DISC BRAKE WITH SLIDABLE BRAKE DISCS

Abstract: A slidable disc brake (10) comprises force applicator springs (44) controlling lateral sliding movement of brake discs (38, 40) and brake pad force applicator spring (71a and 71b) constraining the sliding brake pads (50, 54, 56) against tilting relative to the discs (38, 40) whereby residual brake torque in the brake-off condition is minimised.

Description: DISC BRAKE WITH SLIDABLE BRAKE DISCS This application is a continuation-in-part of PCT application, Application No. PCT/GB97/03388 filed 8 December, 1997, designating the United States and a continuation-in-part of PCT application, Application No. PCT/GB97/03386 filed 8 December 1997, designating the United States. PCT applications PCT/GB97/03388 and PCT/GB97/03386 are hereby incorporated herein by reference in their entirety. Background of the Invention This invention relates to a disc brake system and, more particularly, to a disc brake system for use on production vehicles . Currently, production vehicles such as automobiles often have spot -type disc brakes, having a fixed brake disc and a caliper configuration with an inboard piston and cylinder operated by hydraulic fluid. The caliper is bolted to a suspension member either forward or rearward with respect to a vertical plane through a wheel axle and includes a slidable bridge sliding on pins with an outer brake pad on the outboard end of the bridge. Operation of the brake pedal forces the piston outwardly to engage and to slide an inner brake pad along the bridge into frictional braking engagement with the inner side of the fixed disc, which is rigidly fixed to a hub on which the wheel is mounted. A reaction force on the slidable bridge causes it to slide on the pins and force the outer brake pad tightly against the outer side of the fixed brake disc. Deceleration of the clamped disc and its associated hub and its attached wheel thereby decelerates the vehicle. As the piston is forced to slide to engage the brake pads with the fixed disc, an internal 0 ring seal between the cylinder and the piston is compressed, and energy is stored therein which is released, when the braking fluid pressure is relieved, to slide the piston in the reverse direction to its off brake position in the cylinder. This conventional disc brake hereinafter called a "conventional, fixed disc brake" because its brake disc is fixed to the wheel hub. In contrast thereto, there is disclosed in the patent literature, such as United States Patents 4,844,206 and 4,576,255; U.K. patent application 2 184 801; and South African published application 70/5340, a pair of slidable brake discs that slide axially along a wheel hub and utilize a fixed bridge with a fixed brake pad at a distal end of the bridge; and a hydraulic piston that slides the brake discs and slidable brake pads outwardly to bring an outer side of the outer brake disc into braking engagement with the distal, fixed brake pad. The fixed disc brake system is widely used, particularly to brake the front wheels while the slidable brake disc system is not currently in use on production vehicles. Tn order to be used on vehicles, any brake system must meet a long list of demanding specifications, some of which are explained herein. ' Until now, slidable brake disc systems appear to be unable to meet the rigorous, demanding criteria to the satisfaction of automobile manufacturers or suppliers. Vehicle manufacturers and brake suppliers undertake the risk of product liability lawsuits or product recalls and, therefore, are reluctant to adopt a new braking system unless it has superior qualities such as improved cost, weight, efficiency, longevity or other qualities relative to the standard fixed disc brake. The current fixed brake disc systems used on vehicles are quite heavy and a reduction in weight is a desirable goal for the slidable disc brake system. In the fixed brake, the sliding bridge is quite large and heavy as are the bolts to bolt the caliper unit to the suspension member and heavy slide pins are used to support the slidable bridge. The typical brake disc itself is also quite heavy with its bell or hat shape and with its annular rim for engaging the brake pad. Weight of the fixed brake disc system is detrimental not only to fuel efficiency but also to steering. That is, the brakes represent an unsprung mass on the wheel that must be turned and steered and that also must be supported to withstand high loads including the brake torque and loads due to a wheel going up and down as it travels over uneven road surfaces. The overall size of the fixed, disc brake and its location on the vehicle suspension requires a large space envelope that limits the locking angle and vehicle turning circle, particularly for some types of wheel suspensions. In addition to size, cost and weight, there are the criteria of efficiency, proficiency and longevity. Brake wear is a longevity problem and a longer brake pad life and brake disc life are desired by vehicle manufacturers which are increasingly providing long term service warranties for their vehicles, as well as for the vehicle owner who ultimately pays for brake replacement in one manner or the other. The brake disc life can be adversely affected by a localized, rubbing contact between the brake pads and the brake pad, particularly at the brake-off position of the braking system. If the brake disc is tilted from a true, vertical plane normal to a horizontal axis through the hub, an increased localized rubbing contact of brake pads on the disc results and is a source of disc thickness variation (DTV) , i.e., a different thickness in cross-section of the fixed brake disc at different radial locations from the disc axis. Significant DTV results in vibrations that the driver feels and requires costly brake maintenance to eliminate the vibration problem. Some fixed disc brake systems have noise problems which are cured to a certain extent by the addition of noise suppressors, which add to the size, SUBSTITUTE SHEET RULE 26) weight and cost of the system. Brake systems must be free of rattles and should be free of noise. The current bell or hat shape of the conventional fixed brakes can be noisy because an impact on the disc causes a noise resonance and loud sound due to its bell shape and fixed attachment to the hub. Therefore, it is desirable to eliminate such a noisy shape and fixed mounting of the brake disc to the hub. In addition to above, there also may occur a "feel" problem where the driver experiences a long or deep pedal depression when operating the brakes. Sometimes the deep pedal is the result of "knock back" of the actuator piston in the cylinder in the piston return direction that displaces hydraulic liquid and shifts the piston deeper in the cylinder. A cornering or bumps in the road may deflect the suspension or slidable brake caliper and knock back the piston and cause the vehicle operator to experience a deep pedal braking operation. Another potential source of "knock back" in the conventional sliding bridge, fixed brake disc system is the result of an initial large deflection of the outer distal end of the slidable bridge at heavy braking loads where the bridge distal end is often deflected 0.006 inch or more. The sliding bridges are already quite heavy and massive to withstand the braking torque and to provide the stiffness for the distal end of the bridge. When the brake pressure is released, the distal bridge end rebounds and can cause knock back of the piston in the cylinder . Among the demanding temperature tests that vehicle brakes are subjected to is the Auto Motive Sport (AMS) fade test in which the brake temperature is monitored during ten braking stops as fast as possible over a very short time interval. In brief, the AMS vehicle test involves the driver flooring the gas pedal to accelerate vehicle extremely fast to 100 Kph. and then braking as hard as the driver can to stop the vehicle as quickly as it can be braked to a stop. This is quickly iterated for a total of ten rapid accelerations and decelerations with the temperatures of the brake disc being measured over the course of the ten cycles. It is desired to keep the maximum temperature of the brake disc below its "Judder" effect temperature at which severe disc geometry and metallurgical changes occur and deteriorate the brake disc. The Judder effect temperature is usually in the range of 650° to 700°C; and this AMS test is difficult to pass. In that AMS test of a lightweight automobile having the fixed brake system (against which the slidable disc brake system of this invention is compared) , the brake disc temperature exceeded 650°C. and the temperature drop between braking operations was only about 30°C. The test data described herein is from two identical, production model automobiles of B Class front wheel drive. They have a kerb weight of about 1000 Kgs. and a gross vehicle weight of about 1350 Kgs. Manifestly, the test data for different vehicles may vary substantially from that described herein, which data is given for the purposes of illustration of one embodiment of the invention and is to be construed as a limitation for the invention as defined by the claims attached hereto. Brake disc temperature also can be monitored to provide an indication of "off-brake" residual torque of the braking system. Even though the vehicle operator is not operating the braking pedal and is steering the vehicle along a straight line path, the brake pads are rubbing against the fixed brake and causing the temperature thereof to rise substantially above ambient. The cornering of a vehicle and sharp turning may also shift the slidable brake caliper into rubbing contact with the fixed brake disc. In a current production vehicle of lightweight and having a fixed brake system, the disc temperature was measured at least 35°C. above ambient when the ambient temperature is between 10° to 20°C. This is a good indication that current fixed brake systems have considerable residual torque at the off- brake condition, and concomitant wear and fuel energy waste. It will be recognized that the bell or hat shape of fixed brake disc has non-uniform cross-sectional thickness at the corners and has different fillets that can result in non-uniform expansion thereby causing an increase in the space envelope of the outer rim of the brake disc and resultant rubbing, thereby producing a high off -brake, residual torque. In order to test conventional brakes when used in mountainous terrain having descending, steep grades with much cornering of the vehicle, a conventional disc brake was tested over thirty descents of a steep mountain with each descent lasting about twenty-four minutes. These fixed brakes discs on a lightweight, production car experienced temperature of over 600°C. after about 13 minutes of descent; and they reached a maximum temperature of almost 680°C. at the end of the run. Hence, there is a need for a disc brake system that runs cooler in such a test so that it does not potentially cause a Judder effect deterioration of the brake disc in mountainous usage. These fixed disc brakes had high brake fluid temperatures and poor standing soaking curves after trans-mountain runs. It will be appreciated that in sliding brake disc system that brake disc must slide axially on the hub between an off-brake position, where the residual torque should be low and a braking position where the torque is high, and then return to the off-brake position to reduce the residual torque. The sliding connection between the brake disc and hub must be free to move despite being subjected to corrosive conditions and over a long period of use. The slidable brake disc must not be noisy or squeal under low and high temperature conditions, and it must not wobble or generate dust or produce vibrations that the driver can feel or hear. In the patent literature, such as U.K. patent application 2 184 801 and U.S. Patent 4,576,255, the slidable brake disc systems had spline grooves oversized relative to the size of the disc teeth inserted into the grooves and spring devices where mounted on the hub to push the discs to rotate a driving side, flank of each tooth into mating engagement with a flank of the oversized spline groove. The oversized notches were used to prevent the previously heated and now cooled disc from jamming in the splines To eliminate "knock back" and chattering, springs were inserted into the spline notches to bias the spline flanks on the disc and hub into engagement with one another. Such designs do not provide a good drive connection between the discs and the splined hub, are costly and apparently allow the discs to wobble relative to the hub at high braking loads. From the foregoing, it will be seen that there is a need for a better, slidable disc mounting system that is more efficient and that does not generate noise or squeal as the brake discs expand at high temperatures and that does not wobble at high braking loads. Also, there is a need for a twin disc braking system that operates at low residual torque m an off-brake condition to reduce DTV and energy loss.' In the embodiments of the present invention the disc brake incorporates resilient means both in relation to the mounting of the brake discs on their mounting hub and in relation to the brake friction elements or pads in relation to their fixed mounting or caliper. The resilient means are of a structure and strength chosen to be capable of, both in the case of the brake discs and in the case of the brake friction elements, maintaining these components of the brake assembly in their required working attitudes with respect to the structures on which they are mounted. In other words, the springs or resilient means for the brake discs are constructed so as to hold the brake discs in non-tilted working attitudes as they rotate. Likewise, the resilient means for the friction elements or pads maintain these latter structures in their required attitudes with respect to their fixed mounting or caliper. In both cases, the resilient nature of the resilient means permits, under the dynamic conditions arising during use of the vehicle and due to engine vibration and vehicle motion/road surface induced vibration and similar factors, a degree of movement from the defined working position (as opposed to the linear axial sliding movement needed to effect friction element- to-disc engagement and disengagement when commencing and terminating braking) which is needed under normal conditions of vehicle use. In this regard, it is to be noted that the resilient means or springs used in the embodiments in relation to the friction elements for maintaining same in their normal untilted attitudes, differ significantly from the springs disclosed in WO 98/25804 (docket 2561) and WO 98/26192 (docket 2558) in which the pad springs are mere anti -rattle springs not adapted to hold the brake pads against tilting movement, but merely to avoid rattling. Moreover, in the embodiments of the present invention the springs for the discs and for the pads are balanced in terms of their relative loading applied to the discs and the pads in order to achieve the necessary separation of same when braking is discontinued and yet holding the pads and discs against tilting during use. Thus, the spring forces exerted on the pads or friction elements of the present invention are much stronger than those needed merely to prevent rattling or noise suppression. The spring forces are sufficient to restrain the slidable brake pads or friction elements from moving into contact with the brake discs in an uncontrolled manner. The use of the substantially stronger pad springs in the present embodiments assists in positioning the outer rims of the brake discs in their brake-off position for reducing residual brake torque. We have discovered that, contrary to the teaching in the above- identified WO specifications in which it is suggested that anti-tilt- mounted discs are sufficient in themselves so far as disc/pad alignment is concerned, and all that is required for the pads is the provision of anti- rattle springs, further provision is desirable to reduce residual brake torque. We have now established that a significant reduction in residual torque can be achieved by the adoption of anti-tilt spring means for the friction elements. This feature preferably comprises the combination of resilient means in co-operation with face-to-face complementary attitude-defining surfaces on the friction elements and their guide means, and the arrangement being such that there is a co-operative effect with the anti-tilt mounted brake disc or discs such that the effect of dynamic factors arising during use including engine-and road- induced vibrations leading to micro-scale interactions of the discs and friction elements after brake application produces a relatively well-defined backing-off of the pairs of axially-moveable structures (discs and friction elements) leading to well-defined clearance positions allowing relatively low level residual torque in which the haphazard torque-producing interactions characteristic of the relatively less well-defined friction element positions of the arrangement in the above-identified WO specifications are minimised or avoided. In accordance with the present invention there is provided a new and improved slidable disc brake system particularly adapted for use on production vehicles. This is achieved by the use of a unique mounting and control of the positions of the slidable brake discs and brake pads that results in low frictional face pad wear. and a low, off -brake, residual torque and a good drive connection between the hub and the slidable brake disc. The preferred construction uses force applicators such as leaf springs located between the hub and the brake discs to float the brake discs for axial sliding movement and to hold them against wobbling on the hub while allowing the brake discs to have light, random contact with the brake pads. The rotating brake discs will shift slightly in the axial direction on the hub from their brakes-on position to establish a brakes-off position. These rotating, floating discs also exert axially directed forces on the brake pads to slide them axially to their off-brake positions along the stationary bridge. The brake pads are constrained by force applicators such as leaf springs to keep their pad faces parallel to the brake discs and not to allow the brake pad faces to tilt into a corner engagement with the brake disc as would cause localized rubbing contact, thereby generating disc thickness variation in the brake discs and resultant vibration of the discs. That is, the spring holds the brake pad against tilting movements and axial sliding movements on the supporting bridge by vibration and inertia forces caused by operation of the vehicle. If allowed to tilt on the bridge, the pad faces experience a localized rubbing contact which increases the residual drag torque, pad wear and DTV at the off- brake position. The brake pads are preferably constrained by leaf springs to float on the bridge and the brake discs are constrained by leaf springs between the discs and hub to float on the hub so that the contact between the brake pads and discs is a light, random contact thereby resulting in reduced residual drag torque and disc thickness variation. Preferably, the respective leaf spring forces applied to brake pads and the brake discs are balanced relative to one another so that the system can move from its braking condition to its off-brake position by action of separation forces between the discs and the braking pads; and yet, the brake pads are held in the off -brake position against tilting under vibration and vehicle caused inertial forces and thereby causing a localized rubbing and DTV. More specifically, in the case of a two-brake disc system, when shifting from the brakes on- condition tc brakes off -condition, the outer brake disc slides axially on the hub to separate itself from the stationary, distal brake pad fixed to the bridge; and the central slidable brake pad between the first disc and the second disc slides axially along the bridge away from the first disc to separate its outer pad face from the facing side of the first disc. The second, inner brake disc slides axially along the hub toward the piston and cylinder assembly to separate itself from the inner pad face on the central brake pad. The inner slidable brake pad at the piston slides axially inward toward the piston and cylinder assembly to separate its outer friction face from a facing side of the second brake disc. The respective leaf springs on the bridge and on the hub are balanced to allow this separation and yet hold the brake pads and brake discs from tilting, as would cause DTV or from unwanted axial sliding engagement as would cause a high residual drag torque, under the vibration and vehicle inertial forces being experienced by an unsprung brake system. The floating twin disc, slidable brake discs and floating brake pads of the present invention provide a brake system that passed the AMS fade test with temperatures significantly lower than the conventional disc brake tested which did not pass this test. These twin disc brakes had a maximum temperature of about 120°C lower than the maximum temperature for the fixed brake which was in the Judder range. Also, the cooling of the twin disc brakes was about 80°C between stops relative to a cooling of about only 30°C between stops for the standard fixed brake. Also, very significant results were found in the temperature of the fixed brake disc and the slidable brake discs as the respective brake discs cooled after braking at 100 mph with the fixed brake temperature above ambient being at 3.5 times higher than slidable brake temperature above ambient. This shows that the twin disc, slidable brake has significantly lower drag torque. An objective of the invention is to reduce the drag torque to about 1 newton meter as compared with a tested 6.0 newton meter as compared to a conventional disc brake tested. Thus, the slidable, twin disc brake system of this invention was found to have improved operating characteristics relative to operating temperatures when compared to a standard, fixed disc brake system. In the preferred embodiment of the invention described herein, a significant size and weight reduction are achieved relative with the twin slidable brake system of this invention relative to a conventional fixed disc brake system with its large sliding caliper. More specifically, an unsprung, weight reduction in excess of 2 Kgs . was achieved for each front wheel . This is a very significant weight reduction and has implications for fuel savings, suspension design, vacuum assists, steerability, etc. This weight saving of 2 Kgs. is relative to a lighter, solid, fixed brake disc; and relative to a heavier, ventilated fixed brake disc, the average saving may be as much as 3.6 Kgs . per front wheel. This is an unsprung weight reduction which is desired by production vehicle manufacturers. In accordance with an important aspect of the invention, the brake cylinder is integrally formed in the suspension casting or knuckle above the axle on the vertical centerline. This integral suspension casting reduces the number of parts for the suspension and provides a more compact, and lighter weight system. The floating brake disc system does not knock back the piston during cornering or other dynamic movements as easily as the large sliding caliper standard disc brake. Also, the fixed bridge need not be large and heavy as the sliding caliper bridge which, even though large and heavy, deflects significantly under heavy braking loads by 0.006 inch, for example. These large sliding caliper disc brakes are usually mounted at about 3:00 o'clock or 9:00 o'clock positions rather than a preferred 12:00 o'clock position for the twin slidable disc brake of this invention. Also, the mounting of the bridge above the axle at the vertical centerline position allows an increase in steering angles and vehicle turning circle . The unit cost reduction for the embodiment of the invention illustrated herein relative to a current fixed brake system for the same vehicle is estimated to be substantial and may approach 35% for the same vehicle. The slidable twin disc brake of this invention is designed to pursue the goals of substantial reduction in cost, weight, space envelope; increased longevity of brake pads; and better efficiency in manufacture, assembly and performance. When the slidable disc brake is used with two slidable brake discs and four brake pads, such as on the front wheels of a production vehicle, the braking pressure needed may be about 50% of the braking pressure used today with the conventional systems using a fixed disc and two braking pads . Higher braking pressures applied to the brake disc usually can result in higher disc temperatures. The requirement for high brake pressures has resulted in the large-scale use of braking assists, such as vacuum assists and, in large commercial diesel trucks, the use of vacuum pumps to supply the vacuum for the brake assist system. The vacuum assists add weight and cost to the vehicle. The reduced braking pressure of this invention allows elimination of a vacuum assist system, in some instances, or the use of a smaller assist to generate the reduced brake pressure used in the slidable disc brake. Brief Description of the Drawings FIG. 1 is a perspective view of a slidable, twin disc brake assembly constructed in accordance with a preferred embodiment of the invention; FIG. 2 is a diagrammatic view of an outer spring constraining the brake pads and an inner spring constraining the brake discs; FIG. 3 is a plan view showing the spring constraining the brake pads; FIG. 3A is a cross-sectional view showing the spring applying restraining forces to the tops of the brake pad carriers; FIG. 4 is a diagrammatic view of three leaf spring constraining a brake disc on a hub; FIG. 5 is an exploded view of the illustrative assembly; FIG. 6 is a side elevational view of the illustrative assembly; FIG. 7 is similar to FIG. 6 but shows the illustrative assembly in vertical cross section; FIG. 8 shows temperature decay curves for disc brakes due to residual drag torque with the brakes off; FIG. 9 shows curves for an AMS fade test of a standard fixed brake; FIG. 10 shows the curves for an AMS fade test of a twin disc brake; FIG. 11 is a vertical cross-sectional view taken through a suspension link of the illustrative assembly; FIG. 12 is a view similar to FIG. 16, but of a modification of the illustrative assembly; FIG. 13 is a perspective view of an alternative leaf spring having raised ribs thereon; FIG. 14 is a diagrammatic, enlarged view of the points of contact between the leaf springs and the brake disc; FIG. 15 is an enlarged, fragmentary and exploded view of the driving connection between a hub and slidable brake disc; FIG. 15A is similar to FIG. 15 except that the driving connection is enlarged and meshed to drive the brake disc with rotation of the hub; FIG. 16 is a -/iew taken in the direction of the arrow XVI in FIG. 6 ; FIG. 17 is a view taken in the direction of the arrow XVII in FIG. 7; and FIG. 18 is a fragmentary view of a sealing ring engaging a piston in a hydraulic cylinder. Detailed Description of the Preferred Embodiment As shown in the drawings for purposes of illustration, the invention is embodied in a slidable disc brake assembly 10 which can have either one slidable braking disc 38 or two or more slidable braking discs such as a pair of brake discs 38 and 40 (FIGS. 1 and 2) illustrated herein for. a front wheel drive car. In a front wheel drive automobile suspension and wheel assembly, as illustrated and described herein, the weight of the vehicle is concentrated at the front of the vehicle and more brake torque is applied to the front wheels than is applied to the rear wheels. It is contemplated that the rear wheel brake assembly will have only the single slidable disc; and a single pair of brake pads 50 and 60 , while the front wheel brake assembly will have the second slidable disc 40 and additional brake pads 54 and 56 on a slidable, intermediate pad carrier 58. The present invention is directed to and claims a slidable disc brake system that can have one, two or more slidable discs and that can be used in other applications than automobiles. Conventional disc brakes or production vehicles have a single, fixed brake disc (not illustrated) and a single pair of brake disc pads and this requires considerable pressure, such as 70 BAR, to be applied between the pads and the fixed disc to generate the required braking torque. This higher pressure requirement has resulted in the use of braking assists, such as a vacuum assist or a vacuum pump, to generate sufficient braking force. Th s adds cost and weight to the vehicle and necessitates higher pressure in the brake conduits and stronger and more expensive brake fluid lines to handle the high pressure. The use of the second slidable disc and a second pair of brake pads with a doubling of the engaged brake surfaces provides a braking assembly that works at 50% of the conventional pressure, e.g., 35 BAR. Higher pressure causes more wear and higher temperatures, and it is desirable to reduce pressures for these reasons alone. ' Thus, the second slidable disc enables the braking torque to be shared among four (4) engaged, friction surfaces instead of the conventional two- -thereby reducing pressure, heat generation and wear. As disclosed in the patent literature, there is a problem of rattling and noise generation encountered between the slidable brake discs and the supporting hub on which they slide. As described above, the discs may be heated to 300°C. to 600°C. when being subjected to extreme braking conditions such as cornering and braking down a mountain or when being subjected to the fast and repetitive braking and/or cornering as in the AMS test . These prior slidable twin disc systems were equipped with various spring devices mounted on the hub to push the discs to rotate and to abut a driving side flank of a disc spline tooth against an adjacent, mating flank random nature, thereby resulting in a lower residual, off -brake torque and reduction of DTV. That is, a gentle random touching of the brake pads and brake disc may occur when driving straight ahead with the pads and disc being held in non-tilting positions relative to one another. The inner, radially directed, force applicator is positioned between the slidable disc, and the hub to provide friction forces to the hub and to the disc which holds them against sliding relative to one another and against generating a noise or a high squeal when the brake disc is heated and expanded. That is, when the brake disc was cold, no squeal or noise was generated at the spline interconnection. But, when the disc was heated and expanded, disc spline members or teeth 42 (FIG. 5) were loose and slid in hub splines 20 and generated high pitched squealing noises. As will be explained in greater detail, the preferred radial, inner force applicator 44 comprises springs, preferably flat leaf springs 44a, that are laid tangentially of the hub at their centers 44b (FIGS. 4 and 5) and with their outer ends 44c biased into contact with inner hub surfaces at spaced points, as illustrated in exaggerated form in FIG. 4. More spaced points of contact can be provided by providing raised ribs 44d on the leaf springs 44x, as illustrated in FIGS. 13 and 14. The slidable brake disc 38 is thus supported in a floating manner on points of contact 44c (FIG. 4) with the leaf springs 44a on the hub in a floating manner and the brake disc can be shifted axially with forces applied thereto to overcome the frictional forces being applied by the springs at inner disc hub surface. When the brake disc expands considerably due to a disc high temperature, the disc teeth become loose in the colder spline hubs and the frictional forces between the leaf springs 44a and the brake disc and hub restrain the disc from shifting relative to the hub and a resultant squealing noise. The driving slide flanks of a hub spline groove. The spline grooves in the hub were oversized relative to the size of disc teeth to prevent binding of the spline teeth in the spline grooves, and these oversized grooves allowed the discs to wobble at high braking pressures, as described in the aforesaid patent literature. When the braking pressure is released, the South African patent describes the use of release springs to push the brake disc axially along the hub. Axial directed spring pressures on the brake discs will increase the frictional off-brake, residual torque and should be avoided for this reason. It is a considerable problem to stabilize the slidable brake disc and yet allow the brake disc to slide freely at temperature extremes where the brake and the ambient temperatures are very low or very high after a considerable expansion of the disc particularly at its slidable driving connection to the colder hub. Also, the twin disc brake should have a lower off-brake, residual torque than that of the conventional fixed disc brake. Also, as explained above, for successful adoption by the automotive industry, the slidable twin disc brakes should meet the goals of a substantial reduction in cost, weight, space envelope; increased longevity of brake pads, and efficiency in manufacture, assembly and performance. In accordance with the present invention, there is provided a slidable disc brake assembly having one or more brake discs 38, 40 which are mounted on a hub 14 of a suspension for a vehicle with the braking disc being constrained i.e., positioned on the hub 14, along its inner radial portion by a resilient radially directed force applicator 44 acting between the hub 14 and the brake disc and by an outer force applicator assembly 45 which is positioned at the outer rim of the disc. This construction provides a rotational geometry for the disc to have contact between the disc and the brake pads in a leaf springs 44a impart radially directed forces to the inner hub portion of the brake disc to keep it generally in a plane normal to its rotational axis through the center of the hub. This inner radial positioning by the springs 44a assists in keeping the disc 38 concentric with the rotational axis and within a relatively tight space envelope at the brakes off condition thereby reducing rubbing contact between the brake pad's frictional surfaces and the brake discs 38, 40 and a resultant disc thickness variation (DTV) . . DTV which is a major source of vibration. In accordance with an important aspect of the invention, slidable brake discs 38 and 40 float on the hub 14 and its outer rim portion is constrained to its off-brake position, and each disc seeks or floats to an off-brake position established by engagement with slidable brake pads 50, 54 and 56, which slide on the guide surfaces 68 of the bridge-shaped guide member 64. As best seen in FIGS. 2, 3 and 3A, a brake pad, force applicator 71 is positioned to apply radially directed loads to the slidable brake pads to constrain them from sliding with predetermined spring forces. The spring forces are much stronger than that needed merely to prevent rattling or noise suppression. The spring forces are sufficient to restrain the slidable brake pads from moving into contact with the brake discs in an uncontrolled manner. It has been found that if only a light spring force is supplied to suppress noise, that the noise will be abated; but that the brake pads are free to shift and rub against the brake discs causing wear and DTV. Also, when using very light springs, the brake pads will not assist in positioning the outer rims of the slidable brake discs to reduce off-brake residual torque. The illustrated force applicator 71 comprises a pair of leaf springs 71a and 71b (FIGS. 2 and 5) which form the dual functions of preventing rattle and positioning of the pads and discs relative to each other. After the brake has been applied and released, the rotating brake disc 38 initially rubs against the brake pads and forces from this rubbing cause the disc pads 50 and 56 to slide in opposite directions from the rotating disc. The amount of shifting is controlled by the brake force applicator's frictional force being overcome. Conversely, the off -brake, residual torque position of the rotating brake disc 38 is being constrained by the forced-apart brake pads, which are being held against further sliding by the force applicators. The force applicator springs 44 also are controlling any lateral sliding of the brake disc 38 along the hub. The brake disc 38 is being constrained in its off-load position by the outer force applicators acting on opposite sides of the pair of discs and the inner springs 44 acting on the inner hub portion of the discs. Thus, the disc is controlled to be free to slide and float but not to topple into the brake pads and the brake pads have controlled sliding but are not free to topple or to be free to vibrate into or bang against the discs . The twin disc brake assembly 10 of the present invention, because of its floating geometry as described above, has a significantly lower drag torque, i.e., off- brake residual torque, as will be explained in connection with FIG. 8 which illustrates a typical result for the disc temperature curves from 100 Kph. for a slidable, twin disc brake versus a conventional, fixed disc brake. The conventional fixed brake curves 13A plateaus at best is 35°C above ambient while the slidable, twin disc brake 10 continues to cool and stabilizes at 10° above ambient, as illustrated by the straight line 13B. Usually, the conventional brake was found to be about 50°-70°C above ambient. The assumption made with respect to this test is that dynamic drag due to disc face contact with the pad is proportional to temperature at the disc. The present invention is designed to preferably produce a low residual torque, e.g., about 1 newton meter or less in contrast to about 6 newton meter for the fixed disc brake on the vehicle being tested herein. In accordance with the invention, the brake discs 38 and 40 must be flat and planar in their rotational plane and substantially normal to the rotational axis 9 (FIG. 2) . The brake disc pads have outer planar surfaces 50a, 54a; 56a and 60a which are held by the springs 71a and 71b to be parallel to the disc annular braking surfaces 38a and 40a at the outer rim portion of the brake discs 38 and 40. When the disc geometry is slightly curved, i.e., not a flat planar surface, it has been found that localized rubbing and wear occurred, as illustrated in FIG 2 , at a lower corner 50b of the cylinder brake pads 50 and at the upper outer corner 54b of the opposed brake pad 54 on the slidable pad carrier 58. FIG. 2 shows a very exaggerated tilted disc 38 in lines to illustrate the point being made. The non-flat brake disc did not have random contact with the brake discs 38 and 40; but had localized rubbing contact due to the disc curvature at the inner and outer corners 50b and 54b during each or almost each revolution of the brake disc. Severe disc thickness variations resulted and vibrations of the brake occurred. When the non-flat discs were replaced with flat brake discs the random engagement of the pads and discs was again achieved, the DTV and vibrations associated with the DTV were eliminated. If a localized spot carries the load, you get wear and a pumping action at wheel frequency. While not illustrated herein, it was found that if the slidable brake pad surfaces 50a, 54a, and 56a (FIG. 2) were not held in parallel relationship to the brake disc faces 38a and 40a, but were freely mounted or loosely mounted on the bridge, that the brake pads could tilt or cock and cause DTV and resultant vibration, as described above for a non-flat brake disc. Stated differently, the springs 71a and 71b were strong enough to hold the brake pads against a tilting that would shift their planar pad surfaces 50a, 54a and 56a from planes perpendicular to the rotational axis 9 and would bring a corner thereof into continual, localized rubbing contact with a brake disc in the off -brake position. Thus, the floating geometry for the brake discs and constraint of the brake pads and discs to achieve random contact at the off-brake position is an important aspect of the invention . AMS fade tests were run to compare the performance of a slidable, twin disc brake assembly 10 versus the standard factory equipped fixed brake disc, and the results are shown in FIGS. 9 and 10. As seen in FIG. 9, there are ten peaks on the graph for each of the ten braking stops with the brakes cooling and showing a temperature drop of about 30°C and a maximum disc temperature of about 700°C which is the Judder range. In contrast, the twin slidable brake disc system had a maximum temperature of 580 °C (FIG. 10) or about 120°C lower than the conventional disc brake. The temperature drop between braking events was about 80° compared to only a 30 °C temperature drop for conventional disc brake. Thus, the present invention passed the AMS fade test where the conventional brake being tested did not pass the AMS test. In accordance with the present invention, the preferred drive connection 19 has the brake disc teeth 42 sized to fit the grooves 20 along both of the groove flanks 21 without using oversized grooves. This is in contrast to the prior art which used oversized spline grooves and small springs therein to engage the driving side flanks of the hub and disc; but this prior art solution led to other problems like disc wobble on the hub. Preferably, the driving connection of the present invention is a very efficient one such as that akin to a pair of meshed gears where the contact is a line of contact across the engaged flanks 21 (FIG. 15A) rather than a small point of contact to provide lower unit pressures. Preferably, this line of contact is maintained whether the brake disc has a high or low temperature. The plastic deformation at the engaged spline surfaces keeps the engaged spline members clean from corrosion. The present invention eliminates the brinneling, dust generation, and squirming of the disc at high braking torque . The hub 14 is an integral casting and, as is conventional, has a hollow cylindrical rearward projection 14a which has a splined interior, and an exterior, which provides a mounting for roller bearings 16 (FIG. 7) . A splined projection of a constant velocity joint (not shown) at the end of a drive shaft is received within the projection so that the hub can be rotated on the bearings 16 by the drive shaft. The hub also has an annular disc-like portion 14b from which the portion projects rearwardly. The hub provides a mounting for the wheel (not shown) which is bolted against a forward surface of the portion by bolts received in holes 14d. The hub also has a hollow cylindrical rearward projection 14c of greater diameter than the portion. The portion projects from the outer edge of the portion 14b. The portion 14c has an outer surface provided with grooves 20 running parallel to the axis 22 about which the hub rotates. The grooves 20 are arranged in four equally circumferentially-spaced locations . The suspension link 12 (FIG. 11) is an integral casting and comprises a hollow cylindrical portion 12a of conventional form, which provides a mounting for the bearings 16 so that the hub 14 rotates on the link. The link also comprises top 24 and bottom 26 mountings for supports of the link. The top mounting is provided by a portion 12b of the link which projects rearwardly from a portion 12c which projects upwardly from the portion 12a. The portion 12b is of conventional form and forms two semi-cylindrical arms (FIG. 5) which together form a clamp which can be tightened by a bolt (not shown) which extends through bores 28 in the arms and across a gap between them. A McPherson strut (not shown) can be clamped between the arms of the portion 12b so that the link can pivot about the longitudinal axis of the strut. The bottom mounting 26 is provided by a portion 12d of the link 12, which projects downwardly from the portion 12a thereof. This portion 12d is of conventional form and has a vertical bore 30, to receive a pin cf a ball joint (not shown) , and two horizontal bores 32 in which bolts (not shown) can be received to connect the link to a tie bar (not shown) . The link 12 also comprises an arm 34 for connection to a track rod (not shown) of a steering system of the vehicle. This arm 34 is of conventional form and is provided by a portion 12e of the link 12, which projects sideways from the portion 12a thereof. The arm 34 comprises a vertical bore 36 through which the arm can be pivotally connected to the track rod. In order to steer the vehicle, the track rod is moved to cause the link to pivot on the joint 18 and the mountings 24 and 26. The illustrative assembly 10 also comprises the two brake discs 38 and 40, which are mounted for rotation with the hub 14. The two discs are identical to one another and are mounted for limited movement on the hub 14 in a direction generally parallel to the axis 22 about which the hub rotates. Specifically, each disc is in the form of a flat annular plate and has inwardly-projecting teeth 42. As best seen in FIGS. 5, 15 and 15A, it is preferred that the brake discs 38 and 40 each have a limited number of wide teeth, i.e., the illustrated four teeth 42 that mesh with the spline grooves 20a of splines 20 on the hub. The spline grooves 20a are four in number, in this instance, and have flanking walls 21 (FIG. 15) that match flanking walls 42a on brake disc teeth 42. The engaged flanks 21 and 42a have an angle A for their respective tooth flange angles. Manifestly, the number of teeth and splines may be varied. Because of large stresses generated on the thin teeth 42 on these relatively thin brake discs, there is a tendency of stress cracks to form, particularly after high temperature heating and cooling cycles and high stress cycles. To relieve such stress, there are provided large, curved, stress relief fillets or cuc-outs 42b in the respective brake discs. Herein, as shown in FIGS. 15 and 15A, the stress relieving fillets are provided on each side of a tooth 42 and provide generally semi- cylindrical, cross-sectional openings on each side of each tooth, when the teeth are fitted into a spline grooves, as shown in FIG. 15A. As best seen in FIG. 5, the four grooves 20 on the hub are relatively small compared to the projecting teeth 20b defined between each pair of adjacent grooves 20. These teeth 20b on the hub have large, arcuate surfaces 20c against which are laid the leaf springs 44. Thus, each leaf spring 44 has a large circumferential area contact with inner, arcuate surfaces 42c of the brake disc in the place between depending teeth 42 thereon . Four leaf springs 44 are mounted on the hub 14 to provide resilient force applying means to apply radial forces between the hub and the discs 38 and 40. These radial forces prevent the discs from tilting on the hub, prevent rattling and control sliding of the discs along the hub. The resilience of the springs allows thermal expansion to be accommodated, as explained above. The springs are secured in a suitable manner, such as by screws 46 to the outer surface 20c of the hub portion 14c in the gaps between the spline grooves 20a. Each of the four springs engages both of the discs 38 and 40 in the areas between the teeth 42, giving a resilient four-point mounting for each disc. The discs can slide on the hub parallel to the axis 22 with the teeth sliding in the spline grooves 20a. As best seen in FIG. 4, the flat leaf spring 44 is engaged with and has a pressure line of contact with the hub at point 44b; and the outer ends of the spring 44c have been flexed downwardly to provide pressure line of contact engagement with the discs 38 and 40 at these bent spring ends . Only three springs 44 are shown in the diagrammatic illustration of FIG. 4 to illustrate the flexing of the springs 44; while in the embodiment of the invention described and illustrated in FIG. 5, four springs are used. In order to provide more lines of engagement between the disc and the hub, the spring 44x may be provided with ribs 44d therein, as shown in FIGS. 13 and 14. Also, it is preferred to separate the spring 44 into separate biasing portions 44h and 44i (FIG. 13) separated by a slot 44 j each portion ■ acting on an associated disc 38 or 40 to provide more individualized, independent pressure forces between the associated disc and the hub. The springs 44 are balanced in the force they apply to the brake discs 38 and 40 relative to the force which the springs 71a and 71b apply to the slidable brake pad carriers 52 and 58. Both the brake discs and the brake carriers are constrained against shifting along the hub and the bridge respectively, due to vibrations and inertial forces from the vehicle when it is traveling. Thus, it will be seen that the springs 44 allow the slidable brake discs to: float on the hub, hold the discs in a radial plane normal to the rotational axis, apply frictional forces that prevent squealing; apply frictional forces that aid in holding the discs in position while rotating in their off-bra " ke positions; and permit axial forces from the force actuator to outwardly slide the discs to their braking position with engagement of the disc 40 with the stationary brake pad 60. The illustrative assembly 10 also comprises the friction material pads arranged on opposite sides of each of the discs 38 and 40. These pads comprise the first pad 50 which is mounted on a backing plate 52 and is arranged to engage a side surface of the disc 38, pads 54 and 55, which are mounted on opposite sides of a backing plate 58 and are arranged, respectively, to engage the opposite side surface of the disc 38 and a facing side surface of the disc 40, and the pad 60 which is mounted on a backing plate 62 and is arranged to engage the opposite side surface of the disc 40. The backing plate is fixedly mounted on a guide member or bridge 64, which is, in turn, fixedly mounted on the portion 12c of the link 12. Specifically, two bolts 66 pass through bores through the portion 12c and the guide member 64, and have threaded ends which are received in threaded bores in the backing plate. The stationary guide member 64 provides two guidance surfaces 68 on which the backing plates 52 and 58 slide. The guidance surfaces 68 extend, parallel to the axis 22, along opposite sides of the member 64. The guidance surfaces may take other forms such as the shafts of the bolts 66. Each guidance surface 68 receives a pair of concave, U-shaped projection or hooks of the pad carriers 52 and 58. As best seen in FIG. 3A, the slidable pad carrier 58 has hook-shaped projections 59 with inner sliding surfaces 59a, which are slidably supported on the upwardly- facing support surfaces 68 of the bridge 64. To assist in achieving the desired balance to allow the brake pad carriers 52 and 58 to be pushed apart from and by the brake discs 38 and 40, when they are shifting axially from their brakes-on to their brakes-off positions; and yet constrain the pad carriers and their brake pads from tilting, it is preferred to machine flat the inner sliding surfaces 59a on the carriers and the supporting surfaces 68 on the bridge. Flat machined surfaces on the carriers engaging flat machine surfaces on the bridge assures a more uniform, frictional, constraining force to retain the brake pad carriers against axial sliding from their off -brake positions. Also, the carriers will have broader, wider engagement with bridge supporting surfaces 68 to assist in preventing significant rocking or tilting on the bridge under vehicle inertial forces and/or vibrations when the vehicle is moving, as would cause localized rubbing contact in the off-brake condition. If the slidable brake pad position is not controlled, the slidable brake pad may tilt to engage or to vibrate against the slidable brake disc and generate a random wear pattern on the disc causing DTV and vibration of the disc. The control of the slidable pad and disc is important in a very dynamic situation with the vehicle wheel carrying the slidable brake system over bumpy or smooth roads, cornering with brakes on, cornering with brakes off, with ABS system on, with an ABS system off, etc. On cornering, the hub deflects and moves the disc surface to engage the brake pad; and after cornering, the pad and disc separate as the brake recovers to its steady state of low residual torque at the off-brake position. In the embodiment of the invention, illustrated in FIGS. 2, 3 and 3A, the preferred force applicators comprise flat leaf springs 71a and 71b that have been bent from their flat planar condition to a bow configuration in which outer edges 71c and 71d of the springs abut top end surfaces 52a, 52b, 58a, 58b of the respective slidable brake carriers 52 and 58. The center portion of the leaf spring 71a is secured by a suitable fastener, such as screws 69 threaded through the spring and into the stationary bridge 64 at a central location on the top of the stationary bridge 64. The force applicator 71 may take many forms, and it is herein illustrated in FIG. 3 as having the two separate leaf spring portions 71a and 71b, each of which is separately applied resilient, biasing forces to its associated brake pad holder 52 or 58. The leaf spring portions 71a and 71b are preferably connected by a short integral, central web 71f, which is located between a pair of facing, elongated slots 77 dividing the spring leaf into the two discrete pring force applicator sections. Thus, if one brake pad holder has high points thereon or other force mitigating or amplifying factors affecting it and its associated spring; the other brake pad holder and its associated spring should be isolated therefrom. In the illustrated embodiment of the invention, the brake actuating force used to brake the vehicle is from a brake actuator which is in the form of a hydraulic piston and cylinder assembly 75, although it is contemplated that the actuating force could be from a brake by wire actuator. In a brake-by-wire system, an electric motor drive assembly would force the movable brake pad carriers 52 and 58 to carry the slidable brake pads into their respective braking positions and slide the brake discs axially along the hub 14 into their respective braking positions. The illustrative force actuator system comprises a piston and cylinder assembly operable to urge the pads 50, 54, 56 and 60 into engagement with opposite side surfaces of the discs 38 and 40 to brake the hub 14 and hence, the wheel. The piston and cylinder assembly comprises a cylinder 72 which is defined by the portion 12c of the link 12. Thus, the cylinder is formed integrally with the remainder of the link. A brake-by- wire actuator such as an electric motor could be mounted in the cylinder 72 rather than the piston 74. Herein, the piston 74 of the assembly projects from the cylinder and engages the backing plate 52 on the opposite side thereof to the pad 50. The piston and cylinder assembly is operated by supplying hydraulic fluid under pressure to a bore 76 in the link portion 12c which communicates with the cylinder. Herein, the hydraulic pressure for operating the twin disc brake system was about 30 to 35 BAR which is one-half of the 70 BAR pressure of the conventional fixed disc brake on the other test vehicle. The piston had a face of about 200 mm in area. The piston moves out of the cylinder moving the backing plates 52 and 58 and the discs 38 and 40 until the disc 40 engages the pad 60, which does not move. The hydraulic piston and cylinder assembly 75 includes a seal 79 (FIG. 18) which acts between the cylinder 72 and the piston 74 to prevent egress of hydraulic fluid from the cylinder. This seal is provided by an elastomeric sealing ring 81 (FIG. 18), which is mounted in an annular groove 83 formed in a cylinder wall 72a, the ring projecting from the groove to engage the piston. This sealing ring 81 also serves as an energy storing mechanism. Specifically, when the assembly is operated to move the piston outwardly of the cylinder to put the brake "on", the ring is compressed thereby storing energy therein. When the pressure of the hydraulic fluid in the cylinder is reduced, the ring releases the stored energy therein by moving the piston inwardly of the cylinder (away from the brake disc) . Accordingly, the sealing ring has to engage the piston with a significant force. Movement of the piston away from the disc allows the movable pads 50, 54 and 56 of the brake to be moved away from the disc by forces exerted thereon by the rotating slidable brake discs 38 and 40 overcoming the force of the spring 71a and 71b; thereby putting the brake into a "brakes-off" condition. The return of the piston 74 by the seal 81 reduces the off-brake torque because there is no significant force being applied by the piston to the brake carrier 52 and its brake shoe 50 relative to the facing side of the slidable brake disc 38. Conversely, the floating brake discs 38 and 40 are constrained and float on the hub 14 and will not shift the piston inwardly into the cylinder to displace hydraulic fluid, in the cylinder causing "knock-back" during cornering or other dynamic movements of the wheel assembly. The reduction of knock-back provides a better feel to applying the brakes with less fluid displacement, and eliminates the occasional long pedal displacement feel where substantial fall-back has occurred. From the foregoing, it will be seen that the present invention provides a much smaller disc brake assembly without the very large caliper sliding and bolts as in the conventional, fixed disc brake. The caliper is large because it carries the cylinder and piston and the slidable bridge must withstand and transfer the large torque brake loads. The present invention is smaller because the cylinder can be integrated with the support and the bridge does not slide and carry the piston. Because of knock back and other problems, this large fixed brake is usually mounted at about 3:00 or 9:00 o'clock positions whereas in the present invention the brake is mounted at the top of the unit at the 12:00 o'clock position. The stiffness problem of the bridge with its deflection, e.g., 0.006 inch, is reduced by a factor of four when using four brake pads and one-half the hydraulic line pressure allowing a smaller and lighter weight brake assembly. The time of mounting and assembly of the brake, as well as repair or replacement, is enhanced because of the front bolting and the telescopic sliding of the brake discs and of the brake components versus the bolt from the rear or behind of the fixed brake bolts on which the caliper slides. FIG. 12 is similar to FIG. 16 but illustrates a variation 100 of the illustrative assembly 10 in which like parts to those of the assembly 10 are given the same reference numerals and are not further described. The assembly 100 differs from the assembly 10 in that, instead of the cylinder 72, the portion 12c of the link 12 has two parallel cylinders 102 formed therein. In this case, each of the cylinders 102 has a smaller transverse cross-sectional area than the cylinder 72, but the total area of the cylinders 102 is greater. Each of the cylinders 102 has a piston 104 therein and the pistons 104 cooperate in pressing the backing plate 52. In order to accommodate the two piston and cylinder assemblies, the guide member 64 is modified to arch over the pistons, as shown at 106 and the bolts 66 are replaced by three bolts 108. The use of two piston and cylinder assemblies enables greater force to be applied for the same pressure in the cylinders (or the same force to be applied for lower pressure) and this force can, on average, be applied at a greater distance from the axis 22. If desired, the two cylinders can be of different diameters, e . g. , with the leading cylinder in the normal direction of rotation, being of greater diameter.

Claims: What Is Claimed Is: 1. A disc brake system comprising a hub being mounted for rotation about a central axis through the hub; at least one brake disc having an inner portion slidably mounted on the hub for sliding in a direction parallel to the central axis of the hub between a braking position and off-brake position; a drive connection between the hub and the brake disc to rotate the disc with rotation of the hub and to decelerate the rotation of the hub when the disc : ' s in the braking position; braking pads including at least one slidable brake pad each having a friction pad surface for applying braking torque to opposite sides of the brake disc when in the braking torque position to decelerate the engaged brake disc and thereby the hub; a stationary support mounting the slidable brake pad for travel between an off -brake position and the braking position; an actuator for sliding the slidable brake pad and brake disc into the braking position; a disc force applicator applying a radially directed force between the hub and the inner portion of the brake disc to cause friction between the hub and disc inner portion to retard their sliding axially relative to one another; an outer rim portion on the braking disc rotating while in the off-brake position and engaging the slidable brake pad's friction surface to slide the pad from the braking position to an off -brake pad position; the slidable brake disc floating on the disc force applicator and slidable axially along the hub from a braking position to an off-braking position relative to the braking pads; and Characterised by a brake pad force applicator acting on the slidable brake pad, when its off-brake position, to constrain the friction pad surface engaging the brake disc to reduce tilting of the brake pad on the stationary support and its rubbing on the brake disc that would increase off -brake, residual torque. 2. A disc brake system in accordance with Claim 1 wherein the brake pad force applicator applies force to the slidable brake pad to hold its face in a plane substantially parallel to the plane in which the disc is rotating to minimize tilting of the brake pad into engagement with the brake disc, which would cause disc thickness variation. 3. A disc brake system in accordance with Claim 2 wherein the brake pad force applicator comprises at least one spring pushing on the brake pads in a direction substantially normal to the rotational axis of the brake disc and normal to the path of travel of the brake pads along the stationary support. 4. A disc brake system in accordance with Claim 3 wherein the stationary support comprises a bridge; the slidable brake pad comprises a slidable pad carrier mounted for sliding on the bridge and carrying the frictional pad surface thereon; and the spring is positioned over the brake pad carrier and forces the brake pad carrier downwardly against the bridge. 5. A disc brake system in accordance with Claim 1 wherein two or more brake discs are slidably mounted on the hub; a central slidable brake pad having opposed friction pads thereon is disposed between the twin brake discs and is slidably mounted on the stationary support; and the force applicator comprises at least one spring to constrain the slidable brake pad and the central slidable brake pad and to assist in constraining the rims of the slidable twin disc brakes in their off- brake position. 6. A disc brake system in accordance with Claim 1 wherein in the off-brake position, the disc force applicator holds the brake disc in a first radial plane; and the brake pad force applicator holds its friction pad surface in a second radial plane parallel to the first radial plane to limit contact between the friction surface and brake pad to cause random kind of contact therebetween. 7. A disc brake system in accordance with Claim 1 or Claim 6 wherein the brake pad force applicator comprises resilient means forcing the brake pads against the support to provide predetermined frictional forces therebetween sufficient to assist in positioning the outer rims of the brake discs in an axial direction and position on the hub. 8. A disc brake system in accordance with Claim 1 wherein the force applicator comprises a hydraulic cylinder and a reciprocal hydraulic piston in the cylinder; and a compressible seal ring in the cylinder compressible by the piston movement and storing energy to provide a return force to retract the piston thereby permitting the brake pad to shift axially along its stationary support toward the cylinder during rotation of the brake disc in its off-brake position. 9. A disc brake system in accordance with Claim 1 wherein the drive connection between the disc and hub comprises intermeshed teeth. 10. A disc brake in accordance with Claim 1 wherein the brake pad force applicator is also operable, when the slidable brake pad is in its off-brake position, to prevent the slidable brake pad from contacting the disc by sliding axially on the stationary support. 11. A disc brake system in accordance with Claim 9 wherein the teeth on the brake disc are provided with stress relief fillets at the junctures of the teeth to the remainder of the brake disc. 12. A disc brake system in accordance with Claim 1 wherein: the disc expands at higher temperatures and tends to slide axially relative to the hub; and the disc force applicator between the brake disc and hub comprises a spring applying friction forces for limiting the sliding of the expanded disc on the hub. 13. A disc brake system in accordance with Claim 5 wherein the brake pad force applicator comprises separate springs each engageable with the slidable friction pad and the central slidable friction pad. 14. A disc brake system in accordance with Claim 1 wherein the residual, off-load torque allows the brake discs to cool quickly to less than 20 degrees above an ambient temperature in the range of 10° to 20°C due to residual, off-brake torque. 15. A disc brake system in accordance with Claim 1 wherein: the stationary support has a machined, supporting surface thereon; and the brake pad comprises a slidable carrier mounted on the stationary support and having machined slide surface thereon in sliding frictional contact with the machined, supporting surface on the stationary support ; and the brake pad force applicator comprises a leaf spring positioned over the slidable carrier and pushing the carrier's machined slide surface against the stationary machined supporting surface to prevent tilting of the slidable carrier on the stationary support during the off-brake condition. 16. A disc brake system in accordance with Claim 1 wherein the force applicators hold the brake pad and the brake disc in parallel planes normal to the rotation axis so that engagement of the disc with the pad with revolution of the pad is random and avoids rubbing at the same spot with each revolution as would cause wear and disc thickness variations. 17. A disc brake system comprising a hub being mounted for rotation about a central axis through the hub; at least one brake disc having an inner portion slidably mounted on the hub for sliding in a direction parallel to the central axis of the hub between a braking position and off-brake position; a drive connection between the hub and the brake disc to rotate the disc with rotation of the hub and to decelerate the rotation of the hub when the disc is in the braking position; braking pads arranged on opposite sides of the disc and each having a friction pad surface for applying braking torque to the disc when in a braking position thereof, the braking pads including a slidable brake pad and a stationary brake pad which is fixed relative to the hub; a stationary support mounting the slidable brake pad for travel between an off-brake position and the braking position; an actuator operable to slide the slidable brake pad and disc into a braking condition, the actuator also being operable to create sufficient clearance to allow the slidable brake pad and disc to slide into an off- brake condition; a disc force applicator applying a radially directed force between the hub and the inner portion of the brake disc to cause friction between the hub and disc inner portion to retard their sliding axially relative to one another; an outer rim portion on the braking disc rotating while in the off-brake position and engaging the slidable brake pad's friction surface to slide the pad from the braking position to an off-brake pad position; the slidable brake disc floating on the disc force applicator and slidable axially along the hub from a braking position to an off-braking position relative to the braking pads; and a brake pad force applicator acting on the slidable brake pad wherein the forces applied to the disc by the disc force applicator and to the slidable brake pad by the brake pad force applicator are balanced so that the system can move from its braking condition to its off-brake condition by the action of separation forces between the disc and the braking pads, the disc sliding axially on the hub by a first distance to thereby separate itself from the stationary brake; and the slidable brake pad sliding on the stationary support by a second distance, which is greater than said first distance, to thereby separate itself from the disc, the forces applied by the applicators in the off-brake condition being sufficient to prevent axial sliding of the disc causing contact with either braking pad, and to prevent axial sliding of the slidable pad from causing contact between the disc and the slidable pad. 18. A disc brake system in accordance with Claim 17 wherein the disc force applicator forces the pads against the stationary support with force sufficient to prevent tilting of the slidable pad on the stationary support from causing contact between the slidable pad and the disc . 19. A disc brake system in accordance with Claim 17, including: first and second discs; a central slidable pad; the forces being applied to the discs by the disc force applicator and to the slidable brake pads by the brake pad force applicator are balanced so that the system can move from its braking condition to its off- brake condition by the action of separation forces between the discs and the braking pads, the first disc sliding axially on the hub by a first distance to thereby separate itself from the stationary brake pad, the central slidable brake pad assembly sliding on the stationary support by a second distance, which is greater than said first distance, to thereby separate itself from the first disc, the second disc sliding axially on the hub by a third distance, which is greater than said second distance, to thereby separate itself from the central slidable brake pad, and the other slidable brake pad sliding on the stationary support by a fourth distance, which is greater than said third distance, to thereby separate itself from the second disc, the forces applied by the applicators in the off-brake condition being sufficient to prevent axial sliding of the discs causing contact of either disc with any of the braking pads, and to prevent axial sliding of the slidable pads from causing contact between either disc and either slidable pad. 20. A disc brake system in accordance with Claim 19 wherein: the pad force applicator comprises at least one leaf spring pushing the sliding brake pads against the stationary support; and the disc force applicator comprises at least one leaf spring disposed between the hub and the slidable brake discs. 21. A disc brake system in accordance with Claim 20 wherein: the leaf spring of the pad force applicator comprises separate leaf springs pushing against the respective slidable brake pads; and the disc force applicator comprises a separate leaf spring disposed between each of the first and second brake discs. 22. A disc brake system comprising a hub being mounted for rotation about a central axis through the hub; first and second brake discs each having an inner portion slidably mounted on the hub for sliding in a direction parallel to the central axis of the hub between a braking position and off-brake position; a drive connection between the hub and the brake discs to rotate the discs with rotation of the hub and to decelerate the rotation of the hub when the discs are in the braking position; braking pads each having a friction pad surface for applying braking torque to the disc when in a braking position thereof, the braking pads including a slidable brake pad, a central slidable brake pad between the first and second brake discs, and a stationary brake pad which is fixed relation to the hub; a stationary support mounting the slidable brake pads for travel between an off-brake position and the braking position; an actuator for sliding the slidable brake pads and brake discs into the braking position; a disc force applicator applying a radially directed force between the hub and the inner portion of the brake disc to cause friction between the hub and disc inner portion to retard their sliding axially relative to one another; an outer rim portion on each braking disc rotating while in the off-brake position and engaging the slidable brake pad's friction surface to slide the pad from the braking position to an off-brake pad position; the slidable brake disc being movable axially along the hub from a braking position to an off-braking position relative to the braking pads; and a brake pad force applicator acting on the slidable brake pads wherein the forces applied to the discs by the disc force applicator and to the slidable brake pads by the brake pad force applicator are balanced so that the system can move from its braking condition to its off-brake condition by the action of separation forces between the discs and the braking pads, the first disc sliding axially on the hub by a first distance to thereby separate itself from the stationary brake pad, the central slidable brake pad assembly sliding on the stationary support by a second distance, which is greater than said first distance, to thereby separate itself from the first disc, the second disc sliding axially on the hub by a third distance, which is greater than said second distance, to thereby separate itself from the central slidable brake pad assembly, and the other slidable brake pad sliding on the stationary support by a fourth distance, which is greater than said third distance, to thereby separate itself from the second disc, the forces applied by the applicators in the off- brake condition being sufficient to prevent axial sliding of the discs causing contact of either disc with any of the braking pads, and to prevent axial sliding of the slidable p^ds from causing contact between either disc and either slidable pad. 23. A disc brake system in accordance with Claim 22 wherein: slide supporting surfaces are provided on the stationary support ; the slidable brake pads have pad carriers carrying the pad friction surfaces thereon; spaced friction slide surfaces are provided on the pad carriers; and the pad force applicator comprises at least one leaf spring attached to the stationary support and pushing the friction slide surfaces against the slide supporting surfaces on the stationary support. 24. A disc brake system in accordance with Claim 23 wherein a plurality of leaf springs are positioned between the hub and the inner portion of each brake disc to increase friction between the engaged surfaces of the drive connection of the hub and disc. 25. A vehicle braking and suspension system comprising: a vehicle suspension having a suspension member; a wheel adapted to be carried by the vehicle suspension member; a disc brake and wheel support assembly having a supporting suspension member; a rotatable hub mounted on the suspension member for rotation about a central rotational axis through the hub and carrying the wheel for rotation about the rotational axis; a brake actuator for the disc brake mounted on the supporting suspension member; a stationary bridge on the suspension member and having slidable surfaces thereon; at least one brake disc mounted on the hub for braking the hub and wheel; an outer, fixed brake pad mounted on the bridge for engaging one side of the brake disc; a slidable brake pad mounted on the slidable surfaces of the stationary bridge and slidable by the brake actuator to engage a friction surface thereon with the other side of the disc and to slide the brake disc axially along to the hub from an off-brake, residual torque position to a on-brake position in which the braking pads are engaging opposite sides of the brake disc to brake the disc, hub and wheel; and a brake pad force applicator carried on the stationary bridge applying force to the brake pad to hold the brake pad in a plane parallel to the plane of the slidable brake disc. 26. A vehicle braking system in accordance with Claim 25 wherein the brake pad force applicator comprises a resilient spring member mounted on the stationary bridge . 27. A vehicle braking system in accordance with Claim 25 wherein sliding surfaces on the stationary bridge have sliding frictional engagement with sliding surfaces on the brake disc; and the brake pad force applicator comprises a resilient spring member mounted to overlie the brake pad and to apply a predetermined spring force to the brake pad to increase substantially the friction beyond that needed to prevent rattling of the brake pad on the bridge . 28. A vehicle braking system in accordance with Claim 25 wherein the brake actuator for the disc brake comprises a hydraulic cylinder having a piston for forcing the slidable brake pad into the braking position; a compressible seal ring between the cylinder and piston exerts a return force on the piston when the braking fluid pressure is relieved at the no-load braking position; and the hydraulic cylinder being mounted at an upper vertical position on the suspension. 29. A vehicle braking system in accordance with Claim 25 wherein: a second brake disc is mounted on the hub for axial sliding movement thereon; and a central brake pad carrier having opposed friction pads is slidably mounted on the stationary bridge to engage facing sides of the respective brake discs; the force applicator holding the central pad carrier in an off -brake, residual torque position relative to the rotating brake discs. 30. A vehicle braking system in accordance with Claim 25 wherein a friction force applicator is positioned between the brake disc and the hub to exert friction forces to assist the brake pads in positioning the brake discs at off-brake, residual load positions 31. A vehicle braking system in accordance with Claim 25 wherein intermeshed splines are formed on the brake disc and the hub to provide a positive drive connection therebetween; and spring members are positioned between the hub and the brake disc to apply frictional forces to resist free sliding of the brake disc on the hub as the brake disc is heated and expands and thereafter contracts when cooled . 32. A vehicle braking system in accordance with Claim 25 wherein the two brake discs cool to less than 20 °C. above ambient temperature when the ambient temperature is in the range of 10°C. to 20°C. 33. A vehicle braking system in accordance with Claim 25 wherein the rotating brake disc and the brake pads and the brake pad force applicators position the brake discs for randomly engaging the brake pads at different locations, thereby preventing wear due to engagement at the same spot on the disc during each revolution as would cause disc thickness variation. 34. A method of disc braking employing inner and outer, annular brake discs mounted on a rotatable hub for axial sliding thereon and having a fixed caliper bridge with four brake pad frictional surfaces thereon for engaging opposite sides of the brake discs, said method comprising: applying an actuating force on the slidable brake pads to slide them along the bridge to a braking position to engage rims of the annular discs with the four pad frictional surfaces to generate braking forces to decelerate the discs; pushing the brake discs by the slidable brake pads along the hub to engage an outer side of an outer brake disc with a stationary brake pad on the fixed bridge at the braking position; relieving the actuating force after braking; exerting forces by the rotating brake discs on the slidable brake pads to overcome predetermined spring forces holding the slidable brake pads against sliding to shift the brake pads to off-brake positions; exerting spring forces between each of the brake discs and hub to assist in locating the brake discs on the hub at off -brake positions; and limiting engagement between the rotating brake discs and the brake pads at their respective off-brake positions to only random engagement therebetween to minimize disc thickness variation due to rubbing and to minimize off-load, residual torque between the discs and brake pads . 35. A method in accordance with Claim 34 including the providing of the disc brake assembly on a vehicle suspension; and maintaining the temperature of the brake discs due to off-brake residual torque to less than 20° above ambient temperature when the ambient temperature is in the range of 10° to 20°C. as the vehicle is being driven in a straight line path. 36. A method in accordance with Claim 34 including the providing of the disc brake on a vehicle suspension; and driving the vehicle through the AMS test and maintaining the temperature of the brake discs below 650°C. 37. A method in accordance with Claim 36 including the step of maintaining the brake disc temperature below 600°C. 38. A method in accordance with Claim 34 actuating the brake pads from a position above the rotational axis through the hub and in a vertical plane at a substantial 12:00 o'clock position. 39. A method in accordance with Claim 34 wherein the applying of the actuating force on the slidable brake pads comprises moving a hydraulically operated piston to force at least two slidable brake pads and at least two slidable brake discs to shift to the braking position. 40. A method in accordance with Claim 34 including holding the brake pads against tilting on the supporting bridge to prevent localized rubbing and resultant disc thickness variation while the braking system is experiencing vibration and vehicle inertial forces . 41. A method in accordance with Claim 34 including the step of balancing the spring forces on the brake pads and brake discs to allow separation from one another to shift into an off-brake position and to hold them against tilting to prevent disc thickness variation of the brake discs. 42. A vehicle, front wheel braking assembly comprising : a suspension support casting; a rotatable hub journaled in the suspension support casting for rotation about a substantially horizontal axis of rotation; inner and outer slidable brake discs slidably mounted on the hub and each having an interconnection with the hub to rotate with the hub; a fixed bridge on the suspension supporting casting having slidable support surfaces thereon and having a distal end; a fixed brake pad mounted on the distal end of the fixed bridge to engage an outer face of the outer slidable brake disc; a central brake pad carrier carrying a pair of opposed brake pad surfaces to engage facing sides of the inner and outer brake discs mounted on the slidable support surfaces of the fixed bridge; an inner brake pad carrier having an inner brake pad surface mounted on the slidable surfaces of the fixed bridge ; an integral, hub support portion of the suspension support casting mounting the hub and attached wheel for rotation about the rotational axis; a substantially vertical bore in the suspension support casting to receive a ball joint to permit the suspension support casting to turn about an axis therein; an integral connecting portion on the suspension support casting for connection to a steering system to turn the suspension support casting about a swivel axis; and an integral actuator bore in a top portion of the suspension support casting located above the rotational axis and in a vertical, substantially 12:00 o'clock position with the bridge and brake pad carriers also being at the substantially 12:00 o'clock position for engaging the upper outer rim portions of the slidable discs . 43. A vertical braking assembly in accordance with Claim 42 wherein the integral actuator bore comprises a hydraulic cylinder bore; and a piston is mounted in the integral hydraulic cylinder bore. 44. A vehicle braking assembly in accordance with Claim 42 wherein a brake-by-wire actuator is mounted in the integral actuator bore. 45. A vehicle braking assembly in accordance with Claim 42 wherein the integral support casting comprises a connecting portion for connection to a McPherson strut so that the integral suspension casting can pivot about an axis of the strut .

Inventors: BUNKER KENNETH JAMES, BUNKER, KENNETH, JAMES
Applicants: BUNKER KENNETH JAMES, FEDERAL MOGUL TECHNOLOGY LTD, BUNKER, KENNETH, JAMES, FEDERAL-MOGUL TECHNOLOGY LIMITED
Application year: 2000
Main classification: F16D55
IPC codes: B60T1, B60T8, F16D55, F16D65