Power plants – Pressure fluid source and motor – Expansible chamber type volumetric responsive measuring...
Patent
1998-12-07
2000-10-17
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Expansible chamber type volumetric responsive measuring...
60405, 60406, F16D 3100
Patent
active
061313890
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a hydrostatic steering device with two steering systems, each having a pump, a steering unit provided with an input shaft and a steering motor connected to the steering unit by means of two motor hoses, by which a steering wheel common for both steering units is provided, and both steering motors are mechanically connected with each other on the output side.
Such a steering device is known from DE 29 44 883 C2. The fact that all important components are available twice causes that on failure of one steering system, be it due to a pump failure or a hose damage, it is still possible to steer the vehicle by means of the remaining steering system. This is a condition for such vehicles to be permitted to drive at limited speed on public roads. However, it is a disadvantage that the driving of both steering units requires a relatively high torque.
The task of the invention is to provide a hydrostatic steering device of the kind mentioned in the introduction, by which the torque to be provided on the steering hand-wheel, both during normal operation and during emergency operation, has a relatively low value.
According to the invention, this task is solved by means of a change-over valve which, in an operation position, creates a hydraulic connection of the motor hoses of the second steering system, and in an emergency position, the motor hoses of the first steering system, leaving the motor hoses of the other steering system, respectively, in the separated state, and a switching device reacting on the occurrence of a fault in the first steering system and switching the change-over valve from the operation position to the emergency position.
With this construction, the motor hoses of the second steering system are short-circuited during normal operation, causing that the corresponding steering unit is operated together with the steering unit of the first steering system, however, due to the short-circuit working without pressure. Thus the torque required for the steering is only a little higher than the torque required for the activation of the steering unit of the first system. In most cases it will not even be higher than with one steering system, as the second steering unit can be operated by the first one. When the change-over valve switches to the emergency position, the second steering system is fully effective, whereas the motor hoses of the first steering system are short-circuited. The torque to be provided in case of emergency is thus only a little higher than the torque required for the operation of the second steering system. Thus the torque to be produced manually is in both cases relatively small, and only changes very little when switching from normal operation to emergency operation. An additional advantage is that--even if one steering system is always ineffective--both steering units are operated constantly, causing that, in case of emergency operation, there is no risk that the second steering unit jams and does not function.
For the fault-monitoring there are several opportunities. It is recommended that the switching device activates the change-over valve in dependence of the pressure conditions in the first steering system, as each fault leads to changed pressure conditions.
In a preferred embodiment it is provided that the switching device reacts when the difference between the input pressure of the first steering unit and the load pressure in the first steering system falls below a pre-set value. The input pressure drops to zero, when the pump of the first steering system fails or cannot provide fluid from the tank due to the loss of hydraulic fluid through a hose damage.
It is also advantageous for the change-over valve to have a slide, which is loaded in one end by the input pressure of the first steering unit and in the other end by the load pressure in the first steering system and a spring. In this way, change-over valve and switching device can be combined with each other.
Another recommendable alternative is for the change-over valve to be a solenoid valve supp
REFERENCES:
patent: 3896617 (1975-07-01), Kraina
patent: 4184332 (1980-01-01), Liebert
patent: 4184560 (1980-01-01), Tischer
patent: 5322003 (1994-06-01), Winyard et al.
Danfoss Fluid Power A/S
Lopez F. Daniel
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