WO2003101808A1 - Systeme de direction de vehicule - Google Patents

Systeme de direction de vehicule Download PDF

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Publication number
WO2003101808A1
WO2003101808A1 PCT/GB2003/002346 GB0302346W WO03101808A1 WO 2003101808 A1 WO2003101808 A1 WO 2003101808A1 GB 0302346 W GB0302346 W GB 0302346W WO 03101808 A1 WO03101808 A1 WO 03101808A1
Authority
WO
WIPO (PCT)
Prior art keywords
valve
motor
torque
steering system
shaft
Prior art date
Application number
PCT/GB2003/002346
Other languages
English (en)
Inventor
David Writer
David Chew
Original Assignee
Trw Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Trw Limited filed Critical Trw Limited
Priority to AU2003234050A priority Critical patent/AU2003234050A1/en
Publication of WO2003101808A1 publication Critical patent/WO2003101808A1/fr

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D5/00—Power-assisted or power-driven steering
    • B62D5/06—Power-assisted or power-driven steering fluid, i.e. using a pressurised fluid for most or all the force required for steering a vehicle
    • B62D5/08—Power-assisted or power-driven steering fluid, i.e. using a pressurised fluid for most or all the force required for steering a vehicle characterised by type of steering valve used
    • B62D5/083—Rotary valves
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D5/00—Power-assisted or power-driven steering
    • B62D5/06—Power-assisted or power-driven steering fluid, i.e. using a pressurised fluid for most or all the force required for steering a vehicle
    • B62D5/09—Power-assisted or power-driven steering fluid, i.e. using a pressurised fluid for most or all the force required for steering a vehicle characterised by means for actuating valves

Definitions

  • This invention relates to vehicle steering systems, and in particular but not limited to such steering systems for use in heavy load applications where high steering forces may be present.
  • assistance force is provided by a hydraulic actuator which is operatively connected to a steering rack of the steering system.
  • the steering wheel is connected to the rack through a torsion bar (typically a portion of the shaft of reduced cross section) and as the driver applies a torque to the steering wheel the torsion bar is deflected, in turn rotating a rotary hydraulic valve.
  • the rotation of the valve affects the path of pumped hydraulic fluid from a reservoir via a pump to the hydraulic actuator, and thus controls the assistance force applied by the actuator.
  • Hydraulic systems have been in use for many years. With the advent of advanced steering control systems it has become desirable to apply other forces to the steering system in addition to the usual assistance forces. For example, in a lane guidance system it may be useful to apply a force to the system that assists in keeping a vehicle within a lane on the highway. This type of overlay force has not traditionally been possible using a hydraulic system.
  • a vehicle steering system comprising an input member adapted to be operatively connected to a steering wheel, an output member adapted to be connected to at least one steered wheel of a vehicle, a sensing means which produces an output signal indicative of the torque carried by the input member, a control unit which generates a demand signal indicative of the amount of assistance force that is to be applied to the output member dependent upon the output of the torque sensor, and an electric actuator which is driven by a drive signal dependent upon at least the torque demand signal, the actuator controlling the operation of an hydraulic valve which controls the flow of fluid to an hydraulic actuator which is operatively connected to the output member, the motor thereby controlling the amount of force applied by the hydraulic actuator to the output member as a function of at least the torque applied by the driver.
  • the invention therefore provides for the electronic control of a hydraulic valve and actuator in order to provide assistance torque to the steering system.
  • the use of hydraulics makes the system especially suitable for heavy vehicles where high steering forces are present.
  • the use of an electronically controlled actuator to control the passage of fluid to the hydraulic actuator also provides the advantage that an overlay torque can be provided with a high degree of flexibility.
  • the output member may comprise a rack which will typically be connected to the input member through a pinion gear.
  • the actuator may be adapted to apply a force which tends to push and/or pull the rack in one direction or the other depending upon the sign of the demand signal.
  • the actuator may apply a rotational force to a shaft connected to the input shaft or perhaps to the input shaft itself.
  • the control unit may generate a first demand signal which is based solely on the torque sensed in the intermediary member and additionally may produce a second demand signal based upon additional vehicle parameters such as speed, steering angle, lateral acceleration and yaw rake.
  • the first and second demand signals may be combined to produce an overall torque demand signal which is used to drive the motor.
  • the second signal may additionally take into account signals from a lane guidance or stability control system for example.
  • the input member is preferably a portion of a steering shaft, and the output member is preferably a portion of a steering rack.
  • the input member may be connected to a torsion bar, the opposite end of which is coupled to an intermediate member which is in turn connected to the output member.
  • the torsion bar may be a portion of shaft of reduced section. This arrangement provides a direct connection between the input member and the output member which allows the driver to receive feedback from the wheels and "feel" the torque carried by the steering. This provides a greater feeling of control to the driver. It also ensures that the driver can retain the ability to steer the vehicle in the event of a failure of the motor or the hydraulic assistance. Dog teeth or other such lost motion meshing means may be provided on the input and intermediate members which co-operate in the event of a failure of the torsion bar.
  • the torque and optionally angular position may be sensed by a sensor which measures the angular deflection of the torsion bar.
  • a suitable sensor may be based upon optical technology although a wide range of devices are known in the art.
  • the electric actuator may comprise a motor having a rotor and a stator and the hydraulic valve may additionally comprise a rotary valve having first and second valve portions. Rotation of the motor may be adapted to cause rotation of one portion of the valve in order to control the passage of fluid through the valve to the hydraulic actuator.
  • the motor and the hydraulic valve and the torsion bar may be aligned concentrically about a common axis. They may be provided within a common housing.
  • the intermediary member may pass completely through the centre of the motor and the valve.
  • the steering shaft includes a torsion bar to increase the displacement of the shaft for a given range of torques
  • the torsion bar my pass through the centre of the motor and the valve.
  • Arranging the torsion bar, motor and valve about a common axis results in a unit of particularly compact dimensions. This is especially useful since the space available installation of a steering system may be quite limited.
  • the motor controlled hydraulic valve may be mounted axially offset from the steering shaft or even totally mechanically independent of the steering shaft assembly as a separate unit, as the only functional requirement is that signals from the torque and/or position sensing means are processed so as to drive the motor driven hydraulic valve.
  • the first portion of the valve may comprise an inner spool part which is adapted to rotate within the second portion of the valve.
  • the motor may comprise an armature which is fixed relative to the inner spool portion and a stator which is fixed relative to the outer portion.
  • the armature and the inner spool portion may be arranged concentrically around the steering shaft and the stator and the outer spool part may be fixed to a housing which also provides support, through one or more bearings for the steering shaft.
  • the output member may be connected at an upper end to a steering wheel, and at its other, lower end, the output member may carry a pinion which engages a steering rack.
  • an actuator assembly comprising: a housing, an input shaft and an output shaft connected by a torsion bar provided within the housing; an electric motor comprising a stator secured to the housing and a rotor located within the housing and adapted to rotate within the stator, a rotary hydraulic valve comprising a first hydraulic valve portion including a first flow path for a hydraulic fluid fixed to the housing and a second hydraulic valve portion which includes a second hydraulic fluid flow path which is adapted to rotate within the first valve portion, the second valve portion being fixed to the rotor such that rotation of the rotor produces a rotation of the second valve portion, rotation of the second valve portion affecting the flow of fluid between the first and second flow paths; a sensor which is adapted to produce a torque signal indicative of the torque carried by the torsion bar for output to a processor which is adapted to receive the torque signal and to produce a motor drive signal dependent upon the torque signal which is applied to the motor.
  • the actuator may be used within an electric power assisted steering system or in any other application in which an assistance torque is required. In this case all that is required is to connect the first flow path to a pressurised fluid source and to pass the output of the fluid from the second path to a hydraulic actuator connected to the steering system.
  • the rotation of the valve affects the flow of fluid to the output to vary the force that is applied by the hydraulic actuator to the steering system.
  • the first path may comprise one or more sub-paths which may interconnect with corresponding sub-paths of the second flow path when the valve is in a first position and be isolated from those paths when in a second position. It may also include one or more paths which are isolated from corresponding paths in the second portion when in the first position and which are connected to those paths when in the second position. This allows the flow of fluid to be affected when the valve is rotated.
  • the electric motor and the valve may be arranged concentrically around the torsion bar or the input shaft or the output shaft or all three. This provides a particularly space-efficient arrangement of the components .
  • the torsion bar may comprise a portion of shaft of reduced cross section compared with the cross section of the input and the output shafts.
  • the input shaft may be adapted to be secured to a portion of a steering shaft or a steering wheel.
  • the output shaft may carry a pinion gear which is adapted to engage with a rack gear.
  • the input shaft and output shaft may carry one or more dog teeth which are normally not in contact but which are brought into contact when the torque carried, by the torsion shaft exceeds a predetermined safe limit to provide a direct link from the input shaft to the output shaft which is independent of the torsion bar.
  • the provision of the dog teeth provides additional security in the event that the torsion bar fails.
  • the rotor of the motor may be connected to the stator or the housing through a biasing means which biases the rotor to a self-centring position when no drive signal is applied to the motor.
  • the biasing means may comprise a spring.
  • the processor may form an integral part of the actuator or may be provided separately. It may be part of a common processor which is also used to perform other vehicle control functions.
  • Figure 1 is a cross sectional view of a portion of a vehicle steering system in accordance with a first embodiment of the present invention
  • Figure 2 is a set of cross-sections taken about the lines A-A', B- B' , C-C and D-D' shown in Figure 1.
  • a valve housing 1 is fixed to a gear housing 13.
  • the valve housing 1 contains a servo valve 2 in the form of a rotary spool valve comprising a rotary spool part 2' and a coaxial sleeve part 2" which is firmly mounted in the housing 1.
  • a servo valve 2 in the form of a rotary spool valve comprising a rotary spool part 2' and a coaxial sleeve part 2" which is firmly mounted in the housing 1.
  • Four cross sections through the apparatus are shown in Figure 2 which enable the paths through the rotary spool path and the coaxial sleeve to be clearly seen.
  • the coaxial sleeve part is of similar construction to that which is employed in a conventional HP AS system, the inner bore being machined to close tolerances and containing a number of longitudinally oriented metering ports.
  • the outer diameter is machined with a number of annular grooves, which are variously connected to the metering ports by a series of radial drillings. Additional annular grooves support a number of hydraulic sealing rings which serve to prevent fluid leakage between adjacent portions of the valve, and to contain the fluid between the valve housing and the valve sleeve.
  • the rotary spool part is coaxially mounted on the pinion shaft 10, the outer surface of which is suitably machined to provide a close tolerance bearing surface.
  • the outer surface of the rotary spool part is machined with a number of longitudinally oriented metering slots.
  • the inner bore of the rotary spool part is machined to provide a bearing surface on the pinion shaft, but in addition contains a wide annular groove, which is connected to alternate metering slots on the outer surface by a series of radial drillings.
  • the outer surface is machined with an annular groove which is connected to the wide annular groove on the internal bore by a series of drillings.
  • the wide annular groove on the internal surface of the rotary spool part serves to provide a low restriction route for hydraulic fluid passing across the control valve metering ports and returning to the reservoir via a matching annular groove on the inner surface of the sleeve part.
  • the servo valve 2 includes a pressure connection 3, which is connected to the pressure side of a servo pump 5 that is in communication with the reservoir 4.
  • the servo valve 2 has a low pressure connection 6 which is in communication with the reservoir 4 and two hydraulic actuator connections 7 and 8 which communicate with opposite sides of a double acting piston cylinder unit forming a hydraulic actuator 9.
  • the servo valve 2 includes a so-called open centre whereby all the connections 3 and 6 to 8 are in communication with one another when the rotary spool part 2' and the sleeve part 2" are in a centre position relative to each other. If the rotary spool part 2' is rotated relative to the sleeve part 2" in one or the opposite direction out of the centre position, a certain controllable pressure differential is generated between the hydraulic actuator connections 7 and 8 when the servo pump 5 is operating whereby the hydraulic actuator 9 generates a correspondingly large force action in one or the opposite direction.
  • the rotary spool part 2' and the sleeve part 2" are coupled to one another by a C-spring 12 situated at the lower end of the sleeve part 2", so that they are held resiliently in the centre position relative to one another.
  • an electrically driven torque motor 11 is mounted in the housing 1, the motor having a rotor connected to the rotary spool part 2' so that, upon energisation of the motor a torque is applied to the rotary spool part 2' which is rotated thereby in one or the opposite direction relative to the sleeve part 2" against the force of a C-spring mechanism 12.
  • the C-spring centring mechanism may be replaced by a deformable elastomer element, or a torsion tube mechanism.
  • the proposed implementation is designed to support a maximum relative rotation in the order of + /- 8 to 10 degrees. This enables manufacturing tolerances for the valve metering ports to be relaxed, and also allows for more progressive control of steering assist characteristic at low valve openings.
  • the valve assembly contains mechanical stops to set limits on maximum valve rotation.
  • the pinion shaft 10 is rotatably supported in the gear housing 13 with a ball bearing 14 and a roller bearing 15 interposed therebetween.
  • the pinion shaft 10 has a pinion 10' formed around an outer periphery thereof which meshes with a rack 16' of a rack bar 16 slidably supported in the gear housing 13.
  • the rack bar 16 is connected to the steering control wheels through a tie rod and knuckle (both not shown) .
  • the hydraulic actuator 9 is connected to the rack bar 16 so that the steering force is assisted by driving the hydraulic actuator 9 using hydraulic pressure under the control of the motor driven hydraulic valve.
  • the pinion shaft 10 extends upwards through the housing 1, and is rotatably supported at its upper end by a second ball bearing assembly 21.
  • the pinion shaft contains a machined inner bore, which receives a torsion bar 22.
  • the lower end of the torsion bar 22 is machined with a number of longitudinal splines, and is pressed into the pinion shaft such that the two parts are rigidly fixed.
  • the torsion bar is narrowed in its central section to achieve a desired deflection, which is typically of the order of 4 degrees in the presence of an applied torque of 4 Nm.
  • the upper end of the torsion bar 22 is rotationally supported by, and protrudes from the upper end of the pinion shaft inner bore.
  • the upper end of the pinion shaft is machined with two radial slots.
  • the radial slots in the upper end of the pinion shaft receive drive dogs protruding from the lower end of the input shaft 23, which is located on, and rigidly fixed to the upper end of the torsion bar via a locating pin 24 which is an interference fit between the two parts.
  • the outer surface of the input shaft is machined to achieve a non rotational coupling to the steering column intermediate shaft (not shown), which serves to provide a connection to the steering wheel (not shown) via the steering column assembly (also not shown) .
  • a steering sensor assembly 17 measures the deflection in order to produce a signal to the electronic control unit U which is proportional to steering wheel torque.
  • the steering sensor assembly 17 also provides a steering wheel angle signal to the electronic control unit U.
  • the combined sensing of steering wheel torque and angle information could be achieved using optical sensing technologies such as is known from International patent application no. WO 9939169.
  • the electronic control unit U provides steering angle information and various steering system status information to other vehicle systems (such as ESP) via a serial communications link.
  • the steering sensor assembly 17 provides steering wheel torque information only.
  • the sensing of steering wheel torque could be achieved through inductive means such as is known from US Patent 5 442 956.
  • Steering wheel angle information is provided to the electronic control unit U via a serial communications link from other vehicle systems (for example ESP) which typically employ a steering angle sensor mounted at the upper end of the steering column.
  • ESP vehicle systems
  • the electronic control unit U makes calculations using data from steering wheel angle and torque sensors, a yaw rate sensor 18 which detects the yaw rate of the vehicle, a lateral acceleration sensor 19 which detects lateral acceleration of the vehicle, and a vehicle speed sensor 20 which detects the speed of the vehicle, thereby controlling the driving of torque motor 11 contained within the valve housing 1 to provide continuous control of the rotary valve to achieve the desired steering assist characteristics.
  • the yaw rate, lateral acceleration and road speed signals could be provided from other existing vehicle systems, for example, ESP, via a serial communications link to the electronic control unit U.
  • the functions of the electronic control unit could be integrated with an existing control unit within the vehicle, for example the ESP system, thereby negating the need for a separate electronic control unit for the steering system functions.
  • the magnitude and direction of the output torque from torque motor 11, and thus the relative displacement of the two valve parts is controller by the duty cycle and polarity of the voltage applied to the torque motor 11.
  • control of the relative displacement of the two valve parts may be achieved in a closed loop control circuit through directly sensing valve displacement by appropriate means, or in the preferred embodiment as shown in Figure 1, may be inferred from motor current, which is directly sensed in a closed loop motor current control circuit.
  • the electronic control unit U contains a digital map stored in non volatile memory, which defines the relationship between motor current and valve displacement. Thus, to achieve a desired valve displacement, the duty cycle of the applied voltage is appropriately modulated to achieve the desired current level.
  • the drive circuit provides compensation for variations in supply voltage level, nominal winding resistance, and temperature effects in the torque motor and drive circuit itself.
  • the accuracy of control of valve displacement can be further improved through monitoring changes in the effective inductance of the motor windings, caused as the rotor moves relative to the stator windings. These changes in effective inductance can be observed in the drive circuit by measuring the change in rise time of motor current between two known values.
  • the HP AS torque overlay system concept as described above can be used to continually modify the steering assist characteristic in response to observed vehicle dynamic state. This has the effect of improving feedback of vehicle handling condition to the driver, and also increasing apparent stability of the vehicle in manoeuvres, thus making the vehicle easier to control.
  • the system can be used to modify the steering assist characteristic as a function of road speed, reducing assist levels at highway speeds, to reduce sensitivity to driver inputs thus improving steering feel and vehicle driveability.
  • the system can also be used to improve disturbance rejection arising from cross winds, road surface imperfections, and also to control and reduce steering pull sensitivity under braking, often associated with the use of specific steering geometry configurations.
  • a vision system detects vehicle position within lane markings, and commands the steering system electronic control unit to modify steer angle such that the correct position of the vehicle within the lane is maintained.
  • the concept as described above is also suitable for operation within an EHPS system configuration.
  • the steering angle signal can be processed to provide steering rate, which is used to control pump speed.
  • the electronic circuitry associated with control of the steering mechanism can be integrated into the EHPS control unit.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Steering Control In Accordance With Driving Conditions (AREA)
  • Power Steering Mechanism (AREA)

Abstract

L'invention concerne un système de direction de véhicule. Ce système comprend un élément d'entrée adapté pour être relié de manière opérationnelle à un volant, un élément de sortie adapté pour être relié à un volant d'un véhicule, au moins, un élément intermédiaire (22) reliant l'élément d'entrée à l'élément de sortie. Ce système comporte, en outre, un moyen de détection (17) qui détecte le couple supporté par l'élément intermédiaire, une unité de commande (u) qui génère un signal de demande de couple indiquant l'importance du couple d'assistance qui doit être appliqué à l'élément de sortie en fonction de la sortie du moyen de détection (17) et un organe de commande électrique (11) qui est entraîné par un signal de commande en fonction d'au moins un signal de demande de couple. Cet organe (11) commande le fonctionnement d'une valve hydraulique (2) qui contrôle l'écoulement du fluide vers un organe de commande hydraulique relié de manière opérationnelle à l'élément de sortie. Le moteur commande ainsi le couple appliqué par l'organe de commande hydraulique à destination de l'arbre en fonction du couple, au moins, appliqué par le conducteur. L'élément intermédiaire (22) peut être une barre de torsion autour de laquelle la soupape (2) et l'organe de commande généralement un moteur électrique peuvent être montés de manière coaxiale.
PCT/GB2003/002346 2002-05-30 2003-05-30 Systeme de direction de vehicule WO2003101808A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2003234050A AU2003234050A1 (en) 2002-05-30 2003-05-30 A vehicle steering system

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0212465.9 2002-05-30
GB0212465A GB0212465D0 (en) 2002-05-30 2002-05-30 A vehicle steering system

Publications (1)

Publication Number Publication Date
WO2003101808A1 true WO2003101808A1 (fr) 2003-12-11

Family

ID=9937696

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2003/002346 WO2003101808A1 (fr) 2002-05-30 2003-05-30 Systeme de direction de vehicule

Country Status (3)

Country Link
AU (1) AU2003234050A1 (fr)
GB (1) GB0212465D0 (fr)
WO (1) WO2003101808A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2412637A (en) * 2004-04-01 2005-10-05 Zf Lenksysteme Gmbh Adjustable valve for steering assist system
EP1582437A1 (fr) * 2004-04-01 2005-10-05 TRW Automotive U.S. LLC Dispositif pour commander une direction assistée en fonction de la vitesse du véhicule

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2266499A (en) * 1992-04-23 1993-11-03 Rover Group Hydraulic power-assisted steering system with input force sensor.
US5442956A (en) 1992-06-03 1995-08-22 Trw Inc. Torque sensor for a power assist steering system
DE19541749C1 (de) * 1995-11-09 1997-05-22 Daimler Benz Ag Servolenkung für Kraftfahrzeuge
WO1999039169A1 (fr) 1998-01-31 1999-08-05 Trw Lucas Varity Electric Steering Limited Detecteur combine de couple et de position angulaire
DE19828816A1 (de) * 1998-06-27 1999-12-30 Daimler Chrysler Ag Servolenkung für Kraftfahrzeuge
EP1055583A1 (fr) * 1997-09-24 2000-11-29 Jidosha Kiki Co., Ltd. Direction assistée à crémaillère

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2266499A (en) * 1992-04-23 1993-11-03 Rover Group Hydraulic power-assisted steering system with input force sensor.
US5442956A (en) 1992-06-03 1995-08-22 Trw Inc. Torque sensor for a power assist steering system
DE19541749C1 (de) * 1995-11-09 1997-05-22 Daimler Benz Ag Servolenkung für Kraftfahrzeuge
EP1055583A1 (fr) * 1997-09-24 2000-11-29 Jidosha Kiki Co., Ltd. Direction assistée à crémaillère
WO1999039169A1 (fr) 1998-01-31 1999-08-05 Trw Lucas Varity Electric Steering Limited Detecteur combine de couple et de position angulaire
DE19828816A1 (de) * 1998-06-27 1999-12-30 Daimler Chrysler Ag Servolenkung für Kraftfahrzeuge

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2412637A (en) * 2004-04-01 2005-10-05 Zf Lenksysteme Gmbh Adjustable valve for steering assist system
EP1582437A1 (fr) * 2004-04-01 2005-10-05 TRW Automotive U.S. LLC Dispositif pour commander une direction assistée en fonction de la vitesse du véhicule
GB2412637B (en) * 2004-04-01 2007-06-06 Zf Lenksysteme Gmbh Valve

Also Published As

Publication number Publication date
AU2003234050A1 (en) 2003-12-19
GB0212465D0 (en) 2002-07-10

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