Patent Description:
The invention is applicable on working machines within the fields of industrial construction machines, material handling machines or construction equipment, 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 be used in any working machine where recuperation of braking energy is feasible, such as wheeled excavators, articulated or rigid haulers and backhoe loaders.

In connection with transportation of heavy loads, e.g. in construction work, working machines are frequently used. A working machine may be operated with large and heavy loads in areas where there are no roads, for example for transports in connection with road or tunnel building, sand pits, mines and similar environments.

To improve the fuel efficiency of the working machine, a hydraulic energy handling system may be used. Such hydraulic energy handling system may comprise a hydraulic machine (operative both as a hydraulic pump and as a hydraulic motor) attached to a mechanical driveline of the working machine and a hydraulic energy storage, such as one or more hydraulic accumulators. The hydraulic energy handling system can be charged when excess energy is available, for example by driving the hydraulic machine as a pump and charging the hydraulic accumulator with hydraulic fluid during braking of the working machine. The stored energy can then be returned to the mechanical driveline by driving the hydraulic machine as a motor with hydraulic fluid from the hydraulic accumulator in order to add driving torque to the mechanical driveline. In this manner, kinetic energy from the working machine can be recovered and used later to add power to the mechanical driveline. The hydraulic energy handling system may therefore be said to constitute a hydraulic flywheel.

<CIT> discloses a hydraulic regeneration apparatus for a motor vehicle having an engine, a transmission and a drive shaft. The regeneration apparatus comprises two fixed displacement hydraulic pump/motors, a low-pressure hydraulic accumulator, a high-pressure hydraulic accumulator, a multifunction hydraulic manifold, and an electronic control system for receiving pressure information from the accumulators.

<CIT> discloses a hydrostatic drive for a vehicle comprising hydraulic motors, wheels, a pump pumping pressurized medium into a line, low pressure lines, an accumulator, a hydraulic motor, a pressure relief valve and an electrically operated <NUM>/<NUM>-way valve.

Since the capacity of the hydraulic energy storage is often comparatively low, the hydraulic energy storage will quickly be filled up to maximum when braking the working machine from high speed or during a long downhill slope. When the hydraulic energy storage is full, the braking with the hydraulic energy handling system must be aborted to avoid excessive pressure. It is then no longer possible to brake the working machine by charging the hydraulic energy storage. It is therefore necessary to initiate use of an alternative brake system, e.g. to avoid a dangerous situation. One solution is to control the service brakes by an electronic valve arrangement and thereby fade in the service brakes while fading out the hydraulic energy handling system. However, this solution requires continuous monitoring of the hydraulic energy storage, and an electronically controlled valve system for the service brakes, which is complex and expensive. Moreover, brake blending control algorithms are difficult to tune since the service brakes typically have a quite stiff behaviour, i.e. it is difficult to provide a smooth transition from the braking with the hydraulic energy handling system to the braking with the service brakes.

An object of the invention is to provide a hydraulic energy handling system for a working machine, which hydraulic energy handling system has a simple, cheap, efficient and/or reliable design and/or operation.

The object is achieved by a hydraulic energy handling system for a working machine according to claim <NUM>. This hydraulic energy handling system comprises a high-pressure side; a low-pressure side; a hydraulic machine for mechanically driving a mechanical driveline of the working machine, and for being mechanically driven by the mechanical driveline to pump hydraulic fluid from the low-pressure side to the high-pressure side; at least one high-pressure hydraulic energy storage connected to the high-pressure side; a hydraulic motor having an inlet side and an outlet side; a hydraulic pump arranged to supply hydraulic fluid to the inlet side of the hydraulic motor; and a return line for conducting hydraulic fluid to a hydraulic tank. The hydraulic energy handling system further comprises a pressure relief valve connected between the high-pressure side and the return line, the pressure relief valve being arranged to discharge excess hydraulic energy from the high-pressure side to the return line in order to provide a braking force on the mechanical driveline; and a priority valve arrangement connected to the outlet side of the hydraulic motor, the priority valve arrangement being configured to direct a prioritized flow of hydraulic fluid to the low-pressure side.

During braking of the working machine, braking energy can be stored by pumping hydraulic fluid by means of the hydraulic machine from the low-pressure side to the high-pressure side where the hydraulic fluid is initially stored in the high-pressure hydraulic energy storage. When the high-pressure hydraulic energy storage is full and the braking of the working machine continues, the hydraulic pressure in the high-pressure side rises until the pressure relief valve automatically opens and hydraulic fluid flows from the high-pressure side to the return line. The flow of hydraulic fluid over the pressure relief valve allows the working machine to maintain the braking torque even when the high-pressure hydraulic energy storage is fully charged, without the need for electronically controlled valves to activate the service brakes of the working machine.

Due to the braking force provided by the pressure relief valve when the high-pressure hydraulic energy storage is full, the pressure relief valve may be said to constitute a retarder valve. The invention allows for a simple and seamless transition from the regenerative braking by charging the high-pressure hydraulic energy storage, to the non-regenerative braking by throttling hydraulic fluid through the pressure relief valve, without the need for additional software control and monitoring.

During a longer retarder braking sequence by throttling hydraulic fluid through the pressure relief valve, the supply to the suction side of the hydraulic machine may be reduced, e.g. as a low-pressure hydraulic energy storage is expended. The priority valve arrangement handles the distribution of flow of hydraulic fluid from the hydraulic motor to either the low-pressure side or the return line, where the flow to the low-pressure side is prioritized. Instead of unconditionally guiding the outlet flow of hydraulic fluid from the hydraulic motor to the return line, the priority valve arrangement directs a prioritized flow of hydraulic fluid to the low-pressure side should the hydraulic pressure in the low-pressure side be below a threshold value. Thereby, supply of pressurized hydraulic fluid to the suction side of the hydraulic machine is ensured.

Due to the positioning of the priority valve arrangement in series with the hydraulic motor, i.e. downstream of the hydraulic motor, an already existing hydraulic pump may be used to supply hydraulic fluid to the low-pressure side. Thereby, costs associated with a dedicated hydraulic pump can be avoided. Since the priority valve arrangement is arranged downstream of the hydraulic motor, the supply of pressurized hydraulic fluid to the suction side of the hydraulic machine can be accomplished without compromising the functionality of the hydraulic motor.

Furthermore, the hydraulic motor can be operated at full speed even when a large supply flow of hydraulic fluid is required by the hydraulic machine. The invention thereby effectively addresses the challenge of supplying pressurized hydraulic fluid to the hydraulic machine, while enabling full functionality of both the hydraulic motor and the hydraulic energy handling system. The hydraulic pump, the hydraulic motor and the priority valve arrangement may be said to constitute a supply system for the hydraulic energy handling system.

When accelerating the vehicle, hydraulic fluid is released from the high-pressure hydraulic energy storage to drive the hydraulic machine, which then functions as a motor. In this state, the hydraulic machine adds driving torque to the mechanical driveline and may thereby supplement or replace the driving torque from an internal combustion engine of the working machine.

The hydraulic machine may be coupled to the mechanical driveline via a clutch. By disengaging the clutch, the hydraulic energy handling system can be isolated from the mechanical driveline. Alternatively, the hydraulic machine may be permanently coupled to the mechanical driveline such that the hydraulic machine is always driven by (and always drives) the mechanical driveline.

The hydraulic energy handling system according to the invention may be configured to be used with a hydraulic parallel hybrid driveline of the working machine, where the hydraulic parallel hybrid driveline comprises the mechanical driveline. In this case, the hydraulic machine may be configured to mechanically drive, and to be mechanically driven by, the mechanical driveline of the hydraulic parallel hybrid driveline. With parallel is meant that the hydraulic energy handling system is supplementary to the mechanical driveline and does not interfere with normal operation of the mechanical driveline. Throughout the present disclosure, the terms high-pressure side and low pressure side mean that the pressure is higher in the high-pressure side than in the low-pressure side during operation of the hydraulic energy handling system.

The pressure relief valve may be configured to open automatically when a certain set pressure is reached on the high-pressure side, e.g. to operate only based on a set pressure on the high-pressure side. According to one embodiment, the pressure relief valve is hydromechanical. Since the pressure relief valve is not actively controlled, no additional software control is needed. Due to the absence of complex control, the switching to retarder braking by means of the pressure relief valve can be made seamless for the driver.

According to one embodiment, the hydraulic energy handling system further comprises a fan and the hydraulic motor is arranged to drive the fan. The prioritized flow of hydraulic fluid to the low-pressure side according to the invention is particularly advantageous during high power operations, where a large supply flow of hydraulic fluid to the hydraulic machine is needed at the same time as a high fan power is needed.

The hydraulic pump for the fan constitutes one of several suitable existing pumps that may be used to supply hydraulic fluid to the hydraulic energy handling system according to the present invention. By using an already existing hydraulic pump in the working machine, a dedicated fluid supply pump can be avoided.

According to one embodiment, the priority valve arrangement is configured to direct an excess flow of hydraulic fluid from the outlet side of the hydraulic motor to the return line. The priority valve arrangement may comprise a hydromechanical priority valve. Thus, the priority valve arrangement may function independently and may not require control from e.g. a central control unit of the working machine. The priority valve arrangement may however alternatively be electrically controlled e.g. based on a signal from an electronic sensor for sensing the set pressure on the low-pressure side. As a further alternative, the priority valve arrangement may comprise two on/off valves connected to the outlet side of the hydraulic motor, one connected to the low-pressure side and one connected to the return line.

According to one embodiment, the hydraulic energy handling system further comprises an anti-cavitation valve configured to allow hydraulic fluid to flow from the high-pressure side to the low-pressure side when a hydraulic pressure on the low-pressure side falls below a cavitation threshold value. The anti-cavitation valve thereby ensures to recirculate hydraulic fluid from the high-pressure side to the low-pressure side should the hydraulic pressure on the low-pressure side become critically low despite the supply from the priority valve arrangement, e.g. during a long downhill slope. Each of the at least one high-pressure hydraulic energy storage may be a hydraulic accumulator, such as a hydropneumatic accumulator.

According to one embodiment, the hydraulic energy handling system further comprises at least one low-pressure hydraulic energy storage connected to the low-pressure side. The low-pressure hydraulic energy storage can ensure a sufficient pressure on the low-pressure side to avoid cavitation before the priority valve arrangement directs a prioritized flow of hydraulic fluid to the low-pressure side.

The low-pressure hydraulic energy storage on the low-pressure side also enables the high-pressure side and the low-pressure side to be reversed. Also each of the at least one low-pressure hydraulic energy storage may be a hydraulic accumulator, such as a hydropneumatic accumulator.

According to one embodiment, the hydraulic energy handling system further comprises a control valve arrangement configured to selectively connect the hydraulic machine to the high-pressure side. According to one embodiment, the control valve arrangement may further be configured to selectively connect the high-pressure side to the low-pressure side. The control valve arrangement may however be omitted, for example in case the hydraulic machine is a four quadrant hydraulic machine.

According to one embodiment, the hydraulic energy handling system is for a hydraulic parallel hybrid driveline, Thus, the hydraulic energy handling system may be configured to be used in a hydraulic parallel hybrid driveline.

The invention also relates to a hydraulic parallel hybrid driveline for a working machine, where the hydraulic parallel hybrid driveline comprising a mechanical driveline and a hydraulic energy handling system according to the invention. In this case, the hydraulic machine may be arranged to mechanically drive, and to be mechanically driven by, the mechanical driveline of the hydraulic parallel hybrid driveline. Although not detailed herein, the hydraulic energy handling system of the hydraulic parallel hybrid driveline may alternatively form part of a hydrostatic transmission.

According to one embodiment, the mechanical driveline comprises a gearbox having a gearbox output shaft, and the hydraulic machine is arranged to mechanically drive, and to be mechanically driven by, the gearbox output shaft. The hydraulic machine may however be driven by, and drive, alternative components of the mechanical driveline. The hydraulic parallel hybrid driveline may further comprise an internal combustion engine. In this case, the hydraulic pump may be driven by the internal combustion engine.

The invention also relates to a working machine comprising a hydraulic energy handling system according to the invention or a hydraulic parallel hybrid driveline according to the invention. The working machine may be a wheel loader. Alternatively, the working machine may be a wheeled excavator, an articulated or rigid hauler or a backhoe loader.

In the following, a hydraulic energy handling system for a working machine, a hydraulic parallel hybrid driveline for a working machine, and a working machine, will be described. The same reference numerals will be used to denote the same or similar structural features.

<FIG> is a schematic illustration of a working machine <NUM> according to the invention. The working machine <NUM> comprises a hydraulic parallel hybrid driveline <NUM>, which in turn comprises a mechanical driveline <NUM> and a hydraulic energy handling system <NUM>. The hydraulic parallel hybrid driveline <NUM> constitutes the propulsion system of the working machine <NUM>.

The working machine <NUM> is here exemplified as a wheel loader comprising a front body section <NUM> and a rear body section <NUM>, which sections each has an axle for driving a pair of wheels <NUM>. The rear body section <NUM> comprises a cab <NUM>. The body sections <NUM>, <NUM> are connected to each other in such a way that they can pivot in relation to each other around a vertical axis by means of two first actuators in the form of hydraulic cylinders <NUM>, <NUM> arranged between the two body sections <NUM>, <NUM>. The hydraulic cylinders <NUM>, <NUM> are thus arranged one on each side of a horizontal centerline of the working machine <NUM> in a traveling direction in order to turn the working machine <NUM>.

The working machine <NUM> further comprises an equipment <NUM> for handling objects or material <NUM>. The equipment <NUM> comprises a load-arm unit <NUM>, also referred to as a linkage, and an implement in the form of a bucket <NUM> fitted on the load-arm unit <NUM>. A first end of the load-arm unit <NUM> is pivotally connected to the front body section <NUM>. The bucket <NUM> is pivotally connected to a second end of the load-arm unit <NUM>. The load-arm unit <NUM> can be raised and lowered relative to the front body section <NUM> of the working machine <NUM> by means of two second actuators in the form of two hydraulic cylinders <NUM>, <NUM>, each of which is connected at one end to the front body section <NUM> and at the other end to the load-arm unit <NUM>.

<FIG> is a block diagram of the hydraulic parallel hybrid driveline <NUM> in <FIG> comprising the mechanical driveline <NUM> and the hydraulic energy handling system <NUM>. The mechanical driveline <NUM> comprises an internal combustion engine <NUM> and a gearbox <NUM>. In this example, the mechanical driveline <NUM> further comprises a torque converter <NUM> between the internal combustion engine <NUM> and the gearbox <NUM>. A power take-off (PTO) <NUM> is also provided between the internal combustion engine <NUM> and the torque converter <NUM> for driving hydraulic work functions <NUM>, such as the hydraulic cylinders <NUM>, <NUM>, <NUM>, <NUM> of the working machine <NUM>. The wheels <NUM> of the working machine <NUM> are driven via a gearbox output shaft <NUM>.

The hydraulic energy handling system <NUM> is connected to the mechanical driveline <NUM> with the purpose to store and release energy to boost the mechanical driveline <NUM>. The hydraulic energy handling system <NUM> comprises a high-pressure side <NUM>, a low-pressure side <NUM> and a hydraulic machine <NUM>. In this example, the hydraulic machine <NUM> is a four quadrant hydraulic machine. Thus, the high-pressure side <NUM> and the low-pressure side <NUM> may be reversed.

The hydraulic machine <NUM> comprises a first side <NUM> and a second side <NUM>. In case the hydraulic machine <NUM> operates as a pump (e.g. during braking of the working machine <NUM>), the first side <NUM> is a suction side and the second side <NUM> is a discharge side.

Throughout the present disclosure, the high-pressure side <NUM> and the low-pressure side <NUM> may be constituted by a high-pressure line and a low-pressure line, respectively.

The hydraulic energy handling system <NUM> further comprises a high-pressure hydraulic energy storage <NUM> connected to the high-pressure side <NUM>. In this example, the high-pressure hydraulic energy storage <NUM> is a hydraulic accumulator. The hydraulic energy handling system <NUM> of this example further comprises an optional low-pressure hydraulic energy storage <NUM>, also constituted by a hydraulic accumulator, connected to the low-pressure side <NUM>.

The hydraulic energy handling system <NUM> further comprises a hydraulic tank <NUM> and a return line <NUM> for conducting hydraulic fluid to the hydraulic tank <NUM>. Although two separate hydraulic tanks <NUM> are illustrated in <FIG>, these hydraulic tanks <NUM> may be a common tank.

The hydraulic energy handling system <NUM> further comprises a pressure relief valve <NUM>. The pressure relief valve <NUM> is connected between the high-pressure side <NUM> and the return line <NUM>. The pressure relief valve <NUM> is normally closed and is configured to automatically open when a set pressure in the high-pressure side <NUM> is reached. In this example, the pressure relief valve <NUM> is hydromechanical.

The hydraulic energy handling system <NUM> further comprises a hydraulic pump <NUM> and a hydraulic motor <NUM>. In this example, the hydraulic motor <NUM> is arranged to drive a fan <NUM> of the hydraulic energy handling system <NUM>. The hydraulic motor <NUM> comprises an inlet side <NUM> and an outlet side <NUM>. The hydraulic pump <NUM> is arranged to supply hydraulic fluid to the inlet side <NUM> of the hydraulic motor <NUM>. In the example in <FIG>, the hydraulic pump <NUM> is an auxiliary pump of the internal combustion engine <NUM>, driven by a further PTO of the internal combustion engine <NUM>. The hydraulic pump <NUM> may however be driven in alternative ways.

The hydraulic energy handling system <NUM> of this example further comprises a control valve arrangement <NUM>. The control valve arrangement <NUM> is configured to selectively connect the hydraulic machine <NUM> to the high-pressure side <NUM>. The control valve arrangement <NUM> is also configured to selectively connect the high-pressure side <NUM> to the low-pressure side <NUM>. The control valve arrangement <NUM> may be realized in various ways.

The control valve arrangement <NUM> may also be omitted. The hydraulic energy handling system <NUM> can for example operate without the ability to connect the high-pressure side <NUM> to the low-pressure side <NUM>.

The hydraulic energy handling system <NUM> further comprises a priority valve arrangement <NUM>. The priority valve arrangement <NUM> is connected to the outlet side <NUM> of the hydraulic motor <NUM>. The hydraulic motor <NUM> and the priority valve arrangement <NUM> are thus arranged in series. In the example in <FIG>, the outlet side <NUM> of the hydraulic motor <NUM> is directly connected to an inlet <NUM> of the priority valve arrangement <NUM>. One or more additional hydraulic consumers (not shown) may however be provided between the hydraulic motor <NUM> and the priority valve arrangement <NUM>.

The priority valve arrangement <NUM> is configured to direct a prioritized flow of hydraulic fluid to the low-pressure side <NUM>. The priority valve arrangement <NUM> is also configured to direct an excess flow of hydraulic fluid from the outlet side <NUM> of the hydraulic motor <NUM> to the return line <NUM>. To this end, the priority valve arrangement <NUM> comprises a priority flow outlet <NUM> connected to the low-pressure side <NUM>, and an excess flow outlet <NUM> connected to a bypass line <NUM>. The bypass line <NUM> is connected to the return line <NUM>, downstream of the pressure relief valve <NUM>. Thus, the priority valve arrangement <NUM> handles the distribution of flow of hydraulic fluid from the hydraulic motor <NUM> to either the low-pressure side <NUM> or the return line <NUM>.

A check valve <NUM> is provided on the bypass line <NUM> that only allows flow of hydraulic fluid towards the return line <NUM>. <FIG> further shows an oil cooler <NUM> provided on the return line <NUM>. Throughout the present disclosure, the hydraulic pump <NUM>, the hydraulic motor <NUM> and the priority valve arrangement <NUM> may be referred to as a supply system.

The hydraulic machine <NUM> is arranged to mechanically drive, and to be mechanically driven by, the mechanical driveline <NUM>. The hydraulic machine <NUM> may for example always be driven by rotation of the gearbox output shaft <NUM>. The discharge of hydraulic fluid from the hydraulic machine <NUM> can be varied by varying the displacement. As an alternative, the hydraulic machine <NUM> may be driven by (and drive) a shaft attached to the gearbox output shaft <NUM> via a planetary gear (not shown) and a clutch (not shown).

When storing energy from the mechanical driveline <NUM>, the hydraulic machine <NUM> operates as a pump and transforms mechanical power from the mechanical driveline <NUM> into pressurized hydraulic fluid which is fed to the high-pressure hydraulic energy storage <NUM> via the control valve arrangement <NUM>. This is for instance done when capturing braking energy from the working machine <NUM>.

When the hydraulic machine <NUM> operates to pump hydraulic fluid to the high-pressure side <NUM>, the first side <NUM> (in this case the suction side) of the hydraulic machine <NUM> needs a supply of pressurized hydraulic fluid. Some supply of pressurized hydraulic fluid to the hydraulic machine <NUM> may be provided by the optional low-pressure hydraulic energy storage <NUM>. Thus, when storing energy in the high-pressure hydraulic energy storage <NUM>, the low-pressure hydraulic energy storage <NUM> is emptied. When releasing the energy stored in high-pressure hydraulic energy storage <NUM>, the high-pressure hydraulic energy storage <NUM> is emptied and the hydraulic machine <NUM>, now operating as a hydraulic motor, transforms the hydraulic power to mechanical power to boost the mechanical driveline <NUM>. During this process, the low-pressure hydraulic energy storage <NUM> is refilled.

The pressure relief valve <NUM> is connected to the high-pressure side <NUM> to be used as a "retarder valve" in order to maintain braking torque on the mechanical driveline <NUM> when the high-pressure hydraulic energy storage <NUM> is full. That is, the pressure relief valve <NUM> is arranged to discharge excess hydraulic energy from the high-pressure side <NUM> to the return line <NUM> in order to provide a braking force on the mechanical driveline <NUM>.

As illustrated in <FIG>, the pressure relief valve <NUM> is connected between the high-pressure side <NUM> and the return line <NUM>. When a set pressure on the high-pressure side <NUM> is exceeded, the pressure relief valve <NUM> opens and discharges pressurized hydraulic fluid from the high-pressure side <NUM> to the return line <NUM>. The hydraulic fluid is thereby throttled through the pressure relief valve <NUM>. This throttling provides a braking force on the mechanical driveline <NUM>. The hydraulic energy handling system <NUM> can thereby maintain a braking torque even when the high-pressure hydraulic energy storage <NUM> is full by throttling a flow of hydraulic fluid through the pressure relief valve <NUM>. No additional software control is needed for this transition since the pressure relief valve <NUM> opens automatically when a certain pressure is reached.

One challenge with this type of retarder braking by means of the pressure relief valve <NUM> is that the hydraulic fluid leaves the hydraulic circuit comprising the high-pressure side <NUM> and the low-pressure side <NUM>, in contrast to being cycled back and forth between the high-pressure side <NUM> and the low-pressure side <NUM>. The hydraulic fluid is also heated when passing the pressure relief valve <NUM>. The hydraulic machine <NUM> therefore needs to be supplied with cool pressurized fluid to the first side <NUM> (in this case the suction side) during the retarder braking, at least when the optional low-pressure hydraulic energy storage <NUM> is emptied. During retarder braking by means of the pressure relief valve <NUM>, the priority valve arrangement <NUM>, which is connected in series with the hydraulic motor <NUM>, feeds the hydraulic machine <NUM> with cool pressurized hydraulic fluid to the first side <NUM>. When the pressure on the low-pressure side <NUM> increases after the pressure relief valve <NUM> is closed and the hydraulic machine <NUM> has stopped pumping, the priority valve arrangement <NUM> guides hydraulic fluid from the hydraulic motor <NUM> to the return line <NUM>, in this example via the bypass line <NUM>.

The hydraulic pump <NUM> can be used as a supply pump for the hydraulic energy handling system <NUM> without compromising the functionality of the fan <NUM>. Since the already existing hydraulic pump <NUM> is used not only to drive the hydraulic motor <NUM> for the fan <NUM>, but also to supply pressurized hydraulic fluid to the low-pressure side <NUM>, costs associated with components that would otherwise be dedicated to this supply can be reduced, or avoided. Furthermore, the arrangement of the hydraulic motor <NUM> and the priority valve arrangement <NUM> in series allows the fan <NUM> to be operated at full speed even when a maximum supply flow of hydraulic fluid is required by the hydraulic machine <NUM>.

In <FIG>, the hydraulic motor <NUM> is arranged to drive the fan <NUM>. However, a hydraulic motor according to the present invention, i.e. arranged in series with the priority valve arrangement <NUM>, may be constituted by an alternative hydraulic motor of the working machine <NUM>, such as a hydraulic motor for axle oil cooling, differential lock actuation, lubrication etc..

<FIG> is a block diagram of a priority valve arrangement <NUM> according to an embodiment of the invention. In this embodiment, the priority valve arrangement <NUM> is a hydromechanical priority valve.

As long as the set pressure on the low-pressure side <NUM> is below a threshold value, the inlet <NUM> is in fluid communication with the priority flow outlet <NUM> and hydraulic fluid is guided from the outlet side <NUM> of the hydraulic motor <NUM> to the low-pressure side <NUM>. When the set pressure on the low-pressure side <NUM> exceeds the threshold value, the inlet <NUM> is brought in fluid communication with the excess flow outlet <NUM> and hydraulic fluid is guided from the outlet side <NUM> of the hydraulic motor <NUM> to the bypass line <NUM>. The priority valve arrangement <NUM> is thereby configured to reduce the supply pressure of the hydraulic fluid on the low-pressure side <NUM> to a suitable level required by the hydraulic machine <NUM>, and to direct the flow of hydraulic fluid to the bypass line <NUM> when this pressure level is reached. The priority valve arrangement <NUM> can be implemented without software control, and is consequently simpler and cheaper.

The priority valve arrangement <NUM> in <FIG> is merely one of several possible implementations of a priority valve arrangement <NUM> according to the present invention. Alternative types of priority valve arrangements <NUM> that also do not require software control are possible.

<FIG> is a block diagram of a hydraulic parallel hybrid driveline <NUM> comprising a mechanical driveline <NUM> and a further hydraulic energy handling system <NUM> according to an embodiment of the invention. Mainly differences with respect to the embodiment in <FIG> will be described.

The hydraulic energy handling system <NUM> of this embodiment further comprises an anti-cavitation valve <NUM>. The anti-cavitation valve <NUM> is arranged on a line <NUM> between the high-pressure side <NUM> and the low-pressure side <NUM>. The anti-cavitation valve <NUM> is configured to allow hydraulic fluid to flow from the high-pressure side <NUM> to the low-pressure side <NUM> when a hydraulic pressure on the low-pressure side <NUM> falls below a cavitation threshold value.

When the pressure relief valve <NUM> is used as a retarder valve, e.g. during braking of the working machine <NUM>, and the pressure on the low-pressure side <NUM> becomes critically low, the anti-cavitation valve <NUM> opens such that hydraulic fluid is guided from the high-pressure side <NUM> to the low-pressure side <NUM>. The reason for this pressure drop on the low-pressure side <NUM>, despite the hydraulic motor <NUM> and the priority valve arrangement <NUM>, may be that the pressure relief valve <NUM> is used for retarder braking during a long time, e.g. during a long downhill slope, and/or that the flow from the hydraulic pump <NUM> is limited and cannot supply the same amount of hydraulic fluid as is pumped by the hydraulic machine <NUM>. If such pressure drop on the low-pressure side <NUM> happens, the anti-cavitation valve <NUM> will open and a part of the flow of hydraulic fluid on the high-pressure side <NUM> will be circulated directly to the low-pressure side <NUM>.

<FIG> further shows the positioning of two additional optional hydraulic consumers <NUM>, <NUM> that can be fed with hydraulic fluid by the hydraulic energy handling system <NUM>. One hydraulic consumer <NUM> is positioned on the outlet side <NUM> of the hydraulic motor <NUM>, i.e. between the hydraulic motor <NUM> and the priority valve arrangement <NUM>. One hydraulic consumer <NUM> is positioned on the return line <NUM>, upstream of the oil cooler <NUM>.

Claim 1:
A hydraulic energy handling system (<NUM>) for a working machine (<NUM>), the hydraulic energy handling system (<NUM>) comprising:
a high-pressure side (<NUM>);
a low-pressure side (<NUM>);
a hydraulic machine (<NUM>) for mechanically driving a mechanical driveline (<NUM>) of the working machine (<NUM>), and for being mechanically driven by the mechanical driveline (<NUM>) to pump hydraulic fluid from the low-pressure side (<NUM>) to the high-pressure side (<NUM>);
at least one high-pressure hydraulic energy storage (<NUM>) connected to the high-pressure side (<NUM>);
a hydraulic motor (<NUM>) having an inlet side (<NUM>) and an outlet side (<NUM>);
a hydraulic pump (<NUM>) arranged to supply hydraulic fluid to the inlet side (<NUM>) of the hydraulic motor (<NUM>);
a return line (<NUM>) for conducting hydraulic fluid to a hydraulic tank (<NUM>); and
a pressure relief valve (<NUM>) connected between the high-pressure side (<NUM>) and the return line (<NUM>), the pressure relief valve (<NUM>) being arranged to discharge excess hydraulic energy from the high-pressure side (<NUM>) to the return line (<NUM>) in order to provide a braking force on the mechanical driveline (<NUM>);
characterized in that the hydraulic energy handling system (<NUM>) further comprises:
a priority valve arrangement (<NUM>) connected to the outlet side (<NUM>) of the hydraulic motor (<NUM>), the priority valve arrangement (<NUM>) being configured to direct a prioritized flow of hydraulic fluid to the low-pressure side (<NUM>).