Drive motor arrangement for a hydrostatic transmission

A hydrostatic transmission includes a side having an upstream radial piston motor and a downstream radial piston motor. The motors are connected to each other in series via a connecting line. A flow control valve is configured to discharge pressure medium from the connecting line so that the downstream motor is only engaged in the event of a predetermined amount of slippage of the upstream motor. Each motor has at least two groups of working flanks. Each flank is configured to operatively interact with a high pressure, such that each motor has at least two transmission steps.

This application claims priority under 35 U.S.C. § 119 to patent application no. DE 10 2016 216 382.5, filed on Aug. 31, 2017 in Germany, the disclosure of which is incorporated herein by reference in its entirety.

The disclosure relates to a drive motor arrangement for a hydrostatic transmission having a first continuously driven hydraulic motor and a second hydraulic motor having the ability to be activated or engaged.

BACKGROUND

Publication DE 10 2010 015 498 A1 discloses a hydrostatic transmission, in which a left-hand and a right-hand drive motor arrangement are supplied via a common adjustable pump in a common closed circuit. The two hydraulic motors on each side and each drive motor arrangement are connected to one another in series. The two upstream hydraulic motors are driven in the course of the normal operation of the vehicle concerned in two-wheel drive mode, whereas the two downstream hydraulic motors are essentially only idling. A quantity of pressure medium is discharged constantly from the connecting lines between the two hydraulic motors on each side for this purpose, so that the respective upstream hydraulic motor converts no energy or only little energy and delivers no torque or only little torque. A common or a respective constant flow regulator, which is referred to below as a flow control valve, is connected to the connecting lines for this purpose.

Automatic switching from two-wheel drive mode to four-wheel drive mode takes place if the slippage of an upstream hydraulic motor increases, and if the corresponding wheel accordingly “spins”. The downstream hydraulic motor is then also supplied with pressure medium in such a way that this also converts energy and delivers torque in the sense of an all-wheel drive system.

Publication DE 10 2011 118 255 A1 discloses a similar hydrostatic transmission, of which the performance is improved by a control valve in the event of steering movements by the vehicle concerned. Said valve permits the equalization of the pressure medium between the connecting lines of the two drive motor arrangements, that is to say from the connecting line of the curve inner wheel to the connecting line of the curve outer wheel.

Disclosed in DE 10 2013 211 621 A1 is a drive motor arrangement for one side of a hydrostatic transmission having an upstream hydraulic motor and a downstream hydraulic motor in a closed circuit. The publication discloses an integration of the flow control valve connected to the connecting line into the housing of one of the hydraulic motors.

A disadvantage associated with suchlike drive motor arrangements is that their hydraulic motors always have a fixed displacement, so that a constant speed of travel, that is to say only a single transmission step, results at a constant supply of pressure medium.

SUMMARY

On the other hand, the disclosure has as its object to make available a drive motor arrangement for a hydrostatic transmission, which permits at least two transmission steps at a constant supply of pressure medium.

Said object is accomplished by a drive motor arrangement according to this disclosure.

The disclosed drive motor arrangement is designed to constitute one side of a hydrostatic transmission. The drive motor arrangement has a first radial piston motor and, connected in series, a second radial piston motor, which is capable of activation or engagement in the event of increasing slippage of the first radial piston motor. All the unidirectional high-pressure or working flanks of each radial piston motor are subdivided into at least two groups, the groups being capable of activation individually or jointly. Each radial piston motor thus has a displacement that is variable or adjustable in particular in steps and a corresponding number of transmission steps. A flow control valve is connected to the connection between the outlets of the groups of the first radial piston motor and the inlets of the groups of the second radial piston motor. When the vehicle concerned is driving forwards, this permits the required activation or engagement of the second radial piston motor with the continuously driven first radial piston motor. When the vehicle concerned is driving backwards with a reversed direction of flow of the pressure medium through the drive motor arrangement, the flow control valve permits the required activation or engagement of the first radial piston motor with the continuously driven second radial piston motor.

The flow control valve is preferably constituted by a measuring orifice and a pressure compensator connected in series thereto, of which the valve body is impinged upon in the closing direction by the pressure upstream of the measuring orifice, and in the opening direction by the pressure downstream of the measuring orifice and by the force of a spring.

If the flow control valve is arranged on a housing of one of the radial piston motors or is integrated into the housing, and if an outlet of the flow control valve is connected to an interior space of the housing, housing flushing of the radial piston motor is accomplished. The flow control valve is preferably arranged on the housing of the first radial piston motor or is integrated into its housing, since this radial piston motor converts the most energy and exhibits the greatest heating when driving predominantly forwards and when driving largely in two-wheel drive mode.

The outlets of the groups of the first radial piston motor are connected via respective branch lines on the outlet side to a common connecting line, wherein the connecting line, on the other hand, is connected via respective branch lines on the inlet side of the second radial piston motor to the inlets of the groups of the second radial piston motor. The branch lines are preferably formed as branch ducts in the housing of the radial piston machine concerned. The common connecting line preferably has a respective section of connecting duct in the housing of each radial piston motor.

The flow control valve can be connected according to a first embodiment directly to the connecting line, in particular to the section of connecting duct in the housing of the first radial piston motor. According to a second embodiment, the flow control valve can be connected to one of the branch lines on the outlet side in the housing of the first radial piston motor.

In a particularly preferred further development of the disclosed drive motor arrangement, the at least one further group of each radial piston motor is capable of activation and deactivation with a respective displacement change-over valve.

An inlet and an outlet of the further group are capable of connection or are connected to one another via the displacement change-over valve, preferably in a deactivation position that is pretensioned by a spring, wherein a pressure-equalized circulation or virtually a hydraulic short-circuit of the further group is established.

The inlet of the first group can be connected directly to the inlet of the radial piston motor, or it is permanently connected to the inlet of the radial piston motor via the displacement change-over valve.

According to a device-related, simple first variant, the displacement change-over valve is a 4/2-way valve, via the deactivation position of which the inlet and the outlet of the further group are connected to an outlet of the radial piston motor. As a result, the circulation of the pressure medium in the deactivated further group takes place in the first radial piston motor under the pressure of the connecting line, that is to say an intermediate pressure, or under negative pressure. In the second radial piston motor, the circulation of the pressure medium takes place in the deactivated further group under negative pressure. This is always the case for forward travel.

In a specific embodiment of the first variant, in the deactivation position of the 4/2-way valve, a first connection of the 4/2-way valve connected to the inlet of the radial piston motor is connected to the inlet of the first group, whereas a second connection of the 4/2-way valve connected to the outlet of the radial piston motor is connected to the inlet of the further group. In an activation position of the 4/2-way valve, the first connection connected to the inlet of the radial piston motor is connected to the respective inlets of both groups, whereas the second connection connected to the outlet of the radial piston motor is shut off.

According to a second device-related, more complicated variant, the displacement change-over valve is a 5/2-way valve, via the deactivation position of which the inlet and the outlet of the further group are capable of connection to a control pressure connection.

A shut-off valve, which is switchable into its opening position via the control pressure connection against the force of a spring, can be arranged between the control pressure connection and the 5/2-way valve.

In a specific embodiment of the second variant, in the deactivation position of the 5/2-way valve, a first connection connected to the inlet of the radial piston motor and a second connection connected to the outlet of the radial piston motor are shut off, whereas a third connection connected to the shut-off valve is connected to the inlet and to the outlet of the further group. In an activation position of the 5/2-way valve, the first connection is connected to the inlet of the further group, whereas the second connection is connected to the outlet of the second group. The third connection is shut off in this case.

DETAILED DESCRIPTION

FIG. 1depicts the first illustrative embodiment of the disclosed drive motor arrangement having a first radial piston motor1and a second radial piston motor2, which are connected to one another in series. Pressure medium under high pressure is supplied to the inlet B of the first radial piston motor1via a pump, which is not illustrated here, and a closed hydraulic circuit. A connecting line4or, in particular, a main section4bof the connecting line4is provided between an outlet A of the first radial piston motor and an inlet B of the second radial piston motor. In the second case, the connecting line4has a section4aof connecting duct in the interior of the housing6of the first radial piston motor1and a section4cof connecting duct in the interior of the housing6of the second radial piston motor2.

The radial piston motors1,2each have an output shaft8, which is capable of being brought into operative interaction with a respective first group10and with a second group12of working flanks for the purpose of displacing pressure medium. According to a first variant, the working flanks of both groups are each distributed uniformly on the periphery of a common stroke ring of each radial piston motor1,2. According to a second variant, the two groups10,12are distributed on separate stroke curves of the respective radial piston motor1,2, so that each radial piston motor1,2virtually has two partial motors that are arranged adjacent to one another, both of which are connected to the common drive shaft8of each radial piston motor1,2.

Each radial piston motor1,2has a displacement change-over valve14configured as a 4/2-way valve. Its valve body has the activation position16depicted inFIG. 1that is pretensioned by a spring. In this case, a first connection18connected to the inlet B of the radial piston motor is connected to the inlets20,22of both groups10,12. The outlets24,26of both groups10,12are connected via a respective branch line29on the outlet side and via the first section4aof connecting duct to the outlet A of the radial piston motor1,2. Both groups10,12are thus active in the activation position16of the displacement change-over valve14, whereby the respective radial piston motor1,2has a maximum displacement.

When the displacement change-over valve14is switched into a deactivation position28against the force of the spring by being impinged upon with control pressure medium via a control pressure connection X, the connections and thus the function of the first group10remain unchanged. In the second group12, on the other hand, the inlet22is connected to the outlet26, so that the second group12is pressure-equalized and thus deactivated. The displacement of the respective radial piston motor1,2is reduced as a result. More precisely, the inlet22and the outlet26of the second group12are connected to the first section4aof connecting duct, so that the pressure of the connecting line4acts to either side of the second group12in the first radial piston motor1, whereas the lower pressure of the outlet A acts in the second radial piston motor2.

In order to disengage the wheel of the second radial piston motor2automatically in the event of an increase in the slippage of a wheel (not illustrated here), which is connected to the drive shaft8of the first radial piston motor1, a flow control valve30, having a measuring orifice32and a pressure compensator34connected in series downstream of the measuring orifice32, is provided on the first section4aof connecting duct of the first radial piston motor1on its housing6or in the interior of its housing6, of which the valve body is impinged upon, in the closing direction, by the pressure upstream of the measuring orifice32and, in the opening direction, by the pressure downstream of the measuring orifice32and by the force of a spring. A defined drop in pressure is thus set by the pressure equivalent of the spring via the measuring orifice32. A constant pressure medium volumetric flow rate flowing via the flow control valve30, which is diverted from the connecting line4, is established in conjunction with the size of the flow cross-section of the measurement orifice32. On the outlet side, the flow control valve30discharges into a leakage line36, which is connected to a leakage connection L and a connection F.

FIG. 1depicts the two displacement change-over valves14in their respective activation position, so that both radial piston motors1,2have a maximum displacement. In this case, the entire pressure medium flows, as indicated by the arrows, initially through the inlet B of the first radial piston motor1, then through both groups20,22of the first radial piston motor1, and then to the outlet A of the first radial piston motor1, further via the main section4bof the connecting line4to the inlet B of the second radial piston motor2, and from there via the two groups10,12of the second radial piston pump2to its outlet A.

In the first illustrative embodiment of the disclosed drive motor arrangement according toFIG. 1, it is also possible to drive backwards by reversing the direction of flow (against the indicated arrows), wherein the diversion of the pressure medium from the connecting line4via the flow control valve30is assured, so that automatic switching or activation of the first radial piston motor to the continuously driven second radial piston motor is possible. Deactivation of the respective second group12of the two radial piton motors1,2is not possible, however, in the case of driving backwards.

FIG. 2depicts the second illustrative embodiment of the disclosed drive motor arrangement, wherein the two radial piston motors101,102that are connected in series, of which the respective housings6and the connections A, B, X, L and F respectively formed thereon, including the one flow control valve30, correspond in principle to those of the first illustrative embodiment according toFIG. 1.

In contrast to the first illustrative embodiment according toFIG. 1, the flow control valve30is not connected directly to the connecting line4, but rather to the branch line29on the outlet side, which connects the outlet24of the first group10to the connecting line4.

Due to a more complicated design of the displacement change-over valve114, in the second illustrative embodiment according toFIG. 2, driving forwards and driving backwards respectively are possible with both groups10,12or with only a single group10. For this purpose, the displacement change-over valve114is configured as a 5/2-way valve and, in addition to the first connection18, which is connected to the inlet B, and the second connection19, which is connected to the outlet A of the respective radial piston motor101,102, has a third connection138, which is connected to the control pressure connection X via a control pressure line. A shut-off valve140, which shuts off this connection in a position that is pretensioned by a spring, is provided in this control pressure line.

FIG. 2depicts the respective displacement change-over valve114of the two radial piston motors101,102in the respective activation position16, in which both groups10,12are activated. More precisely, the two groups10,12of the first radial piston motor101are supplied with high pressure in this case, whereas the two groups10,12of the second radial piston motor102are supplied with the reduced pressure of the connecting line4. For this purpose, the first connection18of the displacement change-over valve114is connected to the inlet22of the second group12, whereas the second connection19of the displacement change-over valve114is connected to the outlet26of the second group12.

If it is now wished to shift the disclosed drive motor arrangement into a second transmission step, the two displacement change-over valves114are switched into their respective deactivation position28. This takes place by the impingement of the control pressure connection X with control pressure medium. Since a spring of the displacement change-over valve114is slightly weaker (e.g. equivalent to 12 bar) than a spring of the shut-off valve140(e.g. equivalent to 15 bar), the displacement change-over valve114switches initially into its deactivation position28, before the shut-off valve140opens a control pressure connection from the control pressure connection X to the inlet22and to the outlet26of the second group12. As a result, the second group12is pressure equalized under control pressure. The first connection18and the second connection19of the displacement change-over valve114are then shut off.

Furthermore, a brake142, which can be released by a supply to a connection Z, is provided on each drive shaft8.

The radial piston motors1,2of the first illustrative embodiment require three commutators or rotating unions for the various operating states, whereas the radial piston motors101,102of the second illustrative embodiment require four commutators or rotating unions for the various operating states.

Disclosed is one side of a hydrostatic transmission having an upstream and a downstream radial piston motor, which motors are connected to one another in series via a connecting line. Pressure medium can be discharged from the connecting line via a flow control valve, so that the downstream radial piston motor is only engaged in the event of a certain slippage of the upstream radial piston motor. Each radial piston motor has at least two groups of working flanks, which are capable of being brought into operative interaction with high pressure, so that each radial piston motor possesses at least two transmission steps.

LIST OF REFERENCE DESIGNATIONS

1;101first radial piston motor2;102second radial piston motor4connecting line4afirst section of connecting duct4bmain section4csecond section of connecting duct6housing8output shaft10first group12second group14;114displacement change-over valve16activation position18first connection19second connection20inlet of the first group22inlet of the second group24outlet of the first group26outlet of the second group28deactivation position29branch line on the outlet side30flow control valve32measurement orifice34pressure compensator36leakage line138third connection140shut-off valve142brakeA outlet of the radial piston motorB inlet of the radial piston motorF connectionL leakage connectionX control pressure connectionZ connection