GB2337967A - A power-assisted anti-roll system for a vehicle - Google Patents

Abstract

An anti-roll system is provided for a wheeled land vehicle. A torsional coupling is arranged to couple unsprung masses of suspension units positioned on opposite sides of the vehicle. The coupling comprises torsion bar components 10A, 10B which extend inwardly from each unsprung mass, and a torsion bar coupling means 14A, 14B, 16 coupling the two torsion bars. Upon lateral acceleration of the vehicle body torsional stresses are induced in the coupling which further comprises means 18, 20 whereby equal and opposite torque can be induced into the torsion bars by way of the torsion bar coupling means 14A, 14B, 16.

Description

2337967 VEHICLE POWER-ASSISTED ANTI-ROLL SYSTEM This invention is

concerned with improvements in or relating to anti-roll systems for wheeled land vehicles, and in particular to power5 assisted systems.

Many road vehicles are fitted with anti-roll bars (sometimes referred to as torsion bars) to achieve a better balance between passenger comfort and vehicle road-holding performance than can 'be achieved through wholly independent suspension at each wheel. -in particular, a torsion bar acts to prevent excessive rolling of the vehicle body in cornering, whilst permitting a relatively soft suspension to be maintained to give a comfortable ride when travelling in a straight line.

However, as with any element of the suspension, the selection of an antiroll bar with particular characteristics for a particular vehicle is a compromise, taking into account the intended uses and performance of the vehicle; outside the boundaries of (or even approaching the boundaries of) the intended uses and performance of the vehicle, any chosen passive anti-roll system will prove less than ideal. Selection of a suitable antiroll system for multi-use vehicles (e.g. vehicles intended for crosscountry use as well as on-road) is especially demanding.

For these reasons, anti-roll systems are known which are active, being power-assisted to modify their characteristics in response to the changing demands of different driving conditions in use. However, their construction tends to be complex and their performance deficient in various ways.

2 It is an object of the present invention to provide an improved powerassisted anti-roll system which can be simply engineered and have low power requirements.

The invention provides, in one of its aspects, an anti-roll system for a wheeled land vehicle in which torsional coupling means is arranged to couple unsprung masses of suspension units positioned on opposite sides of the vehicle, whereby upon lateral acceleration of the vehicle body torsional stress may be induced in said coupling means, 'the coupling means comprising a first torsion bar component which extends from one of the unsprung masses, a second torsion bar component which extends from the other of the unsprung masses, component-coupling means coupling said two bar components, and means hereby equal and opposite torque can be induced into said components by way of said component-coupling means.

The component- coupi i ng means may comprise a gear train connecting one component rotationally with the other, each component being mounted for rotation about a common torque axis in sympathy with heightwise movements of the unsprung suspension masses. The gear train may comprise a driven gear secured to each torsion bar component and a driving gear coupled directed or indirectly with the two driven gears, the driving gear being coupled (or arranged to be coupled, e.g. by way of an electromagnetic or other form of clutch) to the torque-inducing means.

The torque-inducing means may comprise actuating means whereby the component-coupling means can be powered to induce torque into the components in either rotational direction. In a preferred arrangement, the actuating means comprises two or more actuating devices which are arranged for application of opposite turning moments to a driving shaft 3 connected to the component-coupling means. To that end, the actuating means may comprise two hydraulic actuators (e.g. conventional piston and cylinder devices) which are arranged to apply opposite turning moments to a lever arm of the actuating means.

In a preferred arrangement, hydraulic actuators are arranged as slaves to master actuators which are themselves arranged to be actuated by means of vacuum powered servo assistors. The assistors may conveniently be connected to an engine manifold.

1 The torque-inducing means may comprise control means responsive to lateral accelerations of the vehicle body. In an arrangement as referred to in the last preceding paragraph, signals from the control means may be responsed to by initiating actuators (e.g. electromagnetic devices) which cause operation of the master actuators by way of the servo assistors.

There now follows a description, to be read with reference to the accompanying drawings, of an active anti-roll system which illustrates the invention by way of example.

In the accompanying drawings:- Figure 1 is a schematic plan view of a two-part anti-roll bar and operating elements; and Figure 2 shows the anti-roll bar as viewed in the direction of arrow 'W' in Figure 1, associated control elements being shown schematically.

4 An active (power-assisted) anti-roll system for a road vehicle comprises an anti-roll bar which is of a substantially conventional form (i.e. as known in passive systems) except that it is in two separate parts 10A and 10B, the bar being split and separated at its mid-point. The two parts 10A and 10B are coupled by means of operating elements 12 of the system whereby equal but opposite torque can be applied to the two parts in order to bias the anti-roll bar torsionally.

Torque can be applied to the two bar parts by means of similar bevel gears 14AMB which are secured to opposed separated ends of the parts, the two bevel 4 gears being coupled by a common driving gear 16; the driving gear is fixed on a driving shaft 18 which extends perpendicularly to a common rotational axis of the bevel gears and the anti-roll bar. The driving shaft 18 has secured to it an operating member 20 to which opposite moments can be applied (i.e. about the common axis of the driving shaft 18 and the driving gear 16) by means of two powered hydraulic cylinders 22A,22B acting on the operating member at equal distances from the axis. By means of the cylinders 22A,22B, therefore, torsional bias can be applied to the anti-roll bar 10 by way of the operating member 20, the driving shaft 18 and the gearing 16,14A,14B. The two hydraulic cylinders 22A,22B, acting on the operating member 20, are slave cylinders powered separately from master cylinders 24A,24B.

The system is under the control of an accelerometer unit 26. This unit can monitor lateral and vertical accelerations of a vehicle to which the system is fitted in use, and can also take into account vehicle speed and steering angles in order to predict conditions. A programmable microprocessor of the unit sends appropriate operating signals to two electromagnetic actuators 28A,28B which by way of vacuum powered servo assistors 30A,30B operate the master cylinders 24A,24B. The servo assistors are connected to the vehicle engine manifold 32.

As is conventional with an anti-roll bar, cranked end portions 34A,34B are coupled at their free ends to the vehicle suspension system unsprung mass M. A bearing housing 36 secured to the vehicle body supports the anti-roll bar parts 10A,10B, adjacent to their ends carrying the bevel gears 14A,14B, and also supports the driving shaft 18. The operating member 20 and the slave cylinders 22A,22B kting thereon are housed within the housing.

Features and benefits of the system will now be described. The system positively counters vehicle roll in cornering, utilising power assistance to add twist centrally to the anti-roll bar. This power assistance proportionally increases with the sharpness of the corner and velocity of the vehicle so as to maintain an upright bodyshell attitude to the road or even to bank the vehicle into the corner. This results in two benefits. First it maintains the bodyshell's designed aerodynamic downforce which increases tyre-to-surface pressure and therefore adhesion at all four wheels, a safety feature. Secondly, passenger travel comfort is enhanced as their G-force cornering weight is not so much pulled laterally and is more pushed down into their seats due to their relative angle.

The system also proportionately increases the stiffness of vehicle suspension relative to the sharpness of the corner and velocity of the vehicle. The suspension is also softened in straight-line travel and slow corners, allowing generally reduced damping. The benefit of this aspect is improved road holding around corners with undulating and uneven surfaces. This in turn allows for generally softer shock absorbers to be fitted for a more comfortable ride.

6 The system holds down the vehicle centre of gravity when cornering, and not only restricts the centre of gravity from moving towards the outside of a curve but will even put it into the curve, reducing the incidence of rollover on cornering at speed.

In straight line travelling or slow cornering the system is not activated, allowing greater anti-roll flexibility which in turn reduces the transmission of road shock from one wheel to another, minimising consequential vehicle body movement. This decreases the weight being lifted when the wheel travels over a burnp, potentially limiting it to a single suspension unit, reducing the loss of vehicle momentum. The vehicle thus benefits from improved fuel economy as a result of reduced vehicle body movement when travelling over undulating surfaces. An additional benefit is that vehicle body shock is particularly reduced in straight-line driving leading to a smoother ride and improving passenger comfort.

The system may be locked (to provide a passive anti-roll bar) or it may be disengaged to remove the anti-roll effect altogether. Off -road vehicles will be able to achieve maximum wheel-to-ground contact over diagonally ridged surfaces such as ditches thus ensuring optimum traction. For the purposes of total disengagement, an electromagnetic clutch may be fitted within the driving shaft 18.

The system does not require additional vee belts or hydraulic pumps to be driven by the flywheel, nor significant additional electrical load placed on the alternator or battery. Engine efficiency and fuel economy can therefore be maintained due to the low power requirements of the system.

7 In high G-force cornering, manifold vacuum will be reduced, since the system will be in heavy use, thus softening the vehicle's servo assisted braking strength in high G-force cornering. Since heavy braking whilst travelling at high speed around corners reduces tyre adhesion and is a 5 dangerous action, this effect is a positive benefit and a safety feature. Servo assistance is automatically at full strength for straight line braking and softened for fast cornering. Fuellair intake (and therefore engine power) will be reduced momentarily.

1 Most of the parts required for the systern are of kinds already present in most vehicles. Few additional components are necessary and their total mass insignificant in relation to the whole. With little extra weight to accelerate or brake, there is no perceptible loss of fuel efficiency.

As most constituent parts of the system already exist they have been developed to a point of high dependability. Being in accessible positions on the vehicle also leads to them being easy to remove and replace should any component failure ever occur. There is likely to be little servicing required, the only need being to check and top up the 20 hydraulic fluid level when necessary. There are no consurnables.

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Claims (12)

1. An anti-roll system for a wheeled land vehicle in which torsional coupling means is arranged to couple unsprung masses of suspension units positioned on opposite sides of the vehicle, whereby upon lateral acceleration of the vehicle body torsional stress may be induced in said coupling means, the coupling means comprising a first torsion bar component which extends from one of the unsprung masses, a second torsion bar component which extends from the other of the unsprung masses, component-coupling means coupling said two bar components, and means whereby equal and opposite torque can be induced into said components by way of said component-coupling means.

2. An anti-roll system according to claim 1, wherein the component-coupling means comprises a gear train connecting one component rotationally with the other, each component being mounted for rotation about a common torque axis in sympathy with heightwise movements of the unsprung suspension masses.

3. An anti-roll system according to claim 1 or 2, wherein the gear train comprises a driven gear secured to each torsion bar component and a driving gear coupled directed or indirectly with the two driven gears, the driving gear being coupled (or arranged to be coupled) to the torqueinducing means.

4. An anti-roll system according to claim 3, wherein the driving gear is arranged to be coupled to the torque-inducing means by way of an electromagnetic or other form of clutch.

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5. An anti-roll system according to any preceding claim, wherein the torque-inducing means comprises actuating means whereby the componentcoupling means can be powered to induce torque into the components in either rotational direction.

6. An anti-roll system according to claim 5, wherein the actuating means comprises two or more actuating devices which are arranged for application of opposite turning moments to a driving shaft connected to the component -coup ling means.

7. An anti-roll system according to claim 6, wherein the actuating means comprises two hydraulic actuators which are arranged to apply opposite turning moments to a lever arm of the actuating means.

8. An anti-roll system according to claim 7, wherein hydraulic actuators are arranged as slaves to master actuators which are themselves arranged to be actuated by means of vacuum powered servo assistors.

9. An anti-roll system according to claim 7, wherein the assistors are 20 connected to an engine manifold.

10. An anti-roll system according to any preceding claim, wherein the torque-inducing means comprise control means responsive to lateral accelerations of the vehicle body.

11. An anti-roll system according to claim 10, wherein the control means are arranged to deliver signals to initiating actuators which are in turn arranged to cause operation of the master actuators by way of the servo assistors.

12. An anti-roll system for a wheeled land vehicle in which torsional coupling means is arranged to couple unsprung masses of suspension units positioned on opposite sides of the vehicle, substantially as herein described with reference to any of the accompanying diagrammatic drawings.