EP1757739A2 - Overload warning device for excavators - Google Patents

Abstract

The overload warning device measures the supporting forces (F1-F4) at the supporting points, places them in increasing order and determines the stability of the support from the ratio of the sum of the forces summed in one direction to the sum of the forces summed in the opposite direction.

Description

The invention relates to an overload warning device for excavators, preferably hydraulic excavators or material handling equipment, according to the preamble of claim 1.

Overload warning devices should give the driver necessary information regarding a possible overload of the device. In hydraulic excavators, which can be used in the construction sector as well as a handling device in the industrial sector, the overload warning devices are primarily used as a safety instrument to prevent tipping over of the device.

• In einer ersten Variante wird der Hydraulikdruck im Hubzylinder gemessen. Wenn der Bagger arbeitet wird stets der Hydraulikdruck im Hubzylinder überwacht. Anhand einer im Vorfeld über die Konfiguration des Gerätes durchgeführten Nutzlastberechnung ist als Referenzwert der niedrigste Hydraulikzylinderdruck ermittelt, bei dem das Gerät in jedem Fall noch sicher steht. Dieser berechnete Druck wird werkseitig mit einem Druckschalter eingestellt. Überschreitet nun der Druck im Hubzylinder während der Lasthebearbeiten den eingestellten Wert, wird der Fahrer durch ein entsprechendes Alarmsignal gewarnt.
• In einer zweiten Variante wird der Hydraulikdruck im Hubzylinder und gleichzeitig die Auslegerposition gemessen. Hier wird also wie bereits zuvor geschildert während des Arbeitens der Hydraulikdruck im Hubzylinder überwacht. Zusätzlich wird jedoch die Stellung des Auslegers entweder über den Winkel oder über die Zylinderposition berücksichtigt. Für die Auslegerkinematik der vorhandenen Konfiguration wird im Vorfeld eine Nutzlastberechnung durchgeführt, bei der für jede Auslegerposition der niedrigste Hubzylinderdruck berechnet wird. Anhand dieser Daten und der Kennlinie des Druckschalters wird eine Kurvenscheibe konstruiert, die sich synchron mit dem Ausleger dreht und für jede Auslegerposition den korrekten Druck am Druckschalter einstellt. Überschreitet der Hubzylinderdruck während der Lasthebearbeiten den eingestellten Wert, wird der Fahrer durch ein Alarmsignal gewarnt.

Overload warning devices in various designs are already known. The following two variants are used:

• In a first variant, the hydraulic pressure in the lifting cylinder is measured. When the excavator is working, the hydraulic pressure in the lifting cylinder is always monitored. Based on a payload calculation carried out in advance via the configuration of the device, the lowest hydraulic cylinder pressure is determined as the reference value in any case, the device is still safe. This calculated pressure is factory set with a pressure switch. If the pressure in the lifting cylinder now exceeds the set value during the lifting operations, the driver is warned by a corresponding alarm signal.
• In a second variant, the hydraulic pressure in the lifting cylinder and at the same time the boom position is measured. Here, as already described above, the hydraulic pressure in the lifting cylinder is monitored during operation. In addition, however, the position of the boom is considered either over the angle or over the cylinder position. For the boom kinematics of the existing configuration, a payload calculation is performed in advance, which calculates the lowest lift cylinder pressure for each boom position. Based on this data and the characteristic curve of the pressure switch, a cam is designed that rotates synchronously with the boom and adjusts the correct pressure at the pressure switch for each boom position. If the lifting cylinder pressure exceeds the set value during lifting operations, the driver is warned by an alarm signal.

Combinations of the two measuring methods are also used. For example, in the unsupported state of an excavator, that is, when working on the tire, the first variant is used, while for the supported state, the second variant is used (or vice versa).

In the previously described overload warning devices, however, there are some problems in practice.

Thus, in the event that the equipment position is not taken into account, the deviation between the calculated tipping load and the actually absorbable tipping load may be up to 40%. If the cantilever angle is included and the least favorable condition is taken into account for the remaining equipment components, the deviation between the calculated tipping load and the actually absorbable tipping load can still be up to 20%.

If you now want to determine the equipment position exactly, then the position must be determined for each equipment component, for example via an angle sensor. This in turn is complicated and expensive.

If the device configuration is not known or has been changed, the overload warning device will no longer work correctly, as the calculation with the wrong configuration will then draw a false conclusion about the stability from the measured data.

The calculation of the load condition can only be determined exactly for the case that the unit is level. When tilted in the longitudinal and / or transverse direction, however, reduces the stationary torque of the machine. In this case, the overload warning device issues the warning signal too late.

Based on the aforementioned problem with known overload warning devices has the task of developing a generic overload warning device such that an overload condition can be determined immediately and accurately and displayed.

According to the invention, this object is achieved by an overload warning device having the features of claim 1.

Accordingly, the four uprising forces are determined at the usually four support points of the excavator, that is, the support or the wheel loads of the excavator are measured because of these loads, the stability of the excavator can be read directly. For this purpose, according to the invention, the contact forces at the four support points are brought down in an order decreasing in their absolute value, so that F ₁ > F ₂ > F ₃ >...> F _n . These values are used to determine the stability according to the following formula: $$S=\frac{{\displaystyle \underset{i=3}{\overset{n}{\Sigma }}{F}_i}}{{\displaystyle \underset{i=1}{\overset{n}{\Sigma }}{F}_i}}\ge S_{\min }$$

For n = 4 uprising points: $$S=\frac{F_3+F_4}{F_1+F_2+F_3+F_4}\ge S_{\min }$$

In the aforementioned rule, it is therefore assumed that in the event that the sum of the two smaller contact forces, based on the sum of the total contact forces, falls below a predetermined amount, the device tends to tip over.

This minimum stability value S _min is usually determined by standards. For example, the standard ISO 10567 applies to hydraulic excavators in the construction and transhipment sector. Here, the rated load is defined at 75% of the static tipping load, which leads to a minimum stability S _min of 25%. Therefore, the preferable value for S _min = 0.25.

Thus, if the corresponding measured value of the contact forces exceeds the value S _min , a corresponding warning signal is output to the excavator operator. Optionally, it can be acted directly on the control of the excavator to prevent it from falling over.

Advantageously, the stability can be determined exactly at any time and for any position with the overload warning device according to the invention. It suffices here to measure the uprising forces of the excavator. For the calculation of stability, no further information is needed. Also, no angles of equipment or uppercarriage position need to be measured. It does not require any preliminary calculations for different device configurations. The Creating and managing trend curves for different configurations is no longer necessary. In contrast to the overload warning device in the prior art, no adjustments on the excavator must be made. Changes to the device configuration itself have no effect on the accuracy of the stability calculation. An inclination of the device, that is a slope in the longitudinal and / or transverse direction, is also taken into account in the stability analysis.

Particular advantages of the invention will become apparent from the subsequent claims to the main claim.

After a first particularly advantageous embodiment of the invention, the contact forces can be measured on the cylinder pressures of the support cylinder of the support. For this purpose, pressure sensors are advantageously attached to each cylinder on the piston side. Based on the known piston surface and the support kinematics, the four support forces can then be calculated. However, it is important to ensure that the cylinders are not allowed to be fully extended to the stop, because then the piston-side pressure alone does not provide sufficient information about the supporting force. In this case, the pressures on the piston and rod side would have to be measured and the resulting forces subtracted from each other.

The measurement of the cylinder pressures in the final cylinders can determine the stability only for the supported state of the device. However, this is already sufficient in most cases, especially in application areas where lifting or lifting work is carried out predominantly or only in the supported state. For the unsupported state of these devices, the first variant of the overload warning device already discussed in the prior art could additionally be used.

Another preferred embodiment of the invention causes the support forces Kraftmeßbolzen or load cells on the support rockers of the respective Supporting device can be determined. This embodiment of the invention has the advantage that the supporting forces are measured directly and do not have to be converted over the support kinematics. The corresponding Kraftmeßbolzen and load cells must be protected against dirt and damage.

Another alternative is that Kraftmeßbolzen be attached to the respective Einolzpunkt of the support cylinder to the undercarriage. This results in a particularly simple cabling and the risk of contamination is largely eliminated. However, in contrast to the previously discussed preferred embodiment, the forces have to be converted again via the support kinematics. About the aforementioned embodiment of the invention, only the support forces can be determined, but not the wheel loads.

However, a further preferred embodiment of the invention lies in determining the wheel loads via strain gauges. For this purpose, strain gauges are to be attached to the axles at a suitable point, and the wheel loads can then be determined via the deflection of the axles. The strain gauges must be protected accordingly from damage here. This measurement methodology requires a prior calibration.

Further features, details and advantages of the invention will become apparent from the embodiment illustrated in the drawing. Figures 1 and 2 respectively show hydraulic excavators according to the present invention.

FIG. 1 shows a hydraulic excavator 10 of conventional configuration, on the undercarriage 12 of which hydraulically extendable support feet 14 are arranged. So here is a corresponding four-point support realized. FIG. 1 shows the contact forces F1, F2, F3 and F4 on the respective support feet 14.

FIG. 2 corresponds to that according to FIG. 1. In the case of the hydraulic excavator 10, however, in contrast to FIG. 1, the corresponding contact forces F1, F2, F3 are present and F4 drawn on the wheels. These are to be considered when the excavator 10 is not supported by the four-point support.

Claims (9)

Overload warning device for excavators, preferably hydraulic excavators or material handling equipment, with three or more pick-up points,
characterized,
that the uprising forces are determined at the Aufstandpunkte that they are brought in a decreasing order by their amount, so that applies F ₁ > F ₂ > F ₃ >...> F _n and that the stability is determined according to the following formula: $$S=\frac{{\displaystyle \underset{i=3}{\overset{n}{\Sigma }}{F}_i}}{{\displaystyle \underset{i=1}{\overset{n}{\Sigma }}{F}_i}}\ge S_{\min }$$

Overload warning device according to claim 1, characterized in that S _{min has} a value of 0.25. Overload warning device according to claim 1 or 2, characterized in that the contact forces are measured via the cylinder pressures of the support cylinders. Overload warning device according to claim 3, characterized in that a pressure sensor is attached to each support cylinder on the piston side and / or rod side. Overload warning device according to claim 1 or 2, characterized in that the contact forces are measured by means of force measuring bolts or load cells on the support rockers of the support. Overload warning device according to claim 1 or 2, characterized in that the contact forces are measured via Kraftmeßbolzen in the points of engagement of the support cylinder on the undercarriage. Overload warning device according to claim 1 or 2, characterized in that the contact forces are determined by measuring the wheel loads. Overload warning device according to claim 7, characterized in that the measurement of the wheel loads takes place via strain gauges. Hydraulic excavator with an overload warning device according to one of claims 1 to 8.

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