WO2017037727A1

WO2017037727A1 - Variable steering mechanism for pure rolling

Info

Publication number: WO2017037727A1
Application number: PCT/IN2015/050133
Authority: WO
Inventors: Dipalkumar Rameshbhai KOLADIA; Meet Vitthalbhai RAKHOLIA; Nikunjkumar Himmatbhai KEVADIYA
Original assignee: Koladia Dipalkumar Rameshbhai; Rakholia Meet Vitthalbhai; Kevadiya Nikunjkumar Himmatbhai
Priority date: 2015-09-02
Filing date: 2015-10-14
Publication date: 2017-03-09
Also published as: IN2015MU03358A

Abstract

Variable steering mechanism for pure rolling is controlled by either continuous variable tie-rod length or continuous variable rack travel. Wherein for continuous variable tie-rod length this mechanism is having mechanical as well as electrical components for controlled variable length of tie-rod. Advantage with mechanism is that, for different steering geometry parameters, values in code and basic length of tie-rod will require to modify and for continuous variable rack travel, this mechanism is having only mechanical components for controlled travel of the rack. For different steering geometry parameters, cam profile will be changed.

Description

FIELD OF THE INVENTION

The present invention relates to Variable Steering Mechanism for pure rolling of vehicle. The invention relates to a vehicle steering mechanism in automobile industries.

BACKGROUND OF THE INVENTION

Presently for the every vehicle existed mostly still using the two wheel steering (2WS) system with Ackerman geometry to control the movement of the vehicle whether it is front wheel drive, rear wheel drive or all-wheel drive. Ackerman steering geometry can be explained by using typical front two wheel steering system. When vehicle is taking turn both the inside and the outside wheels must be turned to correspond to the turn. In order to do this, both wheels will follow distinct arc-paths and ideally center of these arc paths should be same. If this is the case, i-centers of all four wheels will intersect at one point. If this condition will satisfy, there is no scrubbing, skidding and slippage of the wheels and all four wheels have pure rolling. It is clear that in order to do this, inner and outer wheel will have different radius of arc-path. Outer wheel have large radius of arc-path than inner wheel. Hence, outer wheel turning angle will be less than inner wheel turning angle. When the center of rotation of both wheel are coincident, a condition known as perfect Ackerman exists. This condition is shown in fig 1 for front two wheel steering mechanism. Such state is most desirable in a vehicle dynamics sense, because any deviation from this state results in degradation of vehicle handling characteristics, tire wear. But for rack and pinion mechanism using Ackerman geometry for steering, it is not possible to achieve perfect Ackerman condition at all steering angles which can be understood by observing fig 2. This generates slip in the tires leading to tire wear and poor handling at higher cornering speeds.

OBJECT OF THE INVENTION

In all current steering mechanism Ackerman condition can be achieved only at two points either side therefore it results in tire wear due to slippage of tires. The present invented devices enable variable steering mechanism in order to achieve 100% Ackerman at all turning angles.

The present invention can be used for pure rolling of vehicles which reduces wear of tires and prevents skidding. Implementation of this devices in the vehicle will result in better vehicle handling characteristics and stability at high cornering speeds. SUMMARY OF THE INVENTION

To achieve perfect ackerman condition at all turning angles in the present invention, constructional arrangements of two variable steering mechanisms are provided.

1. Continuous variable tie-rod length: This mechanism is having mechanical as well as electrical components for controlled variable length of tie-rod. Advantage with mechanism is that, for different steering geometry parameters, only values in code and basic length of tie-rod will require to modify. This mechanism involves both electrical and mechanical components. High manufacturing accuracy in mechanical components and in their assembly, lead to approximately 100% ackerman.

2. Continuous variable rack travel:

This mechanism is having only mechanical components for controlled travel of the rack. It is compact compare to first one and cheaper in cost. It is more reliable due to mechanical actuation. For different steering geometry parameters, cam profile will be changed and hence with every different steering geometry new cam is required to design. High manufacturing accuracy in cam and follower along with other mechanical components and in their assembly, lead to approximately 100% ackerman.

BRIEF DESCRIPTION OF THE DRAWINGS

It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible, and consequently the particularity of the accompanying drawings is not intended to be limiting of the present invention. Fig. 1 Ackerman condition for two wheel steering

Fig. 2 Deviation from Ackerman condition for rack and pinion steering geometry

Fig. 3 Various steering geometry parameters

Fig. 4 Toe zero condition

Fig. 5 Inner wheel geometry

Fig. 6 Outer wheel geometry

Fig. 7 Perfect ackerman condition for different angles by variable tie- rod length

Fig. 8 Exploded vie of variable tie-rod

Fig. 9 Tie-rod assembly

Fig. 10 Block diagram of variable tie-rod length mechanism

Fig. 11 Working model of continuous variable rack travel mechanism Fig. 12 Flow chart of the logic

DETAILED DESCRIPTION OF THE INVENTION

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the construction and arrangement of parts illustrated in the accompanying drawings. The invention is capable of other embodiments, as depicted in different figures as described above and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation.

Ackerman condition for two wheel steering, shown in Fig.l, is expressed as:

Where,

δο = outer wheel angle

δΐ = inner wheel angle

W = Track width of the vehicle

B = distance between left and right kingpin centerline

L = wheel base of the vehicle

Geometry Parameters:

Here is a list of various steering geometry parameters in case of rack and pinion geometry, shown in Fig.3.

x= steering arm length

y= tie-rod length (in top view)

p= rack casing length

p+2r= rack ball joint center to center length

q= travel of rack

d= distance between front axis and rack center axis

β= Ackerman angle

Geometry Equations:

From Fig. 4,

From Fig. 5,

Value of actual δο is the function of x, y, d, and q and all this values are same for inner wheel geometry and outer wheel geometry and therefore actual outer wheel angle and outer wheel angle require for ackerman condition will be equal for only one value of rack travel q. Now, values of B, ackerman angle β are fixed by wheel base and track width of the vehicle and values of p & r is fixed by dimensions of rack and pinion which is going to be used in steering geometry. In order to get 100% ackerman, it is necessary that one of the geometry parameters i.e. x, y, d or q is different for inner and outer wheel geometry.

If the value of d changes then whole steering column and assembly along with rack mountings require to be movable which is not desirable. Steering arm is integral part of Knuckle so value of x also can't be changed.

So, in the present invention has now only two choices for pure rolling is different length of tie rod or different travel for inner wheel and outer wheel geometry. Based on this analysis, in the present invention, two mechanisms are possible to achieve 100% ackerman.

1. Continuous variable tie-rod length mechanism

One of the option available, in order to achieve 100% ackerman, is by attaining different tie-rod length for inner and outer wheel geometry for each and every angle. Now for simplifying the process if one of the tie-rod length is kept fixed then only another tie-rod length needs to be varied. So, in the present invention, the inner tie-rod length fixed so that only outer tie-rod length needs to be varied. · Basic Tie rod length

Mechanism:

This mechanism is having mechanical as well electrical components in order to controlled variation in length of tie-rod so that perfect ackerman condition at all turning angles.

The mechanical components consists with variable length tie-rod, screw and nut, servo coupling, potentiometer, arduino micro controller, stepper motor. wherein in Fig. 8, the exploded view of tie-rod assembly is shown. Half threaded part is welded with tie-rod part 1 which is coupled with coupler by using nut. Tie-rod part 2 and coupler is joined together by using nut-bolt inserted axially. Hence, this is sliding mechanism and variable length can be achieved. The assemble tie- rod is shown in Fig. 9. For linear actuation, in this mechanism Nut and bolt are used. Servo coupling is used in order to couple stepper motor and screw.

Potentiometer is used for sensing rotation of steering wheel.

Arduino micro controller is used in order to control the number of steps and the direction of rotation of the stepper motor so that perfect ackerman can be achieved at all points.

Stepper motor is used as a drive to screw and nut mechanism. It is rotates clockwise or anti clockwise depending on the output from Arduino. Logic of Arduino code to give command the stepper motor is explained below:

Change in length of tie-rod for outer wheel geometry can be calculated using mathematical calculation of ackerman steering geometry. It can be calculated in the microprocessor Arduino itself but it will take a lot of time. So in order to reduce processing time, required change in length of tie-rod and from that value of no. of steps are calculated outside. These values are then fed in the Arduino with respect to steering wheel rotation. For every half degree of steering wheel rotation required steps of stepper motor are known.

For processor steering wheel rotation is input and no. of steps required to stepper motor is output. Stepper driver is used to enable micro-stepping.

Working of Mechanism:

In order to change the length of the tie rod, linear actuators can be used. We have selected one such linear actuator i.e. SCREW AND NUT for this purpose. Here the tie rod is composed of two parts which are held together by sliding joint. One part has the motor fixed on it. This motor is connected to the screw by means of coupling. The other part has nut fixed on it. Thus when the screw rotates in the nut both the tie rod parts slides into one another. Block diagram of this mechanism is shown in Fig. 10 and explained below.

Input to the steering wheel by the driver is transferred to the rack by the means of pinion. A potentiometer is connected to the pinion which precisely counts the degrees of rotation of the steering wheel. Then it is fed to the microprocessor. The microprocessor uses the steering angle and calculates the wheel angle and compares it with the stored data. The data stored in the microprocessor is a table which gives one to one correspondence between the amounts of degrees that the wheel turns to that of the amount of length change needed in the tie rod to achieve Ackermann at the given wheel angle. Then the corresponding amount of rotation required to achieve desired variation in length is relayed to the motor. As shown in the Fig.10, the motor is connected to the screw which in turn rotates inside the nut and linear motion is achieved. This linear motion as mentioned above slides the two parts within each other and correct tie rod length is achieved for each turning angle. Therefore it is controlled and ultimate output is perfect ackerman condition at all the turning angles i.e. 100% ackerman.

Continuous variable rack travel

One of the option available, in order to achieve 100% ackerman, is by allowing different rack travel for inner and outer wheel geometry for each and every angle.

Travel of rack for the inner wheel geometry can be calculated using following equation.

Where,

Now in order to achieve 100% ackerman, rack travel for outer wheel geometry can be calculated by using following equation.

Where,

Mechanism

: Different rack travel for inner and outer wheel geometry can be achieved by using two different cam profile for both geometry. Cam and follower is the replacement of the rack. Follower at both side will have different travel as per profile of the cam. So the profile of cam should be such that travel of the follower is equal to the travel as calculated from the equation which is required in order to achieve 100% ackerman.

Cam and follower:

In this mechanism, cam and follower is used instead of rack and pinion in order to achieve different travel at both side geometry. Cam has two different profile corresponding to inner wheel and outer wheel geometry. Profiles are made in such a manner that follower's travel enable 100% ackerman for each and every turning angle and therefore profile of cam is critical in this mechanism. Proper design of cam profile will result in 100% ackerman. Both cam are same in structure but the arrangement in geometry is different. Here, in this mechanism, pinion is replaced by gear and cam combination and rack is replaced by follower.

Working:

Working model of this mechanism is shown in Fig. 11. Both cam have two profile corresponding to inner and wheel geometry. When follower 1 is following profile of inner wheel geometry at that time follower 2 is following profile of outer wheel geometry or vice versa. Gears are attached with cam so that both cam have same rotation in same direction. Tie-rod is attached with follower. Due to different profile both follower will have different travel and it is such that for all turning angles 100% ackerman can be achieved.

While, the invention has been described with respect to the given modifications and other applications of the invention may be made. However, it is to be expressly understood that such modifications and adaptations are within the scope of the present invention, as set forth in the following claims.

I Claim

1. Variable steering mechanism for pure rolling is controlled by continuous variable tie-rod length or continuous variable rack travel

wherein continuous variable tie-rod comprising with mechanical and electrical components,

wherein continuous variable rack travel comprising with mechanical components. 2. Variable steering mechanism for pure rolling as claimed in claim 1 wherein in continuous variable tie-rod mechanism mechanical components consists with variable length tie-rod, screw and servo coupling and electrical components consists with potentiometer, microprocessor, and stepper motor.

Variable steering mechanism for pure rolling as claimed in 3.

claim 1 wherein variable tie-rod is consist with tie-rod part-1 , half threaded part (2), nut (3), coupler (4) and tie-rod part-2(5); wherein half threaded part is welded with tie-rod part- 1(1) which is coupled with coupler (4) by using nut (3);

wherein tie-rod part -2(5) and coupler (4) is joined together by using nut-bolt (3) inserted axially for linear actuation. 4. Variable steering mechanism for pure rolling as claimed in claim 1 wherein servo coupling is used in order to couple stepper motor and screw and potentiometer is used for sensing rotation of steering wheel.

5. Variable steering mechanism for pure rolling as claimed in claim 1 wherein micro controller is used in order to control the number of steps and the direction of rotation of the stepper motor and stepper motor is used to drive screw and nut mechanism either clockwise or anti clockwise depending on the output from microprocessor.

6. Variable steering mechanism for pure rolling as claimed in claim 1 wherein in order to change the length of the tie rod, screw and nut linear actuator is used.

wherein the tie rod is composed of two parts which are held together by sliding joint, where the first part is fixed motor which is further connected to the screw by means of coupling and other part has nut fixed on it. 7. Variable steering mechanism for pure rolling as claimed in claim 1 wherein input to the steering wheel by the driver is transferred to the rack by the means of pinion, where a potentiometer is connected to the pinion which precisely counts the degrees of rotation of the steering wheel , which is fed to the microprocessor and the microprocessor uses the steering angle and calculates the wheel angle and compares it with the predetermined stored data to change length needed in the tie rod to achieve ackerman at the given wheel angle, then the corresponding amount of rotation required to achieve desired variation in length is relayed to the motor.

8. Variable steering mechanism for pure rolling as claimed in claim 1 for continuous variable rack travel mechanism has two different cam profile for inner & outer wheel geometry wherein pinion is replaced by gear & cam combination and rack is replaced by follower which is attached with Tie-rod.

9. Variable steering mechanism for pure rolling as claimed in claim 8 gears are attached with cam so that both cam have same rotation in same direction.

10. A method for Variable Steering Mechanism for pure rolling as claimed in claim 1 wherein comprising with following steps: (a) Input to the steering wheel by the driver is transferred to the rack by the means of pinion; (b) A potentiometer is connected to the pinion which precisely counts the degrees of rotation of the steering wheel then it is fed to the microprocessor;

(c) the microprocessor uses the steering angle and calculates the wheel angle and compares it with the stored data, the pre-determined data stored in the microprocessor is a table which gives one to one correspondence between the amounts of degrees that the wheel turns to that of the amount of length change needed in the tie rod to achieve Ackermann at the given wheel angle, then the corresponding amount of rotation required to achieve desired variation in length is relayed to the motor;

(d) the stepper motor is connected to the screw which in turn rotates inside the nut and linear motion is achieved;

(e) this linear motion as mentioned above slides the two parts within each other and correct tie rod length is achieved for each turning angle.

Dated 1^st September 2015

Claims

I Claim

wherein continuous variable rack travel comprising with mechanical components.

2. Variable steering mechanism for pure rolling as claimed in claim 1 wherein in continuous variable tie-rod mechanism mechanical components consists with variable length tie-rod, screw and servo coupling and electrical components consists with potentiometer, microprocessor, and stepper motor.

3. Variable steering mechanism for pure rolling as claimed in claim 1 wherein variable tie-rod is consist with tie-rod part-1 , half threaded part (2), nut (3), coupler (4) and tie-rod part-2(5); wherein half threaded part is welded with tie-rod part- 1(1) which is coupled with coupler (4) by using nut (3);

wherein tie-rod part -2(5) and coupler (4) is joined together by using nut-bolt (3) inserted axially for linear actuation.

4. Variable steering mechanism for pure rolling as claimed in claim 1 wherein servo coupling is used in order to couple stepper motor and screw and potentiometer is used for sensing rotation of steering wheel.

wherein the tie rod is composed of two parts which are held together by sliding joint, where the first part is fixed motor which is further connected to the screw by means of coupling and other part has nut fixed on it.

7. Variable steering mechanism for pure rolling as claimed in claim 1 wherein input to the steering wheel by the driver is transferred to the rack by the means of pinion, where a potentiometer is connected to the pinion which precisely counts the degrees of rotation of the steering wheel , which is fed to the microprocessor and the microprocessor uses the steering angle and calculates the wheel angle and compares it with the predetermined stored data to change length needed in the tie rod to achieve ackerman at the given wheel angle, then the corresponding amount of rotation required to achieve desired variation in length is relayed to the motor.

Dated 1^st September 2015