GB2189053A - Motor systems - Google Patents

Abstract

A motor system comprises a rotary input, and motor control means (14) including a body (15) defining a chamber (16) which contains a vane (17) rotatable by the rotary input to provide sequential application of pressure to pistons (3 to 10) of a motor (1) to cause rotation of the motor (1) to follow the rotation of the vane (17). The body (15) of the motor control means (14) is rotatable relative to the vane (17) to adjust the positional relationship between the motor (1) and the vane. Servo means comprising a spool valve (60) moved by sensing means (73) automatically moves the body (15) via piston (77) on any difference occurring between motor control means (14) and motor (1) positions. <IMAGE>

Description

SPECIFICATION A motor system The present invention relates to a motor system.

Hydraulic motors of the radial and axial piston types have reciprocating pistons which react on for example swash plates, eccentrics, or cams to produce rotary output motion.

It is known for the pistons of such motors to communicate with fluid pressure and then with exhaust by rotation of control means having ports each communicating with a respective piston.

Rotation of the element of the control means causes rotation of the motor, and provided rotation of the motor is not restrained by excessive torque the rotary motion of the motor follows the rotary motion of the control means.

In such an arrangement the torque output of the motor is related to any rotation lag of the motor with respect to the rotation of the control means. For example, in the case of a radial piston motor in which the movement of the pistons causes rotation of an eccentric mounted on an output shaft of the motor, torque increases from zero, when the centre of the pistons subjected to pressure is on the line of the axis of rotation of the shaft and the centre of the eccentric, hereinafter referred to as "zero torque pole", to a maximum when the centre of the pistons subjected to pressure is at 90" to that line hereinafter referred to as "maximum torque pole". Resistance to rotation of the motor due to variations in torque results in variations in the rotary position of the motor relative to the rotary position of the element of the control means.

An object of the present invention is to reduce the variation between the rotary position of the motor and the element.

According to the present invention there is provided a motor system comprising a rotary input, and motor control means including a body defining a chamber which contains an element rotatable by the rotary input to provide sequential application of pressure to drive elements of a motor to cause rotation of the motor to follow the rotation of the element, the body being rotatable relative to the element to adjust the positional relationship between the motor and the element.

The body may be rotatable manually or automatic control means may be provided to effect rotation of the body. The automatic control means may comprise a servo system to rotate the body in relation to the element to achieve a positional relationship between the rotation of the element and the rotation of the motor.

The servo means may comprise a piston and cylinder hydraulic actuator arranged to rotate the body of the motor control means in response to any difference between the rotary position of the element and the rotary position of the motor.

The actuator may be operable by fluid from the same source as that used to apply pressure to the motor.

Should lag of the motor on the element occur due to an increase of torque resistance to the motor the body of the motor control means may be rotated so that the body lags by the same extent on its element thereby advancing the centre of piston force of the motor so that the "zero torque pole" is advanced by the necessary amount and the rotary position of the motor corresponds with that of the element of the motor control means.

The element may comprise a vane, the space within the chamber at one side of the vane communicating with fluid inlet means an4 the space within the chamber at the opposite side of the vane communicating with fluid exhaust means.

The body may comprise a plurality of ports spaced around the circumference thereof, each port being arranged to communicate with a respective piston of the motor so that on rotation of the element fluid pressure is applied sequentially to the pistons.

The motor system may include a motor which comprises a rotatable eccentric, the drive elements comprising radial pistons arranged to rotate the eccentric on sequential application of pressure and exhaust to the pistons.

The motor may comprise three or more pistons.

The motor system may comprise a pumping circuit to pump fluid under pressure to the motor control means.

The motor system may comprise pressure control means to maintain a substantially constant pressure in the circuit such as by the use of a pressure maintaining valve between the pump and the motor control means or by the use of a constant output pump.

The ports of the motor control means may communicate with the drive elements by means of flexible conduits to enable the body of the control means to be rotated relative to the element.

The present invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 shows a schematic side view of a motor control means of a motor system according to the present invention, Figure 2 shows a schematic front view of the motor and motor control means of the motor system shown in Fig. 1 including fluid conduits connecting the motor control means to the motor, and Figure 3 shows a similar view to that shown in Fig. 2 of the motor when the motor has rotated 90 clockwise compared with the view shown in Fig. 2.

Referring to Figs. 1 and 2 there is shown a radial piston hydraulic motor 1 having a body 2 in which eight radial pistons 3, 4, 5, 6, 7, 8, 9 and 10 are free to slide. Each piston 3 to 10 engages an eccentric 11 which has a circular configuration with its centre at 11 a and which is rotatable about an offset axis 12 coincident with the central axis of a cylindrical chamber 13 within the body 2.

As shown in Figs. 1 and 2, motor control means 14 comprises a body 15 having a cylindrical chamber 16 in which is disposed a vane 17 rotatable with a shaft 18. Extending through the walls of the body 15 are eight ports 19, 20, 21, 22, 23, 24, 25 and 26 each communicating by a flexible conduit 27, 28, 29, 30, 31, 32, 33 and 34 to a respective one of the pistons 3 to 10. The shaft 18 of the control means 14 is provided with an axial bore 35 extending from one end of the shaft 18 and another axial bore 36 extending from the opposite end of the shaft 18. The bore 35 communicates with the chamber 16 at the left hand side of the vane 17 (as shown in Fig. 2) through a transverse bore 37 and with the chamber 17 at the right hand side of the vane 17 through a transverse bore 38.

Fluid contained in a reservoir 39 is drawn through line 40 by a pump 41 and pumped through conduit 42 to the outer end of the bore 35 from where the fluid flows through the bores 35 and 37 into the chamber at the left hand side of the vane 17. In the position of the vane shown in Fig. 2, the fluid in chamber 16 at the left hand side of the vane 1 7 flows under pressure through the ports 24, 25 and 26 and the corresponding conduits 32, 33 and 34 to the outer end of the pistons 8, 9 and 10 and urges those pistons against the eccentric 11. The pistons 4, 5 and 6 are, however, not under the influence of fluid pressure because they communicate through ports 20, 21 and 22 of the control means 14 with the chamber at the right hand side of the vane 17, which side communicates with exhaust through bores 38 and 36, and line 43 to reservoir 39.If the vane 17 is kept in the position shown in Fig. 2 and the eccentric 11 is not subject to a load resisting its movement the eccentric 11 will rotate clockwise from the position shown in Fig. 1 at which maximum torque is exerted on the eccentric 11 until it reaches the position shown in Fig. 3 at which no torque is exerted on the eccentric 11. No torque is exerted on the eccentric 11 in the position shown in Fig.

3 because the pistons 8, 9 and 10 act symmetrically on the eccentric 11. No force is exerted on the eccentric 11 by pistons 3 and 7 because the ports 19 and 23 in the chamber 16 are blocked by the ends of the vanes 17.

If the vane is rotated clockwise as shown in Fig. 1 the port 19 will be open to the chamber at the left hand side of the vane 17 so allowing fluid under pressure to pass through conduit 27 and cause the piston 3 to exert a clockwise torque on the eccentric 11 while the port 23 communicates with exhaust. Resulting rotation causes the eccentric 11 to urge the pistons 4 to 7 outwards and fluid within the conduit 28 to 31 is exhausted through ports 20 to 23 into the chamber at the right hand side of the vane 17 and thereafter through bores 38 and 36 into line 43 and back to the reservoir 39. Continued rotation of the vane 17 causes the port immediately behind the vane 17 in its direction of rotation to communicate with its associated piston to provide successive pressurisation and relief of the pistons.Continued rotation of the vane 17 therefore produces continuous rotation of the eccentric 11. The ensure constant pressure in the conduit 42 surplus fluid is delivered to the pump 39 and returned via a pressure maintaining valve 44 to the reservoir 39 as shown in Fig. 3.

In the position shown in Fig. 2 the centre line of piston force is the piston 9. Since the line connecting the centre 1 1a of the eccentric with the axis of rotation 12 of the output shaft of the motor is at right angles to this force the motor is in the maximum torque position.

At the zero torque position the line connecting the centre 1 1a of the eccentric with the axis of rotation 12 of the shaft of the motor would be coincident with the pistons 7 and 3, as shown in Fig. 3.

Clockwise rotation of the vane 17 moves the centre of piston force clockwise causing the motor 1 to rotate clockwise, with the rotation of the motor 1 lagging the rotation of the vane 17 with increase of torque resistance on the output shaft of the motor to a maximum when the lag is 90".

For any given vane position lag of the body 15 has the effect of advancing the centre of piston force so causing advance of motor 1.

For example, referring to Fig. 1, movement of the body 15 in the direction of lag by 45" moves the centre of piston force from piston 9 to piston 10 so advancing the motor 1 without movement of the vane 17. In the same way movement of the body 15 in the direction of lead by 45 , moves the centre of the piston force to piston 8 so that the motor 1 moves in the lead direction.

To provide automatic adjustment of the rotation of the body 15 to ensure than the rotary position of the motor 1 at all times corresponds with the rotational position of the vane 17, servo means are provided in which any differential variation between the rotary position of the motor 1 and the vane 17 causes the servo means to operate to adjust the rotary position of the body 15 of the con trol means 14.

The servo means shown in Fig. 1 for performing such adjustment comprises a spool valve 60 having a cylindrical housing 61 within which is located a spool 62 having three lands 63, 64 and 65. The housing 61 is provided with a port 66 which enables the spool valve 60 to be under the influence of pressurised fluid from the pump 41 through a line 67. The housing is also provided with a port 68 which communicates the spool valve 60 with exhaust through a line 69 to the reservoir 39.

The spool 62 is connected to a lever 70 by means of a pin 71 which is displaceable in a slot 72 in the lever. The lever 70 is connected to means 73 for sensing any variation in rotary position of the motor 1 and the vane 17.

The spool valve 60 is provided with a further port 74 which communicates through line 75 with a port 76 of an acutator 77. The actuator is provided with another port 78 through which pressurised fluid communicates with the actuator via a line 79 from the pump 41. The actuator has a piston 80 provided with a piston rod 81 which is connected to a lever 82 by means of a pin 83 which slides in a slot 84 in the lever 82. The lever is connected to the body 15 of the control means 14.

If the rotary position of the motor 1 lags behind that of the vane 17 the lever 70 moves upwards thereby pulling the spool 62 and its lands 63, 64 and 65 upwards. The upward movement of the land 64 exposes the port 74 to pressurised fluid which consequently acts on the underside of the piston 80 of the actuator 77 via its port 76. Although the upperside of the piston 80 is under the influence of pressurised fluid, due to the area of the piston rod this results in the piston 80 and its piston rod 81 moving upwards. This movement causes the lever 82 to move upwards which in turn rotates the body 15 of the control means to lag until the rotary position of the motor 1 corresponds with that of the vane 17.When the positions correspond the lever 74 and the spool 62 return to their neutral positions at which the land 64 closes port 74 thereby cutting off the supply of pressurised fluid to the actuator 77 until any further lag of the motor 1- occurs.

If the motor 1 should lead the vane 17, the lever 70 moves downwards so that the land 64 also moves downwards and exposes the port 74 to exhaust via the port 68 and the line 69 to the reservoir 39. This results in the piston 80 of the actuator 77 falling under the influence of pressurised fluid acting on the upperside of the piston 80. This in turn moves the piston rod 81 and the lever 82 downwards so that the body 15 of the control means 14 moves in the lead direction until the error due to the lead of the motor is corrected.

The use of the servo mechanism gives precision of rotary position of the motor in following the rotary position of the vane in all conditions whether in continuous or erratic rotary motion, or in static and stepping application in spite of variations of torque on the motor and changes of applied fluid pressure (for example with change of motor speed) within the limits of the design.

Claims (13)

1. A motor system comprising a rotary input, and motor control means including a body defining a chamber which contains an element rotatable by the rotary input to provide sequential application of pressure to driving elements of a motor to cause rotation of the motor to follow the rotation of the element, the body of the motor control means being rotatable relative to the element to adjust the positional relationship between the motor and the element.

2. A motor system as claimed in claim 1, wherein the body is rotatable manually.

3. A motor system as claimed in claim 1, comprising automatic control means to effect rotation of the body.

4. A motor system as claimed in claim 3, wherein the automatic control means comprises a servo system to rotate the body of the motor control means.

5. A motor system as claimed in claim 4, wherein the servo means comprises a piston and cylinder hydraulic actuator arranged to rotate the body of the motor control means in response to any difference between the rotary position of the element and the motor.

6. A motor system as claimed in claim 5, wherein the actuator is operable by fluid from the same source as that used to apply pressure to the motor.

7. A motor system as claimed in any one of the preceding claims, wherein the element comprises a vane, the space within the chamber at one side of the vane communicating with fluid inlet means and the space within the chamber at the opposite side of the vane communicating with fluid exhaust means.

8. A motor system as claimed in any one of the preceding claims, wherein the body comprises a pluraiity of ports spaced around the circumference thereof, each port being arranged to communicate with a respective piston of the motor so that on rotation of the element the pistons communicate sequentially with fluid pressure and with exhaust.

9. A motor system as claimed in any one of the preceding claims including a motor which comprises a rotatable eccentric, the drive elements comprising radial pistons arranged to rotate the eccentric on application of power to the pistons.

10. A motor system as claimed in claim 9, wherein the motor comprises three or more pistons.

11. A motor system as claimed in any one of the preceding claims, wherein the motor system may comprise a pumping circuit to pump fluid under pressure to the motor control means.

12. A motor system as claimed in claim 11, comprising pressure control means to maintain a substantially constant pressure in the circuit.

13. A motor system substantially as hereinbefore described with reference to the accompanying drawings.