Patent Application
20050051377
The present invention generally relates to a Hydraulically Power Assisted Steering system (HPAS-system) arranged to supply a steering assist force to the steering assembly of an automobile or a vehicle. In particularly the invention relates to an HPAS-system including a rotary valve unit, which may be actuated to dynamically alter the steering assist force produced by the HPAS-system.
Various steering arrangements for assisting a driver in steering an automobile or a vehicle are well known in the art. Especially it is well known that the turning direction of a vehicle can be maneuvered by a steering wheel that is mechanically connected to the road wheels through a steering assembly. In assisting the driver it is common to use an auxiliary system to generate an additional steering force, which is applied to the steering assembly of the vehicle. The additional steering force is suitably adapted to reduce the effort required by the driver in changing the direction of the road wheels.
Traditionally, various Hydraulic Power Assisted Steering (HPAS) systems have been used to add a certain amount of assist force or assist force to the steering assembly of a vehicle. These traditional HPAS-systems are typically based on an assist characteristic, a so-called boost-curve. The shape of a boost-curve is typically and essentially determined by the design of the valve and the pump of the HPAS-system. The boost-curve in a traditional HPAS-system is therefore static.
According to the function of a traditional boost-curve a certain torque applied by the driver to the steering wheel result in a certain predetermined assist force supplied by the HPAS-system to the steering assembly of the vehicle. This predetermined assist force increases as the driver applies more torque to the steering wheel, and decreases as the driver applies less torque to the steering wheel. The use of a static boost-curve gives a static relation between a steering effort required from the driver and a corresponding assist force supplied by the HPAS-system, i.e. the relation follows a static and predetermined curve.
Nevertheless, the amount of steering effort required from the driver and the appropriate assist force that should be supplied by the HPAS-system may vary depending on various external circumstances and especially dependent upon the specific driving scenario, e.g. dependent upon the vehicle speed, the vehicle turning angle etc. Future customer functions such as my-split braking aid or Lane Keeping Aid demand more flexible solutions in terms of steering wheel assist force.
From the steering gears perspective this presupposes a more dynamic change in the relation between assist force and drivers torque. This can be achieved with an Electric Power Assisted Steering (EPAS) using an electric motor to supply an assist torque to the vehicle steering assembly. Consequently, the introduction of new steering related customer functions in passenger cars essentially depends of the implementation of EPAS-systems.
However, some HPAS-system has been developed to achieve a more dynamic change in the relation between assist force and drivers torque.
U.S. Pat. No. 5,593,002 (Okada et al.) shows a HPAS-system comprising a rotary valve unit actuated according to a twisting angle provided in a torsion bar connected between an input shaft and a pinion shaft and a pinion, and a conversion mechanism which can change the condition of the rotary valve unit for a given twisting angle of the torsion bar. It should be noted that the flow of oil through the rotary valve in Okada is not directly affected by said change of valve condition. However, when a torque is applied to the steering wheel more or less oil may flow through the valve depending on the valve operative condition, se e.g. col. 5 line 41-col. 6 line 63. The change of condition in Okada may be seen as a multiplicative or lever system affected by the speed of the vehicle.
U.S. Pat. No. 5,513,720 (Yamamoto et al.) shows a HPAS-system that comprises a steering mechanism having a torsion bar, a rotary valve connected to an oil pump and disposed between an input shaft and an output shaft, a valve driving mechanism having a pressed portion projected on either the input shaft or the output shaft and a plunger on the one shaft of the input shaft or output shaft on which the pressed portion is not projected for pressing the pressed portion, setting a target assist force of an assist force obtained by rotating the rotary valve in the torsion direction of the torsion bar and an assist force obtained by rotating the rotary valve in the reverse direction to the torsion direction, a plunger driving mechanism for driving the plunger so that the preset assist force is obtained, controlling the pressure itself of the rotary valve to the operation angle of the rotary valve. This arrangement may be used to achieve a more dynamic change in the relation between assist force and driver torque. However, it should be noted that the rotary valve is rotated by generating in the torsion bar 9 a torsional moment in the forward direction (right direction) or in the reverse direction (left direction), see e.g. col. 8 lines 33-49. This means that the torsion bar is exposed to extra tensional strain, which reduces its deflecting response to driver-applied torque and which may reduce the useful life of the torsion bar. Moreover, the force needed to deflect the torsion bar is fairly large, with a bulkier and heavier construction as a consequence.
To summarise, the prior art cited above may in some respect offer a solution to achieve a more dynamic change in the relation between assist force and drivers torque in an HPAS-system. However, the prior art have several drawbacks.
The invention offers a simple solution to enable a dynamic change in the relation between assist force and drivers torque in an HPAS-system. In particular, the invention offers a solution that may be implemented by simple modifications of conventional HPAS-systems, comprising a rotary valve actuated according to a twisting angle provided in a torsion bar or a similar deflecting device or turnable device connected between a steering shaft attached to a steering wheel and a pinion shaft or similar attached to the steering rack or similar, where the actuation of the rotary valve determines the assist force Fass that is supplied by the HPAS-system to the steering assembly of the vehicle.
Such conventional HPAS-systems may be understood as a servo system having a controller that tries to minimize or reduce the angular difference αΔ between the turning angle αsw of the steering wheel and the turning angle αps of the pinion shaft. In other words these conventional HPAS-systems may be understood as a servo system that tries to reduce or minimize any twisting of the torsion bar.
However, the invention is not limited to conventional HPAS-systems and it should be understood that the torsion bar and other parts of the vehicle steering assembly may be substituted for other parts having the same or similar function, provided that the rotary valve may be actuated to reflect a larger angular difference αΔ when the driver applies more torque to the steering wheel and actuated to reflect a smaller angular difference αΔ when the driver applies less torque to the steering wheel.
As previously stated in the background of the invention the use of a conventional HPAS-system having a static boost-curve gives a static relation between the steering effort required from the driver and the corresponding assist force supplied by the HPAS-system. In other words, the relation between drivers torque and assist force follows a static and predetermined curve, whereby a specific αΔ results in a specific assist force Fass. Obviously there is a need for a more flexible solution than the one offered by the static solution in conventional HPAS-systems.
The invention therefore discloses an arrangement and a method that i.a. enables a varying offset angle αoff to be more or less dynamically added to or subtracted from the angular difference αΔ between the steering wheel turning angle αsw and the turning angle of the pinion shaft αps, i.e. αΔ±αoff.
This may be accomplished by arranging one part of the rotary valve to be non-rotatably supported on the vehicle steering shaft, while another part of the rotary valve, e.g. the valve house, may be supported on the pinion shaft so that it may be displaced in relation to the pinion shaft, preferably rotatably displaceable a small angle αoff with respect to the pinion shaft. The valve house may then rotate together with the supporting pinion shaft, however displaced by a small angle αoff with respect to the pinion shaft. The same applies mutatis mutandis if the valve house or similar part is alternatively supported on the steering shaft.
This means that an angular difference αΔ reflected by the rotary valve may be increased by an small offset angle +αoff, which further opens the rotary valve to increase the hydraulic pressure in a hydraulic piston or similar for supplying an increased steering assist force FΔass to the steering rack, resulting in a total amount of steering assist force Fass+FΔass. The angular difference αΔ may conversely be decreased by a small offset angle −αoff, which slightly closes the rotary valve to decrease the hydraulic pressure for supplying an decreased steering assist force Fass−FΔass.
By arranging the valve house or similar part of the rotary valve to be dynamically actuated a small offset angle αoff in relation to the supporting pinion shaft it is possible to dynamically adjust the assist force Fass corresponding to an angle αΔ, with a certain amount of assist force±FΔass, corresponding to an offset angle±αoff, so that an appropriate assist force Fass±FΔass is delivered by the HPAS-system to fit the specific driving scenario, where a control mechanism determines the offset angle αoff depending on at least one external or internal vehicle input parameter.
The forces needed to obtain an displacement or an offset—e.g. an offset angel αoff—by directly actuating a part of a rotary valve are fairly low, mainly comprising flow forces created within the valve and friction forces emanating from the actuated valve part.
Further advantages will appear from the following detailed description of the invention.
The following figures form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these figures in combination with the detailed description of specific embodiments presented herein.
Reference signs in the Figures are as follows:
The HPAS-System
Referring to
The HPAS-System Steering Assembly
The HPAS-system 100 shown in
It should be appreciated that the steering wheel 120, the steering shaft 121, the pinion shaft 122, the pinion gear assembly 123, the rack 124, the tie rods 125, the connector rods 126 and the road wheels 127 as shown in
Moreover, as will be further explained below the interconnecting assembly 130 of the steering assembly i.a. comprises a torsion bar 210 and a rotary valve 300 connected to a servo pump 128 (schematically indicated in
The Interconnecting Assembly and the Rotary Valve
The interconnecting assembly schematically 130 indicated in
Further, the interconnecting assembly 130 comprises a rotary valve 300. As illustrated in
The rotary valve 300 in
The rotary valve 300 illustrated in
The right side structure of the rotary valve 300 in
The extension of the pinion shaft 122 comprising the rotary valve 300 in
Said second chamber 335 communicates with a second pair of inner through-holes 340 arranged in the first cylindrical valve member 305, where the second pair of through-holes are adapted to dynamically communicate with a second pair of outer through-holes 345 arranged in the second cylindrical valve member 310, where the second outer through-holes 345 communicate with a third chamber 350, which in turn communicates with an outlet through-hole 360 for an outlet of the received pressurized hydraulic fluid, where both the third chamber 350 and the outlet through-hole 360 are arranged in the extension of the pinion shaft 122 for supplying pressurized hydraulic fluid to the servo-motor 129.
The first cylindrical valve member 305 and the second cylindrical valve member 310 of the rotary valve 300 are further illustrated in
It should be added that the valve members 305, 310 may preferably be operatively arranged to vary the position of the through-holes 330, 340 and 325, 345 from a complete overlap, corresponding to a large αΔ, to a gradual decrease of the overlap, corresponding to a decrease in αΔ, where no overlap at all corresponds to αΔ=0. Where there is no overlap at all there is consequently no flow of hydraulic fluid to the servo-motor and there is consequently no assist force Fass delivered from the servo-motor.
The rotary valve 300 may also comprise a flange portion 370 formed as a protrusion of the first cylindrical valve member 305 and arranged at the lower end of said member 305. The flange portion 370 protrudes into a recess chamber 371 arranged in the extended portion of the pinion shaft 122, as can be seen in
By a dynamic change of the hydraulic pressure in said right and left chamber it is possible to dynamically adjust the assist force Fass, corresponding to an angle αΔ, with a certain amount of assist force±FΔass, corresponding to an offset angle±αoff, so that an appropriate assist force Fass±FΔass is delivered by the servo-motor 129 to fit the specific driving scenario, where a control mechanism determines the offset angle αoff depending on at least one external or internal vehicle input parameter, e.g. vehicle speed, vehicle acceleration, vehicle turning angle etc. The choice of control mechanism is not important to the present invention and it may e.g. be any suitably programmed computer system.
The right side structure of the rotary valve 300 has now been described with numbered references to the different parts in
The invention is not limited to the rotary valve 300 illustrated in
In brief, the present invention may generally be implemented in a vast variety of rotary valves that is well known to a person skilled in the art.
Other Embodiments
In a second embodiment of the present invention the rotary valve 300 as illustrated in
According to this embodiment the first cylindrical valve member, 305 is adapted so as to be provided with a cogged ring 415 or a similar toothed device for interaction with the cog wheel 400 or similar. The flange portion 370 has consequently been omitted in this second embodiment. The arrangement in
The second embodiment makes it possible to have the first cylindrical valve member 305 rotated an offset angle αoff by commanding the electric motor 410 to rotate the cog wheel 400 an appropriate angle αcog. Consequently, by commanding the motor 410 to dynamically change the rotation angle αcog of the cog wheel 400 it is possible to dynamically adjust the assist force Fass, corresponding to an angle αΔ, with a certain amount of assist force±FΔass, corresponding to an offset angle±αoff, so that an appropriate assist force Fass±FΔass is delivered by the servo-motor 129 to fit the specific driving scenario, where a control mechanism determines the offset angle αoff depending on at least one external or internal vehicle input parameter, e.g. vehicle speed, vehicle acceleration, vehicle turning angle etc. The choice of control mechanism is not important to the present invention and it may e.g. be any suitably programmed computer system.
It should be noted that the second embodiment is essentially similar to the first embodiment as described above, except for the adaptations now mentioned.
In a third embodiment of the present invention a rotary valve 300 as illustrated in
This may be accomplished by non-rotatably attaching the first cylindrical valve member 305 to a valve house 520 that i.a. encases the first and second cylindrical valve members 305, 310 as shown in
The valve house 520 in this third embodiment may be rotated a small offset angle αoff with respect to the pinion shaft 122 according to the arrangement illustrated in
The rotational movement of the valve house 520 is then preferably obtained by a diagonal track or slot 510, e.g. arranged as a cylindrical flange portion 515 that is arranged to extend axially downward from the lower part of the valve house 520, where the slot 510 is guided by a rivet 511 or some other suitable guiding device that is arranged on the pinion shaft 122. Hence, when the valve house 520 and the cylindrical flange 515 firmly attached thereto are move up or down by a slight rotation of the eccentric axis 505 that is actuated by the motor 500 this will cause the valve house 520 to rotate as the diagonal slot 510 moves guided by the rivet 511. The valve house 520 and the cylindrical flange 525 may be dynamically moved up and down by the eccentric axis 505 actuated by the electric motor 500 so that the diagonal slot 510 may take any position between position A and position B, as indicated in
A small movement of the slot 510 guided by the rivet 511 will cause the valve house 520 rotate a small offset angle αoff with respect to the pinion shaft 122, where a movement of the slot 510 from position A to position B corresponds to the maximum rotation angle αmax of the valve house 520 in this embodiment. This maximum rotation angle αmax is similar to the αmax previously discussed in connection with the first embodiment and
Hence, once the eccentric axis 505 has been rotated an angle αecc by the electric motor 500 to displace the valve house 520 and the first cylindrical valve member 305 attached thereto an offset angle αoff the first cylindrical valve member 305 will rotate together with the pinion shaft 122, however possibly displaced by an small angle αoff with respect to the pinion shaft 122.
The third embodiment makes it possible to have the first cylindrical valve member 305 rotated an offset angle αoff by commanding the electric motor 500 to rotate the eccentric axis 505 an appropriate angle αecc. Consequently, by commanding the motor 500 to dynamically change the rotation angle αecc of the eccentric axis 505 it is possible to dynamically adjust the assist force Fass, corresponding to an angle αΔ, with a certain amount of assist force±FΔass corresponding to an offset angle±αoff, so that an appropriate assist force Fass±FΔass is delivered by the servo-motor 129 to fit the specific driving scenario, where a control mechanism determines the offset angle αoff depending on at least one external or internal vehicle input parameter, e.g. vehicle speed, vehicle acceleration, vehicle turning angle etc. The choice of control mechanism is not important to the present invention and it may e.g. be any suitably programmed computer system.
It should be noted that the third embodiment is essentially similar to the first embodiment as described above, except for the adaptations now mentioned.
All of the processes and/or apparatus disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the processes and/or apparatus of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the apparatus and/or processes and in the steps or in the sequence of steps of the processes described herein without departing from the concept and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the scope and concept of the invention.
