Patent Application
20080091319
Referring to the
Valve 22 includes a spring 23 and a solenoid 25, and valve 24 includes a spring 27 and a solenoid 29.
Valve unit 18 includes first and second solenoid operated 4-way, 2-position proportional valves 40 and 42. Valve unit 20 includes first and second solenoid operated 4-way, 2-position proportional valves 44 and 46. Each valve 40-46 includes a solenoid 48-54, a valve position sensor 56-62, and a spring 64-70. The valves are preferably small low-cost cartridge type valves. The valve position sensors 56-62 may be commercially available LVDT (linear variable differential transformer) type spool position sensors, or a suitable similar position sensor.
Lines 80 and 82 connect the pump 26 and reservoir 28, respectively, to inlet ports of shut-off valves 22 and 24. Line 84 connects a first outlet of shut-off valve 22 to inlets of valves 40 and 42. Line 86 connects a second outlet of shut-off valve 22 to inlets of valves 40 and 42. Line 88 connects a first outlet of shut-off valve 24 to inlets of valves 44 and 46. Line 90 connects a second outlet of shut-off valve 24 to inlets of valves 44 and 46. Check valves in lines 84 and 88 permit one-way fluid flow therethrough to shut-off vales 22 and 24.
Line 92 connects right actuator inlet 16 to an outlet of each of valves 40-46. Line 94 connects left actuator inlet 14 to an outlet of each of valves 40-46. Check valves in line 92 permit one-way fluid flow therethrough from valves 40 and 44 to actuator right inlet 16. Check valves in line 94 permit one-way fluid flow therethrough from valves 42 and 46 to actuator left inlet 14.
A relief and check valve circuit 96 operates in a known manner to limit pressure in the actuator 12 and in lines 92 and 94, such as when a steerable wheel (not shown) strikes an object, such a stump. Shuttle check valves 98, 100 and 102 communicate the highest pressure in the branches of lines 92 and 94 to the line sense port 30 of pump 26 via load sense line 104.
In an alternate embodiment (not shown) each of valve units 18 and 20 may include only a single 4-way, 3-position, spring-centered, dual solenoid operated valve.
Turning now to
Pairs of each of sensors 112 and 116 are connected, respectively, to a first channel 118 and a second channel 120. First channel 118 includes a first main processing unit 122 and a first supervisory control unit 124. The first main processing unit 122 and first supervisory control unit 124 are connected to steering wheel position sensors 112A and 112B, to wheel angle sensors 116A and 116B, to solenoids 48 and 50, and to valve position sensors 56 and 58. The first supervisory control unit 124 is also connected to solenoid 25 of shut-off valve 22.
Second channel 120 includes a second main processing unit 126 and a second supervisory control unit 128. The second main processing unit 126 and the second supervisory control unit 128 are connected steering wheel position sensors 112C and 112D, to wheel angle sensors 116C and 116D, to solenoids 52 and 54, and to valve position sensors 60 and 62. The second supervisory control unit 128 is also connected to solenoid 29 of shut-off valve 24. A dedicated CAN bus 130 communicates non safety critical information, such as diagnostics and/or reprogramming, between the channels 118 and 120. Channels 118 and 120 are also connected to a conventional vehicle battery 119 and an alternator 121.
The main processor units 122 and 126 generate control signals (preferably pulse width modulated “PWM”) for the solenoids of the directional control valve units 18 and 20 as a function of the sensed position of the steering wheel 114 and of the steered wheels (not shown). The supervisor processor units 124 and 128 control the shut-off valves 22 and 24 and operate to isolate the channels 118 and 120 from each other. The supervisor processor units 124 and 128 also monitor the health or condition of both channel by direct monitoring of the PWM outputs of the main processor units 122 and 126.
Lines 132 include the following connections between the controllers: supervisor 124 to main 122, main 122 to main 126, main 126 to main 122, supervisor 128 to main 122. These lines communicate pulse width modulated (PWM) signals between the main and supervisor processors, and when one of the processor detects a fault, that processor communicates the existence of that fault to the other processors by changing the duty cycle of the PWM signal communicated to the other processors. This information allows either channel to understand the health of the opposite channel, and to take the appropriate control action.
In normal conditions, the solenoids of valves 22 and 24 are both energized and valve unit 18 (valves 40 and 42) and valve unit 20 (valves 44 and 46) are all operated to share in the control of hydraulic flow to and from the actuator 12. However, if a fault occurs in valve unit 18 or in the circuitry associated with valve unit 18, then processor 124 will deactivate shut-off valve 22, and all the flow to actuator 12 will flow through shut-off valve 24 and will be controlled by valve unit 20 (valves 44 and 46). Similarly, if a fault occurs in valve unit 20 or in the circuitry associated with valve unit 20, then processor 128 will deactivate shut-off valve 24, and all the flow to actuator 12 will flow through shut-off valve 22 and will be controlled by valve unit 18 (valves 40 and 42).
Thus, the system of this invention includes two nearly identical electric (redundant) channels to guarantee the system functions in the event of a single component failure. In each channel, the main processor is responsible for controlling the directional steering control valves, and the supervisor processor controls the shut-off valve of the associated channel.
Critical input sensor information is communicated directly by a hardwired connection between the sensors and both channels.
In this system, all of the steering-related input sensor signals are communicated to both main and to both supervisor processors. Both the supervisor and main processors can calculate a steering valve control signal, but only main processors are connected to the steering control valves. However, the supervisor processors can monitor the steering control signals generated by the main processors, and can disable oil flow (isolate/shutoff) if a main processor generates an unrealistic or invalid control signal.
While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. For example, this invention could be used in a variety of “by-wire” systems, such as a brake-by-wire system, as well as a steer-by-wire system. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.
