Hydraulic radial piston motor with variable cylinder capacity

Abstract: A variable-displacement hydraulic motor with radial cylinders supplied by a rotary fluid distributor (4) and acting on an eccentric ring (6) axially secured to a crankshaft (7) but capable of moving radially with respect thereto, being provided with a device for operating and controlling the variation of eccentricity of eccentric ring (6) with respect to crankshaft (7), which comprises at least one pair of actuating pistons (8, 9) located in counterposition to and independent of one another, arranged in a radial sense between shaft (7) and ring (6), each of which is made mechanically integral with such eccentric ring (6) via appropriate means of connection (8a, 9a), and at least one pair of cross-connected valves (10) to block the flow of the fluid operating such actuating pistons (8, 9).

Description: The object of this invention is a radial-actuator hydraulic motor, the cylinder capacity of which may be varied by means of an eccentric ring integral with the crankshaft, fitted with a hydraulic device having a dual valve to set and control the variation of eccentricity of such eccentric ring with respect to the crankshaft, and independent shift actuators mechanically linked to the said eccentric ring. It is known that in hydraulic motors of this type the pistons bring about the rotation of the crankshaft, supported by bearings located in seats provided in the housing or integral therewith, acting on its eccentric part. The cylinders in which the pistons slide may be integral with the housing or hinged thereto. In some known versions of variable-displacement radial motors, variation of the cylinder capacity is achieved by varying the eccentricity of the crankshaft by means of hydraulic jacks operated by valves fitted to the said crankshaft, supplied via a rotary manifold obtained by utilizing the link between a pin of the said crankshaft and the housing, with the aid of rotary-shaft gaskets. Such prior art is disclosed into DE-22 03 054 and is included into the preamble of claim 1. The aforesaid variable-displacement radial hydraulic motors have several disadvantages. For example, they do not stably maintain the cylinder capacity at all the values comprised within the range of variation; they need to be removed and detached from the working parts for the maintenance of such rotary-shaft valves and gaskets (which are severely stressed) and they are subject to significant losses of energy as a result of friction and discharge. All the foregoing combines to bring about in such motors inadequate performance, reliability and efficiency which considerably limit their applications. Additionally, the control and setting devices of known type provide for the use of return springs for the movement of the eccentric ring operating pistons, rendering necessary special equipment and arrangements to achieve the positioning thereof inside the said eccentric ring. There is therefore posed the technical problem of providing a variable-displacement radial-piston hydraulic motor fitted with a control and setting device with a high rate of response such as to ensure with certainty the implementation of variation control, and capable of being fitted also to low-capacity motors with reduced housing space. Within the context of such problem, a further aim of the invention is to provide a control device capable of being easily fitted to and/or removed from fixed-displacement motors for the conversion thereof into variable-displacement motors by using a small number of moving parts, gaskets and machined surfaces. Such problem is resolved according to this invention by a variable-displacement hydraulic motor with radial cylinders supplied by a rotary fluid distributor and acting on an eccentric ring axially fixed to a crankshaft but capable of moving radially with respect thereto, such motor being provided with a device for setting and controlling the variation of eccentricity of the eccentric ring with respect to the crankshaft, which comprises at least one pair of actuating pistons located in counterposition to and independent of one another, arranged in a radial sense between the shaft and the ring, each of which is made mechanically integral with such eccentric ring via appropriate means of connection, and at least one pair of alternating-control valves to block the flow of the fluid operating such actuating pistons. According to a preferred form of implementation, provision is made for such means of mechanical coupling between the actuating pistons and the eccentric ring to be comprised of T-shaped pins capable of being inserted lengthwise in the ring and of maintaining the latter secure in the radial direction, and for such flow of fluid to occur between an inlet and an outlet via a four-way distributor and ducts provided in a connection unit interposed between the motor housing and the cover accommodating the rotary distributor supplying the motor cylinders. Provision is also made for the rotary distributor drive shaft to have internal axial channels capable of connecting the valves to the radial ducts communicating with the outlets of the distributor controlling the supply and discharge of fluid. Furthermore, such control valves may be arranged in a radial sense in relation to the same section of shaft on which is fitted the eccentric ring or in an axial sense inside the drive shaft of the rotary distributor supplying the motor cylinders. Further details may be obtained from the following description with reference to the attached drawings, which show: In figure 1 : a schematic cross-section according to a plane perpendicular to the axis of rotation of the shaft; In figure 2 : a cross-section according to plotting plane II-II of figure 1; In figure 3 : a detail of the cylinders which bring about the variation of the cylinder capacity; In figure 4 : a schematic axial cross-section of one of the two control valves; In figure 5 : a diagram of the hydraulic circuit supplying the control valve and the actuating pistons; In figure 6 : a detail of the area of coupling of the eccentric ring with the drive shaft, and In figure 7 : an example of an alternative method of implementation with blocking valves located in an axial sense inside the drive shaft of the rotary oil distributor. As illustrated in the figures, the variable-displacement hydraulic motor according to the invention is comprised of a housing 1 in which are located cylinders 3, each of which is placed in communication with a rotary distributor 4 located in a cover 1a attached to housing 1 by means of screws 1b, operated by a drive shaft 4d and capable of placing cyclically in a supply or discharge setting cylinders 3 in phase with the rotation of crankshaft 7. In cylinders 3, bearing on covers 2, there slide radially pistons 5 which bear against the outer surface of a ring 6 capable of moving eccentrically in a radial sense with respect to the axis of crankshaft 7, such variation of eccentricity bringing about the variation of the cylinder capacity of of the motor. As illustrated in figure 6, shaft 7 has transverse locators 7a, 7b in relation to its zone of engagement with pistons 5. Such locators are capable of maintaining ring 6 centred lengthwise and of enabling it to move in a transverse sense. Inside shaft 7 in relation to the zone of engagement with eccentric ring 6 are located pistons 8 and 9 in counterposition, the outer end of which has T-shaped pins, respectively 8a, 9a, capable of being inserted axially in corresponding seats 6a of eccentric ring 6 with which they become mechanically integral in a radial sense. Such link enables the pistons to follow the eccentric ring when the latter moves radially for reasons other than positive and controlled operation imparted via valves 10 and said pistons 8, 9. In the said zone of location of the eccentric ring, shaft 7 also has longitudinal recesses 7c through which ring 6 is made to strike shaft 7, only in relation to the outer edges of the sliding plane of ring 6, thus making it possible to unload the resultant of the forces generated by pistons 5, which is substantially normal to the thrust axis of pistons 8 and 9, spreading the same equally over such outer edges. This makes it possible to obtain a reduction of stress in relation to the axes of actuating pistons 8 and 9, which stress could bring about deformations with consequent hindrance of the sliding movement thereof. The implementation and control of movement in a transverse sense of each piston 8 and 9, and therefore of eccentric ring 6, is effected via an appropriate valve 10 which blocks the fluid to be supplied/discharged to/from pistons 8, 9 and coming from the rotary connection via axial ducts 4a, 4b provided on drive shaft 4d of distributor 4 which supplies the chambers of cylinders 3. Such valves are of the alternating-control type in order to obtain the discharge of one piston when the other is being supplied, and vice versa. In an initial example of implementation (figs. 2, 3) such valves are located radially inside the portion of shaft guiding eccentric ring 6 and are connected to respective pistons 8 and 9 via appropriate ducts 8b, 9b. Static sealing of the ducts connected to shaft 7 is achieved by means of gaskets 4c, while dynamic sealing is implemented via gaskets 11 forming the subject of another patent in the name of the same applicant. As shown in figure 2, between housing 1 and cover 1a of the motor is interposed a fixed body 1c in which are provided ducts 12 and 13 for the supply of fluid which flows via ducts 4a, 4b of drive shaft 4d to blocking valves 10. Such operating fluid is supplied via an inlet under pressure P and a duct 12 on which is located a cartridge filter 12a. The pressurized fluid emerging from filter 12a is fed via ducts 12 and 13 to a distributor 100 from which flow out pressure controls A and B for the operation of blocking valves 10. To implement the variation and maintenance of intermediate cylinder capacities between maximum and minimum, the fluid supplied to and contained in actuating pistons 8 and 9 should remain intercepted by controllable valves 10 at nil discharge. In greater detail, such valves 10 are comprised (fig. 4) of a cylindrical body 10a provided with radial apertures 10b and 10c connected to fluid supply ducts 12 and 13. Within body 10a is slidingly located a piston 14 capable of acting against a cone-seated shutter 15 housed in a guide tube with conical sealing seat 16a against which shutter 15 is pressed by a spring 15a. The valve is closed at the top by a cap 17. The operation of the variation and control device is as follows: Supplying fluid under pressure from inlet P communicating with distributor 100 and switching on the latter, brings about the supply of fluid to one of inlets 10b, 10c of valves 10 causing the alternating opening/closure of shutter 15 of each valve 10 and the consequent supply/discharge of fluid to/from pistons 8 and 9 respectively, which accordingly move in a transverse direction and in one sense or another, according to whether regulation is aimed at a higher or lower cylinder capacity. The movement of pistons 8, 9 which are integral with eccentric ring 6 via T-shaped pins 8a, 9a brings about the shifting in a transverse sense of said ring 6 and therefore the desired variation of cylinder capacity. The centring of distributor 100 after a preset interval interrupts the flow of fluid which remains under pressure in the circuit and blocks pistons 8 and 9 in the setting attained corresponding to the desired cylinder capacity. It is therefore clear that with the cylinder capacity setting and control device according to the invention it is possible to locate control valves 10 in proximity to actuating pistons 8, 9 to the advantage of the rate of response of the device, and that the mechanical link between the pistons and the eccentric ring makes it possible both to obtain a hydraulic braking effect with consequent increase of stability of positioning and to avoid the use of return springs for the pistons, which may be made solid with consequent elimination of air bubbles in the operating circuit which, because of the compressibility of the air, reduce the accuracy of the setting and control device. As illustrated in fig. 6, with a motor according to the invention blocking valves 10 may also be fitted in an axial sense inside shaft 4d driving rotary distributor 4 while there remains substantially unaltered the previously described features of setting and control of eccentricity of ring 6. Provision is also made for the sections of said two pistons 8 and 9 to be capable of differing from one another according to suitable ratios by reason of the fact that the effort needed to set the eccentricity in order to achieve an increase of cylinder capacity is greater than the effort needed to achieve a reduction of the latter. Many variants may be introduced in the design of the component parts of the invention without thereby departing from the scope of protection of this patent as described in the claims which follow.

Claims: A variable-displacement hydraulic motor with radial cylinders supplied by a rotary fluid distributor (4) and acting on an eccentric ring (6) axially secured to a crankshaft (7) but capable of moving radially with respect thereto, being provided with a device for setting and controlling the variation of eccentricity of eccentric ring (6) with respect to crankshaft (7), comprising at least one pair of actuating pistons (8, 9) located in counterposition to and independent of one another, characterized in that said pistons (8, 9) are arranged in a radial sense between shaft (7) and ring (6), each of which is made mechanically integral with such eccentric ring (6) via appropriate means of connection (8a, 9a), and at least one pair of valves (10) of the alternating control type to block the flow of the fluid operating such actuating pistons (8, 9). A motor according to claim 1, characterized in that such means of mechanical coupling between actuating pistons (8, 9) and eccentric ring (6) are comprised of T-shaped pins (8a, 9a) capable of being inserted lengthwise in ring (6) and of maintaining the latter secure in the radial direction. A motor according to claim 1, characterized in that such flow of fluid occurs between an inlet (P) and an outlet (T) via a four-way distributor (100) and ducts (12, 13) provided in a connection unit (1c) interposed between motor housing (1) and cover (1a) containing rotary distributor (4) supplying motor cylinders (3). A motor according to claims 1 and 3, characterized in that such connection unit (1c) has identical opposed front surfaces for connection with cover (1a) and housing (1) of the motor. A motor according to claim 1, characterized in that such blocking valves (10) are comprised of a cylindrical body (10a) provided with radial apertures (10b, 10c) connected to ducts (12, 13), within body (10a) there being slidingly located a piston (14) capable of operating against a cone-seated shutter (15) housed in a guide tube (16) with conical sealing seat (16a) against which shutter (15) is pressed by a spring (15a) for the opening/closure of the duct connecting with pistons (8, 9). A motor according to claim 1, characterized in that drive shaft (4d) of rotary distributor (4) has internal axial channels (4b) capable of connecting valves (10) to radial ducts (12, 13) communicating with outlets (A, B) of distributor (100) controlling the supply and discharge of fluid. A motor according to claim 1, characterized in that such blocking valves (10) are arranged in a radial sense in relation to the same section of shaft (7) on which is fitted eccentric ring (6). A motor according to claim 1, characterized in that such blocking valves (10) are arranged in an axial sense within drive shaft (4d) of rotary distributor (4) supplying motor cylinders (3). A motor according to claim 1, characterized in that shaft (7) has longitudinal recesses (7c) and transverse locators (7a, 7b) in relation to the zone in which is fitted eccentric ring (6).

Inventors: BREVEGLIERI ALESSANDRO, BREVEGLIERI, ALESSANDRO
Applicants: RIVA CALZONI OLEODINAMICA S P, RIVA CALZONI OLEODINAMICA S.P.A.
Application year: 1995
Main classification: F03C1
IPC codes: F03C1, F04B1, F04B49