Hydraulic system, work vehicle and method

Abstract

A hydraulic system, a work vehicle, and a method for generating hydraulic power to a hydraulic system of a work vehicle. The hydraulic system (Hs) includes a fixed displacement hydraulic pump (Hp) and a speed and torque controlled electric motor (M) for driving the hydraulic pump (Hp). An electric controller (Ec) is configured to regulate the speed of the electric motor, thereby regulating the flow and pressure of generated hydraulic fluid in the system. Additionally, there is a bypass flow path (By) with a throttle element (Te) for directing a limited continuous discharge fluid flow from the system.

Description

[Background technology]

[0001] The present invention relates to a hydraulic system for a work vehicle. The hydraulic system includes a fixed displacement pump and a speed and torque controlled electric motor for generating hydraulic power. The electric motor is controlled by an electric controller.

[0002] The present invention further relates to a work vehicle and a method of generating hydraulic power to a hydraulic system of a work vehicle.

[0003] The field of the invention is more particularly defined in the preambles of the independent claims.

[0004] At different work sites, different work vehicles are used to perform work tasks. The work vehicles may be equipped with hydraulic actuators connected to the vehicle's hydraulic system. In modern hydraulic systems, there may be a fixed displacement hydraulic pump driven by a speed and torque controlled electric motor to generate the required hydraulic power. These types of systems have several advantages. However, known solutions have shown to have several drawbacks, especially in special situations where pressure is needed without the demand for fluid flow. Summary of the Invention

[0005] It is an object of the present invention to provide a new and improved hydraulic system, a work vehicle equipped with such a hydraulic system, and a method for generating hydraulic power to a hydraulic system of a work vehicle.

[0006] The hydraulic system according to the invention is characterised by the characterising features of the first independent device claim.

[0007] The work vehicle according to the invention is characterised by the characterising features of the second independent device claim.

[0008] The method according to the invention is characterized by the characterizing features of the independent method claim.

[0009] The disclosed solution concept is that the hydraulic system of the work vehicle comprises one or more fixed displacement hydraulic pumps powered by one or more speed and torque controlled electric motors controlled by one or more electric controllers for regulating the speed of the electric motors and thereby the flow and pressure of the generated hydraulic fluid in the hydraulic system. Additionally, the hydraulic system comprises one or more bypass flow paths with one or more throttling elements for directing a limited continuous discharge fluid flow from the hydraulic system.

[0010] In other words, the hydraulic system includes a throttling element disposed in parallel with the hydraulic pump so that there is a small hydraulic leakage flow from within the hydraulic system to a hydraulic reservoir or tank. The purpose of the throttling element is to keep the magnitude of the flow in the bypass flow path low so that the bypass flow does not increase energy consumption.

[0011] The advantage of the disclosed solution is that due to the bypass flow, the pump-motor arrangement or hydraulic power unit can be driven continuously, which makes the pressure output of the hydraulic pump stable. Thus, fluctuations in the hydraulic output can be avoided, and the control of the hydraulic system can be smoothed and improved.

[0012] In general, the advantage of the disclosed configuration with a fixed displacement pump and a speed and torque controlled electric motor is that the hydraulic system pressure can be controlled quickly and accurately by the electric controller. The system can keep the system pressure precisely at a controlled value and can quickly and automatically adapt to different required flows of the system by speed adaptation of the motor and pump. The flow supplied to the system is always as required. In this case, the system becomes energy efficient and provides accurate pressure control. However, the internal structure of the fixed displacement pump has a slight leakage, and when the pump is driven in a special situation for a "closed system" (pressure>0 bar and flow rate=0), the slight internal leakage may cause the pump to rotate a little periodically to compensate for the leakage. Since the internal leakage is negligible, the hydraulic pump does not rotate continuously, causing a non-smooth drive and pressure fluctuations of the system pressure. The disclosed bypass flow path and the continuous bypass flow through it provide a smooth drive to the system.

[0013] According to one embodiment, the magnitude of the bypass flow is determined such that the rotation of the hydraulic pump is always at least 30-200 rpm. In other words, the magnitude of the bypass flow is determined to be small by the throttling element, so that the associated power and energy consumption due to the constant rotation caused by the pump-motor arrangement does not occur. In the solution, the slow rotation of the motor and pump is implemented in situations where no fluid flow is required in the system, but there is a pressure demand for the electric controller. The magnitude of the rotation speed may depend, for example, on the power output rating of the hydraulic pump.

[0014] According to one embodiment, the disclosed bypass arrangement is adapted to generate a low rotation speed of the pump of 150 rpm when no fluid flow demand is generated within the electrical controller, in which case the motor's idling power consumption can be low, for example 250-300 W.

[0015] According to one embodiment, the throttle element is an adjustable element, whereby the magnitude of the bypass flow is adjustable. An advantage of the disclosed embodiment is that the bypass flow and the subsequent continuous rotation of the pump can be adjusted on a case-by-case basis to suit different use cases and operating conditions.

[0016] According to one embodiment, the throttling element may be a valve or orifice with an adjustable through opening for fluid flow therethrough.

[0017] According to one embodiment, the throttle element is a pressure compensation element, whereby the magnitude of the bypass flow is configured to be automatically adjusted in response to the magnitude of the pressure prevailing in the hydraulic system. In other words, the bypass flow system can adapt to different output pressure situations, whereby the output of the pump can be kept stable in different operating conditions. The advantage of this solution is that the pressure compensation throttle element can take care that the bypass flow remains low even at high pressures, thereby ensuring good energy efficiency.

[0018] According to one embodiment, the electric controller is a variable frequency drive that serves as an electric motor control device for controlling the torque and rotational speed of the electric motor. In other words, the disclosed solution aims to stabilize the pressure in an inverter-controlled hydraulic system.

[0019] According to one embodiment, the electrical controller is configured to control the torque and speed of the motor to adapt the speed of the hydraulic pump according to the required fluid flow at the requested pressure level.

[0020] According to one embodiment, the disclosed solution relates to a work vehicle comprising a movable carrier, one or more work devices mounted on the carrier, and at least one hydraulic system, the hydraulic system being in accordance with the features and embodiments disclosed herein.

[0021] According to one embodiment, the work vehicle is a mining vehicle comprising at least one hydraulically operated mining actuator connected to a hydraulic system.

[0022] According to one embodiment, the mining vehicle mentioned above is a rock drilling rig, a loading vehicle or a haul vehicle.

[0023] According to one embodiment, the work vehicle is alternatively a forestry machine, a civil engineering machine, or a mobile crane.

[0024] According to one embodiment, the carrier of the work vehicle is equipped with a brake system comprising spring-loaded brakes that can be opened by a hydraulic brake actuator. The brakes are therefore of the normally-on type. The disclosed solution is implemented to power the hydraulic brake actuator while keeping the brakes off during transport drives. In this case, high pressure is required for the brake actuator without the need for fluid flow, since the normally operating actuator is not operable during transport drives.

[0025] According to one embodiment, the disclosed solution relates to a method for generating hydraulic power to a hydraulic system of a work vehicle, the method comprising rotating a fixed displacement hydraulic pump by a speed and torque controlled electric motor and controlling the rotation of the motor by an electric controller for regulating the speed of the hydraulic pump and thereby the flow and pressure of generated hydraulic fluid in the hydraulic system, the method further comprising directing a restricted continuous discharge fluid flow from the output side of the hydraulic pump to a reservoir via a bypass flow path and through a throttling element, whereby the hydraulic pump is continuously driven and the output of the hydraulic pump is stabilized.

[0026] According to one embodiment, a method includes stabilizing pressure fluctuations during operating conditions where pressure is required for the output of a hydraulic pump and fluid flow is not.

[0027] According to one embodiment, the method includes limiting the magnitude of the bypass flow with a throttling element to limit hydraulic energy consumption.

[0028] According to one embodiment, the method includes adjusting a magnitude of bypass flow by a throttling element to accommodate a low rotation speed of the hydraulic pump, between 30 and 200 rpm, in situations where one or more hydraulic actuators connected to the hydraulic system do not require fluid flow but do require pressure.

[0029] The above disclosed embodiments may be combined to form suitable solutions having the above mentioned characteristic solutions required.

[0030] Some embodiments are explained in more detail in the accompanying drawings. [Brief description of the drawings]

[0031] [Figure 1] 1 is a schematic side view of a work vehicle equipped with a hydraulic system. [Diagram 2] 1 is a schematic diagram showing some possible work vehicles in which the disclosed solution can be implemented; [Diagram 3] FIG. 1 is a schematic diagram of a hydraulic diagram of the disclosed hydraulic system. [Figure 4] FIG. 2 is a schematic diagram of an alternative hydraulic diagram of the disclosed hydraulic system. [Diagram 5] FIG. 2 is a schematic diagram of two graphs to show sensed pressure as a function of time. [Figure 6] FIG. 2 is a schematic diagram of two graphs to illustrate the sensed rotational speed of a hydraulic pump as a function of time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] For clarity, the figures show in a simplified manner some embodiments of the disclosed solutions, in which like reference numbers indicate like elements.

[0033] FIG. 1 discloses a work vehicle 1 comprising a mobile carrier 2 and one or more work devices 3. In this case, the work vehicle 1 is a rock drilling rig for drilling holes in a rock surface. The rock drilling rig comprises one or more rock drilling units 4 arranged on one or more drilling booms 5. The rock drilling units 4 comprise a rock drill 6 acting as a hydraulic actuator Ha connected to a hydraulic system Hs. There can also be other hydraulic actuators, such as a feed device 7 and a boom cylinder 8. Other hydraulic actuators on the carrier are also possible, such as a crushing actuator. The hydraulic system Hs comprises a hydraulic pump Hp, an electric motor M and an electric controller Ec for controlling the motor M.

[0034] FIG. 1 is only one example of a work vehicle 1. FIG. 2 discloses a list of some possible work vehicles in which the hydraulic system according to the present disclosure can be implemented. As disclosed in FIG. 2, the work vehicle can be a loading vehicle or a transport vehicle used to transport the removed and crushed rock material in a mine. Furthermore, the work machine can be an earth moving machine or vehicle, such as an excavator, a wheel loader, a bulldozer, or a dump truck. The disclosed solution can also be utilized in forestry machines, such as in harvesters and forwarders. Different mobile cranes and container handling devices can be equipped with the disclosed hydraulic system. Another work device mentioned as an example of a work machine is a pile driver. All the above mentioned work vehicles can have operating situations in which the hydraulic system is subject to high fluid pressure demands without fluid flow.

[0035] 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 an electric controller Ec. The pump-motor combination generates hydraulic power for powering one or more hydraulic actuators Ha. For simplicity, only one hydraulic actuator Ha is presented. In addition, there is a bypass flow path By with at least one throttle element Te for directing a restricted continuous discharge fluid flow to a reservoir Re.

[0036] FIG. 4 differs from the solution of FIG. 3 only in that the throttle element Te is adjustable and the electrical controller Ec is a variable frequency drive Vdf.

[0037] Figures 5 and 6 show a first curve E of a hydraulic system with the disclosed solution and a second curve D of a substantially similar type of hydraulic system without a bypass flow system. As can be seen in Figure 5, the second curve D exhibits significant pressure fluctuations, whereas in a 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 curve E with curve D in Figure 6, which shows the rotational speed of the hydraulic pump. The stable and controlled rotation of the hydraulic pump is clearly shown by curve E. In both Figures 5 and 6, curve E is flat or nearly flat.

[0038] The drawings and the associated description are intended only to illustrate the concept of the invention. In its details the invention may vary within the scope of the claims.

Claims

1. A hydraulic system (Hs) for a work vehicle (1), at least one fixed displacement hydraulic pump (Hp); at least one speed and torque controlled electric motor (M) for driving said hydraulic pump (Hp); at least one hydraulic actuator (Ha); at least one electric controller (Ec) for adjusting the speed of said electric motor (M) and thereby adjusting the flow and pressure of the produced hydraulic fluid in the hydraulic system (Hs); Equipped with said hydraulic system (Hs) comprising at least one bypass flow path (By) comprising at least one throttle element (Te) for directing a restricted continuous discharge fluid flow from said hydraulic system (Hs); The hydraulic system (Hs) The throttle element (Te) is a pressure compensation element, whereby the magnitude of the bypass flow is automatically adjusted in response to the magnitude of the pressure prevailing in the hydraulic system (Hs). characterized in that Hydraulic system (Hs).

2. The magnitude of the bypass flow is determined so that the rotation of the hydraulic pump (Hp) is always at least 30 to 200 rpm.

2. The hydraulic system according to claim 1, wherein:

3. The electric controller (Ec) is a variable frequency drive (Vfd) that functions as an electric motor control device for controlling the torque and rotational speed of the electric motor (M).

2. The hydraulic system according to claim 1, wherein:

4. The electric controller (Ec) is configured to control the torque and the speed of the motor (M) to adapt the speed of the hydraulic pump (Hp) according to the required fluid flow at the required pressure level.

2. The hydraulic system according to claim 1, wherein:

5. a movable carrier (2); at least one working device (3) attached to said carrier (2); at least one hydraulic system (Hs); A work vehicle (1) comprising: The hydraulic system (Hs) is according to any one of claims 1 to 4. characterized in that Work vehicle (1).

6. The work vehicle (1) is a mining vehicle equipped with at least one hydraulically operated mining actuator (4) connected to the hydraulic system (Hs).

6. The work vehicle according to claim 5, wherein:

7. A method for generating hydraulic power to a hydraulic system (Hs) of a work vehicle (1), comprising: a fixed displacement hydraulic pump (Hp) rotated by a speed and torque controlled electric motor (M); controlling the rotation of said motor (M) by an electric controller (Ec) for adjusting the speed of said hydraulic pump (Hp) and thereby adjusting the flow and pressure of the produced hydraulic fluid in the hydraulic system (Hs); directing a restricted continuous discharge fluid flow from the output side of the hydraulic pump (Hp) to a reservoir (Re) via a bypass flow path (By) and through a throttle element (Te), whereby the hydraulic pump (Hp) is continuously driven and the output of the hydraulic pump (Hp) is stabilized; Including, limiting the magnitude of the bypass flow by means of the throttle element (Te) in order to limit hydraulic energy consumption, the magnitude of the bypass flow being configured to be automatically adjusted in response to the magnitude of the pressure prevailing in the hydraulic system (Hs); characterized by, method.

8. Stabilizing pressure fluctuations in operating conditions where pressure is needed for the output of the hydraulic pump (Hp) and fluid flow is not. The method of claim 7, characterized by:

9. and adjusting the magnitude of the bypass flow by the throttle element (Te) to correspond to a low rotation speed of the hydraulic pump (Hp) between 30 and 200 rpm in a situation where one or more hydraulic actuators (Ha) connected to the hydraulic system (Hs) do not require fluid flow but require pressure.

9. The method according to claim 7 or 8, characterized by:

Images