Hydraulic emergency control for changing hydraulic oil pressure

Details Hydraulic emergency control for changing hydraulic oil pressure Hydraulic emergency control for changing hydraulic oil pressure

1997-11-04

1999-10-26

Graysay, Tamara L.

Endless belt power transmission systems or components

Pulley with belt-receiving groove formed by drive faces on...

Fluid pressure actuator for adjustment of member

474 18, 477 48, F16H 5900, B60K 4112

Patent

active

059718765

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a hydraulic emergency control.
A hydraulic emergency control for an electronically controlled, continuously variable transmission (continuously variable transmission, CVT) is described in DE-42 34 103 A1. The CVT transmission which is preferably employed in motor vehicles, has a control for emergency driving operations which, when the electrical control of normal driving operations fails, causes a switching position with a high gear ratio in order to provide more advantageous restart and start-up conditions. Among other things, the ratio of primary to secondary clamping force between the pulling means and the pairs of beveled disks is maintained constant by means of this control through an intermediate gear range. In the intermediate gear range the gear ratio changes as a function of the torque requirements of the power take-off shaft. With a high demand a high gear ratio is selected, while a low gear ratio is set with a low demand. The means required for this are recited in the description of FIGS. 1 and 2.


SUMMARY OF THE INVENTION

The hydraulic emergency control in accordance with the invention is needed in order to be able to utilize a continuously transmitting looped gear without the aid of an electrohydraulic actuator, which is active in normal driving operations, over the entire gear range. It is intended by means of the hydraulic emergency control to set a start-up gear ratio in the low range when a vehicle is started, for example to allow a start up on a hill or out of an underground garage. The emergency control is also intended to set a gear ratio in the overdrive range at high driving speeds and low engine torque. A benefit of this is for one, that the maximum speed can also be attained in an emergency driving operation and, for another, overspeeding of the engine when the electronic actuator fails under maximum speed is prevented.
With the hydraulic emergency control in accordance with the invention, the clamping force ratio is varied as a function of the conveyed pump volume flow or the engine rpm. To this end at least one flow control valve is arranged in an open hydraulic circuit for supplying the respective piston chambers of the secondary and primary axial adjustment devices. Viewed in the flow direction of the pressure medium, the individual flow control valve is located at a place where the pump volume flow is affected between the hydraulic pump--which for example is driven by the vehicle engine--and the outlet from this open hydraulic circuit. The volume flow-dependent pressure change, which results at the respective flow control valve, changes the contact pressure in the corresponding pair of beveled disks.
Flow control valves are provided, with whose aid the primary clamping force is changed, while the flow control valves vary the clamping force in the secondary disk set.
Among other things, the remaining claims describe individual special arrangements for the flow control valves in connection with the pressure limiting valves and other control flow valves.


BRIEF DESCRIPTION OF THE DRAWINGS

Several exemplary embodiments of the invention, besides the prior art, are schematically represented in the drawings in the form of hydraulic circuit diagrams and will be explained in more detail in the following drawing description also with the aid of a simplified or ideally represented diagram. Shown are in:
FIG. 1, a clamping force ratio diagram,
FIG. 2, a hydraulic circuit diagram for a rigid setting of a preselected clamping force ratio,
FIG. 3, a hydraulic circuit diagram for a variable setting of the clamping force conditions by raising the primary pressure,
FIG. 4, a hydraulic circuit diagram as in FIG. 3 with a flow control valve in the outlet area,
FIG. 5, a hydraulic circuit diagram for a variable setting of the clamping force conditions by lowering the secondary pressure,
FIG. 6, a hydraulic circuit diagram as in FIG. 5 with a separate flow control valve in the primary line and,
FIG. 7, a hydraulic circuit diagram as in FIG. 6

REFERENCES:
patent: 4663991 (1987-05-01), Nakamura et al.
patent: 4672864 (1987-06-01), Morimoto
patent: 4685357 (1987-08-01), Sawada et al.
patent: 4702725 (1987-10-01), Kouno et al.
patent: 5085107 (1992-02-01), Tatara

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