Hydraulic system, working vehicle and method

Abstract

A hydraulic system, working vehicle, and method for producing hydraulic power to a hydraulic system of a working vehicle is provided. The hydraulic system includes a fixed displacement hydraulic pump and a speed and torque controlled electric motor for driving the hydraulic pump. An electric controller is arranged to adjust the speed of the electric motor and to thereby adjust produced hydraulic fluid flow and pressure in the system. Further, there is a bypass flow channel including a throttle element for directing limited continuous discharge fluid flow from the system.

Claims

1. A hydraulic system of a working vehicle comprising: at least one fixed displacement hydraulic pump; at least one speed and torque controlled electric motor arranged for driving the hydraulic pump; at least one hydraulic actuator; at least one electric controller arranged for adjusting a speed of the electric motor thereby adjusting produced hydraulic fluid flow and pressure in the hydraulic system; and at least one by-pass flow channel including at least one throttle element arranged for directing limited continuous discharge fluid flow from the hydraulic system, wherein the throttle element is a pressure compensated element whereby magnitude of the by-pass flow is configured to be adjusted automatically in response to a magnitude of pressure prevailing in the hydraulic system.

2. The hydraulic system as claimed in claim 1, wherein the magnitude of the by-pass flow is dimensioned so that rotation of the hydraulic pump is always at least 30-200 rpm.

3. The hydraulic system as claimed in claim 1, wherein the electric controller is a variable frequency drive serving as an electrical motor control device for controlling torque and rotation speed of the electric motor.

4. The hydraulic system as claimed in claim 1, wherein the electric controller is configured to control the torque and speed of the motor to adapt the speed of the hydraulic pump in accordance with needed fluid flow at requested pressure level.

5. A working vehicle, comprising: a movable carrier; at least one work device mounted on the carrier; and at least one hydraulic system; characterized in that the hydraulic system is in accordance with claim 1.

6. The working vehicle as claimed in claim 5, wherein the working vehicle is a mining vehicle including at least one hydraulically operable mining actuator connected to the hydraulic system.

7. A method of producing hydraulic power to a hydraulic system of a working vehicle, the method comprising: rotating a fixed displacement hydraulic pump by means of a speed and torque controlled electric motor; controlling rotation of the motor by means of an electric controller arranged for adjusting a speed of the hydraulic pump and thereby adjusting a produced hydraulic fluid flow and pressure in the hydraulic system; directing a limited continuous discharge fluid flow via a by-pass flow channel and through a throttle element from an output side of the hydraulic pump to a reservoir, whereby the hydraulic pump is driven continuously, and an output of the hydraulic pump is stabilized; and restricting a magnitude of the by-pass flow by means of the throttle element for limiting hydraulic energy consumption, wherein the magnitude of the by-pass flow is configured to be adjusted automatically in response to a magnitude of pressure prevailing in the hydraulic system.

8. The method as claimed in claim 7, further comprising stabilizing pressure fluctuations in operational situations when pressure is needed for the output of the hydraulic pump and fluid flow is not.

9. The method as claimed in claim 7, further comprising adjusting the magnitude of the by-pass flow by means of the throttle element to correspond to a low speed rotation of the hydraulic pump at 30-200 rpm in situation, where one or more hydraulic actuators connected to the hydraulic system require no fluid flow but require pressure.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Some embodiments are described in more detail in the accompanying drawings, in which

(2) FIG. 1 is a schematic side view of working vehicle provided with a hydraulic system,

(3) FIG. 2 is a schematic diagram showing some possible working vehicles wherein the disclosed solution can be implemented,

(4) FIG. 3 is a schematic view of a hydraulic diagram of the disclosed hydraulic system,

(5) FIG. 4 is a schematic view of an alternative hydraulic diagram of the disclosed hydraulic system,

(6) FIG. 5 is a schematic view of two graphs for illustrating sensed pressures as a function of time, and

(7) FIG. 6 is a schematic view of two graphs for illustrating sensed rotation speeds of a hydraulic pump as a function of time.

(8) For the sake of clarity, the figures show some embodiments of the disclosed solution in a simplified manner. In the figures, like reference numerals identify like elements.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

(9) FIG. 1 discloses a working vehicle 1 which comprises a movable carrier 2 and one or more work devices 3. In this case the working vehicle 1 is a rock drilling rig for drilling drill holes to a rock surface. The rock drilling rig comprises one or more rock drilling units 4 arranged on one or more drilling booms 5. The drilling unit 4 comprises a rock drilling machine 6 which serves as a hydraulic actuator Ha connected to a hydraulic system Hs. There may be also other hydraulic actuators such as a feed device 7 and boom cylinders 8. Other hydraulic actuators on the carrier are also possible, such as breaking actuators. The hydraulic system Hs comprises a hydraulic pump Hp, an electric motor M and an electric controller Ec for controlling the motor M.

(10) FIG. 1 is only an example of the working vehicle 1. FIG. 2 discloses a listing of some possible working vehicles wherein the hydraulic system according to this document can be implemented. As it is disclosed in FIG. 2, the working vehicle may be a loading vehicle, or a haling vehicle used for transporting removed broken rock material in mines. Further, the working machine may be an earthmoving machine or vehicle, such as an excavator, a wheel loader, a bulldozer, or a dumper. The disclosed solution can be utilized also in forest machines, such as in harvesters and forwarders. Different mobile cranes and container handling apparatuses may be provided with the disclosed hydraulic system. One more working apparatus to be mentioned, as an example of the working machine, is a pile-driving machine. All the mentioned working vehicles may have operational situations wherein the hydraulic system is subjected to requests for high fluid pressure with no fluid flow.

(11) FIG. 3 discloses a hydraulic system Hs comprising a fixed displacement hydraulic pump Hp rotatable with a speed and torque controlled electric motor M. The electric motor M is controlled by means of an electric controller Ec. The pump-motor combination generates hydraulic power for powering one or more hydraulic actuators Ha. For simplicity reasons only one hydraulic actuator Ha is presented. Further, there is a by-pass flow channel By comprising at least one throttle element Te for directing limited continuous discharge fluid flow to a reservoir Re.

(12) FIG. 4 differs from the solution of FIG. 3 only in that the throttling element Te is adjustable and that the electric controller Ec is a variable frequency drive Vdf.

(13) FIGS. 5 and 6 show first curves E of a hydraulic system with the disclosed solution, and second curves D of a substantially similar kind of hydraulic system without the by-pass flow system. As can be seen in FIG. 5, there occurs significant pressure fluctuation in the second curve D whereas in the hydraulic system implementing the present solution, the first curve E is stabilized. The stabilizing effect of the disclosed solution can also be seen when comparing curves E and D in FIG. 6 showing the rotation speed of the hydraulic pump. Stabile and controlled rotation of the hydraulic pump is clearly shown by the curve E. In both FIGS. 5 and 6 the curves E are flat or almost flat.

(14) The drawings and the related description are only intended to illustrate the idea of the invention. In its details, the invention may vary within the scope of the claims.