Abstract
A method for braking a compaction machine operated by an electric motor. A compaction machine, in particular a tandem roller, single-drum roller or waste compactor, for carrying out the method.
Claims
1. A method for braking a compaction machine operated by an electric motor, in particular a tandem roller, single-drum roller, rubber-tired roller or waste compactor, comprising the steps of: a) (directly or indirectly) driving a travel unit using an electric motor; b) determining an actual value of an operating parameter; c) determining a target value of the operating parameter; d) comparing the actual value of the operating parameter with the target value of the operating parameter; e) generating a braking torque by a hydraulic throttle in a brake hydraulic circuit, the brake hydraulic circuit comprising a brake hydraulic pump, if the actual value of the operating parameter deviates from the target value, in particular is greater than the target value of the operating parameter, the throttle being arranged in a hydraulic line with a hydraulic pump; f) transmitting the braking torque via a mechanical coupling from the brake hydraulic pump to a device directly or indirectly driving the travel unit.
2. The method according to claim 1, wherein the operating parameter is: a speed of the electric motor; and/or a travel speed of the compaction machine; and/or a temperature of the electric motor and/or a converter and/or a battery; and/or a state of charge of a battery; and/or an amperage applied to or output at an electric motor and/or a converter; and/or a torque at the electric motor; or a parameter correlating therewith; or a combination of at least two of the above parameters.
3. The method according to claim 1, wherein the compaction machine comprises a hydraulic system and in particular is a tandem roller, a single-drum roller, a rubber-tired roller or a waste compactor, comprising the steps of: in step a), driving a traction pump in a traction drive hydraulic circuit of the compaction machine by the electric motor; additionally driving a steering feed pump in a steering hydraulic circuit of the compaction machine, wherein the steering feed pump also feeds hydraulic fluid into the traction drive hydraulic circuit, and wherein the steering feed pump is coupled to the traction pump via a mechanical coupling; in step e), generating a braking torque at the steering feed pump by a hydraulic throttle if the actual value of the operating parameter deviates from the target value, in particular is greater than the target value of the operating parameter, the throttle being arranged in a hydraulic line between the steering feed pump and a steering device in the steering hydraulic circuit; and in step f), transmitting the braking torque from the steering feed pump to the traction pump of the traction drive hydraulic circuit via the mechanical coupling.
4. The method according to claim 1, wherein during transmitting of the braking torque, reducing of a displacement of the traction pump is performed.
5. The method according to claim 1, wherein: a tolerance range is provided such that generating of the braking torque at the steering feed pump is only performed when the actual value of the operating parameter exceeds a threshold value above the target value of the operating parameter; and/or a tolerance time is provided such that generating of the braking torque at the steering feed pump is only performed when the actual value of the operating parameter is increased compared to the target value of the operating parameter for longer than the tolerance time.
6. The method according to claim 5, wherein the tolerance range and/or the tolerance time is dynamically adapted to the actual value of the operating parameter by the control device.
7. The method according to claim 1, wherein the braking torque set at the steering feed pump is increased as long as the difference between the actual value of the operating parameter and the target value of the operating parameter increases, wherein the braking torque is kept constant after an increase in the braking torque until the actual value of the operating parameter has fallen back to or below the target value of the operating parameter.
8. The method according to claim 1, wherein the hydraulic system comprises a working hydraulic circuit separate from the traction drive hydraulic circuit and the steering hydraulic circuit, the working hydraulic circuit being operated exclusively by a working pump separate from the steering feed pump.
9. The method according to claim 1, wherein determining of a temperature in the steering hydraulic circuit is performed, and no braking torque is generated at the steering feed pump by the hydraulic throttle when the temperature in the steering hydraulic circuit is greater than a predetermined threshold value.
10. The method according to claim 1, wherein a return path of the steering hydraulic circuit and a return path of the traction drive hydraulic circuit are merged and fed together into a tank.
11. The method according to claim 1, wherein when the braking torque is transmitted via the mechanical coupling from the pump to the device directly or indirectly driving the travel unit, in particular the traction pump or traction motor, a speed transmission takes place.
12. The method according to claim 1, wherein the hydraulic traction motor can be coupled via a mechanical coupling to a brake hydraulic pump, in particular configured with adjustable delivery volume, the brake hydraulic pump being part of a brake hydraulic circuit separate from the traction drive hydraulic circuit, and the hydraulic throttle being arranged in the brake hydraulic circuit, in particular downstream of the brake hydraulic pump, with the step that generating of the braking torque is performed at the brake hydraulic pump by the hydraulic throttle, and that transmitting of the braking torque from the brake hydraulic pump via the mechanical coupling to the hydraulic traction motor of the traction drive hydraulic circuit is performed.
13. The method according to claim 1, wherein the brake hydraulic circuit comprises a hydraulic accumulator connected, in particular, downstream of the hydraulic throttle via an accumulator charging valve, the hydraulic accumulator being charged by hydraulic fluid delivered in the brake hydraulic circuit by the brake hydraulic pump.
14. A compaction machine, in particular a tandem roller, single-drum roller, rubber-tired roller or waste compactor, with a hydraulic system, an electric motor and a control device, wherein the control device is configured for carrying out the method according to claim 1.
15. The compaction machine according to claim 14, wherein it has at least one of the following features: it has a traction drive hydraulic circuit with a traction pump driven by the electric motor, the traction pump being configured in particular as a variable displacement pump; it has a steering feed pump, driven in particular by the electric motor, in a steering hydraulic circuit, the steering feed pump being configured in particular as a fixed displacement pump, for example as a gear pump; the steering feed pump is configured to feed hydraulic fluid into the traction drive hydraulic circuit, which is in particular configured as a closed circuit; the traction pump is coupled to the steering feed pump via a mechanical coupling; a hydraulic throttle is arranged in a hydraulic line between the steering feed pump and a steering device of the steering hydraulic circuit; the hydraulic throttle is configured as a proportional pressure-limiting valve; the hydraulic throttle is configured to be controllable by the control device; a working hydraulic circuit separate from the traction drive hydraulic circuit and the steering hydraulic circuit and having a working pump is provided, the working pump in particular being in drive connection with the electric motor; the steering feed pump and the hydraulic lines it supplies are free of priority valves; a speed sensor is provided at the electric motor and/or at a traction motor of the traction drive hydraulic circuit, which is connected to the control device; the speed sensor is configured to determine an actual speed of the electric motor and/or an actual travel speed of the compaction machine or a parameter correlating therewith; a temperature sensor is provided at the electric motor and/or at a converter and/or at a battery, which is connected to the control device and which is configured in particular to determine an actual temperature of the electric motor and/or of the converter and/or of the battery; a state of charge sensor is provided at the battery, which is connected to the control device and which is configured in particular to determine an actual state of charge of the battery; an amperemeter is provided at the electric motor and/or at the converter, which is connected to the control device and which is configured in particular to determine an actual amperage through the electric motor and/or through the converter; a torque sensor is provided at the electric motor, which is connected to the control device and which is configured in particular to determine an actual torque of the electric motor; a temperature sensor is provided in the steering hydraulic circuit, which is connected to the control device and which is configured in particular to determine an actual temperature of the steering hydraulic circuit; the control device is configured to determine a target value of an operating parameter, in particular a target speed of the electric motor and/or a target travel speed of the compaction machine or a parameter correlating therewith, in particular from a setting of an operating element of the compaction machine; the control device is configured to generate a braking torque at the steering feed pump by the hydraulic throttle if the actual value of the operating parameter is greater than the target value of the operating parameter, in particular if the actual speed and/or the actual travel speed or the parameter correlating therewith is greater than the target speed and/or the target travel speed or the parameter correlating therewith; a return path of the steering hydraulic circuit and a return path of the traction drive hydraulic circuit configured such that they open together into a tank; a hydraulic accumulator is connected to the steering hydraulic circuit via an accumulator charging valve.
16. The ground compaction machine according to claim 14, wherein it has at least one of the following features: it comprises a travel unit driven by a hydraulic motor, in particular directly via a shaft, and a brake hydraulic pump of the brake hydraulic circuit coupled mechanically to this hydraulic motor, in particular via a transmission stage; it comprises a travel unit driven by an electric motor, in particular directly via a shaft, and a coupling gearbox via which the electric motor can be mechanically coupled to a brake hydraulic pump of a brake hydraulic circuit, the brake hydraulic circuit comprising the hydraulic throttle, in particular downstream of the brake hydraulic pump.
17. The ground compaction machine according to claim 14, wherein each of the travel units, in particular each of the compaction drums, has its own brake hydraulic circuit separate from the other ones, and further has at least one of the following features: a separate hydraulic accumulator is assigned to each brake hydraulic circuit; a common hydraulic accumulator is provided, which is connected, in each case via a respective supply line, to at least two brake hydraulic circuits, in each case via a respective accumulator charging valve or via a common accumulator charging valve; the throttles of the two brake hydraulic circuits can be controlled independently of one another, and the control device is configured such that it controls the two throttles independently of one another and/or taking into account the current direction of travel.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The invention will be explained in more detail below by reference to the embodiment examples shown in the figures. In the schematic figures:
[0036] FIG. 1: shows a side view of a compaction machine, in this case a tandem roller;
[0037] FIG. 2: shows a side view of a compaction machine, in this case a single-drum roller;
[0038] FIG. 3: shows a side view of a compaction machine, in this case a waste compactor;
[0039] FIG. 4: shows a diagram of a part of the hydraulic system of a compaction machine relevant in the present context;
[0040] FIG. 5: shows a diagram of the control device and its respective connections to other components;
[0041] FIG. 6: shows a time sequence of various parameters in an exemplary application scenario;
[0042] FIG. 7: shows a flow chart of the method;
[0043] FIG. 8: shows an alternative embodiment of a hydraulic system of a compaction machine;
[0044] FIG. 9: shows a schematic of an alternative drive concept;
[0045] FIG. 10: shows a schematic of another alternative drive concept; and
[0046] FIG. 11: shows a time sequence of various parameters in another exemplary application scenario.
DETAILED DESCRIPTION
[0047] Like parts or functionally like parts are designated by like reference numerals in the figures. Recurring parts are not necessarily designated separately in each figure.
[0048] FIGS. 1, 2 and 3 show examples of various compaction machines 1 according to the invention. For example, FIG. 1 shows a tandem roller, more specifically a pivot-steered tandem roller, which is typically used for asphalt compaction. Alternatively, articulated tandem rollers or rubber-tired rollers may be used, the respective machine frame structure of which is known in the prior art. FIG. 2 shows a single drum roller with a front and a rear carriage, typically used for compacting soil. FIG. 3, in turn, illustrates a waste compactor as used in landfills. The compaction machines 1 typically comprise a machine frame 3 with an operator platform 2 and a travel mechanism with which they move in or against a working direction a over the ground 8 to be compacted. For this purpose, the tandem roller according to FIG. 1 has, for example, a front and a rear compaction drum 5 as travel units 52. The single-drum roller shown in FIG. 2 has a compaction drum 5 at the front and wheels 7 at the rear as travel units 52. The compaction drums 5 may optionally comprise an oscillation or vibration exciter that influences the compaction performed by the compaction drum 5. The waste compactor according to FIG. 3 has only drum-like wheels 7 and also includes a dozer blade 9 that can be used to spread landfill material. All of the embodiments of the compaction machine 1 shown are driven by an electric motor 4 as the primary drive unit or as the traction drive system, and also have a hydraulic system 6. Further, all of the machines shown comprise an accumulator for electric energy or a fuel cell, which is referred to below by way of example as a battery 32. In order to carry out the method and also to control all the involved components of the compaction machine 1, these also comprise, in particular, a control device 10 which, for example, is part of the on-board computer or itself constitutes the on-board computer. In addition, the control device 10 preferably also comprises operating elements, for example control levers or the like, via which an operator controls the compaction machine 1.
[0049] FIG. 4 shows an example of a part of the hydraulic system 6 of the compaction machine 1. In the present embodiment example, all hydraulic pumps of the hydraulic system 6 are preferably driven by the electric motor 4, in particular via an output shaft 28. The electric motor 4 is driven from an accumulator for electric energy, for example a battery 32. A converter 31 or inverter may be arranged between the electric motor 4 and the battery 32. For example, the electric motor 4 drives a traction pump 12 in this way, which is part of a, preferably closed, traction drive hydraulic circuit 16. The traction drive hydraulic circuit 16 preferably comprises at least one traction motor 26, which converts the volume flow of the traction pump 12 into a drive torque for a travel unit 55, in particular a compaction drum 5 or a wheel 7, for moving the compaction machine 1 forward and passes it on to the latter, for example via a shaft. In this case, the electric motor 4 is thus a device which drives the travel unit 55 indirectly. A brake hydraulic pump 54, specifically a steering feed pump 13, is preferably also driven by the output shaft 28 of the electric motor 4. The steering feed pump 13 is preferably part of a brake hydraulic circuit 53, in this case a steering hydraulic circuit 19, which in particular comprises a steering device 27, which is for example a steering orbitrol. The steering feed pump 13 may be a fixed displacement pump. However, a variable displacement pump may also be used to also vary the generated braking torque by changing the delivery volume of the steering feed pump. A throttle 18 is preferably arranged in the hydraulic line 25 between the steering feed pump 13 and the steering device 27. This throttle may preferably be configured as a proportional pressure-limiting valve, as indicated in the embodiment example shown. In addition, a cooler 20 may also be arranged in the steering hydraulic circuit 19, which interacts with a fan, for example, and via which heat is dissipated from the hydraulic medium into the ambient air. What is important is that there is a mechanical coupling 11 between the traction pump 12 and the steering feed pump 13. In the embodiment example shown, this mechanical coupling 11 may be realized, for example, by a through-drive unit or by a common arrangement of the two pumps on the output shaft 28 of the electric motor 4. The important thing here is that torque can be transmitted from the traction pump 12 to the steering feed pump 13 and vice versa. Finally, the hydraulic system 6 preferably has a further hydraulic circuit, more specifically a working hydraulic circuit 17 with a working pump 14, which is likewise driven by the electric motor 4 and in particular also via its output shaft 28. The pumps 12 and 14 may be arranged in a tandem arrangement. The working hydraulic circuit 17 is provided, for example, for operating a vibration exciter in a compaction drum 5.
[0050] As shown in FIG. 4, it is preferred that the traction drive hydraulic circuit 16, the steering hydraulic circuit 19 and the working hydraulic circuit 17 each have their own pump exclusively dedicated to that circuit. In the respective circuit, therefore, hydraulic energy is preferably exclusively generated via the pump associated with the respective circuit. Nevertheless, the steering feed pump 13 is preferably also configured as a feed pump for the traction drive hydraulic circuit 16. This means that a feed line 23 is preferably branched off from the steering hydraulic circuit 19 to supply hydraulic fluid to the traction drive hydraulic circuit 16. The valves etc. required for this are known to the person skilled in the art and are therefore not shown. Preferably, however, the feed line 23 merely provides for cross-scavenging of the traction drive hydraulic circuit 16 and compensates for any leakage losses occurring in the closed traction drive hydraulic circuit. No drive energy is transferred between the steering hydraulic circuit 19 and the traction drive hydraulic circuit 16 via this line. For leakage losses and cross-scavenging, the traction drive hydraulic circuit 16 preferably has a traction return path 22 that opens into the tank 15, for example a hydraulic tank. The steering hydraulic circuit 19 also preferably has a return line, specifically the steering return path 21. Preferably, the traction return path 22 and the steering return path 21 are merged to then open into the tank 15 as a common return line.
[0051] As also shown in FIG. 4, there is preferably at least one speed sensor 24 connected to the electric motor 4 and/or to a traction motor 26. Multiple speed sensors 24 may also be provided to collect the respective data at said components. In particular, the speed sensor 24 is configured to measure the actual speed of the electric motor 4 and/or the actual travel speed of the compaction machine 1 and to transmit these to the control device 10. This is also shown in FIG. 5. The dotted arrows in FIG. 5 indicate the direction of the information flow, for example from the traction motor 26 via the speed sensor 24 to the control device 10 and also from the electric motor 4 via a speed sensor 24 to the control device 10. FIG. 5 also shows other sensors that can be used. For reasons of clarity, these are not shown separately again in FIGS. 4 and 8. For example, there is a temperature sensor 33 at the electric motor 4 and/or at the converter 31 or inverter and/or at the battery 32. Additionally or alternatively, a state of charge sensor 34 may also be provided at the battery 32. Further, an amperemeter 35 may be provided to determine the amperage through the electric motor 4 and/or through the converter 31 or inverter. Again additionally or alternatively, a torque sensor 36 may be provided at the electric motor 4. Finally, another temperature sensor 37 may also be provided to determine the temperature in the steering hydraulic circuit 19. The measured values of all the sensors mentioned are transmitted to the control device 10, which uses them, except for the temperature in the steering hydraulic circuit 19, as the target value of the operating parameter. In addition, the control device 10 preferably determines a target value for the respective operating parameter under consideration, for example the target speed of the electric motor 4 and/or the target travel speed of the compaction machine 1. For this purpose, the control device 10 is connected, for example, to an operating element 29 via which an operator can input control commands to the control device 10 for controlling the compaction machine 1. The operating element 29 may thus be, for example, a control lever or also, for example, a brake lever. The control device 10 preferably derives the target speed of the electric motor 4 and/or the target travel speed of the compaction machine 1 from the respective specifications of the operator. Alternatively, these values may also be derived from an operating situation or an operating state of the compaction machine 1 or from safety considerations.
[0052] The temperature in the steering hydraulic circuit 19 may be used to ensure that the steering hydraulic circuit 19 does not overheat due to the provision of the braking torque at the steering feed pump 13. For example, a braking torque may be provided to the steering feed pump 13 only when the temperature in the steering hydraulic circuit 19 is below a predetermined threshold value. The threshold value is then selected accordingly such that safe operation of the steering hydraulic circuit 19 and in particular of the steering device 27 is ensured.
[0053] The control device 10 thus preferably receives both driving instructions from the operator and actual values of various parameters of the compaction machine 1. For example, the control device 10 may determine whether the identified actual values, for example of the speed and/or the travel speed, exceed the target values, for example also by a certain threshold value and/or beyond the duration of a tolerance time. Based on this information, the control device 10 then preferably controls the components of the compaction machine 1. In particular, the control device 10 controls the speed of the electric motor 4, the delivery volume of the traction pump 12 and the flow resistance of the throttle 18.
[0054] Optionally, furthermore, a hydraulic accumulator 50 may be connected to the hydraulic line 25 of the steering hydraulic circuit 19, in particular to the hydraulic line 25 between the steering feed pump 13 and the steering device 27, via an accumulator charge-discharge valve 51, so that hydraulic energy can be stored, at least transitionally, and can also be fed into the steering hydraulic circuit (or also other hydraulic circuits, in particular for driving work functions, such as the lifting and lowering of an edge cutter, etc.).
[0055] FIG. 6 shows the schematic time sequence of a specific application scenario. In particular, the travel speed F of the compaction machine 1 is considered here. However, such a sequence would be analogous or at least very similar for other operating parameters, so that only this case is discussed below as an example. In the diagrams shown, the time t is plotted on the abscissa, while different parameters, explained below, are plotted on the ordinates. The diagrams are arranged such that the times t.sub.1 to t.sub.5 in each of the diagrams describe the same point in time. For example, the lowest diagram shows the travel speed F of the compaction machine 1 over time. It shows both the progression of the actual value I of the travel speed F and its target value S. For example, the compaction machine 1 travels in working operation with constant travel speed F on level ground 8 until time t.sub.1. From time t.sub.1, the compaction machine 1 descends a slope, causing the compaction machine 1 to accelerate and the travel speed F to increase. At time t.sub.2 the travel speed F exceeds the target value S and continues to accelerate until time t.sub.3. At time t.sub.3 a trend reversal occurs and the travel speed F decreases until, at time t.sub.4, it falls below the target S again and at time is it has decreased back to the initial value. The top diagram shows the pressure drop p across the throttle 18 in terms of amount. The pressure drop p is proportional to the braking torque generated, so that this is also represented by this diagram. Since no braking torque is required at the steering feed pump 13 during normal working operation of the compaction machine 1, the pressure drop p remains constant until time t.sub.2, for example at zero. At time t.sub.2, at which the actual value I of the travel speed F exceeds the target value S, the control device 10 controls the throttle 18 and increases its flow resistance, so that a pressure drop p occurs at the throttle 18. With the pressure drop p, there is also a proportional braking torque at the steering feed pump 13, which can be used to support a torque at the traction pump 12 caused by the overrun and thus contribute to the braking of the compaction machine 1. The control device 10 adjusts the braking torque in particular in proportion to the extent to which the actual value of the travel speed F exceeds the target value S. Since the travel speed F between times t.sub.2 and t.sub.3 continues to increase, for example because the braking torque is insufficient to compensate for the acceleration due to the slope, the pressure drop p and the resulting braking torque also increase during this time period. From time t.sub.3, the travel speed F decreases. However, at least in the case shown, the pressure drop p at the throttle 18 is maintained by the control device 10 at the level reached until the travel speed F falls below the target value at time t.sub.4. Only from this point does the control device 10 then reduce the pressure drop p, for example back to zero.
[0056] The two middle diagrams in FIG. 6 show the delivery volume V and the speed D of the traction pump 12. Up to time t.sub.3, the speed D of the traction pump 12 essentially follows the travel speed F. Up to this point, the delivery volume V of the traction pump 12 also remains constant. However, if the delivery volume V of the traction pump 12 remained constant beyond this time t.sub.3, the speed D of the traction pump 12 would decrease again in line with the traction speed F. However, to enable efficient braking by the braking torque at the steering feed pump 13, it is advantageous if a sufficiently high torque is transmitted from the traction pump 12 to the steering feed pump 13. In order to make this possible also in this temporal section of the method, it is preferred that the control device 10 controls the traction pump 12 such that its delivery volume V is reduced. Due to the reduced delivery volume V, the speed D of the traction pump 12 acting as a motor is increased, or in this case at least kept constant, in order to be able to absorb the volume flow coming from the traction motor 26 acting as a pump. In this way, the speed D of the traction pump 12 does not drop analogously to the travel speed F and a higher speed is transmitted to the steering feed pump 13 via the mechanical coupling 11, which in turn causes a higher braking torque, in particular toward the throttle 18, via the volume flow in the steering hydraulic circuit 19 caused by this. Overall, therefore, the braking performance can be improved in this way.
[0057] FIG. 7 shows a flowchart of the method 40. The method 40 starts by driving 41 the traction pump 12 in the traction drive hydraulic circuit 16 of the compaction machine 1 by the electric motor 4. It further comprises driving 42 the steering feed pump 13 in the steering hydraulic circuit 19 of the compaction machine 1 by the electric motor 4. The steering feed pump 13 also feeds hydraulic fluid into the traction drive hydraulic circuit 16. It is coupled to the traction pump 12 via a mechanical coupling 11 so that torques can be transmitted between the two points. This is followed by determining 43 an actual value of an operating parameter, for example an actual speed of the electric motor 4 and/or an actual travel speed of the compaction machine 1 or a parameter correlating therewith, and determining 44 a target value of the operating parameter, for example a target speed of the electric motor 4 and/or a target travel speed of the compaction machine 1 or a parameter correlating therewith. In particular, these values are forwarded to or collected by the control device 10. In particular, the control device 10 then performs comparing 45 of the actual value of the operating parameter, for example the actual speed and/or the actual travel speed or the parameter correlating therewith, with the target value of the operating parameter, for example the target speed and/or the target travel speed or the parameter correlating therewith. Specifically, the control device 10 identifies cases in which the actual value, for example the actual speed and/or the actual travel speed or the parameter correlating therewith, is greater than the target value, for example the target speed and/or the target travel speed or the parameter correlating therewith. If such a case is detected, the method comprises generating 46 a braking torque 46 at the steering feed pump 13 by a hydraulic throttle 18. For this purpose, the hydraulic throttle 18 is preferably arranged in the hydraulic line 25 between the steering feed pump 13 and the steering device 27 in the steering hydraulic circuit 19. In particular, the hydraulic throttle 18 is controlled by the control device 10 such that its flow resistance increases. The torque required to overcome this flow resistance is available at the steering feed pump 13 as braking torque and can be transmitted to the traction pump 12 via the mechanical coupling 11. The method thus comprises transmitting 47 the braking torque from the steering feed pump 13 to the traction pump 12 of the traction drive hydraulic circuit 16 via the mechanical coupling 11. Optionally, and therefore shown in dashed lines in the figure, the method may further comprise reducing 48 a delivery volume V of the traction pump 12 to ensure that a sufficient speed for providing the braking torque is transmitted to the steering feed pump 13 even during the braking process despite the associated reduction of the volume flow in the traction drive hydraulic circuit 16.
[0058] FIG. 8 shows an alternative embodiment in which the steering feed pump 13 and/or the working pump 14 are not driven by the electric motor 4, but may each have their own electric drive unit 30. The electric drive unit 30 may be an electric motor, for example. Importantly, also in this embodiment, the traction pump 12 is driven by the electric motor 4 and there is a mechanical coupling 11 between the traction pump 12 and the steering feed pump 13. The mechanical coupling 11 may be formed separately from the output of the electric motor 4. Otherwise, the embodiment of FIG. 8 corresponds to that of FIG. 4, so that reference is made to the previous discussion in order to avoid repetition.
[0059] Furthermore, irrespective of the specific embodiment example, a clutch, in particular a switchable clutch, may be comprised in the mechanical coupling 11. In this way, for example, the mechanical coupling between the traction pump 12 and the steering feed pump 13 may be interrupted at least temporarily.
[0060] FIG. 9 illustrates an alternative or additional drive concept compared with the embodiment example. The special feature here is that the traction motor 26, which is also integrated in a traction drive hydraulic circuit not further shown in FIG. 9, is connected by means of a transmission gearbox 56, for example a gear train, to a brake hydraulic pump 54 of a separate brake hydraulic circuit with a corresponding throttle 18. In this way, as also shown in FIG. 9, each individual travel unit, in particular each individual compaction drum 5 of the compaction machine 1, may be assigned its own brake hydraulic circuit and the braking effect generated by the brake hydraulic circuit can be controlled individually. In this case, the traction motor 26 represents a device which drives the travel unit 52 directly.
[0061] Here, too, a hydraulic accumulator 50 with an accumulator charging valve 51 may optionally be provided, although it is possible to assign each of the two brake hydraulic circuits 53 its own, and thus separate, hydraulic accumulator 50 or, as shown in FIG. 9, to assign both brake hydraulic circuits 53 (or even more than two) a common hydraulic accumulator 50. The common hydraulic accumulator 50 is connected to the two brake hydraulic circuits via corresponding connecting lines 57, 58, which are merged in a common accumulator charging valve 51, but which may also be connected to the hydraulic accumulator via individual, independent accumulator charging valves 51. It will be appreciated that the arrangements provided in FIG. 9 for two travel units in a compaction machine 1 may also be provided for only one travel unit of a compaction machine.
[0062] In the drive concept shown in FIG. 10, one of the special features is that the travel unit 52 is driven practically directly by the electric motor 4, in particular without the interposition of a hydraulic transmission stage, with a transmission gearbox 59 being interposed for this purpose. Via this transmission gearbox, the electric motor is mechanically coupled to the brake hydraulic pump 54 and the other components 53 and 18, as already explained with reference to FIG. 9. Also for this embodiment, a hydraulic accumulator 50 may optionally be connected to the brake hydraulic circuit via an accumulator charging valve 51.
[0063] For all of the variants with hydraulic accumulator 50 described in the embodiment examples, it is further possible to provide further hydraulic line branches, but this is not shown in the figures. These hydraulic line branches may be configured to supply hydraulic energy stored in the hydraulic accumulator 50 to further consumers, for example working units such as an edge cutter, etc., and/or to enable additional functionalities, such as a boost function for the traction drive system.
[0064] Finally, FIG. 11 illustrates exemplary curves for the speed rpm of the electric motor, the progression of the travel speed, the delivery volume V of the traction pump 12 and the pressure p between the pump 13/54 and the throttle 18 for the embodiment example shown in FIG. 4. The shown curves relate to a situation in which the compaction machine starts on a horizontal surface and accelerates (t1 to t2), travels at a constant speed (t2 to t3) and then decelerates back to a standstill (t3 to t5). In addition to the above explanations, it is important to note here that the pressure built up via the throttle 18 (t3 to t4) is used for braking and, at the same time, a speed increase of the electric motor is considerably reduced. For an effective braking process, the delivery volume V of the traction pump is reduced at the same time. In this way, overshooting of the speed of the electric motor can be avoided even in this operating situation and, at the same time, the braking torque generated by the throttle can be used to brake the compaction machine.
[0065] Overall, in a compaction machine with a hydraulic system, which is driven by an electric motor and no longer has an internal combustion engine as a traction drive system, the present invention enables efficient and reliable braking by means of a mechanical-hydraulic coupling with a throttle. The fact that this throttle is arranged outside the traction drive hydraulic circuit results in a number of advantages that have already been mentioned above.
