US 20050087384 A1
A steer-by-wire handwheel actuator in a vehicle is presented. The handwheel actuator comprises a driver input shaft; a gear train connected to the driver input shaft; a motor responsive to control signals from a controller and variably geared to the gear train; a electro-mechanical brake responsive to the control signals from the controller and geared to one of the driver input shaft and the gear train; and a stop mechanism attached to a housing and coupled to one of the electro-mechanical brake and the gear train.
1. A steer-by-wire handwheel actuator utilizing a controller operative to accept as input thereto data from the steer-by-wire system and generate therefrom control signals in a vehicle comprising:
a driver input shaft;
a gear train connected to the driver input shaft;
a motor responsive to the control signals from the controller and variably geared to the gear train, the motor including a motor shaft driven therefrom and a motor pulley connected to the motor shaft and having cogs circumferentially arranged;
an electro-mechanical brake responsive to the control signals from the controller and geared to one of the driver input shaft and the gear train; and
a stop mechanism attached to a housing and coupled to one of the electro-mechanical brake and the gear train,
wherein the gear train is a pulley and gear train assembly, said gear train assembly including:
a driver feedback pulley connected to the driver input shaft;
a speed reducer pulley having cogs circumferentially arranged for positive engagement with the motor pulley cogs and being connected to the driver input shaft; and
a spur gear connected to the driver input shaft.
4. The steer-by-wire handwheel actuated as set forth in
5. The steer-by-wire handwheel actuator as set forth in
a modular unit having a biasing member to provide mechanical resistance to one of the driver input shaft and the gear train.
6. The steer-by-wire handwheel actuator as set forth in
7. The steer-by-wire handwheel actuator as set forth in
This application claims the benefit of U.S. provisional application No. 60/299,342, filed Jun. 19, 2001 the contents of which are incorporated by reference herein in their entirety.
This invention relates to a steer-by-wire system, and more particularly to a steer-by-wire handwheel actuator.
It is known in the art to have a steering system with mechanical linkage from the steering wheel to the steerable road wheels. Even with power assist, the driver of a mechanically linked vehicle can feel the forces of the road against the steerable wheels through the steering wheel. Indeed, this is a desired feature of direct linkage and is sought out by purchasers of high performance vehicles in the form of so-called “rack-and-pinion” steering. The road forces felt in the steering wheel give the driver feedback he can use to anticipate and control the vehicle, or at least create the comfortable feeling that he is in control of the vehicle. Remove this feedback, such as in the case of “mushy” power steering, and the driver will have the uncomfortable feeling of being separated from the road wheels, not quite in control, and will tend to oversteer his vehicle, particularly in demanding situations such as sharp or sudden turns.
By definition, a steer-by-wire system has no mechanical link connecting the steering wheel from the road wheels. In effect, the steering wheel is little more than a joystick, albeit an extremely sophisticated joystick. Exemplary of such known steer-by-wire systems is commonly-assigned U.S. Pat. No. 6,176,341, issued Jan. 23, 2001 to Ansari, which is wholly incorporated herein by reference. What is needed is to provide the steer-by-wire driver with the same “road feel” that a driver receives with a direct mechanical link. Furthermore, it is desirable to have a device that provides a mechanical back up “road feel” in the event of multiple electronic failures in the steer-by-wire system. In addition, a device that provides positive on-center feel and accurate torque variation as the handwheel is rotated is also desirable. Existing steer-by-wire devices produce excessive lash, excessive noise and insufficient over-load torque capability as the handwheel is rotated to its end of travel in either direction.
A steer-by-wire steering system is defined as a steering system with no mechanical connection between a steering wheel and a set of steering gears or actuators. Such systems are advantageous because they permit auto and other vehicle designers great latitude in use of space that would normally be taken up by mechanical linkages, among other reasons.
In an exemplary embodiment of the invention, a steer-by-wire handwheel actuator is described, which provides feedback of road forces to the operator of a steer-by-wire vehicle. A handwheel actuator comprises a driver input shaft; a gear train connected to the driver input shaft; a motor responsive to control signals from a controller and connected to the gear train; an electro-mechanical brake responsive to the control signals from the controller and connected to one of the driver input shaft and the gear train; and a stop mechanism attached to a housing and coupled to one of the electro-mechanical brake and the gear train.
Still referring to
With reference to
It should be noted that a preferred embodiment of the handwheel actuator utilizes an electric sine commutated brushless motor 114 for its primary power transmission because the sine wave commutation provides for a low torque ripple. Furthermore, it is preferred that the belt 128 used to transmit the power from the motor 114 is a small-cogged belt to provide positive drive, high efficiency, low noise, and nearly zero lash. In using a cogged belt, it has been found to yield approximately 98% efficiency. In addition, a preferred embodiment uses a magnetic particle brake for the electro-mechanical brake 120, however alternative embodiments also include electro-rheological fluid devices.
Magnetorheological fluids suitable for use in the handwheel actuator 100 are disclosed in U.S. Pat. No. 5,896,965, issued 27 Apr. 1999, to Gopalswamy et al. for a Magnetorheological Fluid Fan Clutch; U.S. Pat. No. 5,848,678, issued 15 Dec. 1998, to Johnston et al. for a Passive Magnetorheological Clutch; U.S. Pat. No. 5,845,752, issued 8 Dec. 1998, to Gopalswamy et al. for a Magnetorheological Fluid Clutch with Minimized Resistance; U.S. Pat. No. 5,823,309, issued 20 Oct. 1998, to Gopalswamy et al. for a Magnetorheological Transmission Clutch; and U.S. Pat. No. 5,667,715, issued 16 Sep. 1997, to Foister, R. T. for Magnetorheological Fluids; the disclosures of all of which are incorporated herein by reference in their entirety. An alternative embodiment utilizing an electro-rheological fluid device having magnetorheological fluid for obtaining a variable resistance to the driver input shaft is disclosed in Patent Application number DP-300272, entitled “Variable Road Feedback Device For Steer-By-Wire System.”
It is to be noted that utilizing a magnetic particle brake or a magnetorheological fluid device provides virtually no resistance to a driver input shaft when there is no magnetic force induced by a control module. However, when it becomes desirable to give the vehicle operator a feel of the road, a control module energizes a magnetic field in the magnetic particle brake or the magnetorheological fluid device causing the magnetic particle brake or the magnetorheological fluid device in turn to provide variable passive resistance. The variable passive resistance along with active resistance provided by the electric motor gives the vehicle operator a feel of the road by transferring the resistance upon the steering wheel. Thus, causing the vehicle operator to “feel” or sense the road.
Still referring to
Bearing assembly 170 is retained in housing 162 with a bearing cap 172 that is mechanically fastened to housing 162 with mechanical fasteners 174. A bearing nut 176 is engageable with another threaded portion of shaft 102 to fix shaft 102 relative to bearing assembly 170 which is fixed relative to housing 162. At an opposite end 178 of housing 162 an end cap 180 encloses a cavity formed in housing 162. At the same end 178 a retaining nut 182 is threaded onto the end of sleeve 144 and an external spring return nut 196 is threaded into housing 162. Disposed against retaining nut 196 and retaining nut 182 is a first spring retaining washer 188 having an aperture allowing ball screw 144 to slide therethrough. A second spring retaining washer 190 is disposed against a shoulder 192 of sleeve 144 and shoulder 198 of housing 162. Like washer 188, washer 190 includes an aperture that allows sleeve 144 to slide therethrough. A plurality of biasing members 194 is disposed intermediate washers 188, 190. Each biasing member is preferably a disc spring or Belleville washer. The plurality of biasing members 194 is more preferably a stack of disc springs circumferentially disposed about sleeve 144 while allowing translation of sleeve 144 therethrough. The stack of disc springs are preferably formed by alternating the orientation of contiguous disc springs to provide a compression type biasing member 194. The spring pack or plurality of biasing members 194 is stacked in series to provide desired spring load and maximum travel. The springs are designed and preferably preloaded to a stack height that gives a non-linear spring rate with a very gradual slope.
Spring retaining nut 182 is preferably configured as an adjustment preload nut that is threaded onto the sleeve 144 and tightened to a specified position to set the appropriate spring preload on the biasing members 194. An external spring return nut 196 has exterior threads threadably engaged with complementary threads in housing 162 at end 178 for engaging washer 188 when sleeve 144 translates toward end 178 pushing washer 192 to compress biasing members 194 which push against washer 188 which is prevented from translating toward end 178 by fixed nut 196. When sleeve 144 translates away from end 178, nut 182 pushes against washer 188 to compress biasing members 194 against washer 192 that is prevented from translating away from end 178 by a shoulder 198 formed in housing 162. The preload on the biasing members 194 is configured to provide an identical bias when shaft 102 is rotated in either direction since the spring pack or plurality of biasing members 194 is configured in a parallel arrangement to bias the shaft indicative of a return-to-center position. It will be recognized that although the plurality of biasing members has been described as a single series stack of disc washers, multiple stacks are also contemplated. More specifically, it is contemplated that a first stack may be disposed on one side of ball nut 168 while a second stack is disposed on the other side of ball nut 168. In this manner, when shaft is rotated in one direction, the first stack is compressed and when shaft 102 is rotated in an opposite direction, the second stack is compressed.
In operation, as the hand wheel 10 is rotated from the center position, the steering shaft 102 rotates at the same speed. As the steering shaft 102 rotates, the ball nut 168 and hence sleeve 144 translates left or right in an axial direction relative to shaft 102 shown in
Referring now to
It will be understood that a person skilled in the art may make modifications to the preferred embodiment shown herein within the scope and intent of the claims. While the present invention has been described as carried out in a specific embodiment thereof, it is not intended to be limited thereby but intended to cover the invention broadly within the scope and spirit of the claims.