Control device for hydrostatic drive, especially for fork lift truck

{
  "publication_number": "US4050248A",
  "country": "US",
  "kind": "A",
  "title": "Control device for hydrostatic drive, especially for fork lift truck",
  "abstract": "A control device for a hydrostatic drive, especially for a fork lift truck, in which an engine drives a reversible variable delivery pump which supplies fluid to a fluid motor connected to the drive wheels of the lift truck. A reversible actuator is connected to a control element for the pump and is connected through a reversing valve with a further engine driven pump. The rate of movement of the actuator is controlled in the opposite directions of movement thereof. The truck includes a lift cylinder supplied by a still further engine driven pump, and when the lift cylinder is under pressure, the rate of movement of the actuator is controlled at a still slower speed of movement in at least one direction of movement.",
  "claims": [
    "1. In a control system for a fork lift truck having a fluid operable lift cylinder and a fluid drive motor and a variable delivery reversible pump connected to the motor and a drive engine connected to drive the pump; said pump having a control element movable from a first position of maximum pump delivery in forward direction through a position of zero pump delivery to a second position of maximum pump delivery in reverse direction, a fluid operable reversible actuator connected to said control element and normally biased toward a center position in which said control element is in zero delivery position, a second pump and a reversing valve having an inlet connected to said second pump and a respective output connected to each side of said actuator, a third pump and a control valve connecting the third pump to the lift cylinder, both of said second and third pumps being driven by the engine, control means for controlling the rate of movement of said actuator at least toward said second position thereof in response to the supply of actuating fluid thereto from said reversing valve.",
    "2. A control system according to claim 1 in which said control means comprises first and second throttle valves connected in parallel between opposite sides of said actuator and the respective outlets of said reversing valve, and a check valve in series with each throttle valve permitting one-way flow only through said first throttle valves toward said actuator and through said second throttle valves away from said actuator.",
    "3. A control system according to claim 2 in which said second throttlve valve through which fluid is expelled from said actuator when the control element is moving toward said second position is variable, and means operable in response to a supply of actuating fluid to said lift cylinder for increasing the degree of restriction of said variable second throttle valve.",
    "4. A control system according to claim 2 in which said first throttle valve through which fluid flows to said actuator when said control element is moving toward said second position is variable, and means operable in response to a supply of actuating fluid to said lift cylinder for increasing the degree of restriction of said variable first throttle valve.",
    "5. A control system according to claim 2 in which said second throttle valve through which fluid is expelled from said actuator when the control element is moving toward said second position is variable, and said first throttle valve through which fluid flows to said actuator when said control element is moving toward said second position is also variable, and means operable in response to a supply of actuating fluid to said lift cylinder for increasing the degree of restriction of said variable first and second throttle valves.",
    "6. A control system according to claim 5 in which the others of said throttle valves are in the form of fixed restrictions.",
    "7. A control system according to claim 2 in which said reversing valve has a centered position in which the opposite sides of said actuator are interconnected.",
    "8. A control system according to claim 2 which includes restrictor means between the discharge side of said second pump and exhaust, a brake pedal, and means operated by the brake pedal for decreasing the restriction of said restrictor means.",
    "9. A control system according to claim 5 which includes a valve interposed between said lift cylinder and said variable throttle valves and adapted to open only at a minimum pressure at said lift cylinder."
  ],
  "cpc": [
    "F16H 61/4157",
    "B60K 17/10",
    "B60T 1/08",
    "B60T 13/585",
    "B60T 8/18",
    "B60W 10/04",
    "B60W 10/18",
    "F16H 61/40"
  ],
  "assignees": [
    "ORENSTEIN & KOPPEL AG"
  ],
  "filing_date": "1976-09-09",
  "publication_date": "1977-09-27",
  "grant_date": "1977-09-27",
  "priority_date": "1975-09-17",
  "application_number": "US-72175876-A",
  "family_id": "5956677",
  "citations": [
    "GB1279693A",
    "US3543508A",
    "US3850272A"
  ]
}