining a correction variable for the specified milling depth, based at least in part on the variable which is characteristic of the milling profile, and instead of the specified milling depth, a value that is corrected using the correction value is continuously set for the milling depth.

33. The self-propelled construction machine of claim 32, wherein the correction variable is a vertical distance between a point on the milling profile at which the milling depth is a minimum and a point on the milling profile at which the milling depth is a maximum.

34. The self-propelled construction machine of claim 33, wherein the value that is corrected using the correction value is a deviation of a value between the minimum milling depth and the maximum milling depth from the maximum milling depth.

35. The self-propelled construction machine of claim 32, wherein the variable which is characteristic of the milling profile is determined on the basis of a functional relationship between the variable which is characteristic of the milling profile and a ratio of the advance speed to the milling drum rotational speed.

36. The self-propelled construction machine of claim 32, wherein the control and processing unit is further configured to: continuously measure values for at least the milling depth of the milling drum and the advance speed of the construction machine; determine a volume of material removed from the ground, based at least on the measured values for the milling depth of the milling drum and a distance travelled by the construction machine; and apply a correction variable for the determined volume of material removed from the ground, based on the determined variable which is characteristic of the milling profile.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0034] In the following, an embodiment of the invention will be described in detail with reference to the drawings, in which:

[0035] FIG. 1 is a side view of a road milling machine as an example of a self-propelled construction machine,

[0036] FIG. 2 is a highly simplified schematic view of the assemblies of the construction machine which are essential to the invention,

[0037] FIG. 3A to 3C are highly simplified schematic views of the milling drum equipped with milling picks for different advance speeds,

[0038] FIGS. 4A and 4B are sections through the milled terrain for different advance speeds of the construction machine,

[0039] FIG. 5A to 5C are enlarged views of the cutting circle of the milling drum, the construction machine being moved at different advance speeds and a relatively deep milling depth being set,

[0040] FIG. 6A to 6C are enlarged views of the cutting circle of the milling drum, the construction machine being moved at different advance speeds and a relatively shallow milling depth being set,

[0041] FIG. 7 is a sectional view showing the height of the elevations in relation to the milling depth,

[0042] FIGS. 8A and 8B are sectional views, composed of individual cutting lines, for a faster advance speed and for a slower advance speed, and

[0043] FIG. 9 shows the functional correlation between a value which is characteristic of the milling profile and the ratio of the advance speed to the milling drum rotational speed.

DETAILED DESCRIPTION

[0044] FIG. 1 shows a road milling machine for milling road surfaces made of asphalt, concrete or the like as an example of a self-propelled construction machine. FIG. 2 is a highly simplified schematic view of the assemblies of the construction machine which are essential to the invention. The construction machine according to the invention may, for example, be a road milling machine or a surface miner.

[0045] The road milling machine comprises a machine frame 2 supported by a chassis 1. The chassis 1 of the milling machine comprises front and rear crawler tracks 3, 4, which are arranged on the right and left side of the machine frame 2 when viewed in the operating direction A. Wheels may also be provided instead of crawler tracks.

[0046] To adjust the height of the machine frame with respect to the surface 16 of the ground, the self-propelled construction machine comprises a lifting device 28 which comprises lifting columns 5, 6, 7, 8 which are associated with the individual crawler tracks 3, 4 and by which the machine frame 2 is supported (FIGS. 1 and 2).

[0047] The construction machine has a milling drum 9, which is equipped with milling tools 10, for example milling picks. The milling drum 9 is arranged on the machine frame 2 between the front and rear crawler tracks 3, 4 in a milling drum housing 11 that is closed off at the longitudinal sides by an edge protector 12, at the front by a hold-down device (not shown), and at the rear by a wiping device (not shown). The milled material which is milled off is transported away by a conveying device 13. The driver's cab 14, comprising a control panel 15 for the machine driver, is located on the machine frame 2, above the milling drum housing 11.

[0048] By retracting and extending the lifting columns 5, 6, 7, 8 of the lifting device 28, the height of the milling drum 9 can be adjusted with respect to the surface 16 of the ground.

[0049] In order to drive the crawler tracks 3, 4 and to drive the milling drum 9 and further assemblies, the construction machine has a drive device 17, which has an internal combustion engine 18. A first drive train I is used to transmit the drive power of the internal combustion engine 18 to the crawler tracks 3, 4, whilst a second drive train II is used to transmit the drive power to the milling drum 9. The first drive train I may comprise a hydraulic transmission system 19 and the second drive train II may comprise a chain and rope drive 20. Drive systems of this type are known to a person skilled in the art.

[0050] In order to control the drive device 17 and the lifting device 28 and further assemblies, the construction machine comprises a preferably central control and processing unit 21, by means of which the crawler tracks 3, 4 are actuated in such a way that the construction machine moves in the operating direction A at a predetermined advance speed v and the milling drum 9 rotates at a specified milling drum rotational speed n. The control and processing unit 21 also actuates the lifting columns 5, 6, 7, 8 in such a way that the machine frame 2 is raised and lowered together with the milling drum 9 in order to set the desired milling depth h.

[0051] The control panel 15 of the construction machine comprises an input unit 22 and a display unit 23. On the input unit 22, for example a touchscreen, the machine driver can input a particular advance speed v, a particular milling drum rotational speed n and a milling depth h, the control and processing unit 21 actuating the drive device 17 in such a way that the construction machine moves at the advance speed v specified by the machine driver and the milling drum 9 rotates at the specified milling drum rotational speed n, and actuates the lifting device 28 in such a way that the specified milling depth h is set.

[0052] FIG. 3A to 3C are highly simplified schematic views of the milling drum 9, which is equipped with milling picks 10, only one milling pick being shown in the drawings. Whilst the milling drum 9 rotates at the specified rotational speed n, the construction machine moves in the operating direction A at the specified advance speed v. The drawings show the line on which the tip of the milling pick 10 moves, the milling drum rotational speed n being constant. FIG. 3A shows the cutting line 29 when the construction machine is stationary, FIG. 3B shows the cutting line 29′ when the construction machine is moving at an advance speed v1, and FIG. 3C shows the cutting line 29″ when the construction machine is moving at an advance speed v2, where v2>v1. A trough 30, 30′, 30″ in the terrain surface 16 is shown.

[0053] FIG. 4A and FIG. 4B are sections through the milled terrain at different advance speeds v1 and v2 of the construction machine, resulting in different milling profiles (v2>v1). The two milling profiles share the continuous sequence of depressions 24 and elevations 25 in the operating direction A of the construction machine, resulting in a certain degree of roughness of the terrain surface.

[0054] FIGS. 4A and 4B show that the height of the elevations 25 is dependent on the advance speed v1 or v2. A faster advance speed v2 results in higher elevations 25 than a slower advance speed v1. The milling profile is characterized by “maxima” and “minima”, in other words points at which the milling depth is smallest and points at which the milling depth is greatest. The vertical distance between the surface 16 of the original terrain and the point at which the milling depth is smallest thus defines a minimum milling depth h.sub.min, and the vertical distance between the surface 16 of the terrain and the point at which the milling depth is greatest thus defines a maximum milling depth h.sub.max, which corresponds to the specified milling depth h. It is found that the maximum milling depth h.sub.max is independent of the advance speed v. However, the minimum milling depth h.sub.min is found to be dependent on the advance speed v.

[0055] FIG. 5A to 5C are enlarged views of the cutting circle of the milling drum 9, the construction machine moving at different advance speeds v1 and v2 and the milling drum rotational speed n being constant. In the embodiment, it is assumed that the milling drum 9 has a cutting circle diameter d of 1020 mm and that a milling depth h1 of 10 mm is set. The milling drum rotational speed n is 100 rpm. The length of the cut in the milling direction A when v=0 is shown as s. This results in a cut length s of approximately 201 mm (h=h1). In general, the cut length s is calculated as follows:

s=2√{square root over (dh−h.sup.2)}

[0056] FIG. 5A shows the stationary milling drum 9. FIG. 5B shows the milling drum moving in the milling direction at an advance speed v1 of 2 m/min, and FIG. 5C shows the milling drum moving in the milling direction at an advance speed v2 of 5 m/min. FIG. 5B shows that, at the advance speed v1, the milling drum moves a distance in the milling direction A corresponding to approximately 1/10 s during a rotation, in other words approximately 20 mm/rotation. FIG. 5C shows that, at the advance speed v2, the milling drum moves a distance in the milling direction A corresponding to approximately ¼ s during a rotation, in other words approximately 50 mm/rotation.

[0057] FIG. 6A to 6C show an embodiment in which the milling drum 9 has the same cutting circle diameter d of 1020 mm, but a milling depth h2 of 3 mm is set. The milling drum rotational speed n is once again 100 rpm. The cut length is approximately 101 mm FIG. 6A shows the stationary milling drum. FIG. 6B shows the milling drum moving in the milling direction at an advance speed v1 of 2 m/min, and FIG. 6C shows the milling drum moving in the milling direction at an advance speed v2 of 5 m/min FIG. 6B shows that, at the advance speed v1, the milling drum moves a distance in the milling direction corresponding to approximately ⅕ s during a rotation, in other words approximately 20 mm/rotation. FIG. 6C shows that, at the advance speed v2, the milling drum moves a distance in the milling direction corresponding to approximately ½ s during a rotation, in other words approximately 50 mm/rotation.

[0058] Although the height of the elevations 25 is identical for both embodiments, it can be seen from FIG. 7 that, in relation to the maximum milling depth h.sub.max, the elevations 25 are greater in the second embodiment at the smaller milling depth than in the first embodiment at the greater milling depth.

[0059] The milling drums 9 have a plurality of milling picks 10 which are arranged around the circumference of the milling drum and are axially offset from one another, each milling pick producing a cutting line in a particular time interval. This thus results in a cutting profile characterized by a plurality of cutting lines shifted with respect to one another.

[0060] FIG. 8A shows the cutting profile composed of the individual cutting lines for a faster advance speed v2, and FIG. 8B shows said cutting profile for a slower advance speed v1. Again, a minimum and maximum milling depth h.sub.min, h.sub.max are shown, the minimum milling depth h.sub.min being dependent on the advance speed v and the milling drum rotational speed n. It can clearly be seen that at a faster advance speed v2, the minimum milling depth h.sub.min is smaller than at a slower advance speed v.

[0061] If for example an operating result is desired in which, above a particular level, no more material remains in the milled track, the milling depth has to be corrected in such a way that the minimum milling depth h.sub.min corresponds to the desired milling depth. The actual milling depth hell is thus equal to the minimum milling depth h.sub.min.

[0062] In the following, the control and processing unit of the construction machine according to the invention is described in detail.

[0063] For a constant milling drum rotational speed n, FIG. 9 shows the dependency of the minimum milling depth h.sub.min on the ratio of the advance speed v to the milling drum rotational speed n. At an advance speed of zero, the minimum milling depth h.sub.min corresponds to the maximum milling depth h.sub.max, in other words no elevations 25 or depressions 24 are found since the milling drum has dug into the ground vertically. As the advance speed v increases, the minimum milling depth h.sub.min continuously decreases since the height of the elevations continuously increases.

h.sub.max=h.sub.min+Δ(v)

[0064] The deviation Δ(v) of the minimum milling depth h.sub.min from the maximum milling depth h.sub.max, in other words the magnitude of the difference between the minimum milling depth h.sub.min and the maximum milling depth h.sub.max, is calculated using the following equation:

[00001]$\Delta =\frac{d}{2}-\frac{1}{2}\sqrt{d^2-x^2}$

where x=advance speed v [mm/min]/milling drum rotational speed n [rpm].

[0065] For example, for an advance speed of v=5 m/min and a rotational speed of n=100 rpm, in accordance with the above equation, a milling drum 9 having a cutting circle diameter of d=1020 mm results in a deviation Δ(v) of approximately 0.6 mm.

[0066] FIG. 9 merely shows the dependency of the milling depth h on the advance speed v. However, the milling depth h is also dependent on the milling drum rotational speed n. The minimum milling depth hmin decreases as the milling drum rotational speed n decreases. The milling depth h is in particular dependent on the ratio of the advance speed to the milling drum rotational speed v/n. Doubling the milling drum rotational speed has the same effect on the change in the milling depth as halving the advance speed.

[0067] The milling depth h is also dependent on the particular type of milling drum. Different types of milling drum which have the same cutting circle diameter d may for example differ in the number of milling picks. For example, two milling picks arranged on a line instead of one milling pick have the same effect on the change in milling depth h as halving the advance speed or doubling the milling drum rotational speed.

[0068] In the present embodiment, the deviation Δ(v, n) of the minimum milling depth h.sub.min from the maximum milling depth h.sub.max is the variable which is characteristic of the milling profile. In the present embodiment, this variable is used as a correction value for controlling the milling depth. However, a variable derived from the deviation Δ(v, n) of the minimum milling depth h.sub.min from the maximum milling depth h.sub.max may also be used as the correction variable, for example the deviation Δ(v, n) of a value between the minimum milling depth h.sub.min and maximum milling depth h.sub.max from the maximum milling depth h.sub.max. The value between the minimum milling depth h.sub.min and the maximum milling depth h.sub.max can specify an average milling depth, the desired milling depth corresponding to an average milling depth.

[0069] In an embodiment, the variable which is characteristic of the milling profile may be used as, or as a basis for determining, a correction variable for a determined volume of material removed from the ground. Volume measurements as previously known in the art may be obtained via, e.g., continuously measured values for at least a milling depth of the milling drum and an advance speed of the construction machine. The width of the milling drum may further be treated as an actual milling width for the purposes of determining the volume of material removed, or in an embodiment (also as previously known in the art), the volume measurements may further be obtained via continuously measured values for a profile of a ground surface to be milled in front of the milling drum, wherein the volume measurements account for the surface width potentially being less than the milling drum width. Accordingly, a volume of material removed from the ground may be determined, based on measured values for the milling depth of the milling drum, and/or a distance travelled by the construction machine, and/or a width of the milling drum or a determined actual milling width, and then further corrected in view of the present disclosure by applying the correction variable for the determined volume of material removed from the ground, based on the determined variable which is characteristic of the milling profile.

[0070] The control and processing unit 21 may be a data processing unit, on which a data processing program (software) runs so as to carry out the method steps described below.

[0071] The control and processing unit 21 comprises a memory 26, in which, for different types of milling drum which differ in the cutting circle diameter d and the number and arrangement and design of the milling picks 10, the above-disclosed functional relationship between the deviation Δ(v, n) of the minimum milling depth h.sub.min from the maximum milling depth h.sub.max and the advance speed v and the milling drum rotational speed n or the ratio of the advance speed to the milling drum rotational speed v/n are stored in the form of the coefficients of a mathematical function or in the form of a table of values. The advance speed v and the milling drum rotational speed n are known to the control and processing unit 21 when these values are input into the input unit 22 by the machine driver. However, the advance speed v and/or the milling drum rotational speed n can also be measured continuously. Sensors suitable for this purpose exist in the art.

[0072] During operation of the construction machine, the control and processing unit 21 continuously determines the correction variable Δ(v, n) for a particular milling drum type at a specified or measured advance speed v and milling drum rotational speed n.

[0073] On the basis of the known functional relationship, the correction variable Δ(v, n) can be calculated according to the above equation and/or read from a memory 26 of the control and processing unit 21 as an empirically determined value. This correction variable changes continuously when the advance speed v and/or milling drum rotational speed n change.

[0074] The value of the correction variable or a value derived therefrom can be displayed to the machine driver on the control panel 15 on the display unit 23. The value may also be read from the memory 26 of the control and processing unit 21. Interfaces suitable for this purpose exist in the art.

[0075] The correction to the setting of the milling depth, known as automatic milling depth regulation, is described in the following.

[0076] While the construction machine is stationary, the machine driver lowers the milling drum 9 manually until the tips of the milling pick 10 just touch the surface 16 of the ground. At this moment, the control and processing unit 21 will specify a value of zero for the milling depth. The levelling device is thus calibrated.

[0077] The machine driver can input a value for a milling depth h on the input unit 22. This value is stored in the memory 26 of the control and processing unit 21.

[0078] The control and processing unit 21 reads the value for the milling depth h, specified by the machine driver, from the memory 26 and subsequently lowers the milling drum 9 while the construction machine is stationary until the specified milling depth h is set.

[0079] When the machine driver has set the construction machine in motion, the control and processing unit 21 actuates the drive device 21 in such a way that the construction machine moves in the operating direction A at the predetermined advance speed v, which can also be changed during the advancement, and the milling drum 9 rotates at the specified milling drum rotational speed n, which can also be changed during the advancement.

[0080] The control and processing unit 21 determines a correction value Δ(v, n), in other words the deviation of the minimum milling depth h.sub.min from the maximum milling depth h.sub.max, for each advance speed v or milling drum rotational speed n, in particular for each ratio n/v of the advance speed v to the milling drum rotational speed n, the maximum milling depth h.sub.max being the milling depth specified when the construction machine is stationary. The milling drum is subsequently lowered by the correction value, with respect to the height specified when the machine is stationary, as the construction machine advances.

[0081] When the construction machine sets off, the milling drum is lowered since the advance speed increases as the machine accelerates. When the construction machine is moving at a constant advance speed v, and with a constant milling drum rotational speed, no further correction takes place. By contrast, when the advance speed v and/or the milling drum rotational speed changes, correction takes place continuously. When the construction machine comes to a halt, the milling drum is raised again since the advance speed decreases when the machine is braked, and therefore the correction value by which the milling drum is being lowered also decreases.

[0082] One embodiment provides that the control and processing unit 21 is configured in such a way that the value for the milling depth, which value is corrected using the correction variable, is compared with a specified threshold value, a control signal being generated if the threshold value is exceeded or undershot. The construction machine comprises an alarm unit 27, which is connected to the control and processing unit 21 and may be arranged on the control panel 15. When the alarm unit 27 receives the signal from the control and processing unit 21, it generates an optical and/or acoustic alarm. For example, a threshold value h.sub.limit for the current maximum milling depth h.sub.max resulting after the correction may be specified as the threshold value. A threshold value of this type may for example be specified if material is to be prevented from being removed in a region located below a particular level or if a greater milling depth is not to be adjusted in relation to the advance speed v and/or milling drum rotational speed n.

[0083] The control and processing unit may be configured in such a way that, if a threshold value is exceeded, the milling depth is not corrected. When a threshold value is exceeded, the alarm can prompt the machine driver to intervene in the machine control.

[0084] If in practice it were necessary to lower the milling drum 9 further to correct the milling depth, but a threshold value for a maximum milling depth is not to be exceeded, the alarm indicates to the machine driver that, in order to resolve this conflict, the advance speed v is intended to be reduced and/or the milling drum rotational speed n is intended to be increased. However, the control and processing unit 21 according to the invention may also be formed in such a way that in this situation the advance speed v is reduced and/or the milling drum rotational speed n is increased automatically.

[0085] If the milling tools become worn, the vertical distance between the lowest point of the milled surface and the original terrain surface changes in accordance with the depth of wear of the milling tools. When the milling depth is corrected, the current state of wear of the milling tools may be taken into account. For this purpose, the state of wear of the tools is recorded automatically using a suitable measurement value sensor or is input manually. The control and processing unit is configured in such a way that the wear of the milling tools is taken into account when determining the correction value.