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
  • B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
  • B62D5/0457—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear characterised by control features of the drive means as such
  • B62D5/0481—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear characterised by control features of the drive means as such monitoring the steering system, e.g. failures
• • 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
  • B62D5/008—Changing the transfer ratio between the steering wheel and the steering gear by variable supply of energy, e.g. by using a superposition gear

Definitions

• the invention relates to an auxiliary power-assisted steering system of a motor vehicle, with a steering gear for converting the steering request specified by the driver with his steering handle into a displacement movement of the steering rods assigned to the steerable wheels, and with a superimposition unit with which the steering angle specified by the driver is a rectified or counter-directional additional Steering angle can be added, so that the gear ratio between the steering angle specification of the driver and the stroke of the tie rod pivot point on the steering gear can be changed compared to a gear ratio specified by the steering gear.
• a superimposition unit with which the steering angle specified by the driver is a rectified or counter-directional additional Steering angle can be added, so that the gear ratio between the steering angle specification of the driver and the stroke of the tie rod pivot point on the steering gear can be changed compared to a gear ratio specified by the steering gear.
• Steering ie turning steerable wheels of a motor vehicle, requires force or power, and the more so the lower the rotational speed of the steered wheels.
• the greatest power requirement is thus when the vehicle is parked with braked wheels, ie when the steerable wheels are braked and thus blocked against turning and at the same time turned, ie steered.
• the power requirement in the area of the two possible end positions ie close to the maximum possible steering angle in each case, is particularly high, inter alia because the lateral tensions in the wheel tire increase with increasing wheel steering angle.
• Steering systems or mechanical steering gears are usually designed in such a way that in the vicinity of the end stop, i.e.
• auxiliary power steering systems are usual, the auxiliary power being applied primarily hydraulically; however, auxiliary electric motor systems are also known.
• auxiliary system being installed in a specific application, due to the described high power requirement of an auxiliary steering system, a correspondingly large dimensioning of the auxiliary support is required, among other things, in the end positions of the rack and pinion stroke or in the area of large steering angles (near the respective end stop).
• strong motors or hydraulic pumps must be provided, the drive of which in turn requires a lot of energy, which is at the expense of the energy balance or the consumption of the drive unit of the motor vehicle, after this usually (directly or indirectly) also the unit providing the assistant for the steering system drives.
• the design of the steering gear is made in such a way that in each case in an intermediate area between the zero position and a relatively direct gear ratio is provided for the respective end stop.
• steering systems according to the preamble of claim 1, which are equipped with a so-called superimposition unit, which can add a rectified or counter-directed additional steering angle to the steering angle specified by the driver with his steering wheel (generally his steering handle).
• This superposition unit can be an actuator with a planetary gear, the first input of which is connected to the driver's steering wheel, the second input of which is connected to the electric one.
• Servomotor driven worm gear is connected and its output is mechanically connected to the input of the steering gear.
• An additional steering angle can thus be controlled via the electric motor with the worm drive, which is then passed on to the steering gear.
• the solution to this problem is characterized in that when a performance limit value for the system providing the auxiliary power assistance or a limit value for the steering angle specification is exceeded, the transmission ratio between the steering angle specification of the driver and the stroke of the tie rod articulation point on the steering gear, at least from a temporal perspective is set more indirectly compared to the specified transmission ratio.
• Advantageous training forms the content of the subclaims. Basically, it is therefore proposed to implement one of the measures for reducing the power requirement of the auxiliary power support, which will be described in more detail below, only as required, ie essentially as a function of the power currently required of the unit providing the auxiliary power assistance. A comparison can be made with a (preferably predetermined) threshold value or limit value, but this is not absolutely necessary.
• a measure reducing the power requirement can also be carried out if it is to be expected that a power limit will be exceeded. If, on the other hand, a specific threshold value is specified for the power requirement, this is preferably selected in such a way that it is only achieved in extreme situations, for example in a parking process with a very rapid deflection to the high friction value. A measure to reduce the power requirement is only initiated if this threshold value is reached or exceeded.
• a proposed measure for reducing the power requirement is - initially described generally - that, at least from a temporal perspective, the transmission ratio between the steering angle specification of the driver and the stroke of the tie rod articulation point on the steering gear compared to one by the steering gear predetermined transmission ratio is set indirectly. As explained above, a more indirect gear ratio results in a lower power requirement. Specifically, in the sense of an indirect gear ratio, the displacement speed of the tie rod pivot point (on the steering gear) can be reduced compared to the change speed of the steering angle specification by adding a superimposed additional steering angle to the steering angle specified by the driver, i.e.
• the so-called superposition steering provides after exceeding the said limit value (power limit value or steering angle limit value) uses a more indirect steering ratio and thus reduces the rack lifting speed in the case of rack and pinion steering with unchanged steering angle setting speed. This avoids that the maximum power is required, but this increases the necessary steering angle up to the steering end stop by the amount of the additional steering angle added.
• the advantage of this function compared to the power-dependent steering ratio is that the steering angle remains unchanged until the (mechanical) steering stop is reached. Depending on the time delay, the rack lifting speed and thus the power requirement on the tie rods can be reduced by a certain amount.
• the steering wheel angle and the steering angle on the steerable vehicle wheels are in principle built independently of one another and the steering wheel should reach the stop before the steering operation on the wheel, it may be advisable to add an additional actuator or the like Representation of the steering stop, for example in the steering column or with effect on the steering wheel of the driver.
• This function can be performed, for example, by an electric steering wheel lock.
• Exceeding a limit or threshold value for the steering wheel angle or the steering angle specification or for the power requirement of the auxiliary Support providing aggregate can be initiated. Whether the limit or threshold value is exceeded can either be estimated from the respective requirement profile or it can be specifically determined that a performance threshold value has been reached. For example, to calculate the total force in the tie rods in the case of electromechanical power steering (power assist), the current consumed by the associated electric motor can be measured. In the case of hydraulic steering assistance, a suitable sensor system, for example in the form of strain gauges, can be provided on the tie rods. If necessary, the current consumption of the superimposed unit (superimposed steering) driven by an electric motor can also provide information about the force relationships in the tie rods or on the rack or the like of the steering gear.
• power assist the current consumed by the associated electric motor can be measured.
• a suitable sensor system for example in the form of strain gauges, can be provided on the tie rods. If necessary, the current consumption of the superimposed unit (superimposed steering) driven by an electric motor can also provide information about the
• corresponding measures reducing the power requirement can also be initiated in certain operating states. Such a measure is therefore taken when a reduction in the power requirement is actually necessary, for example during a parking process.
• This can be described, for example, in that the driving speed of the motor vehicle is below 5 km / h.
• a naturally high-power steering when the vehicle is stationary with braked wheels also represents an operating state in which a proposed change in the transmission ratio is implemented, i.e. counter-directed additional steering angles can be added, in particular when the driver specifies large steering angles, in order to obtain a more indirect steering ratio.
• the steering ratio essentially only in such a range in which a more indirect setting is a relatively large one Reduce the power requirement causes to perform. Then, in certain states or operating states at steering angles specified by the driver, which lie above a range of between a steering angle request of 0 ° and the maximum predefinable steering angle, the steering stroke of the tie rod articulation point (am Steering gear) with increasing steering angle specification by superimposing opposing additional steering angles. In order to reduce the power requirement on the steering gear, the steering ratio in the steering gear is made more indirect, but only in those areas and operating states in which the
• the ratio is set indirectly by specifying a negative additional steering angle.
• the translation process therefore has a sloping section near the end positions and thereby reduces the power requirement.
• This area with the "sloping" section near the end positions can also be described in such a way that it lies above an essentially desired steering angle in the range between a desired steering angle of 0 ° and the maximum specifiable steering angle.
• the curve marked with the reference number "0" represents the basic design of the translation curve, i.e. a design that applies to many operating states of the vehicle that are not the "certain operating states" in the sense of the present invention.
• the curve marked with the reference number "1" represents a steering ratio reduced by 5% for high steering angles, which, since the power to be provided is proportional to the lifting speed of the tie rod pivot point on the steering gear, a reduction of the required power by 5% compared to the basic design. (assuming the same steering angle speed on the driver's steering wheel) A corresponding steering ratio is now set in certain operating states by superimposing a suitable opposite steering angle for higher steering angles specified by the driver.
• the steering ratio in the zero position range is also set more directly by positive additional steering angles, mathematically, to meet this requirement, the integral of these two curves 0, 1 must have the same value over the steering angle. This is the case if the in the Figure hatched areas are the same size.
• two further translation processes are shown with the reference numbers 2, 3, with which an even greater line reduction of 10% by 15% can be achieved, but the spread of the translation process increases with increasing power reduction, which makes a desired steady transition to the basic translation characteristic curve more difficult.

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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)

Priority Applications (4)

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Citations (2)

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• 2004
  • 2004-11-09 EP EP04797723A patent/EP1682399B1/de not_active Expired - Lifetime
  • 2004-11-09 JP JP2006538765A patent/JP4945244B2/ja not_active Expired - Lifetime
  • 2004-11-09 DE DE502004004829T patent/DE502004004829D1/de not_active Expired - Lifetime
  • 2004-11-09 WO PCT/EP2004/012641 patent/WO2005047079A1/de not_active Ceased
• 2006
  • 2006-05-12 US US11/432,519 patent/US7389850B2/en not_active Expired - Lifetime

Patent Citations (2)

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