GB2351794A

GB2351794A - Hydrostatic propulsion drive

Info

Publication number: GB2351794A
Application number: GB0014111A
Authority: GB
Inventors: Helmut Bracke; Horst Tobias
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 1999-07-08
Filing date: 2000-06-10
Publication date: 2001-01-10
Also published as: DE19931924A1; GB0014111D0; FR2796011A1

Abstract

A hydrostatic drive comprises first hydrostatic motor 1 and second motor 2 coaxially back-to-back with and rotationally coupled to the first motor between and driving axles 9,10 At least one of the motors is of variable displacement and may be reversible. In a low speed range speed is controlled by variation of a primary pump displacement with both motors at full capacity for maximum torque. Speed is increased by reducing the displacement of the variable motor so that fluid supplied at a constant rate from the pump is supplied to the other motor to increase its speed. The motors are preferably hydrostatic axial piston swash-plate motors and may be mounted on a common control base 3 with a common fluid supply and return. Both motors may be flanged to an axle 10 (Fig. 2). Further speed increase is obtained by reducing the other motor displacement.

Description

2351794 HYDROSTATIC PROPULSION DRIVE This invention relates to a

hydrostatic propulsion drive with a hydrostatic motor and at least one axle driven by the motor.

A propulsion drive of the above kind is known from DE 42 06 085 Al. In this case, a constant-displacement axial piston motor. which has no motor shaft of its own, is drivingly connected at the output side to a planetary gear train disposed coaxially with the axial piston motor. The output shaft of the planetary gear train passes centrally through the axial piston motor. The output speed of the planetary gear train is variable.

The object of the present invention is to provide a compact and improved hydrostatic propulsion drive which is of simple construction and suitable for a large speed range.

According to the present invention there is provided a hydrostatic propulsion drive comprising first and second hydrostatic motors and at least one axle driven thereby, wherein the first and second motors are coaxially interconnected and rotationally synchronously coupled, at least one of the motors being of variable displacement.

Such an arrangement allows stepless ratio changing (conversion) on the motor side of the hydrostatic propulsion drive without interrupting the tractive force. The variable mechanical gear box used until now to increase the speed range can be eliminated. In the low speed range of a vehicle equipped with the hydrostatic propulsion drive according to the invention, both motors are initially set for maximum displacement. Speed changes take place initially on the primary side, that is to increase the speed the displacement 2 of a variable-displacement pump feeding the motors is increased. In this setting, the propulsion drive produces its maximum driving torque. If the quantity of inflowing fluid remains constant, the displacement of the variable-displacement motor is then reduced to increase the speed further. The released fluid is then available to the other motor so that the output speed and hence the vehicle speed is increased in the desired manner.

The motors may comprise hydrostatic axial piston motors of swash-plate construction and may be disposed back-to-back.

The construction of the hydrostatic propulsion drive according to the invention is simplified and the dimensions are minimised if the two axial piston motors are mounted on a common control base and further so if a common fluid supply and return are provided.

The conversion range of the hydrostatic propulsion drive according to the invention can be increased by a development of the invention in which the two axial piston motors are of variable displacement. This means that a high top speed is attainable.

In a further embodiment of the invention, at least one of the motors is reversible. This allows a further increase in speed. In the reversed state with the first motor turning in a constant direction, the direction of flow of the fluid is reversed in the second (reversed) motor. This allows additional fluid to be supplied to the first motor, that is in the reversed state the second variable-displacement propulsion unit acts as a pump driven by the first motor and the displacement of which further increases the output rotational speed. As a result, the conversion range, that is the 3 rotational speed range of the hydrostatic propulsion drive according to the invention, is increased by this operating state.

Both motors may be flanged to the axle. Such a propulsion drive can be used for example as a single-axle drive.

An output may be provided on the outer side of each of the two interconnected motors. In this case, a second consumer of hydraulic power can be connected in addition to the driven axle. According to one embodiment of the invention, this can be a second driven axle for example. The motors are then disposed between two driven axles and each motor is coupled to one of the axles (all-wheel drive).

Expediently, a drive shaft, in particular a propeller shaft, is disposed between at least one driven axle and one motor. If the two motors are not flanged to one of the axles, the connection to the two axles is then provided by a drive shaft in each case. Thus, the two motors are integrated in the drive line.

The two motors may each be provided with a motor shaft with the two motor shafts rotationally synchronously coupled to one another by means of a coupling sleeve disposed axially between the motors. This makes it possible to use largely standardised motors of the same design.

The use of the propulsion drive in a working machine, in particular a construction machine, is particularly advantageous. On the one hand, when working, i.e. on site, such machines require a high driving torque at low speed, and on the other hand such machines must be able to travel to the next place of use as quickly as possible, which requires the 4 highest possible speed on the road. The propulsion drive according to the invention can also be employed in agricultural, forestry and street cleansing vehicles which are provided with one or more driven axles.

For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

Figure 1 shows one embodiment of a hydrostatic propulsion drive according to the present invention with two driven axles and the motors disposed centrally; Figure 2 shows another embodiment of a hydrostatic propulsion drive according to the present invention with two driven axles, the motors being flanged to one of the axles; and Figure 3 shows a further embodiment of a hydrostatic propulsion drive according to the present invention with one driven axle and motors flanged thereto.

Figures 1 and 2 in each case show a hydrostatic propulsion drive according to the present invention as all-wheel drive. As shown in Figures 1 and 2, two motors 1 and 2 in the form of axial piston motors of swash-plate construction are connected to one another and are synchronously rotationally coupled. The connection is such that the motors 1 and 2 are flanged to one another coaxially and disposed in a so- called back-to-back arrangement.

The two motors 1 and 2 are mounted on a common control base 3 and are provided with a common fluid supply and return. The rotationally synchronous connection of the motors 1 and 2 is effected by means of a coupling sleeve 4 connecting the motor shafts la and 2a.

The two connected motors 1 and 2 are in each case provided on their outer sides with an output 5 and 6. In the embodiment according to Figure 1, the output 5 is connected to a drive shaft 7 in the form of a propeller shaft, and the output 6 is connected to a drive shaft 8 also in the form of a propeller shaft. The drive shaft 7 is connected to an axle 9, while the drive shaft 8 is connected to an axle 10.

In the embodiment according to Figure 2, the connected motors 1 and 2 are flanged to the driven axle 10. A (lengthened) drive shaft 7 is provided to drive the axle 9. Therefore, in the embodiment of Figure 2 only one drive shaft is required for an all-wheel drive.

In the embodiment according to Figure 3, only the axle 10 is driven. The two connected motors I and 2 are flanged to axle 10. Such a propulsion drive forms a single-axle drive. With this it is also possible to connect a consumer power take-off at the end of the connected motors 1 and 2 remote from the axle.

In all the embodiments illustrated in Figures 1, 2 and 3, at least one of the motors 1 or 2 is of variable displacement. This allows stepless changing of the ratio of the hydrostatic propulsion drive. In the low speed range of a vehicle equipped with a hydrostatic propulsion drive according to the present invention, both motors 1 and 2 are set for maximum displacement. The propulsion drive produces its maximum driving torque in this setting.

6 If the quantity of inflowing fluid remains constant, the displacement of the variable-displacement motor is reduced to increase the speed. The released fluid is then available to the other motor so that the output rotational speed is increased.

If both motors 1 and 2 are of variable displacement, the conversion range of the hydrostatic propulsion drive according to the invention can be increased further and as a result a higher top speed is obtainable.

In addition, one of the motors can be reversed to increase the speed. In the reversed state with the first motor turning in a constant direction, the direction of flow of the fluid is reversed in the second (reversed) motor. This allows additional fluid to be supplied to the first motor, that is in the reversed state the second variable-displacement propulsion unit acts as a pump driven by the first motor, and the resulting additional displacement further increases the output rotational speed. As a result, the conversion range, that is the rotational speed range of the hydrostatic propulsion drive according to the present invention, is increased in this operating state.

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Claims

1. A hydrostatic propulsion drive comprising first and second hydrostatic motors and at least one axle driven thereby, wherein the first and second motors are coaxially interconnected and rotationally synchronously coupled, at least one of the motors being of variable displacement.

2. A hydrostatic propulsion drive as claimed in claim 1, wherein the motors comprise hydrostatic axial piston motors of swash-plate construction and are disposed back-to-back.

3. A hydrostatic propulsion drive as claimed in claim 2, wherein the two axial piston motors are mounted on a common control base.

4. A hydrostatic propulsion drive as claimed in claim 3, wherein the two axial piston motors are provided with a common fluid supply and return.

5. A hydrostatic propulsion drive as claimed in any preceding claim, wherein both motors are of variable displacement.

6. A hydrostatic propulsion drive as claimed in any preceding claim, wherein at least one of the motors is reversible.

7. A hydrostatic propulsion drive as claimed in any preceding claim, wherein the interconnected motors are flanged to the driven axle.

8. A hydrostatic propulsion drive as claimed in any preceding claim, wherein an output is provided at the outer side of each of the two interconnected motors.

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9. A hydrostatic propulsion drive as claimed in claim 8, wherein the motors are disposed between two driven axles. each motor being coupled to one of the axles.

10. A hydrostatic propulsion drive as claimed in claim 9, wherein a drive shaft is disposed between at least one of the driven axles and the respective motor.

11. A hydrostatic propulsion drive as claimed in claim 10, wherein a drive shaft comprises a propeller shaft.

12. A hydrostatic propulsion drive as claimed in any preceding claim, wherein the two motors are each provided with a motor shaft and the two motor shafts are rotationally synchronously coupled to one another by means of a coupling sleeve disposed axially between the motors.

13. A hydrostatic propulsion drive substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

14. A working machine incorporating a hydrostatic propulsion drive as claimed in any preceding claim.

15. A working machine as claimed in claim 14, wherein the working machine comprises a construction machine.