Regenerative lowering of load in a material handling vehicle
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-02-03
- Publication Date
- 2026-08-13
Smart Images
Figure EP2026052711_13082026_PF_FP_ABST
Abstract
Description
[0001] Regenerative lowering of load in a material handling vehicle
[0002] TECHNICAL FIELD
[0003] The present disclosure relates to the field of material handling vehicles, such as industrial forklift trucks, and, more specifically, to a material handling vehicle as defined in the introductory parts of the independent claims.
[0004] BACKGROUND ART
[0005] Regenerative lowering in forklifts refers to a process where the energy produced during the lowering of a load is captured and reused, rather than being wasted as heat.
[0006] In a battery-powered electrical forklift, this may be achieved by directing a pressurized flow of hydraulic fluid released from the lift cylinder during lowering of the load back to the hydraulic pump. Instead of the pump consuming power from an electric motor (as it does during lifting operations), the flow of pressurized hydraulic fluid through the pump causes it to rotate and essentially operate as a hydraulic motor using the energy from the pressurized hydraulic fluid to generate mechanical rotational energy. This mechanical rotational energy is transferred from the pump to the electric motor which then operates in reverse, acting as a generator. The electrical energy generated by the motor when acting as a generator may, for example, be used to charge the battery of the forklift.
[0007] In order to use additional hydraulic functions of the forklift during regenerative lowering of the load, the regenerative hydraulic fluid flow may be returned to the suction side of the pump. This allows the forklift to execute multiple functions simultaneously, such as lowering a load while adjusting the mast angle or driving and steering the forklift.
[0008] In material handling vehicles, precise regulation of small hydraulic flows is crucial for the ability to fine-tune the position of the load carrier carrying the load, and for gentle unloading of load from the load carrier. Therefore, the lowering valve for regulating the hydraulic fluid flow during lowering of the load is typically a relatively small valve dimensioned for precise regulation of small hydraulic flows. The relatively small dimension of the lowering valve sets a limitation for the maximum lowering speed of the load carrier.
[0009] DE102020131046 A1 presents a solution that enables higher lowering speeds by the use of two hose rupture valves per lifting cylinder. Also two lowering valves per lift cylinder is used which provides the possibility to regulate small flows while allowing the maximum loweringspeed of the load carrier to be twice the normal speed, by fully opening both lowering valves. In some embodiments, both lowering valves are connected to a hydraulic line for conveying hydraulic fluid passing through the valves to a non-pressurized hydraulic fluid reservoir of the forklift. In an alternative embodiment, one of the lowering valves is connected to the hydraulic fluid reservoir while the other lowering valve is connected to the hydraulic pump for enabling regenerative lowering according to the principles described above. This enables some of the hydraulic fluid flow released from the lift cylinder to be regenerated during lowering of the load. Nevertheless, there is a need for an even more energy-efficient solution that still enables precise and fast lowering operations in material handling vehicles.
[0010] SUMMARY
[0011] It is an object of the present disclosure to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages in the prior art.
[0012] In particular, it is an object of the present disclosure to provide a material handling vehicle capable of performing lowering operations in a precise, fast and energy-efficient manner. These and other objects are achieved according to the invention by a material handling vehicle as defined by the appended claims.
[0013] According to a first aspect of the present disclosure there is provided a material handling vehicle comprising: a hydraulic system comprising a pump, a pump motor and at least a first hydraulic cylinder; a load carrier configured to lift and lower a load by means of the first hydraulic cylinder; a first lowering valve configured to receive a first flow of hydraulic fluid released from the first hydraulic cylinder during lowering of the load, and; a second lowering valve configured to receive a second flow of hydraulic fluid released from the first hydraulic cylinder during lowering of the load. The material handling vehicle further comprises a downstream valve arranged downstream of, and in fluid communication with, the first and second lowering valves, wherein the downstream valve is coupled both to a regenerative hydraulic line for conveying a regenerative hydraulic fluid flow back to the pump during lowering of the load, and to a non-regenerative hydraulic line for conveying a non-regenerative hydraulic flow to a hydraulic fluid container during lowering of the load. The material handling vehicle also comprises a control computer operatively connected to the downstream valve and configured to selectively control the downstream valve to be operated in any of a regenerative lowering mode in which the control computer controls the downstream valve to direct hydraulic fluid flow from the first and second lowering valves to the regenerative hydraulic line, and a non-regenerative lowering mode in which the control computer controls the downstream valveto direct hydraulic fluid flow from the first and second lowering valves to the non-regenerative hydraulic line.
[0014] By coupling the first and second lowering valves to a directional control valve for directing the hydraulic fluid from the first and second lowering valves into any or both of the regenerative and non-regenerative hydraulic lines, the eligibility to choose how much of the flow from both the first and the second lowering valves that is regenerated becomes possible.
[0015] Furthermore, the use of two lowering valves enables precise regulation of small hydraulic flows while still allowing high lowering speeds.
[0016] According to some embodiments, the first and second lowering valves are low-flow valves having a respective first and second maximum flow capacity, the downstream valve being a high-flow valve having a maximum flow capacity exceeding the flow capacity of each of the first and second lowering valves.
[0017] The low-flow characteristics of the first and second lowering valves enables precise regulation of small hydraulic flows while the high-flow characteristics of the downstream valve enables regeneration of a hydraulic flow exceeding the maximum flow capacity of each individual lowering valve.
[0018] Preferably, the maximum flow capacity of the downstream valve corresponds to at least the total maximum flow capacity of the first and second lowering valves. This way, the entire hydraulic flow released from the first hydraulic cylinder can be regenerated during lowering of the load at maximum speed.
[0019] According to some embodiments, the first and second lowering valves and the downstream valve are dimensioned and configured to support lowering speeds of the load carrier of at least 1.2 m / s.
[0020] The maximum lowering speed of the load carrier depends on the load it carries, as well as the dimensions and configuration of other components in the hydraulic system. The fact that the first and second lowering valves, as well as the downstream valve, are dimensioned and configured to support lowering speeds of at least 1.2 m / s means that they can achieve this speed within the hydraulic system they operate in when the load carrier is carrying sufficient load.
[0021] According to some embodiments, the regenerative lowering mode is a hybrid lowering mode in which the control computer controls the downstream valve to distribute the hydraulic fluid flowfrom the downstream valve between the regenerative hydraulic line and the non-regenerative hydraulic line.
[0022] This selective control of the downstream valve allows for the regeneration of none, some, or all of the hydraulic flow passing through the first and second lowering valves, thereby enabling more versatile operation of the material handling vehicle. In some embodiments, the downstream valve is a proportional control valve, providing precise and variable control over the flow of hydraulic fluid directed into any or both of the regenerative and non-regenerative hydraulic lines.
[0023] According to some embodiments, the material handling vehicle comprises a load sensor for measuring a load on the load carrier, wherein the control computer is configured to control the downstream valve to be operated in either the regenerative lowering mode or the non-regenerative lowering mode based on the load on the load carrier. In some embodiments, the control computer is configured to control the downstream valve to be operated in the regenerative lowering mode only when the load exceeds a minimum load threshold value. If the load on the load carrier is insufficient, the pressure drop across the hydraulic pump may not be enough to achieve the desired lowering speed. Therefore, by operating the downstream valve in regenerative lowering mode only when the load exceeds a minimum threshold, a consistent minimum lowering speed can be ensured.
[0024] According to some embodiments, the material handling vehicle comprises a temperature sensor for measuring a temperature of the hydraulic fluid, wherein the control computer is configured to control the downstream valve to be operated in either the regenerative lowering mode or the non-regenerative lowering mode based on the temperature of the hydraulic fluid. In some embodiments, the control computer is configured to control the downstream valve to be operated in the regenerative lowering mode only when the hydraulic fluid temperature exceeds a minimum hydraulic fluid temperature threshold value. Low hydraulic fluid temperatures can negatively impact the hydraulic performance of the material handling vehicle during regenerative lowering. This can be prevented by controlling the lowering mode based on the fluid temperature.
[0025] According to some embodiments, the material handling vehicle comprises a main lift configured to lift and lower the load by means of both the first hydraulic cylinder and a second hydraulic cylinder, wherein the first lowering valve is configured to receive a first flow of hydraulic fluid released from the second hydraulic cylinder during lowering of the load, and the second lowering valve is configured to receive a second flow of hydraulic fluid released fromthe second hydraulic cylinder during lowering of the load. Thus, the material handling vehicle may, in some embodiments, comprise at least two hydraulic cylinders for performing one and the same lowering action, wherein each of the at least two hydraulic cylinders is connected to both the first and the second lowering valves.
[0026] According to some embodiments, the material handling vehicle further comprising a free lift configured to lift and lower the load by means of at least a third hydraulic cylinder. In this case, the material handling vehicle may comprise a third lowering valve configured to receive a first flow of hydraulic fluid released from the third hydraulic cylinder during lowering of the load, and a fourth lowering valve configured to receive a second flow of hydraulic fluid released from the third hydraulic cylinder during lowering of the load, wherein the downstream valve is arranged downstream of, and in fluid communication with, also the third and the fourth lowering valves. According to some embodiments, the control computer comprises a prediction module configured to predict at least one characteristic of a future lowering movement of the load carrier based on at least one of a current status and a previous action of the material handling vehicle, wherein the control computer is configured to select lowering mode for the lowering movement based on the predicted characteristic of the lowering movement.
[0027] The current status and / or the previous action of the material handling vehicle may be used by the prediction module to predict an intent of the lowering movement by the operator of the vehicle, whereby the prediction module may predict the at least one characteristic of the lowering movement based on the intent of the operator. By predicting the characteristics of a lowering movement to be performed by an operator of the material handling vehicle and selecting lowering mode for the lowering movement (when performed) based on the prediction, the lowering mode can be selected to prioritize precise manoeuvrability of the material handling vehicle when needed, and to maximise the recovery of energy in situations where precise manoeuvrability of the material handling vehicle is not required.
[0028] According to some embodiments, the current status of the material handling vehicle comprises at least one of a current position of the load carrier and a current position of the material handling vehicle. For example, the current status of the material handling vehicle may include one or more of a vertical position of the load carrier (e.g., a height above ground of the load carrier), a horizontal position of the load carrier (e.g., in relation to a mast or another point of reference on the material handling vehicle), and a position of the material handling vehicle. Both the vertical and horizontal position of the load carrier, as well as the position of the material handling vehicle may be indicative of an intent of a future lowering movement by theoperator and may therefore be advantageously used as input parameters to the prediction module.
[0029] According to some embodiments, the previous action of the material handling vehicle comprises at least one of a previous movement of the load carrier and a previous movement of the material handling vehicle. For example, the previous action of the material handling vehicle may include one or more of a vertical movement of the load carrier, a horizontal movement of the load carrier (e.g., a so-called reach-out-reach-in movement), and a movement of the material handling vehicle.
[0030] According to some embodiments, the prediction module is configured to predict the at least one characteristic of the future lowering movement based on both a current status and previous actions of the material handling vehicle.
[0031] According to some embodiments, the prediction of the at least one characteristic of the future lowering movement comprises a prediction of a lowering distance of the lowering movement. According to some embodiments, the control computer is configured to select the regenerative lowering mode for the lowering movement only if the predicted lowering distance exceeds a minimum lowering distance threshold value. During regenerative lowering, the minimum lowering speed of the load carrier is limited by the minimum rotational speed of the hydraulic pump. The relatively high minimum lowering speed makes fine-tuning of the position of the load carrier difficult during regenerative lowering. Therefore, by preventing regenerative lowering for predicted lowering distance shorter than a certain threshold value, fine-tuning of the position of the load carrier is facilitated.
[0032] According to some embodiments, the prediction of the at least one characteristic of the future lowering movement comprises a prediction of whether the lowering movement is an unloading movement for unloading a load from the load carrier.
[0033] According to some embodiments, the control computer is configured to select the regenerative lowering mode only if the lowering movement is predicted not to be an unloading movement. The relatively high minimum lowering speed of the load carrier during regenerative lowering also makes regenerative lowering unsuitable for lowering movements involving unloading of the load from the load carrier since the load typically should be unloaded from the load carrier in a gentle manner. Therefore, by preventing regenerative lowering for predicted unloading movements, gentle unloading of load from the load carrier is facilitated.According to some embodiments, the prediction module is configured to use the load on the load carrier as input parameter to the prediction of the at least one characteristic of the future lowering movement.
[0034] The load (load weight) on the load carrier is a parameter relating to the current status of the material handling vehicle and may, as such, be used as input parameter to the prediction module for predicting the at least one characteristic of the future lowering movement. It may, however, also be used as a separate control parameter that prevents regenerative lowering of the load if the weight of the load falls below a minimum load threshold value, regardless of the predicted characteristic of the lowering movement.
[0035] According to some embodiments, the prediction of the at least one characteristic of the future lowering movement comprises a prediction of a lowering distance of the lowering movement and a prediction of whether the lowering movement is an unloading movement for unloading a load from the load carrier, wherein the control computer is configured to:
[0036] select the non-regenerative lowering mode for the lowering movement if:
[0037] o the predicted lowering distance falls below a minimum lowering distance threshold value, or
[0038] o the predicted lowering movement is an unloading movement, or
[0039] o the load on the load carrier falls below a minimum load threshold value, and select the regenerative lowering mode for the lowering movement if:
[0040] o the predicted lowering distance exceeds the minimum lowering distance threshold value, and
[0041] o the predicted lowering movement is not an unloading movement, and
[0042] o the load on the load carrier exceeds the minimum load threshold value.
[0043] Thus, in some embodiments, the control computer is configured to select the regenerative lowering mode if, and only if, the predicted lowering distance exceeds the minimum lowering distance threshold value, the predicted lowering movement is not an unloading movement, and the load on the load carrier exceeds the minimum load threshold value.
[0044] According to some embodiments, the prediction module is configured to use the temperature of the hydraulic fluid as input parameter to the prediction of the at least one characteristic of the future lowering movement.
[0045] The temperature of the hydraulic fluid is a parameter relating to the current status of the material handling vehicle and may, as such, be used as input parameter to the predictionmodule for predicting the at least one characteristic of the future lowering movement. Similar to the load weight on the load carrier, hydraulic fluid temperature may, however, also be used as a separate control parameter that prevents regenerative lowering of the load if the hydraulic fluid temperature falls below a minimum load threshold value, regardless of the predicted characteristic of the lowering movement, and regardless of the load on the load carrier.
[0046] According to some embodiments, the prediction of the at least one characteristic of the future lowering movement comprises a prediction of a lowering distance of the lowering movement and a prediction of whether the lowering movement is an unloading movement for unloading a load from the load carrier, wherein the control computer is configured to:
[0047] select the non-regenerative lowering mode for the lowering movement if:
[0048] o the predicted lowering distance falls below a minimum lowering distance threshold value, or
[0049] o the predicted lowering movement is an unloading movement, or
[0050] o the load on the load carrier falls below a minimum load threshold value, or o the temperature of the hydraulic fluid falls below a minimum hydraulic fluid temperature threshold value, and
[0051] select the regenerative lowering mode for the lowering movement if:
[0052] o the predicted lowering distance exceeds the minimum lowering distance threshold value, and
[0053] o the predicted lowering movement is not an unloading movement, and o the load on the load carrier exceeds the minimum load threshold value, and o the temperature of the hydraulic fluid exceeds the minimum hydraulic fluid temperature threshold value.
[0054] Thus, in some embodiments, the control computer is configured to select the regenerative lowering mode if, and only if, the predicted lowering distance exceeds the minimum lowering distance threshold value, the predicted lowering movement is not an unloading movement, the load on the load carrier exceeds the minimum load threshold value, and the temperature of the hydraulic fluid exceeds the minimum hydraulic fluid temperature threshold value.
[0055] According to some embodiments, the prediction module is configured to predict the at least one characteristic of the future lowering movement by employing a rule-based algorithm using a fixed set of predefined rules for a first set of parameters relating to the current status and / or the previous action of the material handling vehicle.According to other embodiments, the prediction module is configured to predict the at least one characteristic of the future lowering movement by employing a machine learning algorithm, using a first set of parameters relating to the current status and / or the previous action of the material handling vehicle as input parameters to the machine learning algorithm. By employing a machine learning algorithm, the predictions of the at least one characteristics of the lowering movement can improve over time.
[0056] According to some embodiments, the control computer is configured to obtain a second set of parameters relating to the lowering movement of the load carrier, and to enable training of the machine learning algorithm based on the first and second sets of parameters. By collecting a second set of parameters related to characteristics of the actual lowering movement (once performed) and using them as input to the machine learning algorithm during training, these parameters can be compared with the predictions made using the first set of parameters. This comparison enables adjustments to the algorithm's weights, optimizing its performance over time.
[0057] According to some embodiments, the regenerative hydraulic line is connected to a suction side of the pump, such that the regenerative flow of hydraulic fluid flows through the pump in a pumping direction of the pump motor. As discussed above, this allows other hydraulic functions of the material handling vehicle to be used during regenerative lowering of the load. According to some embodiments, the material handling vehicle is an industrial truck, such as an industrial forklift truck.
[0058] Other effects and advantages of the material handling vehicle of the present disclosure will become apparent from the detailed description following hereinafter. The detailed description and its specific examples disclose preferred embodiments of the disclosure by way of illustration only. Those skilled in the art understand from guidance in the detailed description that changes and modifications may be made within the scope of the disclosure.
[0059] Hence, it is to be understood that the disclosure is not limited to the particular component parts of the devices described or steps of the methods described since such devices and method steps may vary. It is also to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It should be noted that, as used in the specification and the appended claim, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context explicitly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may includeseveral devices, and the like. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.
[0060] BRIEF DESCRIPTIONS OF THE DRAWINGS
[0061] The above objects, as well as additional objects, features and advantages of the present disclosure, will be more fully appreciated by reference to the following illustrative and nonlimiting detailed description of example embodiments of the present disclosure, when taken in conjunction with the accompanying drawings.
[0062] Fig. 1 illustrates a material handling vehicle according to an exemplary embodiment of the present disclosure.
[0063] Fig. 2 illustrates components of a hydraulic system of a material handling vehicle, according to an exemplary embodiment of the present disclosure.
[0064] Fig. 3 illustrates schematically a control computer of a material handling vehicle, according to an exemplary embodiment of the present disclosure.
[0065] Fig. 4 illustrates components of a hydraulic system of a material handling vehicle, according to another exemplary embodiment of the present disclosure.
[0066] Figs. 5A-5B illustrates a lift arrangement of a material handling vehicle, according to an exemplary embodiment of the present disclosure.
[0067] Fig. 6 illustrates components of a hydraulic system of a material handling vehicle equipped with the lift arrangement in Figs. 5A-5B, according to yet another exemplary embodiment of the present disclosure.
[0068] DETAILED DESCRIPTION
[0069] The present disclosure will now be described with reference to the accompanying drawings, in which preferred example embodiments of the disclosure are shown. The disclosure may, however, be embodied in other forms and should not be construed as limited to the herein disclosed embodiments. The disclosed embodiments are provided to fully convey the scope of the disclosure to the skilled person.
[0070] Figure 1 illustrates a material handling vehicle 1 according to an exemplary embodiment of the present disclosure. The material handling vehicle 1 comprises a lift arrangement for lifting and lowering a load carried by a load carrier 7. The material handling vehicle 1 of the presentdisclosure may be any type of material handling vehicle with a lift arrangement for lifting and lowering a load, such as an industrial truck. In the illustrated example, the material handling vehicle 1 is a forklift truck and, more specifically, a so-called reach truck.
[0071] The lift arrangement of the material handling vehicle 1 comprises a mast assembly 19 for facilitating lifting, lowering and positioning of loads carried by a load carrier 7. In this example, the load carrier 7 consists of a pair of forks, but alternative attachments such as clamps, load platforms, jibs or boom attachment, buckets, or suction mechanisms may also be used, depending on the application.
[0072] The material handling vehicle 1 further comprises a chassis 101 that houses and supports most of its key components, and an operator compartment 103 from which an operator of the material handling vehicle can steer the vehicle and control its hydraulic functions, including the lift arrangement for lifting and lowering the load carrier 7. In other embodiments (not shown), the material handling vehicle 1 of the present disclosure may be an automated ground vehicle (AGV) without any operator compartment 103.
[0073] The material handling vehicle 1 may be an electric material handling vehicle comprising a rechargeable battery 30 for powering both the hydraulic functions and a drive motor of the vehicle. The battery 30 may be a lead-acid battery, a lithium-ion battery, or any other suitable type of battery known in the art.
[0074] The material handling vehicle 1 further comprises a hydraulic system 2 for lifting and lowering the load carrier 7 using pressurized hydraulic fluid. An electric motor, powered by the battery 30, drives a hydraulic pump of the hydraulic system 2, which pump serves to convert the electrical energy stored in the battery 30 into mechanical energy in the form of pressurize hydraulic fluid.
[0075] The energy contained in the pressurized hydraulic fluid may be recovered during regenerative lowering of the load carrier 7. In accordance with the principles of the present disclosure, the hydraulic system 2 of the material handling vehicle 1 is adapted to optimize energy recovery while maintaining precise and fast lowering operations, as will be described in more detail below with reference to Fig. 2.
[0076] Fig. 2 illustrates components of a hydraulic system 2 of a material handling vehicle 1 in accordance with an exemplary embodiment of the present disclosure. The depicted components are specifically those involved in the lowering operation of the load carrier 7. For simplicity and clarity, hydraulic lines and components of the hydraulic system purely related tolifting operations or other hydraulic functions of the vehicle have been omitted to avoid cluttering the illustration with unnecessary details.
[0077] The hydraulic system 2 comprises a hydraulic pump 3 for pressurizing hydraulic fluid, and a hydraulic pump motor 4 for powering the hydraulic pump 3. The motor 4 is an electric motor powered by the rechargeable battery 30. Besides lifting and lowering the load carrier 7 (see Fig. 1), the hydraulic pump 3 may be configured to supply pressurized hydraulic fluid to other additional or auxiliary hydraulic functions of the material handling vehicle 1 , illustrated by the dashed box denoted by reference numeral 20.
[0078] The hydraulic system 2 further comprises at least a first hydraulic cylinder 5 configured to lift and lower the load carrier 7 of the material handling vehicle 1. The load carrier 7 is lifted by pumping hydraulic fluid from the hydraulic pump 3 to the cylinder 5 (via a hydraulic line not shown in the drawing), whereby the cylinder is extended and the load carrier raised. The load carrier 5 is lowered by releasing hydraulic fluid from the cylinder 5, whereby the cylinder is retracted. The lowering movement of the load carrier 7 is controlled by controlling the flow of hydraulic fluid released from the cylinder 5.
[0079] To this end, the hydraulic system 2 comprises a valve arrangement 8 comprising a first lowering valve 14 configured to receive a first flow of hydraulic fluid released from the cylinder 5 during lowering of the load carrier 7, and a second lowering valve 15 configured to receive a second flow of hydraulic fluid released from the cylinder 5 during lowering of the load carrier 7. The first and second lowering valves 14,15 are typically low-flow valves, meaning that they are relatively small in dimension and configured for precise regulation of relatively small flows of hydraulic fluid. Thereby, the lowering movement and the position of the load carrier 7 can be very precisely controlled by controlling the first and second lowering valves 14, 15.
[0080] Furthermore, the valve arrangement 8 comprises a downstream valve 16 arranged downstream of, and in fluid communication with, the first and second lowering valves 14,15. The downstream valve 16 is coupled both to a regenerative hydraulic line 9 for conveying a regenerative hydraulic fluid flow back to the pump 3 during lowering of the load, and to a non-regenerative hydraulic line 10 for conveying a non-regenerative hydraulic flow to a hydraulic fluid container or reservoir 11 during lowering of the load carrier 7. The regenerative hydraulic line 9 preferably connects to the suction side of the pump 3, such that the regenerative flow of hydraulic fluid flows through the pump 3 in a pumping direction of the pump motor 4. The non-regenerative hydraulic line 10 typically comprises a return filter 1 T for filtering the non-regenerative hydraulic flow before returning it to the hydraulic fluid container 11. The hydraulicfluid container 11 may also be arranged to receive an additional non-regenerative hydraulic fluid flow from hydraulic components of the auxiliary hydraulic functions 20 of the material handling vehicle 1, e.g. via an additional non-regenerative hydraulic line 10’ for supplying the additional non-regenerative hydraulic flow to the hydraulic fluid container 11 , via the return filter 1 T. The hydraulic fluid stored in the hydraulic fluid container 11 may then be reused by the hydraulic pump 3 drawing hydraulic fluid from the hydraulic fluid container 11 through a suction line 3’.
[0081] The downstream valve 16 is typically a high-flow valve, meaning that it is configured to allow relatively high flows of hydraulic fluid to pass through the valve. That the downstream valve 16 is a high-flow valve whereas the first and second lowering valves 14, 15 are low-flow valves has the effect of enabling precise regulation of the lowering movement and the position of the load carrier 7 during non-regenerative lowering of the load carrier 7 while enabling regeneration of all or a substantial part of the hydraulic fluid released from the cylinder 5 during regenerative lowering of the load carrier 7.
[0082] During regenerative lowering of the load carrier 7, the first and second downstream valves 14, 15 may be fully opened and the downstream valve 16 may direct the entire flow released from the cylinder 5 and passing through the downstream valves 14, 15 into the regenerative hydraulic line 9 and back to the hydraulic pump 5. This allows the pump 5 to operate as a hydraulic motor using the energy from the pressurized hydraulic fluid to drive the electric motor 4 in reverse, thereby causing the motor to act as a generator. The electrical energy generated by the motor 4 when acting as a generator may, for example, be used to charge the battery 30 of the material handling vehicle 1. In this scenario, the hydraulic fluid flow released from the cylinder 5, and thus the lowering speed of the load carrier 7, is controlled by the rotational speed of the pump motor 4.
[0083] The downstream valve 16 may, in some embodiments, be a directional valve operating in discrete states for directing the flow of hydraulic fluid into any or both of the regenerative hydraulic line 9 and the non-regenerative hydraulic line 10. Preferably, however, the downstream valve 16 is a proportional control valve providing both directional control and precise modulation of flow and pressure in the regenerative hydraulic line 9 and the non-regenerative hydraulic line 10.
[0084] The first and second lowering valves 14, 15 may have the same or different maximum flow capacities. In some embodiments, the first and second lowering valves 14, 15 have substantially the same maximum flow capacity. Preferably, the downstream valve 16 has amaximum flow capacity that exceeds the maximum flow capacity of each of the first and second lowering valves 14, 15. This way, at least more than half the hydraulic fluid flow released from the cylinder 5 can be regenerated during regenerative lowering of the load carrier 7. Even more preferably, the downstream valve 16 has a maximum flow capacity corresponding at least to the sum of the maximum flow capacities of the first and second lowering valves 14, 15. This way, the entire flow of hydraulic fluid released from the cylinder 5 during lowering of the load carrier 7 can be regenerated. Preferably, the first and second lowering valves 14,15 and the downstream valve 16 are dimensioned and configured to support lowering speeds of the load carrier 7 of at least 1.2 m / s when the load carrier 7 carries sufficient load. More specifically, the valves should be dimensioned and configured to support lowering speeds of at least 1.2 m / s when the weight of the load corresponds to at least a substantial part of the material handling vehicle's rated capacity (maximum load weight).
[0085] The hydraulic system 2 is controlled by a control computer 12 of the material handling vehicle 1. The control computer 12 may be any type of electronic computational device and is typically an embedded system comprising at least one microcontroller, field programmable gate array (FPGA) or industrial-grade processor. The control computer 12 may be configured to control all controllable components of the hydraulic system 2, including but not limited to the lowering valves 14, 15, the downstream valve 16, the pump motor 4, and the additional hydraulic functions 20 of the material handling vehicle 1.
[0086] The control computer 12 is operatively connected to the valve arrangement 8 and configured to control both the first and second lowering valves 14, 15 and the downstream valve 16.
[0087] During lowering of the load, the control computer 12 is configured to selectively control the downstream valve 16 to be operated in any of a regenerative lowering mode in which the control computer 12 controls the downstream valve 16 to direct hydraulic fluid flow from the first and second lowering valves 14,15 to the regenerative hydraulic line 9, and a non-regenerative lowering mode in which the control computer 12 controls the downstream valve 16 to direct hydraulic fluid flow from the first and second lowering valves 14,15 to the non-regenerative hydraulic line 10. The control computer 12 is also operatively connected to the pump motor 4 to control the rotational speed of the motor 4 and hence the hydraulic pump 3, thereby controlling the hydraulic fluid flow through the regenerative hydraulic line 9 during regenerative lowering of the load.
[0088] In the regenerative lowering mode, at least some and typically a substantial part of the hydraulic fluid flow from the first and second lowering valves 14, 15 is directed into theregenerative hydraulic line 9 by the downstream valve 16. In some embodiments, the regenerative lowering mode may be a mode in which the control computer 12 controls the downstream valve 16 to direct the entire hydraulic fluid flow from the first and second lowering valves 14, 15 into the regenerative hydraulic line 9. In other embodiments, the regenerative lowering mode may be hybrid mode in which the control computer 12 controls the downstream valve 16 to distribute the hydraulic fluid flow from the downstream valve 16 between the regenerative hydraulic line 9 and the non-regenerative hydraulic line 10.
[0089] In the non-regenerative lowering mode, no hydraulic fluid flow from the first and second lowering valves 14, 15 is directed into the regenerative hydraulic line 9. Instead, in the non-regenerative lowering mode, the control computer 12 controls the downstream valve 16 to direct the entire hydraulic fluid flow from the first and second lowering valves 14, 15 into the non-regenerative hydraulic line 10.
[0090] The control computer 12 may be configured to take various parameters into consideration in the selection of lowering mode for a lowering movement.
[0091] In some embodiments, the control computer 12 may be configured to control the downstream valve 16 to be operated in either the regenerative lowering mode or the non-regenerative lowering mode based on the load (i.e. , load weight) on the load carrier 7. To this end, the hydraulic system 2 may comprise at least one load sensor 17 for measuring the load on the load carrier 7. In the exemplary embodiment illustrated in Fig. 2, the load sensor 17 is a pressure sensor for measuring a hydraulic pressure indicative of the load on the load carrier 7. The control computer 12 may be configured to determine if the load on the load carrier 7 exceeds a minimum load threshold value, and to select the regenerative lowering mode if the load exceeds the minimum load threshold value. If the load falls below the minimum load threshold value, the control computer 12 may be configured to select the non-regenerative lowering mode for the lowering movement.
[0092] In some embodiments, the control computer 12 may be configured to select lowering mode for the lowering movement based a temperature of the hydraulic fluid in the hydraulic system 2. To this end, the hydraulic system 2 may comprise a temperature sensor 18 for measuring a temperature of the hydraulic fluid. The control computer 12 may be configured to select the regenerative lowering mode if the hydraulic fluid temperature exceeds a minimum hydraulic fluid temperature threshold value. If the hydraulic fluid temperature falls below the minimum hydraulic fluid temperature threshold value, the control computer 12 may be configured to select the non-regenerative lowering mode for the lowering movement.In some embodiments, the control computer 12 may be configured to select the regenerative lowering mode only if both the load on the load carrier 7 and the temperature of the hydraulic fluid exceed their respective minimum threshold value.
[0093] The control computer 12 may be configured to select lowering mode for a lowering movement in response to reception of a signal indicating a desire by the operator of the material handling vehicle 1 to lower the load carrier 7. The control computer may, for example, be configured to determine the lowering mode based on the load on the load carrier 7 and / or the temperature of the hydraulic fluid at the time of reception of the steering signal.
[0094] Instead of, or in addition to, the load on the load carrier and / or the temperature of the hydraulic fluid, the control computer 12 may be configured to select lowering mode for the lowering movement based on predicted characteristics of the lowering movement.
[0095] To this end, the control computer 12 may comprise a prediction module 13 configured to predict at least one characteristic of a future lowering movement of the load carrier 7 based on at least one of a current status and a previous action of the material handling vehicle 1. The lowering mode for the future lowering movement (when performed) may then be selected by the control computer 12 based on the at least one predicted characteristic of the lowering movement.
[0096] In this context, the term 'future lowering movement' refers to any lowering action that could potentially be initiated by the operator of the material handling vehicle 1 in the near future. For instance, the prediction module 13 can be configured to predict, at any given moment, the characteristics of a lowering movement that would occur if initiated immediately, based on the current status and / or previous actions of the material handling vehicle 1 at the moment of prediction. The prediction can be performed either substantially continuously or intermittently, with the lowering mode for each potential lowering movement (referred to as 'the future lowering movement') being selected based on the most recent prediction.
[0097] The current status of the material handling vehicle may be derived by the control computer 12 based on any parameter or combination of parameters relating to the current status of the material handling vehicle 1, including but not limited to a current position of the load carrier 7, a current position of the material handling vehicle, the load on the load carrier 7, and the temperature of the hydraulic fluid.
[0098] The previous action of the material handling vehicle 1 may be derived by the control computer 12 based on any parameter or combination of parameters relating to previous actionsperformed by the material handling vehicle 1 , including but not limited to parameters relating to a previous movement of the load carrier 7 (e.g. parameters relating to previous positions of the load carrier 7 over time), and parameters relating to a previous movement of the material handling vehicle 1 (e.g. parameters relating to previous positions of the vehicle overtime). Thus, although not illustrated in the drawings, it should be realized that the material handling vehicle 1 is typically equipped with various additional sensors for measuring parameters relating to the current status and / or previous actions of the vehicle. For example, besides the above-mentioned load sensor 17 and temperature sensor 18, the material handling vehicle may be equipped with one or more position sensors for measuring the position and movement of the load carrier 7, e.g., linear position sensors, rotary encoders, ultrasonic sensors, string potentiometers, proximity sensors, etc., and one or more position sensors for measuring the position and movement of the material handling vehicle 1, e.g., Global Navigation Satellite System based sensors, inertial measurement units, wheel encoders, vision-based sensors, LIDAR sensors, ultrasonic sensors, magnetometers, radio-frequency based sensors, laser distance sensors, etc..
[0099] The current status and / or previous actions of the material handling vehicle 1 can be utilized by the prediction module 13 to anticipate the operator's intent regarding a lowering movement. Based on this intent, the prediction module 13 may estimate one or more characteristics of the future lowering movement.
[0100] For instance, the operator's intent for the lowering movement could be:
[0101] to unload a load from the load carrier,
[0102] to lower a load to a transport position in preparation for moving it to an unloading site, or to fine-adjust the height of the load carrier for picking up a load from the ground, a storage shelf, or a rack.
[0103] The prediction module 13 can interpret such intents by analysing the current status and / or previous actions of the material handling vehicle 1, thereby forecasting the characteristics of the anticipated lowering movement.
[0104] For example, the prediction module 13 may be configured to predict that the future lowering movement is a lowering movement for unloading the load from the load carrier 7 based on, e.g., a height above ground of the load carrier 7 and / or a position and / or previous movement of the material handling vehicle 1. If the load carrier 7 is positioned at a height typically used for transporting load, then it is likely that the load is either being transported to an unloading sitewhere load is typically unloaded or is already at such a site. Consequently, the next lowering movement is likely intended to unload the load from the load carrier 7. If the material handling vehicle 1 is located at, or approaching, the unloading site, then it is also likely that the next lowering movement is intended to unload the load from the load carrier 7.
[0105] Conversely, the prediction module 13 may predict that the future lowering movement is not intended for unloading based on, e.g., a previous movement of the load carrier 7 and / or a position and / or previous movement of the material handling vehicle 1. For example, if the load carrier 7 recently performed a reach-out-reach-in movement, i.e. a horizontal extension and retraction of the load carrier 7, it is likely the next lowering movement will not be an unloading movement but a lowering movement for lowering a load assumingly picked up during the reach-out-reach-in movement to a transport position for subsequent transportation to an unloading site. If the material handling vehicle 1 is located at, or approaching, a site where load is often picked up but rarely unloaded, then it is also likely that the next lowering movement will not be an unloading movement.
[0106] Also, the prediction module 13 may predict a lowering distance of the future lowering movement based on, e.g., a height above ground of the load carrier 7. If, for example, the prediction module has predicted that the future lowering movement is likely to a be a lowering movement for lowering a load into a transport position, then the prediction module may predict the lowering distance of the future lowering movement based on the current height above ground of the load carrier 7 and its standard height in the transport position. Likewise, the prediction module 13 may predict a lowering distance of the future lowering movement based on, e.g., a previous movement of the load carrier 7. If, for example, the vertical position of the load carrier has recently been fine-adjusted and no reach-out-reach-in movement has been performed after the vertical fine-adjustment, then the prediction module 13 may assume that the operator is still fine-tuning the vertical position of the load carrier 7 in order to pick up a load, and hence that any further lowering movement performed prior to a reach-out-reach-in movement will be a short-distance lowering movement for fine-tuning the position of the load carrier 7.
[0107] The prediction of the at least one characteristic of the future lowering movement may hence comprise a prediction of whether the lowering movement is an unloading movement for unloading a load from the load carrier, and / or a prediction of a lowering distance of the lowering movement.In some embodiments, the control computer 12 may be configured to select the regenerative lowering mode for the future lowering movement only if the prediction indicates that the lowering movement is not an unloading movement. Likewise, the control computer 12 may be configured to select the regenerative lowering mode for the future lowering movement only if the lowering distance of the future lowering movement is predicted to exceed a certain minimum lowering distance threshold value.
[0108] From the above, it should be realized that there may be at least four mandatory requirements that have to be fulfilled in order for the control computer 12 to select the regenerative lowering mode for the future lowering movement, namely that:
[0109] the predicted lowering distance exceeds the minimum lowering distance threshold value, the predicted lowering movement is not an unloading movement,
[0110] the load on the load carrier exceeds the minimum load threshold value, and
[0111] the temperature of the hydraulic fluid exceeds the minimum hydraulic fluid temperature. If one or more of these requirements are not met, the control computer 12 may be configured to select the non-regenerative lowering mode for the lowering movement.
[0112] Thus, the load (load weight) on the load carrier 7 and / or the temperature of the hydraulic fluid may be used as separate control parameters for preventing regenerative lowering of the load if the weight of the load and / or the temperature of the hydraulic fluid falls below a respective minimum threshold value, regardless of the predicted characteristics of the lowering movement. However, any or both of the load on the load carrier 7 and the temperature of the hydraulic fluid may advantageously also be used as input parameters to the prediction module 13 for predicting the at least one characteristic of the future lowering movement. For example, the load on the load carrier 7 is preferably used as input parameter to the prediction module 13 in each of the above prediction examples since the load on the load carrier 7, alone or in combination with other parameters, may be indicative both of the type of the future lowering movement (unloading movement or not unloading movement) and the lowering distance of the future lowering movement.
[0113] Fig. 3 illustrates schematically the control computer 12 of the material handling vehicle 1, according to an exemplary embodiment in which the control computer 12 is configured to select the lowering mode of the future lowering movement based on a prediction of the characteristics of the lowering movement.In this scenario, as discussed above, the control computer 12 may be configured to receive various parameters Pi-Pe from different sensors of the material handling vehicle 1 , and to use the parameters as input parameters to the prediction module 13 for predicting the at least one characteristic of the future lowering movement. For example, parameters P1-P4 may relate to positions of the load carrier 7 and the material handling vehicle 1, which positions may further be used by the control computer 12 to derive previous actions and movements of the load carrier 7 and the material handling vehicle 1. The parameter P5 may, for example, relate to the load on the load carrier 7, e.g. as measured by the load sensor 17. The parameter Pe may, for example, relate to the temperature of the hydraulic fluid, e.g. as measured by the temperature sensor 18.
[0114] When the prediction module has predicted the at least one characteristic of the future lowering movement, the prediction is provided as input to a control module 22 of the control computer. Optionally, the parameters P5-P6 relating to the load on the load carrier 7 and the temperature of the hydraulic fluid are provided as separate input parameters to the control module 22, along with the prediction. Based on the prediction of the at least one characteristic of the future lowering movement, the load on the load carrier 7, and the temperature of the hydraulic fluid, the control module 22 determines the lowering mode of the future lowering movement, e.g. in accordance with the principles described above.
[0115] The control module 22 is further configured to receive steering signals S representing input signals from levers or joysticks manipulated by the operator of the material handling vehicle 1 in order to control the load carrier 7 (e.g. to lift, lower or tilt the load carrier), and to send control signals C1-C2 to the valve arrangement 8 and the pump motor 4 to control the movement of the load carrier 7 in accordance with the steering signals.
[0116] If the steering signal S indicates that the operator wants to lower the load carrier 7, the control module selects lowering mode for the lowering movement in accordance with the abovedescribed principles, and generates control signals C1-C2 to control the valve arrangement 8 and the pump motor in accordance with the steering signals and the selected lowering mode. For example, if the regenerative lowering mode is selected for the lowering movement, the control module 22 sends a control signal C1 to the valve arrangement 8 causing the lowering valves 14, 15 (see Fig. 2) to open and the downstream valve 16 to direct the hydraulic fluid flow from the first and second lowering valves 14, 15 into the regenerative hydraulic line 9. At the same time, the control module 22 sends a control signal C2 to the pump motor 4 (operating as a generator in the regenerative mode) for controlling the speed of the motor and hence thelowering speed of the load carrier 7. The lowering speed may be selected by the control module 22 based on a desired lowering speed indicated by the operator and reflected by the steering signal S, and / or it may be selected by the control module 22 based on the prediction of the at least one characteristic of the lowering movement made by the prediction module 13. As indicated in the drawing, the steering signal S, may also be used as input parameter to the prediction module 13 and used in the prediction of the at least one characteristic of the future lowering movement. Steering signals from various levers and joysticks of the material handling vehicle 1 can be used instead of, or in addition to, the aforementioned position sensors for determining the current status and / or previous actions of the material handling vehicle 1 , including positions and previous movements of the load carrier 7 and the vehicle itself.
[0117] The prediction module 13 may be configured to predict the at least one characteristic of the future lowering movement by employing a rule-based algorithm using a fixed set of predefined rules for a first set of parameters relating to the current status and / or the previous action of the material handling vehicle.
[0118] Preferably, however, the prediction module 13 is configured to predict the at least one characteristic of the future lowering movement by employing a machine learning algorithm, using a first set of parameters relating to the current status and / or the previous action of the material handling vehicle as input parameters to the machine learning algorithm. With reference to Fig. 3, this first set of parameters may include any of, or any combination of, the parameters Pi-Pe and S.
[0119] By employing a machine learning algorithm, the prediction module 13 may continuously improve the accuracy of predicting characteristics of future lowering movements over time. In addition to enhancing predictions generally, the prediction module 13 may also learn the steering behaviour and habits of individual vehicle operators, thereby further improving the prediction of the intent of a current operator and thus the at least one characteristic of the future lowering movement over time.
[0120] In order to train the machine learning algorithm, the control computer 12 may be configured to obtain a second set of parameters relating to the actual lowering movement of the load carrier 7 (once performed), and to enable training of the machine learning algorithm based on the first and second sets of parameters. The second set of parameters may be any type of data indicative of the actual outcome of the predicted characteristics of the lowering movement, e.g. data indicative of whether the lowering movement was an unloading movement, the loweringdistance of the lowering movement, etc. The second set of parameters may be obtained by various sensors of the material handling vehicle 1, which sensors may or may not be the same sensors used for obtaining the first set of parameters. The control computer 12 may be configured to enable training of the machine learning algorithm by transmitting the input parameters (i.e., the first set of parameters) and data indicative of the actual outcome (i.e. , the second set of parameters) to a remote training server (not shown), in order for a machine learning algorithm residing on the server to be trained based on the data received from the material handling vehicle 1 , possibly aggregated with data from other material handling vehicles. The control computer 12 may then receive data relating to the trained machine learning algorithm from the remote training server, and update a local version of the machine learning algorithm residing in the prediction module 13 based on the received data.
[0121] Fig. 4 illustrates components of a hydraulic system 2 of a material handling vehicle 1 in accordance with another exemplary embodiment of the present disclosure.
[0122] In this embodiment, the hydraulic system 2 includes a first hydraulic cylinder 5a and a second hydraulic cylinder 5b for lifting and lowering the load carrier of the material handling vehicle. The first 5a and second 5b cylinders may, for example, operate as a cylinder pair for a main lift 23 of the vehicle.
[0123] As shown in the drawing, during the lowering of the load, the first lowering valve 14 is configured to receive hydraulic fluid flows from both the first hydraulic cylinder 5a and the second hydraulic cylinder 5b. Similarly, the second lowering valve 15 is configured to receive hydraulic fluid flows from both the first hydraulic cylinder 5a and the second hydraulic cylinder 5b during lowering of the load. Consequently, each of the hydraulic cylinders 5a and 5b is connected to both the first lowering valve 14 and the second lowering valve 15.
[0124] Apart from utilizing two hydraulic cylinders 5a and 5b instead of a single cylinder, the hydraulic system depicted in Fig. 4 is identical to, and operates in the same manner as, the hydraulic system shown in Fig. 2.
[0125] In another exemplary embodiment, the hydraulic system of the material handling vehicle may comprise two hydraulic cylinders operating as a cylinder pair for a main lift of the vehicle, as described above with reference to Fig. 4, and one hydraulic cylinder operating as a single cylinder for a free lift of the vehicle. This is a common lift arrangement configuration for reach trucks.A reach truck is a type of industrial forklift designed specifically for material handling in warehouse environments, particularly for lifting and retrieving loads at great heights and in narrow aisle spaces. It is widely used in industries where maximizing storage space is crucial. Reach trucks can typically lift loads to significant heights (often up to 10 meters or more), making them suitable for stacking pallets on tall racks.
[0126] Figs. 5A-5B illustrates an exemplary lift arrangement of a reach truck, such as the reach truck illustrated in Fig. 1.
[0127] The lift arrangement comprises a mast assembly 19 consisting of a multi-stage, collapsible mast that includes an inner mast section for a free lift 21 of the lift arrangement, and outer mast sections for a main lift 23 of the lift arrangement. The load carrier 7 is mounted onto a carriage 7’ and the free lift 21 is configured to raise the carriage 7’ and hence the load carrier 7 vertically within the inner mast section without extending the outer mast sections, whereas the main lift 23 is configured to raise the load carrier 7 to greater vertical heights by extending the outer mast sections once the free lift height is exceeded.
[0128] The free lift 21 comprises a central hydraulic cylinder for lifting and lowering the load carrier 7 during the free lift stage, and the main lift 23 comprises two side-mounted hydraulic cylinders for lifting and lowering the load carrier 7 during the main lift stage. The two side-mounted hydraulic cylinders of the main lift 23 hence constitute a first 5a and a second 5b hydraulic cylinder of the lift arrangement, and the central hydraulic cylinder of the free lift 21 constitutes a third hydraulic cylinder 5c of the lift arrangement.
[0129] Fig. 6 illustrate components of a hydraulic system 2 of a material handling vehicle equipped with the lift arrangement shown in Figs. 5A-5B.
[0130] As illustrated in the drawing, the main lift 23 is devised and configured in accordance with the main lift illustrated in Fig. 4, meaning that each of the first 5a and second 5b hydraulic cylinders of the main lift 23 is connected to each of the first 14 and second 15 lowering valves. The third hydraulic cylinder 5c of the hydraulic system 2, constituting a single hydraulic cylinder of the free lift 21, is connected to both a third lowering valve 14’ and a fourth lowering valve 15’ in the hydraulic system 2. These third and fourth lowering valves 14’, 15’ are connected to the same downstream valve 16 as the first and second lowering valves 14, 15.
[0131] This configuration allows for highly precise lowering movements of both the free lift 21 and the main lift 23, making it suitable for situations where fine positioning of the load carrier 7 isrequired. Additionally, it enables high-speed lowering of the load carrier and full regeneration of the hydraulic fluid flow from both the free lift 21 and the main lift 23 in scenarios where precise positioning or gentle deceleration of the load carrier 7 is unnecessary.
Claims
25CLAIMS1. A material handling vehicle (1) comprisinga hydraulic system (2) comprising a pump (3), a pump motor (4) and at least a first hydraulic cylinder (5; 5a);a load carrier (7) configured to lift and lower a load by means of the first hydraulic cylinder (5; 5a);a first lowering valve (14) configured to receive a first flow of hydraulic fluid released from the first hydraulic cylinder (5; 5a) during lowering of the load;a second lowering valve (15) configured to receive a second flow of hydraulic fluid released from the first hydraulic cylinder (5; 5a) during lowering of the load;a downstream valve (16) arranged downstream of, and in fluid communication with, the first and second lowering valves (14, 15), wherein the downstream valve (16) is coupled both to a regenerative hydraulic line (9) for conveying a regenerative hydraulic fluid flow back to the pump (3) during lowering of the load, and to a non-regenerative hydraulic line (10) for conveying a non-regenerative hydraulic flow to a hydraulic fluid container (11) during lowering of the load, anda control computer (12) operatively connected to the downstream valve (16) and configured to selectively control the downstream valve (16) to be operated in any of a:o regenerative lowering mode in which the control computer (12) controls the downstream valve (16) to direct hydraulic fluid flow from the first and second lowering valves (14, 15) to the regenerative hydraulic line (9), and o a non-regenerative lowering mode in which the control computer (12) controls the downstream valve (16) to direct hydraulic fluid flow from the first and second lowering valves (14, 15) to the non-regenerative hydraulic line (10).
2. The material handing vehicle of claim 1, wherein the first and second lowering valves (14, 15) are low-flow valves having a respective first and second maximum flow capacity, the downstream valve being a high-flow valve having a maximum flow capacity exceeding the flow capacity of each of the first and second lowering valves (14,15).
3. The material handling vehicle of claim 1 or 2, wherein the first and second lowering valves (14, 15) and the downstream valve (16) are dimensioned and configured to support lowering speeds of the load carrier (7) of at least 1.2 m / s when the load carrier (7) carries load.
4. The material handing vehicle (1) of any of the preceding claims, wherein the regenerative lowering mode is a hybrid lowering mode in which the control computer (12) controls the downstream valve (16) to distribute the hydraulic fluid flow from the downstream valve (16) between the regenerative hydraulic line (9) and the non-regenerative hydraulic line (10).
5. The material handling vehicle (1) of any of the preceding claims, comprising a load sensor (17) for measuring a load on the load carrier (7), wherein the control computer (12) is configured to control the downstream valve (16) to be operated in either the regenerative lowering mode or the non-regenerative lowering mode based on the load on the load carrier (7).
6. The material handling vehicle (1) of any of the preceding claims, comprising a temperature sensor (18) for measuring a temperature of the hydraulic fluid, wherein the control computer (12) is configured to control the downstream valve (16) to be operated in either the regenerative lowering mode or the non-regenerative lowering mode based on the temperature of the hydraulic fluid.
7. The material handing vehicle (1) of any of the preceding claims, comprising a main lift (21) configured to lift and lower the load by means of both the first hydraulic cylinder (5a) and a second hydraulic cylinder (5b), wherein the first lowering valve (14) is configured to receive a first flow of hydraulic fluid released from the second hydraulic cylinder (5b) during lowering of the load, and the second lowering valve (15) is configured to receive a second flow of hydraulic fluid released from the second hydraulic cylinder (5b) during lowering of the load.
8. The material handling vehicle (1) of claim 7, further comprising a free lift (23) configured to lift and lower the load by means of a third hydraulic cylinder (5c), the material handling vehicle (1) further comprisinga third lowering valve (14’) configured to receive a first flow of hydraulic fluid released from the third hydraulic cylinder (5c) during lowering of the load, anda fourth lowering valve (15’) configured to receive a second flow of hydraulic fluid released from the third hydraulic cylinder (5c) during lowering of the load, wherein the downstream valve (16) is arranged downstream of, and in fluid communication with, also the third and the fourth lowering valves (14’, 15’).
9. The material handling vehicle (1) of any of the preceding claims, further comprising a prediction module (13) configured to predict at least one characteristic of a future loweringmovement of the load carrier (7) based on at least one of a current status and a previous action of the material handling vehicle (1), wherein the control computer (12) is configured to select lowering mode for the lowering movement based on the predicted characteristic of the lowering movement.
10. The material handling vehicle (1) of claim 9, wherein the current status of the material handling vehicle (1) comprises at least one of a current position of the load carrier (7) and a current position of the material handling vehicle (1).
11. The material handling vehicle (1) of claim 9 or 10, wherein the previous action of the material handling vehicle (1) comprises at least one of a previous movement of the load carrier (7) and a previous movement of the material handling vehicle (1).
12. The material handling vehicle (1) of any of the claims 9-11, wherein the prediction of the at least one characteristic of the future lowering movement comprises a prediction of a lowering distance of the lowering movement.
13. The material handling vehicle (1) of claim 12, wherein the control computer (12) is configured to select the regenerative lowering mode for the lowering movement only if the predicted lowering distance exceeds a minimum lowering distance threshold value.
14. The material handling vehicle (1) of any of the claims 9-13, wherein the prediction of the at least one characteristic of the future lowering movement comprises a prediction of whether the lowering movement is an unloading movement for unloading a load from the load carrier (7).
15. The material handling vehicle (1) of any of the preceding claims, wherein the material handling vehicle (1) is an industrial forklift truck.