DE102007016517A1 - Hydrostatic transmission for e.g. tractor, has mechanical torque/rotary speed converter i.e. planetary gear, connected with output shaft, where mechanical torque change is simultaneously balanced by inverse torque change on shaft - Google Patents

Abstract

The transmission has a hydraulic motor e.g. axial-piston motor, with an electrical torque/rotary speed-transformation having a constant displacement volume. A mechanical torque/rotary speed converter i.e. planetary gear, is mechanically connected with an output shaft of the hydraulic motor. A mechanical torque change is simultaneously balanced by an inverse torque change on the output shaft of the hydraulic motor. The torque change takes place via a shorter or longer connection of cylinders in an operating phase with a low pressure connection.

Description

I. Field of application

The Invention is directed to self-propelled, in particular roadworthy, Working machines, z. As tractors, excavators, wheel loaders and certain trucks.

II. Technical background

there the problem is that these are on the road should drive fast (high wheel speed at low required Wheel torque), in heavy ground conditions and under Workload but a very high torque on the drive wheels have to realize, but then at low wheel speed. The torque on the drive wheels and the inverse with it correlated speed must therefore be a very high factor can be spread. In contrast, requires a good efficiency the internal combustion engine a possible constant torque at a high level, resulting only in a relatively narrow speed range is reachable. Therefore it needs between the constant ones Motor and the variable wheel torque a widely spread transmission gear.

mechanical Manual transmissions can easily fulfill this task, but need duckling with frequent switching one train interruption via a clutch and / or a high construction cost, especially for a desired Automation of switching operations or avoidance of train interruption. That's why self-propelled machines - the ones for Need the line drive anyway pressurized oil - often a hydraulic / mechanical traction drive, in which the output shaft of the internal combustion engine drives a hydraulic unit that over Gear stages with the drive axle and the drive wheels is coupled. This unit usually consists of one Pump and a motor, where at least the displacement volume the engine is adjustable.

These Solution, however, is associated with significant disadvantages. The so-called "displacement control", by means of Adjustment of the swash plate or the eccentric, costs a lot of power and requires a heavy hydraulic device, which reacts accordingly slowly, is expensive and carries losses brings. In addition, with axial piston machines, the distance goes from the middle angular position of the disc increasingly at the expense the efficiency. A spreading factor over 4 is therefore not more practicable and the losses can, in part-load operation, add up to one third of the power of the internal combustion engine.

Therefore, the development tends to torque change at a constant displacement volume, by controlling the time proportion, wherein the engine receives pressure oil during one revolution. So there are radial piston engines, whereby - as for example in the WO 2005/095800 described - per revolution for each cylinder between drive and idle (or low pressure running to avoid cavitation) is decided. If at least one cylinder is to drive, the torque can be changed by a factor of 6 to 8. A cylinder with partially rotatable valve plate, according to the DE, achieves a similar value. A bridge between the two valve openings can be displaced with respect to the other, whereby the cylinder chamber can be connected to the high and low pressure connections for a shorter or longer time and the supply pressure with tank pressure is reduced can.

The, in comparison to adjusting motors, size spreading factors, however, require an equally greater dimensioning, while - at least in the Axialkolbenvariante - the oil flow even multiplied by the spreading factor accordingly. It also offers spreading factor 8th not yet what is increasingly demanded by the market and offered by mechanical gearboxes.

III. Presentation of the invention

It It is therefore an object of the invention to provide the time-controlled axial piston and radial piston engines in such a way that their translation range the of mechanical gears at least equal, in a competitive Framework of costs, losses and sizing. The task becomes solved by the main claim 1. Advantageous embodiments emerge from the dependent claims.

Therefore the motor drives the wheel or axle via a planetary gear set at. This is not new in itself. Are known hydraulic motors, with Collaborate planetary sets, which in pre-election stages switchable or in a particular sub or translation are fixed. Also there are hydraulic motors that are in contact with planets form the drive switchable transmission gear. There However, both work rather side by side, because the drive energy over distributed to them before later - summed up - on to get the wheels.

In contrast, hydraulic motor and planetary gear according to the invention interact in proper interaction. The time control costs little power and thus little time. Even the largest possible torque change lasts only milliseconds and can be synchronized with an opposite torque adjustment of the abruptly switching planetary gear. As a result, the engine / planetary gear unit functions as a continuously variable, load-switchable car matic translation gear, whose spreading factor is the product of both individual spreading factors and even if you halve the spreading factor of the motor to 4, which is equal to the mechanical competition effortless, with low installation dimensions, modest costs and low losses.

The Invention will be explained with reference to FIGS. Show it:

I. Timing of an axial piston constant-speed motor;

II. Mounting and switching positions of the planetary gear;

III. Axial piston constant-displacement motor with cooperating hydraulic and mechanical torque adaptation;

IV. Interaction of hydraulic and mechanical torque adjustment.

I , is taken from the DE and shows the valve plate ( 7 ) of a timed axial piston motor It consists of a rotatable outer ring ( 8th ) and a stationary inner part ( 9 ), wherein the usual two valve openings between the cylinder chambers and the oil ports here exemplarily connect at the point A, where the chamber is smallest during the rotation, to an opening. The bridge, which separates the two valve openings in adjusting motors at this point, became the inner part reaching projection on the outer ring ( 10 ). The ring is over a toothing ( 11 ) of an electric motor ( 12 ) rotatable to the left or right, controlled by a computer, which is informed of the need situation by a sensor. By the rotation of the projection moves within the now a valve opening and thus changes the intake ratio of high and low pressure oil: the torque. Since the projection is displaceable over the point A, the control functions in both directions of rotation or driving.

II.a. Contains the basic form of the planetary gear ( 1 ), which is equally suitable for the cylinder-controlled radial piston motor and the pressure-variable axial piston motor. The output shaft ( 2 ) of the engine drives the sun gear ( 3 ), the planet carrier ( 4 ) acts as the output shaft of the transmission ( 6 ). The ring gear ( 5 ) can be switched in three positions: In position I, it is firmly connected to the sun gear or (not shown here) the planet carrier, the gear turns as a block, the ratio is 1: 1. In position II, the ring gear is braked, the planets roll on its sprocket, the planet carrier rotates in the determined by the numbers of teeth of ring gear and sun gear ratio slower than the sun gear (this has, for example, only half as many teeth, slowing down the speed by factor 3, translation 1: 1/3). In position III. the ring gear is neither firmly connected nor braked; it moves freely, the power flow is interrupted.

II.b. vice versa shows the basic form: the output from the engine drives the planet carrier, the output from the transmission is taken over by the sun gear. It results in the translation 1: 3. This variant allows higher wheel speeds and is especially suitable for the slower rotating radial motors.

II.C. shows two planetary gear sets in a row, wherein the planet carrier of the first is also the sun gear of the second. The translation range expands to 1: 1/9. The variant offers very large moments at low speed, and is intended primarily for axial motors in so-called heavy duty applications.

III. shows a design according to Axialkolbenbauart, the engine and planet are advantageously flanged to a drive unit. The average D-DD refers to the in I , shown valve plate ( 7 ). Synchronous with a change in the planetary gear set, the motor performs an equal but opposite torque / speed conversion; These processes thus do not make the torque and speed of the output shaft noticeable. Since the rotation of the outer ring lasts only milliseconds, but still longer than a switch in the planetary gear set, this first switches to the intermediate position III and only after the said milliseconds in the appropriate position I or II. The same applies to the radial piston motor; turning on or off one or more cylinders takes even less time.

The IV. illustrate both the constant torque adjustment in the engine as its sudden torque changes to compensate for a simultaneous, but inverse translation change in the planetary gear. IV.A. concerns the axial piston variant. The drive starts in the short translation. The driver regulates the speed by means of the volume flow generated by the pump - in this example - 399 bar constant pressure. The computer-controlled electric motor meanwhile turns the outer ring of the valve plate in the engine, so that low-pressure oil virtually "dilutes" the high-pressure oil up to the pressure actually required for the traction drive.When the pressure drops below 100 bar, the transmission changes to the long gear ratio The electric motor rotates the outer ring back: the low pressure component decreases abruptly, the pressure - ie the torque - jumps to 300 bar, while the engine speed with a factor of 3 goes back exactly to the level that the reduced oil flow at the long gear for the same permanent wheel speed needs. The translation remains long until the pressure exceeds 399 bar. At this moment, the planets switch again briefly, the pressure drops back to 133 bar, the engine speed increases accordingly and the wheel speed remains untouched by everything. As long as the pressure is above 100 bar, the translation remains short. The translation spread has a factor of 4 × 3 = 12; at two planetary gear sets 36.

The system is stable if the momentum jump of the planets (in this case factor 3) is significantly smaller than the torque range of the motor (in this case factor 4). This implies that a relatively small extension of this range allows a larger planetary jump, which multiplies the translation spread - how IV.B. illustrated by the example of a cylinder-controlled engine with six cylinders, of which per revolution at least one cylinder drives (factor 6). The planetary set skips z. With a factor of 4. The translation spread reaches a factor of 24.

However, large spreading factors solve the task only partially; Also, the costs and losses of the hydrostatic drive should be brought to the level of mechanical competition. This is achieved if a free-piston engine is used as the upstream drive unit. Being freely in the cylinder reciprocating piston compresses the gas mixture in the compression stroke and pumps oil in the expansion stroke to pressure. Chemical energy is converted directly into hydraulic; Crankshaft and separate pump are unnecessary. A variant works particularly efficiently, which runs only with concrete performance demand, and whereby cycle time and piston movement are always the same and optimized independently of frequency and external circumstances; like in the EP 1232335 explained. Their control range - at the same time optimum range - goes from close to zero to the highest frequency. The efficiency is significantly better than that of conventional engines and hydraulic pump units, and the production is much cheaper. In addition, she works very wear-resistant.

Also the free piston engine would be served with this connection. He supplies constant pressure oil. Until recently, he stood in the way of his use. A traction drive, which only has the torque spread of an adjusting motor, and a working drive, which verzich ten to the variable working pressure of a variable, are only partially marketable. Meanwhile have hydrotransformers, such as in the EP 0882181 B1 described this problem solved for the linear working drive (cylinder); they convert an input current at a certain pressure into an output current at a different pressure. So far, however, was still missing the hydrostatic drive, which realizes a market-compliant spread on the basis of a constant supply pressure. In this sense, the proposed hydraulic gear at the same time also form the missing link in terms of a constant pressure system for self-propelled machines, in which the hydraulic circuit secondary, ie the demand pressure is controlled - much easier than in a primary control over the supply current, as is customary today is.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 2005/095800 [0005]
• - EP 1232335 [0022]
• EP 0882181 B1 [0023]

Claims (5)

Hydrostatic transmission, consisting of a hydraulic motor with electric torque / speed conversion at a constant displacement, and connected to the output shaft of the hydraulic motor mechanical torque / speed converter, characterized in that a mechanical torque change at the same time by an equal inverse torque change to the output shaft of the Hydraulic motor is balanced. Transmission according to claim 1, characterized that the hydraulic motor is an axial piston motor with constant Displacement volume is whose torque change by shorter or longer connection of the cylinders takes place in its working phase with the low-pressure connection. Transmission according to claim 1, characterized that the hydraulic motor is a radial piston motor with constant Displacement volume is whose torque change by switching the individual cylinders from drive to idle or vice versa. Transmission according to claim 1, characterized that the mechanical torque / speed converter is a planetary gear is, and the output shaft of the hydraulic motor rotatably connected to either the sun gear of the planetary gear, wherein the web acts as the output shaft of the hydrostatic transmission, or with the planet carrier of the planetary gear, wherein the Sun gear acts as the output shaft of the hydrostatic transmission. Transmission according to one of the preceding claims, characterized in that a free-piston engine to the hydraulic motor supplied with pressure oil.