US3911679A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Closed center hydraulic system with pump and accumulator output for high speed lift
Assignee: AC MATERIAL HANDLING Corp 777 MANOR PARK DRIVE COLUMBUS OHIO 43228 A CORP OHIO
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Filing: 1974-12-26
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Granted: 1975-10-14
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Expires: 1994-12-26
Abstract
Abstract A single pump and a relatively large accumulator are used in a closed center hydraulic system for a lift truck to provide hydraulic pressure fluid for vehicle steering, load lifting, mast tilting and attachment operations. The operator may selectively utilize combined pump and accumulator output for high speed lift. This is achieved by pump contactor control means which the operator can selectively operate, when in the lift condition, independently of the pressure sensitive pump control means which automatically maintains the accumulator pressure between predetermined minimum and maximum pressures.
Inventors
- 👤 Dean A Matthews
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 17:51
CPC Classifications
F; F15; F15B; F15B1/00; F15B1/02; F15B11/00; F15B11/16; F15B2211/00; F15B2211/20; F15B2211/205; F15B2211/2053; F15B2211/21; F15B2211/212; F15B2211/265; F15B2211/40; F15B2211/405; F15B2211/40576; F15B2211/40584; F15B2211/415; F15B2211/41509; F15B2211/41518; F15B2211/41527; F15B2211/46; F15B2211/47; F15B2211/473; F15B2211/50; F15B2211/505; F15B2211/50509; F15B2211/50518; F15B2211/515; F15B2211/5151; F15B2211/55; F15B2211/60; F15B2211/63; F15B2211/6303; F15B2211/6306; F15B2211/6309; F15B2211/665; F15B2211/6651; F15B2211/70; F15B2211/71; Y; Y10; Y10S; Y10S60/00; Y10S60/911
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
227 words
A two speed lift system for a lift truck, comprising: a reservoir, an accumulator, a pump connected in fluid receiving relation to said reservoir and fluid delivery relation to said accumulator, a lift jack, a closed center control valve having neutral, raise and lower positions of adjustment, a fluid supply line interconnecting said accumulator and said control valve, a fluid delivery line interconnecting said control valve and said lift jack, a source of electric energy, an electric motor connected in driving relation to said pump, a power circuit interconnecting said electric motor and said source of electric energy, first electric control means operatively associated with said motor, source of electric energy and accumulator automatically maintaining the pressure in said accumulator between predetermined minimum and maximum values, and second electric control means including a manually operable switch for selectively energizing said electric motor to cause same to drive said pump independently of the value of the pressure in said accumulator when said switch is actuated, said lift jack being supplied with fluid from said accumulator when said control valve is placed in its raise position of adjustment of said manually operable switch is not actuated, said lift jack being supplied with fluid from said accumulator and from said pump when said control valve is placed in its raise position of adjustment and said manually operable switch is actuated.
Claim 2
Dependent Claim
227 words
A two speed lift system for a lift truck, comprising: a reservoir, an accumulator, a pump connected in fluid receiving relation to said reservoir and fluid delivery relation to said accumulator, a lift jack, a closed center control valve having neutral, raise and lower positions of adjustment, a fluid supply line interconnecting said accumulator and said control valve, a fluid delivery line interconnecting said control valve and said lift jack, a source of electric energy, an electric motor connected in driving relation to said pump, a power circuit interconnecting said electric motor and said source of electric energy, first electric control means operatively associated with said motor, source of electric energy and accumulator automatically maintaining the pressure in said accumulator between predetermined minimum and maximum values, and second electric control means including a manually operable switch for selectively energizing said electric motor to cause same to drive said pump independently of the value of the pressure in said accumulator when said switch is actuated, said lift jack being supplied with fluid from said accumulator when said control valve is placed in its raise position of adjustment of said manually operable switch is not actuated, said lift jack being supplied with fluid from said accumulator and from said pump when said control valve is placed in its raise position of adjustment and said manually operable switch is actuated.
Claim 3
Dependent Claim
23 words
The system of claim 1 wherein said switch is selectively operable only when said control valve is in its raise position of adjustment.
Claim 4
Dependent Claim
54 words
The system of claim 2 wherein said control valve is a metering type valve with a predetermined metering range in its raise position between partial flow and full flow positions and wherein said manually operable switch is actuatable only when said control valve is adjusted in said metering range to said full flow position.
Claim 5
Dependent Claim
34 words
The system of claim 1 and further comprising manually operated valve control means operatively associated with said control valve including a shiftable element and wherein said switch is operatively associated with said shiftable element.
Claim 6
Dependent Claim
48 words
The system of claim 4 wherein said shiftable element is moved in one direction a predetermined distance when said control valve is shifted from its neutral position to its raise position and wherein a small additional shifting movement of said element in said one direction actuates saId switch.
Claim 7
Dependent Claim
28 words
The system of claim 5 and further comprising resilient biasing means operatively associated with said manually operated valve control means resisting said additional shifting movement of said element.
Claim 8
Dependent Claim
42 words
The system of claim 6 and further comprising a pressure relief valve operatively associated with said accumulator and said reservoir operable to discharge fluid to the latter when a predetermined fluid pressure greater than said maximum value is reached in said accumulator.
Claim 9
Dependent Claim
61 words
The system of claim 7 and further comprising a fluid delivery line interconnecting said pump and said accumulator and a one way valve in said delivery line permitting flow from said pump to said accumulator and preventing flow from the latter to said pump and wherein said relief valve is connected to said delivery line downstream of said one way valve.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-10-13 | 1979-04-14 | 1979-10-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-10-13 | 1983-04-14 | 1983-10-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-10-13 | 1987-04-14 | 1987-10-14 | $7700.00 | Window Closed / Lapsed |