Motor vehicles – Steering by driving
Reexamination Certificate
2000-05-03
2001-08-21
Swann, J. J. (Department: 3611)
Motor vehicles
Steering by driving
C180S307000, C180S308000, C060S484000, C060S486000
Reexamination Certificate
active
06276468
ABSTRACT:
The invention relates to a hydrostatic vehicle drive according to the preamble of claim
1
.
A hydrostatic vehicle drive according to the preamble of claim
1
is known from EP 0 378 742 A2. The hydrostatic vehicle drive presented in this specification comprises two hydraulic circuits which are separated from one another when the vehicle travels around bends, a hydropump and a hydromotor being provided in each hydraulic circuit. The two hydropumps are driven via a common drive shaft by a drive motor, for example a diesel engine. Via a suitable gearing system, the hydromotors each drive a track mechanism, for example the left-hand track mechanism and the right-hand track mechanism of a digger.
When the vehicle is travelling straight ahead, a problem can occur in that the left-hand and right-hand drive tracks can be subjected to different degrees of slip. In extreme cases, one of the two drive tracks can spin completely. This problem is dispensed with in EP 0 378 742 A2 in that the drive shafts of both hydromotors are rigidly connected to one another during straight-ahead travel operation by a coupling which can be electromagnetically actuated. In order to connect the electromagnetically actuated coupling to the two hydromotors, additional links are required. The mechanical outlay for connecting the two hydromotors is considerable, so that a cost-effective realisation of the hydrostatic vehicle drive disclosed in EP 0 378 742 A2 is impossible.
In order to improve straight-ahead travel properties, it is further proposed to connect the two hydraulic circuits, which are separated during bend travel operation, by electromagnetically operable valves during straight-ahead travel operation, in order to compensate unequal pressure conditions in the two hydraulic circuits by cross flows.
A similar state of the art is disclosed in DE 30 38 175 A1. Here too, in order to improve the straight-ahead travel properties, it is proposed to connect the two hydromotors on the drive side with one another by means of a hydraulically operable direct coupling and suitable gearing during straight-ahead travel operation, and furthermore to connect the two hydraulic circuits to one another in parallel via a connecting valve in the case of straight-ahead travel operation. Here too, the structural outlay for the mechanical connection of the two drive lines is considerable.
It is the object of the invention to provide a hydrostatic vehicle drive, in which good straight-ahead travel properties are ensured particularly in the case of slip in one of the drive lines, which can nevertheless be realised in a cost-effective manner.
This object is attained by the characterising features of both claim
1
and claim
7
, in each case in association with the generic features.
The solution according to the invention according to claim
1
is based upon the knowledge that a rigid coupling of the hydromotors with the hydropumps can be attained by an alternate, series connection of the first hydropump, followed by the first hydromotor, followed by the second hydropump, followed by the second hydromotor. In the design according to the invention, the hydropumps and the hydromotors are therefore arranged in series, whilst in conventional hydrostatic vehicle drives the hydropumps and the hydromotors are either arranged in separate hydraulic circuits or these separate hydraulic circuits are connected during straight-ahead travel operation in such a manner that all hydromotors and hydropumps are arranged parallel to one another. If, in the case of this conventional design of the drive line, one of the two hydromotors experiences a large degree of slip or even spins in extreme cases, then the main conveyed flow flows mainly through this hydromotor connected to the spinning drive line, which additionally increases the rotational speed of said hydromotor, so that the hydrostatic vehicle drive is rendered ineffective. In contrast, in the solution according to the invention, the conveyed flow conveyed by the hydropumps is forcibly guided through the hydropumps of all drive lines, so that the absorption volume of both hydromotors corresponds. The hydromotors are each hydraulically supported by the upstream hydropump, so that excessive slip or spinning of the drive lines connected to the hydromotors is prevented.
Claims
2
to
6
relate to advantageous developments of the hydrostatic vehicle drive according to claim
1
.
According to claim
2
, a changeover valve is advantageously provided, which allows for a changeover from straight-ahead travel operation to bend travel operation. During bend travel operation, the two hydromotors and the two hydropumps are separated from one another and connected to each other in separate hydraulic circuits in each case. However, during straight-ahead travel operation, the hydropumps and the hydromotors are arranged alternately in series as described above. According to claim
3
, a changeover valve of this type can be realised in a cost-effective manner as a simple 4/2-way valve with a parallel and a crossed switching position.
According to claim
4
, a third and fourth hydromotor can be added to the first and second hydromotors, the third hydromotor being connected in parallel with the first hydromotor and the fourth hydromotor being connected in parallel with the second hydromotor. In this respect, the individual hydromotors drive four drive wheels, for example, it being possible to associate the first and third hydromotor with a first vehicle axle and the second and fourth hydromotor with a second vehicle axle. In order to switch off one of the vehicle axles in each case, according to claim
5
switching valves can be provided, which switch off the corresponding hydromotors. When switching off the hydromotors, it is advantageous according to claim
6
to supply the switched-off hydromotors with a supply pressure via a supply device. In this manner, the switched-off hydromotors are prevented from running without connection to the pressure fluid. As a result of the development according to the invention, it is ensured that the hydromotors are at least acted upon by the supply pressure of the supply device, so that sufficient lubrication and cooling of the hydromotors is guaranteed.
The solution according to claim
7
is based upon the knowledge that a slip-free hydraulic vehicle drive can also be realised by using double motors in a special crossed mixed circuit arrangement. Since all hydromotors are not only connected to a hydropump, but the two partial hydromotors are connected either at their inlet or outlet to both hydropumps, it is ensured that the hydromotors of both drive lines are supported by both hydropumps. As a result of the measure according to the invention, it is ensured in the event of slip or even spinning of one of the drive lines that the conveyed flow conveyed by the hydropumps is prevented from flowing mainly only through the hydromotors of this drive line. Rather, a forced pressure supply of the other drive line is also ensured.
Claims
8
to
14
relate to advantageous developments of the hydrostatic vehicle drive according to claim
7
.
In the advantageous development according to claim
8
, not two but four hydromotors are provided, which can drive different drive wheels in each case. The additional hydromotors are also constructed as double hydromotors comprising two partial hydromotors in each case and are supported either at their outlet or inlet by both hydropumps, none of the four hydromotors being connected to the two hydropumps in the same manner. In this respect, the hydromotors can be connected according to claim
9
in such a manner that two hydromotors as a pair drive a vehicle axle in each case.
Alternatively, it is possible according to claim
10
to provide only a single further hydromotor, which drives s third vehicle wheel. It is not necessary to construct this third hydromotor as a double hydromotor. The input of this third hydromotor is preferably connected to the first hydropump, whilst its output is connected to the second hydropump, so that a crossed c
Essig Heinz-Gerhard
Shrive Chris
Brueninghaus Hydromatik GmbH
Scully Scott Murphy & Presser
Swann J. J.
Zeender F.
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