Patent Application
20060042861
This invention relates to steering assist mechanisms, and more particularly to mechanisms for vehicles or other devices requiring physical effort to steer or drive. The invention is applicable for power assistance during turning to such devices as tractors, passenger cars, trucks, busses, cranes, agricultural combines, power shovels, material handling equipment, earth moving equipment, aircraft controls and marine applications.
It is an object of the present invention to provide an improved power steering assist mechanism which is electrically controlled and serves to supply a variable amount of torque assist to the steering linkage in accordance with the turning effort demanded by resistance such as the road resistance of an automotive vehicle.
It is another object to provide an improved power steering assist mechanism which has a compact arrangement of parts and can be manufactured as a package unit for installation in conventionally-steered vehicles, which has an inherent feedback function, may be conveniently placed into or out of operation, and need have no hydraulic connections or hydraulically actuated elements.
It is a further object to provide an improved power steering assist mechanism of the above nature which may be driven by electrical means independent of the vehicle engine, so that power assistance can be supplied to the steering linkage even upon failure or stalling of the engine, or may be driven by a power take-off directly from the engine or by other sources of rotary power.
It is also an object to provide an improved power steering assist mechanism of the above character, which may be installed at various points in the steering linkage or on the steering shaft itself, and which may utilize a unidirectional or a reversible motor.
It is another object to provide an improved power steering assist mechanism of the above nature, which includes means for predetermining the strength of the applied power assistance, thereby allowing the individual operator to choose the proper rate of power assistance according to his or her needs.
It is further object, in one form of the invention, to provide an improved power steering assist mechanism of the above nature, in which electrical means are provided to vary the torque applied by the power assist means to the driven member of the steering system simultaneously with variations in the manual torque and at a rate proportional to the manually applied torque.
It is also an object, in one form of the invention, to provide a power steering assist mechanism having the above characteristics, in which electromagnetically actuated clutches are utilized to connect the power means with the steering linkage, so that the applied torque may be varied by adjusting the degree of energization of the clutches.
It is a further object to provide a power steering device of the above nature which is capable of use with different types of electromagnetically actuated clutches such as friction clutches and magnetic particle clutches and in which the clutches may be energized to some degree at all times so as to minimize the time delay in initiating power actuation.
It is a further object, in one form of the invention, to provide a power steering assist mechanism having the above characteristics, in which means are provided for energizing the electromagnetically actuated clutches as any desired function, whether linear or non-linear, of the manual torque exerted by the operator.
It is also an object to provide an improved power steering mechanism of the above nature in which the operator is al all times capable of applying manual torque to the steering linkage in addition to the power actuation, so that when the torque limit of a clutch is exceeded additional manual turning effort may be applied to the linkage.
Other objects, features, and advantages of the present invention will become apparent from the subsequent description, taken in conjunction with the accompanying drawings.
Referring to the embodiment of FIGS. 1 to 6, and more particularly to the schematic showing of
The steering assist driving means includes a pair of coaxial oppositely rotating gears 18 and 19 which normally freely rotate on an assist shaft 21, but which are adapted to be alternately clutched to said shaft be means of magnetic clutches 22 and 23 respectively. These clutches may be of any suitable construction, including electromagnetic construction, and are preferably of a type transmitting variable torque up to a predetermined limit. The gears are driven by an electric motor 24 which is of a unidirectional type and rotates a drive pinion 25, and the clutches are energized by the closing of a switch arrangement generally indicated at 26 which is responsive to resistance in the steering linkage when the steering wheel 13 is manually rotated. In other words, the pitman arms 16 are normally controlled solely by steering wheel 13 through the conventional gear reduction drive, and the power assist only comes into play when a predetermined road resistance is encountered by the steering linkage.
Motor 24 may be powered for example by the vehicle battery 27 or other electrical power source, and its circuit is controlled by an on-and-off switch 28, this switch being in circuit leg 29 leading from the positive battery terminal to the motor, the other side of the motor circuit being connected to battery through ground. The position of switch 28 may be controlled by the position of vehicle ignition switch 30 shown in dotted lines, to disconnect the motor when the ignition is off. If desired, suitable electrical controls (not shown) of a conventional nature may be installed in the power supply circuit of the motor to permit its operation at the proper speed when the battery voltage has been temporarily reduced, and to cut out the motor in case of impending damage to the battery. Electromagnetic clutches 22 and 23 are connected to ground through a conduit 31 and branch connections 32 and 33 leading to clutches 22 and 23 respectively. Switch 28 also may control to opening of this circuit as shown to disconnect the clutches when the ignition is off. Normally disengaged contact 34 of switch 26 is connected to clutch 22 and normally disengaged contact 35 is connected to clutch 23, these connections being be means of leads 36 and 37 respectively, and the circuit is completed to either clutch by central contact 38 connected to the positive side of battery 27. Inserted in conduit 31 is a variable resistor 39, preferably mounted in such position as to be operator-controlled, by which means the amount of current flowing through the electromagnetic clutches and their subsequent clutching effect may be varied. Shaft 21 is connected with the steering linkage through a pinion 40 which meshes with gear sector 17.
In describing the operation of the mechanism shown in
The operator first closes switch 28 setting motor 24 in operation and enabling the clutch circuits, so that gears 18 and 19 rotate freely and continuously in opposite directions on shaft 21. Upon turning the steering wheel 13 in either direction, if too little steering resistance is encountered to engage contacts 34 or 35, pitman arms 16 will be moved in the conventional manner through gear reduction unit 14, and gear sector 17 will cause shaft 21 to idle freely through its connection with pinion 40. Should steering resistance be encountered which is sufficient to close contacts 34 and 38, current flowing through lines 31, 32 and 36 will energize clutch 22 causing gear 18 to be clutched to shaft 21, and pinion 40 will drive gear sector 17 in the direction in which the manual effort is being applied. Upon the attainment of a stable steering condition, that is, one in which the manual effort required to hold the linkage in position is below the predetermined amount, contacts 34 and 38 will open as later described in detail and gear 18 will be declutched from shaft 21. In actual operation of course gear 18 may under certain conditions be clutched and declutched with respect to shaft 21 several times in the course of a continuous turning movement of steering wheel 13, depending on the momentary forces in the steering linkage. A similar situation obtains of course with respect to the closing of contacts 35 and 38 and clutching of gear 19 when turning in the opposite direction.
It should be noted that the arrangement of
The presence of variable resistor 39, it should be noted, lends added flexibility to the system, since the clutching force and hence the steering assistance may be varied at all times to suit the particular driving conditions. Moreover, the device may be conveniently placed out of operation when only manual steering is required, merely be opening manual switch 28. The electrical arrangement is such that the system will be “fail safe”; that is, should lines 36 or 37 be grounded the clutch circuits will not be completed with the possibility of loss of vehicle control. It should also be noted that the power steering mechanism in no way interferes with the normal function of the steering linkage in returning of its own accord to a straight-ahead position when a turn is completed. In this situation the operator either allows the steering wheel to rotate freely or urges it slightly in one direction or the other; contacts 34 and 35 will therefore remain disengaged and the steering assist mechanism will not come into play. It should also be observed that when the road wheels encounter obstacles tending to deflect them from their path, the assist mechanism will come into play to maintain the wheels on course. With the operator resisting such deflecting force at the steering wheel, either contact 34 or 35 will be engaged, and the assist mechanism will further counteract the effect of the obstacle.
A housing 44 encloses gears 18 and 19 as well as magnetic clutches 22 and 23, the housing being coaxial with shaft 21 and supported at its ends by sleeves 45 attached to end hubs 46 of the housing. A motor and gear support housing 47 is secured to one side of housing 44 be means of bolts 48 and an intermediate bearing support 49 for pinion 25, the latter being disposed between housings 44 and 47. Motor 24 is secured to one side of housing 47, the latter supporting a bearing 51 for the motor shaft which includes a flexible coupling 52. Pinion shaft 53 is supported at one end by a bearing 54 in housing 47 and at an intermediate point by bearing 55 within support 49. This shaft carries a worm wheel 56 which is driven by worm 57 on the motor shaft, and thus drives pinion 25.
The magnetic clutches 22 and 23 include rotors 58 outwardly of the driving gears having hubs 59 keyed at 61 to sleeve 41, and annular fields 62 secured to housing end hubs 46 by bolts 63. Fields 62 are adapted to attract armatures 64, which are secured to gears 18 and 19 by bolts 65, toward to frictional faces 66 carried by rotors 58. Springs 67 are disposed between hubs 59 of the rotors, which are held against axial movement by snap rings 68, and armatures 64 of gears 18 and 19. These springs therefore urge the armatures away from their respective rotors 58, gears 18 and 19 engaging a central thrust bearing 69 for positioning purposes. The outer edges of armatures 64 engage seals 70 held by housing 44 to prevent lubricant leakage from the area of the gears. It should be noted that if desired the entire housing may be filled with oil, in which case seals 70 may be dispensed with.
In the operation of the driving mechanism of
A yieldable connection is provided between steering wheel 13 and steering column 12 so that contact 38 may engage contacts 34 or 35 upon the attainment of a predetermined torque on the steering column. In the present embodiment, this resilient means includes a flexible coupling 77 which is of annular shape and is secured to hub 72 of the steering wheel on its outer surface and the splined portion 78 of steering column 12 on its inner portion. It will therefore be seen that when steering wheel 13 is rotated, assuming steering column 12 is held stationary by the road resistance, either contacts 34 or 35 will be rotated into engagement with contact 38 secured to the steering column, and the circuit to one of the electromagnetic clutches will be closed to set the steering assist mechanism into operation. When the steering linkage is drive thereby, column 12 will be rotated so as to move contact 38 out of engagement with its mating contact, and it will therefore be seen that the system inherently includes a feedback mechanism for constantly resetting the control switch.
It will be noted that ordinarily the manual torque is transmitted from the steering wheel to the steering column through flexible coupling 77. However, an additional positive lost-motion connection may be provided for safety purposes, and this means includes a lost-motion key-and-slot connection 79 between the steering wheel hub and steering column 12. With this connection, the driver can furnish additional turning effort to the steering linkage after the torque limit of clutches 22 or 23 has been reached, and the lost-motion connection permits operation of switch assembly 26 while preventing damage to the switch parts. A drive release mechanism (not shown) such as that discussed below with respect to
As indicated previously, the driving unit of the power assist mechanism may be mounted on the steering column itself, and
Clutches 89 and 91 are controlled by a rheostat 104 of the sliding contact arm type, and the position of contact arm 105 of the rheostat is determined by the manual torque applied to steering wheel 106. The terminals 107 and 108 at opposite ends of rheostat 104 are connected to clutches 89 and 91 respectively by conductors 109 and 110, and contact arm 105 is connected to battery 113 by conductor 111. The other ends of the clutch coils are connected through a variable resistor 112, similar in function to resistor 39 of
If desired, means may be provided for de-energizing motor 92 when contact arm 105 is in its central position. As shown schematically in
As shown schematically in
In operation, rotation of steering wheel 106 in either direction will be resisted by one of the yieldable pins 125, and if road resistance is encountered there will be a differential in rotating between steering wheel 106 and steering column 119. This relative movement will cause gear sector 117 to rotate angularly with respect to mounting plate 121, and pinion 115 will be rotated on its axis, thus swinging contact arm 105 and energizing motor 92. The amount of such swinging movement of the contact arm will depend upon the amount of compression of the spring 126 being compressed, and this in turn will depend upon the road resistance encountered during turning. It will therefore be seen that the angular movement of contact arm 105 is proportional to the road resistance and thus to the amount of power assistance required.
When arm 105 is moved from its central position toward one of the terminals, say terminal 107, the energizing current to corresponding clutch 89 will be increased an amount depending both on the degree of movement of the contact arm and the electrical characteristics of the rheostat. At the same time the current in clutch 91 will be decreased, although it will be noted that some current still passes through this clutch. Pinion 96 will therefore be driven by constantly rotating shaft 93, the force transmitted from the shaft to the pinion depending upon the degree of energization of clutch 89. It should be observed that since the rheostat is of the sliding type, the application of torque to pinion 96 will be smooth rather than abrupt, so that the power assistance transmitted from output gear 98 to shaft 99, pinion 101, gear sector 102 and pitman arms 103 will not produce a jarring effect on the steering linkage. It is therefore seen that the power assistance is automatically adjusted to be proportional to that required by the road resistance. As indicated above, rheostat 104 may be wound so as to produce a linear relation between steering wheel torque and applied power, or a non-linear relation could be produced by properly choosing the rheostat characteristics.
The inherent feedback function of the steering assist mechanism will be apparent from the foregoing description. When power assistance is applied to the steering linkage from driving unit 86, the steering column 119 is driven in a direction so as to relieve the compression on the compressed spring 126 and to carry mounting plate 121 back to its neutral position so that both clutches 89 and 91 will be equally and weakly energized, and the supply of power assistance will cease. Of course, during an actual turning sequence the parts may continually vary between extreme positions depending upon the momentary forces involved, but at any instant it will be seen that the steering assistance is regulated by the amount of manual effort exerted by the operator.
As either spring 126 is compressed, additional manual turning effort will cause a direct application of torque from the steering wheel to the steering linkage. This is important in view of the torque limiting characteristics of the clutches, since it will be seen that after the maximum torque which the clutches can transmit has been surpassed, additional turning effort may nevertheless be applied to the road wheels by the operator. It should be noted however that there is no inherent looseness in the steering system since the operator uses manual effort to drive the wheels even when a spring 126 is initially compressed. The compression of either spring 126 transmits a turning force to the steering column 119 in addition to causing the power assist mechanism to come into play so that the turning effort applied to the road wheels is always a combination of manual and power sources. The operator thus always has “road fee” and is cognizant at all times of the forces acting on the wheels of the vehicle. Although compression type springs are shown in the illustrated embodiment as the resilient connection between the steering wheel and the steering column, it will be understood of course that other types of flexible couplings could replace these elements. It should also be noted that movement of the rheostat contact arm throughout its range requires no substantial effort per se, since the contact arm is mounted for free pivotal movement. The rate of change of electrical resistance with torque may thus be accurately and conveniently controlled or adjusted by means of the flexible coupling, without having to take into account the effort required to move the resistor parts.
It should be observed that the pre-energization of clutches 89 and 91 has several important advantages in the steering arrangement. As pointed out above, such pre-energization minimized the time lag between the appearance of road resistance in the system and the application of power assistance, and also contributes to the smoothness of application of the power. In prior construction such as that shown in patent on Penrose No. 2,587,377 issued Feb. 26, 1952 for Electric Power Apparatus for Steering and the Like, the clutches are normally de-energized, and the clutch elements must be moved into engagement upon each actuation of the unit. It has been found that a major proportion of current and time is consumed in the initial buildup of the magnetic field and in carrying such electromagnetic clutch parts into operative condition. The present arrangement therefore provides a highly efficient and improved construction, since the clutches are at all times on the threshold of usefulness. In addition, the constant energization of the clutches serves to cause quicker response of the assist mechanism when a road obstacle is encountered tending to deflect the wheels. In such a case the damping effect of the weakly energized clutches will serve to absorb the forces in the steering linkage and minimize the force transmitted to the steering wheel. Furthermore, whatever force differential is set up by the operator's resistance at the steering wheel will be immediately translated into power assistance tending to keep the wheels on course.
A suitable construction for the rheostat assembly and the resilient connection between the steering wheel and steering column is shown in
Gear sector 117 is secured to steering wheel hub 122 by means of bolts 134 and dowel 135. The gear sector is provided with an apertured portion 136 for accommodating steering column 119, the latter having an end portion 137 of reduced diameter which rotatably supports hub 122. Pin 123 is secured by such means as welding to the side of hub 122 opposite the teeth of gear sector 117, and extends into a block member 138 is slidable on mounting plate 121 in the direction of the axes of pins 125, and the inner ends 139 of the pins are threadably secured to block 138 and held by lock nuts 141. A dovetail connection 142 between the block 138 and collar 127 holds the block in place during its sliding movement. Pin 123 extends through an enlarged aperture 143 in block 138 and through an elongated aperture 144 in mounting plate 121, the inner ends of pins 125 engaging pin 123. The outer end portions of pins 125 are slidably supported by lugs 145 at the corners of the mounting plate, and are provided with stops 146 shown in the form of lock nuts. Springs 126 are disposed between lugs 145 and stops 147 secured to pins 125, so that when pin 123 is moved in either direction it will compress one of the springs 126 and cause sliding movement of block 138 as well as axial movement of the corresponding pin 125. Stops 147 are preferably of an adjustable nature so that the initial compression of springs 126 and consequently the effort needed to initially slide block 138 may be predetermined.
The operation of the foregoing device will be apparent from the above description. When in its neutral position the counterbalancing effects of springs 126 will maintain pin 123 in a central position with respect to elongated slot 144, and the engagement of pinion 115 and gear sector 117 will therefore be such as to hold contact arm 105 in its neutral or intermediate position on rheostat 104. If desired, detent means (not shown) such as a recess may be provided for the central position of contact arm 105 to prevent minor oscillations from affecting its setting. When the steering wheel is rotated by the driver and road resistance is encountered, one of the springs 126 will be compressed, moving pin 123 within elongated slot 144 and causing sliding movement of block 138. Gear sector 117 will thus be angularly rotated with respect to mounting plate 121, and contact arm 105 will be adjusted along rheostat 104 in accordance with the principles described with respect to
Coils 158 carried by driven members 155 and 156 are connected in circuit with rheostat 104 and the source of electrical power, and when energized these coils cause a magnetic field to pass through the fluid, orienting the particles in such a fashion as to transmit torque from the driving to the driven members. By adjusting the position of contact arm 105 on rheostat 104, an infinite number of torque transmission settings within the range can be effected in each clutch 152, so that the power transmitted through either pinion 96 or 97 to driven gear 98 may be varied. Gear 98 is secured to shaft 99 which is supported by bearings 159 in housing 148, and pinion 101 at the outer end of shaft 99 meshes with gear sector 102 as previously described. It should be kept in mind that clutches other than the magnetic particle clutches illustrated may be used in the driving unit shown in
As pointed out above, various sources of rotary power, such as vehicle engine take-offs of hydraulic motors, may be used for the driving unit, and
It should be noted that the variations in engine speed which occur during normal driving conditions will not affect the efficiency of the steering assist mechanism, even if these variations should occur while a power assist steering operation is taking place. This is because of the fact that the energization of the clutches is directly dependent upon the instantaneous amount of effort being exerted by the driver on the steering wheel, so that for example if the applied power is increased due to speeding up of the engine, the clutch energization will be automatically and instantaneously decreased to compensate for this increase in input torque.
In the operation of the embodiment shown in
While it will be apparent that the preferred embodiment of the invention here in disclosed are well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.
