Patent Description:
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a soil compactor, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as an asphalt roller or a road roller.

A working machine that is used for compacting the ground on which the working machine travels may be referred to as a compaction machine. Generally, a compaction machine comprises one or more ground engagement elements, adapted to propel the compaction machine, as well as a vibrator for vibrating at least one of the ground engagement elements. An example of such a compaction machine is presented in <CIT>.

In a compaction machine, energy may be transmitted from a power source to the ground engagement elements via a hydrostatic drive line since a hydrostatic driveline implies a versatile power distribution to the ground engagement elements. However, a hydrostatic drive line for compaction machines may generally be associated with relatively large energy losses, for instance when the one of more of the ground engagement elements slip against the ground.

For example, <CIT> relates to a control system and method for a hydrostatic drive system that includes an internal combustion engine and a variable displacement hydraulic pump. <CIT> describes another known example of hydraulic system.

An object of the invention is to provide a hydraulic system for a working machine which can distribute energy from a power source to a plurality of hydraulic machines that can be used for a compaction operation of the working machine, which hydraulic system implies appropriately low power losses.

According to a first aspect of the invention, the object is achieved by a device according to claim <NUM>.

As such, the first aspect of the present invention relates to a hydraulic system for a working machine. The hydraulic system comprises:.

According to the first aspect of the present invention, at least one of the variable displacement hydraulic machines is adapted to drive a vibrator for vibrating a ground engagement element of the working machine.

As such, the first aspect of the present invention proposes a "power grid" to which the feeding pump can feed fluid at a certain flow rate and at a certain pressure. Each one of the variable displacement hydraulic machines connected in parallel to the feeding pump can thereafter consume a required portion of the hydraulic power produced by the feeding pump. This in turn implies an appropriate control of the feeding pump since the feeding pump can be controlled so as to provide hydraulic power required for the variable displacement hydraulic machines but not necessarily providing hydraulic power in excess thereof.

Optionally, the plurality of variable displacement hydraulic machines is connected to the feeding pump in parallel through a circuit conduit assembly, preferably through a closed circuit conduit assembly. The circuit conduit assembly, and in particular the closed circuit conduit assembly, implies an appropriate energy usage. For instance, the circuit conduit assembly, and in particular the closed circuit conduit assembly, implies that energy may be recuperated in a straightforward manner. As an example, with a closed circuit conduit assembly, hydraulic power produced by one or more variable displacement hydraulic machines may be consumed by one or more of the other variable displacement hydraulic machines.

Optionally, the closed circuit conduit assembly comprises an accumulator. The accumulator further increases the possibility to recuperate hydraulic energy. For instance, when a variable displacement hydraulic machine adapted to drive a vibrator is switched off, e.g. by changing the displacement of the associated variable displacement hydraulic machine, hydraulic energy produced by that hydraulic machine may be stored in the accumulator and thereafter be reused when the vibrator is started again.

Optionally, at least one, preferably each one, of the variable displacement hydraulic machines that is adapted to drive a ground engagement element of the working machine is adapted to operate both as a hydraulic pump and as a hydraulic motor. As such, when the speed of the working machine is reduced, e.g. when the working machine is braked, one or more of the variable displacement hydraulic machines adapted to drive ground engagement elements may be set so as to have a negative displacement such that each one of the associated variable displacement hydraulic machines acts as a pump feeding hydraulic energy to other portions of the hydraulic system, such as the accumulator mentioned hereinabove. The energy fed to the hydraulic system, e.g. stored in the accumulator, may thereafter be used when it is desired to move the working machine again.

Optionally, the hydraulic system comprises a set of speed sensors, each speed sensor being adapted to determine a value indicative of a rotational speed of one of the variable displacement hydraulic machines that is adapted to drive a ground engagement element of the working machine. The speed sensors may be used for a plurality of purposes. As one non-limiting example, the speed sensors may be used for determining the speed of the working machine. As another non-limiting example, the speed sensors may be used for detecting a slip of one or more of the ground engaging elements. This in turn implies an appropriate motion control of the ground engaging elements.

Optionally, the hydraulic system comprises a set of displacement control devices, each displacement control device being adapted to control the displacement of one of the variable displacement hydraulic machines. This in turn implies that each variable displacement hydraulic machine can be controlled individually, thereby enabling increased possibilities to control the working machine.

Optionally, the hydraulic system comprises a master control unit adapted to issue a signal to each displacement control device in the set of displacement control devices.

Optionally, at least one ground engagement element is a compactor drum.

Optionally, the feeding pump has a variable displacement. The variable displacement of the feeding pump implies that fluid can be fed to the variable displacement hydraulic machines at a desired pressure. As a non-limiting example, with respect to e.g. efficiency, noise and/or durability, it may be beneficial to keep the pressure fed by the feeding pump at a low level whilst still meeting the hydraulic power requirements of the variable displacement hydraulic machines.

A second aspect of the present invention relates to a powertrain comprising a power source and a hydraulic system according to any one of the preceding claims. The power source is operably connected to the feeding pump of the hydraulic system.

A third aspect of the present invention relates to a working machine, preferably a road compactor, comprising a powertrain according to the second aspect of the present invention and/or a hydraulic system according to the first aspect of the present invention.

Optionally, the working machine comprises a set of ground engagement elements, the set of ground engagement elements comprising at least one of a wheel and a compactor drum.

A fourth aspect of the present invention relates to a method for operating a working machine, preferably a road compactor, comprising a powertrain which in turn comprises a power source and a hydraulic system. The hydraulic system comprises:.

The method according to the fourth aspect of the present invention further comprises:.

Optionally, the plurality of variable displacement hydraulic machines is connected to the feeding pump in parallel through a circuit conduit assembly, preferably through a closed circuit conduit assembly, and wherein the closed circuit conduit assembly comprises an accumulator. The method further comprises:.

A fifth aspect of the present invention relates to a control unit for operating a working machine, preferably a road compactor, comprising a powertrain which in turn comprises a power source and a hydraulic system. The hydraulic system comprises:.

<FIG> illustrates the schematic configuration of a working machine <NUM>, exemplified as a soil compactor. Moreover, as illustrated in <FIG>, the working machine <NUM> comprises ground engagement elements <NUM>, <NUM>. In the <FIG> embodiment, the ground engagement elements <NUM>, <NUM> are exemplified as a front compactor drum <NUM> and a rear compactor drum <NUM>. However, it is also envisaged that other embodiments of the working machine may, instead of or in addition to the <FIG> compactor drums, comprise other types of ground engagement elements. As non-limiting examples, it is envisaged that embodiments of the working machine <NUM> may, as ground engaging elements, comprise one or more wheels (not show) and/or one or more crawlers (not shown). A working machine, such as the <FIG> working machine, preferably comprises a powertrain.

<FIG> illustrates an embodiment of a powertrain <NUM>. Purely by way of example, the <FIG> powertrain <NUM> may be used for propelling the <FIG> working machine <NUM>. As may be gleaned from <FIG>, the embodiment disclosed therein comprises a power source <NUM> and a hydraulic system <NUM>. As a non-limiting example, the power source <NUM> may comprise, or be constituted by, an internal combustion engine such as a diesel engine. However, it is also envisaged that the power source <NUM> may comprise, or be constituted by, other types of power generating means such as an electric motor (not shown). Moreover, as indicated in <FIG>, the power source <NUM> is operably connected to a feeding pump <NUM> of the hydraulic system <NUM>. Purely by way of example, and as exemplified in the <FIG> embodiment, the power source <NUM> may be mechanically connected to the feeding pump <NUM>, for instance via a shaft <NUM>.

The hydraulic system <NUM> comprises the feeding pump <NUM>. A plurality of variable displacement hydraulic machines <NUM>, <NUM>, <NUM>, <NUM> is connected in parallel to the feeding pump <NUM>.

At least one, preferably a plurality, of the variable displacement hydraulic machines is adapted to drive a ground engagement element of the working machine. In the <FIG> embodiment, the hydraulic system <NUM> comprises two variable displacement hydraulic machines <NUM>, <NUM>, each one of which being adapted to drive a respective ground engagement element <NUM>, <NUM> of the working machine. In particular, in the <FIG> embodiment, a first variable displacement hydraulic machine <NUM> is adapted to drive a first ground engagement element <NUM>, such as the front compactor drum <NUM> of the <FIG> working machine. Moreover, as exemplified in <FIG>, a second variable displacement hydraulic machine <NUM> may be adapted to drive a second ground engagement element <NUM>, such as the rear compactor drum <NUM> of the <FIG> working machine. However, it is also envisaged that embodiments of the hydraulic system <NUM> may comprise only one variable displacement hydraulic machine adapted to drive a ground engagement element. As another non-limiting example, embodiments of the hydraulic system <NUM> may comprise only three or more variable displacement hydraulic machines, each one of which being adapted to drive a ground engagement element, such as a respective ground engagement element.

Moreover, as indicated in <FIG>, at least one of the variable displacement hydraulic machines <NUM>, <NUM> is adapted to drive a vibrator for vibrating a ground engagement element of the working machine. In particular, in the <FIG> embodiment, a third variable displacement hydraulic machine <NUM> is adapted to drive a first vibrator <NUM>, such as a vibrator for the front compactor drum <NUM> of the <FIG> working machine. Moreover, as also exemplified in <FIG>, a fourth variable displacement hydraulic machine <NUM> may be adapted to drive a second vibrator <NUM>, such as a vibrator for the rear compactor drum <NUM> of the <FIG> working machine.

As a non-limiting example, and as is illustrated in <FIG> with reference to the first vibrator <NUM>, a vibrator may comprise a vibrator shaft <NUM> comprising a vibrator eccentricity <NUM>. As such, when the vibrator shaft <NUM> rotates, a vibration is produced by means of the vibrator eccentricity <NUM>. However, it is also envisaged that implementations of the vibrator may produce a vibrations using other means (not shown).

Moreover, as exemplified in <FIG>, the plurality of variable displacement hydraulic machines <NUM>, <NUM>, <NUM>, <NUM> may be connected to the feeding pump <NUM> in parallel through a circuit conduit assembly <NUM>. Preferably, the plurality of variable displacement hydraulic machines <NUM>, <NUM>, <NUM>, <NUM> may be connected to the feeding pump <NUM> in parallel through a closed circuit conduit assembly <NUM> as indicated in <FIG>.

Purely by way of example, the feeding pump <NUM> may comprise a high pressure side <NUM> and a low pressure side <NUM>. Moreover, the circuit conduit assembly <NUM> may comprise a high pressure line <NUM> fluidly connecting the high pressure side <NUM> of the feeding pump <NUM> to each one of the plurality of variable displacement hydraulic machines <NUM>, <NUM>, <NUM>, <NUM>. Further, the circuit conduit assembly <NUM> may comprise a low pressure line <NUM> fluidly connecting the each one of the plurality of variable displacement hydraulic machines <NUM>, <NUM>, <NUM>, <NUM> to the low pressure side <NUM> of the feeding pump <NUM>.

Purely by way of example, and as indicated in the <FIG> embodiment, the closed circuit conduit assembly may comprise an accumulator <NUM>. The accumulator <NUM> may be used for recuperating hydraulic energy, as will be elaborated hereinbelow. As a non-limiting example, and as indicated in the <FIG> embodiment, the accumulator <NUM> may be fluidly connected to the high pressure line <NUM> of the circuit conduit assembly <NUM>.

Moreover, at least one, preferably each one, of the variable displacement hydraulic machines that is adapted to drive a ground engagement element of the working machine may be adapted to operate both as a hydraulic pump and as a hydraulic motor. In the embodiment illustrated in <FIG>, each one of the first and second variable displacement hydraulic machines <NUM>, <NUM> is adapted to operate both as a hydraulic pump and as a hydraulic motor.

As such, when it for instance is desired to brake the working machine hosting the <FIG> power train, each one of the first and second variable displacement hydraulic machines <NUM>, <NUM> may be actuated so as to operate as a hydraulic pump thus pumping fluid from the low pressure line <NUM> to the high pressure line <NUM> of the circuit conduit assembly <NUM>. The fluid thus pumped may be used for charging the accumulator <NUM> such that energy is stored by the accumulator <NUM>.

The energy stored in the accumulator <NUM> may thereafter be used, e.g. for feeding fluid to one or more of the variable displacement hydraulic machines <NUM>, <NUM> for propelling the working machine and/or for feeding fluid one or more variable displacement hydraulic machines <NUM>, <NUM> connected to a vibrator <NUM>, <NUM>.

Moreover, the hydraulic system <NUM> may comprise a set of speed sensors. Each speed sensor is adapted to determine a value indicative of a rotational speed of one of the variable displacement hydraulic machines that is adapted to drive a ground engagement element of the working machine. <FIG> illustrates a portion of a hydraulic system <NUM> and the <FIG> further illustrates an example of a speed sensor <NUM>. The <FIG> speed sensor <NUM> is adapted to determine the rotational speed of a variable displacement hydraulic machine <NUM> adapted to drive a ground engagement element <NUM>. Purely by way of example, the <FIG> variable displacement hydraulic machine <NUM> and ground engagement element <NUM> may be the components with the same reference numerals discussed hereinabove in relation to <FIG>.

In the <FIG> implementation, the speed sensor <NUM> is adapted to determine the rotational speed of a shaft <NUM> rotationally connected to the variable displacement hydraulic machine <NUM>. However, other implementations are also envisaged, e.g. implementations in which the speed sensor <NUM> is adapted to determine the rotational speed of a component that does not rotate at the same rotational speed as a shaft of the variable displacement hydraulic machine <NUM> but wherein the a ratio between the rotational speed of the component and the rotational speed of the variable displacement hydraulic machine <NUM> is known or at least can be determined. As a non-limiting example, a speed sensor <NUM> may be adapted to determine the rotational speed of the ground engagement element <NUM>.

As a non-limiting example, and as illustrated in <FIG>, the value indicative of the rotational speed of the variable displacement hydraulic machine <NUM> may be transmitted to a variable displacement hydraulic machine control unit <NUM>.

Furthermore, the hydraulic system may comprise a set of displacement control devices. Each displacement control device is adapted to control the displacement of one of the variable displacement hydraulic machines.

The above is exemplified in <FIG> illustrating a displacement control device <NUM> adapted to control the displacement of the variable displacement hydraulic machine <NUM>. Moreover, the implementation illustrated in <FIG> further comprises a displacement sensor <NUM> adapted to determine a value of an actual displacement of the variable displacement hydraulic machine <NUM>. The value of the actual displacement may be used in a feedback loop control for controlling the displacement control device <NUM>.

The displacement of the variable displacement hydraulic machine <NUM> and the pressure of the fluid fed to the variable displacement hydraulic machine <NUM> will result in a torque produced by the variable displacement hydraulic machine <NUM>. As such, by controlling the displacement control device <NUM> to thereby control the displacement of the variable displacement hydraulic machine <NUM>, the torque produced by the variable displacement hydraulic machine <NUM> is controlled.

Further, as indicated in the <FIG> implementation, the variable displacement hydraulic machine control unit <NUM> may be adapted to receive a signal <NUM> from another control unit (not shown). Purely by way of example, the signal <NUM> may comprise information indicative of a desired speed and/or an actual speed of the working machine <NUM>. As another non-limiting example, the signal <NUM> may comprise information indicative of a pressure of the fluid fed to the variable displacement hydraulic machine <NUM>.

As such, though purely by way of example, if the signal <NUM> comprises information indicative of a desired speed of the working machine <NUM>, the variable displacement hydraulic machine control unit <NUM> may control the displacement control device <NUM> such that the rotational speed of the variable displacement hydraulic machine <NUM> corresponds to the speed thus desired. For instance, a requisite speed of the variable displacement hydraulic machine <NUM> may be determined by determining a requisite speed of the ground contacting portion, e.g. the circumference, of the ground engagement element <NUM> in order to obtain the desired speed of the working machine <NUM> and from the requisite speed thus determined determining a requisite rotational speed of the variable displacement hydraulic machine <NUM>, for instance taking the radius of the ground engagement element <NUM> and possibly a gear ratio between the variable displacement hydraulic machine <NUM> and the ground engagement element <NUM> into account.

Instead of, or in addition to, controlling the displacement control device <NUM> such that the rotational speed of the variable displacement hydraulic machine <NUM> results in a desired speed of the working machine <NUM>, the displacement control device <NUM> may be adapted to control the displacement control device <NUM> in order to avoid slip of the ground engagement element <NUM>. As such, though purely by way of example, if the signal <NUM> comprises information indicative of an actual speed of the working machine <NUM>, it is possible to determine whether or not the absolute value of the difference between the speed of the ground contacting portion of the ground engagement element <NUM> and the speed of the working machine is within a predetermined range.

If the absolute value of the above difference is outside the above range, this is an indication that the ground contacting portion of the ground engagement element <NUM> slides on the ground. In such an event, the displacement control device <NUM> is preferably controlled in order to mitigate such a sliding condition.

For instance, if the speed of the ground contacting portion of the ground engagement element <NUM> is lower than the speed of the working machine, this is an indication that the ground contacting portion is dragged on the ground and this may be avoided by increasing the speed of the ground contacting portion, by increasing the torque imparted thereon, by increasing the rotational speed of the variable displacement hydraulic machine <NUM> which in turn may be achieved by increasing the displacement thereof by actuating the displacement control device <NUM>.

As another example, if the speed of the ground contacting portion of the ground engagement element <NUM> is greater than the speed of the working machine, this is an indication of a slip of the ground engagement element <NUM> which may be avoided by reducing the speed of the ground contacting portion, by reducing the torque imparted thereon, by decreasing the rotational speed of the variable displacement hydraulic machine <NUM> which in turn may be achieved by decreasing the displacement thereof by actuating the displacement control device <NUM>.

<FIG> illustrates an embodiment in which each one of the variable displacement hydraulic machines <NUM>, <NUM> adapted to drive a ground engagement element <NUM>, <NUM> is connected to a variable displacement hydraulic machine control unit <NUM>, <NUM>, a displacement control device <NUM>', <NUM>", a speed sensor <NUM>', <NUM>" and a displacement sensor <NUM>', <NUM>" in the manner that has been discussed hereinabove in relation to <FIG>. Moreover, as indicated in the <FIG> embodiment, the hydraulic system <NUM> may comprise a master control unit <NUM> adapted to issue a signal to each displacement control device <NUM>', <NUM>" in the set of displacement control devices.

In the embodiment illustrated in <FIG>, the master control unit <NUM> is adapted to issue a signal to each displacement control device <NUM>', <NUM>" in the set of displacement control devices via the respective variable displacement hydraulic machine control units <NUM>, <NUM>. However, it is also envisaged that, in embodiments of the hydraulic system <NUM>, the master control unit <NUM> may issue a signal directly to each respective displacement control devices, alternatively via another control unit (not shown).

Further, in the embodiment illustrated in <FIG>, the master control unit <NUM> may be adapted to issue signals to control the displacement of each one of the variable displacement hydraulic machines <NUM>, <NUM> being adapted to drive a vibrator <NUM>, <NUM>.

Moreover, as indicated in <FIG>, the hydraulic system <NUM> may comprise a first pressure sensor <NUM> adapted to issue a high pressure signal indicative of the fluid pressure in the high pressure line <NUM>. For instance, the high pressure signal may be transmitted to the master control unit <NUM>.

Additionally, the hydraulic system <NUM> may comprise a second pressure sensor <NUM> adapted to issue a low pressure signal indicative of the fluid pressure in the low pressure line <NUM>. For instance, the low pressure signal may be transmitted to the master control unit <NUM>. Moreover, as indicated in each one of the <FIG> and <FIG> embodiments, the feeding pump <NUM> may have a variable displacement. For example, and as indicated in <FIG>, the hydraulic system <NUM> may comprise a second control unit <NUM> adapted to issue a control signal to a feeding pump displacement control device <NUM> controlling the displacement of the feeding pump <NUM>. Here, it should be noted that the hydraulic system <NUM> may also comprise a feeding pump speed sensor <NUM> adapted to determine a value indicative of a rotational speed of the feeding pump <NUM>. Further, the hydraulic system <NUM> may comprise a feeding pump displacement sensor <NUM> adapted to determine a value of an actual displacement of the feeding pump. It is also envisaged that embodiments of the hydraulic system <NUM> may comprise a single control unit adapted to perform the operations performable by the master control unit <NUM> and the second control unit <NUM> as described hereinabove.

The second control unit <NUM>, the feeding pump displacement control device <NUM>, the feeding pump speed sensor <NUM> and the feeding pump displacement sensor <NUM> may be adapted to interact in the same way as the corresponding components interact in <FIG> and as described hereinabove.

Moreover, as indicated in <FIG>, the second control unit <NUM> may also be adapted to issue a control signal to the power source <NUM>. As a non-limiting example, the feeding pump <NUM> and possibly also the power source <NUM> may be operated so as to produce a pressure and flow in the high pressure line <NUM> sufficient to supply requisite hydraulic power to each one of the variable displacement hydraulic machines <NUM>, <NUM>, <NUM>, <NUM> being connected in parallel to the feeding pump <NUM>. Moreover, again as a non-limiting example, the feeding pump <NUM>, and possibly also the power source <NUM>, may be controlled such that a fluid pressure in the high pressure line <NUM> does not excessively exceed a pressure required for the variable displacement hydraulic machines <NUM>, <NUM>, <NUM>, <NUM>. As a non-limiting example, the feeding pump <NUM>, and possibly also the power source <NUM>, may be controlled such that a fluid pressure in the high pressure line <NUM> at maximum exceeds a determined required pressure by a predetermined pressure tolerance. Purely by way of example, such a pressure tolerance may be a predetermined percentage, such as <NUM>% or <NUM>%, of the determined needed pressure.

As such, though purely by way of example, the torque currently required by each one of the variable displacement hydraulic machines <NUM>, <NUM>, <NUM>, <NUM> may be determined, and from the torque values thus determined a pressure required in the high pressure line <NUM> may be determined. The feeding pump <NUM>, and possibly also the power source <NUM>, may thereafter be operated such as to produce a pressure the magnitude of which is the required pressure plus a pressure tolerance.

It should be noted that although the embodiments presented hereinabove discloses variable displacement hydraulic machines which are adapted to either drive a ground engaging member or a vibrator, it is also envisaged that embodiments of the hydraulic system <NUM> may comprise a plurality of variable displacement hydraulic machines being connected in parallel to the feeding pump <NUM>, wherein at least one variable displacement hydraulic machine is adapted to drive another component of the working machine <NUM>. Non-limiting examples of such components include a fan (not shown) driven by a variable displacement hydraulic machine, a steering assembly (not shown) driven by a variable displacement hydraulic machine and any other type of hydraulically powered actuator, such as an actuator adapted to move an implement (not shown) of a working machine.

Claim 1:
A hydraulic system (<NUM>) for a working machine (<NUM>), said hydraulic system (<NUM>) comprising:
- a feeding pump (<NUM>);
- a plurality of variable displacement hydraulic machines (<NUM>, <NUM>, <NUM>, <NUM>) being connected in parallel to said feeding pump (<NUM>);
- at least one (<NUM>, <NUM>), preferably a plurality, of said variable displacement hydraulic machines (<NUM>, <NUM>, <NUM>, <NUM>) being adapted to drive a ground engagement element (<NUM>, <NUM>) of said working machine (<NUM>), characterized in that
- at least one of said variable displacement hydraulic machines (<NUM>, <NUM>, <NUM>, <NUM>) is adapted to drive a vibrator (<NUM>, <NUM>) for vibrating a ground engagement element (<NUM>, <NUM>) of said working machine (<NUM>).