Arrangement And A Method For Controlling A Work Vehicle

Abstract

An arrangement for controlling a work vehicle including a hydraulic system that includes at least one pump and at least one actuator operatively driven by hydraulic fluid delivered from the pump is provided. At least a first pump is a variable displacement pump. The system is of load-sensing type in that the pump displacement is controlled by a pilot pressure representing a load exerted on the system. The arrangement includes an arrangement for reducing the pilot pressure delivered to the first pump so that the first pump displacement is regulated down when there is a need for limiting hydraulic power consumption.

Description

BACKGROUND AND SUMMARY [0001] The present invention relates to an arrangement for controlling a work vehicle comprising a hydraulic system. The hydraulic system comprises at least one pump and at least one actuator operatively driven by hydraulic fluid delivered from said pump, wherein at least a first pump is a variable displacement pump. The system is of load-sensing type in that the pump displacement is controlled by a pilot pressure representing a load exerted on the system. [0002] The pump is normally operatively driven by an internal combustion engine arranged for propelling the work vehicle. [0003] The term work vehicle comprises different types of material handling vehicles like construction machines, such as a wheel loader, a backhoe loader, a motor grader and an excavator. The invention will be described below in a case in which it is applied in a wheel loader. This is to be regarded only as an example of a preferred application. [0004] Said actuator may be a linear actuat...

AI Technical Summary

Benefits of technology

[0006] In order for the work vehicle to function well, the engine, transmission and hydraulic system must be balanced with regard to available power and output power. It is difficult to find an engine that exactly manages the desired power outputs at different engine speeds. The problem with different output power demand is particularly pronounced at low engine speeds. If the driver utilizes the power from the engine at low engine speeds to drive the vehicle's half shafts at the same time as the hydraulic system is activated, then there is a risk that the engine will cut out or that the engine will “stick”, that is it will not be able to increase the engine speed when the driver depresses the accelerator pedal. The driver can, of course, adjust the power consumption via various controls, when he senses a loss of engine speed, but this can be problematical, particularly when the engine suddenly cuts out. Further, even skilled drivers overcompensate and therefore unnecessarily reduce the amount of hydraulic work the hydraulic system is truly capable of performing. As a result, machine productivity is reduced.

[0007] There are known arrangements, which are adapted to relieve the engine load by reducing pump displacement when there is a risk for stalling the engine.

[0012] More specifically, the pump displacement is reduced by pressure control. This arrangement may easily be introduced in a conventional load-sensing system.

[0015] In the case that the hydraulic system comprises at least two variable displacement pumps for delivering hydraulic fluid to said actuator the displacement of a second pump is preferably controlled by a pilot pressure representing the load exerted on the system in a non-manipulated form. Thus, only the input pilot pressure signal to the first pump is manipulated. Existing load-sensing hydraulic systems may easily and cost-efficiently be amended for achieving the limitation of the hydraulic power to relieve engine load in this way.

Problems solved by technology

It is difficult to find an engine that exactly manages the desired power outputs at different engine speeds.

The problem with different output power demand is particularly pronounced at low engine speeds.

If the driver utilizes the power from the engine at low engine speeds to drive the vehicle's half shafts at the same time as the hydraulic system is activated, then there is a risk that the engine will cut out or that the engine will “stick”, that is it will not be able to increase the engine speed when the driver depresses the accelerator pedal.

The driver can, of course, adjust the power consumption via various controls, when he senses a loss of engine speed, but this can be problematical, particularly when the engine suddenly cuts out.

Further, even skilled drivers overcompensate and therefore unnecessarily reduce the amount of hydraulic work the hydraulic system is truly capable of performing.

As a result, machine productivity is reduced.

A disadvantage is that when a higher flow is used for a function, the pump may stick on maximum displacement and cannot increase the pressure to the maximum level.

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