# US 11,440,780 B2 · Control system for lowering forklift lever

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- Number: US 11,440,780 B2
- Document ID: US11440780B2
- Status: Granted
- Kind: B2
- Application number: 16/719,750
- Filed: 2019-12-18
- Published: 2020-06-25
- Granted: 2022-09-13
- Earliest claimed: 2018-12-20
- Assignees: Doosan Industrial Vehicle Co., Ltd.
- Applicants: Doosan Corporation
- Inventors: Jaesung Choi; Jinyong Lee; Dongho Han; Beomkyun Yu
- Web page: https://patentgrep.com/patent/US11440780B2

## CPC

- B66F 9/0755: {Position control; Position detectors}
- B66F 9/22: Hydraulic devices or systems
- B60W 10/30: including control of auxiliary equipment, e.g. air-conditioning compressors or oil pumps
- F15B 11/05: specially adapted to maintain constant speed, e.g. pressure-compensated, load-responsive {(F15B11/161 takes precedence)}
- B60W 2300/121: Fork lift trucks, Clarks
- B66F: HOISTING, LIFTING, HAULING OR PUSHING, NOT OTHERWISE PROVIDED FOR, e.g. DEVICES WHICH APPLY A LIFTING OR PUSHING FORCE DIRECTLY TO THE SURFACE OF A LOAD ({invalid lifting devices A61G7/10; } mounting artificial islands on piles or like supports E02B17/00; scaffolding combined with lifting devices E04G1/22; lifting devices for sliding forms E04G11/24; lifting of buildings E04G23/06; shores or struts E04G25/00; lifts or other hoisting devices on ladders E06C7/12; props for mining E21D15/00)
- B60W: CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- F15B: SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR

## Abstract

A system of controlling a lowering speed of a work lever of a forklift which includes, a hydraulic motor connected to the work lever through a hydraulic line to transmit a power to the work lever; an electronic solenoid valve for controlling the hydraulic motor connected to the work lever; a weight sensor provided at one side of the work lever, the weight sensor measuring a weight of a load placed on the work lever and transmitting the measured value to a controller; and a controller for controlling an RPM of the hydraulic motor and a current amount of the electronic solenoid valve based on the measured value transmitted from the weight sensor.

## Claims

### Claim 1

A system of controlling a lowering speed of a work lever of a forklift, comprising:
a hydraulic motor connected to the work lever through a hydraulic line to transmit a power to the work lever;
an electronic solenoid valve configured to control the hydraulic motor connected to the work lever;
a weight sensor provided at one side of the work lever, the weight sensor configured to measure a weight of a load placed on the work lever, to convert the weight into a load voltage, and to transmit the load voltage corresponding to a measured value to a controller; and
a controller configured to control an RPM of the hydraulic motor and to control a current amount applied to the electronic solenoid valve based on a maximum current determined with respect to the measured value transmitted from the weight sensor, such that a rate of change in a lowering speed of the work lever is unaffected by the weight of the load placed on the work lever,
wherein the controller includes a preset table in which is stored a maximum current under a full load condition and a maximum current under a no-load condition that represent the determined maximum current for those respective conditions, and
wherein the controller is configured to determine the maximum current where the work lever has a load less than a full load, between the maximum current under the full load condition and the maximum current under the no-load condition, according to the load voltage transmitted by the weight sensor.

### Claim 2 (depends on 1)

The system of claim 1, wherein the controller determines the maximum load current of the electronic solenoid valve based on the load voltage and the following equation:
H
=
(
B
-
C
)
(
E
-
D
)
×
(
G
-
D
)
+
C
where: B is the maximum current under full load condition, C is the maximum current under no-load condition, D is a minimum weight voltage, E is a maximum weight voltage, G is the load voltage, and H is the determined maximum load current.

### Claim 3 (depends on 2)

The system of claim 2, wherein a table according to a height of a work machine operation device is preset in the controller, and
the controller determines a valve current applied to the electronic solenoid valve, based on the determined maximum load current.

### Claim 4 (depends on 3)

The system of claim 3, wherein the controller determines the valve current based on the following equation:
I
=
A
+
F
1000
×
(
H
-
A
)
where A is the minimum current, D is the minimum weight voltage, F is a height value in a range of 0-1000 corresponding to the height of the work machine operation device, H is the determined maximum load current, and I is the valve current.