EP1664549A1

EP1664549A1 - Hydrostatic gear

Info

Publication number: EP1664549A1
Application number: EP04762708A
Authority: EP
Inventors: Ralf Bonefeld
Original assignee: Bosch Rexroth AG
Current assignee: Bosch Rexroth AG
Priority date: 2003-09-10
Filing date: 2004-08-23
Publication date: 2006-06-07
Anticipated expiration: 2024-08-23
Also published as: ATE354031T1; DE502004002922D1; DE10342102A1; WO2005026559A1; EP1664549B1

Abstract

A hydrostatic gear comprising an output motor (5), supplied with a pressure medium by means of a pump (14) driven by a motor (18). The hydrostatic gear is provided with a charge device (6) having two charge pumps (30,32) driven by a common charge motor (3) and used to respectively supply a pressure chamber (10,8) of the output motor with a pressure medium, in order to compensate for leakage and for the gripping of the output motor.

Description

Description Hydrostatic transmission

The invention relates to a hydrostatic transmission according to the preamble of claim 1. A hydrostatic transmission is understood to mean the combination of a hydraulic pump (primary part) with a hydraulic motor (secondary part), in the simplest case with a hydraulic cylinder, the displacement chambers of which are ideally connected without flow resistance during operation. Due to the external leakage of the hydraulic-mechanical converter (in particular pumps, hydraulic motors, to a lesser extent also hydraulic cylinders), such hydrostatic transmissions always require a device that realizes the supply of hydraulic fluid to the transmission in order to compensate for these losses and to maintain the functionality of the transmission , This device must in particular prevent cavitation phenomena from developing in the pressure chambers. A transmission with double-sided clamping of the driven motor (secondary unit) has proven to be particularly advantageous. This clamping enables both the drive dynamics and the load rigidity to be significantly improved compared to conventional gears with open hydraulic circuits.

DE 40 08 792 AI shows a hydrostatic transmission in which a differential cylinder is supplied with pressure medium via two variable displacement pumps. The variable displacement pumps are driven by a common motor, an annular space with a bottom-side cylinder space of the Cylinder is connected, while the other variable pump supplies the cylinder chamber with pressure medium from a tank.

The two variable pumps are controlled via a control unit such that, for example, when the hydraulic cylinder is extended, the cylinder space is supplied with a little more pressure medium than is required for the extension movement, while the annular space is supplied with an excess amount when the cylinder is retracted. This control creates a counter pressure in the other pressure chamber, so that the piston is clamped on both sides. The disadvantage of this solution is that the control and installation of the variable displacement pumps requires considerable outlay in terms of device technology.

A hydrostatic transmission is known from CA 605,046, in which the secondary unit is supplied with pressure medium via two constant pumps driven by a common motor. Pressure medium can be conveyed from one of the pressure chambers of the hydraulic cylinder into the respective other pressure chamber via one of the constant pumps, while the second pump of the primary part supplies the bottom-side cylinder chamber with pressure medium from a hydrostatic accumulator. When the two pumps are bypassed, this hydrostatic accumulator can be connected to the pressure chambers of the hydraulic cylinder, so that leakage losses are compensated for and clamping on both sides takes place in accordance with the pressure in this accumulator.

A disadvantage of both solutions is that the

Clamping the secondary unit (output motor) is extremely difficult to adapt to different operating conditions. Furthermore, both require Known variants described above a high effort to control the two pumps of the primary part.

In contrast, the invention has for its object to provide a hydrostatic transmission, in which the clamping of the output motor is made possible with little outlay on equipment.

This object is achieved by a hydrostatic transmission with the features of claim 1.

According to the invention, the hydrostatic transmission has a primary part with a pump, via which pressure chambers of an output motor can be supplied with pressure medium. To compensate for leaks and, if necessary, to clamp the driven motor (secondary part), a charging device is provided according to the invention, which has two charging pumps driven by a common charging motor. These are each assigned to a pressure chamber of the output motor, so that the output motor can be clamped on both sides and the leakage compensated for by suitable regulation of the loading motor. The charging device with the charging motor and the two charging pumps, which are preferably designed as constant pumps, can be implemented with an extremely low expenditure on device technology, the clamping of the charging motor being very easy to adapt to different operating conditions by regulating the charging motor.

It is preferred if the charging motor is torque-controlled. The drive torque of the

Loading motor preferably regulated proportionally to the total pressure of the hydrostatic transmission. This dependence of the drive torque M ^ can be calculated using the equation Calculate ^M A = 1A ^X PA + ^V 1B x PB, where V is the absorption volume of the two charge pumps and p is the pressure in the two pressure chambers of the output motor.

In a preferred variant of the invention, the absorption volumes of the two charge pumps are of the same size.

The output motor can be a differential cylinder, but it is also possible to use other consumers, for example a hydraulic motor or a synchronous cylinder as a secondary part. When using a differential cylinder as the output motor, the primary part is designed with two pumps, one connecting the two pressure chambers to one another and the other connecting the larger pressure chamber to the tank. The pumps of the circuit are preferably controlled in a speed-controlled manner. The swallowing volumes must be adjusted to the consumer (hydraulic motor) so that the balance of the displacement volume flows is balanced. Other advantageous developments of the invention are the subject of further dependent claims.

Preferred exemplary embodiments of the invention are explained in more detail below with the aid of schematic drawings. FIG. 1 shows a hydraulic diagram of a hydrostatic transmission with a differential cylinder as a consumer, and FIG. 2 shows an exemplary embodiment with a synchronous cylinder as a consumer. FIG. 1 shows a hydrostatic transmission 1 with a primary part 2, a secondary part 4 and a charging device 6. The secondary part 4 is formed in the illustrated embodiment by a hydraulic cylinder 5, which is designed as a differential cylinder. A differential piston 7 of the hydraulic cylinder divides the latter into a cylinder chamber 8 on the bottom side and a cylinder chamber 10 on the piston rod side. A load L acts on a piston rod of the differential piston 7 in the direction of the arrow.

The primary part 2 has two pumps 12, 14 which are seated on a common drive shaft 16 of a speed-controlled motor 18. This is in the

Reversible direction of rotation, so that accordingly

Delivery direction of the two pumps 12, 14 is reversible.

The two connections of the pump 14 are via lines 20, 22 with the annular space 10 and the

Cylinder chamber 8 of the hydraulic cylinder 5 connected so that when this pump 14 is actuated by a pressure medium

Pressure room in the other pressure room can be promoted. A pressure connection of the further pump 12 is connected to the cylinder space 8 of the hydraulic cylinder 5 via a pressure line 24. A suction line 26 leads to a tank, so that pressure medium can be conveyed from the tank into the cylinder space 8 or from there to the tank T.

The charging device 6 has two charging pumps 30, 32, which are driven by a common charging motor 34 and a shaft 28. The loading motor 34 is designed as a synchronous machine in the exemplary embodiment shown, but in principle an asynchronous machine can also be used. The pressure connections of the two charge pumps 30, 32 are connected via lines 36 and 38 to lines 20 and 22, respectively, which are connected to rooms 8, 10. The two suction connections of the charging pumps 28, 30 are connected to the tank T via tank lines 40, 42, so that when the charging motor 34 is actuated, pressure medium from this tank T can be conveyed via the charging lines 26, 38 to the pressure chambers 8, 10 of the hydraulic cylinder 5, to compensate for leakage losses and / or to clamp the hydraulic cylinder 5 on both sides.

In the embodiment shown in Fig. 1, the swallowing volumes of the two pumps 12, 14 and

Swallowing volumes of the two charge pumps 28, 30 each have the same design. The area ratio α des

Differential cylinder 5 must then be 2: 1.

When the charging motor 34 is activated, both charging pumps 28, 30 deliver pressure medium from the tank T into the two pressure chambers 8, 10 of the hydraulic cylinder 5. The pressures P _A and PB in the pressure chambers act in proportion to the delivery volume of the respective charging pump 30, 32 as load moments on the Drive shaft 28. Neglecting friction and acceleration moments, the moment balance on the shaft of the loading unit is then

PA x V _{1 # A} + p _B V _{1; B} = M ^, where p is the pressures in the pressure chambers, V is the swallowing volume and M is the output torque of the motor 34 acting on the shaft 28 of the loading unit 6.

The total pressure of the transmission p _SU m is calculated where ß are weighting factors, the derivation of which is explained in detail below. In the concept according to the invention, the pressures in the pressure chambers 8, 10 are used as information about the state of charge of the transmission, but it is distinguished by the fact that, due to the compressibility of the pressure medium, pressure changes resulting from changes in the load state of the hydraulic cylinder 5 do not interact the charger.

As can be seen from the two previously described equations for calculating M ^ and p _su .m, a sum of the output torques takes place on the shaft 28 of the loading device, which is proportional to the formation of total pressure (Psum) if the ratio of the swallowing volumes V _] _ _A , V _] _ _{ß of} the two charge pumps 30, 32 is equal to the ratio of the weighting factors ß _A , ß _ß . The specification of the total pressure can be controlled via the

Drive torque. respectively. Every change in the actual total pressure causes a change in the speed, so that the balance is restored by providing the required charge volume flow.

In simple words, when the loading motor 34 is actuated, pressure medium is conveyed into the two pressure chambers 8, 10 via the two loading pumps 30, 32, so that the hydraulic cylinder 5 is clamped on both sides. A pressure p _A , pg builds up in the pressure chambers, which results in a restoring torque acting on the shaft 28 of the charging device 6. This restoring torque counteracts the drive torque of the charge pumps 30, 28. The motor current is set via the torque control of the charging motor 34 in such a way that the controlled or regulated drive torque corresponds to the corresponds to the restoring torque. In the event that there is no leakage of the hydrostatic transmission, this restoring torque remains essentially constant if no change in the preload is to be made.

Accordingly, the solution according to the invention comes with a

Minimum of sensors, since, for example, the pressures in the pressure rooms do not have to be recorded, as is the case, for example, in the solution according to DE 40 08 792 AI.

Based on the attached table, some theoretical considerations regarding the choice of the weighting factors ß _A and ß _{ß are} explained below for better understanding.

The pressures in the pressure chambers 8, 10 can be used to derive the state of charge of the hydrostatic transmission 1. However, these pressures are also determined by the size of the load. In the state without load (L = 0), the pressures p are determined on the one hand by the area ratio α (see equation a) in the table) and on the other hand indicate the preload of the hydrostatic transmission. If the hydraulic cylinder 5 is assumed to be leak-free and the line connections of the hydraulic cylinder 5 are hermetically sealed, the pre-tension that has been set is retained and the chamber pressures P _A 'PB change only as a function of the load L. One chamber pressure increases while the second decreases. The sum p _su (see above) of the weighted pressures p should therefore remain constant and serve as a measure of the preload. The change in the pressures p _A , pg due to an external load L must be determined in the determination of the weight factors ß _A and ß _{ß come} in. These depend on the area ratio α and the hydraulic capacities of the cylinder chambers and thus on the current piston position. Assuming a constant compression module, the dependence on the hydraulic capacities can be traced back to a consideration of the length of the two oil columns. If the origin of the movement coordinates is chosen for a stroke x in the center position of the differential piston 7, then ^V _A = V _{A # t} ot + < ^h / ² + ^χ) x ^A A = ⁽ ^ + X ⁾ A _A , where L = V tot / ^A A ^{+ n 2} • The same applies to the volume VB, with a negative sign for the deflection from the center position. The ratio γ (see equation g) in the table) to the length of the oil columns is characteristic of the influence of the hydraulic capacities on the opposite change in pressures p _A , p _ß in pressure chambers 8, 10 under load L. In the table mentioned, these considerations are summarized in mathematical form. The result is the weighting factors according to equations k) and 1), which allow a summation from the pressures p _A and p _ß , for which an influence of the load conditions is eliminated and which makes the desired information about the preload of the transmission accessible. In the table, the parameters required for calculating the weighting factors can be found in equations f) and e). The pressure changes occurring in the pressure chambers 8, 10 as a function of a load can be determined using equations c) and d). Equation i) stands for the sum pressure in the case in which no load acts. The total pressure in the load case is calculated according to equation j). TABLE

In the exemplary embodiment according to the invention, the weighting factors β _A and β g can be determined by a suitable choice of the swallowing volumes V _] _ _A and V _] _ g of the two charge pumps 30, 32 in order to determine the required weighting of the pressures in the pressure chambers 8, 10 when the sum is formed to achieve the resulting load moments. The ratio of the swallowing volume is then given by:

Vl, A / i _B = ßA / ß _B = Y = (L _A + X) / (L _B - x)

(see table).

For the practice-relevant case of constant swallowing volumes V, it must be designed for one operating point. For example, if the center position of the piston 7 is selected as the working point, then the stroke x = 0 in this case and thus the required ratio of the swallowing volumes γ = L _A / L _ß = 1 Charge pumps with an identical stroke volume can be used. When designing the charging device for a different operating point, the stroke volumes of the charging pumps must then be adjusted according to the equations listed in the table in order to carry out the above-described leakage compensation and the clamping of the secondary part 4.

In the exemplary embodiment described above, the driven motor is formed by a differential cylinder (5) which is supplied with pressure medium via the charging device (6) and the pump arrangement (2) with the two speed-controlled pumps (12, 14).

FIG. 2 shows an embodiment in which a synchronous cylinder (44) is used instead of the differential cylinder, in which the two pressure chambers (46, 48) have the same volume in the middle position shown. Since in a synchronous cylinder (44) the two pressure chambers (46, 48) are designed with the same cross-section, the area ratio is α = 1. Pump 12 can then be used are dispensed with, via which pressure medium can be conveyed from the tank T into the larger cylinder chamber (8) or in the opposite direction from this tank T in the above-described embodiment in order to compensate for the displacement volume flows. In FIG. 2 above it is also indicated that another consumer, for example a hydraulic motor 50, can also be used instead of the synchronous cylinder 44. Otherwise, the circuit from FIG. 2 corresponds to the exemplary embodiment described above, so that further explanations are unnecessary.

Instead of the charge pumps 30, 32 designed as constant pumps, variable pumps could also be used, although this would be a more precise control or

Regulation of the clamping would allow, however

Increase investment costs. Disclosed is a hydrostatic transmission with an output motor which is supplied with pressure medium via a pump driven by a motor. To compensate for leaks and to clamp the output motor, the hydrostatic transmission is designed with a charging device which, according to the invention, has two charging pumps driven by a common charging motor, via which a pressure chamber of the output motor can be supplied with pressure medium. hydrostatic transmission

primary part

secondary part

hydraulic cylinders

loader

piston

Zylinderräum

annulus

pump

drive shaft

engine

management

pressure line

suction

wave

charging pump

loading motor

charging cable

tank line

Rod cylinders

pressure chamber

hydraulic motor

Claims

claims

1. Hydrostatic transmission with an output motor (5, 44) whose inlet and return connection are connected to at least one pump (14) driven by a motor (18), via the pressure medium between a pressure chamber (8, 10, 46, 48) and another pressure chamber (10, 8, 46, 48) of the driven motor (5, 44) can be conveyed and with a charging device (6), via which the driven motor (5, 44) can be hydraulically clamped on both sides, characterized in that the charging device ( 6) has two charging pumps (30, 32) driven by a common, regulated charging motor (34), each of which has a pressure chamber (8, 10, 46, 48) of the output motor (5, 44) from a tank (T) with pressure medium can be supplied so that leakages can be compensated for and / or the predetermined preload of the driven motor (5) can be set.

2. Hydrostatic transmission according to claim 1, wherein the loading motor (34) is torque-controlled.

3. Hydrostatic transmission according to claim 2, wherein the regulated drive torque (AM) of the loading motor (34) in dependence on: 1, A x PA + ^V 1, B x PB

is adjustable, whereby

^v _{l A} ^v _l B ^: Swallowing volumes of the charge pumps (30, 32) and

P _A 'PB ^: pressure in the pressure chambers (8, 10) of the drive motor is

Hydrostatic transmission according to claim 3, wherein the absorption volume (V) of the charge pumps (30, 32) is the same.

Hydrostatic transmission according to one of the preceding claims, wherein the charge pumps (30, 32) are constant pumps.

6. Hydrostatic transmission according to one of the preceding claims, wherein the drive motor is a differential cylinder (5), the larger cylinder space (8) via a second pump (12) with the tank (T), so that pressure medium between this tank (T ) and the cylinder chamber (8) is conveyable.

7. Hydrostatic transmission according to claim 6, wherein the pumps (12, 14) are designed with the same absorption volume and the area ratio (α) of the differential cylinder (5) is 2: 1.

8. Hydrostatic transmission according to a preceding claim, wherein the existing pumps (12, 14) are speed-controlled.