EP4176139A1

EP4176139A1 - Control system of an arm of a loader vehicle (cwl)

Info

Publication number: EP4176139A1
Application number: EP21737672.2A
Authority: EP
Inventors: Adriano GARRAMONE; Mario GIRARDI; Andrea Gravili; Stefano Liberti
Original assignee: CNH Industrial Italia SpA
Current assignee: CNH Industrial Italia SpA
Priority date: 2020-07-01
Filing date: 2021-07-01
Publication date: 2023-05-10
Anticipated expiration: 2041-07-01
Also published as: EP4176139B1; IT202000015922A1; WO2022003085A1

Abstract

Method of controlling an arm (B) of a mechanical shovel (CWL), in which the mechanical shovel is equipped with a hydrostatic transmission (HY) comprising a first hydraulic pump (HP) arranged to power only a hydraulic motor (HM), a second pump (P) arranged to feed vehicle hydraulic actuators (A1, A2,...), including a first actuator (A1) arranged to control at least the lifting of the arm (B), a hydraulic accumulator (ACC) to accumulate energy under form of pressure, the method comprising the following steps: pressurization of the accumulator exclusively by said hydraulic motor, operating as a pump, during a regenerative braking, supplementation of said second pump by means of said accumulator (ACC) exclusively to supply the first actuator during at least the lifting of the arm (B).

Description

CONTROL SYSTEM OF AN ARM OF A LOADER VEHICLE (CWL)

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Field of the invention

The present invention relates the field of the control systems of the loader vehicles and in particular compact wheel loaders.

State of the art

Work vehicles or agricultural vehicles are well known for handling materials and performing specific heavy demanding tasks. They are often equipped with a hydraulically operated lift arm to move a shovel or bucket.

A wheel loader is a heavy machine used in construction to move earth or materials such as asphalt, demolition debris, snow, feed, gravel, logs, raw minerals, recycled material, rock, sand, wood chips, etc. . in or on top of another type of machinery, such as a truck, conveyor belt, feed hopper, or rail car. There are many types of mechanical loaders, which, depending on the design and application, are called by various names, including bucket loader, front loader, front loader, loader, shovel, shovel, skip loader, wheel loader or shovel compact or Compact wheel loader.

Usually, the movement of the boom and shovel is controlled by the user via a joystick placed inside the cab to accommodate the operator of the work vehicle.

The compact loaders, due to their compactness, are equipped with a prime mover, an internal combustion engine with reduced power. The prime mover drives in rotation a hydraulic pump that powers the on-board actuators, including that of the arm and that of the blade and the hydrostat pump. The arm, for a first end, is hinged to the vehicle frame, while the bucket is hinged to a second end of the arm, opposite to the first.

A hydraulic motor is operatively connected with the hydraulic pump defining a so-called hydrostat, in which a hydraulic outgoing line F and a hydraulic return line R interconnect the hydraulic pump with the hydraulic motor.

This implies that when the vehicle is in motion, the energy available to operate the various hydraulic actuators is reduced . This problem is particularly felt when the arm has to lift a load while the vehicle is moving forward, for example to load material into a truck.

The advancement of the vehicle and the simultaneous lifting of the arm are two very frequent concomitant operations that sometimes involve having to stop the advancement of the vehicle to give the arm time to rise to the desired height. This obviously affects the performance of the vehicle and the execution times of the activities.

If not specifically excluded in the detailed description that follows, what is described in this chapter is to be considered as an integral part of the detailed description.

Summary of the invention

Scope of the present invention is to improve the lifting speed of a load of a compact wheel loader, equipped with a hydrostatic transmission.

The basic idea of the present invention is to install a hydraulic oil accumulator arranged to be loaded with pressurized hydraulic oil during the recovery of kinetic energy during vehicle braking and arranged to power the arm actuator during its lifting.

The use of a hydraulic recovery unit is known, but it is inefficient, as the vehicle is generally equipped with a mechanical transmission that dissipates precious kinetic energy during vehicle braking. On the contrary, according to the present invention, the implementation of a fully hydraulic transmission allows to optimize the pressurization of the recuperator.

Furthermore, according to the present invention, the recuperator is connected exclusively to the boom lifting actuator and a processing unit allows to combine the flow of oil coming from the hydraulic pump with the flow of oil coming from the recuperator to operate the actuator of the arm as quickly as possible.

The dependent claims describe preferred variants of the invention, forming an integral part of this description. Brief description of the figures

Further objects and advantages of the present invention will become clear from the following detailed description of an example of its embodiment (and its variants) and from the annexed drawings given purely by way of non-limiting explanation, in which:

Figure 1 shows an example of a propulsion scheme of a work or agricultural vehicle according to the known art, closest to the present invention,

Figure 2 shows a hydraulic diagram of a preferred implementation of the present invention;

Figure 3 shows a compact wheel loader object of the implementation of the present invention;

Figure 4 shows a flow chart representative of an example of operation of the system object of the present invention. The same reference numbers and letters in the figures identify the same elements or components or functions.

In the context of this description, the term "second" component does not imply the presence of a "first" component. These terms are in fact used as labels to improve clarity and should not be understood in a limiting or ordinal way.

Solid lines indicate plumbing connections, while dashed lines indicate electrical or data bus connections.

The elements and features illustrated in the various preferred embodiments, including the drawings, can be combined with each other without however departing from the scope of this application as described below.

Detailed description of exemplary embodiments

Figure 1 shows a schematic of the propulsion system of a compact work or agricultural vehicle.

The propulsion system comprises a prime mover E, generally an internal combustion engine, for example Diesel or with positive ignition.

The prime mover is configured to drive a hydrostat HY in rotation, that is a variable geometry pump HP, which feeds a hydraulic motor HM by means of a forward F and return hydraulic line R.

The hydraulic motor has a shaft operatively associated with a driving axle RA of the vehicle.

Preferably, this association is achieved by means of a discrete gearbox GB. Generally, the secondary shaft of the gearbox GB rotates a port of a differential DF, to guide in rotation the two drive shafts of the driving axle RA. The configuration shown in Figure 1 is four-wheel drive, so that a rear driving axle RA and a front driving axle FA are identified. The configuration shown by itself is known. According to the present invention, the pump and the hydraulic motor can be controlled independently of each other by means of respective electro-hydraulic valves, not shown. The prime mover is in no way connected with the driving axles, except through the hydrostat. In other words, the prime mover is connected to at least one driving axle by means of only the hydrostat. An engine control processing unit ECU controls the operation of the prime mover.

A vehicle processing unit UCM interfaces with the engine control processing unit ECU and controls the hydraulic transmission HY as well as monitors the position of vehicle control levers, buttons and commands, both in relation to vehicle movement and operation of the arm, shovel, etc. which the work vehicle is equipped with or can be equipped. The existence of two distinct processing units is completely optional. A single processing unit can control both the prime mover and all the other vehicle functions and monitor the activation of commands by the operator.

Figure 2 shows a preferred electro-hydraulic circuit HC to implement the present invention, to be implemented in a compact wheel loader CWL shown in Figure 3. This diagram is, in some ways, horizontally overturned with respect to the diagram in Figure 1, since the prime mover E is shown on the right. The only component extraneous to the electrohydraulic circuit is the prime mover E, which is however represented to clarify the interaction between the electro-hydraulic circuit and the prime mover.

According to the present invention, the prime mover drives in rotation the hydrostat pump HP and a pump P for powering, exclusively, the hydraulic actuators of the users, including the actuator A1 for lifting (and lowering) the arm and the actuator A2 for adjusting the inclination of the tool which can be a shovel or a fork.

Therefore, there are two separate pumps, one dedicated to powering the on-board actuators and one dedicated to the hydrostatic transmission HY.

The hydraulic motor, according to this scheme, is connected directly to the wheels of the vehicle, but it is not excluded that there may be additional mechanical components, such as a discrete gearbox, differentials, and transmission shafts as shown in figure 1.

As in figure 1, the prime mover E is not mechanically connected to the wheels, except through the hydrostat HY.

A first electro-hydraulic valve VI is interposed between the flow lines F and return R of the hydrostat, identifying two branches FI, F2 of the flow line and two branches R1 and R2 of the return line.

In the example shown in Figure 2, the first valve VI includes three boxes, with a stable position schematized by the central box, indicated with 2. Therefore, the notation Vl_2 indicates the configuration relating to the box number 2 of valve VI.

The boxes 1 and 3 are intended to perform the regenerative braking backwards and forwards respectively, in relation to the indication of the forward and return lines. In fact, it is assumed that during forward travel, the pressure in the flow line F1/F2 is greater than in the return line R1/R2.

FI and R1 are directly connected with the HP hydraulic pump, while F2 and R2 are directly connected with the HM hydraulic motor.

When the box Vl_2 is active, the diagram refers, from a functional point of view, to the diagram of figure 1.

It is known that the hydraulic motor and the hydraulic pump of the hydrostat are reversible machines, each being able to function as a motor or pump depending on the circumstances.

During a forward regenerative braking, the hydraulic motor HM acts as a pump and therefore the pressure on the return line R1/R2 is higher than in the forward line F1/F2 (F). Then, according to the present invention, the first valve VI is commanded to activate the third box Vl_3, according to which the forward line F is kept active, i.e. the branches FI and F2 remain interconnected, while the branch R2 is disconnected from the branch R1 and is connected to the line AP, which feeds the hydraulic accumulator ACC. At the same time, the branch R1 of the return line is connected with the hydraulic oil tank T, so that the hydraulic pump HP can suck hydraulic oil from the hydraulic oil tank T. This hydraulic line AP is the only line that feeds the hydraulic accumulator. In other words, the hydraulic accumulator can only be pressurized by the hydrostat and in particular by the first valve VI arranged between the hydrostat supply and return lines. If the pressure measured in the accumulator ACC by the sensor SAC exceeds the maximum pressure value Pmax with which the accumulator can be charged, then the first valve VI is deactivated and returns to the released condition Vl_2 by stopping the charging of the accumulator. In the event that, during regenerative braking, the accumulator pressure is already greater than Pmax, valve VI remains in the released position and the accumulator is not recharged. Conversely, when the vehicle travels in reverse, the hydraulic oil pressure is higher on the R1/R2 (R) return line than on the F1/F2 (F) forward line. During regenerative braking in reverse, the pressure on the forward line is greater than the return line, but opposite to normal forward travel, the hydraulic motor acts as a hydraulic pump. Then, the pressure present in the delivery line is used to pressurize the hydraulic accumulator ACC. To do this, the first valve VI is commanded to activate the first box Vl_l, according to which the return line is kept active, i.e. the branches R1 and R2 are mutually interconnected, the branch F2 is connected to the AP line to pressurize the hydraulic accumulator ACC, while the branch FI is connected to the hydraulic oil tank T, so that the hydraulic pump HP can suck hydraulic oil from the hydraulic oil tank T. A first valve CK1 is arranged on the line AP in order to prevent any pressurized oil reflux towards the hydrostat HY. Pump P, as anticipated above, powers several actuators. In the lower part of figure 2 it is disclosed that the pump P feeds the actuator A1 through a conduit PI and a third valve V3. The third valve V3 includes three boxes 1 - 3. In a released configuration, corresponding to the second box V3_2, the third valve connects the pipe PI with the hydraulic oil tank T, closing the opposing chambers of the actuator A1. The hydraulic actuator A1 shown in figure 2 includes two opposing chambers, "Lift UP" and "Lift down" and depending on the pressurized chamber, determines the displacement of a mobile piston in extension or retraction. The chambers are indicated with the same function, according to Anglo-Saxon terminology, that they perform. Therefore, the Lift up chamber determines the lifting of the arm B of the CWL vehicle .

Conversely, the Lift down chamber determines the lowering of arm B. The first box V3_l of the third valve V3 determines the connection of the pipe PI with the Lift up chamber, while the opposite Lift down chamber is connected with the hydraulic oil tank T. Vice versa, the third box V3_3 of the third valve V3 determines the connection of the pipe PI with the Lift down chamber, while the opposite Lift up chamber is connected with the hydraulic oil tank T. Therefore when the first box V3_l is active the arm is raised, while, when the second box V33 is active the arm is lowered. Although valve V3 may have a built-in or implicit non-return valve, this is explicitly shown as "CK3" arranged on line PI.

According to the present invention, the accumulator ACC is connected exclusively to the Lift up chamber of the A1 actuator. Therefore, the accumulator is arranged to supplement the second pump exclusively to power the first actuator A1 arranged at least for lifting the arm.

Being a double action actuator, then the supplementation could also be performed for lowering the arm. This fact justifies the "at least" just mentioned.

This is achieved by means of a second valve V2, for example of the ON/OFF type, normally closed. A second non-return valve CK2 is arranged between the second valve V2 and the Lift up chamber. In particular, the output of the first box V3_l of the third valve and the output of the second valve V2 converge on a common duct PLU connected to the Lift Up chamber .

According to the present invention, the lifting of the arm is always operated by switching the third valve so as to activate the first box V3_l.

If the pressure in the accumulator exceeds the pressure generated by said second pump by a predetermined right pressure threshold, then the second valve V2 is enabled to switch to ON, causing an acceleration (boost) of the boom lifting .

If the boost function, i.e. acceleration, of the arm lifting is active, then the second valve switches to ON immediately after the switching of the third valve with the activation of the relative first box V3_l.

This means that when the boost function is active, the Lift up chamber is powered simultaneously by the pump P and the hydraulic accumulator. In other words, the pump P is supplemented by the accumulator ACC.

Figure 4 shows an example of a flow chart relating to the implementation of the present invention. The steps/blocks S10 and Sll respectively indicate the verification that the boost function is active (ON) and that the arm B is operated to lift with the appropriate control lever, for example a joystick.

The arm lifting command signal is indicated by the symbol "V3_l", which corresponds to the first box (or spool) of the third valve V3 which is activated as a consequence of the command signal itself, generated for example by a control lever, and is higher than a certain value DP.

The command signal is proportional to the inclination of the control lever or to the lowering of a pedal. When the lever exceeds a predetermined inclination, then, the command signal exceeds a corresponding threshold value DP which cooperates to cause the activation of the boost function.

If both checks S10 & Sll return a positive result (yes) then at step S12 it is checked whether the pressure measured in the accumulator is higher than the pressure generated by pump P to lift arm B, further to the aforementioned predetermined value DX.

The pressure value DX is a so-called guard value chosen in order to ensure a significant flow rate of additional hydraulic oil.

If this check also returns a positive result then, at step S14, the second valve V2 is commanded to open, otherwise, if any of the checks S10, Sll, S12 return a negative result, then the second valve V2 is commanded to close and it starts again from steps S10, Sll.

It is worth noting that steps S10 and Sll are of equal rank, in the sense that they can be performed in parallel or in succession to each other without detecting appreciable operating differences in the lifting system of the arm B.

It is also worth noting that step S13 is replicated in two points of the diagram only for greater clarity of the same diagram.

It is worth highlighting that each of the three-box valves VI and V3 has the central box n.2 as a released condition, that is the spool that is activated naturally when no command is applied to the same valves. Furthermore, these three-box valves can be replaced by groups of valves which have functions equivalent to those described here.

It is worth noting that in the diagram in Figure 2, the hydraulic oil tank T is shown in different points of the diagram only to facilitate the representation of the same diagram.

This tank T can be at atmospheric pressure.

The diagram in figure 4 is performed cyclically indefinitely and assumes that the Boost function is enabled.

Enabling the Boost function can be done in several ways. According to a preferred variant of the present invention, a first three-position slider MDA is arranged on the dashboard .

A first position A indicates the automatic activation of the boost function, a second position D deactivates the boost function and a third position M activates the boost function manually .

When the boost function is active automatically, this is equivalent to eliminating the control S10 from the diagram of Figure 4, so that the check steps remain only Sll and S12.

When the boost function is disabled, this is equivalent to the fact that step S10 always and invariably returns "no". When the boost function is active in manual, then "yes" is returned by step S10 when a second button BOO, preferably monostable and located on the boom lift control lever RIS, is simultaneously pressed while the lever is operated by the operator to raise the arm. According to this last operating condition, therefore, three commands must return an enable/activate signal simultaneously. In particular, the first slider and the second button return a signal enabling the boost function, while the boost function is actually performed when the arm control lever is operated so as to cause the arm to be raised.

The functions of the first slider can also be integrated into a man/machine interface comprising a tactile display (touchscreen) with relative menus and setting submenus. Preferably, to improve the performance of the present technical solution, during a regenerative braking, the hydraulic motor HM, which operates as a pump, is controlled in such a way as to increase the relative displacement in order to maximize both the braking effect and the recharge of the hydraulic accumulator.

In order to detect the occurrence of a regenerative braking it must be found that the pressure on the return line must be greater than on the forward line when the vehicle is moving forward and vice versa when moving backward.

These checks can be carried out by means of two pressure sensors SF and SR arranged respectively on branches F2 and R2, shown in figure 2.

When these conditions are met then the hydraulic motor is controlled to achieve its maximum possible displacement. Figure 2 shows a processing unit "Control Unit", which supervises the operation of the hydraulic circuit described above. This processing unit is arranged to acquire, in a per se known manner, at least one of

- The condition of the F/N/R switch, respectively forward gear "F", neutral "N" and reverse "R";

- The position of the arm control lever (Joystick),

- The speed of rotation of the prime mover,

- The condition of the first slider enabling the automatic or manual boost function, or relative disabling,

The condition of the second monostable button to activate/deactivate the manual boost function,

- The condition of the accelerator pedal AP.

Please note that the vehicle can also be equipped with an hand accelerator lever HT.

The processing unit "Control Unit" in Figure 2 may coincide with the processing unit indicated in Figure 1 with the "UCM" symbol.

According to a preferred variant of the present invention, regenerative braking can occur only when the vehicle is in motion and the accelerator lever is released.

According to another preferred variant of the invention which is combined with the previous one, when the vehicle is in motion and the brake pedal is pressed below a predetermined pressure threshold then braking is only of the regenerative type, while beyond the aforementioned threshold also the vehicle braking means are activated.

Preferably, the release of the accelerator pedal causes a regenerative braking with a first braking intensity, while, the activation of the brake pedal below the aforementioned pressure threshold causes a regenerative braking with a second regenerative braking intensity greater than first intensity, while, the activation of the brake pedal above the aforesaid pressure threshold determines a regenerative braking with a third regenerative braking intensity greater than the second intensity.

The present invention is preferably implemented in the vehicle processing unit UCM, but there is no impediment to implement it in the ECU.

The present invention can be advantageously realized by means of a computer program, which comprises coding means for carrying out one or more steps of the method, when this program is executed on a computer. Therefore, it is intended that the scope of protection extends to said computer program and further to computer readable means comprising a recorded message, said computer readable means comprising program coding means for carrying out one or more steps of the method. , when said program is run on a computer.

Implementation variants of the described non-limiting example are possible, without however departing from the scope of protection of the present invention, including all the equivalent embodiments for a person skilled in the art, to the content of the claims.

From the above description, the person skilled in the art is able to realize the object of the invention without introducing further construction details.

Claims

1. Method for controlling an arm (B) of a loader vehicle (CWL), wherein the loader vehicle is equipped with . a hydrostatic transmission (HY) comprising a first hydraulic pump (HP) arranged to power only a vehicular propulsion hydraulic motor (HM), a second pump (P) arranged to feed vehicle hydraulic actuators (Al, A2, ...), including a first actuator (Al) arranged to control at least the boom lift (B),

. a hydraulic accumulator (ACC) arranged to store energy in the form of pressure, the method comprising the following steps pressurization of the accumulator exclusively by said hydraulic motor, operating as a pump, during regenerative braking, supplementation of said second pump by means of said accumulator (ACC) exclusively to supply said first actuator during at least the arm lift.

2. Method according to claim 1, wherein said supplementation is carried out so that only said first actuator is powered also by said accumulator (ACC).

3. Method according to any one of claims 1 or 2, wherein said supplementation is carried out only if the following conditions are all simultaneously verified: a supplementation enabling signal (Boost ON = yes) is active, - an arm lift control signal exceeding a predetermined threshold (DP) (V3_l> DP = yes) is present, a pressure in the accumulator exceeds the pressure generated by said second pump by a predetermined pressure threshold (DX) (SAO S3 + DX = yes).

4. Method according to any one of the preceding claims, comprising the step of increasing or maximizing the displacement of the hydraulic motor during regenerative braking.

5. Method according to any of the preceding claims, wherein the regenerative braking is activated when the vehicle is in motion and the accelerator lever is completely released.

6. Computer program comprising program coding means adapted to perform all steps (S10 - S14) of any one of claims 1 to 5, when said program is run on a computer.

7. Computer readable means comprising a recorded program, said computer readable means comprising program coding means suitable for carrying out all steps (S10 - S14) of any one of claims 1 to 5, when said program is run on a computer.

8. Control system of an arm (B) of a loader vehicle (CWL), wherein the mechanical shovel is equipped with a hydrostatic transmission (HY) comprising a first hydraulic pump (HP) arranged to power only a vehicular propulsion hydraulic motor (HM), a second pump (P) arranged to feed vehicle hydraulic actuators (Al, A2, ...), including a first actuator (Al) arranged to control at least the boom lift (B),

. a hydraulic accumulator (ACC) to store energy in the form of pressure,

. a hydraulic circuit (HC) arranged for

- pressurize the accumulator exclusively by means of said hydraulic motor, operating as a pump, during regenerative braking, the second pump is supplemented by means of said accumulator (ACC) exclusively to supply said first actuator (Al) during at least the arm lift.

9. System according to claim 8, wherein said hydrostat comprises a hydraulic forward line (F) and return (R) line and wherein said forward line is divided into a first branch (FI) directly connected with said first pump and a second branch (F2) directly connected with said hydraulic motor, said return line is divided into a first branch (Rl) directly connected with said first pump and a second branch (R2) directly connected with said hydraulic motor, - a first valve (VI) arranged to connect said second branch

(F2, R2) of the forward or return line with the accumulator (ACC) during a regenerative braking forwards or backwards respectively, in order to charge the hydraulic accumulator,

- a third valve (V3) arranged to connect said second pump (P) with said first actuator to determine the lifting of the arm (B),

- a second valve (V2) arranged to connect said hydraulic accumulator (ACC) exclusively with said first actuator to supplement the second pump (P) in supplying the first actuator.

10. System according to one of claims 8 or 9, wherein said second valve (V2) is arranged to switch to open at least when a pressure in the hydraulic accumulator exceeds the pressure generated by said second pump by a predetermined pressure threshold (DX) (SAO S3 + DX = yes).

11. System according to claim 10, wherein the pressure generated by the second pump is measured by means of a third pressure sensor (S3) located between the third valve and the first actuator (Al).

12. System according to any one of the preceding claims 9 -

11, further comprising a processing unit (UCM, CONTROL UNIT) configured to command opening of said second valve (V2) when the following conditions are all simultaneously verified - a supplementation activation signal (Boost ON = yes) is present, an arm lift control signal exceeding a predetermined threshold (DP) (V3_l> DP = yes) is present, the pressure in the hydraulic accumulator exceeds the pressure generated by said second pump by a predetermined pressure threshold (DX) (SAO S3 + DX = yes).

13. Work vehicle, in particular a compact wheel loader vehicle (CWL), comprising a prime mover (E), an arm (B) and an arm actuation system (B) according to any one of claims 8 to 12, wherein said prime mover is arranged to drive said first and second hydraulic pumps (HP, P) in rotation.