Phase maintaining control for a hydraulic steering system

• US 6,550,566 B1
• Filed: 10/17/2001
• Issued: 04/22/2003
• Est. Priority Date: 10/17/2001
• Status: Expired due to Fees

• Current Assignee: Deere & Company
• Original Assignee: Deere & Company
• Inventors: Engelbrecht, Joshua J.
• Primary Examiner(s): Morris, Lesley D.
• Assistant Examiner(s): WINNER, TONY H
• Application Number:
  US09/978,977
• Publication Number:
  US 20030070865A1
• Time in Patent Office: 552 Days
• Field of Search: 180/432, 180/442, 180/403, 180/417, 914/61, 137/625.6, 137/625.61, 603/84, 603/87, 603/92
• US Class Current: 180/432
• CPC Class Codes: B62D 5/09 characterised by means for actuating valves
• CPC Class Codes: F15B 11/003 Systems with load-holding valves
• CPC Class Codes: F15B 2211/20561 reversible
• CPC Class Codes: F15B 2211/5059 using double counterbalance valves
• CPC Class Codes: F15B 2211/513 the positions being continuously variable, e.g. as realised by proportional valves
• CPC Class Codes: F15B 2211/5155 being connected to multiple output members
• CPC Class Codes: F15B 2211/528 actuated by fluid pressure
• CPC Class Codes: F15B 2211/57 Control of a differential pressure
• CPC Class Codes: F15B 2211/7114 with direct connection between the chambers of different actuators
• CPC Class Codes: F15B 2211/782 Concurrent control, e.g. synchronisation of two or more actuators

Abstract

A dual counterbalance valve is added in the hydraulic lines between the steering unit and the steering cylinders on an implement to maintain pressure in the steering lines by metering hydraulic fluid to and from the cylinders under pressure so that the steered wheels stay in phase. Since the steering system is kept under constant pressure, the wheels can only be steered by the steering unit and not by tractive soil forces so toe in and toe out problems are eliminated without need for a mechanical tie rod connecting the steered wheels. The valve is added in-line to the system so that current machines can be easily retrofitted.

Claims

1. In a hydraulic steering system for an off-road implement having at least first and second steerable wheels, first and second hydraulic steering cylinders connected to the respective steerable wheels, a steering unit for selectively supplying hydraulic fluid under variable pressure to the hydraulic cylinders for steering of the wheels, hydraulic lines connecting the cylinders for movement of the wheels in phase independently of a mechanical tie rod, wherein forces on the steerable wheels cause loss of pressure in the cylinders and movement of the wheels out of phase under certain steering conditions, the improvement comprising:

a valve assembly connected between the steering unit and the cylinders, the valve assembly including an input side connected to the steering unit, an output side connected to the hydraulic cylinders, the valve assembly including a variable orifice structure selectively restricting return flow of hydraulic fluid from the cylinders to the steering unit to maintain the hydraulic fluid from the cylinders under pressure.

2. The improvement as set forth in claim 1 above wherein the variable orifice structure includes a pilot operated orifice responsive to the variable pressure of the hydraulic fluid supplied from the steering unit, the pilot operated orifice having decreased flow resistance with an increase in the variable pressure.

3. The improvement as set forth in claim 1 wherein the variable orifice structure includes pilot structure connected to the cylinders and reducing the restriction of the return flow when the cylinder pressure reaches a preselected maximum pressure level thereby preventing an overpressure situation in the cylinders.

4. The improvement as set forth in claim 1 including a one-way valve connected in parallel with the variable orifice structure facilitating relatively unrestricted fluid flow towards the cylinders and directing fluid flow from the cylinders through the variable orifice.

5. In a hydraulic steering system for an off-road implement having at least first and second steerable wheels, first and second hydraulic steering cylinders connected to the respective steerable wheels, a steering unit for selectively supplying hydraulic fluid under variable steering pressure to the hydraulic cylinders for steering of the wheels, first and second hydraulic lines connecting the first and second cylinders for movement of the wheels in phase independently of a mechanical tie rod, wherein forces on the steerable wheels cause loss of pressure in the cylinders and movement of the wheels out of phase under certain steering conditions, the improvement comprising:

a valve assembly connected between the steering unit and the cylinders, the valve assembly including an input side with first and second input ports connected to the steering unit, an output side with first and second output ports connected to the hydraulic cylinders, the valve assembly including a variable orifice structure having first and second pilot operated orifices selectively restricting return flow of hydraulic fluid from the cylinders to the steering unit in dependence on the variable steering pressure from the steering unit to the cylinders to maintain the hydraulic fluid from the cylinders under pressure.

6. The improvement as set forth in claim 5 wherein the pilot operated orifices have decreased flow resistance with an increase in the variable pressure.

7. The improvement as set forth in claim 5 wherein the first pilot operated structure is connected in series with the first hydraulic line and includes a first pilot line connected to the second hydraulic line and the second pilot operated orifice is connected in series with the second hydraulic line and includes a second pilot line connected to the first hydraulic line.

8. The improvement as set forth in claim 7 including a one-way valve connected in parallel with the variable orifice structure facilitating relatively unrestricted fluid flow towards the cylinders and directing fluid flow from the cylinders through the variable orifice structure.

9. The improvement as set forth in claim 5 including a pilot line connecting the first hydraulic line to a control input of the variable orifice structure and controlling the variable orifice structure to reduce the restriction of the return flow when the cylinder pressure reaches a preselected maximum pressure level thereby preventing an overpressure situation in the cylinders.

11. The improvement as set forth in claim 9 including first and second check valves connected in parallel with the first and second orifices, respectively, and providing generally free flow from the steering unit towards the cylinders through one of the check valves and compelling a return flow of hydraulic fluid from the cylinders to the steering unit to pass restricted through one of the orifices.

12. The improvement as set forth in claim 9 further including a pilot line structure connected to the cylinders and the pilot operated orifices, the orifices responsive to an overpressure situation in the cylinders to reduce restriction of the flow of fluid between the cylinders and the steering unit to relieve the overpressure situation.

10. In a hydraulic steering system for an off-road implement such as a self-propelled sprayer having at least first and second steerable wheels, first and second hydraulic steering cylinders connected to the respective steerable wheels, a cylinder-connecting line extending between the cylinders, a steering unit for selectively supplying hydraulic fluid under variable steering pressure to the first and second hydraulic cylinders through first and second hydraulic lines, respectively, for steering of the wheels, the first and second hydraulic lines and the cylinder-connecting line connecting the first and second cylinders for movement of the wheels in phase in first and second steered directions independently of a mechanical tie rod, wherein forces on the steerable wheels cause loss of pressure in one or more of the lines and a resulting movement of the wheels out of phase under certain steering conditions, the improvement comprising:

first and second pilot operated orifices connected to the first and second lines, respectively, and selectively restricting flow of hydraulic fluid between the cylinders and the steering unit in dependence on the variable steering pressure from the steering unit to the cylinders to maintain the hydraulic fluid in the lines under pressure, wherein the first pilot operated orifice includes a control input and a pilot line connecting the control input to the second hydraulic line, and the second pilot operated orifice includes a second control input connected to the first hydraulic line, whereby restriction to a return fluid flow of hydraulic fluid from one of the cylinders is dependent on the pressure applied to the other of the cylinders.