DE102021133256A1 - Hydrostatic-mechanical power split transmission - Google Patents

Abstract

Power-split transmission for a drive train of a vehicle with a mechanical branch and a hydrostatic branch. The hydrostatic branch of the power-split transmission includes a hydrostatic variable displacement pump and a hydrostatic variable displacement motor in a bent-axis design with a valve segment for adjusting the displacement volume of the hydrostatic variable displacement motor. The maximum swept volume of the hydrostatic variable displacement motor is greater than the maximum swept volume of the hydrostatic variable displacement pump

Description

The present invention relates to hydrostatic-mechanical power-split transmissions according to the preamble of claim 1.

Hydrostatic-mechanical power-split transmissions are often used in agriculture to drive tractors, for example. However, such power-split transmissions can also be used to drive auxiliary drives in agriculture or for other vehicles or drive trains outside of agriculture, such as road construction machines or even trains. Hydrostatic-mechanical power-split transmissions combine the advantages of mechanical transmissions and hydrostatic transmissions, so that a high degree of efficiency is achieved and, at the same time, infinitely variable speed adjustment is possible. Another advantage lies in the area of energy consumption due to the possibility of continuous speed adjustment without torque interruption.

Hydrostatic-mechanical power-split transmissions split an incoming power flow into a mechanical and a hydrostatic branch. The hydrostatic branch consists of a hydrostatic variable displacement pump and a hydrostatic variable displacement motor. Often, particularly in drive applications, hydrostatic adjustment units are used in an axial design, with the pump being able to be designed as a swash plate pump and the motor or motors being skewed axis motors. The displacement volume of the hydrostatic variable motor is adjusted by means of a yoke, with a yoke being provided for each hydrostatic variable unit in the hydrostatic branch of power-split transmissions. Yoked bent axis motors offer excellent hydrostatic drive transmission efficiency. In propulsion applications in particular, good efficiency is important in order to reduce the fuel consumption of the driven vehicle.

So revealed US 6,257,119 B1 an exemplary embodiment of a hydrostatic adjustment unit whose displacement volume is adjusted by pivoting a yoke. The yoke is held in a housing of the adjustment unit by means of pivots and is pivoted by an adjustment device. The adjusting device consists of elongated rods which form a ball and socket joint with the yoke.

However, swash plate adjustment units, which are adjusted via a yoke, require a relatively large amount of space due to the pivotable yoke, the associated hydraulic lines and the yoke adjustment device. Therefore, yoke-type bent-axis units are also expensive, requiring complex construction and a large number of parts. The use of hydrostatic-mechanical power-split transmissions, which are equipped with yoke-controlled bent-axis units according to the prior art, is therefore favorable since a large adjustment range of the power-split transmission is generally required.

It is therefore an object of the invention to provide an economical power-split transmission with high efficiency, but with a simplified structure and correspondingly lower production costs than in the prior art.

A power-split transmission according to the invention can be used, for example, in a drive train of a vehicle. The power split transmission has a mechanical branch and a hydrostatic branch. The hydrostatic branch comprises a hydrostatic variable displacement pump and a hydrostatic variable displacement motor in bent-axis design, which are fluidically connected to one another. In other words: A hydrostatic transmission is provided in the hydrostatic branch. The hydrostatic variable displacement motor in bent-axis design has a tilting cylinder block. If the angle of inclination between an axis of rotation of the cylinder block in relation to the axis of rotation of an output shaft of the hydrostatic variable displacement motor is increased, the displacement volume of the hydrostatic variable displacement motor increases. If the inclination angle is reduced, the displacement volume is reduced. The speed behaves inversely and is minimal at the maximum angle of inclination or maximal at the minimum displacement volume, assuming a constant flow through the hydrostatic variable motor. Since the mode of operation of a hydrostatic adjusting motor with a bent-axis unit is known to a person skilled in the art, a detailed description of the mode of operation of this type of hydrostatic unit is not provided.

According to the invention, the displacement volume of the hydrostatic variable displacement motor, i.e. the angle of inclination of the cylinder block, is adjusted by means of a valve segment. The valve segment is housed in the hydrostatic variable displacement motor housing and is coupled to the hydrostatic variable displacement motor cylinder block, whereby a set position of a variable displacement element is transmitted to the cylinder block while hydraulic fluid is directed to and from the cylinder bores.

According to the invention, the maximum swept volume of the hydrostatic variable displacement motor is greater than the maximum swept volume of the hydrostatic variable displacement pump. The maximum stroke volume is the displacement volume at which the hydrostatic variable displacement pump or the hydrostatic variable displacement motor is adjusted to its maximum angle of inclination. The maximum stroke volume is therefore the maximum displacement volume of the hydrostatic variable displacement pump or the hydrostatic variable displacement motor per revolution. When designing the specific stroke volume, the maximum stroke volume of the pump depends on the power of a drive motor, e.g. B. drives the hydrostatic variable displacement pump. The maximum swept volume of the hydrostatic variable displacement motor depends on the required maximum power and the required maximum speed of an output shaft that is driven by the hydrostatic variable displacement motor.

In the prior art, the displacement volume of the hydrostatic variable motor is adjusted by means of yoke technology, while valve segment technology is used according to the invention. When designing a power-split transmission for driving a vehicle, the focus is on the torque and speed behavior of the vehicle. The yoke technology allows a larger maximum angle of inclination of the axis of rotation of the cylinder block in relation to the axis of rotation of the output shaft of the hydrostatic variable displacement motor. For example, a yoke may provide tilt angles from -45° to +45°, where 0 to 45° may be used when the yoke is incorporated into a prior art variable displacement hydrostatic motor of a hydrostatic transmission. This provides a larger range of inclination angles for adjusting the displacement volume of the hydrostatic motor than with valve segment technology, which provides inclination angles of 0° to 32°, for example. In addition, the yoke technology has a large cross-section for guiding the hydraulic fluid to the cylinder bores in the cylinder block over the entire tilting range. With valve segment technology, the cross-sections are smaller, especially with large angles of inclination.

According to the invention, the maximum swept volume of the hydrostatic variable displacement motor is greater than the maximum swept volume of the hydrostatic variable displacement pump. As a result, when using a valve segment, the disadvantage of a reduced tilt angle for adjusting the displacement volume is compensated for by the higher swept volume of the hydrostatic variable displacement motor, since the motor with a high maximum swept volume is supplied with a small fluid flow from the pump with a lower swept volume. Since the engine is operated below its maximum flow rate, the available area for fluid flow in a variable displacement hydrostatic engine with valve segment technology has little effect on the performance of the hydrostatic transmission. Rather, the engine is optimized for the torque and speed requirements of the hydrostatic transmission, which are not negatively influenced by the use of valve segment technology. A design that is simplified compared to the yoke technology is thus provided.

Several embodiments for a hydrostatic variable displacement pump are known to those skilled in the art. All of these embodiments fall within the scope of the invention. In one embodiment of the invention, the hydrostatic variable displacement pump is preferably also designed as a bent-axis design. The displacement volume can be adjusted by means of a valve segment or a yoke. A yoke is preferably provided, e.g. with a tilting angle range of +/- 45°, since the pump should be pivotable in both directions perpendicular to the longitudinal axis. Furthermore, the demands on the variable displacement pump are aimed at the hydraulic delivery capacity, whereby according to the invention the maximum displacement of the pump unit can be less than the displacement of the motor unit.

However, a person skilled in the art can also provide a hydrostatic variable displacement pump with a radial piston design, e.g. if the axial dimensions of the hydrostatic branch are to be reduced. An axial piston pump with a swash plate design can be provided if, for example, the shaft of the axial piston pump is to protrude in the axial direction on both end faces of the cylinder block, or if the angle of inclination is to be adjustable in both directions relative to the longitudinal axis of the hydrostatic axial piston pump. This means that with a swash plate assembly, greater than zero pitch angle adjustment can be provided to change the direction of flow through the hydrostatic axial piston assembly.

The power-split transmission according to the invention can further have a second hydrostatic variable displacement motor of the bent-axis type. The second hydrostatic variable displacement motor has a valve segment or a yoke for adjusting the displacement volume. A valve segment is preferably provided for the second hydrostatic variable displacement motor. The second hydrostatic motor can be supplied with hydraulic fluid by the same hydrostatic variable displacement pump as the (first) hydrostatic variable displacement motor. This means that the hydrostatic pump is able to supply both the first hydrostatic variable displacement motor and the second hydrostatic variable displacement motor with hydraulic fluid at the same time. The performance of the hydrostatic variable displacement pump is dependent on the hydrostatic variable displacement motors distributed to the mechanical loads acting on the motors.

The invention also includes the fact that more than two hydrostatic adjusting motors are provided in the hydrostatic branch of the power-split transmission. For example, a third motor could be provided to drive a PTO shaft or a third axle of the vehicle. Alternatively, a hydrostatic adjusting motor could also be arranged on each wheel of the driven vehicle.

If a second motor is provided, at least the sum of the maximum displacements of the first and second hydrostatic motors according to the invention is greater than the maximum displacement of the hydrostatic variable displacement pump. The maximum swept volume of each of the hydrostatic variable displacement motors is preferably greater than the maximum swept volume of the hydrostatic variable displacement pump. In this case, too, the second hydrostatic variable motor can be equipped with a valve segment instead of a yoke for the reasons described in connection with the (first) hydrostatic variable motor in order to make the hydrostatic branch of a power-split transmission according to the invention simpler and to reduce the system-related costs. With two or more engines in the hydrostatic branch, the occurrence of large amounts of fluid through each engine is even less likely, since the sum of the fluid flows divided between the engines must be provided by a single hydrostatic pump with a maximum displacement less than the sum of the maximum swept volume of the hydrostatic bent axis motor(s).

According to the invention, the valve segment can be pivoted via an adjustment element that can be actuated hydraulically, electrohydraulically, mechanically or pneumatically. The adjustment element can be mechanically coupled to the valve segment, for example. In one embodiment of the invention, an adjustment unit or adjustment device comprises a servo piston. The adjusting element, which is arranged in a servo unit, for example, can move with the servo piston along a longitudinal axis of the servo cylinder. This defines two pressure chambers, one on each side of the servo piston. The pressure chambers can be supplied with pressurized hydraulic fluid in order to move the servo piston. The servo piston is coupled to the valve segment via the adjusting element, e.g. B. via a pin that interacts with the servo piston and the valve segment.

Preferably, e.g. in order to keep the dimensions/installation space of the hydrostatic transmission of the hydrostatic branch as small as possible, the hydrostatic variable displacement pump and the at least one hydrostatic variable displacement motor can be arranged in a common housing. A common housing protects the hoses and lines of the hydrostatic transmission. In addition, the hydrostatic variable displacement units, i.e., the variable displacement pump and the at least one variable displacement motor, can be arranged to minimize the number and complexity of additional components.

The position of the adjustment element or of components of the adjustment unit can be determined by a mechanical, electromechanical or electrical adjustment sensor. In one embodiment of the invention, a rotary encoder is arranged in an end area of the adjustment unit. The rotary encoder interacts with one or more longitudinally movable parts of the adjustment unit, so that a longitudinal displacement of parts of the adjustment unit causes the rotary encoder to rotate. The adjustment sensor may be able to detect the rotation of the rotary encoder and generate an electrical signal corresponding to the measured longitudinal displacement of parts of the adjustment element. The rotary encoder can be a bush, for example, which is arranged in a longitudinally displaceable manner in an end region of a servo cylinder of the adjustment unit. Longitudinal displacement of a servo piston mechanically coupled to the sleeve causes rotation of the sleeve. The rotation can also be detected, for example, by an inductive sensor that generates an electrical signal based on the rotation of the bush.

In a further exemplary embodiment of the invention, the adjusting element can be controlled electrically between a first end position and a second end position. For example, an electromagnet could be provided, which can move parts of the adjustment unit by means of an electromagnetic force. The end positions can be adjustable, e.g. B. by end stops that can be attached to a housing of the adjustment in a suitable position.

According to the invention, the valve segment of the at least one hydrostatic variable motor serves to supply and discharge hydraulic fluid to and from the cylinder bores in the cylinder block of the hydrostatic variable motor. For this purpose, the valve segment can have first and second kidney-shaped pressure connections on a sliding surface of the valve segment. The kidney-shaped pressure connections are preferably designed to be rotationally symmetrical to the axis of rotation of the cylinder block of the hydrostatic variable displacement motor. The fluid channels that carry hydraulic fluid to and from Pressure chambers in the cylinder block are arranged on an arc of a circle whose center coincides with the axis of rotation of the cylinder block and whose diameter is substantially equal to the center line of the first and second kidney-shaped pressure ports. That is, the radially outer edges of the fluid passages and the radially outer edges of the kidney-shaped pressure ports are in the same radial position relative to the axis of rotation of the cylinder block. A plurality of concave hydrostatic bearing recesses may extend radially outward from the radially outer edges of the first and second pressure ports on the sliding surface of the valve segment.

The displacement volume of the hydrostatic variable displacement pump can preferably be adjusted independently of the at least one hydrostatic variable displacement motor. If more than one hydrostatic variable displacement motor is provided, the displacement of each hydrostatic unit, i.e. each hydrostatic variable displacement motor and each hydrostatic variable displacement pump, can be adjusted separately. This enables the use of stepless driving states with a large hydrostatic transfer rate depending on the current driving situation of the vehicle. For example, the hydrostatic pump could be pivoted to maximum displacement and the hydrostatic motor(s) to zero displacement if the hydrostatic branch of the power split transmission is to be locked. In this case, the entire power flow is transmitted via the mechanical branch of the power-split transmission.

According to the invention, the power flows can be brought together via the first hydrostatic variable displacement motor of the hydrostatic branch and via the mechanical branch in order to drive a first drive shaft which, for example, drives a first axle of the vehicle. In other words, both the first hydrostatic variable displacement motor of the hydrostatic branch and the mechanical branch cooperate in rotation, preferably via a combining component, e.g. via a gear set with the first drive shaft. The power flows can be combined, for example, by interacting with a common shaft or a common gearbox. However, a person skilled in the art can also use other concepts for combining the power flows via the mechanical branch and the first hydrostatic variable displacement motor.

Similar to the previous example, the blocking of the hydrostatic branch, z. B. by pivoting the adjusting motor to 0 °, d. H. to zero flow, for example in driving situations where a high rotational speed of the axle with low torque is required, e.g. B. when a high speed of the vehicle is required while driving on a paved road. With this configuration, the vehicle speed essentially depends on the speed of the drive motor and the mechanical transmission ratio between the drive motor and the drive shaft.

In one exemplary embodiment, the output shaft of the hydraulic motor is connected in a rotationally fixed manner to a first axle via a reversing gear. For example, the reverse gear may be capable of establishing a direct rotary connection, or alternatively a positive gear ratio, between the first axle and the drive shaft when a first clutch is engaged and a second clutch is disengaged. Alternatively, the reverser can establish a negative gear ratio using a first gear set when the first clutch is disengaged and the second clutch is engaged. This type of construction avoids the disadvantage that, without the reversing gear, the hydraulic power is fed back via the mechanical branch when the working machine is being driven in reverse. Instead, with the help of the reversing gear, the direction of rotation of the drive shaft of the hydrostatic motor remains constant even if the direction of rotation of the first axis changes, and there is no recirculation of rotational energy when the power flows from the hydrostatic variable displacement motor and the mechanical branch are combined.

According to the invention, a second hydrostatic variable displacement motor can drive a second axle of the vehicle. In this configuration, the power flows in the hydrostatic branch of the power-split transmission can be adjusted accordingly depending on the environmental conditions, e.g. the load acting on the wheels of the vehicle. For example, the front axle and the rear axle of a vehicle could each be driven by a hydrostatic variable displacement motor. Such a vehicle with two driven axles is able to make tighter turns compared to a vehicle with only one driven axle. Since e.g. For example, when the front wheels have to turn a little faster in corners, a driven front axle can pull the vehicle in the corner because the power is transferred to the front axle. This effect can B. be useful in agriculture or forestry. This effect can be amplified if each wheel on the front axle is driven by a separate hydrostatic motor, since the inner wheel turns slower than the outer wheel when cornering. In this way, a differential gear can also be dispensed with.

In a further embodiment of the invention, a (third) clutch is provided between the first axle and the second axle. The clutch can create a mechanical connection between the two axles or between the drive shafts of the hydraulic motors driving the axles, which causes both axles to be mechanically coupled and, for example, to rotate at the same speed. If the output torque of a hydrostatic variable displacement motor is not supported, e.g. B. because the wheels of the vehicle are slipping on the ground, the slipping wheels provide less support for the hydrostatic power than the non-slipping wheels driven by the other engine. Since the flow of power always takes the path of least resistance, all of the power would flow through the spinning wheels of the axle, which are connected to the first hydrostatic variable displacement motor. Consequently, all of the hydrostatic power generated by the variable displacement hydrostatic pump would be directed to the engine with the spinning wheels. After closing the (third) clutch, however, the torque can be mechanically transferred from the slipping axle of one hydrostatic motor to the non-slipping axle, which is connected to the other hydrostatic variable displacement motor. Hatching conditions often occur in agriculture and forestry. The (third) clutch and the intelligent transfer of torque between the two axles of the vehicle ensure that the vehicle's traction can be maximized in every driving situation.

Since opening the third clutch offers the possibility of mechanically separating the first axle from the second axle, the third clutch can also be opened when the direction of rotation of one axle is opposite to the direction of rotation of the other axle, e.g. B. when a reverser reverses the direction of rotation of an axle compared to its associated drive shaft. Then the other axis can rotate freely without the gear ratio between the two axes leading to mechanical restrictions.

In an alternative embodiment of the invention, the (third) clutch is provided between the output shaft of the first hydrostatic motor and the output shaft of the second hydrostatic motor. As a result, a mechanical connection can be established between the slipping output shaft and the non-slipping output shaft, similar to the coupling between the axles of the vehicle described above.

According to one embodiment of the invention, the power-split transmission comprises a planetary gear whose planetary carrier is driven, for example, by a drive motor, e.g. an internal combustion engine or an electric motor. A ring gear of the planetary gear drives the hydrostatic variable displacement pump of the hydrostatic branch and a sun gear of the planetary gear drives the mechanical branch. The hydrostatic variable displacement pump of the hydrostatic branch preferably directs pressurized hydraulic fluid to two hydrostatic variable displacement motors, the displacement volume of which is adjusted via a valve segment. The split power streams via the hydrostatic branch or the mechanical branch can be connected by a summation gear that z. B. drives an output shaft or an axle of the vehicle.

• 1 zeigt eine schematische Darstellung eines Leistungsverzweigungsgetriebes gemäß einer ersten Ausführungsform der Erfindung.
• 2 zeigt eine schematische Darstellung eines Leistungsverzweigungsgetriebes gemäß einer zweiten Ausführungsform der Erfindung.
• 3 zeigt eine schematische Darstellung eines Leistungsverzweigungsgetriebes gemäß einer dritten Ausführungsform der Erfindung.
• 4 zeigt eine Schnittdarstellung einer beispielhaften Ausführungsform eines hydrostatischen Verstellmotors für ein Leistungsverzweigungsgetriebe gemäß der Erfindung.
• 5 zeigt eine isometrische Ansicht einer beispielhaften Ausführungsform eines Ventilsegments für einen hydrostatischen Verstellmotor für ein erfindungsgemäßes Leistungsverzweigungsgetriebe.

The system according to the invention is explained in more detail below with reference to preferred embodiments of the invention in the accompanying figures. However, those skilled in the art will recognize that the principle according to the invention is not limited to the embodiments shown. Rather, the embodiments shown can be combined or modified in accordance with the present disclosure without departing from the scope of the principle according to the invention.

• 1 shows a schematic representation of a power-split transmission according to a first embodiment of the invention.
• 2 shows a schematic representation of a power-split transmission according to a second embodiment of the invention.
• 3 shows a schematic representation of a power-split transmission according to a third embodiment of the invention.
• 4 shows a sectional view of an exemplary embodiment of a hydrostatic variable displacement motor for a power split transmission according to the invention.
• 5 shows an isometric view of an exemplary embodiment of a valve segment for a hydrostatic variable displacement motor for a power-split transmission according to the invention.

In the following description of preferred embodiments with reference to the accompanying figures, the same reference numerals are used for the same components in different preferred embodiments to improve the comprehensibility and readability of the present description.

1 shows a schematic representation of a power-split transmission 1 according to a first embodiment of the invention. The power-split transmission 1 shares an incoming Power flow ends in a power flow via a mechanical branch 100 and a power flow via a hydrostatic branch 200 . The hydrostatic branch 200 comprises a variable displacement hydrostatic pump 210 which is fluidically connected to a variable displacement hydrostatic motor 250 . In detail, a high-pressure line 202 connects the output of the hydrostatic variable displacement pump 210 to the input of the hydrostatic variable displacement motor 250. A low-pressure line 204 connects the input of the hydrostatic variable displacement pump 210 to the output of the hydrostatic variable displacement motor 250. The hydrostatic variable displacement motor 250 is designed in a bent-axis design and has a valve segment 260 (see 4 & 5 ) for setting the displacement volume of the hydrostatic variable displacement motor 250. According to the invention, the hydrostatic variable displacement motor 250 has a larger maximum stroke volume, i.e. a larger maximum displacement volume per revolution, than the hydrostatic variable displacement pump 210.

Although a valve segment 260 limits the displacement range of an inclination angle of the variable displacement hydrostatic motor 250 compared to a yoke, the maximum displacement of the variable hydrostatic motor 250 is still matched with the displacement of the variable displacement hydrostatic pump 210 .

The power flow supplied can be provided by a drive motor 5, for example. The drive motor 5 can be an internal combustion engine or an electric motor, for example. The power of the drive motor 5 can be divided by a planetary gear 10, for example. For example, the incoming power flow can drive a planet carrier 12 of the planetary gear set 10 . In a preferred embodiment, the planet carrier 12 carries a variably selectable number of planets which interact with a sun gear 16 and a ring gear 14 . Ring gear 14 drives hydrostatic variable displacement pump 210 of hydrostatic branch 200 . The sun gear 16 meshes simultaneously with the output of the variable displacement hydrostatic motor 250 and with the planets carried by the planet carrier 12 . In addition, the sun gear 16 interacts with a first input shaft 25 of the power-split transmission 1, which transmits power to a first axle 20 of a vehicle in which the power-split transmission 1 is installed. The first axle 20 can be, for example, the rear axle of the vehicle. However, the first axle 20 can also be the front axle of the vehicle. One skilled in the art will recognize that driving the vehicle's first axle 20 would be sufficient to propel the vehicle. As in the embodiment according to 1 shown, however, a second axle 40 can be provided, which is also connected via a second drive shaft 45 to the sun gear 16 in rotation. Therefore, the sun gear 16 can drive both the first axle 20 and the second axle 40 via the first drive shaft 25 and the second drive shaft 45, respectively. The second axle 40 can be the front axle of a vehicle, for example.

In order to create other operating options in addition to the drive, a power take-off shaft 110 can be provided. The PTO shaft 110 can, for example, interact directly with an output shaft of the drive motor 5, i. H. with the shaft that supplies the power-split transmission 1 with the power of the engine 5. Consequently, in this embodiment, the direction of rotation of the PTO shaft 110 is independent of the direction of rotation of the power split transmission 1. However, a person skilled in the art could choose a different arrangement of the PTO shaft or the power distribution via the planetary gear set.

2 shows a schematic representation of a power-split transmission 1 according to a second embodiment of the invention. The power-split transmission 1 according to 2 has essentially the same features as the power-split transmission 1 according to with 1 illustrated embodiment. In order to improve the legibility and comprehensibility of the present description, a detailed description of the parts that are already associated with the description of 1 were specified, waived.

The hydrostatic branch 200 of the power split transmission 1 according to 2 includes in addition to the components of in 1 illustrated embodiment a second hydrostatic variable displacement motor 300. The second hydrostatic variable displacement motor 300 is fluidly integrated into the hydraulic circuit formed between the hydrostatic variable displacement pump 210 and parallel to the first hydrostatic variable displacement motor 250. An input of the second hydrostatic variable displacement motor 300 is connected to the high pressure line 202 and an output of the second hydrostatic variable displacement motor 300 is connected to the low pressure line 204 .

Consequently, the hydrostatic variable displacement pump 210 supplies the first hydrostatic variable displacement motor 250 and the second hydrostatic variable displacement motor 300 with hydraulic fluid. The second hydrostatic variable displacement motor 300 can have a valve segment 260 or a yoke for adjusting its displacement volume. A yoke would offer a larger range of possible angles of inclination compared to valve segment technology, ie a larger angle of inclination to which the displacement volume of the hydrostatic adjustment mo tors 300 can be adjusted. Although this would increase efficiency, it would result in higher costs for the second motor compared to using a valve segment hydraulic motor with the same displacement. According to the invention, therefore, a valve segment 260 (see 4 & 5 ) as adjusting element 270 of second hydrostatic adjusting motor 300. A valve segment hydraulic motor 260 has a simpler construction than a yoke hydraulic motor, so that the design, manufacture, assembly and maintenance of the power split transmission 1 can be facilitated/simplified.

In order to match the maximum displacements of the first and second hydrostatic variable displacement motors 250 & 300 to the maximum displacement of the hydrostatic variable displacement pump 210, at least the sum of the maximum displacements of the hydrostatic variable displacement motors 250 & 300 is greater than the maximum displacement of the hydrostatic variable displacement pump 210. In one case, the hydrostatic variable displacement pump 210 have a higher maximum displacement than each of the two hydrostatic variable displacement motors 250 & 300, with the sum of the maximum displacements of the two hydrostatic motors 250 & 300 being greater than the maximum displacement of the hydrostatic variable displacement pump 210. The hydrostatic variable displacement pump 210 is in able to pump a specific maximum amount of hydraulic fluid, which in most operating cases is supplied neither exclusively to the first hydrostatic motor 250 nor exclusively to the second hydrostatic motor 300, but almost always to a combination of the first hydrostatic variable motor 250 and the second hydrostatic variable motor 300. One skilled in the art will understand that alternatively, the maximum displacement of each of variable displacement hydrostatic motors 250 and 300 may be greater than the maximum displacement of variable displacement hydrostatic pump 210. In this case, the considerations above apply, but each of hydrostatic motors 250 and 300 would also be capable of receiving the hydraulic fluid supplied by the variable displacement hydrostatic pump 210 alone.

In the embodiment according to 2 drives the second hydrostatic variable motor 300 via a second drive shaft 45 a second axle 40 of the vehicle, z. B. the front axle. In other words: the first axle 20 of the vehicle is driven by the first hydrostatic variable displacement motor 250 and the second axle 40 of the vehicle is driven by the second hydrostatic variable displacement motor 300 . As a result, both axles can be driven by the power distributed to the hydrostatic branch 200 of the power-split transmission 1 in certain operating states. By adjusting the displacement of the first hydrostatic motor 250 in relation to the displacement of the second hydrostatic motor 300, the ratio of the torque transmitted to the first axle 20 to the torque transmitted to the second axle 40 can be adjusted according to the current driving situation.

In addition, a (third) clutch 60 can be provided, which couples the rotation of the second axis 40 to the rotation of the first axis 20 (for explanations of the first clutch 124 and the second clutch 128, see 3 ). To this end, a mechanical connection is established between the first axle 20 and the second axle 40 when the clutch 60 is engaged. Depending on the transmission ratio between the two axles 20 and 40, the torque and the rotational speed of one axle are transmitted to the other axle. This can be useful if one of the axles is not supported, for example because the wheels on this axle are spinning. For the sake of simplicity, the mode of operation is explained below using a spinning first axle 20 . However, a person skilled in the art will readily transfer the technical teaching to an embodiment with a slipping second axle 40 .

There are driving situations in which a power-split transmission according to the invention is used in a vehicle which is operated in slippery conditions, for example in the field in wet weather. For example, if the vehicle's first axle 20 slips, the torque transmitted to that axle will no longer be supported. Since the power flow always takes the path of least resistance, the entire power flow would flow away via the axle 20 slipping. However, if the clutch 60 is closed, a mechanical connection is established between the slipping first axle 20 and the second axle 40, which still has traction. Therefore, the power that would otherwise be transferred to the spinning axle 20 is diverted to the traction axle 40 and the vehicle continues to be propelled.

A fourth clutch 62 may be provided to provide the ability to decouple the second variable displacement hydrostatic motor 300 from the second axle 40 . If, for example, a high speed of the vehicle is required, the entire power of the drive motor is transmitted to the first axle 20 via the mechanical branch 100 . In this case, the second hydrostatic motor 300 is not actively rotated by hydrostatic power. According to the embodiment shown, the connection of the second hydrostatic variable displacement motor 300 has of the second axle 40 has a higher gear ratio than the connection between the first hydrostatic variable displacement motor 250 and the first axle 20. As a result, the second hydrostatic motor 300 reaches its maximum rotational speed earlier than the first hydrostatic motor 250. Therefore, drag losses would be Overspeed of the second hydrostatic variable motor 300 occur when the second hydrostatic variable motor 300 would still be coupled to the second axle 40. Opening the fourth clutch 62 separates the second hydrostatic variable displacement motor 300 from the second axle 40, and drag losses can be avoided.

3 shows a schematic representation of a power-split transmission 1 according to a third embodiment of the invention. The power-split transmission 1 according to 3 has some of the same features as the power-split transmission 1 according to the 1 and 2 illustrated embodiments. In order to improve the legibility and comprehensibility of the present description, a detailed description of the parts that are already associated with the descriptions of the 1 and 2 were mentioned.

In addition to the characteristics of the 1 and 2 illustrated embodiments includes the embodiment according to 3 a reversing gear 120 between the first drive shaft 25 and the first axle 20. The reversing gear 120 transmits the combined power flow from the drive shaft 25 to the first axle 20. For this purpose the reversing gear 120 has a first clutch 124 which is able to rotationally couple and decouple the first drive shaft 25 to the first axle 20 . The reversing transmission 120 further includes a second clutch 128 capable of coupling and decoupling the first drive shaft 25 to the first axle 20 via a first (reversing) gear set 122 having a negative gear ratio. As an alternative to direct connection between the first input shaft 25 and the first axle 20, a second gear set may be provided which establishes a positive gear ratio between the first input shaft 25 and the first axle 20 when the first clutch 124 is engaged.

With a reverser 120, the direction of rotation of the first drive shaft 25 can be maintained regardless of the direction of the first axis 20. When the first drive shaft 25 rotates with respect to the first axis 20, power can be increased by engaging the first clutch 124 and disengaging the second clutch 128 are transmitted directly. Conversely, if the first driveshaft 25 is to counter-rotate with respect to the first axis 20, power flow may be transmitted through the first gear set 122 to reverse the direction of rotation of the first driveshaft 25 by disengaging the first clutch 124 and engaging the second clutch 128. Since the direction of rotation of the first drive shaft 25 is kept constant regardless of whether the vehicle is running forward or backward, the first variable displacement hydrostatic motor 250 is not forced to change its direction of rotation when the vehicle's running direction is changed. As a result, no power from the hydrostatic branch 200 is fed back to the planetary transfer case 10 via the mechanical branch 100 . As a result, in the hydrostatic branch 200 according to the invention, hydrostatic variable displacement units, i.e. hydrostatic variable displacement motors and hydrostatic variable displacement pumps, can be used with a reduced power rating. By using reduced rated power for the (adjustment) units of the hydrostatic branch 200, the installation space for the power-split transmission 1 according to the invention is reduced in comparison to a power-split transmission known from the prior art, since hydrostatic units of reduced size can be used.

4 shows a sectional view of an exemplary embodiment of a hydrostatic variable displacement motor 250, 300 for a power-split transmission 1 according to the invention. The adjusting motor 250, 300 comprises a rotatable cylinder block 252 with cylinder bores 256 in which working pistons 253 move back and forth. The working pistons 253 seal pressure chambers in the cylinder bores 256, which can be supplied with a pressurized liquid in order to be able to exert a force on the working pistons. The adjusting motor 250, 300 also has an output shaft 254 which defines an axis of rotation 255. The displacement volume of the adjusting motor 250, 300, i.e. the size of the sealed pressure chambers in the cylinder bores 256, is dependent on the pivoting angle between a central axis of the cylinder block and the axis of rotation 255 of the output shaft 254. The larger the pivoting angle, the larger the displacement volume of the adjusting motor 250 , 300.

According to the invention, a valve segment 260 is preferably provided in order to adjust the displacement volume of at least one of the adjusting motors 250 & 300. The preferred embodiment of the valve segment 260 is based on 5 explained. An adjusting element 270, in the case of the embodiment according to 4 a servo piston, is coupled to the valve segment 260 by a pin 258 which engages an adjustment pin 259 fixed to the valve segment 260 . Therefore, the valve segment 260 follows the linear movement of the Adjusting element 270 on a curved guide surface 269. An adjustment of the adjusting element 270 thus causes the pivoting angle of the adjusting motor 250, 300 to increase or decrease.

5 shows an isometric view of an exemplary embodiment of a valve segment 260 for a hydrostatic variable displacement motor 250, 300 for a power split transmission 1 according to the invention. The valve segment 260 is slidably accommodated in a housing 280 of the hydrostatic variable displacement motor 250, 300 and has a sliding surface 268 via which the valve segment 260 is in contact with the rotatable cylinder block 252. Kidney-shaped first and second pressure openings 262 are formed on the sliding surface 268 . Either the first or the second pressure port 262 is connected to a pressure input of the hydrostatic variable displacement motor 250, 300. The other of the two pressure connections 262 is connected to an outlet of the hydrostatic variable displacement motor 250, 300. Because of the particular shape of the first and second pressure ports 262 , hydraulic fluid can be supplied under pressure to one half of the cylinder bores 256 , while hydraulic fluid is discharged from the other half of the cylinder bores 256 . For example, to reduce friction at the sliding surface 268 between the rotating cylinder block 252 and the non-rotating valve segment 260, a hydrostatic bearing may be provided between the mating surfaces of the two components. For example, hydrostatic bearing recesses 264 can be provided on the radially outer and/or peripheral edges 266 of the kidney-shaped first and second pressure connections 262 . The bearing recesses 264 preferably have a concave shape that enables hydraulic fluid to be routed from the pressure ports 262 into the space formed between the contact surfaces of the cylinder block 252 and the sliding surface on the valve segment 260 .

From the above description and the attached figures as well as the claims, it is clear that the power-split transmission 1 according to the invention offers many possibilities and advantages over the prior art. It is also apparent to those skilled in the art that further modifications and changes can be made to a power-split transmission 1 according to the invention without departing from the spirit of the invention. Therefore, all such modifications and changes fall within and embrace the scope of the claims. Furthermore, it should be understood that the examples and embodiments described above are for illustration only and that various modifications, changes or combinations of embodiments suggested by those skilled in the relevant arts fall within the spirit and scope of the present application.

Reference List

1

power split transmission

5

drive motor

10

planetary gear set

12

planet carrier

14

ring gear

16

sun gear

20

first axis

25

First driveshaft

40

second axis

45

Second drive shaft

60

Third clutch

62

Fourth clutch

100

mechanical branch

110

PTO shaft

120

reverse gear

122

First gear set

124

First clutch

128

Second clutch

200

hydrostatic branch

202

high pressure line

204

low pressure line

210

Hydrostatic variable displacement pump

250

First hydrostatic variable displacement motor

252

cylinder block

253

working piston

254

output shaft

255

axis of rotation

256

cylinder bores

258

Pen

259

adjustment pin

260

valve segment

262

First and second connection

264

Hydrostatic bearing recesses

266

Radial outer edges

268

sliding surface

269

guide surface

270

adjustment element

280

Housing

300

Second hydrostatic variable displacement motor

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US6257119B1 [0004]

Claims (17)

Power-split transmission (1) for a drive train of a vehicle, with a mechanical branch (100) and a hydrostatic branch (200), which has a hydrostatic variable displacement pump (210) and a hydrostatic variable displacement motor (250) in a bent-axis design with a valve segment (260) for adjusting the Displacement volume of the hydrostatic variable displacement motor (250), wherein the maximum displacement volume of the hydrostatic variable displacement motor (250) is greater than the maximum displacement volume of the hydrostatic variable displacement pump (210). Power split transmission (1) after claim 1 , wherein the hydrostatic variable displacement pump (210) is designed in a bent-axis design, the displacement volume of which can be adjusted by means of a valve segment (250) or a yoke. Power split transmission (1) after claim 1 or 2 , wherein the hydrostatic variable displacement pump (210) is a radial piston pump. Power-split transmission (1) according to one of Claims 1 until 3 , further comprising a second hydrostatic variable displacement motor (300) of bent-axis design with a valve segment (260) or a yoke for adjusting the displacement volume, wherein the second hydrostatic motor (300) can be supplied with hydraulic fluid flow by the same hydrostatic variable displacement pump (210). Power split transmission (1) after claim 4 , wherein at least the sum of the maximum displacements of the hydrostatic variable displacement motors (250, 300) or the maximum displacement volume of each individual hydrostatic variable displacement motor (250, 300) is greater than the maximum displacement volume of the hydrostatic variable displacement pump (210). Power-split transmission (1) according to one of the preceding claims, in which the valve segment (260) can be pivoted by means of an adjusting element (270) which can be actuated hydraulically, electrohydraulically, mechanically or pneumatically. Power split transmission according to one of the preceding claims (1), wherein the hydrostatic variable displacement pump (210) and the at least one hydrostatic variable displacement motor (250, 300) are arranged in a common housing. Power split transmission (1) according to one of the preceding claims, wherein the position of the adjustment element (270) is measured by a mechanical, electromechanical or electrical adjustment sensor. Power split transmission (1) after claim 8 , wherein the adjustment sensor detects a rotation of a rotary encoder, which is caused by a longitudinal displacement of the adjustment element (270). Power split transmission (1) after claim 8 or 9 , wherein the adjusting element (270) is actuated electrically between a first adjustable end position and a second adjustable end position. Power-split transmission (1) according to one of the preceding claims, wherein the valve segment (260) of the at least one hydrostatic variable displacement motor (250, 300) has kidney-shaped first and second connections (262) for supplying and draining hydraulic fluid into/from fluid channels of a cylinder block (252) of the variable displacement hydrostatic motor (250, 300), and wherein a plurality of concave hydrostatic bearing recesses (264) extends from the radially outer edges (266) of the first and second ports (262) on a sliding surface (268) of the valve segment (260). . Power-split transmission (1) according to one of the preceding claims, wherein the displacement volume of the hydrostatic variable displacement pump (210) and the at least one hydrostatic variable displacement motor (250, 300) can be adjusted independently of one another. Power-split transmission (1) according to one of the preceding claims, wherein the power flows via the first hydrostatic variable displacement motor (250) in the hydrostatic branch (200) and via the mechanical branch (100) are brought together in order to drive a first drive shaft (25) which has a first Axis (20) of the vehicle drives. Power split transmission (1) after Claim 13 wherein the first drive shaft (25) is rotationally connected to the first axle (20) via a reverser (120) capable of direct rotational connection when a first clutch (124) is engaged and a second clutch (128) is disengaged, and to alternate a negative gear ratio established by a first gear set (122) when the first clutch (124) is disengaged and the second clutch (128) is engaged. Power-split transmission (1) according to one of Claims 4 until 14 , wherein the second hydrostatic variable displacement motor (300) drives a second axle (40) of the vehicle. Power-split transmission (1) according to one of Claims 13 until 15 , wherein between the first axle (20) and the second axle (40) a third clutch (60) is provided, which is able to establish a mechanical connection between the first and the second axle (20, 40), the Rotational speed of the first axis (20) mechanically coupled to the rotational speed of the second axis (40). Power-split transmission (1) according to one of the preceding claims, with a planetary gear (10) whose planet carrier (12) is driven by a drive motor (5), with a ring gear (14) of the planetary gear (10) controlling the hydrostatic variable displacement pump (210) of the hydrostatic Branch (200) drives and a sun gear (16) of the planetary gear (10) the mechanical branch (100).

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