STEERING SYSTEM FOR ARTICULATED VEHICLES

• US 3,795,285 A
• Filed: 04/03/1972
• Issued: 03/05/1974
• Est. Priority Date: 04/03/1972
• Status: Expired due to Term

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Edward J. Moyer, Richard E. Klein, Rolland D. Scholl, Terry W. Glynn
• Inventors: Scholl, Rolland D., Moyer, Edward J., Glynn, Terry W., Klein, Richard E.
• Primary Examiner(s): Betts, Kenneth H.
• Assistant Examiner(s): Paperner, Leslie J.
• Application Number:
  US05/240,588
• Time in Patent Office: 701 Days
• Field of Search: 180/79.1,79.2R,79.2B,82R,103 114/144R 307/48,66 318/587,621,663,674 340/249
• US Class Current: 180/271
• CPC Class Codes: B62D 12/00 Steering specially adapted for vehicles operating in tandem or having pivotally connected frames steering endless tracks or the like B62D11/00; steering specially adapted for trailers B62D13/00
• CPC Class Codes: B62D 53/02 comprising a uniaxle tractor unit and a uniaxle trailer unit see B60B11/00 - B60B11/08

Abstract

The front frame of an articulated vehicle is pivoted relative to the back frame for steering purposes by fluid motors controlled through an electrically operated valve. The valve is controlled by the output of an amplifier which produces a signal indicative of the difference between a command signal obtained from a potentiometer coupled to the operator'"'"''"'"'s steering wheel and an actual articulation signal from another potentiometer responsive to changes in the angle of the vehicle frames. Thus a difference between the position of the steering wheel and the actual articulation of the vehicle results in operations of the fluid motors to eliminate such difference. A phase lag is provided in the feedback loop defined by the system to counteract the effects of oil mass resonance which otherwise causes instability unless steps are taken that have adverse side effects such as slowing response and decreasing precision in fluid motor operated systems. Safety means are provided for maintaining electrical energization in the event of failure of the primary power supply and for blocking starting of the vehicle engine if steering wheel position does not conform with actual articulation.

Claims

1. A steering system for a vehicle having an articulated body with front and rear body sections coupled together by pivot means providing for articulation of said vehicle about a vertical axis of said pivot means, comprising a source of pressurized fluid, at least one fluid motor coupled between said front and rear body sections of said vehicle for forcing articulation about said pivot axis, an electrically controlled valve means connected between said fluid source and said motor for actuating said motor to articulate said vehicle about said axis, a manually manipulatable operator'"'"''"'"'s steering control, command signal generating means coupled to said operator'"'"''"'"'s steering control for producing an electrical command signal indicative of movement of said steering control, actual articulation signal generating means coupled between said front and rear body sections of said vehicle for producing an electrical signal indicative of the actual articulation of said vehicle, circuit means connected between said command signal generating means and said valve means for causing said valve means to actuate said motor in response to movement of said operator'"'"''"'"'s steering control and having, comparison circuit means connected between said command signal generating means and said actual articulation signal generating means and said electrically controlled means for transmitting an electrical actuating signal to said valve when said command signal differs from said actual articulation signal, and phase shifting means coupled to the feedback path defined by said actual articulation signal generating means and said comparison circuit means for establishing a predetermined phase lag therethough to inhibit fluid mass resonance effects in said steering system.

2. A vehicle steering system as defined in claim 1, wherein said operator'"'"''"'"'s steering control is a rotatable steering wheel and wherein said command signal generating means is a first potentiometer having a movable contact coupled to said steering wheel and having means for producing an output voltage having a polarity indicative of the direction of movement of said steering wheel away from the centered position thereof and a magnitude indicative of the extent of said movement of said steering wheel sway from said centered position, and wherein said actual articulation signal generating means is a second potentiometer having a second movable contact mechanically coupled to one of said vehicle body sections and having means for producing an output voltage which has a polarity indicative of the direction of articulation of said vehicle and which has a magnitude indicative of the extent of said articulation of said vehicle, the polarity of said output voltage of said second potentiometer being opposite from the polarity of said output voltage of said first potentiometer, and wherein said comparison circuit means comprises an amplifier having input means receiving said first and second potentiometer output signals whereby said output signals cancel at said amplifier input means when the position of said steering wheel corresponds to the actual articulation of said vehicle and wherein said amplifier produces an output signal when the position of said steering wheel and the actual articulation of said vehicle are out of conformity, the amplifier output signal having a polarity and magnitude indicative oF the direction and extent of such disconformity, means for transmitting said amplifier output to said valve for actuating said valve to conform the articulation of said vehicle with the position of said steering wheel, and wherein said phase shifting means is a resistance-capacitance network means connected between the input and output of said amplifier.

3. A vehicle steering system as defined in claim 2 wherein said phase shifting means comprises means establishing a substantially 90* phase lag in said electrical actuating signal transmitted from said comparison circuit means to said electrically controlled valve means.

4. A steering system for a vehicle having an articulated body with front and rear body sections coupled together by pivot means providing for articulation of said vehicle about a vertical axis of said pivot means, wherein said vehicle has an engine and starter means for cranking said engine, comprising:

a source of pressurized fluid, at least one fluid motor coupled between said front and rear body sections of said vehicle for forcing articulation about said pivot axis, an electrically controlled valve means connected between said fluid source and said motor for actuating said motor to articulate said vehicle about said axis, a manually manipulatable operator'"'"''"'"'s steering control, command signal generating means coupled to said operator'"'"''"'"'s steering control for producing an electrical command signal indicative of movement of said steering control, circuit means connected between said command signal generating means and said valve means for causing said valve means to actuate said motor in response to movement of said operator'"'"''"'"'s steering control, means producing an error signal indicative of a predetermined amount of difference in the position of said operator'"'"''"'"'s steering control and the actual articulation of said vehicle, and means receiving said error signal for blocking operation of said engine starter means when said error signal indicates said difference is at least equal to said predetermined amount.

5. A vehicle steering system as defined in claim 4 wherein said error signal has a magnitude indicative of the amount of said difference and an electrical polarity indicating the angular direction of said difference, further comprising an indicator means receiving said error signal for informing said operator of said amount and direction of said difference.

6. A vehicle steering system as defined in claim 4 wherein said engine starter means is electrically actuated through a set of electrical contacts and wherein said error signal producing means produces said error signal in the form of an output voltage having a polarity indicative of the direction of the difference in the position of said steering control and the actual articulation of said vehicle and having a magnitude indicative of the extent of said difference, further comprising an electrically controlled means for operating said contacts, a first amplifier connected between said error signal producing means and said contact operating means and actuating said contact operating means to open said contacts in response to a positive output voltage from said error signal generating means of a predetermined magnitude, and a second amplifier connected between said error signal generating means and said contact operating means and actuating said contact operating means to open said contacts in response to a negative output voltage from said error signal generating means of a predetermined magnitude.

7. A steering system for an articulated vehicle having forward and rear body sections pivoted together to provide for articulation of said vehicle about a substantially vertical axis, comprising at least one hydraulic cylinder connected between said front and rear body sections for articulating said vehicle about said axis in either direction in response to fluid flow supplied to said cylinder, a source of pressurized hydraulic fluid carried on said vehicle, an electrically controlled valve means connected between said source of fluid and said cylinder and having a centered position at which fluid flow to said cylinder is blocked and a right turn position at which fluid is directed to one end of said cylinder while being released from the other end thereof and a left turn position at which fluid is directed to said other end of cylinder while being released from said one end thereof, said valve means having electrical control means with an input conductor wherein an input voltage of first polarity shifts said valve to said right turn position in an amount proportional to the magnitude of said voltage and an input voltage of opposite polarity shifts said valve to said left turn position in an amount proportional to the magnitude of said voltage, a steering wheel mounted on said vehicle for manipulation by the operator thereof, a source of DC electrical current of predetermined voltage, a command signal generating potentiometer having a resistive element connected across said power source and having a movable contact coupled to said steering wheel for operation thereby and having a center tapped ground connection whereby turning of said steering wheel away from the centered position thereof produces a command signal output voltage which has a first polarity relative to said ground and a magnitude indicative of the extent of said turning and turning of said steering wheel in the opposite direction from said second position produces a command signal output voltage having an opposite polarity and having a magnitude indicative of the extent of said opposite turning of said wheel, an actual articulation signal generating potentiometer secured to one of said body sections and having a resistive element connected across said power supply and having a center tap to said ground connection and having a movable contact coupled to the other of said body sections whereby articulation of said vehicle in one direction produces an actual articulation signal output voltage having a polarity opposite to the polarity of said first potentiometer and having a magnitude indicative of said actual articulation of said vehicle and whereby articulation of said vehicle in the opposite direction produces an actual articulation signal output voltage having a reversed polarity and a magnitude indicative of the extent of said opposite articulation, a summing amplifier having an output coupled to said input conductor of said electrically controlled valve means and having an input coupled to said movable contacts of said first potentiometer and second potentiometer whereby said amplifier receives an input voltage which is a summation of said output voltages of said potentiometers and is therefore zero when said steering wheel position corresponds to the actual articulation of said vehicle and which otherwise has a polarity indicative of the direction of disconformity of said steering wheel with said actual articulation and a magnitude indicative of the extent of said disconformity causing said amplifier to transmit an output voltage to said electrically controlled valve means to maintain said actual articulation of said vehicle in substantial conformity with the position of said steering wheel, and a feedback circuit coupled to said output of said amplifier and to said input thereof, said feedback circuit having means for introducing a predetermined phase lag into the signal path between said amplifier input and said input conductor of said electrically controlled valve means to counteract fluid mass resonance effects in said steering system.