Abstract:
A method to evaluate a secondary steering system including the steps of lowering the first hydraulic fluid pressure, determining the first hydraulic fluid pressure, sensing a second hydraulic fluid pressure, and comparing the first hydraulic fluid pressure to the second hydraulic fluid pressure. The lowering step includes lowering the first hydraulic fluid pressure provided by the primary steering system power source while the vehicle is traveling at a substantially predetermined speed. The sensing step includes sensing the second hydraulic fluid pressure provided by the secondary steering system power source while an operator of the vehicle is steering the vehicle as the vehicle travels at the predetermined speed. The comparing step includes comparing the first hydraulic fluid pressure to the second hydraulic fluid pressure to determine if the second steering system power source provided fluid to steer the ground-engaging device.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a secondary steering test method for a vehicle, and, more particularly, to a secondary steering system testing method for a vehicle that is performed in the operating environment. 
       BACKGROUND OF THE INVENTION 
       [0002]    Steering is a term applied to a collection of components, linkages, and systems to allow a vehicle to be directed to follow a desired course. The basic aim of steering is to ensure that the wheels are directed to a desired position. This is generally achieved by a series of linkages, rods, pivots, gears, hydraulic systems, etc. 
         [0003]    Many vehicles use a rack and pinion steering mechanism where a steering wheel turns the pinion gear and a pinion moves the rack, which is a linear gear that meshes with the pinion, converting circular motion into linear motion along the transverse axis of the vehicle. This motion applies steering torque to ball joints that are connected to tie rods and a short lever arm called the steering gear. 
         [0004]    A hydraulic power steering system uses hydraulic pressure supplied by a pump to assist in the motion of turning the steering wheel. There are also electrical power steering systems to assist in the steering of the vehicle. 
         [0005]    Four-wheel steering, on some vehicles, is utilized to improve steering response, increase the vehicle stability while maneuvering at high speed and/or to decrease turning radius at low speed. In most active four-wheel steering systems, the rear wheels are steered by a controller and actuators. The rear wheels generally cannot turn as far as the front wheels in most systems. Some vehicles utilize what is called a passive steering system to correct for the rear wheel tendency to toe-out. The passive steering system utilizes lateral forces generated in a turn, through the suspension geometry, to correct the tendency and to steer the rear wheels slightly to the inside of the corner. 
         [0006]    Some vehicles utilize rear wheel steering, such as some forklift trucks and some other construction equipment. In many construction vehicles, steering is done by a hydraulic system that is activated by the steering wheel, causing the steered wheels to turn based on hydraulic pressure supplied thereto. Some systems are referred to as steer-by-wire, with the aim of this technology to do away with as many mechanical components, such as a steering shaft, steering column, gear reduction mechanisms, etc. Steering systems that utilize hydraulic power to either assist or to completely control the steering of a vehicle utilize pressurized hydraulic fluid supplied by an engine-driven pump. For many systems, a secondary steering system is also provided to utilize the forward momentum of the vehicle to supply a secondary source of pressurized hydraulic fluid to the system in the event that the primary system ceases to function. For example, if the engine were to cease operation for some reason, steering power is still available as the forward momentum of the machine provides the pressurized hydraulic fluid for the steering system. 
         [0007]    The testing of the secondary and primary steering systems can be done in a test stand environment where the systems are activated, deactivated, and checked for functioning using the connections and interaction of the test stand. Another method utilizes a system in which the engine is shut off during operation to see if the secondary system is functioning. This sort of test has several disadvantages in that the engine power is not available and requires the bypassing of safety systems in order to test the secondary system. 
         [0008]    What is needed in the art is a secondary steering system test that can be conducted without bypassing safety criteria built into a vehicle&#39;s operating system and without the need for a specialized test stand. 
       SUMMARY The present invention provides a secondary steering system test, and, more particularly, a secondary steering system test for a vehicle in an operating environment. 
       [0009]    The invention in one form is directed to a vehicle having a ground-engaging device, a primary steering system power source, a secondary steering system power source, and a controller. The primary steering system power source is configured to provide steering power to the ground-engaging device. The secondary steering system power source is also configured to provide steering power to the ground-engaging device. The controller is communicatively coupled to the primary steering system power source and the secondary steering system power source. The controller is configured to execute steps of a method to evaluate the secondary steering system power source. The method executed by the controller includes the steps of lowering the first hydraulic fluid pressure, determining the first hydraulic fluid pressure, sensing a second hydraulic fluid pressure, and comparing the first hydraulic fluid pressure to the second hydraulic fluid pressure. The lowering step includes lowering the first hydraulic fluid pressure provided by the primary steering system power source while the vehicle is traveling at a substantially predetermined speed. The sensing step includes sensing the second hydraulic fluid pressure provided by the secondary steering system power source while an operator of the vehicle is steering the vehicle as the vehicle travels at the predetermined speed. The comparing step includes comparing the first hydraulic fluid pressure to the second hydraulic fluid pressure to determine if the second steering system power source provided fluid to steer the ground-engaging device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0011]      FIG. 1  is a schematical illustration of a vehicle incorporating an embodiment of the steering system test method of the present invention; 
           [0012]      FIG. 2  is a schematic illustrating part of the control system utilized by the method of the present invention on the vehicle of  FIG. 1 ; 
           [0013]      FIGS. 3A through 3C  are a schematical flowchart illustrating the steps of an embodiment of the method of the present invention utilized with the vehicle of  FIG. 1  and the control system of  FIG. 2 . 
       
    
    
       [0014]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one embodiment of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION 
       [0015]    Referring now to the drawings, and more particularly to  FIG. 1 , there is illustrated, in a schematical fashion, a vehicle  10  having ground-engaging devices  12 , an engine  14 , a primary steering system power source  16 , a secondary steering system power source  18 , a controller  20 , a steering input  22 , and steering actuators  24 . Vehicle  10  may be in the form of an articulated vehicle or other ground-engaging vehicle utilized for construction, agricultural, forestry, mining, and other related vehicles that have primary and secondary steering systems. Ground-engaging devices  12  may be wheels, tracks, or other devices allowing vehicle  10  to proceed over the ground. Although illustrated as wheels  12  that are being steered, other forms of steering, including an articulated vehicle, are anticipated and steering actuators  24  refer generally to those actuators, which are utilized in steering vehicle  10 . Engine  14  may be an internal combustion engine in the form of a diesel engine providing power to various functions of vehicle  10  including driving a hydraulic pump that is a part of primary steering system power source  16 . 
         [0016]    Primary steering system power source  16  provides hydraulic pressure and fluid flow under the direction of controller  20  to steering actuators  24  as directed by information from steering input  22 . Primary steering system power source  16  may also provide hydraulic fluid pressure and flow for other functions not discussed herein. 
         [0017]    Secondary steering system power source  18  is driven by a mechanical linkage by way of a connection to at least one ground-engaging device  12 . The forward movement of vehicle  10  provides a driving force to the pump in secondary system power source  18  so that when vehicle  10  is moving, an alternate source of pressurized hydraulic fluid flow is available in the event that primary steering system power source  16  fails or provides inadequate pressure. Controller  20 , which may be a combination of hydraulic and electrical elements, receives steering information from steering input  22 , which may be in the form of a steering wheel or joystick, etc. Controller  20  utilizes steering information and directs hydraulic pressure appropriately to steering actuators  24  to steer ground-engaging devices  12 . It is understood that controller  20  may actually be integral with some other portion of vehicle  10 , including steering actuators  24 , so that steering information provided by steering input  22  is then expressed in the steering of vehicle  10 . For the sake of clarity, steering actuators  24  can be considered to be hydraulic cylinders that effect the steering of vehicle  10  and can be the steering of all or some of the ground-engaging devices  12  or by articulated movement of vehicle  10  or by a combination thereof. 
         [0018]    Now, additionally referring to  FIG. 2 , there is illustrated a portion of controller  20  with some relevant circuits connected for the purposes of illustrating the function of the primary and secondary steering system power sources  16  and  18  and how the testing of secondary steering system power source  18  is undertaken. Primary steering system power source  16  includes a primary pump  26  that is driven by engine  14 . Primary pump  26  supplies pressurized hydraulic fluid to controller  20 . Secondary steering system power source  18  includes a secondary pump  28  that is driven by a ground-engaging device  12  by way of mechanical linkages therebetween. Pressure regulator  30  and a pressure switch valve  32  are also illustrated. Pressure regulator  30  provides for a release of hydraulic fluid in the event the pressure generated by secondary pump  28  exceeds a predetermined value, such as 200 bar. Pressure switch valve  32  monitors the pressure difference between primary pump  26  and the load sense line (LSEP), and in the event that the pressure difference falls below a predetermined value, such as 10 bar, pressure switch valve  32  is activated and moved to the position as shown in  FIG. 2 , causing the fluid flow from secondary pump  28  to supply hydraulic fluid flow to controller  20 . If the difference between the primary pump  26 , and the pressure requirement from the steering system as communicated through LSEP is 10 bar or more, then pressure switch valve  32  directs the fluid flow from secondary pump  28  back to the reservoir, and controller  20  utilizes hydraulic fluid flow from primary pump  26 . A transducer  34  is connected into the pressure supply line from pump  26  by way of primary manifold PM to monitor the pressure for purposes of the testing method described herein. A pressure transducer  36  is connected to the supply line P 2  from pump  28  for monitoring of the pressure of secondary steering system power source  18 . A signal from the load sense line (LSEP) is sent to valve  32  that reflects the amount of pressure that the steering valve needs to continue to function properly. The primary manifold PM line sends a signal to the secondary steering manifold that reflects the amount of pressure primary pump  26  is currently providing. If, at any time, the LSEP signal becomes within 10 bar of the PM signal, valve  32  will change position, causing secondary steering system power source  18  to be active and pressure to be applied to the main manifold steering circuit by way of line P 2 . 
         [0019]    During the secondary steering test, the artificial situation of pump  26  not supplying fluid is created by cutting the load sense signal (LSP) to primary pump  26 . This is done by actuating valve  38  between the LSP line and primary pump  26 . This causes the LSP from the main manifold to be blocked with the fluid of load sense signal (LSP) being sent to the reservoir tank. If primary pump  26  doesn&#39;t see a load sense signal LSP, it provide a minimal pressure, so that valve  32  activates when a steering command is given, causing secondary pump  28  to provide pressurized hydraulic fluid flow to controller  20 . This condition is then verified by transducers  34  and  36  and vehicle  10  will continue to be able to steer utilizing fluid flow from secondary pump  28 . 
         [0020]    Now, additionally referring to  FIG. 3 , there is illustrated a flowchart that outlines steps that can be utilized in the carrying out of inventive method  100 . Method  100  begins at step  102  and, when a test is requested at step  104 , several items are checked to see if the vehicle is in condition for carrying out the test. First, a check of the vehicle attitude is undertaken to ensure that vehicle  10  is on substantially level ground at step  106 . If the vehicle is not on a substantially level ground, then the test aborts at step  108  and information is provided to the operator that the test cannot be carried out until the vehicle attitude is corrected. At step  110 , a check is undertaken to ensure that vehicle  10  is otherwise in working order by checking the diagnostic codes. If the diagnostic codes are not satisfactory, then the test is aborted and this condition is conveyed to the operator. If the diagnostic codes are OK, then, at step  112 , it is checked to see if safety critical systems are in their proper state. The safety critical items include such items, for example, as results of a brake test, tire pressures being at acceptable levels, and the inner axle differential lock (IDL) being inactive. If the safety critical items are acceptable, then method  100  proceeds to step  114 . If not, the operator is informed at step  108  of this condition and is requested to disengage the differential lock. At step  114 , a check is undertaken to see if vehicle  10  is loaded. If vehicle  10  is loaded, then method  100  proceeds to step  108  and the test is aborted, informing the operator that the test needs to be undertaken with no load in the vehicle. This is to ensure that the test is preformed with the vehicle at substantially the same vehicle weight each time the test is performed. If the vehicle is not loaded, then the test initiates at step  116 . 
         [0021]    At step  116 , pressure reduction of the fluid supplied by primary pump  26  is accomplished by activating valve  38 . At step  118 , controller  20  may actuate a speed limit limiting the speed at which the operator may operate vehicle  10  to a predetermined speed. At step  120 , the operator is informed to achieve this predetermined speed, which may be  12  kilometers per hour. A check then is carried out at step  122  to see if the predetermined speed has been achieved for a predetermined time. The predetermined time required to ensure that the speed has been achieved may be, for example, two seconds. If the predetermined speed has been achieved, then method  100  proceeds to step  124  in which the operator is informed to steer the vehicle. Once the vehicle has been steered as requested in step  124 , then at step  126 , the steering angle is checked by way of an angular steering sensor to ensure that the operator has steered the vehicle sufficiently above a predetermined minimum angle, thereby confirming that the steering operation has been carried out. 
         [0022]    At steps  128  and  130 , the primary steering fluid pressure and the secondary fluid pressure are checked using transducers  34  and  36  and, even though these are shown as sequential steps, these two steps may be carried out during the execution of other steps, such as steps  116  through  138 , to particularly ensure that the steering accomplished in steps  124  and  126  was carried out by fluid flow from secondary pump  28 . At step  132 , a check is undertaken to see that the secondary pressure was greater than the primary pressure during the functional aspects of the test. If the primary pressure was equal to or greater than the secondary pressure, then failure of the test is conveyed to the operator at step  134 . Additionally, if the operator intervened at step  136  during the functioning of the steering test, such as application of a service brake or a parking brake, or if the accelerator is released at any stage during the test after the initial acceleration, then this information is conveyed to the operator at step  134  that the test has failed and may need to be restarted. If the operator did not intervene in the test and the secondary pressure was greater than the primary pressure as checked at step  132 , then a message is displayed to the operator, at step  138 , indicating that the test was successful and this data may be logged into a memory device for future analysis. The test ends at step  140  and primary pump  26  is reactivated by the de-energizing of valve  38 , which causes valve  32  to shift so that secondary pump  28  is not supplying pressurized fluid and primary pump  26  is supplying pressurized fluid to controller  20 . 
         [0023]    While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.