Field of the Invention

The present invention relates to a lift arrangement for a working machine.

The invention is applicable on working machines within the fields of industrial construction machines, in particular wheel loaders. Although the invention will be described with respect to a wheel loader, the invention is not restricted to this particular machine, but may also be used in other working machines such as excavators, backhoe loaders, skid steer loaders or other construction equipment.

Technical Background

A working machine is provided with a bucket, container, attachment bracket or other type of tool for lifting, carrying and/or transporting a load.

Such a working machine may for example be a wheel loader having a lift arrangement for raising and lowering the tool, such as a bucket. The lift arrangement commonly comprises an arm, one or more hydraulic cylinders for movement of the arm and of the bucket connected to the arm. Hydraulic cylinders are arranged for lifting the arm and for tilting the tool connected to the arm.

The wheel loader also has a pair of hydraulic cylinders for

turning/steering the wheel loader by pivoting a front part and a rear part of the wheel loader relative to each other.

The hydraulic system of the wheel loader may preferably comprise a working cylinder pump and a steering cylinder pump. The same pump may be used for feeding lift, tilt and steering together with additional functions, or the steering cylinder may have a separate pump. The pumps may typically be powered by the internal combustion engine of the wheel loader.

The lift arrangement affects the behavior of the wheel loader regarding bucket breakout torque, visibility and machine capacity, among other things. Accordingly, the geometry and configuration of the lift arrangement is important for determining performance parameters of a working machine.

Additionally, for some applications, it is desirable to be able to control the tilt of bucket while raising the arm, for example in order to maintain the bucket in a fixed tilt angle with relation to the ground so that none of the load escapes the bucket. The position of the bucket may for example be controlled through electronic control of the tilt cylinder. However, such a solution may result in high losses for a machine where the pump feeds both the lift cylinder and the tilt cylinder. If there is a difference in load pressure in the different cylinders, the pump has to be adjusted to the highest load pressure which means that the pressure has to be reduced for the work function requiring a lower pressure. Such a pressure drop (over a valve) will result in energy loss and lead to a reduced energy efficiency of the wheel loader.

A solution to the above problem of controlling the tilt position of the tool is provided by US4344734 which discloses a mechanical self leveling bucket linkage for a working machine. In US4344734, the lift arrangement comprises a number of mechanical elements arranged so that the bucket is

automatically maintained in a position level to the ground when the lift arms are raised.

However, as the weight of the lift arrangement affects the energy consumption of the wheel loader, and the configuration and dimensioning of the hydraulic system must be adapted to handle the weight, it is desirable to reduce the weight of the lift arrangement. In general, there is a trade-off between the lifting capacity and weight of the lift arrangement.

Summary of the Invention

It is an object of the present invention to provide an energy efficient lift arrangement for a working machine which is able to control the position of the bucket while moving the lift arrangement in order to achieve a more energy efficient working machine. The object is achieved by a lift arrangement for a working machine according to claim 1. The present invention is based on the realization that a lift arrangement without a mechanical self-leveling mechanism, i.e. a lift arrangement comprising a non-self leveling tool linkage, may be formed by providing a hydraulic actuator for controlling a tilt position of a tool, where the hydraulic tilt actuator is driven by a pump separate from the pump for controlling the lift actuator. In such a lift arrangement according to the present invention, a desired parallel alignment of the tool in relation to the tool linkage is controlled by the tilt actuator. In the present context, a non-self leveling tool linkage refers to a tool linkage where the leveling of the tool is not automatically controlled as a result of the mechanical arrangement of the tool linkage. Instead, the tilt position of a tool connected to the tool linkage is controlled by a hydraulic actuator driven by a pump, whereas a self-leveling bucket linkage has a linkage system for automatically maintaining the orientation of a bucket while the lift arm is moved. In particular, such a mechanical self-leveling mechanism includes one or more links joined to the lift arm in a manner such that a bucket position mechanism is displaced to counteract the motion of the bucket induced by the lift arm, thereby providing a self leveling tool linkage.

An advantage of the lift arrangement according to the present invention is that it is mechanically simple, comprising few mechanical parts. Thereby, the lift arrangement according to embodiments of the invention leads to a reduced weight, and as a result to a reduced energy consumption of a working machine to which the lift arrangement is connected.

A further advantage of using a mechanically simple linkage is that the arm and lift cylinder of the lift arrangement may be made smaller, thereby improving the visibility for an operator of the working machine.

According to one embodiment of the invention, the tool linkage may further comprise a substantially vertically arranged first link comprising a first joint connected to the second hydraulic actuator and a second joint connected to the arm. Furthermore, the tool linkage may comprise a substantially horizontally arranged second link comprising a first joint connected to a third joint of the first link, and a second joint connectable to the tool. Additionally, the second joint of the first link may be jointly connected to the arm at the position where the first hydraulic actuator is connected to the arm. A common joint for connecting both the first link and the first hydraulic actuator to the arm simplifies the linkage and leads to a reduction in weight compared to if two separate joints were to be used.

The aforementioned configuration of a tool linkage is further

advantageous in that it may provide an optimized breakout torque while using few moving parts and a relatively limited number of joints.

In one embodiment of the invention, the arm may advantageously be a single boom. Providing a lift arrangement where the arm is a single boom offers further advantages related to low weight and improved visibility.

However, the arm may also comprise two or more structural elements.

In one embodiment of the invention, the lift arrangement may further comprise a control system for controlling the second hydraulic actuator configured to control a tilt of said tool. The control system is preferably configured to control the tilt position of the tool when the arm is lifted so that an operator does not have to control the tilt position manually.

Moreover, the control system may advantageously be configured to control the second hydraulic actuator based on a position of the arm. In an application where the tool is a bucket for lifting material, it may be desirable to maintain the tool horizontally level as the arm is lifted. This may be achieved by the control system based on the position of the arm, for example by receiving input from the system controlling the operation of the lift actuator.

According to one embodiment of the invention, the control system may advantageously comprise a sensor for determining a position of said arm. The sensor may for example determine the position of the arm by detecting an extension of the lift actuator, thereby providing information to the control system relating to the position of the arm. The sensor may also be a motion sensor or a tilt sensor able to determine the position of the arm.

In one embodiment of the invention, the lift arrangement may further comprise a first motor for driving the first hydraulic pump and a second motor for driving the second hydraulic pump. By providing a separate motor for each of the first and second hydraulic pump, motors may be provided which are adapted to the requirements of the first and second pump, and thereby to the first and second actuator, respectively. Thereby, the efficiency of the lift arrangement may be improved as losses resulting from a mismatch between motor capacity and pump/actuator requirements can be avoided.

According to one embodiment of the invention, the first motor may advantageously be an electrical motor providing power to the first hydraulic pump, and the second motor may advantageously be an electrical motor providing power to the second hydraulic pump. In general, electrical motors are more energy efficient compared to combustion engines, therefore, a further improvement in energy efficiency is provided.

In one embodiment of the invention, the lift arrangement may further comprise an energy storage electrically connected to the first motor and to the second motor. Furthermore, the energy storage may preferably be a battery. The energy storage may also be a super-capacitor.

In one embodiment, the energy storage may be configured to be charged by an internal combustion engine via a generator. Thereby, a hybrid system is provided where a combustion engine is used to power the propulsion of a working machine while electrical motors which can be powered both by the energy storage and the combustion engine are used to drive the lift and tilt actuators of the lift arrangement. Furthermore, the combustion engine and generator can be downsized compared to in a non- hybrid system as the power from the energy storage can support transient loads. Additionally, the loads from the lift and tilt functions are separated from the propulsion system to allow further downsizing of the combustion engine. Furthermore, at least one of the first motor and the second motor may preferably be configured to convert pressure in the first hydraulic actuator and the second hydraulic actuator, respectively, into electrical energy for charging the energy storage. By providing at least one of the motors as an electrical machine, or a reversible motor, excess power in the hydraulic actuators may be utilized to generate energy for recharging the battery. For example, energy can be recuperated by the energy storage when lowering the lift arrangement. Thereby, energy which in a conventional hydraulic system is lost can be recycled, thus improving the energy efficiency of the working machine.

Moreover, both the first electric motor and the second electric motor are preferably four quadrant motors, thereby being able to operate each cylinder to both retract and extract with the load at any direction.

Brief Description of the Drawings

These and other aspects of the present invention will now be described in more detail with reference to the appended drawings showing an example embodiment of the invention, wherein:

Fig. 1 schematically illustrates a working machine comprising a lift arrangement according to an embodiment of the invention;

Fig. 2 schematically illustrates a lift arrangement according to an embodiment of the invention; and

Fig. 3 is a schematic illustration of a hydraulic system for a lift arrangement according to an embodiment of the invention. Detailed Description of Preferred Embodiments of the Invention

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person. Like reference characters refer to like elements throughout.

An embodiment of a lift arrangement according to the present invention will mainly be discussed with reference to a lift arrangement for a wheel loader.

Fig. 1 illustrates a working machine 1 in the form of a wheel loader. The wheel loader 1 is to be considered as an example of a working machine onto which a lift arrangement according to the invention can be attached. The wheel loader has a forward machine part 8 and a rear machine part 9. Each of these machine parts comprises a frame and wheels 12 arranged on an axle. The rear machine part 9 comprises a cab 10 for an operator of the wheel loader 1. The machine parts 8, 9 are connected to each other in such a way that they can pivot relative to each other about a vertical axis by means of two hydraulic cylinders (steering cylinders) 7a, 7b which are arranged between the machine parts 8, 9 and attached thereto. The hydraulic cylinders 7a, 7b are thus arranged one on each side of a centre line extending in the longitudinal direction of the working machine 1 in order to turn or steer the wheel loader by means of the hydraulic cylinders. In other words, the wheel loader 1 is a so called frame-steered working machine.

The wheel loader further comprises a lift arrangement 2 for handling different loads, such as objects or material. The lift arrangement 2 comprises a tool linkage and a tool 3 in the shape of a bucket which is mounted on the tool linkage. The tool linkage comprises a lift arm 5, a substantially vertically arranged first link 15 and a substantially horizontally arranged second link 16. A first end of the lift arm 5 is pivotally connected to the forward machine part 8 in order to achieve a lift motion of the bucket 3. The bucket 3 is pivotally connected to a second end of the lift arm 5 in order to allow a tilt motion of the bucket. The lift arm 5 unit can be raised and lowered relative to the forward machine part 8 of the vehicle by means of a hydraulic actuator, here a hydraulic cylinder (lift cylinder) 17. The hydraulic cylinder 17 is at a first end coupled to the forward machine part 8 and at the second end to the lift arm 5. Even though the lift cylinder is illustrated as a single cylinder, two cylinders arranged in parallel may equally well be used to provide the lift function. The bucket 3 can be tilted relative to the lift arm 5 by means of a further hydraulic cylinder (tilt cylinder) 18, which at a first end is coupled to the substantially vertically arranged first link 15 and at the second end is coupled to the lift arm 5 or the bucket 3.

Fig. 2 schematically illustrates the lift arrangement 2 of Fig. 1 illustrating the arm 5 in the form of a single boom 5 having a first joint 25 for pivotably connecting to the forward machine part 8 of the working machine 1 and a second joint 26 for pivotably connecting to the bucket 3. The tool linkage comprises a substantially vertically arranged first link 15 having a first joint 20 connected to the second hydraulic cylinder 18 and a second joint 21 connected to the arm 5. The substantially horizontally arranged second link 16 has a first joint 22 connected to a third joint 22 of said first link, and a second joint 24 connected to the tool 3. It is further illustrated that the second joint 21 of the first link 15 is jointly connected to the arm 5 at the position where the first hydraulic cylinder 17 is jointly connected to the arm 5.

Length sensors (not shown) are also arranged on the lift cylinder 17 for sensing the extension of the lift cylinder. The sensor is connected to the control system in which the position of the arm can be determined from the received sensor data. Based on the position of the arm, the tilt cylinder can be controlled so that the bucket may be kept in a desired tilt position for all positions of the arm and during movement of the arm.

In Fig. 3, a schematic illustration of the hydraulic system 30 is provided. An energy generator 31 in the form of an internal combustion engine connected to a generator 32 provides energy to a grid. Also connected to the grid is an energy storage system 38 in the form of a battery. A first motor 33 is connected to the grid for driving a first hydraulic pump (or hydraulic machine) 34 providing hydraulic fluid to the first hydraulic cylinder 17 for controlling the lift position of the arm 5. Furthermore, a second electrical motor 35 is connected to the grid for driving a second hydraulic pump (or hydraulic machine) 36 providing hydraulic fluid to the second hydraulic cylinder 18 controlling the tilt position of the bucket 3. At least one of the first motor 33 and the second motor 35 is a reversible electrical motor which is able to convert energy in the form of pressure in the hydraulic cylinders 17,18, via the first and/or second pumps (hydraulic machines) 34,36, respectively, into electrical energy for charging the energy storage. Thereby, energy stored in the form of excess pressure in each of the actuators may be recycled instead of dumped, which improves the overall energy efficiency of the hydraulic system.

Additionally, variations to the disclosed embodiments can be

understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.