HYDRAULIC MOTOR WITH AXIAL PISTONS Technical Field

The present invention relates to a hydraulic motor with axial pistons, particularly for wheel drives of the type used to drive the tracks of miniexcavators or the like. Background Art

It is known that the building sector uses extensively large or small excavators to remove, lift and move soil, sand, gravel, et cetera.

Smaller excavators, on average with sizes between 1 and 6 tons, are commonly known as miniexcavators and due to their small dimensions are used in all the operations performed in confined yards and with limited maneuvering space.

Traditional miniexcavators are provided with a track drive which is actuated by means of hydraulic wheel drives. These wheel drives consist of a hydraulic motor, generally of the type with axial pistons, which is associated with an epicyclic reduction unit which transmits the motion to the tracks of the miniexcavator.

The hydraulic motor, which is associated with the hydraulic supply circuit of the miniexcavator, can have different shapes and architectures. A first known type of motor for miniexcavators is constituted by fixed-displacement motors, which in practice process a preset capacity of oil, determined during design, to allow the machine to perform the most onerous and heavy work, such as for example overcoming grades or performing turning maneuvers, without blocking the tracks of the miniexcavator.

It is in fact necessary to bear in mind that the pressure of the oil that drives the motor tends to increase as the maneuver of the miniexcavator becomes more onerous, until a maximum pressure value, determined by the safety components of the hydraulic circuit, is reached. At this maximum pressure value, the oil is redirected directly to the

discharge of the hydraulic circuit, bypassing the motor and consequently blocking the movements of the miniexcavator.

These motors of the traditional type are not free from drawbacks, including the fact that they cause the miniexcavators on which they are mounted to be scarcely versatile and practical.

In order to allow the miniexcavators to work even in particularly onerous working conditions, the displacement of the motors is in fact usually very high (oversized), since this, other factors being equal, allows to transmit to the tracks a large ground traction torque, to the detriment however of a severe limitation of the travel and maneuvering speed of the vehicle.

In view of the increasingly felt need to optimize the performance of the machines and yard work times, the limited speed of travel of the miniexcavators is a considerable drawback. In order to obviate these problems, miniexcavators have been devised which are provided with variable-displacement motors, i.e., capable of working in maximum-displacement conditions, which correspond to a low travel speed of the miniexcavator and to a considerable track driving torque, or in minimum-displacement conditions, which correspond to an increased transfer speed and limited driving torque.

In such machines, displacement variation is usually performed by means of a manual switching mechanism, which can be operated by the operator according to the operating requirements, i.e., depending on whether high performance in terms of vehicle travel speed or in terms of track driving torque is required.

However, even these miniexcavators have drawbacks, including the fact that disadvantageously they require the intervention of the operator not only to perform ordinary driving and maneuvering of the machine but also to change the displacement of the motor. Moreover, one must also consider that displacement changing while

the miniexcavator is moving is not at all gradual and comfortable, since it allows to work alternately in the two extreme configurations of the motor (minimum or maximum displacement), and is usually performed only by skilled and expert operators. Most of the time, this displacement changing is performed after the vehicle has stopped completely, disrupting and slowing down the work performed by the miniexcavator. Disclosure of the Invention

The aim of the present invention is to eliminate the drawbacks noted above of known motors, by providing a hydraulic motor with axial pistons which is capable of operating efficiently even in mutually very different operating conditions and allows to optimize the performance of the machines on which it is mounted and their productivity, all without needing direct intervention of the operator and interruption of the translational motion of the machines on which it is mounted.

Within this aim, an object of the present invention is to provide a hydraulic motor which is simple, relatively easy to provide in practice, safe in use, effective in operation, and has a relatively low cost.

This aim and these and other objects which will become better apparent hereinafter are achieved by the present hydraulic motor with axial pistons, which comprises a casing for containing a motor shaft and a plurality of pistons which are substantially parallel to said motor shaft and act on a swash plate which is mounted around said motor shaft so as to oscillate between a maximum-displacement configuration and a minimum- displacement configuration, at least one first duct and one second duct for connecting said pistons to a circuit for supplying a working fluid, and hydraulic means for varying the inclination of said swash plate as a function of the higher pressure of the working fluid in said connecting ducts, characterized in that it comprises valve means for enabling and disabling said hydraulic means which can be moved functionally between a first

working position, in which said hydraulic means are disabled and said swash plate is arranged in said maximum-displacement configuration, and a second working position, in which said hydraulic means are enabled and said swash plate is arranged in any angular configuration, comprised between said maximum- and minimum-displacement configurations, of equilibrium for said applied higher pressure, said swash plate being able to oscillate continuously and bidirectionally between the maximum- and minimum-displacement configurations .

Brief description of the Drawings Further characteristics and advantages of the present invention will become better apparent from the following detailed description of a preferred but not exclusive embodiment of a hydraulic motor with axial pistons, illustrated by way of non-limiting example in the accompanying drawings, wherein: Figure 1 is a hydraulic diagram of the motor according to the invention, applied to an epicyclic reduction unit for wheel drives;

Figure 2 is a sectional view, taken along a longitudinal plane, of the motor according to the invention in the maximum-displacement configuration; Figure 3 is a sectional view, taken along the line III-III of Figure 2, with the enabling and disabling valve means arranged in a first working configuration;

Figure 4 is a sectional view, taken along a longitudinal plane, of the motor according to the invention, in the minimum-displacement configuration;

Figure 5 is a sectional view, taken along the line V-V of Figure 4, with the enabling and disabling valve means arranged in a second working configuration;

Figure 6 is a sectional view, taken along a longitudinal plane, of the motor according to the invention, in a possible configuration which is

intermediate between the minimum- and maximum-displacement configurations;

Figure 7 is a sectional view, taken along the line VII-VII of Figure 6, with the enabling and disabling valve means arranged in the second working position;

Figure 8 is a sectional view, taken along the line VIII-VIII of Figure 2;

Figure 9 is an enlarged-scale view of a portion of Figure 2 related to the hydraulic means of the motor according to the invention. Ways of carrying out the Invention

With reference to the figures, the reference numeral 1 generally designates a hydraulic motor with axial pistons, particularly for wheel drives of the type used to drive the tracks of miniexcavators or the like.

Conveniently, the motor 1 can be mounted on a miniexcavator, not shown in the figures, and composes, together with an epicyclic reduction unit R to which it is connected, a so-called wheel drive for driving tracks.

The motor 1 comprises a casing 2, which is divided into a first portion 2a and a second portion 2b, which acts as a lid, said portions being mutually fixed by way of conventional screw means 3. The first portion 2a is hollow and accommodates internally a motor shaft 4 and a plurality of pistons 5 which are parallel thereto and act on an oscillating swash plate 6 which has mutually inclined opposite faces. The second portion 2b can be provided in two or more parts which are coupled to each other. Each piston 5 is provided with a spherical head 5a which is engaged in a corresponding spherical receptacle 6a which is rigidly coupled to the swash plate 6, so as to allow the transfer of its translational motion to said swash plate as its inclination varies.

The swash plate 6 has, in its central portion, a hole 6b in which the motor shaft 4 is arranged so as to pass through it. The swash plate 6 is in

fact mounted around the motor shaft 4 so that it can oscillate continuously and bidirectionally between a maximum-displacement configuration and a minimum-displacement configuration.

The pistons 5 are accommodated so that they can slide within corresponding cylinders 7, which are connected to at least one first duct 8 and to at least one second duct 9 for connection to a circuit for supplying a working fluid under pressure, such as oil or the like.

A conventional distribution element 10 is interposed between the cylinders 7 and the ducts 8 and 9. The inlet of the ducts 8 and 9 into the casing 2 is arranged in the second portion 2b and proximate to said inlet there is a balancing valve 11 , which is interposed between said ducts and is not described in detail since it is of a type which is known to the person skilled in the art.

Downstream of the balancing valve 11, along the portions 8a and 9a, respectively, of the ducts 8 and 9 which lead to the pistons 5, there are means for limiting the pressure of the working fluid inside said ducts; said limiting means consist of a pair of limiting valves 12a and 12b, which are interposed between the portions 8a and 9a and are adapted to discharge the working fluid between the ducts 8 and 9. Inside the casing 2 there are hydraulic means 13 for varying the inclination of the swash plate 6 as a function of the pressure of the motor 1, where the expression "motor pressure" is used to reference the highest pressure between the pressure of the working fluid that is present in the first duct 8 and in the second duct 9 respectively. Conveniently, according to the invention, the angular position gradually assumed by the swash plate 6 is proportional to the pressure of the motor 1.

Conveniently, there are valve means 14 for enabling and disabling the hydraulic means 13 which are hydraulically connected thereto.

The valve means 14 are functionally movable between a first working position, in which the hydraulic means 13 are disabled and the swash plate 6

remains constantly arranged in the maximum-displacement configuration, and a second working position, in which the hydraulic means 13 are enabled and the swash plate 6 oscillates continuously and bidirectionally, passing through infinite stable equilibrium positions, between said maximum- and minimum-displacement configurations.

With the hydraulic means 13 in the second working position, the swash plate 6 is arranged in the equilibrium configuration that corresponds to the pressure of the motor 1 on the pistons 5.

Figures 6 and 7 illustrate by way of example a possible intermediate configuration, in which the swash plate 6 is arranged in one of the infinite possible conditions of stable equilibrium along the oscillation between the maximum inclination (maximum displacement) and the minimum inclination (minimum displacement).

The valve means 14 comprise a five-way valve of the type with two discrete positions, provided with a longitudinal receptacle 15 which is formed in the second portion 2b and is functionally connected to the hydraulic means 13, to a tank 16 for discharging and recovering fluid and to two compartments 17 and 18 for connection respectively to the ducts 8 and 9 in output from the balancing valve 11. The longitudinal receptacle 15 is connected to the tank 16 through a discharge duct 16a.

A slider 19 is arranged slidingly and snugly within the longitudinal receptacle 15 and is provided with a contoured portion 19a, which is adapted to allow/prevent the passage of fluid through said receptacle.

Further, the valve means 14 comprise means 20 for actuating the sliding of the slider 19 along the longitudinal receptacle 15 between the first working position, which corresponds to the connection of the hydraulic means 13 to the discharge duct 16a, and the second working position, which corresponds to the connection of the hydraulic means 13 to the ducts 8 and 9. Conveniently, the hydraulic means 20 are of the hydraulically driven

type and comprise a chamber 21 for containing a driving fluid, which faces a first end 19b of the slider 19 and can be connected to means for supplying the driving fluid which are adapted to push said fluid against the transverse surface of said slider in contrast with elastic compression means 22, such as a helical spring, which are interposed between a second end 19c, which lies opposite the first one, of the slider 19 and the casing 2.

In particular, the containment chamber 21 is formed monolithically in the second portion 2b at the first end 19b and is arranged so as to face the transverse surface of the slider 19. Advantageously, the hydraulic means 13 comprise at least one actuator 23 of the single-acting linear type, which is associated with the interior of the casing 2 and is adapted to actuate the oscillation of the swash plate 6 so as to move from the maximum-displacement configuration toward the minimum-displacement configuration. The actuator 23 acts on the face of the swash plate 6 that lies opposite the face on which the pistons 5 act, along a direction which is substantially parallel and opposite with respect to the directions of said pistons.

More preferably, the hydraulic means 13 provide two actuators 23, only one of which is visible in the figures, which are mutually parallel and are offset on opposite sides of the motor shaft 4.

The swash plate 6 can oscillate about an axis which coincides with an edge 24, which is formed by a shoulder 25 which protrudes inside the first portion 2a and on which the swash plate 6 is arranged in abutment in the maximum-displacement configuration. The actuators 23 are equidistant from the edge 24.

Each actuator 23 is constituted by a piston 26, which is accommodated so that it can slide within a cylindrical jacket 27 which is formed monolithically in the first portion 2a.

Advantageously, each piston 26 is composed of a cup 28 for guiding a linkage 29, which protrudes from said cup toward the swash plate 6 and

has end portions which have a spherical shape and are coupled in corresponding receptacles formed in the cup 28 and in the swash plate 6.

Said spherical couplings allow to contain friction and ensure optimum transfer of motion to the swash plate 6, achieving considerable efficiency and reliability of the motor 1 regardless of the operating conditions

(displacement).

In the figures, the reference numerals 29a and 29b designate mutually opposite end portions of the linkage 29, the reference numeral 6c designates a spherical receptacle which is formed on the surface of the swash plate 6 which is engaged with the portion 29a, and the reference numeral 28a designates a spherical receptacle which is formed in the cup 28 in which the portion 29b is accommodated.

A conventional sealing ring 30 retaining the portion 29b in the receptacle 28a is provided. Elastic compression means, such as a helical spring 31, are interposed between each cup 28 and the bottom of the corresponding jacket 27.

Further, the hydraulic means 13 comprise a circuit 32 for connecting the jackets 27 to the valve means 14. The circuit 32, in the first working position, is connected to the fluid discharge and recovery tank 16, and in the second working position is connected to the ducts 8 and 9.

The circuit 32 consists of two tubular portions 32a and 32b, each of which is interposed between a corresponding actuator 23 and the valve means 14 and, in the second working position, is connected respectively to the first duct 8 and to the second duct 9. The hydraulic means 13 are further provided with a pressure cutoff valve 33, which is interposed between the circuit 32 and the tank 16 and is adapted to discharge the working fluid from the actuators 23 if the pressure of the motor, i.e., the maximum pressure of the working fluid in the ducts 8 and 9, exceeds a preset threshold value. The pressure cutoff valve 33 is provided with a longitudinal

receptacle 34, which is formed monolithically in the second portion 2b and is provided with an intake port 34a, which can be connected to the tubular portions 32a and 32b, and with a discharge port 34b, which is connected to the tank 16. A flow control slider 35 is engaged so that it can slide snugly within the longitudinal receptacle 34 and is arranged in contact with a reaction pin 36, which faces a chamber 37 which can be connected to the ducts 8 and 9. In an alternative embodiment of the invention, the flow control slider 35 can extend at one end so as to form a shank which is monolithic therewith and replaces the reaction pin 36.

Between the casing 2 and the flow control slider 35, on the opposite side with respect to the reaction pin 36, there are interposed elastic compression means 38 for contrasting said pin, such as a helical spring.

Advantageously, the hydraulic means 13 also comprise a first selection valve 39, which is provided with two intakes 39a and 39b which are connected respectively to the first and second tubular portions 32a and 32b, and with an outlet 39c, which coincides with the intake port 33a of the pressure cutoff valve 33; there is also a second selection valve 40, which is provided with two intakes 40a and 40b which are connected respectively to the first and second ducts 8 and 9 and with an outlet 40c which is connected to the chamber 37.

The operation of the present invention is as follows. During the startup of the miniexcavator on which the motor 1 is mounted, the pressure of the driving fluid sent into the containment chamber 21 is not sufficient to overcome the opposition of the elastic means 22, which accordingly keep the slider 19 in the first working position.

In this position, the connecting circuit 32 and the actuators 23 which are associated therewith are connected to the discharge duct 16a, arranging the pistons 26 in the position that corresponds to the maximum- displacement configuration.

During the normal operation of the miniexcavator, the operator can decide to continue to work in maximum-displacement conditions, leaving the slider 19 in the first working position, or to act on the actuation means 20 in order to switch the valve means 14 into the second working position and allow the enabling of the hydraulic means 13, which are adapted to automatically change the displacement of the motor 1 in any intermediate configuration comprised between the minimum- and maximum- displacement configurations depending on the operating requirements of the miniexcavator. By sending pressurized working fluid into the containment chamber

21, in practice the slider 19 is moved in contrast with the elastic means 22, opening the ports for the passage of the working fluid between the compartments 17 and 18 and the tubular portions 32a and 32b.

In these circumstances, the switching of the displacement of the motor 1 is determined by the pressure cutoff valve 33 and depends on the working conditions of the miniexcavator.

In working conditions which are not particularly heavy, for example, the pressure of the motor decreases and the hydrostatic load of the working fluid which acts on the reaction pin 36 becomes lower than the set value of the elastic means 38; the flow control slider 35, therefore, is arranged so as to block the passage between the intake port 34a and the discharge port 34b and the pressure of the working fluid in the connecting circuit 32 and in the actuators 23 increases, consequently moving the swash plate 6 from the maximum-displacement configuration toward the minimum-displacement configuration.

When instead the working conditions of the miniexcavator become heavier, for example while climbing or turning, the pressure of the motor 1 rises beyond the set value of the elastic means 38 and the working fluid that is present in the connecting circuit 32 and in the actuators 23 is discharged through the pressure cutoff valve 33, varying the inclination of the swash

plate 6 and gradually restoring the maximum-displacement configuration of the motor 1.

In practice it has been found that the described invention achieves the proposed aim and objects. The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

All the details may further be replaced with other technically equivalent elements. In practice, the materials used, as well as the contingent shapes and dimensions, may be any according to requirements without thereby abandoning the scope of the protection of the appended claims.

The disclosures in Italian Patent Application No. MO2006A000122 from which this application claims priority are incorporated herein by reference.