GROUND PROCESSING MACHINE

Abstract

In a ground processing machine having two drive rollers arranged longitudinally and rotatable about a respective axis of rotation, wherein each drive roller comprises two drive roller segments aligned along the direction of the associated axis of rotation, having a hydraulic drive system for the drive rollers, a first fluid connection of a first traction drive hydraulic pump is connected or connectable by means of a first hydraulic line to a first and second traction drive hydraulic motor, and a first fluid connection of a second traction drive hydraulic pump is connected or connectable by means of a second hydraulic line to a third and fourth traction drive hydraulic motor. A second fluid connection of the first pump is connected or connectable by means of a third hydraulic line to the second and third motors, and a second fluid connection of the second pump is connected or connectable by means of a fourth hydraulic line to the first and fourth motors.

Claims

1. A ground processing machine having two drive rollers arranged one after the other in a machine longitudinal direction and rotatable about a respective axis of rotation, wherein each drive roller comprises two drive roller segments arranged one after the other in the direction of the associated axis of rotation, and having a hydraulic drive system for the drive rollers, wherein the hydraulic drive system comprises: in association with a first drive roller segment of the two drive rollers, a first traction drive hydraulic motor, in association with a second drive roller segment of the two drive rollers, a second traction drive hydraulic motor, in association with a third drive roller segment of the two drive rollers, a third traction drive hydraulic motor, in association with a fourth drive roller segment of the two drive rollers, a fourth traction drive hydraulic motor, a first traction drive hydraulic pump, a second traction drive hydraulic pump, at least one drive motor for driving the first traction drive hydraulic pump and the second traction drive hydraulic pump for supplying hydraulic fluid to the traction drive hydraulic motors, wherein: a first fluid connection of the first traction drive hydraulic pump is connected or connectable by means of a first hydraulic line to a first fluid connection of the first traction drive hydraulic motor and a first fluid connection of the second traction drive hydraulic motor, a first fluid connection of the second traction drive hydraulic pump is connected or connectable by means of a second hydraulic line to a first fluid connection of the third traction drive hydraulic motor and a first fluid connection of the fourth traction drive hydraulic motor, a second fluid connection of the first traction drive hydraulic pump is connected or connectable by means of a third hydraulic line to a second fluid connection of the second traction drive hydraulic motor and a second fluid connection of the third traction drive hydraulic motor, a second fluid connection of the second traction drive hydraulic pump is connected or connectable by means of a fourth hydraulic line to a second fluid connection of the first traction drive hydraulic motor and a second fluid connection of the fourth traction drive hydraulic motor.

2. The ground processing machine of claim 1, wherein both traction drive hydraulic pumps are driven by a common drive motor for pumping hydraulic fluid, or/and in that both traction drive hydraulic pumps have the same delivery volume, or/and in that all traction drive hydraulic motors have the same displacement volume.

3. The ground processing machine of claim 1, wherein the at least one drive motor (E) is an electric motor.

4. The ground processing machine of claim 1, wherein each traction drive hydraulic pump is a pump with a fixed delivery volume, or/and in that each traction drive hydraulic motor is a motor with a fixed displacement volume.

5. The ground processing machine of claim 1, wherein: in association with the second fluid connection of the first traction drive hydraulic motor, a first valve unit is provided for selectively establishing and interrupting a connection of the second fluid connection of the first traction drive hydraulic motor to the third hydraulic line and a second valve unit is provided for selectively establishing and interrupting a connection of the second fluid connection of the first traction drive hydraulic motor to the fourth hydraulic line, and in association with the second fluid connection of the second traction drive hydraulic motor, a third valve unit is provided for selectively establishing and interrupting a connection of the second fluid connection of the second traction drive hydraulic motor to the third hydraulic line and a fourth valve unit is provided for selectively establishing and interrupting a connection of the second fluid connection of the second traction drive hydraulic motor to the fourth hydraulic line.

6. The ground processing machine of claim 5, wherein a control arrangement is provided for controlling the first valve unit, the second valve unit, the third valve unit and the fourth valve unit, wherein the control unit is designed to: when the first valve unit for establishing the connection of the second fluid connection of the first traction drive hydraulic motor to the third hydraulic line and the fourth valve unit for establishing the connection of the second fluid connection of the second traction drive hydraulic motor to the fourth hydraulic line are operated, the second valve unit for interrupting the connection of the second fluid connection of the first traction drive hydraulic motor to the fourth hydraulic line and the third valve unit for interrupting the connection of the second fluid connection of the second traction drive hydraulic motor to the third hydraulic line are operated, and when the first valve unit for interrupting the connection of the second fluid connection of the first traction drive hydraulic motor to the third hydraulic line and the fourth valve unit for interrupting the connection of the second fluid connection of the second traction drive hydraulic motor to the fourth hydraulic line are operated, the second valve unit for establishing the connection of the second fluid connection of the first traction drive hydraulic motor to the fourth hydraulic line and the third valve unit for establishing the connection of the second fluid connection of the second traction drive hydraulic motor to the third hydraulic line are operated.

7. The ground processing machine according to claim 1, wherein a fluid feed arrangement is provided for feeding fluid into at least one fluid line of the first fluid line, second fluid line, third fluid line, and fourth fluid line.

8. The ground processing machine according to claim 1, wherein a first drive roller of the two drive rollers comprises the first drive roller segment and the second drive roller segment and a second drive roller of the two drive rollers comprises the third drive roller segment and the fourth drive roller segment.

9. The ground processing machine of claim 8, wherein, relative to a machine longitudinal direction, the first drive roller segment and the third drive roller segment are arranged on a first side of the ground processing machine and the second drive roller segment and the fourth drive roller segment are arranged on a second side of the ground processing machine.

10. The ground processing machine of claim 1, wherein at least one drive roller of the two drive rollers is a ground processing roller, wherein each drive roller segment of the at least one drive roller is provided by a roller segment, or/and in that at least one drive roller of the two drive rollers comprises at least two wheels, wherein each drive roller segment of the at least one drive roller comprises at least one wheel.

11. The ground processing machine of claim 1, wherein a slip detection arrangement is provided for detecting a slip state of at least one drive roller segment.

12. The ground processing machine of claim 11, wherein the slip detection arrangement comprises a rotational speed sensor in association with at least one drive roller segment.

Description

[0039] The present invention is described in detail below with reference to the attached figures. Wherein:

[0040] FIG. 1 shows a schematic representation of a ground processing machine designed as a ground compactor having two ground processing rollers;

[0041] FIG. 2 shows a schematic representation of an alternative embodiment of a ground processing machine designed as a ground compactor;

[0042] FIG. 3 shows an embodiment of an electro-hydraulic drive system for a ground processing machine;

[0043] FIG. 4 shows an alternative embodiment of an electro-hydraulic drive system for a ground processing machine.

[0044] FIG. 1 shows a schematic representation of a ground processing machine designed as a ground compactor and generally designated by 10. The ground processing machine 10 designed as a ground compactor comprises two drive rollers 12, 14 arranged one after the other in a machine longitudinal direction R thereof and each designed as a ground processing roller. The drive roller 12 is rotatable about a first axis of rotation D.sub.1, and the drive roller 14 is rotatable about a second axis of rotation D.sub.2. Each of the two drive rollers 12, 14 is associated with two traction drive hydraulic motors M.sub.1, M.sub.2 or M.sub.3, M.sub.4. For example, the traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4 associated with a respective drive roller 12 or 14 can each be arranged at their axial ends.

[0045] The two drive rollers 12, 14 are designed as split ground processing rollers with respective drive roller segments 12a, 12b and 14a, 14b. Each of the drive roller segments 12a, 12b, 14a, 14b is associated with one of the four traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4, so that the two drive roller segments 12a, 12b can be driven independently of one another by the traction drive hydraulic motors M.sub.1, M.sub.2 associated with them to rotate about the axis of rotation D.sub.1, and the two drive roller segments 14a, 14b can be driven independently of one another by the traction drive hydraulic motors M.sub.3, M.sub.4 associated with them to rotate about the axis of rotation D.sub.2.

[0046] FIG. 2 shows an alternative embodiment of such a ground processing machine 10, for example designed as a ground processing roller. The ground processing machine 10 of FIG. 2 comprises in one of its longitudinal end regions the drive roller 12 designed as a ground processing roller with the two traction drive hydraulic motors M.sub.1, M.sub.2 associated therewith. In this embodiment, the drive roller 12 also comprises two drive roller segments 12a, 12b which can be driven independently of one another by a respective associated traction drive hydraulic motor M.sub.1, M.sub.2 for rotation about the axis of rotation D.sub.1. In the other longitudinal end region of the ground processing machine 10, the drive roller 14 comprises wheels 16, 18, 20, 22. These can be associated with one another in pairs, for example, and each pair of wheels 16, 18 or 20, 22 forms a drive roller segment 14a, 14b, which can be driven by the traction drive hydraulic motor M.sub.3 or M.sub.4 associated therewith for rotation about the axis of rotation D.sub.2.

[0047] It should also be noted that other embodiments of such ground processing machines can be applied in the context of a hydraulic drive system described hereinafter. For example, in the case of a ground processing machine designed as a ground compactor, a pair of drive wheels, each forming a drive roller segment of a drive roller, can be provided on a rear carriage, while a ground processing roller divided into roller segments can act as a drive roller on the front carriage. The principles of the present invention can be applied to pivot-steered ground processing machines or ground compactors as well as to ground processing machines divided into front and rear carriages.

[0048] FIG. 3 shows a hydraulic drive system 24, which in the illustrated embodiment is an electro-hydraulic drive system and can be used, for example, in conjunction with the ground processing machines described above with reference to FIGS. 1 and 2.

[0049] The hydraulic drive system 24 comprises two traction drive hydraulic pumps P.sub.1, P.sub.2 and the four traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4 in a hydraulic circuit 26. The two traction drive hydraulic pumps P.sub.1, P.sub.2 can be driven jointly by a drive motor E designed as an electric motor.

[0050] A first fluid connection 28 of the first traction drive hydraulic pump P.sub.1 is connected via a first hydraulic line L.sub.1 to a first fluid connection 30 of the first traction drive hydraulic motor M.sub.1 and a first fluid connection 32 of the second traction drive hydraulic motor M.sub.2. A first fluid connection 34 of the second traction drive hydraulic pump P.sub.2 is connected via a second hydraulic line L.sub.2 to a first fluid connection 36 of the third traction drive hydraulic motor M.sub.3 and a first fluid connection 38 of the fourth traction drive hydraulic motor M.sub.4.

[0051] A second fluid connection 40 of the first traction drive hydraulic pump P.sub.1 is connected via a third fluid line L.sub.3 to a second fluid connection 42 of the second traction drive hydraulic motor M.sub.2 and a second fluid connection 44 of the third traction drive hydraulic motor M.sub.3. A second fluid connection 46 of the second traction drive hydraulic pump P.sub.2 is connected via a fourth fluid line L.sub.4 to a second fluid connection 48 of the first traction drive hydraulic motor M.sub.1 and a second fluid connection 50 of the fourth traction drive hydraulic motor M.sub.4.

[0052] Depending on the direction in which the ground processing machine 10 is to be moved, for example when driving forward, the drive motor E can be controlled by a control unit 52 for operating the traction drive hydraulic pumps P.sub.1, P.sub.2 in such a conveying direction that they feed fluid at their respective first fluid connections 28, 34 into the first hydraulic line L.sub.1 or the second hydraulic line L.sub.2 and therefore feed the fluid under high pressure, for example hydraulic oil, via the respective first fluid connections 30, 32, 36, 38 into the traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4.

[0053] In this state, the traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4 release the fluid under significantly reduced pressure at their respective second fluid connections 48, 42, 44, 50 into the third hydraulic line L.sub.3 or the fourth hydraulic line L.sub.4, via which the fluid flows back to the second fluid connections 40, 46 of the traction drive hydraulic pumps P.sub.1, P.sub.2.

[0054] If the ground processing machine 10 is to be moved in the opposite direction, for example in reverse, the drive motor E is controlled such that the traction drive hydraulic pumps P.sub.1, P.sub.2 driven by it release the fluid via their respective second fluid connections 40, 46 into the third hydraulic line L.sub.3 or the fourth hydraulic line L.sub.4. The fluid delivered by the first traction drive hydraulic pump P.sub.1 flows via the third hydraulic line L.sub.3 to the second fluid connections 42, 44 of the second traction drive hydraulic motor M.sub.2 and the third traction drive hydraulic motor M.sub.3. The fluid delivered by the second traction drive hydraulic pump P.sub.2 flows via the fourth hydraulic line L.sub.4 to the second fluid connections 48, 50 of the first traction drive hydraulic motor M.sub.1 and the fourth traction drive hydraulic motor M.sub.4, respectively. In this operating state, the first traction drive hydraulic motor M.sub.1 and the second traction drive hydraulic motor M.sub.2 deliver fluid at their first fluid connections 30, 32 via the first hydraulic line L.sub.1 to the first fluid connection 28 of the first traction drive hydraulic pump 28, and the third traction drive hydraulic motor M.sub.3 and the fourth traction drive hydraulic motor M.sub.4 deliver fluid at their first fluid connections 36, 38 via the second fluid line L.sub.2 to the first fluid connection 34 of the second traction drive hydraulic pump P.sub.2.

[0055] By means of a feed arrangement generally designated 53, fluid leaks occurring in particular in the area of the traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4 can be compensated by feeding fluid onto the low-pressure side of the hydraulic circuit 26. For this purpose, the feed arrangement 54 comprises a feed pump S, which is driven, for example, by a drive motor associated therewith, which pump draws fluid from a fluid reservoir F and feeds it via four feed valves E.sub.1, E.sub.2, E.sub.3, E.sub.4 into the first hydraulic line L.sub.1, the second hydraulic line L.sub.2, the third hydraulic line L.sub.3, and the fourth hydraulic line L.sub.4, respectively.

[0056] In the hydraulic drive system 24 shown in FIG. 2, regardless of the direction in which the ground processing machine 10 is moved or the direction in which the traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4 associated with the various drive roller segments 12a, 12b, 14a, 14b rotate, two traction drive hydraulic motors are each connected on the high-pressure side, that is, on the inflow side, to the same traction drive hydraulic pump P.sub.1 or P.sub.2. When fluid is delivered via the respective first fluid connections 28, 34 of the traction drive hydraulic pumps P.sub.1, P.sub.2, the traction drive hydraulic motors M.sub.1, M.sub.2 are connected on the high-pressure side to the first traction drive hydraulic pump 28 and the traction drive hydraulic motors M.sub.3, M.sub.4 are connected on the high-pressure side to the second traction drive hydraulic pump P.sub.2.

[0057] However, on the low-pressure side, that is, the outflow side, the traction drive hydraulic motors that are also connected to one of the traction drive hydraulic pumps on the high-pressure side are not also connected to the same traction drive hydraulic pump. Only one of the traction drive hydraulic motors connected to a traction drive hydraulic pump on the high-pressure side is also connected to this traction drive hydraulic pump on the low-pressure side, while the other traction drive hydraulic motor is connected to the other traction drive hydraulic pump on the low-pressure side. In the illustrated embodiment, this means that, when fluid is delivered via the first fluid connections 28, 34 of the traction drive hydraulic pumps P.sub.1, P.sub.2, the second traction drive hydraulic motor M.sub.2 and the third traction drive hydraulic motor M.sub.3 are connected to the first traction drive hydraulic pump P.sub.1 via the third hydraulic line M.sub.3, while the first traction drive hydraulic motor M.sub.1 and the fourth traction drive hydraulic motor M.sub.4 are connected to the second traction drive hydraulic pump P.sub.2 via the fourth hydraulic line M.sub.4.

[0058] When moving in the opposite direction, that is, when fluid is released via the respective second fluid connections 40, 46 of the traction drive hydraulic pump P.sub.1, P.sub.2, the second traction drive hydraulic motor M.sub.2 and the third traction drive hydraulic motor M.sub.3 are connected to the first traction drive hydraulic pump 28 on the high-pressure side, that is, via the third hydraulic line L.sub.3, while the first traction drive hydraulic motor M.sub.1 and the fourth traction drive hydraulic motor M.sub.4 are connected to the second traction drive hydraulic pump P.sub.2 via the fourth hydraulic line L.sub.4. In this state, on the low-pressure side, the first traction drive hydraulic motor M.sub.1 and the second traction drive hydraulic motor M.sub.2 are connected to the first traction drive hydraulic pump P.sub.1 via the first hydraulic line L.sub.1, while the third traction drive hydraulic motor M.sub.3 and the fourth traction drive hydraulic motor M.sub.4 are connected to the second traction drive hydraulic pump P.sub.2 via the second hydraulic line L.sub.2.

[0059] Since in such a hydraulic drive system 24 each of the traction drive hydraulic pumps P.sub.1, P.sub.2 can only take in as much fluid on the low-pressure side as it delivers on the high-pressure side during delivery operation, it is important that in this cross-connection of the traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4 with the traction drive hydraulic pumps P.sub.1, P.sub.2, each of the traction drive hydraulic pumps P.sub.1, P.sub.2 delivers substantially the same amount of fluid and each of the traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4 takes in substantially the same amount of fluid. In particular, when designed as an electro-hydraulic drive system, it is advantageous if the traction drive hydraulic pumps P.sub.1, P.sub.2 have a constant delivery volume and the traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4 have a constant displacement volume. Changes in the delivery rate can be generated solely by changing the rotational speed of the drive motor E, which is designed as an electric motor. With such a design of the traction drive hydraulic pumps P.sub.1, P.sub.2 and traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4, each having the same delivery volume or displacement volume, all traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4 rotate at the same rotational speed or drive the drive roller segments 12a, 12b, 14a, 14b associated with them to rotate at the same rotational speed. This in turn requires that all drive roller segments 12a, 12b, 14a, 14b have the same diameter. If the drive rollers 12, 14 provided in association with the various axes of rotation D1, D2 have different diameters, traction drive hydraulic motors with different displacement volumes can be used for the drive roller segments 12a, 12b on the one hand and the drive roller segments 14a, 14b on the other hand in the association of the traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4 with the drive roller segments 12a, 12b, 14a, 14b, as shown in particular in FIGS. 1 and 2.

[0060] The cross-connection of the traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4 ensures that none of the drive roller segments 12a, 12b, 14a, 14b can enter a slip state in which an excessively large amount of fluid flows out of the associated traction drive hydraulic motor due to an increase in rotational speed of the motor. If, for example, slippage were to occur on the first drive roller segment 12a due to a loss of traction, this would result in the drive hydraulic motor M.sub.1 taking in and accordingly releasing a larger quantity of fluid due to a correspondingly higher rotational speed. Since the first traction drive hydraulic motor M.sub.1, in a state in which it receives fluid from the first traction drive hydraulic pump P.sub.1 via the first hydraulic line L.sub.1, for example, releases the absorbed fluid into the fourth fluid line L.sub.4, and since the fourth traction drive hydraulic motor M.sub.4 fed by the other traction drive hydraulic pump P.sub.2 releases the amount of fluid corresponding to normal traction into the fourth hydraulic line L.sub.4 in this state, the fourth hydraulic line La can only absorb the amount of fluid that it would basically also release in a slip-free state from the first traction drive hydraulic motor M.sub.1. The first traction drive hydraulic motor M.sub.1 could therefore in principle not rotate faster than the other traction drive hydraulic motors M.sub.2, M.sub.3, M.sub.4, even in the event of a loss of traction of the associated first drive roller segment 12a, and therefore also not lead to an excessive outflow of fluid from the first hydraulic line L.sub.1.

[0061] However, due to the fluid leaks mentioned above, there is basically the possibility that the first drive hydraulic motor M.sub.1 briefly releases a larger amount of fluid when a loss of traction occurs at the associated first drive roller segment 12a than would be the case in the non-slipping state. This larger amount of fluid fed into the fourth hydraulic line L.sub.4 via the first traction drive hydraulic motor M.sub.1 then does not have to be replenished by the feed arrangement 53 to maintain the defined pressure on the low-pressure side of the hydraulic circuit 26.

[0062] Such a short-term slip-related increase in rotational speed of the first drive hydraulic motor M.sub.1 leads to a spontaneous drop in pressure on the high-pressure side, in this case in the first hydraulic line L.sub.1. This pressure drop results in a decrease of the drive torque generated at the first drive hydraulic motor to such a value that the first drive roller segment 12a, which has lower traction, is again operated without slip. This decrease in the drive torque at the first traction drive hydraulic motor M.sub.1 also leads to a corresponding decrease in the drive torque of the second traction drive hydraulic motor M.sub.2, which is subjected to the same pressure. Since the drive power of the drive motor E is basically maintained, a correspondingly higher pressure is created in the second hydraulic line L.sub.2 fed from the second drive hydraulic pump P.sub.2, so that the drive hydraulic motors M.sub.3, M.sub.4 fed from the second hydraulic line L.sub.2 are operated at a correspondingly increased drive torque.

[0063] The previously described independent adjustment of the drive torque or the rotational speed of a drive roller segment when a loss of traction occurs is independent of which of the drive roller segments the loss of traction occurs on and in which direction the ground processing machine 10 is moved. Due to the connection on the outflow side of each traction drive hydraulic motor M.sub.1, M.sub.2, M.sub.3, M.sub.4 with another traction drive hydraulic motor which is not fed from the same traction drive hydraulic pump, the traction drive hydraulic motors block each other against a slip-related increase in rotational speed.

[0064] Despite this mutual blocking of the drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4 which are linked to one another on the outflow side, there is the possibility, particularly in the case of association of the drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4 to the drive roller segments 12a, 12b, 14a, 14b as shown in FIGS. 1, 2 and 3, that when cornering, the respective inner pair of drive roller segments 12a, 14a or 12b, 14b rotates at a lower rotational speed than the respective outer pair of drive roller segments 12a, 14a or 12b, 14b. A lower fluid outflow of the first traction drive hydraulic motor M.sub.1 caused, for example, by a lower rotational speed of the drive roller segment 12a is compensated by a correspondingly increased fluid outflow of the fourth traction drive hydraulic motor M.sub.4, such that their joint fluid outflow again corresponds to the sum of the fluid outflow quantities of these two traction drive hydraulic motors M.sub.1, M.sub.4 at the same rotational speed. The same applies to the traction drive hydraulic motors M.sub.2, M.sub.3 or to any pairing of traction drive hydraulic motors linked together on the outflow side when moving in the other direction of travel.

[0065] FIG. 4 shows an embodiment of the hydraulic drive system 24 in which the probability of a slip condition occurring on one of the drive roller segments 12a, 12b, 14a, 14b is further reduced. It can be seen in FIG. 4 that, for example, two valve units V.sub.1, V.sub.2 and V.sub.3, V.sub.4 are provided in association with the first traction drive hydraulic motor M.sub.1 and in association with the second traction drive hydraulic motor M.sub.2. The second fluid connection 48 of the first traction drive hydraulic motor M.sub.1 can be optionally connected to or separated from the third hydraulic line L.sub.3 by the first valve unit V.sub.1. The second fluid connection 48 of the first traction drive hydraulic motor M.sub.1 can be optionally connected to or separated from the fourth hydraulic line L.sub.4 by the second valve unit V.sub.2.

[0066] The valve units V.sub.1, V.sub.2 controlled by the control unit 52 are basically controlled in such a way that when one of the valve units V.sub.1, V.sub.2 establishes a connection of the second fluid connection 48 of the first traction drive hydraulic motor M.sub.1, the other valve unit interrupts the connection with the associated hydraulic line. The second fluid connection 48 of the first traction drive hydraulic motor M.sub.1 is therefore either in connection with the third fluid line L.sub.3 or in connection with the fourth fluid line L.sub.4.

[0067] The third valve unit V.sub.3 associated with the second traction drive hydraulic motor M.sub.2 optionally establishes a connection of the second fluid connection 42 with the third hydraulic line L.sub.3 or interrupts it. Likewise, the fourth valve unit V.sub.4 optionally establishes a connection between the second fluid connection 42 of the second traction drive hydraulic motor M.sub.2 and the fourth fluid line M.sub.4 or interrupts it. The two valve units V.sub.3, V.sub.4 are also controlled by the control unit 52 in such a way that when one of the valve units establishes the connection with the associated hydraulic line, the other valve unit is in its interrupted state.

[0068] Furthermore, the four valve units V.sub.1, V.sub.2, V.sub.3, V.sub.4 are controlled or operated by the control unit 52 such that a state in which the two second outlet connections 48, 42 of the traction drive hydraulic motors M.sub.1, M.sub.2 are in connection with the same hydraulic line L.sub.3 or L.sub.4 does not occur. When the second fluid connection 48 of the first traction drive hydraulic motor M.sub.3, as shown in FIG. 3, is in communication with the fourth hydraulic line L.sub.4, the second fluid connection 42 of the second traction drive hydraulic motor M.sub.2 is in communication with the third fluid line L.sub.3, and vice versa.

[0069] The switching state of the valve units V.sub.1, V.sub.2, V.sub.3, V.sub.4 shown in FIG. 4 thus basically corresponds to the connection state that is unchangeably present in FIG. 3, in which the second fluid connection 48 of the first traction drive hydraulic motor M.sub.1 is in connection with the fourth hydraulic line L.sub.4 and the second fluid connection 42 of the second traction drive hydraulic motor M.sub.2 is in connection with the third fluid line L.sub.3.

[0070] If, in such a state, a loss of traction were to occur at the two drive roller segments 12a, 14a or 12b, 14b positioned on the same side of the ground compactor 10 with respect to the machine longitudinal direction R, that is, on the same side in the machine transverse direction Q, a fluid short circuit can occur in the hydraulic circuit 26, in which the entire fluid delivered by the traction drive hydraulic pumps P.sub.1, P.sub.2 flows away via the traction drive hydraulic motors associated with the slipping drive roller segments, while no fluid flows via the traction drive hydraulic motors associated with the non-slipping drive roller segments.

[0071] To counteract this problem, in the hydraulic drive system 26 shown in FIG. 4, rotational speed sensors 54, 56, 58, 60 of a slip detection arrangement 62 are provided in association with the traction drive hydraulic motors M.sub.1, M.sub.2, M.sub.3, M.sub.4. The rotational speed signal emitted by the rotational speed sensors 54, 56, 58, 60 provides the control unit 52 with information about which of the drive roller segments 12a, 14a, 12b, 14b is experiencing a loss of traction.

[0072] If, for example, a loss of traction with corresponding slip occurs simultaneously at the drive roller segments 12b, 14b, which in the switching state shown in FIG. 3 would result in all of the fluid fed into the second hydraulic line L.sub.2 flowing out via the fourth traction drive hydraulic motor M.sub.4 and all of the fluid fed into the first hydraulic line L.sub.1 flowing out via the second traction drive hydraulic motor M.sub.2, the four valve units V.sub.1, V.sub.2, V.sub.3, V.sub.4 can be switched starting from the switching state shown in FIG. 3, such that the first traction drive hydraulic motor M.sub.1 is then coupled on the outflow side to the third hydraulic line L.sub.3, while the second traction drive hydraulic motor M.sub.2 is coupled on the outflow side to the fourth hydraulic line L.sub.4. In this state, the two drive hydraulic motors M.sub.2, M.sub.4, which are associated with the drive roller segments 12b, 14b having a loss of traction, are then linked to one another on the outflow side, such that again due to the fact that the second drive hydraulic pump P.sub.2 can only take up a defined amount of fluid at its second fluid connection 46, the amount of fluid flowing out via these drive hydraulic motors M.sub.2, M.sub.4 is again substantially limited to the amount of fluid that flows through them even in the non-slipping state.

[0073] It should be noted that, in an alternative embodiment, the variability introduced by the valve units V.sub.1, V.sub.2, V.sub.3, V.sub.4 could also be achieved if these were provided in conjunction with the traction drive motors M.sub.3, Ma and the hydraulic lines L.sub.3, L.sub.4 or if these were provided in conjunction with the traction drive hydraulic motors M.sub.2 and M.sub.3 or in conjunction with the traction drive hydraulic motors M.sub.1, M.sub.4, each in association with the first hydraulic line L.sub.1 and the second hydraulic line L.sub.2.