Motor vehicles – Steering by driving – Auxiliary steering motor
Reexamination Certificate
1999-10-13
2001-01-30
Hurley, Kevin (Department: 3619)
Motor vehicles
Steering by driving
Auxiliary steering motor
Reexamination Certificate
active
06179072
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the hydrostatic steering system for a vehicle and in particular to a supplemental charge for the steering pump.
2. Description of the Related Art
A typical hydrostatic steering system includes a variable displacement pump coupled to a fixed displacement motor. A charge pump provides a constant supply of oil to the main steering pump for controlling the main steering pump and to provide cooled oil to the steering system. Such steering systems are only functional as long as the charge pump and steering pump are operating properly. If the charge pressure drops below a certain level, steering ability will be reduced. Increased steering inputs will be required to achieve a given turn. The stability of steering charge pressure is thus critical to maintaining normal function of the hydrostatic steering system. During low pump speed and high steering load conditions, charge flow may not be sufficient to make up for the oil exchange and the charge pressure would consequently drop. This can occur, for example, when turning a vehicle into or out of a building when high steering input is needed but the engine speed is low. Charge pressure may also be reduced by poor charge pump suction during extremely cold temperature
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a means to supply an appropriate charge pressure in the event the steering charge pressure drops too low.
The present invention provides an oil line connection between an existing transmission oil pump and the outlet of the hydrostatic steering system charge pump.
A check valve prevents oil flow from the steering system to the transmission and prevents oil flow from the transmission oil pump to the steering charge pump unless the charge pump pressure drops below the operating pressure of the transmission pump. When the steering charge pressure drops below the transmission oil pressure, the check valve opens and the transmission oil pump maintains the charge oil pressure at the transmission oil pressure. Transmission oil is provided to the main steering pump. In the event of a permanent loss of charge pressure or a relatively long drop of charge pressure, a pressure transducer in the oil line activates a warning signal to the vehicle operator.
It is an advantage of the present invention that an existing transmission oil pump is used to supplement the steering charge, a dedicated pump is not required, thus reducing cost.
It is a further advantage that in cold conditions, if the transmission oil pressure rises due to increased resistance in the transmission oil cooler, excess pressure can be relieved by opening the check valve and delivering oil to the steering system.
REFERENCES:
patent: 4649705 (1987-03-01), Williamson
patent: 4955442 (1990-09-01), Crabb et al.
patent: 5390751 (1995-02-01), Puetz et al.
patent: 5948029 (1999-09-01), Straetker
patent: 6062332 (2000-05-01), Stephenson et al.
Deere & Company
Hurley Kevin
LandOfFree
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