Hydraulic circuit for backhoe

• US 7,069,674 B2
• Filed: 08/26/2003
• Issued: 07/04/2006
• Est. Priority Date: 12/26/2002
• Status: Expired due to Fees

• Current Assignee: Kubota Corporation
• Original Assignee: Kubota Corporation
• Inventors: Arii, Kazuyoshi
• Primary Examiner(s): Beach, Thomas A.
• Application Number:
  US10/649,601
• Publication Number:
  US 20040123499A1
• Time in Patent Office: 1,043 Days
• Field of Search: 373/48, 373/82, 604/20, 604/21, 604/22, 604/94, 915/12, 915/16, 915/32, 915/34
• US Class Current: 37/348
• CPC Class Codes: E02F 3/325 Backhoes of the miniature type
• CPC Class Codes: E02F 9/2235 including an electronic controller
• CPC Class Codes: E02F 9/2242 including an electronic controller
• CPC Class Codes: E02F 9/2292 Systems with two or more pumps
• CPC Class Codes: E02F 9/2296 Systems with a variable displacement pump

Abstract

A hydraulic circuit for use with a backhoe includes first, second and third pumps; left and right traveling unit valve sections-receiving pressure oil from the first and second pumps independently of each other; a front implement valve section receiving combined pressure oil including oil from respective center oil passages of the left and right traveling unit valve sections; and a swiveling valve section receiving pressure oil from the third pump. A parallel oil passage having a restrictor extends parallel to a center oil passage of the swiveling valve section. The front implement valve section also receives pressure oil from the center oil passage of the swiveling valve section and the parallel oil passage. A load sensing system controls flow amounts of the first and second pumps according to a hydraulic load generated in a front implement operation.

Claims

1. A hydraulic circuit for a backhoe, comprising:

first, second and third pumps driven by an engine;

left and right traveling unit valve sections configured to receive pressure oil from the first pump and the second pump independently of each other;

a front implement valve section configured to receive combined pressure oil including oil discharged from a center oil passage of said left traveling unit valve section and oil discharged from a center oil passage of the right traveling unit valve section;

a swiveling valve section configured to receive pressure oil from the third pump; and

a parallel oil passage having a restrictor and disposed parallel to a center oil passage of said swiveling valve section;

wherein said front implement valve section is configured to receive also pressure oil from the center oil passage of the swiveling valve section and the parallel oil passage; and

there is provided a load sensing system for controlling flow amounts of the first and second pumps according to a hydraulic load generated in a front implement operation.

2. The hydraulic circuit for a backhoe according to claim 1, wherein said load sensing system comprises an outer-orifice type load sensing system.

3. The hydraulic circuit for a backhoe according to claim 2, wherein said load sensing system comprises pressure compensation valves connected to the downstream of spools of respective control valves included in the front implement valve section and an unload valve connected to the upstream of the pressure oil supply passage of the front implement valve section.

4. The hydraulic circuit for a backhoe according to claim 3, wherein a system relief valve is connected to the downstream of said pressure oil supply passage.

5. A hydraulic circuit for a backhoe, comprising:

first, second and third pumps driven by an engine;

left and right traveling unit valve sections configured to receive pressure oil from the first pump and the second pump independently of each other;

a front implement valve section configured to receive combined pressure oil of said left and right traveling unit valve sections;

a swiveling valve section configured to receive pressure oil from the third pump; and

a parallel oil passage having a restrictor and disposed parallel to a center oil passage of said swiveling valve section;

wherein said front implement valve section is configured to receive also pressure oil from the center oil passage of the swiveling valve section and the parallel oil passage; and

there is provided a load sensing system for controlling flow amounts of the first and second pumps according to a hydraulic load generated in a front implement operation.

6. The hydraulic circuit for a backhoe according to claim 5, wherein said load sensing system comprises an outer-orifice type load sensing system.

7. The hydraulic circuit for a backhoe according to claim 6, wherein said load sensing system comprises pressure compensation valves connected to the downstream of spools of respective control valves included in the front implement valve section and an unload valve connected to the upstream of the pressure oil supply passage of the front implement valve section.

8. The hydraulic circuit for a backhoe according to claim 7, wherein a system relief valve is connected to the downstream of said pressure oil supply passage.