ES2743708T3 - Lifting vehicle with a telescopic lifting arm equipped with an impact absorption system - Google Patents

Abstract

Lifting vehicle including: - a self-propelled chassis (12), - a telescopic arm (18) provided at a distal end with a tool mounting accessory (22), and including a base section (30) hinged to the chassis ( 12) and at least one telescopic section (32), - at least one lifting cylinder (28) arranged between the telescopic arm (18) and the chassis (12), - at least one extension cylinder (34) arranged to control the movement of said at least one telescopic section (32) between a retracted position and multiple extracted positions, characterized in that it further comprises - a hydraulic circuit (36) that includes a hydraulic distributor (40) connected to said extension cylinder (34) through first and second hydraulic lines (42, 44) connected, respectively, to first and second chambers (46, 48) of the extension cylinder (34), in which a pressure controlled blocking valve (52) is arranged in bliss first hydraulic line (42), in which the hydraulic circuit (36) includes a shock absorption system (54) that includes at least one gas accumulator (56) connected to a part of said first hydraulic line (42) comprised between said first chamber (46) of the extension cylinder (34) and said blocking valve (52).

Description

DESCRIPTION

Lifting vehicle with a telescopic lifting arm equipped with an impact absorption system

Field of the Invention

The present invention relates to a lifting vehicle with a telescopic lifting arm provided with a tool mounting accessory.

Description of the prior art

Lift vehicles of this type may be equipped with different types of tools, for example, forks, shovels, aerial platforms, etc. When the vehicle operates with a shovel, fork or similar tool that loads the ground, it is possible that the tool collides with rigid obstacles located at a close distance from the vehicle, such as walls, pavements or protruding wells. Lift vehicles have a high kinetic energy or momentum, essentially due to the considerable mass of the vehicle, so that frontal collisions, even at slow speeds, cause high tensions in the structure of the vehicle, in particular the arm, chassis and arm joint pin, and expose the operator to dangerous situations.

Lift vehicles, loaders and tractors with a front loader, currently on the market, do not have any protection against collisions, and this can cause injury to the operator, as well as damage to the machines. US-A-4280589 discloses a telescopic arm controlled by an extension cylinder. A platform is articulated at a distal end of the telescopic arm. The telescopic arm comprises a joint designed to prevent the telescopic arm from breaking if the platform receives heavy impact strokes that attempt to swing it around its articulation axis.

Object and summary of the invention

The object of the present invention is to provide a lifting vehicle with a telescopic lifting arm that allows it to mitigate the effects of frontal collisions.

According to the present invention, this object is achieved by a lifting vehicle having the characteristics that make up the object of claim 1.

As will be evident in the following description, the vehicle according to the invention is equipped with an impact absorption system associated with the telescopic arm extension cylinder. The shock absorption system allows a gradual return of the telescopic section of the arm in the event of a frontal collision, with a consequent reduction of the effects of inertia on the vehicle. Thanks to the shock absorption system, damage to the vehicle is limited and the risks to which the driver would be subjected in the event of a frontal collision are reduced. The shock absorption system according to the present invention is also particularly useful in all thrust stages with a shovel, blade or similar tools, since it mitigates the stresses imposed in the normal work process, even in the absence of frontal collisions.

Brief description of the drawings

The present invention will now be described in detail with reference to the accompanying drawings, provided only by way of non-limiting example, in which:

- Figure 1 is a perspective view of a lift vehicle with a telescopic arm.

- Figure 2 is a diagram of the hydraulic circuit associated with the telescopic arm of a vehicle according to the present invention.

- Figure 3 is a cross section of a solenoid valve indicated by arrow III in Figure 2, - Figure 4 is a perspective view of an accumulator assembly, and

- Figure 5 is a diagram showing the pressure variation as a result of a frontal collision in a system according to the present invention.

Detailed description

With reference to Figure 1, the number 10 indicates a lift vehicle comprising a self-propelled chassis 12 having a front axle 14 and a rear axle 16. The vehicle 10 comprises a telescopic arm 18 articulated in the rear section 12 of the chassis around a transverse axis 20. The telescopic arm 18 is provided at one end of a accessory 22 to connect different types of tools.

The telescopic arm 18 is located in the center of the chassis 12, between a driving cabin 24 and an engine assembly 26. The vehicle 10 comprises a lifting cylinder 28 with ends articulated to the chassis 12 and the arm 18. The lifting cylinder 28 is operable to control the inclination of the arm 18 around the transverse axis 20 between a lowered position, in which the arm 18 It extends in the horizontal or lower direction, and multiple elevated positions.

The telescopic arm 18 includes a base section 30 that is articulated to the chassis 12 around the transverse axis 20 and a telescopic section 32, which is movable inside the base section 30 along a direction parallel to the longitudinal axis of the arm 18. The telescopic arm 18 comprises an extension cylinder 34 that controls the telescopic movement of the telescopic section 32 along the longitudinal axis of the arm 18 between a retracted position and multiple extracted positions.

In the example illustrated in Figure 1, the telescopic arm 18 has a single telescopic part. Alternatively, the telescopic arm may have multiple telescopic parts, each of which is associated with a respective extension cylinder, or with one or more cylinders with cable or chain drives for movement.

With reference to Figure 2, the vehicle 10 has a hydraulic circuit 36 comprising a main pump 38 driven by the thermal engine of the vehicle 10. The hydraulic circuit 36 includes a hydraulic distributor 40 that receives pressurized fluid from the pump 38 and controls the extension cylinder 34 by means of a first hydraulic line 42 and a second hydraulic line 44, connected, respectively, to a first chamber 46 and a second chamber 48 of the extension cylinder 34. The pressure in the first chamber 46 controls the removal of the rod 50 from the hydraulic cylinder 34 and the pressure in the second chamber 48 controls the return 50 of the rod.

A pressure-controlled blocking valve 52 is arranged in the first hydraulic line, which prevents a return of fluid from the first chamber 46 to the distributor 40 in the absence of a pressure in the second hydraulic line 44 that is higher than a preset value. .

The hydraulic circuit 36 includes an impact absorption system 54 associated with the extension cylinder 34. The shock absorption system 54 includes at least one gas accumulator 56. In a preferred embodiment, the impact absorption system 54 includes multiple gas accumulators 56 that have different respective operating pressures and that are connected in parallel to each other to a manifold 58. Figure 4 shows a constructive example of an embodiment of the assembly of accumulators 56.

The manifold 58 of the shock absorption system 54 is connected to the first hydraulic line 42 through a line 60 connected to a part of the first hydraulic line 42 between the first chamber 46 and the blocking valve 52.

The shock absorption system 54 may be associated with a safety device 63 that includes an extension sensor 62, a solenoid valve 64 disposed on line 60, and an electronic unit 66. Figure 3 shows a constructive example in which the valve 64 has a rotating disk 66 in a block 68, which has a channel 70 connected to the line 60 and a hole 72 connected to the manifold 58 of the accumulators 56. The valve 64 of Solenoid is a CLOSED / OPEN valve that is normally closed, and is opened by the electronic unit 66 when the extension sensor 62 signals that the extension 34 of the cylinder is below a predetermined threshold. When the extension 34 of the cylinder exceeds the predetermined threshold, the solenoid valve 64 is in a closed position.

The operation of the impact absorption system 54 is as follows.

Under normal operating conditions, the extension cylinder 34 is fed through the distributor 40. When the extension cylinder 34 has reached a required extension corresponding to the required length of the telescopic arm 18, the distributor 40 is in a central position. In the central position, the distributor blocks the passage of oil. In addition, if there is no pressure in the second line 44, the blocking valve 52 closes and blocks the flow of fluid along the first line 42 between the extension cylinder 34 and the distributor 40.

The extension sensor 62, formed by a micro-switch or an equivalent sensor, detects whether the extension 34 of the cylinder is less than or greater than a threshold limit. If the extension 34 of the cylinder is less than the threshold limit, the electronic unit 66 switches the solenoid valve 64 to the open position. When the solenoid valve 64 is open, the accumulators 56 are in hydraulic communication with the first chamber 46 of the cylinder 34.

In the case of a frontal collision with an obstacle, the rod 50 of the cylinder 34 retracts. The volume of hydraulic fluid leaving the first chamber 46 is sent to the accumulators 56. When the pressure of the hydraulic fluid in the accumulators 56 exceeds its preload pressure, the hydraulic fluid compresses the gas in the accumulators 56. The accumulators 56 are loaded with the hydraulic fluid from the cylinder 34 and gradually slows the return of the arm and, therefore, slows the forward movement of the vehicle. The number of accumulators 56 depends on the maximum braking stroke that is required, or rather, on the return length of the arm inside of which the arm stop the machine

When the extension length of the cylinder 34 exceeds a threshold limit, the safety device 63 inhibits the shock absorption system 54 by closing the solenoid valve 64. The safety device 63 performs a safety function in the sense that, if the volume of hydraulic fluid directed towards the accumulators 56 becomes too high, there would be a risk that the accumulators will explode. In an alternative representation, in addition to, or instead of, the solenoid valve 64 and the extension sensor 62, a pressure limiting valve could be provided on line 60, which laminates the hydraulic fluid to the discharge if the pressure exceeds maximum permissible pressure of the accumulators.

The calibration pressure of the accumulators 56 must not be too low, otherwise, the telescopic section 32 of the arm 18 would retract under low loads that do not correspond to a collision situation. At the same time, the accumulator calibration pressure should not be too high, otherwise the vehicle would still have a dangerous initial collision.

The pressure trend during the operation of the impact absorption system 54 is shown schematically in the graph of Figure 5.

The time t0 indicates the moment at which the frontal collision occurs. Before the collision, the vehicle is moving and the pressure in the chamber 46 of the cylinder 34 is equal to the base value p0. Immediately after the collision, there is an almost instantaneous increase in hydraulic fluid pressure. When the fluid pressure reaches a p1 value equal to the value of the accumulator calibration pressure p *, the gas inside the accumulators begins to compress. At this stage, between moments t1 and t2, the telescopic section 32 of the arm 18 retracts, opposing a progressively increasing force to the movement of the vehicle. This force gradually slows down the vehicle, until the vehicle stops at time t2, which corresponds to a pressure p2. The pressure p2 must be less than the maximum pressure (pmax) of the accumulators.

The safety device 63 serves to prevent the fluid pressure in line 60 from exceeding the maximum pressure of the accumulators.

Next, the sizing procedure of the impact absorption system 54 will be provided. The diameter d of the cylinder and the maximum stroke x within which the moving vehicle should stop are known. Therefore, the maximum AV volume of the fluid to be dissipated can be calculated:

The vehicle that collides frontally against a fixed obstacle has a kinetic energy that must be dispersed to brake the vehicle. The kinetic energy E is calculated based on the mass m of the vehicle and its collision speed vmax that is hypothesized in the design phase:

In other words, the shock absorption system 54 is sized to brake the machine to a certain speed vmax, without impacts.

The kinetic energy is largely dissipated by the accumulators, by means of a very rapid compression of the gas (nitrogen). Therefore, it has an adiabatic transformation:

PlVl = P2V2V = k = * P = kV ~ r

Where p ¹ and p ² are the initial and final pressures of the gas (and oil) and V ¹ and V ² are the initial and final gas volumes.

The energy stored in the accumulator is equal to the compression work that the hydraulic fluid can exert on the gas compartment:

or

Once the initial volume is established, the final volume is calculated as V ² = V ¹ - AV The final p ² pressure is imposed at a value equal to the maximum value that can be supported by the accumulator (approximately 250 bar), while the initial pressure is Calculate as:

If L> E, then the system is capable of dissipating all kinetic energy. Volume Vi must be set to the lowest possible value to reduce the volume of gas required and, therefore, the number of accumulators, always maintaining a certain safety margin capable of guaranteeing the dissipation of all energy, even in conditions that exceed to those of the design.

Once the maximum necessary parameters have been identified, then the data necessary for sizing and the number of accumulators can be identified.

Since the transformation is not linear, the compression of the gas must begin at a precise pressure value defined by pi, on which basis the accumulator preload is chosen. In the catalogs it is recommended to use a precharge pressure for the accumulators equal to 90% of the minimum for reasons of wear, therefore

Actually, in this case, wear is not a big problem since the air compartments are compressed occasionally and not cyclically. In addition, as indicated, to dissipate the energy provided, it is necessary that the oil begins to compress the compartment at the set pressure and not before, because a job done at a lower pressure for the same volume dissipates less energy and there would be a risk of reaching the end of the route without having braked the vehicle and, therefore, with a speed that is not equal to zero. For this reason, the precharge value of the accumulators remains the same as the initial compression:

The volume Vo, total required nominal ^tot can be calculated according to the catalog of the accumulators:

At this point, it is easy to calculate the minimum number of nacc accumulators required as:

Where Vacc is the volume of a single accumulator.

Once these system parameters have been defined, the maximum pressure actually achieved and the effective arm stroke before the machine stops can be calculated, and then the safety margin can be evaluated. Pressure losses are also present in the system, which function as a damping system. Therefore, the deceleration of the arm will be aided in part by dissipations inside the hydraulic components.

The impact absorption system described above, as well as its deactivation by the safety device 63, according to the extension of the telescopic arm 18, can also be deactivated by an order from the operator or automatically by an angle sensor that detects the tilt of the telescopic arm 18.

Of course, without prejudice to the principle of the invention, construction details and representations may vary widely with respect to those described and illustrated, without thereby departing from the scope of the invention as defined in the following claims.

Claims (5)

1. Lifting vehicle that includes: - a self-propelled chassis (12), - a telescopic arm (18) provided at a distal end of a tool mounting accessory (22), and which includes a base section (30) articulated to the chassis (12) and at least one telescopic section (32), - at least one lifting cylinder (28) arranged between the telescopic arm (18) and the chassis (12), - at least one extension cylinder (34) arranged to control the movement of said at least one telescopic section (32) between a retracted position and multiple extracted positions, characterized in that it further comprises - a hydraulic circuit (36) that includes a hydraulic distributor (40) connected to said extension cylinder (34) through first and second hydraulic lines (42, 44) connected, respectively, to chambers (46, 48) first and second of the extension cylinder (34), in which a pressure-controlled blocking valve (52) is arranged in said first hydraulic line (42), wherein the hydraulic circuit (36) includes an impact absorption system (54) that includes at least one gas accumulator (56) connected to a part of said first hydraulic line (42) comprised between said first chamber (46) of the extension cylinder (34) and said blocking valve (52). 2. Lift vehicle according to claim 1, characterized in that said impact absorption system (54) includes multiple accumulators (56) connected in parallel to a common manifold (58). 3. Lift vehicle according to claim 2, characterized in that said accumulators have respective calibration pressures that are different from each other. 4. Lifting vehicle according to any one of the preceding claims, characterized in that said impact absorption system (54) includes an OPEN / CLOSED valve (64) that blocks the connection between said at least one accumulator (56) and said first line (42) hydraulic when the extension of said cylinder (34) is greater than a predetermined threshold value, or when the angle of the telescopic arm (18) is greater than a predetermined value, or when the impact absorption system (54) It is deactivated by the operator. 5. Lifting vehicle according to any one of claims 1-4, characterized in that said impact absorption system (54) includes a pressure limiting valve, which laminates the hydraulic fluid towards a discharge when the pressure in the accumulator exceeds a limit value predetermined.