WO2008004915A1

WO2008004915A1 - Method and system for avoiding dropping a load

Info

Publication number: WO2008004915A1
Application number: PCT/SE2006/000822
Authority: WO
Inventors: Joakim SJÖGREN; Jörgen BERGSTEN
Original assignee: Volvo Construction Equipment Ab
Priority date: 2006-07-03
Filing date: 2006-07-03
Publication date: 2008-01-10

Abstract

The invention relates to a method and a system for avoiding dropping a load carried by a load carrier, comprising the steps of detecting an operational parameter which is indicative of a condition of the load, - comparing the detected operational parameter with a predetermined limit value, which is associated to a predefined instability condition of the load carrier, and - preventing dropping the load if the detected operational paramete exceeds the predetermined limit value. The invention also relates to a work machine comprising such a system, a computer program and a computer program product for implementing the method.

Description

Method and system for avoiding dropping a load

TECHNICAL FIELD AND BACKGROUND ART

The present invention relates to a method for avoiding dropping a load carried by a load carrier. The term "load carrier" comprises both mobile and stationary devices. The invention is particularly directed to vehicles, like trucks and mobile machines, like work machines, which are provided with a crane or other type of work implement for carrying a load.

The term "work machine" comprises different types of material handling vehicles like construction machines, such as a wheel loader, a backhoe loader and an articulated hauler. Further terms frequently used for work machines are "earth-moving machinery" and "off- road work machines". The invention will be described below in a case in which it is applied in a frame- steered work machine constituting a wheel loader. This is to be regarded only as an example of a preferred application.

The work machine comprises a load arm unit and a work implement attached to the load arm unit for moving/transporting material. According to one example, the work implement forms a crane.

A wheel loader may be used for transporting heavy loads from one location to another, often encountering a series of turns and varying degree of slopes on the route between two locations . If the load being carried is quite heavy, the weight of a portion of the wheel loader carrying the load may not be adequately offset by an opposite portion of the wheel loader, thus causing an unstable condition. This condition may occur when the wheel loader is at a standstill or during movement. This condition is dependent on the weight and position of the load, the ground condition (slope etc) and speed and/or acceleration of the vehicle. Thus, the stability of a wheel loader may be less than optimal in certain instances, which may cause the wheels of the wheel loader to lift from the ground and providing discomfort to the operator. In extreme conditions, the wheel loader can tip over.

The operation of the load is normally controlled via a hydraulic system. An operator manouevrable means (a lever or joystick) is adapted to control movement of the load via hydraulic actuators (cylinders) . As a safety measure for the operator/machine, it is known to arrange an overflow valve in a hydraulic line connected to the hydraulic actuator. In a situation where the hydraulic pressure in the line exceeds a preset value, the overflow valve is automatically opened, which leads to that the crane is dropped (with the load) wherein the machine is prevented from entering the instability condition. However, the dropping of the load may lead to material damage when the load hits the ground, or even worse, personal injury.

DISCLOSURE OF INVENTION

A first object of the invention is to achieve a method which improves the safety during operation of the load carrier.

This object is achieved in the method disclosed in claim 1. Thus, it is achieved by the steps of detecting an operational parameter which is indicative of a condition of the load,

- comparing the detected operational parameter with a predetermined limit value, which is associated to a predefined instability condition of the load carrier, and preventing dropping the load if the detected operational parameter exceeds the predetermined limit value .

The condition of the load may indicate a position of the load relative to the load carrier body and/or a weigth of the load and/or a velocity and/or acceleration of the load and/or the load carrier.

The predetermined limit value may correspond to the limit at which the previously known overflow valve is automatically opened.

According to a preferred embodiment, the method comprises the step of preventing or dampening movement of the load and/or the load carrier in such a manner that the load carrier does not end up in the instability condition.

Thus, instead of allowing the load to end up in a condition, in which the load carrier is unstable, the movement of the load may be actively prevented when the detected operational parameter exceeds the predetermined limit value. Thus, movement of the load relative to the load carrier may be prevented. Further, in case the load carrier constitutes a mobile unit, like a work machine, acceleration of the work machine itself may lead to the instability condition. Therefore, the movement of the load carrier itself may be braked or at least further acceleration may be prevented.

According to a further development of the preferred embodiment above, an operator manouevrable means is adapted to control movement of the load, wherein the method comprises the step of disconnecting the load from being controlled via the operator manouevrable means when the operator manouevrable means is moved in a manner which would cause the instability condition and connecting the load to being controlled via the operator manouevrable means when the operator manouevrable means is moved in a manner associated to a safe condition.

At least one operational parameter indicative of a condition of the load is detected. According to a preferred embodiment, the detected operational parameter comprises a hydraulic pressure associated to a hydraulically controlled actuator, which controls movement of the load.

A second object of the invention is to achieve a load carrier safety system which improves safety during operation of the load carrier.

This object is achieved in the system disclosed in claim 10. Thus, it is achieved by a system comprising

- means for detecting an operational parameter which is indicative of a state of the load, means for comparing the detected operational parameter with a predetermined limit value, which is associated to the instability condition, and

- means for preventing dropping of the load if the detected operational parameter exceeds the predetermined limit value.

Other advantageous embodiments of the invention and its associated advantages are apparent from the other patent claims and from the following description.

BRIEF DESCRIPTION OF DRAWINGS The invention will be described in greater detail in the following, with reference to the embodiments shown in the attached drawings, in which FIG 1 schematically shows a wheel loader equipped with a crane in a side view, FIG 2 schematically shows a first embodiment of a safety system for the wheel loader, FIG 3 schematically shows a second embodiment of a safety system for the wheel loader,

FIG 4 is a flow chart for the method according to a first example.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a wheel loader 101. The body of the wheel loader 101 comprises a front body section 102 with a front frame, and a rear body section 103 with a rear frame. A rear axle 112 forms a pendulum axle allowing the right and left wheel to move vertically relative to one another. A forward axle 113 is rigidly connected to the forward frame. The rear body section 103 comprises a cab 114. The body sections 102,103 are connected to each other via an articulation joint in such a way that they can pivot in relation to each other around a vertical axis . The pivoting motion is achieved by means of two first actuators in the form of hydraulic cylinders 104,105 arranged between the two sections. Thus, the wheel loader is an articulated work vehicle. The hydraulic cylinders 104,105 are thus arranged one on each side of a horizontal centerline of the vehicle in a vehicle traveling direction in order to turn the wheel loader 101.

The wheel loader 101 comprises an equipment 106 for handling objects or material. The equipment 106 comprises a load-arm unit 107, or boom, and an implement 111 in the form of a crane fitted on the load-arm unit. A first end of the load-arm unit 107 is pivotally connected to the front vehicle section 102. The crane 111 is pivotally connected to a second end of the load-arm unit 107. The load-arm unit 107 can be raised and lowered relative to the front section 102 of the vehicle by means of two second actuators in the form of two hydraulic cylinders 108,109, each of which is connected at one end to the front vehicle section 102 and at the other end to the load-arm unit 106. The crane 111 can be tilted relative to the load-arm unit 107 by means of a third actuator in the form of a hydraulic cylinder 110, which is connected at one end to the front vehicle section 102 and at the other end to the crane 111 via a link mechanism.

Figure 2 schematically shows a safety system 201 for the wheel loader 101. The safety system comprises a hydraulic system 203. The hydraulic system 203 comprises a pump 205 which is adapted to draw hydraulic fluid from a container 207 and supply the lift cylinders 104,105 and the tilt cylinder 110 with hydraulic fluid via lines 209,211. The pump 205 is a variable displacement pump and is driven by a power source 213. The power source 213 is in this case formed by the internal combustion engine for propelling the wheel loader 101.

Further, the hydraulic system 203 comprises an electrically controlled valve 215 arranged on the line 209 in order to control the supply of hydraulic fluid to the tilt cylinder 110. Similarly, an electrically controlled valve 217 is arranged on the line 211 in order to control the supply of hydraulic fluid to the lift cylinders 104,105.

The safety system 201 comprises at least one operator manouevrable means 219,221, which is adapted to control movement of the load. More specifically, a first manually operated lever 219 is arranged for controlling the lift cylinders 104,105 and a second manually operated lever 221 is arranged for controlling the tilt cylinder 110. The two control levers 219,221 are electrically connected to a controller, an Electronic Control Unit (ECU) , 223. The controller 223 is electrically connected to the lift control valve 217 and the tilt control valve 215.

An overflow valve unit 225 is arranged in a hydraulic line 227 connected to the tilt cylinder 110. In a situation where the hydraulic pressure in the line 227 exceeds a preset value, the overflow valve is automatically opened. Similarly, an overflow valve unit 229 is arranged in a hydraulic line 231 connected to the lift cylinders 104,105.

The safety system 201 further comprises a means 233 for detecting an operational parameter which is indicative of a state of the load. More specifically, said detection means 233 constitutes a pressure sensor adapted to sense a hydraulic pressure associated to one of the hydraulically controlled cylinders 104,105,110, which controls movement of the load. More specifically, the pressure sensor 233 is adapted to sense the pressure in the line 227 connected to the tilt cylinder 110.

The controller 223 comprises storage means which comprises a predetermined pressure limit value, which is associated to an instability condition. The controller 223 further comprises means for comparing the detected pressure with the predetermined limit value. The comparison means is formed by software program segments in the controller.

The safety system further comprises means 215 for preventing dropping of the load if the detected operational parameter exceeds the predetermined pressure limit value. The dropping prevention means 215 is formed by the tilt control valve 215 according to the first embodiment. The tilt control valve 215 is adapted to prevent further movement of the load in such a manner that the wheel loader 101 does not end up in the instability condition if the detected pressure exceeds the predetermined pressure limit value. Thus, the controller 223 is adapted to disconnect the tilt control lever 221 from controlling the tilt cylinder 110 when the predetermined pressure limit value is reached.

Preferably, the controller 223 is adapted to disconnect the load from being controlled via the tilt control lever 221 when the tilt control lever 221 is moved in a manner which would cause the instability condition and connect the load to being controlled via the tilt control lever 221 when the tilt control lever 221 is moved in a manner associated to a safe condition.

A second embodiment of the invention is schematically shown in figure 3. A tilt control lever 321 is adapted to directly control a tilt control valve 315 via- hydraulic signals. A pressure sensor 333 is adapted to sense the pressure in a line 327 connected to the tilt cylinder 110 (not shown) . A controller 323 is connected to the pressure sensor 333. An electronically controlled switch 351 is arranged in a hydraulic line between the tilt control lever 321 and the tilt control valve 315. The switch 351 is adapted to connect and disconnect, respectively, the connection between the tilt lever 321 and the tilt control valve 315. The controller 323 is operatively connected to the switch 351 in order to control it between an open and a closed position. Thus, the switch 351 forms a means for preventing dropping of the load if the detected pressure exceeds the predetermined pressure limit value.

Figure 4 illustrates a flowchart of the logic of the present invention. The logic starts at a start block 401. The controller 223 then proceeds to the read block 403, in which it reads an operational parameter which is indicative of a condition of the load. According to the first embodiment, the operational parameter is a detected hydraulic pressure associated to the tilt cylinder 110. In a comparison block 405, the controller compares the detected operational parameter with a predetermined limit value, which is associated to a predefined instability condition of the load carrier. If the detected operational parameter is less than the predetermined limit value, the controller returns to the start block 401. If the detected operational parameter is greater than or equal to the predetermined limit value, the controller sends an output signal to a prevention means 215,351 in a block 407 in order to prevent dropping the load. Thus, the prevention means 215 disconnects the connection between the tilt control lever 221 and the tilt cylinder 110.

The controller 223 comprises a memory, which in turn comprises a computer program with computer program segments, or a program code, for implementing the control method when the program is run. This computer program can be transmitted to the controller in various ways via a transmission signal, for example by downloading from another computer, via wire and/or wirelessly, or by installation in a memory circuit. In particular, the transmission signal can be transmitted via the Internet.

The invention also relates to a computer program product comprising computer program segments stored on a computer-readable means for implementing the measurement _

method when the program is run. The computer program product can consist of, for example, a diskette or a CD.

The invention is not to be considered to be limited to the embodiments described above, a number of additional variants and modifications being possible within the framework of the following patents claims .

According to an alternative or complement to the embodiments described above, an active warning system may be used, wherein the operator is warned before the work machine ends up in the unstable condition. Such a warning system may comprise light and/or sound signals in the operator cab.

According to an alternative to a crane, the work implement may be formed by a bucket or other material handling device.

According to an alternative or complement to using a detected pressure as the operational parameter, other operational parameters, like work machine velocity, work machine acceleration, work implement direction, work implement speed, and work implement acceleration may be used.

Claims

1. A method for avoiding dropping a load carried by a load carrier, comprising the steps of detecting an operational parameter which is indicative of a condition of the load,

- comparing the detected operational parameter with a predetermined limit value, which is associated to a predefined instability condition of the load carrier, and - preventing dropping the load if the detected operational parameter exceeds the predetermined limit value.

2. A method as claimed in claim 1, comprising the step of preventing or dampening movement of the load and/or the load carrier in such a manner that the load carrier does not end up in the instability condition if the detected operational parameter exceeds the predetermined limit value.

3. A method as claimed in claim 1 or 2 , wherein an operator manouevrable means is adapted to control movement of the load, comprising the step of preventing operation of the operator manouevrable means to cause that the load carrier ends up in the instability condition.

4. A method as claimed in claim 3, comprising the step of disconnecting the load from being controlled via the operator manouevrable means when the operator manouevrable means is moved in a manner which would cause the instability condition and connecting the load to being controlled via the operator manouevrable means when the operator manouevrable means is moved in a manner associated to a safe condition.

5. A method as claimed in any of claims 1-4, wherein the detected operational parameter is a hydraulic pressure associated to a hydraulically controlled actuator, which controls movement of the load.

6. A method as claimed in any preceding claim, wherein the load carrier comprises a moveably arranged crane, which carries the load.

7. A method according to claim 4 or 5 and 6 , wherein the hydraulically controlled actuator is adapted for tilting at least part of the crane.

8. A method as claimed in any preceding claim, wherein the load carrier constitutes a mobile unit.

9. A method as claimed in any preceding claim, wherein the load carrier constitutes a work machine.

10. A load carrier safety system for avoiding dropping a load, comprising - means (233,333) for detecting an operational parameter which is indicative of a state of the load, means (223,323) for comparing the detected operational parameter with a predetermined limit value, which is associated to the instability condition, and - means (215,351) for preventing dropping of the load if the detected operational parameter exceeds the predetermined limit value.

11. A load carrier safety system as claimed in claim 10, wherein the prevention means (215,351) is adapted to prevent or damp movement of the load and/or the load carrier in such a manner that the load carrier does not end up in the instability condition if the detected operational parameter exceeds the predetermined limit value.

12. A load carrier safety system as claimed in claim 11, wherein the system comprises an operator manouevrable means (221,321) adapted to control movement of the load, wherein the prevention means (215,351) is adapted to prevent operation of the operator manouevrable means to cause that the load carrier ends up in the instability condition.

13. A load carrier safety system as claimed in claim

12, wherein the system comprises means (215,351) adapted to disconnect the load from being controlled via the operator manouevrable means (221,321) when the operator manouevrable means is moved in a manner which would cause the instability condition and connect the load to being controlled via the operator manouevrable means when the operator manouevrable means is moved in a manner associated to a safe condition.

14. A load carrier safety system as claimed in any of claims 10-13, wherein the operational parameter detection means is a pressure sensor (233,333) adapted to sense a hydraulic pressure associated to a hydraulically controlled actuator, which controls movement of the load.

15. A load carrier safety system as claimed in any of claims 10-14, wherein the system comprises a moveable crane (111) , which carries the load.

16. A load carrier safety system as claimed in claims 13 or 14 and 15, wherein the hydraulically controlled actuator (110) is adapted for tilting at least part of the crane.

17. A work machine (101) comprising the safety system of any of claims 10-16.

18. A work machine according to claim 17 comprising a forward frame, a rear frame and an articulation joint connecting the forward frame to the rear frame, which allows pivoting about a vertical axis for steering the machine .

19. A work machine according to claim 17 or 18, wherein the work machine constitutes a wheel loader.

20. A computer program comprising computer program segments for implementing the method as claimed in any one of claims 1-9 when the program is run on a computer .

21. A computer program product comprising computer program segments stored on a computer-readable means for implementing the method as claimed in any one of claims 1-9 when the program is run on a computer.