Powerboost hub

Abstract

A series hydraulic hybrid system for a vehicle is described. The hydraulic hybrid system has a hydraulic circuit and a high pressure accumulator. The hydraulic circuit has a first hydraulic displacement unit in fluid communication with a second hydraulic displacement unit. The high pressure hydraulic accumulator is in fluid communication with the hydraulic circuit and a low pressure hydraulic accumulator in fluid communication with the hydraulic circuit. The high pressure hydraulic accumulator is in fluid communication with the hydraulic circuit through a proportional flow control valve. The proportional flow control valve is adapted to continuously vary a flow of hydraulic fluid between the high pressure hydraulic accumulator and the hydraulic circuit.

Claims

1. A series hydraulic hybrid system for a vehicle, comprising: a hydraulic circuit comprising a first hydraulic displacement unit in fluid communication with a second hydraulic displacement unit through a first main fluid line and through a second main fluid line; and a high pressure hydraulic accumulator in fluid communication with the hydraulic circuit and a low pressure hydraulic accumulator in fluid communication with the hydraulic circuit; a first pressure-actuatable shut-off valve selectively fluidly connecting the high pressure hydraulic accumulator with the first main fluid line; a second pressure-actuatable shut-off valve selectively fluidly connecting the high pressure hydraulic accumulator with the second main fluid line; a pressure actuatable proportional flow control valve fluidly connecting the high pressure hydraulic accumulator with the hydraulic circuit; and a pilot fluid line for piloting the first pressure-actuatable shut-off valve, the second pressure-actuatable shut-off valve and the pressure actuatable proportional flow control valve via the pilot fluid line.

2. The series hydraulic hybrid system of claim 1, wherein the low pressure hydraulic accumulator is selectively fluidly connected with the first main fluid line through a third shut-off valve and with the second main fluid line through a fourth shut-off valve.

3. The series hydraulic hybrid system of claim 2, wherein the third shut-off valve and the fourth shut-off valve are cartridge valves adapted to be actuated by a hydraulic pi of pressure applied to the third shut-off valve and to the fourth shut-off valve via the pilot fluid line.

4. The series hydraulic hybrid system of claim 2, further comprising isolation valves for selectively fluidly disconnecting the first hydraulic displacement unit from the second hydraulic displacement unit and from the first, second, third, and fourth shut-off valves.

5. The series hydraulic hybrid system of claim 4, further comprising a by-pass valve adapted to selectively directly fluidly connect a first fluid port of the first hydraulic displacement unit to a second fluid port of the first hydraulic displacement unit.

6. The series hydraulic hybrid system of claim 1, wherein the high pressure hydraulic accumulator is selectively fluidly connected with the first shut-off valve and with the second shut-off valve through the proportional flow control valve.

7. The series hydraulic hybrid system of claim 1, wherein the first shut-off valve and the second shut-off valve are cartridge valves.

8. The series hydraulic hybrid system of claim 1, wherein the pilot fluid line is in fluid communication with the high pressure shut hydraulic accumulator through a first check valve, with the low pressure hydraulic accumulator through a second check valve, with the first main fluid line through a third check valve and with the second main fluid line through a fourth check valve, such that the hydraulic pilot pressure in the pilot fluid line is at least equal to the maximum system pressure.

9. The series hydraulic hybrid system of claim 8, wherein the first check valve is configured to allow a flow of fluid from the high pressure accumulator to the pilot fluid line through the first check valve and to block a flow of fluid from the pilot fluid line to the high pressure accumulator through the first check valve; wherein the second check valve may is configured to allow a flow of fluid from the low pressure accumulator to the pilot fluid line through the second check valve and to block a flow of fluid from the pilot fluid line to the low pressure accumulator through the second check valve; wherein the third check valve is configured adapted to allow a flow of fluid from the first main fluid line to the pilot fluid line through the third check valve and to block a flow of fluid from the pilot fluid line to the first main fluid line through the third check valve; and wherein the fourth check valve is configured to allow a flow of fluid from the second main fluid line to the pilot fluid line through the fourth check valve and to block a flow of fluid from the pilot fluid line to the second main fluid line through the fourth check valve.

10. The series hydraulic hybrid system of claim 1, wherein the proportional flow control valve is adapted to be actuated by a hydraulic pilot pressure provided to the proportional flow control valve through the pilot fluid line via a pressure-reducing valve.

11. The series hydraulic hybrid system of claim 1, further comprising a pressure relief valve in fluid communication with the high pressure hydraulic accumulator.

12. The series hydraulic hybrid system of claim 1, further comprising a pressure relief valve in fluid communication with the low pressure hydraulic accumulator.

13. The series hydraulic hybrid system of claim 1, further comprising an electric relief valve in fluid communication with the high pressure hydraulic accumulator for selectively draining the high pressure hydraulic accumulator when the vehicle is shut down.

14. The series hydraulic hybrid system of claim 1, further comprising an electric relief valve in fluid communication with the low pressure hydraulic accumulator for selectively draining the low pressure hydraulic accumulator when the vehicle is shut down.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the presently proposed system are described in the following detailed description and are depicted in the accompanying drawing in which:

(2) FIG. 1 shows a series hydraulic hybrid system including a hydraulic circuit comprised of a hydrostatic pump in fluid communication with a hydrostatic motor, and hydraulic accumulators selectively fluidly connected to the hydraulic circuit through a powerboost hub;

(3) FIG. 2 shows a hydraulic circuit diagram of a first embodiment of the powerboost hub of FIG. 1;

(4) FIG. 3 shows a hydraulic circuit diagram of a second embodiment of the powerboost hub of FIG. 1;

(5) FIG. 4 shows a detail of the circuit diagram of FIG. 2 including a cartridge selectively fluidly connecting a high pressure hydraulic accumulator to the hydraulic circuit;

(6) FIG. 5 shows a further detail of the circuit diagram of FIG. 2 including a proportional flow control selectively fluidly connecting the high pressure hydraulic accumulator to the cartridge valve of FIG. 4;

(7) FIG. 6 shows a further detail of the circuit diagram of FIG. 2 including pressure relief valves and electronic relief valves; and

(8) FIG. 7 shows a further detail of the circuit diagram of FIG. 2 including isolation valves for selectively fluidly isolating the hydrostatic pump from the hydraulic accumulators and from the hydrostatic motor.

DETAILED DESCRIPTION OF THE INVENTION

(9) FIG. 1 shows a series hydraulic hybrid system 1 arranged in an off-highway vehicle. The system 1 includes a hydraulic pump 2 which is in fluid communication with a hydraulic motor 3. The pump 2 is drivingly engaged with an internal combustion engine (ICE) 4. The motor 3, on the other hand, is drivingly engaged with a vehicle output 5. The vehicle output 5 may include at least one of a drive shaft, a final drive, a vehicle axle, and one or more wheels, for example. The pump 2 may be a hydrostatic axial piston pump having a movable swashplate, and the motor 3 may be a hydrostatic axial piston motor in bent-axis design or having a movable swashplate, for example.

(10) The pump 2 and the motor 3 are in fluid communication with each other through a first main fluid line 6, a second main fluid line 7, and through a powerboost hub 8. The hub 8 is a mechatronic unit comprising a plurality of fluid lines, valves and electric actuators. The hub 8 is configured to selectively fluidly connect the pump 2 and the motor 3 through the main fluid lines 6 and 7 to form a closed hydrostatic circuit 9.

(11) Specifically, the pump 2 has a first fluid port 2a and a second fluid port 2b. The motor 3 has a first fluid port 3a and a second fluid port 3b. The hub 8 has fluid ports 8a, 8b, 8c, and 8d. A section 6a of the first main fluid line 6 fluidly connects the fluid port 2a of the pump 2 to the fluid port 8a of the hub 8. A section 6b of the first main fluid line 6 fluidly connects the fluid port 8b of the hub 8 to the fluid port 3a of the motor 3. A section 7a of the second main fluid line 7 fluidly connects the fluid port 2b of the pump 2 to the fluid port 8c of the hub 8. A section 7b of the second main fluid line 7 fluidly connects the fluid port 8d of the hub 8 to the fluid port 3b of the motor 3.

(12) The system 1 further includes a high pressure bladder accumulator 10 and a low pressure bladder accumulator 11. A fluid port 10a of the high pressure accumulator 10 is fluidly connected to a fluid port 8e of the hub 8 through a fluid pipe 12. A fluid port 11a of the low pressure accumulator 11 is fluidly connected to a fluid port 8f of the hub 8 through a fluid pipe 13. The accumulators 10 and 11 are in fluid communication with the hydrostatic circuit 9 through the hub 8. In other words, the hub 8 is configured to selectively fluidly disconnect the accumulators 10, 11 from the hydrostatic circuit 9 and to selectively fluidly connect the accumulators 10, 11 to the hydrostatic circuit 9. Specifically, the hub 8 is configured to selectively fluidly connect the high pressure accumulator 10 to the first main fluid line 6 or to the second main fluid line 7. Also, the hub 8 is configured to selectively fluidly connect the low pressure accumulator 11 to the first main fluid line 6 or to the second main fluid line 7.

(13) The system 1 may be operated in a hydrostatic mode. In the hydrostatic mode, the hub 8 fluidly disconnects the accumulators 10, 11 from the hydrostatic circuit 9. Further, in the hydrostatic mode the hub 8 fluidly connects the fluid port 2a of the pump 2 to the fluid port 3a of the motor 3 through the first main fluid line 6, and fluidly connects the fluid port 2b of the pump 2 to the fluid port 3b of the motor 3 through the second main fluid line 7. In the hydrostatic mode, mechanical energy may be transmitted from the ICE 4 to the vehicle output 5 through the hydrostatic circuit 9.

(14) The system 1 may further be operated in one or more hybrid modes by fluidly connecting the accumulators 10, 11 to the hydrostatic circuit 9 through the hub 8.

(15) In one hybrid mode, the hub 8 fluidly connects the high pressure accumulator 10 to the first main fluid line 6 and fluidly connects the low pressure accumulator 11 to the second main fluid line 7. The ICE 4 may then drive the pump 2 to displace hydraulic fluid from the low pressure accumulator 11 to the high pressure accumulator 10, thereby increasing a hydraulic pressure in the high pressure accumulator 10 and decreasing a hydraulic pressure in the low pressure accumulator 11 (energy accumulation).

(16) In another hybrid mode, the hub 8 may fluidly connect the accumulators 10, 11 to the fluid ports 3a, 3b of the motor 3, respectively, such that the motor 3 may absorb kinetic energy from the vehicle output 5 and use the absorbed kinetic energy to displace hydraulic fluid from the low pressure accumulator 11 to the high pressure accumulator 10, thereby increasing a hydraulic pressure in the high pressure accumulator 10 and decreasing a hydraulic pressure in the low pressure accumulator 11 (regenerative braking). The hub 8 may be configured to fluidly connect the accumulators 10, 11 to the fluid ports 3a, 3b of the motor 3 to perform regenerative braking during both forward and rearward movement of the vehicle. The hub 8 may further be configured to fluidly disconnect the pump 2 from the motor 3 and from the accumulators 10, 11 during regenerative braking.

(17) In another hybrid mode, the hub 8 may fluidly connect the accumulators 10, 11 to the fluid ports 3a, 3b of the motor 3 in such a way that hydraulic fluid is displaced from the high pressure accumulator 10 to the low pressure accumulator 11 through the motor 3 to drive the motor 3, thereby decreasing a hydraulic pressure in the high pressure accumulator 10 and increasing a hydraulic pressure in the low pressure accumulator 11 (boosting). In this manner, hydraulic energy stored in the accumulators 10, 11 may be transmitted to the vehicle output 5 to drive the vehicle. The hub 8 may be configured to fluidly connect the accumulators 10, 11 to the fluid ports 3a, 3b of the motor 3 such that the boosting operation may be performed during both forward and rearward movement of the vehicle.

(18) In another hybrid mode, the hub 8 may fluidly connect the accumulators 10, 11 to the fluid ports 2a, 2b of the pump 2 such that hydraulic fluid may be displaced from the high pressure accumulator 10 to the low pressure accumulator 11 through the pump 2 to drive the pump 2 and to start the engine 4.

(19) FIG. 2 shows a hydraulic circuit diagram of the powerboost hub 8 shown in FIG. 1. Here and in the following, recurring features are designated by the same reference signs. In order to increase the readability of the circuit diagrams of FIG. 2 seq., crossing fluid lines that are fluidly connected to each other at a given crossing are explicitly marked with a dot at this crossing. Crossing fluid lines whose crossing is not marked with a dot are not fluidly connected to each other at this crossing.

(20) The hub 8 in FIG. 2 comprises a section 6c of the first main fluid line 6. The section 6c provides fluid communication between the fluid ports 8a and 8b of the hub 8. Furthermore, the hub 8 comprises a section 7c of the second main fluid line 7. The section 7c provides fluid communication between the fluid ports 8c and 8d of the hub 8. As shown in FIG. 1, the fluid ports 8a, 8c of the hub 8 are fluidly connected to the pump 2, and the fluid ports 8b, 8d of the hub 8 are fluidly connected to the motor 3. Further, as shown in FIG. 1, the fluid port 8e of the hub 8 in FIG. 2 is fluidly connected to the high pressure accumulator 10, and the fluid port 8f of the hub 8 in FIG. 2 is fluidly connected to the low pressure accumulator 11. FIG. 2 shows a plurality of further fluid ports of the hub which are not designated by reference signs. These are mere measuring ports who are of no particular relevance to the functionality of the hub 8.

(21) The high pressure accumulator 10 is in fluid communication with the section 6c of the first main fluid line 6 through the fluid port 8e of the hub 8, a fluid line 20, a proportional flow control valve 500, a fluid line 21, a first shut-off valve 100, and a fluid line 22. The high pressure accumulator 10 may be fluidly connected to the first main fluid line 6 by opening the proportional flow control valve 500 and by opening the first shut-off valve 100. The high pressure accumulator 10 may be fluidly disconnected from the first main fluid line 6 by closing the first shut-off valve 100. The proportional flow control valve 500 may additionally be closed to fluidly disconnect the high pressure accumulator 10 from the first main fluid line 6.

(22) The high pressure accumulator 10 is in fluid communication with the section 7c of the second main fluid line 7 through the fluid port 8e of the hub 8, the fluid line 20, the proportional flow control valve 500, the fluid line 21, a second shut-off valve 200, and a fluid line 23. The high pressure accumulator 10 may be fluidly connected to the second main fluid line 7 by opening the proportional flow control valve 500 and by opening the second shut-off valve 200. The high pressure accumulator 10 may be fluidly disconnected from the second main fluid line 7 by closing the second shut-off valve 200. The proportional flow control valve 500 may additionally be closed to fluidly disconnect the high pressure accumulator 10 from the second main fluid line 7.

(23) The low pressure accumulator 11 is in fluid communication with the section 6c of the first main fluid line 6 through the fluid port 8f of the hub 8, a fluid line 30, a third shut-off valve 300, and a fluid line 31. The low pressure accumulator 11 may be fluidly connected to the first main fluid line 6 by opening the third shut-off valve 300. The low pressure accumulator 11 may be fluidly disconnected from the first main fluid line 6 by closing the third shut-off valve 300.

(24) The low pressure accumulator 11 is in fluid communication with the section 7c of the second main fluid line 7 through the fluid port 8f of the hub 8, the fluid line 30, a fourth shut-off valve 400 and a fluid line 32. The low pressure accumulator 11 may be fluidly connected to the second main fluid line 7 by opening the fourth shut-off valve 400. The low pressure accumulator 11 may be fluidly disconnected from the second main fluid line 7 by closing the fourth shut-off valve 400.

(25) The high pressure accumulator 10 is selectively fluidly connected to the shut-off valves 100, 200 through the proportional flow control valve 500. That is, the proportional flow control valve 500 is positioned between the high pressure accumulator 10 and the first shut-off valve 100. The proportional flow control valve 500 and the first shut-off valve 100 are arranged in series between the high pressure accumulator 10 and the first main fluid line 6. That is, hydraulic fluid flowing from the high pressure accumulator 10 to the first main fluid line 6 through the proportional flow control valve 500 and the first shut-off valve 100 first passes through the proportional flow control valve 500 and only subsequently passes through the first shut-off valve 100. Similarly, the proportional flow control valve 500 is positioned between the high pressure accumulator 10 and the second shut-off valve 200. The proportional flow control valve 500 and the second shut-off valve 200 are arranged in series between the high pressure accumulator 10 and the second main fluid line 7. That is, hydraulic fluid flowing from the high pressure accumulator 10 to the second main fluid line 7 through the proportional flow control valve 500 and through the second shut-off valve 200 first passes through the proportional flow control valve 500 and only subsequently passes through the second shut-off valve 200.

(26) The proportional flow control valve 500 may be actuated to continuously vary a flow of fluid through the proportional flow control valve 500. For example, the proportional flow control valve 500 may have a continuously variable cross-section through which hydraulic fluid may pass through the valve 500. The cross-section of the valve 500 may be varied by varying the position of a valve piston or valve spool 530. The position of the piston or spool 530 of the valve 500 may be controlled by applying a hydraulic pilot pressure to the piston or spool 530, as will be explained in further detail below with reference to FIG. 5, which shows a detailed view of the proportional flow control valve 500.

(27) The shut-off valves 100, 200, 300, 400 are configured as identical cartridge valves with theoretically zero leakage. The shut-off valves 100, 200, 300, 400 each comprise a seated conically shaped cartridge respectively designated by 130, 230, 330, 430 and a closing spring respectively designated by 180, 280, 380, 480 forcing the cartridge into the closed position (see FIG. 4).

(28) As an example of the identical shut-off valves 100, 200, 300, 400, the first shut-off valve 100 is shown in detail in FIG. 4. The valve 100 has a ring-shaped first fluid port 100a and a second fluid port 100b. The cartridge valve 100 is adapted to be piloted by applying a hydraulic pilot pressure to a top surface 140 of the cartridge 130. The top surface 140 is larger than the sum of further surfaces 150 and 160 on a bottom side of the cartridge 130. Through the first fluid port 100a and through the second fluid port 100b an opening force may be applied onto the surfaces 150 and 160 to force the cartridge 130 into the open position. In the closed position, the cartridge 130 blocks a flow of fluid between the fluid ports 100a and 100b. In the open position, the cartridge 130 allows a flow of fluid between the fluid ports 100a and 100b.

(29) The hydraulic pilot pressure for piloting the first shut-off valve 100 is provided by a pilot fluid line 600 (see FIGS. 2 and 4). The pilot fluid line 600 is selectively fluidly connected to an actuation chamber 170 of the shut-off valve 100 through a 3/2-way pilot valve 110 and a fluid line 120. The pilot valve 110 has two spool positions 110a and 110b. When switched to the first spool position 110a, the pilot valve 110 fluidly connects the pilot fluid line 600 to the actuation chamber 170 so that the pilot pressure in the pilot fluid line 600 is applied to the top surface 140 of the cartridge 130 through the actuation chamber 170.

(30) As will be explained in more detail below, the pilot pressure in the pilot fluid line 600 is regulated such that the cartridge 130 is forced into the closed position when the pilot valve 110 is switched to the first spool position 110a. When switched to the second spool position 110b, the pilot valve 110 fluidly connects the actuation chamber 170 of the shut-off valve 100 to a low pressure drain line 700. The drain line 700 may be fluidly connected to a fluid tank at atmospheric pressure, for example.

(31) When the pilot valve 110 is actuated to be switched to the second spool position 110b, the hydraulic pressure acting on the cartridge 130 through the fluid ports 100a, 100b may force the cartridge 130 into the open position.

(32) The cartridges 230, 330, 430 of the shut-off valves 200, 300, 400 are piloted in the same manner as the cartridge 130 of the first shut-off valve 100. That is, the shut-off valves 200, 300, 400 are associated with corresponding 3/2-way pilot valves 210, 310, 410, which selectively fluidly connect actuation chambers 270, 370, 470 of the shut-off valves 200, 300, 400 to the pilot fluid line 600 or to the low pressure drain line 700. The pilot valves 110, 210, 310, 410 for piloting the shut-off valves 100, 200, 300, 400 may be independently electrically controlled. In other words, the shut-off valves 100, 200, 300, 400 may be controlled independently.

(33) The hub 8 further comprises check valves 610, 620, 630, 640, 650, 660 (see FIG. 2) which provide fluid communication between the accumulators 10, 11 and the main fluid lines 6, 7 on the one hand and the pilot fluid line 600 on the other hand in such a way that the pilot pressure in the pilot fluid line 600 is at least equal to the highest system pressure. The highest system pressure is the highest hydraulic pressure of the hydraulic pressures in the accumulators 10, 11 and in the main fluid lines 6, 7. This ensures that the pilot pressure in the pilot fluid line 600 is at all times large enough to securely close the shut-off valves 100, 200, 300, 400, if desired. The check valves 630, 660 are merely optional in the arrangement shown in FIG. 2.

(34) Specifically, the pilot fluid line 600 is in fluid communication with the high pressure accumulator 10 through the fluid port 8e of the hub 8, the fluid line 20, and the check valves 610 and 630. The check valves 610, 630 allow a flow of fluid from the high pressure accumulator 10 to the pilot fluid line 600 and block a flow of fluid from the pilot fluid line 600 to the high pressure accumulator 10.

(35) The pilot fluid line 600 is in fluid communication with the low pressure accumulator 11 through the fluid port 8f of the hub 8, the fluid line 30, and the check valves 620 and 630. The check valves 620, 630 allow a flow of fluid from the low pressure accumulator 11 to the pilot fluid line 600 and block a flow of fluid from the pilot fluid line to the low pressure accumulator 11.

(36) The pilot fluid line 600 is in fluid communication with the first main fluid line 6 through the fluid line 31 and the check valves 650 and 660. The check valves 650, 660 allow a flow of fluid from the first main fluid line 6 to the pilot fluid line 600 and block a flow of fluid from the pilot fluid line 600 to the first main fluid line 6.

(37) The pilot fluid line 600 is in fluid communication with the second main fluid line 7 through the fluid line 23 and the check valves 640 and 660. The check valves 640, 660 allow a flow of fluid from the second main fluid line 7 to the pilot fluid line 600 and block a flow of fluid from the pilot fluid line 600 to the second main fluid line 7.

(38) In an alternative embodiment not explicitly depicted here the pilot pressure for piloting the shut-off valves 100, 200, 300, 400 is not provided by the pilot fluid line 600. Rather, in this alternative embodiment each of the shut-off valves 100, 200, 300, 400 is equipped with at least two check valves. Each of these two check valves provides fluid communication between one of the fluid ports of the shut-off valve and the actuation chamber of the shut-off valve. For example, with regard to the first shut-off valve 100 shown in FIG. 4, the first of the two check valves associated with the shut-off valve 100 according to this alternative embodiment provides fluid communication between the first fluid port 100a and the actuation chamber 170, and the second of the two check valves associated with the shut-off valve 100 according to this alternative embodiment provides fluid communication between the second fluid port 100b and the actuation chamber 170. The first check valve is then adapted to allow a flow of fluid from the first fluid port 100a to the actuation chamber 170 and to block a flow of fluid from the actuation chamber 170 to the first fluid port 100a. Similarly, the second check valve is then adapted to allow a flow of fluid from the second fluid port 100b to the actuation chamber 170 and to block a flow of fluid from the actuation chamber 170 to the second fluid port 100b. According to this alternative embodiment, each of the further shut-off valves 200, 300, 400 may be equipped with corresponding first and second check valves in the same manner. The two check valves associated with a given shut-off valve according to the above described alternative embodiment ensure that the highest hydraulic pressure acting on the shut-off valve through the fluid ports of that shut-off valve is used for piloting that shut-off valve, thereby guaranteeing a leak-free closure. In this alternative embodiment, the pilot bore of the shut-off valve is preferably associated with an additional on-off pilot valve that allows selective application of the pilot pressure to the actuation chamber.

(39) Back to the embodiment shown in FIG. 2, the pilot fluid line 600 further provides a pilot pressure for piloting the proportional flow control valve 500. This pilot pressure may be selectively applied to the spool 530 of the proportional flow control valve 500 through an actuation chamber (not shown) of the proportional flow control valve 500. This Actuation chamber of the proportional flow control valve 500 may be selectively fluidly connected to the pilot fluid line 600 or to the drain line 700 through a proportional 3/2-way pilot valve 510.

(40) FIG. 5 shows a detailed view of the proportional flow control valve. When switched to a first spool position 510a, the pilot valve 510 fluidly connects the drain line 700 to the actuation chamber of the proportional flow control valve 500, wherein a flow of fluid through the pilot valve 510 may be continuously varied. When switched to a second spool position 510b, the pilot valve 510 provides fluid communication between the actuation chamber of the proportional flow control valve 500 and the pilot fluid line 600, wherein a flow of fluid through the pilot valve 510 may be continuously varied. When the pilot valve 510 is switched to the second spool position 510b, the actuation chamber of the proportional flow control valve 500 is in fluid communication with the pilot fluid line 600 through a pressure-reducing valve 520. The pressure-reducing valve 520 reduces the pilot pressure in the pilot fluid line 600 to a suitable pilot pressure for piloting the spool 530 of the proportional flow control valve 500.

(41) As shown in FIGS. 2 and 6, the hub 8 further comprises a first pressure relief valve 50 and a first electric relief valve 51 providing fluid communication between the fluid port 8e of the hub 8 and a relief line 800 which is fluidly connected to a fluid tank at atmospheric pressure (not shown). The pressure relief valve 50 prevents a hydraulic pressure in the high pressure accumulator 10 from exceeding a first threshold pressure above which the high pressure accumulator 10 may be damaged. The electric relief valve 51 may be used to selectively drain hydraulic fluid from the high pressure accumulator 10 to the fluid tank, for example when the vehicle is shut down.

(42) The hub 8 further comprises a second pressure relief valve 60 and a second electric relief valve 61 providing fluid communication between the fluid port 8f and the relief line 800. Like the corresponding valves 50, 51 the valves 60, 61 are configured to limit a hydraulic pressure in the low pressure accumulator 11 to a second threshold pressure and to selectively drain hydraulic fluid from the low pressure accumulator 11 to the fluid tank, respectively.

(43) As shown in FIGS. 2 and 7, the hub 8 further comprises 2/2-way isolation valves 40, 41 and a 2/2-way bypass valve 42. The valves 40, 41, 42 may be configured as cartridge valves with theoretically zero leakage, just like the shut-off valves 100, 200, 300, 400. The isolation valves 40, 41 are configured to selectively fluidly disconnect or isolate the pump 2 from the motor 3 and from the accumulators 10, 11. This may be useful during regenerative braking, for example. When isolating the pump 2 in this manner by closing the isolation valves 40, 41, the bypass valve 42 may be opened, thereby directly fluidly connecting the fluid ports 2a, 2b of the pump 2 to each other (see FIG. 1). This may be useful to avoid cavitation in the pump 2 when isolating the pump 2 from the motor 3 and from the accumulators 10, 11.

(44) The powerboost hub 8 shown in FIGS. 1-7 is configured as a single block or manifold which the various components of the hub 8 shown in FIGS. 2-7 are integrated in.

(45) An alternative embodiment of the hub 8 of FIG. 2 and FIGS. 4-7 is the powerboost hub 8 shown in FIG. 3. The various components of the hub 8 are integrated in a modular design, where each component is integrated in one modular block. The custom made modular blocks of the hub 8 are then bolted together to form the hub 8. The functionality of the components of the hub 8 and their mutual fluid connection is identical to that of the corresponding components shown in FIG. 2 and FIGS. 4-7. The modular hub 8 is compact, enables series production of components and introduces extra flexibility. The flexibility enables the possibility to easily add or remove functions and allows easy maintenance or replacement of a single component.

(46) The design for the powerboost hub 8, 8 is capable of being operated in two operating modes (using the HT and operation as the SHS described above) and in a transition mode from one mode to the other. Particularly, the powerboost hub 8, 8 is able to perform the following: In the HT mode, the accumulators need to be disconnected from the hydraulic circuit. In the SHS mode, the accumulators need to be connected to the hydraulic circuit. During the transition mode from HT to SHS mode and vice versa, the transition needs to happen in a predefined, controllable manner.

(47) Components of the powerboost hub 8, 8 must also be able to meet the following criteria: Economical, for example, able to be produced in a cost effective manner. Able to resist high pressures and also allowing high flow rates, for example, such properties are important for sizing and actuation purposes. Able to be effectively controlled, for example, components that have a fast response time. Capable of high efficiency operation, for example, leak free and low pressure drop operation.

(48) Such requirements raise several issues, which are addressed by the powerboost hub 8, 8. The issues are listed here below: No availability of commercial off-the-shelf components which resist high pressure (450 bar) and permit high flow (400 l/min). Connect or disconnect particular accumulators (accumulator 10 or accumulator 11) to particular side of Hystat. Control of transient phase/prevent shock effect, during connection and disconnection of high pressure accumulators to/from the hydrostatic circuit. Prevent excessive pressure in the accumulators. While connected to the Hystat, accumulator 10 can leak via pump, even with pump on zero displacement.

(49) A solution for connection and disconnection of accumulators to the hydraulic circuit is given by the powerboost hub 8, 8. The powerboost hub 8, 8 is a mechatronic unit that comprises a plurality of hydraulic valves and electronic actuation devices. The powerboost hub 8, 8 can be positioned in two different manners: The normal representation is positioning the powerboost hub between a hydrostatic pump, one or more hydrostatic motors, and a pair of accumulators (see FIG. 1). Alternatively it can be represented as being positioned between the hydraulic circuit and the pair of accumulators. This solution is not followed in this invention as it disables the use of particular functions.

(50) The possible solutions S1.1 through S5.2 below are related to the issues listed above and are described in further detail here below: S1.1 Customized manifold containing all the components. S1.2 Customized modular blocks bolted together. S2.1 Shut-off valves for each system location: accumulator 10line 6, accumulator 10line 7, accumulator 11line 6, accumulator 11line 7. S2.2 Cartridge valves with theoretical zero leakage are used as shut-off valves. S2.3 A minimum of 4 check valves put the highest system pressure on the pilot line. This pilot pressure feeds all cartridge valves in the Hub. S3.1 A proportional valve in between accumulator 10 and the accumulator 10 shut-off valves. S3.2 A proportional valve in between accumulator 10 and the accumulator 10 shut-off valves with additionally a by-pass valve for one direction usage. S3.3 A minimum of 4 check valves put the highest system pressure on the pilot line. Pilot pressure for the proportional valve is provided by reducing the highest system pressure on the pilot line. S3.4 Accurate control of displacement of hydro motors. S4.1 Pressure relief valves integrated at the accumulator connection ports. S4.2 Electric relief valves integrated at the accumulator connection ports. S5.1 Isolation valves between Hub and Hystat Pump, integrated in Hub. Isolation valves are implemented as previously mentioned cartridge valves. S5.2 Isolation valves between Hub and Hystat Pump, integrated in Hub. Additional by-pass valve integrated in Hub in between isolation valves allow immediate use of isolation valves without pump cavitation. Isolation valves and by-pass valve are implemented as previously mentioned cartridge valves.

(51) S1.1Customized components are required that combine a high maximum working pressure with a high maximum flow rate. Ail the separate components can be integrated in a single manifold, which serves as the second powerboost hub (see FIG. 2). The manifold is a compact design compared to single components connected by hydraulic pipes or hoses.

(52) S1.2Custom components are required that combine a high maximum working pressure with a high maximum flow rate. The components can be integrated in a modular design, where each component is integrated in one modular block. These custom made modular blocks bolted together in a single Hub (see FIG. 3). The modular Hub is compact, enables series production of components and introduces extra flexibility. The flexibility enables the possibility to easily add or remove functions and allows easy maintenance or replacement of a single component.

(53) S2Shut-off valves can be used to provide the connection between the different systems. The accumulators can be connected to either the hydrostatic line 6 or 7. Accordingly, each accumulator uses two shut-off valves. A total of four equal cartridge valves may be used: shut-off valve 100 for connection Accu 10 to Hydrostat 6, shut-off valve 200 for connection Accu 10 to Hydrostat 7, shut-off valve 300 for connection Accu 11 to Hydrostat 6, shut-off valve 400 for connection Accu 11 to Hydrostat 7.

(54) S2.2Alternatively to the previous solution, cartridge valves can be used as shut-off valves, enabling the following benefits: Cartridge valves are an economical solution compared to other valves combining high flow and high pressure. Cartridge valves are actuated by pilot pressure, an economical actuation for strong forces. Cartridge valves prevent leakage from accumulators or from Hydrostat. In closed state, leakage between Hydrostat and accumulators is prevented by the conical shape of the cartridge nose.

(55) All four cartridge valves can be identical (see FIG. 4). The cartridge valves comprise a cover and a cartridge element. The cover is provided with pilot bores. The cartridge comprises a housing, a valve poppet (optionally with a damping nose) and a closing spring.

(56) The medium can flow through the cartridge valve from the first fluid port to the second fluid port or vice versa. When the top surface is pressurized due to the pilot oil from the external pilot oil supply, line 6 is leak-free closed. The pilot pressure should be the highest pressure between the two fluid ports of the cartridge valve.

(57) The cartridge valves are normally closed due to the design of the pilot valve. When the pilot valve is not actuated, pilot pressure is acting on the top surface. However when the valve is energized, the top surface is relieved from pressure due to the tank connection that is established.

(58) S2.3Cartridge valves are closed if the force acting on the top surface is equal to or greater than the sum of the forces acting on the nose and side surfaces. To ensure the force on the top surface is always of this magnitude, the pressure on this surface must always by equal to or higher than the highest pressure on either the nose or the side of the cartridge. Shuttle valves can be used to check highest pressure between nose and side of each cartridge, but this requires the use of many components.

(59) The pilot pressure for cartridges can be derived using four check valves. Each check valve connects to a specific location in the system (Hydrostat 6, Hydrostat 7, Accu 10 and Accu 11). These locations correspond to the pressures acting on the cartridge valves. The check valves will connect the pilot pressure line to the system location with the highest pressure. The pilot pressure line can thus foresee all cartridge valves with the current highest system pressure.

(60) S3.1A proportional flow control valve can be used for smooth transition (see FIG. 5). The flow control valve is located between the high pressure accumulator and the two shut-off valves connecting it to the hydrostat circuit. To control the flow control valve, pilot pressure is required to overcome the high actuation forces. A pilot pressure is controlled by the proportional pilot valve.

(61) S3.2A proportional valve causes pressure drop and should be by-passed as much as possible. Additionally to the previously described solution, a check valve can be used to by-pass the flow control valve when the medium flows towards Accu 10.

(62) S3.3A minimum of four check valves can be used to put the highest system pressure on the pilot pressure line. Pilot pressure for the proportional valve can be provided by reducing the highest system pressure of the pilot line to a preferred value.

(63) S3.4A proportional valve is an expensive component. Another solution is to work without proportional valve and provide smooth transition of vehicle behavior by using displacement control in the hydromotors. In this case, the shut-off valves are connected directly to Accu 10. Note that a pressure shock is not prevented, it is merely unnoticed by the operator.

(64) S4.1Pressure relief valves can be integrated at the accumulator connection ports to prevent excessive pressure in the accumulators (see FIG. 6). The maximum pressure in Accu 10 and Accu 11 is determined by the setting of their respective pressure relief valves. If the pressure relief setting is reached, the superfluous flow and pressure are relieved to the tank. The pressure relief valves should be leak free to avoid leakage from the accumulators or the Hydrostat system to tank.

(65) S4.2. Accumulator discharge is needed in order to set the machine on zero energy level when the vehicle is shut down. Electrically controlled relief valves allow discharge of the accumulators to tank (see FIG. 6). Without these valves, discharging can be done only via the hydrostatic circuit or via manual relief valves. The electric relief valves can be implemented in the form of cartridge shut-off valves, although in a different manner to the ones previously mentioned. The electric relief valves should be dimensioned in order to discharge the accumulators fast enough without causing damage to the accumulator bladder.

(66) S5.1Shut-off valves in the Hub can be used to isolate the Hydrostat pump from the rest of the circuit. This isolation can improve the performance of the system by avoiding accumulator leakage via the Hydrostat pump during accumulator connection. Two cartridge valves designed as previously mentioned can be used as isolation valves.

(67) S5.2To prevent cavitation in the Hydrostat circuit, the Hydrostat pump must be at zero displacement before isolation. Alternatively, a by-pass valve can be used to shortcut the Hydrostat pump ports. A cartridge valve designed as previously mentioned can be used as by-pass valve (see FIG. 7 below).