Hydrostatic multi-motor drive

p0001The invention relates to a hydrostatic multi-motor drive with at least two hydraulic motors which apply a common load.

p0002Hydraulic actuators with two motors are essentially known in two different designs.

p0003In a first design, the two drives are firmly connected by a shaft and thus both run continuously. In arrangements in which at least one of the motors is designed to be adjustable and this motor is adjusted to zero to achieve high speeds by adjustment of its displacement volume, it is disadvantageous that the zero-set motor is entrained along with the resultant high mechanical losses. To avoid such problems, two-motor drives are also known in which the two motors are connected to one another by gearing and clutches, so that in the operating ranges in which the adjustable motor is set to zero, the latter can be mechanically decoupled from the second motor. A disadvantage of this solution is, in particular, the high complexity of the clutch and transmission arrangement, which is necessary to ensure the synchronization of the two machines during engagement and disengagement, thus enabling a sliding transition between the various operating regions. Light.<patcit id="pcit0001" dnum="EP482524A0"><text>EP-A0482524</text></patcit> Shows a drive with the features of the preamble of claim 1.

p0004From the <patcit id="pcit0002" dnum="DE10060679A1"><text>DE 100 60 679 A1</text></patcit> A further hydrostatic two-motor drive is known, the two motors of which are connected to at least one clutch. Such a drive also has the above-described disadvantages.

p0005The invention is therefore based on the object of avoiding these disadvantages and to provide a multi-motor drive which covers a wide operating range by the use of a plurality of motors, thereby ensuring a simple and unproblematic coupling of the motors. In addition, a method for controlling the drive is to be specified, which allows continuous transitions between the different operating ranges.

p0006The invention achieves this by the characterizing features of claims 1 and 6.

p0007The use of several motors has the advantage that smaller motors can be used and nevertheless a high torque can be generated in common operation. In addition, by virtue of their small design, they enable a high rotational speed, which makes sense, for example, for the rapid travel of mobile work machines. By using a freewheel, it is possible that all the motors can be operated together in the blocking direction of the freewheel for generating a high output torque. In areas of high-speed travel, the motors arranged behind the respective freewheels are then decoupled by the freewheel from the free-running engine, which is thereby provided with the entire volume flow of the pump (s) to achieve a high speed. Thus, with a large engine displacement volume, a high torque can be generated at a low speed and, conversely, the engine speed can be increased when the pressure medium supply remains constant when the motor displacement volume is reduced. The reduction of the motor displacement volume to zero means the motors arranged behind the freewheel and are then no longer involved in the drive power until their displacement volume is set to zero.

p0008Problems with synchronization do not occur because, as soon as the displacement volume of the motors arranged behind the freewheel is again increased, the rotational speed increases until the freewheel locks and the torque generated by the previously uncoupled motors is transmitted via the freewheel to the drive axle, ie The torques of all motors can be used to drive the load.

p0009If a common pressure medium circuit is used for all engines, a force balance is automatically established in the entire system, and a gentle starting or deceleration of the motor decoupled by the freewheel is achieved without additional control technology devices.

p0010When using such motors, the advantages of the freewheel can be exploited particularly advantageously, since in the low-speed range with high torques, the motors are mechanically coupled by the freewheel. By reducing the motor volume, the speed increases until the volume of one of the motors is reduced to zero, so that only the remaining motors, which are now decoupled by the freewheel, serve as drive. Embodiments of the invention result from the subclaims. Thus, the pressure sensor in the line (s) between pump and motor can accelerate or decelerate to distinguish the operating state.

p0011The multi-motor drive according to the invention has an adjustable pump for supplying the pressure medium to the motors. The use of an adjustable pump has a number of advantages compared to the constant-flow pump with control valve. It is thus possible to achieve continuously controllable pressure medium flows, which can be used to control the drive. The controllable pressure medium supply, in conjunction with the motor control, offers the possibility to vary the engine power in wide ranges and to enable continuous power transitions. By dispensing with control valves in the power branch, the drive system is also very energy-saving by avoiding energy losses in the valve arrangements.

p0012In a further embodiment of the invention, it is provided that the motors are connected parallel to the freewheel by a switchable clutch. The parallel switchable clutch allows a power transmission even in free-wheeling. This has the advantage that the freewheel can be bridged in cases in which the drive is to have a comparable power characteristic in both the forward and reverse directions. Thus, in all directions, all existing motors can be operated together and a correspondingly high output torque can be provided at the output axle.

p0013To achieve the object set, the invention also proposes a method according to claim 6 for influencing the power of the drive. In order to accelerate a multi-motor drive in the forward direction, the delivery volume of the pump is first of all increased. To further increase the rotational speed, the volume of the motor arranged behind the freewheel is reduced and the volume of further motors arranged behind the freewheel is reduced.

p0014By increasing the delivery volume of the pump, the pressure medium flow through the motors increases, which leads to an acceleration of the drive. If the rotational speed is to be further increased, the volume of a first motor is reduced, which leads to an increase in the rotational speed with a decreasing output torque when the pressure medium flow to this motor remains constant. If a plurality of mechanically coupled motors are mounted on the same pressure medium circuit, the pressure medium flow is re-divided when the volume of a motor is reduced, in which a larger proportion of the pressure medium flows to the motors with a constant volume, which results in an overall increase in the rotational speed of all the motors. If the volume of an engine is reduced to zero, no more pressure medium flows through it, it does not release any output torque, and can not be driven by the remaining motors before the freewheel over the freewheel in the freewheel direction, so that it is decoupled by the freewheel And the entire pressure medium flow flows through the remaining motors.

p0015The maximum speed is reached when, at the maximum pumped volume of the pump, the volume of all the motors is reduced to the minimum value, and in the extreme case, all but one motor, and the remaining motor decoupled from the stationary motors by the total pressure flow, Of zero different volumes with maximum speed.

p0016A further method according to the invention is used to decelerate a multi-motor drive and is characterized in that the pump operates as a motor, all motors arranged before the freewheel operate with a displacement volume greater than zero as pump and the volume of the further motors arranged behind the freewheel are zero is provided.

p0017With this method, it is possible to achieve a particularly energy-saving deceleration of the drive. In this case, the power delivered at the driving shaft of the pump during motor operation of the pump can be used for driving further mechanical components and does not have to be converted into heat loss. In order to achieve this, the desired deceleration behavior of the drive is achieved by appropriate control measures on the variable pumps and motors. Such a state occurs when the differential pressure across the motor (s) reverses its sign and the kinetic energy of the load is delivered to the hydraulic circuit. By adjusting the delivery volume of the pump and using a motor controllable by displacement of the displacement volume before the freewheel, the deceleration of the drive (the load) and the amount of energy delivered to other consumers coupled to the pump side can be regulated.

p0018A method according to the invention for accelerating the multi-motor drive in the reverse direction consists in reversing the delivery direction of the pump, increasing the delivery volume of the pump, and reducing the rotational speed further by freeing up its displacement volume to further increase the rotational speed. This method is used for the simple operation of the multi-motor drive in the reverse direction. Zero-adjustable pumps allow a reversal of the delivery direction of the fluid flow in the circuit. As a result, the motors also move in the opposite direction. By increasing the delivery volume of the pump and reducing the displacement volume of the variable motor, the rotational speed of the drive and thus of the driven load can be increased, as already explained above.

p0019The invention also relates to a method for accelerating the multi-motor drive in the reverse direction, which is characterized in that the switchable clutch is closed in order to bridge the freewheel in the free-wheeling direction, and the direction of transport of the pump is reversed and the delivery volume of the pump is increased Of the rotational speed, the volume of a first motor is reduced and, if appropriate, the volume of the further motors is reduced.

p0020In order that such a multi-motor drive in the long-stroke drive has the same drive characteristics in the forward as in the reverse direction, a clutch parallel to the freewheel can be used as described above. The clutch is then closed for backward operation, and then the pump's delivery direction is reversed, thereby driving all motors with a volume greater than zero in the reverse direction by the reverse oil flow. By increasing the delivery volume of the pump, the speed of the drive can be increased since the oil flow is automatically divided between the drives. In order to further increase the rotational speed, the volume of the motors is then successively reduced in a manner analogous to the method in the forward direction until a maximum rotational speed of the overall arrangement is reached.

p0021Further features, details and advantages of the invention will become apparent from the following description and from the drawings. These show in:<dl id="dl0001" compact="compact"><dt>FIG</dt><dd>A schematic overview of a multi-motor drive according to the invention with a controllable motor,</dd><dt>FIG</dt><dd>A cross-section through an exemplary freewheel for the solution of the multi-motor arrangement according to the invention,</dd><dt>FIG</dt><dd>A schematic overview of the multi-motor drive with two controllable motors,</dd><dt>FIG</dt><dd>A representation of the drive with a switchable clutch,</dd><dt>FIG</dt><dd>1 is a representation of the hydraulic circuit diagram for a multi-motor drive according to the invention, and FIG</dd><dt>FIG</dt><dd>4 shows a representation of the driving characteristic curve of the multi-motor drive.</dd></dl>

p0022A multi-motor drive, indicated generally at 1, has a hydraulic motor 2, which can be adjusted in the motor volume, and a hydraulic motor with a constant displacement volume 3. These are connected to each other via a mechanical freewheel 4. An adjustable hydraulic pump 5 supplies the hydraulic circuit via lines 6 and 7 with pressure medium.

p0023At least one pressure sensor with measuring signal converter 8 measures the pressure in the hydraulic circuit and passes it on to a control unit 9 in the form of an electrical signal. This calculates the actuating signals from the measured state variables in the circuit and the nominal values ​​specified by the operator and thus controls the motor volume of the variable motor 2 via the motor controller 9b and the displacement volume of the adjustable pump 5 with the pump controller 9a.

p0024Depending on the volume flow of the pump 5 and the motor volume of the variable motor 2, a rotational speed of the motors thus occurs. Depending on the setting of the variable motor 2, the volume flow of the pump 5 is divided between the two motors 2 and 3, the same pressure difference being applied across both motors and the freewheel being blocked as long as the torques of the two motors are adjusted The output shaft can be transmitted until the torque delivered by the variable-speed motor is equal to zero and this torque is then stopped. For example, the two motors 2 and 3 jointly drive a load 10, for example a chassis of a vehicle.

p0025The freewheel 4, as shown in FIG <figref idrefs="f0001">FIG</figref> For example, an outer ring 11 which is non-positively connected to the load-side motor. Inside the ring 11 is a star wheel 12, which is connected to the variable motor 2. When the star wheel 12 is driven, metal balls 13 rolling on the outer slot surfaces are jammed with the inner surface of the ring 11 and thus effect a force transmission from the stem wheel 12 to the outer ring 11. If the outer ring 11 moves faster than the star wheel 12, Spheres in recesses of the wheel 12 and there is no transmission of the movement from the outer ring 11 to the star wheel 12 so that the ring 11 can rotate freely in this direction.

p0026An alternative possibility, in which both motors are adjustable, is in <figref idrefs="f0002">FIG</figref> Respectively. In this case, the load-side motor 3 'can also be adjusted in addition to the first adjustable motor 2 and can be adjusted by the control unit 9, depending on the current state of the drive and the desired setpoint variables. This makes it possible to further enlarge the operating range of the drive.

p0027In the case of reversing, no force transmission from the motor 2 to the load 10 is possible by the freewheel 4. In the event that the maximum torque is to be available at the load during reverse operation, as in forward operation, a controllable clutch 14 is provided parallel to the freewheel as shown in FIG<figref idrefs="f0002">FIG</figref> Respectively. This is closed in reverse operation and thus allows a force transmission from the motor 2 via the motor 3 to the load 10 also in the free-wheeling direction of the freewheel 4.

p0028The design of the hydraulic circuit is in <figref idrefs="f0003">FIG</figref> In more detail. A combustion engine 15 drives the variable displacement pump 5 and, at the same time, a constant pump 16; Which pretensions the low-pressure circuit 18, which essentially consists of a pressure medium supply container 17 and a pressure valve 19.

p0029The low-pressure circuit 18 is connected to the high-pressure circuit via two non-return valves 20 and 21. This is protected by two overpressure valves 22 and 23 from being destroyed by overpressures in the circuit. The drive part with the two hydraulic motors 2 and 3, which are connected to each other by a freewheel 4 which can be bridged by the unlockable clutch 14, is connected by way of the pressure medium lines 6 and 7.

p0030The power delivered to the load 10 is determined by the variable pump 5, which is driven by the internal combustion engine 15 at a certain speed. The dispensed pressure medium volume flow is determined by the setting of the displacement volume of the pump 5. The ratio of the rotational speed and the torque that this output is delivered to the load 10 is determined by the adjustment of the motor volume of the variable motor 2.

p0031The resultant driving characteristic curve of the drive 1 in forward operation is shown in FIG <figref idrefs="f0004">FIG</figref> In principle. This shows a diagram in which the load torque is plotted against the rotational speed. To start the motor at point A the displacement volume is increased, whereby the motor volume of the variable motor is maximum. By increasing the pump volume flow, the speed of the motor increases to the maximum or a previously selected setting value of the pump displacement volume at point B. To further increase the speed, the motor volume of the variable motor is now reduced, resulting in a reduction in the torque delivered to the load . The decrease in the motor volume causes the volume flow provided to flow through the motor volume, which in total is smaller for both motors, as a result of which the speed increase is effected. At point C, the volume of the variable motor 2 is reduced to zero so that the entire available volume flow only flows through the motor 3. Here, in the case that only the motor 2 is adjustable and the pump is already set to the maximum displacement volume, the maximum rotational speed is reached. If the motor 3 'is also adjustable, its motor volume can also be reduced, which results in a further speed increase. The maximum rotational speed is then reached at point D at which the maximum pump volume flow flows through the minimum motor volume of the variable motor 3 'and the motor 2 is through its reduced volume, being decoupled from the load by the freewheel 4. Of course, the invention is not limited to the above examples, but can also be varied in many ways without departing from the basic idea. In particular, the number of motors is not limited to two, but can be considerably more, as a result of which the flexibility of the drive is further increased since a significantly larger rotational speed range or larger motor torques can be achieved. Also, the combination of variable and non-variable motors is not limited to the above example. In addition, such a drive can also be integrated into global hydraulic circuits in which a plurality of hydraulically moved loads present in a truck driven in this way are operated with a comprehensive control concept.

List of references

p0032<dl id="dl0002" compact="compact"><dt>1</dt><dd>Multi-motor drive</dd><dt>2</dt><dd>Adjustable hydraulic motor</dd><dt>3</dt><dd>Hydraulic motor with constant displacement volume</dd><dt>3 '</dt><dd>on-load motor</dd><dt>4</dt><dd>mechanical freewheel</dd><dt>5</dt><dd>hydraulic pump</dd><dt>6</dt><dd>management</dd><dt>7</dt><dd>management</dd><dt>8th</dt><dd>Measuring transducer</dd><dt>9</dt><dd>control unit</dd><dt>9a</dt><dd>pump control</dd><dt>9b</dt><dd>Motor control</dd><dt>10</dt><dd>load</dd><dt>11</dt><dd>outer ring</dd><dt>12</dt><dd>star wheel</dd><dt>13</dt><dd>rolling metal balls</dd><dt>14</dt><dd>controllable clutch</dd><dt>15</dt><dd>combustion engine</dd><dt>16</dt><dd>constant pump</dd><dt>17</dt><dd>Pressure medium reservoir</dd><dt>18</dt><dd>Low pressure circuit</dd><dt>19</dt><dd>pressure valve</dd><dt>20</dt><dd>Check valve</dd><dt>21</dt><dd>Check valve</dd><dt>22</dt><dd>pressure relief valve</dd><dt>23</dt><dd>pressure relief valve</dd></dl>