Patent Publication Number: US-2003230449-A1

Title: Steered wheel angle sensor using hydraulic flow to steering cylinder

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The invention relates to a steering system. More particularly the invention relates to a hydraulic steering system adapted to be used to measure the steered wheel angle.  
       [0003] 2. Related Art  
       [0004] Hydraulic steering systems provide a known means for steering vehicles. In a typical hydraulic steering system, an operator manually adjusts the position of a steering mechanism, such as a steering wheel. This action causes a steering valve to adjust the flow of hydraulic fluid supplied from a pump to a steering cylinder. This change in the flow of hydraulic fluid results in a change in direction of the steered wheels. Problems arise, however, in developing automatic steering systems. In particular, an automatic steering system needs to determine or measure the steered wheel angle in order to monitor and/or control the steering of the vehicle.  
       [0005] One problem with measuring a steered wheel angle is that the wheels and the steered wheel axis are potentially subject to harsh environmental conditions. This makes locating measurement systems or sensors difficult. Environmental conditions such as dirt or water can adversely impact the accuracy of sensor measurements or damage sensors. Some prior art solutions place sensors in the steering cylinder to measure the position of the steering cylinder. Placing sensors in the steering cylinder also subjects sensors to harsh environmental conditions.  
       [0006] Thus, it is a primary object of the present invention to provide a steering system that improves upon the state of the art.  
       [0007] Another object of the present invention is to provide a steering system that can be used to determine the steered wheel angle of a wheel of a vehicle.  
       [0008] Yet another object of the present invention is to provide a sensing system that can be used to determine a steered wheel angle without directly connecting sensors to the wheels of the vehicle.  
       [0009] A still further object of the present invention is to provide a steering system having a means that can be used to determine wheel angle that need not be located near the steered axle or steered wheels.  
       [0010] These and other objects of the present invention will become apparent from the specification and claims.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011] The present invention is a steering system adapted for determining a steered wheel angle of a vehicle. According to the present invention, a vehicle has a spaced apart pair of steered wheels such as may be located along a steered axle. A two-way hydraulic steering cylinder is operatively connected to the steered wheels. A hydraulic circuit is connected to the hydraulic steering cylinder. The hydraulic circuit includes a hydraulic two-way valve and a hydraulic pump for supplying fluid under pressure, to the circuit, the hydraulic pump being hydraulically connected to the valve.  
       [0012] The cylinder has a single moveable shaft to move in opposite directions to steer the wheels in one of two angular directions. The steered wheel angle sensing steering system provides for determining wheel angle by placing a hydraulic motor in the circuit between the cylinder and the valve. An output shaft on the motor is adapted to rotate in one of two directions depending on the direction of flow of fluid through the motor. A pair of sensors adjacent the shaft are used to determine the direction of motion of the shaft and hence an angular steering position of the wheels, the motion of the shaft being related to the steering position of the wheels.  
       [0013] The present invention provides the advantage of a means of determining the wheel angle that may be used as feedback to a control loop of an automatic steering system. Further, the present invention does not require sensors to be directly connected to the steered wheels. In addition, portions of the invention, including the hydraulic motor can be placed well away from the steered axle of the wheels and in a more protected location. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014]FIG. 1 is a schematic showing the steering system according to the present invention.  
     [0015]FIG. 2 is a front view of the steering angle sensor according to the present invention.  
     [0016]FIG. 3 is a top view of the steering angle sensor according to the present invention; and  
     [0017]FIG. 4 is a top view similar to FIG. 3 showing an alternative form of the invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0018] The invention provides for a steering system that includes steered wheel angle sensing in a hydraulic steering system. As shown in FIG. 1, the steering system  10  includes wheels  12 A and  12 B. Each of these wheels is connected through a linkage  14  (i.e.,  14 A and  14 B) to a two-way hydraulic steering cylinder  18 . The two-way hydraulic steering cylinder  18  has a single moveable shaft  16  to move in opposite directions in order to steer the wheels  12  (i.e.,  12 A and  12 B) in one of two angular directions.  
     [0019] The hydraulic steering cylinder  18  forms a portion of a hydraulic circuit. The hydraulic circuit includes a hydraulic two-way steering valve  20  hydraulically connected to the steering cylinder. The two-way hydraulic steering valve  20  is also hydraulically connected to a hydraulic pump  22 . The pump  22  provides for supplying fluid under pressure to the hydraulic circuit.  
     [0020] The present invention also provides that the steering valve  20  may be connected through a steering column  24  to a steering mechanism  26  such as a steering wheel. This provides for manually controlled steering in the conventional manner, where manual control is desirable.  
     [0021] The steering valve  20  is preferably mounted on the bottom of the steering column  24 . Also connected to the steering valve  20  is the angle sensor  28 . The angle sensor  28  is also hydraulically connected to the steering cylinder  18 . The angle sensor  28  is best shown in FIG. 2. The angle sensor is mounted on the vehicle frame, a vehicle axle, in the cab of a vehicle or elsewhere.  
     [0022] In FIG. 2, the angle sensor  28  is shown as having a hydraulic motor  34  in the hydraulic circuit located between a cylinder and the valve. The hydraulic motor  34  has a shaft  36 . This output shaft  36  on the motor  34  is adapted to rotate in one of two directions depending on the direction of flow of fluid through the hydraulic motor  34 . By measuring the motor shaft motion and direction, the steering angle is inferred.  
     [0023] The relationship between motor shaft motion and steering angle is given by the change in steering angle to the amount of change in motor shaft motion and can vary based on the components used. The change in fluid flow from the steering cylinder corresponds to changes in fluid flow in the hydraulic motor, thus a relationship between shaft motion and steering angle is present. For example, where an operator steers in one direction, there is increased fluid flow to the steering cylinder and therefore a greater steering angle. The fluid flow to the hydraulic motor  34  also increases resulting in an increased speed of rotation of the shaft  36 .  
     [0024] To measure the motor shaft motion and direction, a pair of sensors  30 , (i.e.,  30 A and  30 B) adjacent the shaft are used. This is best shown in FIG. 3. In FIG. 3, a toothed wheel  32  is connected to the shaft  36 . The sensors  30 A and  30 B are placed adjacent the toothed wheel. The sensors  30  may be magnetic sensors such as hall effect sensors. The sensors  30  are placed in a quadrature configuration and thus may be used to measure transitions between teeth  38  and gaps  40  of the toothed wheel  32 . In this configuration, the sensors  30  are used to measure the amount of rotation, such as by counting the number of teeth  38  that pass by one or both of the sensors in a given period of time. Further, a change of direction of rotation is also detectable as this configuration allows the transitions between the teeth  38  and unteethed portions  40  of the wheel to be detected and evaluated.  
     [0025] Although preferably a toothed wheel  32  is used, the present invention contemplates that measurements can be taken of the shaft  36  itself instead of the toothed wheel  32  connected to the shaft  36 . Where a toothed wheel  32  is used, one convenient size of toothed wheel is a five inch diameter wheel, but the present invention contemplates any size. The present invention also contemplates that other types and placements of sensors may be used.  
     [0026] This configuration provides a number of advantages. By measuring the direction of rotation and amount of rotation of cylinder corresponds to changes in fluid flow in the hydraulic motor, thus a relationship between shaft motion and steering angle is present. For example, where an operator steers in one direction, there is increased fluid flow to the steering cylinder and therefore a greater steering angle. The fluid flow to the hydraulic motor  34  also increases resulting in an increased speed of rotation of the shaft  36 .  
     [0027] This configuration provides a number of advantages. By measuring the direction of rotation and amount of rotation of the motor shaft, the steered angle can be determined thus that this information can be used within an automatic steering system. In an automatic steering system, the steered wheel angle can be used as feedback in a control loop. Another advantage of this configuration is that the steer angle sensor  28  may be placed well away from the steering cylinder  18 , steered axle or wheels  12 . Preferably, the steered wheel angle sensor  28  is placed in a more environmentally secure position, instead of near the steered wheels  12  or steered axis. For example, where the steering system of the present invention is used in farm equipment, the steering angle sensor  28  can be placed in a cab of the vehicle or otherwise positioned in order to be better protected from environmental conditions that could affect the sensors.  
     [0028] Further, the sensors  30  need not be directly connected to the shaft  36 . As shown, the present invention contemplates that the hall effect sensors  30  or other noncontact sensors can be used to measure the direction and amount of rotation of the motor shaft.  
     [0029] An alternative form of the invention is shown in FIG. 4. A two-way cylinder  18 A is pivotally secured by one end to the vehicle frame  16 B. Cylinder  18 A is connected by suitable hydraulic hoses to the same components that cylinder  18  is connected as shown in FIG. 1. A reciprocal piston rod  16 A extends from the other end of cylinder  18 A. The outer end of rod  16 A is pivotally secured by linkage  16 B to elongated tie rod  16 C. Rod  16 C is pivotally connected to wheels  12 A and  12 B by linkage  14 A and  14 B. When the reciprocal rod  16 A moves, tie rod  16 C moves correspondingly to steer the wheels  12 A and  12 B in one direction or the other via links  14 A and  14 B, respectively. This arrangement has all the functional advantages of the cylinder elated hydraulic components of FIG. 1.  
     [0030] Thus, a steered wheel angle sensing steering system has been disclosed which solves problems and deficiencies in the art.