GB2167138A - Control for a hydrostatic piston motor - Google Patents

Abstract

In a hydrostatic radial piston motor, the conventional mechanical control of the supply and exhaust of working fluid to the cylinders is replaced by electromagnetic changeover valves which are actuated, in dependence upon the position of the motor shaft 2, by a microprocessor 22. An angle detector 20 cooperating with a toothed ring 19 secured to the motor shaft 2 detects the position thereof. This arrangement allows the energization and de-energization of the valves 14 to be programmed as required in dependence upon the angle of motor shaft rotation. This programmable feature enables the motor to have any required acceleration curve and deceleration curve. <IMAGE>

Description

SPECIFICATION Control for a hydrostatic piston motor THE INVENTION relates to a control for a hydrostatic piston motor having a number of pistons reciprocating in cylinders, the translational kinetic energy of the pistons being converted at least indirectly into rotational energy of a common motor shaft, the work cylinders being supplied with hydraulic work medium in dependence on the angle of motor shaft rotation. A hydrostatic motor of this character is herein referred to as being of the kind specified.

All the known controls for hydrostatic piston motors, more particularly hydraulic radial piston motors, are mechanical, one end of the motor shaft being so devised as to distribute the incoming flow to the work cylinders and to collect the return flow.

To this end, it is known for radial piston motors whose pistons are borne internally to have control rings which co-operate with the motor casing and with an eccentric connected to the motor shaft to bound an outer annular chamber and an inner annular chamber. As the eccentric moves the rings between the valve plate and a casing cover, the inner annular chamber and the outer annular chamber communicate alternately with the work cylinders.

Externally, the annular chambers extend to the pressure intakes for the motor.

Also, of course, one end of the motor shaft can be formed with turned-in grooves and recesses to enable the work medium to be supplied and removed from the work cylinders in dependence upon the angle of motor shaft rotation.

Motor controls of this kind have basically proved satisfactory in practice. However, since they are always closed systems, they cannot be controlled externally. The effective absorption capacity of the motors cannot therefore be varied, so that additional flow-control and change-over valves are required in open circuit. An effective absorption capacity once adjusted is operative in all the acceleration and deceleration phases of the motor. Since relatively long ducts and bores are present between the mechanical control and the work cylinders, a relatively large detrimental compression chamber volume is correspondingly present. The only way of achieving hydraulic positioning in the known case is to provide additional valves in the lines preceding and/or following the motor control.The second end of the motor shaft cannot be used for drive purposes since the mechanical control is always an obstacle to a lead-through of the shaft.

It is the object of the invention so to improve the control for a hydrostatic piston motor of the kind specified that the effective absorption capacity and, therefore, the motor torque can be controlled in any operative position without additional flow valves and change over valves.

According to the invention, thre is provided a control for a hydrostatic piston motor having a number of pistons reciprocating in cylinders, the translational kinetic energy of the pistons being converted at least indirectly into rotating energy of a common motor shaft, the work cylinders being supplied with hydraulic work medium in dependence upon the angle of motor shaft rotation, wherein a respective electromagnetic valve, controlling the admission and exhaustion of the work medium, is provided for each work cylinder and the valves are actuated through the agency of a microprocessor which is programmable in dependence upon motor shaft position and which is connected to a motor shaft angle detector.

Preferably said valves, in the form of servo valves or proportional valves, are secured individually to the work cylinders.

Thus, the conventional mechanical control at one end of the motor shaft is replaced by change over valves, more particularly of the constant-flow kind and in the form of servo or proportional valves, which are associated directly with the various work cylinders and which are actuated electromagnetically in dependence upon motor shaft position. Accordingly, an angle detector connected to a microprocessor detects motor shaft position. The microprocessor can be accurately programmed to make the constant-flow valves pick up or drop in dependence upon the angle of motor shaft rotation. Any required motor acceleration and deceleration curve can therefore be programmed. For example, in difficult starting conditions the motor can initially be operated at maximum absorption capacity exactly at its top and bottom dead centre positions.Once the motor has run up to speed and the load to be driven has accelerated, the valves can be adjusted in dependence upon the angle of motor shaft rotation to reduce the effective absorption capacity and, therefore, the torque.

Consequently, unlike the case of mechanical control, in which an effective absorption capacity set up once and for all is operative in all the acceleration and deceleration phases of the motor, the effective absorption capacity can be adjusted to ensure optimum use of the available pressure.

Also, the invention makes hydraulic locking possible. For example, the motor of a winch arrangement can have full pressure applied to it immediately although it is still stationary.

The brake can then be fully released without any risk of the load causing the motor to race if the pressure is too low or of the motor rubbing against a still "on" brake if the pressure is too high. The motor can be held stationary by positioning the valves exactly in such a way as to make up leakage losses in the motor arising from the countering of the externally applied forces. This advantage is a useful feature, more particularly in cases in which external forces such as those associated with the negative lift of a hanging load tend to rotate the motor.

The invention also makes possible an arrangement which enables energy to be recovered. Thus, when the motor is working in connection with lowering of a load, power can be returned to the supply network.

The invention also enables a motor to be readily connected to a constant-pressure hydraulic network yet for the available energy to be used optimally whatever the stressing of the motor.

Another advantage is that a free wheel feature can be devised, all that is required for this purpose being appropriate programming to bring all the constant-flow valves into a position in which they are connected on both sides either to the pressure side or to the return side.

Since the work cylinders can be accurately energized in the top and bottom dead centre positions, for example, with pre-admission, the motor runs very quietly and very efficiently.

The acceleration, deceleration and speed pattern can readily be determined beforehand.

Also, the effective absorption capacity can be varied steplessly by phase control; for instance, the pressure can be operative through 270 rotation and the exhaust or return of the fluid operative over the remaining 90 of rotation. This enables the hydraulic energy to be used optimally, for instance, in the case of a constant-pressure network. Also, the motor can run at very low speeds, since leakage losses cannot have the negative effect of causing the motor to stop. Losses are made up independently. A direct changeover by way of proportional valves is possible. Since the constant-flow valves are associated directly with the work cylinders, the supply of work medium can readily be reversed in dependence upon the angular position of the motor shaft.

The pressure and return connections can be disposed directly on the motor casing. Distances between the valves and the work cylinders are then short, with a consequent considerable reduction in compression chamber volume. Another advantage of short distances is improved cooling of the work medium, since the injected work medium is always removed substantially completely after an operating cycle and replaced by fresh work medium.

Yet another advantage of the invention is that it allows both ends of the motor shaft to be used. In the known systems the mechanical control is an obstacle to the lead-through of a shaft. For example, the second end of the shaft can be hollow, in which event two motors can be directly interconnected mechanically. Consequently, the power of a drive unit can be increased without special action and at comparatively reduced outlay and compactly.

The motor shaft angle detector may comprise a sensor arranged to co-operate with a gear or toothed ring secured to one end of the motor shaft.

Thanks to the invention, electromagnetic constant-flow valves can be used not only with hydrostatic radial piston motors whose pistons are borne internally but also with hydrostatic piston motors of the so-called spread-out or "exploded" kind. In the latter case, the pistons can have rollers and bear on a cam track; alternatively, the pistons may be eccentrically pivoted by way of connecting rods to pinions meshing with a larger gear. In the latter arrangement the number of work cylinders disposed around the periphery of the larger gear is sufficient to ensure uniform operation.

Embodiments of the invention are described below, by way of example, with reference to the accompanying drawings wherein: Figure 1 is a view in vertical longitudinal section of a hydrostatic radial piston motor whose pistons are borne internally; Figure 2 is a diagrammatic fragmentary cross-section through a hydraulic piston motor having rollers bearing on a cam track, and Figure 3 is a diagrammatic view of part of a hydrostatic piston motor having pinions which are disposed peripehrally of a larger gear and which are drivable by work cylinders.

Referring to Fig. 1, a hydrostatic radial piston motor whose pistons are borne internally has a casing 1. Extending therethrough is a motor shaft 2 carried in bearings 3 in casing 1. A cover 4 through which a journal 5 of shaft 2 extends secures the motor shaft 2 axially. A sealing element 6 is provided between the journal 5 and cover 4 and seals off the inside of the casing from the exterior.

The other end 7 of the shaft 2 is hollow. A sealing element 8 is disposed between the hollow shaft end 7 and the casing 1 and seals off the casing interior from the exterior.

The central longitudinal portion of the motor shaft is in the form of an eccentric 9. By way of connecting rods 12 and shoes 13, pistons 11 reciprocable in work cylinders 10 of the casing 1 bear slidingly on the eccentric 9. For example, five work cylinders 10 with pistons 11 are distributed around the periphery of the radial piston motor, but to simplify the illustration one of the two cylinders 10 illustrated has been offset in the peripheral direction.

An electromagnetic constant-flow valve 14 is disposed on the periphery of casing 1 in radial extension of each cylinder 10. To simplify the illustration the valves are shown merely in symbolic form.

The hydraulic work medium is supplied to the valves 14 by way of a pressure connection P into an annular duct 15 in casing 1 and therefrom through radial branch ducts 16 to the valves 14. Work medium returns from the valves 14 through radial branch ducts 17 to an annular duct 18 in casing 1 and thence to a return connection R.

Secured to the hollow end 7 of shaft 2 is a gear or toothed ring 19 which rotates past a sensor 20 acting as an angle detector and mounted in the casing 1. The detector 20 is connected by a line 21 to a microprocessor 22 which is connected by lines 23 to electromagnets 24 of the valve 14.

The microprocessor 22 is programmable, in dependence upon required angles, to the energization and de-energization of the valves 14.

Accurate acceleration, deceleration and speed patterns of the motor can be set up by appropriate programming.

In the embodiment of Fig. 2 work cylinders 25 which have work pistons 26 and which are arranged in a star shape are provided (only two of the cylinders 29 are shown). The pistons 26 bear by way of rollers 27 on a cam track 28 in the casing 29.

Associated with each cylinder 25 is an electromagnetic constant-flow valve 14. The electromagnets 24 of valve 14 are connected by lines 23 to a microprocessor 22 connected by a line 21 to a sensor 20 which, in association with a toothed ring 19 secured to the motor shaft 2, detects the position thereof and acts as an angle detector.

The hydraulic work medium is supplied to and collected from the valves 14 and, therefore, supplied to and collected from the cylinders 25 by way of annular ducts 15, 18 associated with connections P and R which are not shown in greater detail and which are similar to those in the embodiment shown in Fig. 1.

In the embodiment shown in Fig. 3, a plurality of work cylinders 3 1 is provided peripherally of a larger gear 30, only one of the cylinders 31 and part of the gear 30 being shown.

Associated with each cylinder 31 is a respective electromagnetic constant-flow valve 14 which, as in the embodiments shown in Figs.

1 and 2, can be adjusted through the agency of a microprocessor 22 in dependence upon motor shaft position.

In each cylinder 31 a respective piston 32 is reciprocable and has a respective piston rod 53 which extends through an end face of the cylinder housing 34. A respective connecting rod 35 is pivoted to the free end of each rod 33 and the rods 35 are connected eccentrically at their other ends to respective pinions 36 meshing with the periphery of the gear 30.

Work cylinders 31 are arranged around the periphery of gear 30 at sufficiently frequent intervals to ensure uniform operation.

In this embodiment the positions of the pistons 32 in the cylinders 31 can be detected by means of an angle detector 20 sensing the teeth of one of the pinions 36, for example and, through the agency of the microprocess or 22, the valves 14 are actuated correspondingly.

Claims (11)

1. A control for a hydrostatic piston motor having a number of pistons reciprocating in cylinders, the translational kinetic energy of the pistons being converted at least indirectly into rotating energy of a common motor shaft, the work cylinders being supplied with hydraulic work medium in dependence upon the angle of motor shaft rotation, wherein a respective electromagnetic valve, controlling the admission and exhaustion of the work medium, is provided for each work cylinder and the valves are actuated through the agency of a microprocessor which is programmable in dependence upon motor shaft position and which is connected to a motor shaft angle detector.

2. A control according to claim 1, in which said valves, in the form of servo valves or proportional valves, are secured individually to the work cylinders.

3. A control according to claim 1, in which the motor shaft angle detector co-operates with a gear or toothed ring secured to one end of the motor shaft.

4. A control according to claim 1 or 3, in which the angle detector is an analog or digital detector.

5. A control according to any of claims 1 to 4, used in a hydrostatic radial piston motor with internally supported pistons.

6. A control according to any one of claims 1 to 4, used in an exploded or spreadout type hydrostatic piston motor.

7. A control according to claim 6, in which the pistons have rollers and bear on a cam track.

8. A control according to claim 6, in which the pistons are eccentrically pivoted by way of connecting rods to pinions meshing with a larger gear.

9. A control for a hydraulic piston motor, substantially as hereinbefore described with reference to, and as shown in, Figs. 1, 2 or 3 of the accompanying drawings.

10. A hydraulic piston motor substantially as hereinbefore described with reference to, and as shown in, Figs. 1, 2 or 3 of the accompanying drawings.

11. Any novel feature or combination of features disclosed herein.