Neutral override for servo controlled hydrostatic units

Power plants – Pressure fluid source and motor – Servo-motor having externally operated control valve sets...

Reexamination Certificate

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

C060S468000

Reexamination Certificate

active

06606858

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to the field of hydrostatic units used to propel vehicles. More particularly, this invention relates to a neutral override circuit or system for servo controlled hydrostatic units.
A skid steer loader is one type of vehicle that often utilizes one or more hydrostatic transmissions for propulsion. Typically, the vehicle's engine drives a servo-controlled variable displacement hydraulic pump that fluidly drives a hydraulic motor. The hydraulic motor powers one or more of the vehicle wheels.
Some skid steer loader manufacturers have added service and/or parking brakes to their hydrostatically propelled machines to prevent them from rolling away or being moved inadvertently (inadvertent movement can sometimes occur if the pump of the hydrostatic transmission is accidentally stroked out of its neutral position). In fact, new regulatory requirements are demanding parking brakes on skid steer loaders bound for European markets. Current methods of providing braking systems require the brake to absorb the full torque capability of the hydrostatic transmission. Current braking systems are hard pressed to handle increasing hydrostatic torque capability and machine weight.
One approach to resolving this problem has been to isolate and reduce only the source pressure for the displacement control of the pump. However, this approach requires additional machined passages and valving to separate the control portion of the circuit from the supercharge portion of the circuit.
Therefore, a primary objective of the present invention is a provision of simple neutral override system or circuit that prevents the hydrostatic pump from stroking out of neutral.
Another objective of the present invention is the provision of a neutral override circuit that prevents the hydrostatic transmission from stroking out of neutral yet provides enough charge pressure to lubricate the rotating elements of the pump.
Another objective of the present invention is the provision of a neutral override system that is easy to retrofit to existing hydrostatic transmissions.
Another objective of the present invention is the provision of a neutral override system that is economical to manufacture, as well as durable and reliable in use.
These and other objectives will be apparent from the drawings, as well as from the description and claims which follow.
SUMMARY OF THE INVENTION
The present invention relates to the field of hydrostatic units used to propel vehicles. More particularly, this invention relates to a neutral override brake control valve and circuit or system for servo controlled hydrostatic units.
The neutral override circuit of this invention includes a variable displacement pump controlled by a servo fluidly connected to a displacement control valve. The displacement control valve is biased to a neutral position. A charge pump is connected to the pump and the displacement control. A solenoid-operated neutral override brake control valve is connected to the charge circuit upstream of the displacement control valve.
The brake control valve is normally biased to an open position. However, the solenoid urges the brake control valve to a closed position in a response to a signal indicating that the parking brake has been released. In the open position, the neutral override brake control valve dumps the charge flow to the pump case until the charge pressure is inadequate to overcome the centering bias of the displacement control. However, characteristics of the valve can be set so that some minimal charge pressure and lubricating flow are still provided to the rotating elements of the pump.


REFERENCES:
patent: 3365886 (1968-01-01), Moon, Jr.
patent: 3588285 (1971-06-01), Moon, Jr.
patent: 3739578 (1973-06-01), Roeske
patent: 4055047 (1977-10-01), Hara
patent: 4417649 (1983-11-01), Frost
patent: 4432585 (1984-02-01), Nezuka
patent: 4457341 (1984-07-01), Aspinwall
patent: 4461147 (1984-07-01), Myers
patent: 4588057 (1986-05-01), Weich et al.
patent: 4596118 (1986-06-01), Heiser
patent: 5050700 (1991-09-01), Kim
patent: 5531071 (1996-07-01), Asano
patent: 22 64 442 (1974-02-01), None
patent: 27 59 197 (1979-07-01), None
patent: 0 127 123 (1984-12-01), None

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

Neutral override for servo controlled hydrostatic units does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Neutral override for servo controlled hydrostatic units, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Neutral override for servo controlled hydrostatic units will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-3086965

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.