AXIAL PISTON MACHINE HAVING AN ADJUSTABLE BENT AXIS VALVE SEGMENT AND A VARIABLE UNIT FOR THE ELECTRICALLY PROPORTIONAL ADJUSTMENT OF THE DISPLACEMENT

Abstract

The invention relates to an axial piston machine having an bent axis segment which is adjustable by means of an actuating piston, and a variable unit for the electrically proportional adjustment of the displacement. The variable unit has a control piston for controlling the oil pressure which displaces the actuating piston, an electrically controllable proportional solenoid which acts on the control piston, a feedback spring on the control piston for retracting the instantaneous Bent axis valve segment and a adjustment mechanism for setting the start current. To set the start current, the adjustment mechanism has a setting spring which acts on the armature of the proportional solenoid with an adjustable force.

Description

BACKGROUND OF THE INVENTION

The invention relates to an axial piston machine having an adjustable Bent axis valve segment and a variable unit f or the electrically proportional adjustment of the displacement according to the features of claim 1.

To set the displacement, axial piston machines of this type which are embodied as variable displacement motors have a Bent axis valve segment, the position of which can be adjusted by means of an actuating piston. The actuating piston is controlled by a control spool which, when displaced along its longitudinal axis, connects or disconnects ducts in such a way that oil which is at a certain pressure is made available to displace the actuating piston. Axial piston machines are often equipped with electrically proportional adjustment means. The input signal in a variable unit of this type is an electric current which controls a proportional solenoid which displaces and acts on the control piston. The output signal is the hydraulic pressure which acts on the actuating piston.

In order to adjust the axial piston machine to the displacement set by the adjustment device, a feedback spring is provided which closes the control loop. The instantaneous swivel angle of the valve segment is fed back to the control piston by the feedback spring in such a way that when the set value is reached, said control piston is returned to its initial position by the force of the feedback spring which opposes the setting force of the proportional solenoid.

When starting up using hydrostatic drives, the variable displacement pump which supplies the motor is generally initially set to the maximum feed volume, before the variable displacement motor, which is normally initially at the maximum angle when starting up occurs, is to begin swiveling. The electrically controlled, servo-adjusted hydrostatic variable displacement motors are intended to depart from the initial swivel angle, and thus vary the displacement per revolution, at a defined current, the start current. Normally, a fixed current value is provided by the electronics for this purpose.

However, the elements used for adjustment and closed-loop position control such as a proportional solenoid, piston, feedback springs etc. have unavoidable tolerances which leads to considerable fluctuations in the forces which occur. The deviations in the force ratios are normally so large that, without compensation for the tolerances, the variable displacement motors would actually depart from the initial swivel angle at very different start currents, and the driving behaviour would correspondingly vary from vehicle to vehicle.

The tolerances are normally compensated for by means of the feedback spring system, the force action of which is directed counter to the actuating force of the magnet, with the result that the return force which forces the system into the initial position is set. A complex adjustment mechanism and at least one further spring, the force action of which is adjustable and is likewise directed counter to the proportional solenoid, are necessary for this purpose.

SUMMARY OF THE INVENTION

With the present invention, it is intended to produce an axial piston machine having an improved setting capability to compensate for deviations from the desired start current.

According to the invention, this goal is achieved with an axial piston machine having an adjustable Bent axis valve segment which is adjustable by means of an actuating piston, and a variable unit for the electrically proportional adjustment of the displacement, which machine has a control piston for controlling the oil pressure which moves the actuating piston, an electrically controllable proportional solenoid which acts on the control piston, a feedback spring on the control piston for retracting the instantaneous Bent axis valve segment and a adjustment mechanism for setting the start current, the adjustment mechanism having a setting spring which acts on the armature of the proportional solenoid with an adjustable force.

One particular advantage of the setting spring according to the invention is the fact that the force of said setting spring is directed counter to the force of the feedback spring, resulting in a particularly favourable setting capability for the force ratio between the proportional solenoids and the feedback spring.

The setting spring is preferably integrated into the proportional solenoid. The adjustment mechanism forms, together with the magnet, one structural unit, which considerably reduces the number of individual elements for assembly.

A further advantage of the arrangement according to the invention is that the setting spring and the armature of the proportional solenoid and also the control valve can be arranged along a common axis, along which the feedback spring and the actuating piston can also be arranged, resulting in an inline return system, which requires no additional attachments to the end housing, along the Bent axis.

The feedback spring is preferably held at one side by a bore of the actuating piston, while resting at the other side on the control spool via a spring seat. The setting spring force which acts on the armature is adjustable by means of a adjustment screw which is arranged in the longitudinal direction of the Bent axis, as a result of which it is possible to adjust the preload with which the spring acts on the armature, and thus the force ratio between the actuating force of the magnet and the spring force of the feedback spring, and also, as a result, a defined start current.

Further features and advantages are disclosed in the following description of the exemplary embodiment presented with reference to FIG. 1.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view of an axial piston machine.

DETAILED DESCRIPTION OF THE INVENTION

The figure shows an axial piston machine 1 of bent axis design having a valve segment 14, the swivel angle of which is adjustable by means of the swivel mechanism 13. The swivel mechanism 13 is actuated by the actuating piston 10, the displacement of the motor being set in accordance with the swivel angle of the valve segment 14. 011 pressure is applied to the actuating piston 10 via ducts formed in the valve block 11 and in the end housing 12 and during this time, it executes a linear movement along the Bent axis 15.

For the adjustment of the actuating piston, the variable unit 2 has a control valve and a proportional solenoid 3 which are arranged one behind the other along the common Bent axis 15. When displaced along this axis 15, the control spool 7 opens or closes the ducts in the valve block 11 which lead to the actuating piston, and is operatively connected to the ram or the armature 5 of the proportional solenoid 3.

An adjustment mechanism 16 is integrated into the proportional solenoid 3, which adjustment mechanism 16 serves to compensate for tolerances and comprises a setting spring 4 and a adjustment screw 17 which are both arranged in the direction of the Bent axis 15. The adjustable force of the setting spring 4 acts here on the armature 5, which is situated within the winding 6, of the proportional solenoid 3 with a force which opposes that of the feedback spring 9. The opening through which the adjustment screw 17 leads out is sealed off by means of a sealing element 18.

The feedback spring 9 is clamped between the spring seat 8 of the control spool 7 and the actuating piston 10. It rests at one side on the spring seat 8 of the control spool 7 and at the other side on the actuating piston 10 where it is partially held by a bore in the actuating piston 10.

The arrangement operates as follows:

If a certain current is applied to the proportional solenoid 3, its armature 5 is displaced, and with it moves the control spool 7 which thus moves out of its initial position until the actuating force of the magnet 3 is in equilibrium with the opposing force of the feedback spring 9. At the same time, oil pressure is applied to the actuating piston 10 via the unblocked ducts. Said actuating piston 10 likewise moves out of its neutral position and, by means of the swivel mechanism 13, adjusts the swivel angle of the valve segment 14 and thus the displacement of the axial piston machine.

As the actuating piston 10 is displaced out of its initial position, the force of the feedback spring 9 increases and from then on overcomes the actuating force of the magnet 3, and it retracts the control spool 7 again until, when the set swivel angle is reached, said control spool 7 reaches its initial position again in which the ducts leading to the actuating piston 10 are closed. The adjustment mechanism 16 which is integrated into the proportional solenoid 3 is provided to compensate for tolerance deviations. The preload of the setting spring is increased or decreased by turning the adjustment screw 17. Its spring force acts, via the armature 5 of the proportional solenoid 3, on the control spool 7 and changes the force equilibrium of the proportional solenoid 3 and of the feedback spring 9 which is connected to the control spool 7 by means of the spring seat 8. The force of the setting spring 4 is directed here in the direction of the actuating force of the magnet counter to the force of the feedback spring 9.

A simple adjustment mechanism for setting the start current is produced by means of this arrangement, the complex and costly apparatuses which are otherwise provided for this purpose being dispensed with.

Claims

1. Axial piston machine having a Bent axis valve segment which is adjustable by means of an actuating piston, and a variable unit (2) for the electrically proportional adjustment of the displacement, which has a control spool (7) for controlling the oil pressure which displaces the actuating piston (10), an electrically controllable proportional solenoid (3) which acts on the control spool (7), a feedback spring (9) on the control spool (7) for retracting the instantaneous Bent axis valve segment and a adjustment mechanism (16) for setting the start current, the adjustment mechanism (16) having a setting spring (4) which acts on the armature (5) of the proportional solenoid (3) with an adjustable force.

2. Axial piston machine according to claim 1, in which the force of the setting spring (4) is directed counterto the force of the feedback spring (9)

3. Axial piston machine according to claim 1, in which the setting spring (4) is integrated into the proportional solenoid (3).

4. Axial piston machine according to claim 1, in which the setting spring (4) and the armature (5) of the proportional solenoid (3) and also the control valve are arranged along a common axis.

5. Axial piston machine according to claim 1, in which the setting spring (4), the armature (5), the control spool (7), the feedback spring (9) and the actuating piston (10) are arranged along a common axis.

6. Axial piston machine according to claim 1, in which the feedback spring (9) is held at one side by a bore of the actuating piston (10) and rests at the other side on the control spool (7) via a spring seat (8)

7. Axial piston machine according to claim 1, in which the setting spring (4) force which acts on the armature (5) is adjustable by means of a adjustment screw (17) which is arranged in the longitudinal direction of the Bent axis.