CA1100852A - Rotatable sleeve rack - Google Patents
Rotatable sleeve rackInfo
- Publication number
- CA1100852A CA1100852A CA359,455A CA359455A CA1100852A CA 1100852 A CA1100852 A CA 1100852A CA 359455 A CA359455 A CA 359455A CA 1100852 A CA1100852 A CA 1100852A
- Authority
- CA
- Canada
- Prior art keywords
- sleeve
- rack
- assembly
- bar
- drive member
- Prior art date
- Legal status (The legal status 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 status listed.)
- Expired
Links
Landscapes
- Transmission Devices (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An improved variable ratio steering apparatus is used to effect turning movement of steerable wheels of a vehicle. The apparatus includes a longitudinally extending force transmitting member or bar which is connected with the steerable vehicle wheels. A drive member is rotatably mounted on the bar. In order to effect axial movement of the bar and turning movement of the vehicle wheels, a pinion gear is disposed in meshing engagement with an array of helical rack gear teeth on the drive member. A cam track is also provided on the drive member. This cam track is coextensive with the array of rack gear teeth. The cam track cooperates with a follower to effect rotational movement of the drive member as the drive member and force transmitting bar are moved axially. This rotational movement of the drive member causes an interaction between the pinion and rack gear teeth to vary the rate of axial movement of the drive member and the force transmitting bar. The follower advantageously engages the cam track at a location which is axially aligned with the location where the pinion gear is disposed in meshing engagement with the rack gear teeth. This tends to minimize deflection of the components of the steering apparatus. Although an apparatus constructed in accordance with the present invention is advantageous-ly used to turn the steerable wheels of a vehicle, it is also contemplated that the apparatus can be used in other environments.
An improved variable ratio steering apparatus is used to effect turning movement of steerable wheels of a vehicle. The apparatus includes a longitudinally extending force transmitting member or bar which is connected with the steerable vehicle wheels. A drive member is rotatably mounted on the bar. In order to effect axial movement of the bar and turning movement of the vehicle wheels, a pinion gear is disposed in meshing engagement with an array of helical rack gear teeth on the drive member. A cam track is also provided on the drive member. This cam track is coextensive with the array of rack gear teeth. The cam track cooperates with a follower to effect rotational movement of the drive member as the drive member and force transmitting bar are moved axially. This rotational movement of the drive member causes an interaction between the pinion and rack gear teeth to vary the rate of axial movement of the drive member and the force transmitting bar. The follower advantageously engages the cam track at a location which is axially aligned with the location where the pinion gear is disposed in meshing engagement with the rack gear teeth. This tends to minimize deflection of the components of the steering apparatus. Although an apparatus constructed in accordance with the present invention is advantageous-ly used to turn the steerable wheels of a vehicle, it is also contemplated that the apparatus can be used in other environments.
Description
110Qt352 BACKGROUND OF Tl-~ INVENTION
This invention relates generally to a force transmitting apparatus and more specifically to a force transmitting apparatus which is advantageous-ly utilized to effect turning movement of a steerable wheel of a vehicle.
A known variable ratio steering apparatus is disclosed in Canadian Patent Application Serial No. 294,635 filed January 10, 1978 by Frederick John Adams and Ralph Malcolm Lehman and entitled "Improvements In Or Relating To Rack And Pinion Assemblies". The steering apparatus disclosed in that application includes a pinion having teeth which mesh with helical gear teeth on a rack bar. The rack bar is displaced longitudinally relative to a housing upon rotation of the pinion. A cam 10track is disposed on the rack bar and is engaged by a follower which is connected with the housing. The cam track and follower cooperate to effect rotation of the rack bar upon longitudinal movement of the rack bar. This rotation of the rack bar causes the rack gear teeth and pinion gear teeth to interact in such a manner as to vary the rate of axial movement of the rack bar.
Although the steering apparatus disclosed in the aforementioned application is believed to be generally satisfactory in its construction and mode of operation, it is believed that after extended usage, ball joints at opposite ends of the rack bar may tend to wear. This wear of ~Othe ball joints is, to some extent at the least, induced by the rotation of the rack bar.
In addition, the cam track of the steering apparatus disclosed in the aforementioned application is axially offset from the rack gear teeth. Therefore, the rack bar must have a minimum length which is at least t~ice as great as the length of the array of rack gear teeth. It is - 1 - ~
~. .
believed that this relatively long length may be objectionable if the steering apparatus is used with relatively small vehicles. In addition, by having the cam track axially offset from the rack gear teeth, the rack gear is subjected to both torsional and bending forces when the rack gear is rotated by the cam follower.
SUMMARY OF THE PRESENT INVENTION
_ _ _ _ _ , The present invention provides a variable ratio gear assembly comprising a pinion rotatably mounted in a housing and in meshing engagement ~ith a rack of a longitudinally extending sleeve, said sleeve forming part of a rack assembly having a longitudinally extending bar on which the sleeve is rotatably mounted and relative to which the sleeve is restrained from longitudinal displacement, said rack assembly being longitùdinally displaceable in response to rotation of the pinion through a first region and through at least one further region which extends from the first region, and wherein control means is provided which substantially restrains the ~leeye from rotating relative to the housing during its displacement through said first region so that the ratio of the gear is substantially constant and which imparts controlled rotation for the sleeve relative to the housing during longitudinal displacement of the rack assembly through the or a said further region so that the ratio of the gear is varied as 2Q compared with the substantially constant ratio provided during displacement of the rack assembly through the first region.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing features of the present invention will become more apparent upon a consideration of the following description taken in ~OQ~352 connection with the accompanying drawings wherein:
Figure 1 is a fragmentary sectional view of a variable ratio steering apparatus;
Figure 2 is a fragmentary sectional view of a portion of the steering apparatus of Figure 1 and illustrating the relationship between an array of rack gear teeth and a cam track disposed on a rotatable drive member;
Figure 3 is a sectional view, taken generally along the line 3-3 of Figure 2, and illustrating the relationship between the drive member and a pinion gear which is disposed in meshing engagement with the rack gear teeth, a cam follower which engages the cam track, and a support member uhich presses the rack gear teeth into engagement with the pinion gear;
Figure 4 is a fragmentary sectional view, generally similar to Figure 1, of an embodiment which is utilized in associatin with a machine tool;
Figure 5 is an elevational view, taken generally along the line 5-5 of Figure 4 and depicting the relationship between a cam track on a rotatable drive member and a cam follower; and Figure 6 is a sectional view, taken generally along the line 6-6 of Figure 5, and illustrating the interaction between a pinion and rack gear teeth formed on the rotatable drive member.
DESCRIPTION OF SPECIFIC PREFERRED
EMBODIMENTS OF THE INVENTION
A variable ratio steering apparatus 10 is illustrated in Figure 1. The steering apparatus 10 is connected with a pair of steerable wheels ~not shown) of a vehicle in a well known manner by a suitable linkage. This .
. ~ ' , .
~1008SZ
linkage includes a tie rod 12 connected with one of the steerable vehicle wheels and a second tie rod 14 connected with the other steerable wheel.
The two tie rods 12 and 14 are connected with opposite ends of a longitudinally extending force transmitting member or bar 16 by a pair of ball joints 18 and 20. Upon axial movement of the bar 16 relative to a housing 24, the steerable wheels of the vehicle are turned to effect a desired steering action.
A tubular drive member or sleeve 28 is rotatably mounted on a central portion of the bar 16 and can be rotated without rotating the bar 16. To this end a bearing assembly 30 is disposed between a cylindrical inner surface 32 of the drive member 28 and the bar 16. The bearing assembly 30 cooperates with a needle bearing assembly 34 to rotatably support the drive member 28 on the bar 16 in a coaxial relationship with the bar.
The bearing assembly 30 is effective to hold the drive member 28 against axial movement relative to the bar 16.
A longitudinally extending array 38 of helical rack gear teeth 40 is formed on the drive member 28 ~see Figures 1 and 2). The rack gear teeth 40 extend only part way around the cylindrical outer surface of the drive member 28 and are disposed in meshing engagement with a rotatable pinion gear 42. Upon rotation of the pinion gear 42 about its central axis in response to turning of a steering wheel, the pinion gear 42 and rack gear teeth 40 cooperate to cause the drive member 28 and bar 16 to be moved along their common central axis 46. This effects turning movement of the steerable vehicle wheels in a known manner.
It is contemplated that during parking and other low speed operations in which the vehicle wheels are sharply turned, it may be desirable to decrease the effort required to turn the vehicle wheels by increasing the steering gear ratio. In order to increase the steering gear ratio, the drive member 28 is rotated about its central axis 46. This is accomplished by the interaction between a cam track 50 ~Figure 2) and a follower 52 ~Figure 3).
Rotation of the drive member 28 causes the helical rack gear teeth 40 to slide relative to the helical teeth on the pinion gear 42.
This sliding action displaces the drive member 28 longitudinally relative to the housing 24. This longitudinal movement of the drive member 28 is in a direction opposite to the direction in which the drive member is being moved relative to the housing 24 by the pinion gear 42 to thereby increase the steering gear ratio. If the pinion gear 42 is rotated in a counterclockwise direction as viewed in Figure 2, the drive member 28 and bar 16 move toward the right (as viewed in Figure 2). During this right-~ard movement, the follower 52 engages a downwardly (as viewed in Figure 2) curving end portion 54 of the cam track 50. This rotates the drive member 48 upwardly (as viewed in Figure 2) or in a clockwise direction ~as viewed in Figure 3).
The helical rack gear teeth 40 extend at an acute angle to the longitudinal central axis 46 of the drive member 28. Therefore, rotation of the drive member 28 about its central axis 46 causes the flanks on the rack gear teeth to effect a sliding or camming action against the flanks of the helical teeth of the pinion gear 42. This camming action moves the drive member toward the left (as viewed in Figure 2) with a screw type action. This results in a reduction in the rate of rightward (as viewed in Figure 2) movement of the drive member 28 and bar 16 to thereby effect an increase in the mechanical advantage provided by the steering gear assembly.
- .
1100~52 Similarly~ the pinion 42 is rotated in a clockwise direction (as viewed in Figure 2) to effect movement of the drive member 28 and bar 16 toward the left (as viewed in Figure 2). As this occurs, an arcuately upwardly curving end portion 58 of the cam track 50 engages the cam follower 52 to rotate the drive member 48 downwardly ~as viewed in Figure 2). The resulting interaction between the helical rack and pinion gear teeth reduces the rate of leftward ~as viewed in Figure 2) movement of the drive member 28 and bar 16.
It should be noted that the cam track 50 has a central portion 62 which extends parallel to the longitudinal axis 46 of the drive member 28. Therefore when the cam follower 50 is engaging the central portion 62 of the cam track 50, the cam follower and cam track are ineffective to cause rotation of the drive member 28 relative to the housing 24. Therefore the steering ratio remains constant at this time.
The cam track 50 is axially coextensive with the array 38 of rack gear teeth 40. Thus, the oppositely curving end portions 54 and 58 of the cam track 50 are disposed adjacent to axially opposite ends of the array 38 of rack gear teeth. By having the length of the cam track 50 coextensive with the axial length of the array 38 of rack gear teeth 40, the overall length of the drive member 28 is minimized. It is believed that this feature will be particularly advantageous when the steering apparatus 10 is utilized in association with a relatively small or compact vehicle.
In order to maintain solid meshing engagement between the pinion gear 42 and the array 38 of rack gear teeth 40 during rotation of the drive member 28, the array 38 of rack gear teeth has a curving configuration which is the same as the curv m g configuration of the cam track 50. Thus, a ' 110~8S2 longitudinally extending edge portion 66 of the array 38 of rack gear teeth has a central portion which extends parallel to the straight central portion 62 of the cam track 50. The opposite ends of the edge portion 66 of the array 38 of rack gear teeth curve in opposite directions in the same manner as do the opposite end portions 54 and 58 of the cam track 50.
Accordingly, the edge portion 66 of the array 38 of rack gear teeth is parallel to the longitudinal central axis of the cam track 50. The opposite edge portion of the array 38 of rack gear teeth ~not shown) has the same configuration as the edge portion 66. Therefore the array 38 of rack gear teeth has a substantially constant circumferential extent of about 140 about the drive member 28.
The cam follower 52 engages the cam track 50 at a location which is axially aligned with the location at which the pinion gear 42 meshingly engages the rack gear teeth 40 ~see Figure 3). By having the location at which the cam follower 52 engages the cam track 50 axially aligned with the area where the pinion gear 42 meshingly engages the rack gear teeth, the application of torsional loads to the drive member 28 is minimized.
In addition, sidewise loads and bending moments applied to the drive member 28 are minimized. If the cam follower 52 engaged the cam track 50 at a location which was axially offset from the location where the pinion gear 42 meshes with the rack gear teeth 40, the forces applied to the drive member 28 by the cam follower 50 would be offset from the forces applied to the drive member by the interaction between the rack and pinion gear teeth. By having these forces aligned with each other so that there are no bending moments tending to twist the drive member about a transverse .
.
- . . . .
:
- . .
1~0(~85~
a~is, the loading applied to the support structure for the drive member 28 and the bar 16 is minimized.
The rack gear teeth 40 and the drive member 28 are continuously pressed into meshing engagement with the pinion gear 42 under the influence of a support yoke 70. The support yoke 70 is pressed upwardly against a lower side of the drive member 28 under the influence of a biasing spring 72 (see Figure 1). It should be noted that the support yoke 70 engageS the drive member 28 at a location which is directly opposite from the location where the pinion gear 42 meshingly engages the rack gear teeth 40 so that the gear tooth forces which tend to separate the rack and pinion gears are offset by the support yoke. lhe cam follower 52 engageS the cam track 50 at a location between the support yoke 70 and the area of meshing engagement between the rack and pinion gears.
In the embodiment of the invention illustrated in Figures1-3, the apparatus is utilized to effect turning movement of the steerable wheels of a vehicle. However, it is contemplated that the apparatus could be utilized in environments other than in association with the steerable ~heels of a vehicle. For instance, it is contemplated that the apparatus could be utilized to move the traverse slide of a machine tool relative to the bed of the machine tool. An embodiment of the invention particularly adapted for use in association with a machine tool is illustrated in Figures 4-6. Since the embodiment of the invention illustrated in Figures 4-6 has many components which are generally similar to the components of the embodiment of the invention illustrated in Figuresl-3, similar numerals will be utilized to designate the components of Figures 4-6, the suffix letter "a" being associated with the embodiment of the invention illustrated ~10085Z
in Figures 4-6 to avoid confusion.
A drive assembly 10a ~Figure 4) includes a housing 24a which is connected with a bed ~not shown) of a machine tool. One end portion of a longitudinally extending force transmitting member or bar 16a is connected with a traverse slide 80 of the machine tool. Upon rotation of a pinion 42a, an array 38a of rack gear teeth 40a on a drive member 28a effects axial movement of the drive member 28a and the bar 16a to thereby move the traverse slide 80.
In order to change the rate at which the slide 80 is moved even though the rate of rotation of the pinion gear 42a remains constant, a follower 52a cooperates with a cam track 50a formed in the drive member 28a. The cam track 50a is axially coextensive with the array 38a of rack gear teeth 40a. In addition, the array 38a of rack gear teeth 40a has longitudinal edge portions which curve in the same manner as does the cam track 50a to provide for meshing engagement between the pinion gear 42a and rack gear teeth 40a upon rotation of the drive member 28a. The drive member 28a is supported for rotation about the central axis of the bar 16a by bearing assemblies 30a and 34a.
In the embodiment of the invention illustrated in Figures 4 through 6, the cam follower 52a engages the cam track 50a at a location ~hich is directly opposite from the location where the pinion gear 42a meshingly engages the rack gear teeth 40a ~see Figure 6). Therefore, axially inward forces applied to the drive member 28a by the pinion gear 42a and cam follower 52a offset each other. It should be noted that in the embodiment of the invention illustrated in Figures 4-6, the bar 16a is supported for axial movement relative to the housing 24a by a pair of 1~0()~352 cylindrical bushing 84 and 86 (see Figures 4 and 5).
It is contemplated that the forces to which the drive assembly lOa may be subjected will be relatively large. Therefore, the drive assembly lOa has relatively heavy components which are capable of with-standing these forces. In addition, wear of the cam follower 52a is minimized by rotatably supporting the cam follower 52a in bearings 90 ~see Figures 4 and 6). This enables the cam follower 50a to be rotated about its central axis under the influence of friction forces applied against a frusto-conical side surface 92 of the cam follower by the sides of the cam track 50a.
Although the rotatable cam follower 50a has been illustrated in Figures4-6, it is contemplated that the cam follower 50 of the embodiment of the invention shown in Figures 1-3 could be rotatably supported on bearings similar to the bearings90 of Figure 6. In addition, it is contemplated that the force transmitting bar 16 of the embodiment of the invention illustrated 1n Figures 1-3 could be supported for axial move-ment by a pair of bearing sleeves similar to the bearing sleeves 84 and 86 in the embodiment of the invention shown in Figure 4. If this was done, the support yoke 70 could be omitted. Omission of the support yoke 70 ~ould enable the cam follower 52 of the embodiment of the invention illustrated in Figures 1-3 to be mounted directly opposite from the pinion gear 42 in the manner shown in the second embodiment of the invention ~see Figure 6).
It is also contemplated that it may be desirable, under certain circumstances, to mount the cam track 50 or 50a on the housing 24 or 24a and to mount the cam follower 52 or 52a on the drive member 28 or 28a. If this was done, the interaction between the cam track and the cam follower ~10(~8S2 would be the same as previously described to effect rotation of the drive members 28 and 28a relative to the longitudinally extending bars 16 and 16a to thereby vary the gear ratio of the apparatus 10 and lOa upon axial movement of the bars 16 and 16a and drive members 28 and 28a. It is also contemplated that the bar 16 or 16a could be formed by a pair of bars having inner end portions connected with the rotatable drive member 28 or 28a by a pair of bearing assemblies similar to the bearing assembly 30 or 30a.
.. ~
This invention relates generally to a force transmitting apparatus and more specifically to a force transmitting apparatus which is advantageous-ly utilized to effect turning movement of a steerable wheel of a vehicle.
A known variable ratio steering apparatus is disclosed in Canadian Patent Application Serial No. 294,635 filed January 10, 1978 by Frederick John Adams and Ralph Malcolm Lehman and entitled "Improvements In Or Relating To Rack And Pinion Assemblies". The steering apparatus disclosed in that application includes a pinion having teeth which mesh with helical gear teeth on a rack bar. The rack bar is displaced longitudinally relative to a housing upon rotation of the pinion. A cam 10track is disposed on the rack bar and is engaged by a follower which is connected with the housing. The cam track and follower cooperate to effect rotation of the rack bar upon longitudinal movement of the rack bar. This rotation of the rack bar causes the rack gear teeth and pinion gear teeth to interact in such a manner as to vary the rate of axial movement of the rack bar.
Although the steering apparatus disclosed in the aforementioned application is believed to be generally satisfactory in its construction and mode of operation, it is believed that after extended usage, ball joints at opposite ends of the rack bar may tend to wear. This wear of ~Othe ball joints is, to some extent at the least, induced by the rotation of the rack bar.
In addition, the cam track of the steering apparatus disclosed in the aforementioned application is axially offset from the rack gear teeth. Therefore, the rack bar must have a minimum length which is at least t~ice as great as the length of the array of rack gear teeth. It is - 1 - ~
~. .
believed that this relatively long length may be objectionable if the steering apparatus is used with relatively small vehicles. In addition, by having the cam track axially offset from the rack gear teeth, the rack gear is subjected to both torsional and bending forces when the rack gear is rotated by the cam follower.
SUMMARY OF THE PRESENT INVENTION
_ _ _ _ _ , The present invention provides a variable ratio gear assembly comprising a pinion rotatably mounted in a housing and in meshing engagement ~ith a rack of a longitudinally extending sleeve, said sleeve forming part of a rack assembly having a longitudinally extending bar on which the sleeve is rotatably mounted and relative to which the sleeve is restrained from longitudinal displacement, said rack assembly being longitùdinally displaceable in response to rotation of the pinion through a first region and through at least one further region which extends from the first region, and wherein control means is provided which substantially restrains the ~leeye from rotating relative to the housing during its displacement through said first region so that the ratio of the gear is substantially constant and which imparts controlled rotation for the sleeve relative to the housing during longitudinal displacement of the rack assembly through the or a said further region so that the ratio of the gear is varied as 2Q compared with the substantially constant ratio provided during displacement of the rack assembly through the first region.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing features of the present invention will become more apparent upon a consideration of the following description taken in ~OQ~352 connection with the accompanying drawings wherein:
Figure 1 is a fragmentary sectional view of a variable ratio steering apparatus;
Figure 2 is a fragmentary sectional view of a portion of the steering apparatus of Figure 1 and illustrating the relationship between an array of rack gear teeth and a cam track disposed on a rotatable drive member;
Figure 3 is a sectional view, taken generally along the line 3-3 of Figure 2, and illustrating the relationship between the drive member and a pinion gear which is disposed in meshing engagement with the rack gear teeth, a cam follower which engages the cam track, and a support member uhich presses the rack gear teeth into engagement with the pinion gear;
Figure 4 is a fragmentary sectional view, generally similar to Figure 1, of an embodiment which is utilized in associatin with a machine tool;
Figure 5 is an elevational view, taken generally along the line 5-5 of Figure 4 and depicting the relationship between a cam track on a rotatable drive member and a cam follower; and Figure 6 is a sectional view, taken generally along the line 6-6 of Figure 5, and illustrating the interaction between a pinion and rack gear teeth formed on the rotatable drive member.
DESCRIPTION OF SPECIFIC PREFERRED
EMBODIMENTS OF THE INVENTION
A variable ratio steering apparatus 10 is illustrated in Figure 1. The steering apparatus 10 is connected with a pair of steerable wheels ~not shown) of a vehicle in a well known manner by a suitable linkage. This .
. ~ ' , .
~1008SZ
linkage includes a tie rod 12 connected with one of the steerable vehicle wheels and a second tie rod 14 connected with the other steerable wheel.
The two tie rods 12 and 14 are connected with opposite ends of a longitudinally extending force transmitting member or bar 16 by a pair of ball joints 18 and 20. Upon axial movement of the bar 16 relative to a housing 24, the steerable wheels of the vehicle are turned to effect a desired steering action.
A tubular drive member or sleeve 28 is rotatably mounted on a central portion of the bar 16 and can be rotated without rotating the bar 16. To this end a bearing assembly 30 is disposed between a cylindrical inner surface 32 of the drive member 28 and the bar 16. The bearing assembly 30 cooperates with a needle bearing assembly 34 to rotatably support the drive member 28 on the bar 16 in a coaxial relationship with the bar.
The bearing assembly 30 is effective to hold the drive member 28 against axial movement relative to the bar 16.
A longitudinally extending array 38 of helical rack gear teeth 40 is formed on the drive member 28 ~see Figures 1 and 2). The rack gear teeth 40 extend only part way around the cylindrical outer surface of the drive member 28 and are disposed in meshing engagement with a rotatable pinion gear 42. Upon rotation of the pinion gear 42 about its central axis in response to turning of a steering wheel, the pinion gear 42 and rack gear teeth 40 cooperate to cause the drive member 28 and bar 16 to be moved along their common central axis 46. This effects turning movement of the steerable vehicle wheels in a known manner.
It is contemplated that during parking and other low speed operations in which the vehicle wheels are sharply turned, it may be desirable to decrease the effort required to turn the vehicle wheels by increasing the steering gear ratio. In order to increase the steering gear ratio, the drive member 28 is rotated about its central axis 46. This is accomplished by the interaction between a cam track 50 ~Figure 2) and a follower 52 ~Figure 3).
Rotation of the drive member 28 causes the helical rack gear teeth 40 to slide relative to the helical teeth on the pinion gear 42.
This sliding action displaces the drive member 28 longitudinally relative to the housing 24. This longitudinal movement of the drive member 28 is in a direction opposite to the direction in which the drive member is being moved relative to the housing 24 by the pinion gear 42 to thereby increase the steering gear ratio. If the pinion gear 42 is rotated in a counterclockwise direction as viewed in Figure 2, the drive member 28 and bar 16 move toward the right (as viewed in Figure 2). During this right-~ard movement, the follower 52 engages a downwardly (as viewed in Figure 2) curving end portion 54 of the cam track 50. This rotates the drive member 48 upwardly (as viewed in Figure 2) or in a clockwise direction ~as viewed in Figure 3).
The helical rack gear teeth 40 extend at an acute angle to the longitudinal central axis 46 of the drive member 28. Therefore, rotation of the drive member 28 about its central axis 46 causes the flanks on the rack gear teeth to effect a sliding or camming action against the flanks of the helical teeth of the pinion gear 42. This camming action moves the drive member toward the left (as viewed in Figure 2) with a screw type action. This results in a reduction in the rate of rightward (as viewed in Figure 2) movement of the drive member 28 and bar 16 to thereby effect an increase in the mechanical advantage provided by the steering gear assembly.
- .
1100~52 Similarly~ the pinion 42 is rotated in a clockwise direction (as viewed in Figure 2) to effect movement of the drive member 28 and bar 16 toward the left (as viewed in Figure 2). As this occurs, an arcuately upwardly curving end portion 58 of the cam track 50 engages the cam follower 52 to rotate the drive member 48 downwardly ~as viewed in Figure 2). The resulting interaction between the helical rack and pinion gear teeth reduces the rate of leftward ~as viewed in Figure 2) movement of the drive member 28 and bar 16.
It should be noted that the cam track 50 has a central portion 62 which extends parallel to the longitudinal axis 46 of the drive member 28. Therefore when the cam follower 50 is engaging the central portion 62 of the cam track 50, the cam follower and cam track are ineffective to cause rotation of the drive member 28 relative to the housing 24. Therefore the steering ratio remains constant at this time.
The cam track 50 is axially coextensive with the array 38 of rack gear teeth 40. Thus, the oppositely curving end portions 54 and 58 of the cam track 50 are disposed adjacent to axially opposite ends of the array 38 of rack gear teeth. By having the length of the cam track 50 coextensive with the axial length of the array 38 of rack gear teeth 40, the overall length of the drive member 28 is minimized. It is believed that this feature will be particularly advantageous when the steering apparatus 10 is utilized in association with a relatively small or compact vehicle.
In order to maintain solid meshing engagement between the pinion gear 42 and the array 38 of rack gear teeth 40 during rotation of the drive member 28, the array 38 of rack gear teeth has a curving configuration which is the same as the curv m g configuration of the cam track 50. Thus, a ' 110~8S2 longitudinally extending edge portion 66 of the array 38 of rack gear teeth has a central portion which extends parallel to the straight central portion 62 of the cam track 50. The opposite ends of the edge portion 66 of the array 38 of rack gear teeth curve in opposite directions in the same manner as do the opposite end portions 54 and 58 of the cam track 50.
Accordingly, the edge portion 66 of the array 38 of rack gear teeth is parallel to the longitudinal central axis of the cam track 50. The opposite edge portion of the array 38 of rack gear teeth ~not shown) has the same configuration as the edge portion 66. Therefore the array 38 of rack gear teeth has a substantially constant circumferential extent of about 140 about the drive member 28.
The cam follower 52 engages the cam track 50 at a location which is axially aligned with the location at which the pinion gear 42 meshingly engages the rack gear teeth 40 ~see Figure 3). By having the location at which the cam follower 52 engages the cam track 50 axially aligned with the area where the pinion gear 42 meshingly engages the rack gear teeth, the application of torsional loads to the drive member 28 is minimized.
In addition, sidewise loads and bending moments applied to the drive member 28 are minimized. If the cam follower 52 engaged the cam track 50 at a location which was axially offset from the location where the pinion gear 42 meshes with the rack gear teeth 40, the forces applied to the drive member 28 by the cam follower 50 would be offset from the forces applied to the drive member by the interaction between the rack and pinion gear teeth. By having these forces aligned with each other so that there are no bending moments tending to twist the drive member about a transverse .
.
- . . . .
:
- . .
1~0(~85~
a~is, the loading applied to the support structure for the drive member 28 and the bar 16 is minimized.
The rack gear teeth 40 and the drive member 28 are continuously pressed into meshing engagement with the pinion gear 42 under the influence of a support yoke 70. The support yoke 70 is pressed upwardly against a lower side of the drive member 28 under the influence of a biasing spring 72 (see Figure 1). It should be noted that the support yoke 70 engageS the drive member 28 at a location which is directly opposite from the location where the pinion gear 42 meshingly engages the rack gear teeth 40 so that the gear tooth forces which tend to separate the rack and pinion gears are offset by the support yoke. lhe cam follower 52 engageS the cam track 50 at a location between the support yoke 70 and the area of meshing engagement between the rack and pinion gears.
In the embodiment of the invention illustrated in Figures1-3, the apparatus is utilized to effect turning movement of the steerable wheels of a vehicle. However, it is contemplated that the apparatus could be utilized in environments other than in association with the steerable ~heels of a vehicle. For instance, it is contemplated that the apparatus could be utilized to move the traverse slide of a machine tool relative to the bed of the machine tool. An embodiment of the invention particularly adapted for use in association with a machine tool is illustrated in Figures 4-6. Since the embodiment of the invention illustrated in Figures 4-6 has many components which are generally similar to the components of the embodiment of the invention illustrated in Figuresl-3, similar numerals will be utilized to designate the components of Figures 4-6, the suffix letter "a" being associated with the embodiment of the invention illustrated ~10085Z
in Figures 4-6 to avoid confusion.
A drive assembly 10a ~Figure 4) includes a housing 24a which is connected with a bed ~not shown) of a machine tool. One end portion of a longitudinally extending force transmitting member or bar 16a is connected with a traverse slide 80 of the machine tool. Upon rotation of a pinion 42a, an array 38a of rack gear teeth 40a on a drive member 28a effects axial movement of the drive member 28a and the bar 16a to thereby move the traverse slide 80.
In order to change the rate at which the slide 80 is moved even though the rate of rotation of the pinion gear 42a remains constant, a follower 52a cooperates with a cam track 50a formed in the drive member 28a. The cam track 50a is axially coextensive with the array 38a of rack gear teeth 40a. In addition, the array 38a of rack gear teeth 40a has longitudinal edge portions which curve in the same manner as does the cam track 50a to provide for meshing engagement between the pinion gear 42a and rack gear teeth 40a upon rotation of the drive member 28a. The drive member 28a is supported for rotation about the central axis of the bar 16a by bearing assemblies 30a and 34a.
In the embodiment of the invention illustrated in Figures 4 through 6, the cam follower 52a engages the cam track 50a at a location ~hich is directly opposite from the location where the pinion gear 42a meshingly engages the rack gear teeth 40a ~see Figure 6). Therefore, axially inward forces applied to the drive member 28a by the pinion gear 42a and cam follower 52a offset each other. It should be noted that in the embodiment of the invention illustrated in Figures 4-6, the bar 16a is supported for axial movement relative to the housing 24a by a pair of 1~0()~352 cylindrical bushing 84 and 86 (see Figures 4 and 5).
It is contemplated that the forces to which the drive assembly lOa may be subjected will be relatively large. Therefore, the drive assembly lOa has relatively heavy components which are capable of with-standing these forces. In addition, wear of the cam follower 52a is minimized by rotatably supporting the cam follower 52a in bearings 90 ~see Figures 4 and 6). This enables the cam follower 50a to be rotated about its central axis under the influence of friction forces applied against a frusto-conical side surface 92 of the cam follower by the sides of the cam track 50a.
Although the rotatable cam follower 50a has been illustrated in Figures4-6, it is contemplated that the cam follower 50 of the embodiment of the invention shown in Figures 1-3 could be rotatably supported on bearings similar to the bearings90 of Figure 6. In addition, it is contemplated that the force transmitting bar 16 of the embodiment of the invention illustrated 1n Figures 1-3 could be supported for axial move-ment by a pair of bearing sleeves similar to the bearing sleeves 84 and 86 in the embodiment of the invention shown in Figure 4. If this was done, the support yoke 70 could be omitted. Omission of the support yoke 70 ~ould enable the cam follower 52 of the embodiment of the invention illustrated in Figures 1-3 to be mounted directly opposite from the pinion gear 42 in the manner shown in the second embodiment of the invention ~see Figure 6).
It is also contemplated that it may be desirable, under certain circumstances, to mount the cam track 50 or 50a on the housing 24 or 24a and to mount the cam follower 52 or 52a on the drive member 28 or 28a. If this was done, the interaction between the cam track and the cam follower ~10(~8S2 would be the same as previously described to effect rotation of the drive members 28 and 28a relative to the longitudinally extending bars 16 and 16a to thereby vary the gear ratio of the apparatus 10 and lOa upon axial movement of the bars 16 and 16a and drive members 28 and 28a. It is also contemplated that the bar 16 or 16a could be formed by a pair of bars having inner end portions connected with the rotatable drive member 28 or 28a by a pair of bearing assemblies similar to the bearing assembly 30 or 30a.
.. ~
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A variable ratio gear assembly comprising a pinion rotatably mounted in a housing and in meshing engagement with a rack of a longitudin-ally extending sleeve, said sleeve forming part of a rack assembly having a longitudinally extending bar on which the sleeve is rotatably mounted and relative to which the sleeve is restrained from longitudinal displace-ment, said rack assembly being longitudinally displaceable in response to rotation of the pinion through a first region and through at least one further region which extends from the first region, and wherein control means is provided which substantially restrains the sleeve from rotating relative to the housing during its displacement through said first region so that the ratio of the gear is substantially constant and which imparts controlled rotation for the sleeve relative to the housing during longitudinal displacement of the rack assembly through the or a said further region so that the ratio of the gear is varied as compared with the substantially constant ratio provided during displacement of the rack assembly through the first region.
2. A gear assembly as claimed in claim 1 in which the first region is a central region of longitudinal displacement of the rack assembly and two said further regions are provided which extend one from each end of said central region.
3. A gear assembly as claimed in claim 1 in which the control means comprises a co-operating longitudinally extending track and a track follower one of which track and track follower is mounted to be secured against longitudinal displacement in the assembly and the other of which is located on the sleeve so that the track follower is displaced relatively along the track during longitudinal displacement of the rack assembly and the sleeve is caused to be rotated in accordance with the path of the track.
4. A gear assembly as claimed in claims 2 and 3 in which the central region of the track is substantially rectilinear and parallel to the axis of the rack assembly and each said further region of the track communicating with said first region extends longitudinally and is of substantially helical form.
5. A gear assembly as claimed in claim 3 in which the track is located on the sleeve and extends longitudinally substantially over the same portion of the sleeve as that on which the rack is located.
6. A gear assembly as claimed in claim 5 in which the rack teeth extend part way only around the periphery of the sleeve and to an extent that they maintain engagement with the pinion teeth throughout the intended rotational movement of the sleeve during longitudinal displacement of the rack assembly.
7. A gear assembly as claimed in claim 6 in which the track is a groove which is located in a working surface formed by the non-toothed per-ipheral part of the sleeve and the track follower engages within said groove.
8. A gear assembly as claimed in claim 7 wherein the track follower is rotatably mounted to roll along said groove during relative longitudinal displacement between the sleeve and the track follower.
9. A gear assembly as claimed in claim 7 wherein the track follower is mounted to engage the groove substantially in a plane which extends per-pendicularly relative to the axis of the rack assembly and which plane includes the position of engagement between the rack and pinion teeth.
10. A gear assembly as claimed in claim 9 wherein the track follower engages with the groove at a position which substantially is directly opposite to the pinion and on the side of the sleeve remote from its rack teeth.
11. A gear assembly as claimed in claim l in which bearing means is provided by which the rack assembly is supported both for its longitudinal displacement through a housing of the gear and for maintaining the rack of the sleeve in meshed engagement with the pinion.
12. A gear assembly as claimed in claim 11 in which the bar of the rack assembly extends through the sleeve and said bearing means mounts the bar in the housing for longitudinal displacement of the rack assembly and also to restrain the bar and thereby the rack assembly from displacement radially relative to the longitudinal axis of the rack assembly.
13. A gear assembly as claimed in claim 12 in which the bearing means comprises two bearings for the bar, said bearings being located at longitudinally spaced positions in the housing and mounting the bar on longitudinally opposite sides of the sleeve.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA359,455A CA1100852A (en) | 1977-03-15 | 1980-09-02 | Rotatable sleeve rack |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB10867/77A GB1546339A (en) | 1977-03-15 | 1977-03-15 | Gear assemblies |
| GB10867/77 | 1977-03-15 | ||
| CA299,038A CA1096755A (en) | 1977-03-15 | 1978-03-14 | Rotatable sleeve rack |
| CA359,455A CA1100852A (en) | 1977-03-15 | 1980-09-02 | Rotatable sleeve rack |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1100852A true CA1100852A (en) | 1981-05-12 |
Family
ID=27165560
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA359,455A Expired CA1100852A (en) | 1977-03-15 | 1980-09-02 | Rotatable sleeve rack |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1100852A (en) |
-
1980
- 1980-09-02 CA CA359,455A patent/CA1100852A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| DE4236771C2 (en) | Steering device with variable steering angle ratio for a steering lever control mechanism | |
| DE19823721B4 (en) | vehicle steering | |
| EP0528200B1 (en) | Speed reduction device for steering devices | |
| EP0013074B1 (en) | A variable ratio rack and pinion gear | |
| US5284219A (en) | Steering apparatus with variable steering angle ratio | |
| US5489004A (en) | Variable ratio steering system | |
| US5386879A (en) | Steering angle ratio varying device for a vehicle | |
| US4270397A (en) | Rotatable sleeve rack | |
| CA1096755A (en) | Rotatable sleeve rack | |
| EP0003678A1 (en) | A gear assembly | |
| DE60111914T2 (en) | Steering control device for motor vehicle | |
| JPH06107218A (en) | Neutral return mechanism for rear wheel steering device | |
| CA1085702A (en) | Steering gears | |
| CA1100852A (en) | Rotatable sleeve rack | |
| CA1082002A (en) | Rack and pinion assemblies | |
| KR920006188A (en) | Rear wheel steering of the vehicle | |
| US3983763A (en) | Pinion for variable ratio rack and pinion steering gear | |
| US5020812A (en) | Four-wheel steering system in wheeled vehicle | |
| JPS6210523Y2 (en) | ||
| US4263816A (en) | Steering gear assemblies | |
| JPH03136975A (en) | Rear-wheel steering device of front-and-rear-wheel steering vehicle | |
| US4984815A (en) | Steering device for a motor vehicle with four steered wheels | |
| EP0131674A1 (en) | Steering system for vehicles | |
| JPH0624304Y2 (en) | Rear wheel steering system for front and rear wheel steering vehicles | |
| JP2660735B2 (en) | Rear wheel steering mechanism |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |