DE8336853U1 - Hydrostatic drive - Google Patents

Description

Description

The invention relates to a hydrostatic drive of the type specified in the preamble of patent claim 1.

In such known travel drives, a flow divider is usually used in the main circuit, which supplies the two hydraulic motors with hydraulic medium in equal parts. The flow divider causes a differential lock, so that when one wheel is lifted, the other drives with half the drive line. A slight differential compensation is achieved by

a cross connection with a cover is provided. However, this differential compensation is not sufficient for cornering to drive both wheels at different speeds but with the same traction. Therefore, the flow divider can be switched on, i.e. for normal driving without differential lock, it is bypassed so that the two hydraulic motors are pressurized from the main pump to a level that corresponds to their respective speed. However, as soon as a wheel lifts off or slips, it is fully pressurized from the main pump so that the other wheel and thus the vehicle comes to a standstill. The flow divider and the control measures for switching it on and off are complex and expensive. The most serious disadvantage of the flow divider is its poor efficiency, which reduces the overall efficiency, especially when differential lock is required.

3Q degree of drive deteriorates. Another disadvantage is that with this design, while ensuring sufficient traction for each wheel, a very limited upper speed range is achieved, so that a gearbox is required between the hydraulic motor and the wheel, with which higher speeds are also possible for ferry operations. Such gearboxes

but are extremely expensive and take up a lot of space. The operator is required to pay particular attention to engaging and disengaging the differential lock. Since the differential compensation is insufficient for normal driving when the differential lock is engaged, there is a risk of overheating or damage if the operator intentionally or inadvertently fails to release the differential lock.

The invention is based on the object of creating a hydrostatic drive of the type mentioned at the beginning, in which both a differential compensation with equal tractive force distribution and a differential lock that works automatically when required are provided with little technical effort. In addition, there is the requirement for an upwardly extended driving speed range for the drive wheels, which avoids the need for a gear box between each hydraulic motor and its wheel.

The stated object is achieved according to the invention by the features specified in the characterizing part of patent claim 1.

As a result of the series connection of the two hydraulic motors, an automatically acting differential lock is provided, with which each wheel continues to drive the vehicle when the other wheel is lifted or spins, whereby the tractive force of the wheel that continues to grip is approximately the same as the tractive force exerted by both wheels during normal driving. It is necessary that the two hydraulic motors are designed in terms of their displacement to match the maximum delivery capacity of the main pump, so that each hydraulic motor actually absorbs the full delivery capacity of the pump.

This dimensioning of the hydraulic motors results in a higher driving speed with

still sufficient traction, since the 5

As much traction as possible can be easily converted into an increase in speed. When cornering, the pressure difference across the hydraulic motor inside the curve increases, while the pressure difference across the hydraulic motor outside the curve decreases. As a result of the series connection, different traction forces would result from both wheels. However, the control valve arranged in the secondary circuit compensates for this difference in traction by giving the hydraulic motor, which operates with a lower pressure difference,

motor a quantity of hydraulic medium with which the pressure difference between the two hydraulic motors and thus their tractive forces are equalized. Since the control valve is arranged in the secondary circuit, a reduction in the efficiency of the travel drive is avoided or kept to a negligible low value, since the hydraulic medium flowing in the main circuit is not subject to the influence of the control valve. The additional cost of over-dimensioning the hydraulic motors is more than offset by the elimination of gear boxes between the hydraulic motors and the wheels. Even with two axles each driven by a hydraulic motor, the control valve equalizes the pressure differences that arise when cornering due to different ^turning circle radii.

An expedient embodiment of a travel drive according to the invention, in which two main pumps are provided, is evident from claim 2. In particular, in the case of soil cultivation machines or work machines that require an additional main pump for the operation of work elements in order to

In order to be able to move the two elements independently and simultaneously, the second main pump can be used to advantage for the travel drive during driving when it is not needed to operate the working elements. By switching on the second main pump, an additional driving stage is then available, in which the driving speed is doubled _; without the need for expensive, space-consuming and heavy manual transmissions.

A further, expedient embodiment of the invention is evident from claim 3. In this embodiment, the drive can be connected between a parallel circuit

and a series connection of the hydraulic motors, whereby an even higher driving speed is achieved in the series connection. In both switching positions of the switching valve device, both an automatically activated differential lock and

the differential compensation required for cornering is provided, whereby in the switching position for series connection of the hydraulic motors the control valve supplies the balancing hydraulic medium quantity from the auxiliary pump to the hydraulic motor that has the smaller pressure difference, i.e. rotates faster than the other. When driving straight ahead, the hydraulic medium quantity from the auxiliary pump is evenly distributed between the two hydraulic motors. In relation to the performance of the main pumps, this design

any reduction in efficiency due to the influence of the control valve is avoided. With the differential lock that is effective when the hydraulic motors are connected in parallel, if a wheel lifts off or slips, the traction of the wheel that is still driving will only reach a value that depends on the delivery capacity of a main pump. With the differential lock

When the hydraulic motors are connected in series, the wheel that is the only driving wheel when a wheel is lifted or spinning will transfer the full traction force, which depends on the delivery capacity of both main pumps.

A further, expedient embodiment is evident from claim 4. The auxiliary pump ensures the necessary differential compensation when cornering if the main circuits are separate or connected in parallel.

The idea of claim 5 is also important,

separate pump units, the control pressure for adjusting the main pumps during differential compensation is not affected.

The feature of claim 6 is also important, since

When the hydraulic motors are connected in parallel via a return flow connection, the auxiliary pump returns the balancing hydraulic quantity that it pumps into one of the main circuits.

Another important feature of the invention is evident from claim 7. This control valve for the travel drive, which can be manufactured simply and inexpensively, compares the pressure differences between the two hydraulic motors and, depending ^on this, regulates the equalization of the two pressure differences completely automatically, so that the hydraulic motors reliably transmit the same tractive forces when cornering.

^5 A further, expedient embodiment of the invention is apparent from claim 8. With this design of the control valve, it can be used both

for a travel drive with one or two main pumps that can be switched in parallel as well as for a travel drive with one or two main pumps that can be switched in parallel and an auxiliary pump, whereby depending on the purpose of the control valve, one of the orifice openings is rendered inoperative by a sealing plug. This is advantageous in terms of manufacturing technology.

The embodiment of claim 9 is expedient so that the differential compensation becomes effective when a pressure difference occurs between the hydraulic motors of both wheels. With this arrangement, the control valve is immediately informed of the pressure conditions in each hydraulic motor during driving and can therefore follow changes in the pressure conditions without the operator having to influence them.

An alternative embodiment is also evident from claim 10. Here, the balancing hydraulic medium quantity from the auxiliary pump is used by the control valve in a way that corresponds to the pressure conditions in both hydraulic motors. The flow passage, which is created to bypass the hydraulic motor with the larger pressure difference, is located in the intermediate chamber of the first cylinder chamber of the control valve, which intermediate chamber in itself forms a control chamber for the piston. This dual function of the intermediate chamber, however, has no negative influence on the perfect control behavior of the control valve.

Furthermore, the idea of claim 11 is also important, since this dimensioning of the openings ensures that, up to the smallest possible

Turning circle of the vehicle equipped with the drive system ensures automatic differential compensation and that the control valve does not impair the locking effect when the differential is locked.

Finally, the simple measure IQ of claim 12 can be used to effectively dampen the pistons of the control valve against vibrations.

Embodiments of the invention are explained with reference to the drawings. They show

Fig. 1 is a schematic block diagram of a

first embodiment of a hydrostatic drive, whereby unimportant details for differential compensation and a differential lock

are omitted,

-&dgr;&igr; Fig. 2 is a schematic block diagram of a second

Design of a hydrostatic drive,

Fig. 3 is a detailed block diagram based on the embodiment of Fig. 2, and

Fig. 4 shows the schematic sectional view through a

Control valve used in the travel drives shown in Fig. 1 to 3.

The drive systems described below are primarily intended for off-road vehicles such as earth-moving and moving vehicles, agricultural vehicles, military vehicles etc., in which at least one internal combustion engine is used as the primary drive source for the

hydrostatic drive.

According to Fig. 1, a hydrostatic drive has a hydraulic main circuit 1 consisting of an inflow line 2 and a return line 3. In the main circuit 1,2,3,

a, preferably adjustable, main pump 4 is arranged, which is driven by the primary drive source (not shown). In the main circuit 1, 2, 3, two, preferably adjustable, hydraulic motors 5, 6 are also connected in series. If a second main pump 8 is present in the vehicle, which is normally intended for the movement of other components of the vehicle, the second main pump 8 can also be integrated into the travel drive by connecting it via a line for travel operation parallel to the first main pump 4 in

^Q is switched to the main circuit 1.

A secondary circuit 9 is connected to the main circuit 1,2,3, which serves to actuate a control valve 10, the purpose of which will be explained later. A secondary circuit branch 11 branches off from the inflow line 2 in front of the first hydraulic motor 5 to a connection opening 12 of the control valve.

valve 10. In the flow direction behind the first

Hydraulic motor 5, a secondary circuit branch 13 branches off to a connection opening 14 of the control valve 10. g In the flow direction upstream of the second hydraulic motor 6, a secondary circuit branch 15 branches off from the main circuit 1 to a connection opening 16 of the control valve 10. In the flow direction downstream of the second hydraulic motor 6, a secondary circuit branch 15 branches off from the return flow line 3.

,Q secondary circuit branch 17 to a connection opening 18 of the control valve 10. Between the two hydraulic motors 5,6, a secondary circuit branch 19 is connected to the main circuit 1, which leads to an orifice opening 22 of the control valve 10, while in the flow

,,- direction behind the second hydraulic motor 6, a secondary circuit branch 20 is connected to the return flow line 3, which leads to an orifice opening 21 of the control valve 10. The secondary circuit branches 13 and 17 are control lines that transmit the respective pressure behind the first hydraulic motor 5 and behind the second hydraulic motor 6 to the control valve 10, while the secondary circuit branches 11,15 are control lines and at the same time delivery lines for an equalizing hydraulic medium quantity. The secondary circuit branches 19 and 20 are only delivery lines for equalizing hydraulic medium quantities.

The control valve is divided by a fixed partition 27 into two cylinder chambers A, B, in _each of which there is a movable piston 24, 25. The two pistons 24, 25 are connected by a piston rod 23 which passes through the partition 27 in a sealed manner. Each piston 24, 25 is loaded by a spring 26. The two springs 26 hold the pistons 24,

_ocr 25 in a coat position in which a piston with the top

A one-piece closing element 65 closes the two apertures 21 and 22. The piston

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Rod 23 is continuous due to the equal piston surfaces. The springs 26 are not absolutely necessary.

The piston 24 divides the cylinder chamber A into an end chamber 28 and a separate intermediate chamber 29. The connection opening 12 leads to the end chamber 28, while the connection opening 16 leads to the intermediate chamber 29. In the same way, the piston 25 divides the cylinder chamber B into an end chamber 30, to which the connection opening 14 leads, and into an intermediate chamber 31, to which the connection opening 18 leads.

The two hydraulic motors 5,6 are each connected to a wheel via a transmission gear

or flanged to an axle. 20

The drive system shown in Fig. 1 works as follows:

The main circuit 1 is a closed circuit. The main pump 4 delivers with the set delivery

power, the hydraulic medium flows through the main circuit 1, with the hydraulic motors 5,6 running at the same speed when the vehicle is travelling straight ahead. At the same speed, the same pressure difference exists in the main circuit for each hydraulic motor 5, as the two hydraulic motors 5,6 divide the entire pressure difference between the intake and pressure sides of the main pump 4 evenly between themselves. The two wheels work with the same tractive force, which corresponds to half the maximum possible tractive force. By changing the delivery rate of the main pump 4, the driving speed can be changed, while at the same time the

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By adjusting the position of the hydraulic motors 5,6, the traction force can be adjusted so that, for example, the greatest traction force c is applied at low driving speeds or the smallest traction force is applied at the highest driving speeds. By connecting the second main pump 8 to the main circuit 1, a higher driving level can be selected, at which the driving speed is increased accordingly.

Assuming that the vehicle is still travelling straight ahead, the pressure differences on both hydraulic motors 5,6 are equal, whereby the pistons 24,25 of the control valve 10 in the secondary circuit 9 are in the middle position, in which the orifice openings 21,22 are closed. This is because the pressures acting on the two pistons 23,24 in the end chambers 28 and 38 and in the intermediate chambers 29 and 31 cancel each other out.

As soon as a wheel starts to spin or lift off, a strong reduction in the pressure difference in the main circuit via this hydraulic motor occurs. At the same time, the

"P- pressure difference in the other hydraulic motor, as this is forced to transmit the entire tensile force alone. This difference in the pressure differences of the two hydraulic motors results in an adjustment movement for the pistons 24,25 to _one side or the other, whereby either the orifice opening 22 or the orifice opening 21 is released by the closing element 65 and thus a flow passage from the end chamber 28 to the secondary circuit branch 19 or from the intermediate

_,_ chamber 29 is released to the secondary circuit branch 20. A small amount of hydraulic medium flows through this flow connection where the higher pressure difference

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with hydraulic motor and is fed into the main circuit in front of the hydraulic motor that widens the smaller pressure difference in order to equalize the pressure differences. If there is only partial slippage at one wheel, the power of its hydraulic motor is increased by equalizing the pressure differences until the wheel is effective with the same tractive force as the other, non-spinning wheel. The vehicle continues to drive with undiminished total tractive force.

However, if the wheel passes through empty or is completely lifted, the amount of hydraulic medium through the open flow passage in the control valve 10 is no longer sufficient to equalize the speed or traction, but the wheel that is not lifted transfers almost the full traction provided by the output of the main pump to the ground. The lifted wheel rotates through empty at a slightly increased speed. Since this wheel does not transfer any traction, there is no pressure difference in the associated hydraulic motor, so that the entire pressure difference provided by the main pump 4 is used by the hydraulic motor of the wheel that is not lifted to generate almost the full traction.

When cornering, the hydraulic motor on the outside of the curve works faster than the hydraulic motor on the inside of the curve. In order for the two wheels driven at different speeds to transmit the same traction when cornering, the flow passage (either from the end chamber 28 to the secondary circuit branch 19 or from the intermediate chamber 29 to the secondary circuit branch 20) is released in the control valve which

creates a bypass of the hydraulic motor in the main circuit, which has the higher pressure difference. The hydraulic medium flowing through the flow passage is fed to the hydraulic motor with the lower pressure difference by either being drawn from the inflow line 2 in front of the first hydraulic motor 5 and fed to the main circuit in front of the first hydraulic motor 5 via the orifice 22 and the secondary circuit branch 19.

_in the second hydraulic motor 6 or from the main circuit 1 in front of the second hydraulic motor 6 via the secondary circuit branch 15 and the intermediate chamber 29 as well as via the orifice 21 and the secondary circuit branch 20 into the return flow line 3 via

.j. the main pump 4 and the inflow line 2 is fed to the first hydraulic motor 5. This balancing hydraulic medium quantity contributes to the fact that the wheel on the outside of the curve applies the same traction as the wheel on the inside of the curve. The balancing hydraulics

_The medium quantity is taken from the main circuit and then returned to it. It only bypasses the hydraulic motor that has the larger pressure difference.

_oc If one of the two wheels lifts off when cornering, the differential lock will automatically be activated again (as mentioned above), with the full tractive force then being applied by the wheel that is not lifted off.

By switching on the second main pump 8, the driving speed can be increased.

The main pump 4 is reversible. The control valve 10 also works when the main pump is reversing. Braking is possible when driving downhill.

The drive shown in Fig. 2 differs

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from the embodiment of Fig. 1 in that in addition to the first main pump 4 and possibly a second main pump 8, an auxiliary pump 3.2 is provided, which is connected to the return flow line 3 by a return flow line 33 and to the inflow line 2 by an inflow line. In this embodiment, the control valve 10' is also provided with a separate closing element 38 attached to the piston rod 23, which works together with two orifice openings 21' and 36 in such a way that it keeps the orifice openings closed in the middle position of the pistons 24, 25. A secondary circuit branch 35 is connected to the orifice opening 36, which in turn is connected to the flow line 34 of the auxiliary

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pump 32 is connected. A secondary circuit branch 37 to the return flow line 33 to the auxiliary pump 32 is connected to the orifice opening 21". The secondary circuit branches 11, 13, 17 are control lines which transmit the pressure in front of the first hydraulic motor, behind the first hydraulic motor and behind the second hydraulic motor to the end chamber 28, intermediate chamber 31 and end chamber 30. The secondary circuit branch 15, like the secondary circuit branches 35 and 37, is a delivery line for the balancing hydraulic medium quantity, which in this embodiment is not drawn from the main circuit 1, 2, 3, but is applied by the auxiliary pump 32 in order to ensure differential compensation when cornering or when a wheel begins to slip.

The drive works as follows:

When driving straight ahead, the pistons 24, 25 in the control valve 10' are in their center position. The orifice openings 36, 21 are closed. The hydraulic medium delivered by the auxiliary pump 32 enters the main circuit in front of the first hydraulic motor 5 and is drawn off from the main circuit behind the second hydraulic motor 6.

As soon as a wheel, e.g. the wheel associated with the hydraulic motor 6, spins fully or is lifted, the pressure difference in this hydraulic motor 6 decreases, while the pressure difference in the hydraulic motor 5 increases. The pistons 24, 25 are moved to the right in Fig. 2 until the orifice opening 36 is free and the hydraulic medium delivered by the auxiliary pump 32 is fed via the secondary circuit branch 35, the intermediate chamber 29 and the secondary circuit branch 15 to the main circuit 1 immediately before the second hydraulic motor 6. However, since the hydraulic motor 6 runs through empty, the pistons 24, 25 move to their right end position. The hydraulic motor 5 is connected to the

The connected wheel transmits the total traction force applied by the main pump 4 or the main pump 4 and the main pump. The differential lock is automatically effective. The hydraulic medium quantity fed in by the auxiliary pump is withdrawn again via the return flow line 33 without affecting the delivery capacity of the main pump 4 or the main pumps 4 and 8.

When cornering, where a speed difference occurs between the two wheels, the pressure difference of the hydraulic motor assigned to the wheel on the outside of the curve (e.g. hydraulic motor 5) is smaller than the pressure difference in the other hydraulic motor (here hydraulic motor 6). This means that the pistons 24, 25 in Fig. 2 are moved to the left so that the flow connection between the secondary circuit branch 15 and the secondary circuit branch 37 is released, via which the hydraulic motor 6, which has the higher pressure difference, is bypassed. The hydraulic motor 5 is supplied with the equalizing hydraulic medium quantity via the auxiliary pump 32 until the pressure difference between the two hydraulic motors 5, 6 is equal to one another and the hydraulic motor 5 on the outside of the curve also applies the same tractive force as the hydraulic motor 6 on the inside of the curve. The control valve 10' always regulates the tractive force equalization in direct dependence on the turning angle of the wheels, i.e. when the wheel turning angle is reduced, the equalizing hydraulic medium quantity supplied to the hydraulic motor on the outside of the curve is also reduced accordingly.

The drive according to Fig. 2 is also in reversing mode

drive functional.

g In Fig. 3, a travel drive similar to that in Fig. is shown in detail, with the difference that the two hydraulic motors 5 and 6 can be connected either in series or in parallel. The main pumps 4,8 are not reversible.

The two main pumps 4,8 are mechanically coupled via a rod 42 for the purpose of synchronous adjustment, which can be actuated with an adjustment cylinder 41. An auxiliary pump 32,32a is connected to each main pump 4,8.

. _ connected, whereby the auxiliary pump 32 is used to pump the &igr;&ogr;

The auxiliary pump 32a is used to adjust the hydraulic medium quantity for cornering and the auxiliary pump 32a is used to adjust or control the main pump and to compensate for leakage oil. The auxiliary pump 32a is connected to a line on the suction side

61 to a hydraulic reservoir and on the pressure side over 20

a line 44 is connected to an adjustment valve arrangement 43 consisting of an adjustment valve and a 3/2-way valve for the adjustment cylinder 41. A line 45 branches off from the line 44 to an adjustable pressure relief valve 46 and to connection 25

lines 47, which are connected to the inlet and outlet lines 2a,3a and 2b,3b of the two main circuits of the hydraulic motors 5,6 via check valves arranged in pairs and 49 in connecting lines 50,51 for leakage oil compensation. 30

The two main circuits are connected to one another via a switching valve device 52, which consists of a 6/2-way valve and a 5/2-way valve, which can be actuated electromagnetically and connected via a connection 35

are electrically coupled. The switching valve device 52 separates the two main circuits from each other in the first switching position shown in Fig. 3.

However, there is a return flow connection via a flow channel 64 in the 6/2-way valve between the back flow line 3a of the main circuit of the hydraulic motor 5 and a line branch 40 with the return flow connection between the return flow line 3a of the main circuit of the hydraulic motor 5 and a line branch 40 with the return flow line 3b of the main circuit of the hydraulic motor 6. Furthermore, the control valve 10' in the secondary circuit N is connected to the return flow line 3a of the main circuit of the hydraulic motor 5 via a secondary circuit branch 55, this flow connection being open in the first switching position via the 5/2-way valve. The control valve 10' is connected to the 5/2-way valve via the secondary circuit branch 15 and is switched off in its first switching position. In the second switching position, however, the secondary circuit branch 15 is connected to the inflow line 2b. The secondary circuit branch 37 connects the control valve 10' with the return flow line 3b of the main circuit of the hydraulic motor 6.

In the first switching position, the secondary circuit branch 35 of the control valve 10' is connected to the inflow line 2b via the 5/2-way valve. In the second switching position, the connection is blocked.

The auxiliary pump 32 is connected on the suction side to the return flow

line 3b, while on the pressure side it is connected via 30

a check valve 54 and a line 34a are connected to the line 39 leading to the inflow line 2a on the one hand and via the line 34b to the inflow line 2b to the hydraulic pump 8.

Each hydraulic motor 5,6 has a 2/2-way valve 59 with electro-

magnetic actuation, which works together with an actuating cylinder 56. The hydraulic motors 5,6 are reversible. A 4/3-way valve 58 with electromagnetic actuation is provided in the main circuit to reverse the direction of travel. Pressure relief valves 57 serve to safeguard the system pressure. The two-point adjustment of the hydraulic motors IQ 5,6 allows their displacement to be adjusted, so that two driving ranges are available, e.g. a slow driving range and a fast driving range, or a high or low tractive force.

In the first switching position of the switching valve device 52 according to Fig. 3, the hydraulic motors 5, 6 are connected separately to a main pump 4, 8 each.

2Q As soon as the valves 58 for one direction of travel are activated and the main pump 4,8 and the auxiliary pump 32,32a deliver accordingly, the vehicle moves. When driving straight ahead, the hydraulic motors 5,6 operate at the same speed; their wheels exert the same tractive forces. The auxiliary pump 32 delivers equally into both main circuits via the check valves 54 and sucks the hydraulic medium in equal parts from the return flow via the outlets 33 and the connection 40,64.

OQ lines 3a and 3b. As soon as one wheel goes through or lifts off, only the traction force of the other wheel, which depends on the output of a main pump, is available.

Oj- When cornering, the auxiliary pump 32 supplies the outside hydraulic motor with an equalizing hydraulic medium quantity in order to compensate for the pressure exerted by the outside wheel.

to keep the applied traction force equal to the traction force of the wheel on the inside of the curve. This is done automatically and depending on a pressure difference between the inflow lines 2a and 2b. The auxiliary pump 32 then sucks the amount of hydraulic medium from the return line of the hydraulic motor on the outside of the curve. The hydraulic medium

₁ q quantity is designed in such a way that even with the tightest curve radius, a tractive force adjustment is ensured. The operator does not need to worry about engaging the differential lock or the differential compensation, as both are automatically

₁₍ - become effective when they are needed. The control valve 10 ^f is switched off via the 5/2-way valve.

After actuation of the switching valve device 52 into the second switching position, the 6/2-way

__ valve connects the inflow line 2b to the inflow line 2a via line 39 and simultaneously the return flow line 3b to the return flow line 3a via line 40. Furthermore, the return flow line 3a is connected between the valve 58 and the 6/2-way valve of the switching valve device 52 to the inflow line 2b leading from the 6/2-way valve to the other valve 58. The secondary circuit branch 55 is separated from the return flow line 3a via the 5/2-way valve, while 34b only remains connected to the _n secondary circuit branch 35.

The two main pumps 4,8 are connected in parallel to each other, while the hydraulic motors 5,6 are connected in series.

When accelerating and driving straight ahead and assuming that both wheels have the same grip, the

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Pressure differences in the hydraulic motors 5,6 are equal, so that the pistons 24,25 in the control valve 10' (see Fig. 2) are in the middle position. The entire hydraulic medium delivered by the auxiliary pump 32 flows back to the auxiliary pump 32 via both hydraulic motors 5,6. Each wheel transmits half of the maximum possible tractive force, which depends on the set output of the two main pumps 4,8 plus the delivery output of the auxiliary pump 32.

When cornering with the hydraulic motor 5 assigned

, _c arranged wheel on the outside of the curve reduces Ib

the pressure difference in the hydraulic motor 5. The pistons 24,25 move to the left in Fig. 2, so that a connection is opened between the secondary circuit branch 15 and the secondary circuit branch 37 via the intermediate chamber 29. The secondary circuit branch 35 or the orifice opening 36 remains blocked, so that the auxiliary pump 32 supplies more hydraulic medium via the output 34a and the line 39 of the inflow line 2a in Fig. 3, which is used to increase the pressure.

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difference in the hydraulic motor 5 to the pressure difference in the hydraulic motor 6, whereupon the outside wheel, despite its higher speed

applies the same traction as the wheel on the inside of the curve. The additional amount of equalizing hydraulic medium required by the first hydraulic motor 5 flows via the secondary circuit branch 15, the intermediate chamber 29 and the secondary circuit branch 37 into the line 33 back to the auxiliary pump 32, i.e. past the second hydraulic motor 6.

When cornering with the wheels turned in opposite directions, the pistons 24, 25 move to the right so that the orifice opening 21' is closed and the orifice opening 36 is opened, whereupon the auxiliary pump 32 supplies the equalizing hydraulic medium quantity to the second hydraulic motor 6 via the secondary circuit branch 35, the intermediate chamber 29 and the secondary circuit branch 15, bypassing the first hydraulic motor 5, the pressure difference of which is thus equalized to the pressure difference of the hydraulic motor 5.

The equalizing hydraulic quantity is then discharged from the main circuit via line 33 in the flow direction behind the second hydraulic motor 6.

When a drive wheel spins, there is practically no pressure difference in the associated hydraulic motor. The control valve 10' then bypasses the other hydraulic motor, so that the entire hydraulic medium quantity from the auxiliary pump 32 through the respective orifice 36 or 21' is fed via the hydraulic motor for the spinning wheel, which rotates faster than the engaging drive wheel. The engaging drive wheel, however, applies the full traction to the ground, namely in this case the traction resulting from the power of both main pumps 4,8. The pistons 24,25 are then either on the left or right stop. With the power provided by the main pumps, no

There is a loss of power because, due to the closed main circuit, the entire hydraulic medium delivered by the main pumps must pass through the hydraulic motor connected to the driving wheel.

In this design, the two hydraulic motors are each dimensioned so large that each of them alone can absorb the entire power of both main pumps.

,Q can take. With this large dimensioning of the

Hydraulic motors have a large displacement, which has the advantage that an extraordinarily high driving speed can be achieved, so that a manual transmission, which was previously located between the hydraulic motor

jg and the wheel for such a high driving speed can be eliminated. Alternatively, a high starting tractive force can be generated from this. A further advantage is that when a wheel is lifted off, the driving wheel applies the full tractive force when the hydraulic motors are connected in series.

Due to the automatic differential compensation, both wheels produce the same tractive force when driving, both when the hydraulic motors are connected in parallel and when they are connected in series.

_O c the floor.

AD

Fig. 4 finally shows a longitudinal section through an embodiment of a control valve, which, depending on the intended use, can be used as a control valve 10 according to Fig. ₁ or as a control valve 10' according to Figs. 2 and 3. For this purpose, in a housing 60 of the control valve 10, 10', the two pistons 24, 25 in the cylinder chambers A, B are connected to one another via the piston rod 23, which is connected via the

Pistons 24,25 and penetrates with its extensions 63 holes 62 of the housing 60. On the piston rod 23 there is another, through-

ducts 64 containing a piston which forms the closing element 38, which is connected to the two

p. apertures 36 and 21 or 21' work together in such a way that both apertures are closed in the middle position of the pistons 24,25 and are alternately released depending on the direction of movement of the pistons 24,25. The piston

_n 24, which is designed with its outer circumference 65 as a closing element, works together with the aperture 22, such that in the middle position of the pistons 24,25 the aperture 22 is closed, while with each movement

,_ the piston 24,25 to the right the aperture 15

22 is open.

Of the total of three orifice openings 22, 36, 21 or 21', the orifice opening 22 is closed by a plug (not shown) if the control valve 10 is used in a main circuit without an auxiliary pump, while in a control valve 10' the orifice opening 36 is closed by a plug (not shown)

is when the control valve 10' for a main 25

circuit with an auxiliary pump. This basic type of control valve 10,10' can be easily modified for both purposes.

The openings 16,22 have a certain diameter 30

aisle cross-section, which is based, among other things, on the maximum adjustment hydraulic quantity with the smallest turning circle.

Since the control valve has the task of controlling the pressure difference 35

only to compare both hydraulic motors and if there is a difference between the

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In order to carry out an adjustment movement due to pressure differences, with which, depending on the direction of the adjustment movement, a flow connection must be created that forms a bypass for a hydraulic motor, the control valve can also be designed differently, e.g. as a piston slide or in two parts, whereby

^q in one part of the control valve only the comparison of the pressure difference takes place, while in the other part the flow connections are opened or closed. The control valve 10,10' can be equipped with a conventional damping device

,c to suppress oscillations during control. However, effective damping can be achieved particularly easily,
if the connection opening 16 is designed as a damping throttle with a predetermined small cross-section

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Summary

&kgr; The invention relates to a hydrostatic drive for a vehicle, preferably an off-road vehicle _; with at least one driven axle and with at least two hydraulic motors which are assigned _to the driven axles or the wheels on each axle, with at least one main pump for supplying the hydraulic motors during driving and with a hydraulic differential compensation and a differential lock. In known drive systems of this type, the differential lock must be switched on and off. According to the invention, the hydraulic motors are connected in series in a main circuit and a control valve is arranged in a secondary circuit connected to the main circuit, which has two flow passages for an equalizing hydraulic quantity, of which one can be automatically released in the event of a difference between the pressure differences in the two hydraulic motors until the differences are equalized in order to bypass the hydraulic motor with the greater pressure difference. The differential lock no longer needs to be engaged and disengaged. The same traction force is transmitted even when a wheel is spinning. The differential compensation is given in all driving conditions. With the same starting tractive force

double the driving speed is possible. 30

Claims (12)

claims 1. Hydrostatic drive for a vehicle, preferably an off-road vehicle, with at least one driven axle and with at least two hydraulic motors, which are assigned to the driven axles or the wheels on each driven axle, with at least one main pump driven by a drive motor for pressurizing the hydraulic motors during driving, and with a hydraulic differential compensation and a hydraulic differential lock 2 between the driven axles or the wheels of the driven axles, characterized in that the hydraulic motors (5, 6) are connected in series in a main circuit (1, H), in that in a main circuit (1, H) connected to the main circuit (1, H) in the flow direction in front of and behind each A control valve (10,10') is arranged in the secondary circuit (9,N) connected to the hydraulic motor (5,6), and that the control valve (10,10') has two flow passages for an equalizing hydraulic quantity, of which, in the event of a difference between the pressure differences in both hydraulic motors (5,6), one can be automatically released to bypass the hydraulic motor (5 or 6) having the greater pressure difference until the pressure differences are equalized. 2. Hydrostatic travel drive according to claim 1, wherein two main pumps are provided, characterized in that for travel operation the second main pump (8) in the main circuit (1,H) can be switched in parallel to the first main pump (4). 3- Hydrostatic drive according to claims 1 and 2, characterized in that two parallel main circuits (1,H,2a,3a,2b,3b) are provided, each with a main pump (4,8) and a hydraulic motor (5,6), that an auxiliary pump (32,32a) is provided for adjusting both main pumps (4,8), that the two main circuits (2a, 3a,2b, 3b) are connected to a switching valve device (52), in the first switching position (Fig. 3) of which the two main circuits are separated from each other and in the second switching position of which the two main circuits are connected to each other by connecting the hydraulic motors (5,6) in series and the two main pumps (4,8) are connected in parallel, and that the control valve (10') arranged in the secondary circuit (N) is connected to the auxiliary pump in the second switching position of the switching valve device (52). (32) and connects these to the main circuit (2a,3a or 2b,3b) of the hydraulic motor (5 or 6) that has the smaller pressure difference in its main circuit until the pressure differences of both hydraulic motors (5,6) are equalized. -3- 4. Hydrostatic travel drive according to claim 3, characterized in that in the first switching position of the switching valve device (52) the control valve (10') is switched off, that the auxiliary circuit (32, 32a) is connected to both main circuits (2a, 3a, 2a, 3b), and that in each connecting line (34a, 34b) to a main circuit a check valve (54) opening in the flow direction to the main circuit is arranged. 5. Hydrostatic drive according to at least one of claims 1 to 4, characterized in that the auxiliary pump (32, 32a) consists of two separate pump units, one of which (32a) is provided for adjusting the position of the main pumps (4, 8) and for compensating for leakage oil and the other (32) for equalizing pressure differential differences between the hydraulic motors (5, 6), and that one pump unit (32a) is connected to each main circuit (Ä, 2b, 3a, 3b) via a pair of opposing check valves (48, 49). 6. Hydrostatic drive according to at least one of claims 1 to 5, characterized in that the switching valve device (52) has a return flow connection (64) which is open in the first switching position between the return flow lines (3a, 3b) of the two main circuits (1, 2a, 3a, 2b, 3b) to the auxiliary pump (32). 7. Hydrostatic drive according to at least one of the Claims 1 to 6, characterized in that the control valve (10, 10') has first and second separate cylinder chambers (�A, β) indicates that a foil (24,25) can be moved in a sealed manner in each cylinder cavity 35 and an Ehdkammer (28,30) and an intermediate chamber (29,31) forms that the Ifolben (24,25) are coupled together for common movement (coupling 23) and by . Springs (26) are loaded to a middle position, that with the I-bolts (24) in Cylinder chamber (A) a locking element (38,65) is connected in such a way that a connection opening (12,14,16,16) opens into each end and each intermediate chamber, and that either a first diaphragm opening (21) cooperating with the closing element (65) (21) opens into the first cylinder chamber (A) to the intermediate chamber (29) and a second diaphragm opening (22) cooperating with the piston (24) arranged in the first cylinder chamber (A) (28) opens into the end chamber or first and second diaphragm openings (21,36) cooperating with the closing element (38) are provided in the first cylinder chamber to the intermediate chamber (29), which are spaced apart in the direction of movement of the closing element (38), which are closed in the middle position and alternately open when the pistons (24,25) move from the middle position. 8. Hydrostatic drive according to claim 7, characterized in that in the first cylinder chamber (A) there are three apertures (21, 36, 22) arranged at intervals in the direction of movement of the pistons (24, 25), of which either the middle aperture (36) or the aperture (22) associated with the piston (24) is closed off by a closure plug. 9. Hydrostatic travel drive according to at least one of claims 1 to 8, characterized in that the connection opening (12) of the end chamber (28) of the first cylinder chamber (A) is connected to a secondary circuit branch (11) connected to the main circuit (1,2,2a) upstream of the first hydraulic motor (5), that the connection opening (14) of the end chamber (30) of the second cylinder chamber (B) is connected to a secondary circuit branch (13) connected to the main circuit (1,3a,3) downstream of the first hydraulic motor (5), that the connection opening (16) of the intermediate chamber (29) of the first cylinder chamber (A) is connected to a secondary circuit branch (15) connected to the main circuit (1,2a,2) upstream of the second hydraulic motor (6), that the connection opening (18) of the intermediate chamber (31) of the second cylinder chamber (B) is connected to a weaving circuit branch (17) connected to the main circuit (1,3,3b) behind the second hydraulic motor (6), that the first aperture opening (21) cooperating with the closing element (65) is connected to a secondary circuit branch (20) connected to the main circuit (1,3b,3) behind the second hydraulic motor (6), and that the second aperture opening (22) is connected to a secondary circuit branch (19) connected to the main circuit (1,2a,2) between the two hydraulic motors (5,6). 10. Hydrostatic travel drive according to at least one of claims 1 to 8, characterized in that the connection opening (12) of the end chamber (28) of the first cylinder chamber (A) is connected to a secondary circuit branch (11) connected to the main circuit (1,2,2a) in front of the first hydraulic motor (5), that the connection opening (14) of the end chamber (30) of the second cylinder chamber (B) is connected to a secondary circuit branch (13) connected to the main circuit (1,3a, 3) behind the first hydraulic motor (5), that the connection opening (16) of the intermediate chamber (29) of the first cylinder chamber (A) is connected to a secondary circuit branch (15) connected to the main circuit (1,2a,2) in front of the second hydraulic motor (6), that the connection opening (18) of the intermediate chamber (31) of the second cylinder chamber (B) is connected to a secondary circuit branch (13) connected to the main circuit (1,3,3b) behind the second hydraulic motor (6), that the first orifice opening (21') working together with the closing element (38) is connected to a secondary circuit branch (37) connected to the main circuit (1,3,3b) behind the second hydraulic motor (6) and to a return flow line (33) to the auxiliary pump (32), and that the second orifice opening (36) working together with the closing element (38) is connected to a secondary circuit branch (35) connected to the auxiliary pump (32) and to the main circuit (2) of the first hydraulic motor (5;). -6- 11. Hydrostatic drive according to at least one of claims 1 to 10, characterized in that the openings (16, 22) in the control valve (10, 10') for limiting an equalizing hydraulic quantity are dimensioned in their cross-section depending on the difference in pressure differences present at the tightest curve radius between the hydraulic motors (5, 6). 12. Hydrostatic drive according to at least one of claims 1 to 11, characterized in that the connection opening (14) of the control valve . _c (10,10·) as damping throttle for the pistons (24,25) lo is trained.