Patent Application
20100206674
The present invention relates, in general, to vehicle disc brake systems and in particular to the rotor components thereof. More particularly, the present invention relates to tilted vane disc brake rotors.
Motor vehicle disc brake systems utilize, at each wheel, a brake rotor connected to an axle hub of a rotatable axle of the motor vehicle, and an opposing set of selectively movable brake pads connected to a non-rotating brake caliper which carries a set of brake pads. The brake rotor includes opposing brake pad engagement surfaces, or rotor cheeks, wherein when braking is to occur, the braking system causes the caliper to press the brake pads upon respective brake pad engagement surfaces of the rotor cheek. Frictional interaction between the rotating rotor cheeks and non-rotating brake pads causes braking of the motor vehicle to transpire, the rate of braking depending upon the pressure of the brake pads against the rotor cheeks.
In the automotive art, modern hydraulic braking systems typically include an operator or driver interface, such as a brake pedal. As the driver applies force to this pedal, this force is transmitted by means of control arms and other related devices to the master cylinder. The master cylinder accepts mechanical force as an input and produces hydraulic pressure, in the form of pressurized brake fluid, as an output. This pressure is conveyed by means of pressurized brake fluid through lines and valves of the motor vehicle to interface with each brake corner, found at each wheel of the motor vehicle.
Turning now to
In the normal course of the operation of a conventional brake system, the forces applied by the brake pads 32a and 32b to the rotor cheeks 30a, 30b of the brake rotor 30 can generate significant heating. This heating is undesirable, as the resulting elevated temperature can result in non-uniform thermal gradients across the brake rotor which, in turn, can result in thermal distortions of the brake rotor 30 and the brake pads 32a and 32b. At the very least, these distortions promote more rapid brake component wear and thereby higher maintenance costs. As a result, much effort has been expended to create brake rotors which have been designed in a fashion to facilitate the management of elevated brake rotor temperature. Elevated brake rotor temperature management is a complex dynamic, wherein design changes can impact both the heating rate and the cooling rate of the brake rotor.
Management of elevated brake rotor temperature, well known in the art, is by use of vented brake rotors, wherein the vanes 36 serve to hold the rotor discs together, yet keep open the cooling region 40 therebetween for the purpose of delivery of elevated heat of the brake rotor to the atmosphere. In this regard, heat is generated due to the interaction of the rotor cheeks 30a, 30b with the brake pads 32a, 32b, and flows conductively to the inside disc surfaces 38a, 38b, and further to the vanes 36, whereupon heat is dissipated in the cooling region 40 by convective heat transfer to the air circulating between the vanes. Thus, the flow of heat out through the cooling region 40 while yet maintaining stability and strength of the vanes 36 are the critical aspects of the design of a brake rotor.
In the prior art, innovations have been developed to enhance air flow between the vanes, as for example vane shapes which are intended to facilitate speeding up of the rate of air flow through the cooling region between the rotor discs.
In the overall design of brake rotors, if too much material is removed from the brake rotor, then the heating rate of the brake rotor may increase because of the lower heat capacity of the rotor discs and the brake rotor may not be durable enough to function long-term dependably in repeated braking processes without distortion. Further, the design of brake rotors needs to include considerations of optimal thermal dissipation characteristics and meet driver expectations for brake feel.
Historically, engineering of the human interface with a braking system has been a subjective endeavor. With the advent of a Brake Feel Index (BFI) as reported in SAE technical paper 940331 “Objective Characterization of Vehicle Brake Feel” (1994), a method was developed to correlate objective engineering parameters to these subjective assessments. In the case of BFI, such aspects as pedal application force, pedal travel and pedal preload are compared to desired target values which correlate to a particular type of response desired and the deviation from these target values is reflected in a lower index value. In disc brake systems, some of the causes of undesirable brake pedal feel have been related to noise and vibration.
The noise and vibration characteristics of a conventional brake rotor can be studied using the technique of normal coordinate analysis, well known in the art. This type of analysis indicates that brake rotors of the conventional type (i.e., shown at
The art has attempted to mitigate some of these rotor vibration problems. Swept vanes (see for example U.S. Pat. No. 6,119,820) and pillar-post vanes (see for example U.S. Pat. Nos. 6,405,839 and 6,454,058) have been attempted which could mitigate the noise issues. But, these types of perpendicular vanes can interfere with the flow of air through the cooling region. Increasing the perpendicular vane cross-sectional width and/or providing large pillars at the outer periphery (i.e., rotor outer diameter) will enhance the conductive heat transfer from the rotor discs to the perpendicular vanes and serve to increase rigidity of the brake rotor structure, but such perpendicular vanes will limit air flow through the cooling region and thereby limit convective heat transfer to the air and will also add weight to the vehicle and thereby lower mileage.
Accordingly, what remains needed in the art is a means to reduce the rotor noise level during braking without negatively impacting the thermal properties of the conventional rotor or the mileage of the vehicle.
The present invention is a brake rotor vane configuration which reduces the rotor noise level due to braking without negatively impacting the thermal properties (as per a conventional rotor) or the mileage of the vehicle.
In contradistinction to the perpendicular vanes of conventional brake rotors, the brake rotors of the present invention utilize tilted vanes, in the sense that the vanes are oriented with respect to the inside disc surfaces at other than 90 degrees, defined by an acute intersection angle with respect to either of the inside disc surfaces (of course, being equivalently defined by the opposite obtuse angle with respect to the inside disc surface). The tilted vanes according to the present invention may be, for example, paired and oriented serially around the circumference of the rotor discs so as to provide a series of vane pairs in the form of: a series of alternately inverted V-shapes, a series of same oriented V-shapes, or a series of X-shapes.
One purpose of the tilted vanes is to increase the connection stiffness between the two (i.e., first and second) rotor discs, thereby increasing the frequency of the racking mode vibrations so that their frequency will be outside the normal human hearing range. This effect occurs because the tilted vanes of the present invention serve to counteract the compression due to frictional forces, rather than simply bend as the conventional perpendicular vanes would do. Also the tilting disrupts the node diametrical mode, while additionally increasing the frequencies.
Another purpose of the tilted vanes is to provide excellent heat management and structural stability. By increasing the tilted vane height (length), the thickness of the tilted vanes can be reduced and yet provide stability of the brake rotor. Conductive heat transfer to the tilted vanes from the rotor discs is excellent, and since the air circulation between the tilted vanes is kept free, the convective heat transfer from the tilted vanes to the atmosphere is also excellent.
This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment.
Referring now to the Drawing,
Turning attention firstly to
Each tilted vane 108 is “tilted” in the sense that the tilted vanes are oriented with respect to the inside disc surfaces 104a, 104b at other than 90 degrees, defined by an acute intersection angle α with respect to either of the inside disc surfaces (of course, being equivalently defined by the opposite obtuse angle with respect to the inside disc surface). The tilted vanes 108 are, in this example, grouped into vane pairs 110a which are oriented serially around the circumference of the rotor discs 104a, 104b so as to provide a series of vane pairs in the form of a series of alternately inverted V-shapes 110b, 110c. Each tilted vane 108 has a height (length) L, a width W, a mutual spacing S, and generally extends across the radius R of the rotor discs 104a, 104b.
Turning attention now to
At
Each tilted vane 108′ is “tilted” in the sense that the tilted vanes are oriented with respect to the inside disc surfaces 104a′, 104b′ at other than 90 degrees, defined by an acute intersection angle α′ with respect to either of the inside disc surfaces (of course, being equivalently defined by the opposite obtuse angle with respect to the inside disc surface). The tilted vanes 108′ are, in this example, grouped into vane pairs 110a′ which are oriented serially around the circumference of the rotor discs 104a′, 104b′ so as to provide a series of vane pairs in the form of a series of same oriented V-shapes 110d. Each tilted vane 108′ has a height (length) L′, a width W′, a mutual vane spacing S′, and generally extends across the radius R′ of the rotor discs 104a′, 104b′.
At
Each tilted vane 108″ is “tilted” in the sense that the tilted vanes are oriented with respect to the inside disc surfaces 104a″, 104b″ at other than 90 degrees, defined by an acute intersection angle α ″ with respect to either of the inside disc surfaces (of course, being equivalently defined by the opposite obtuse angle with respect to the inside disc surface). The tilted vanes 108″ are, in this example, grouped into vane pairs 110a″ which are oriented serially around the circumference of the rotor discs 104a″, 104b″ so as to provide a series of vane pairs in the form of a series of X-shapes 110e. Each tilted vane 108″ has a height (length) L″, a width W″, a mutual vane spacing S″, and generally extends across the radius R″ of the rotor discs 104a″, 104b″.
By way of exemplification the tilted vanes 108, 108′, 108″ have, respectively, an acute intersection angle α, α′, α″ ranging from about 80 degrees to about 36 degrees, and preferably by way of example of about 58 degrees.
A brief functional comparison of the conventional perpendicular brake rotor with respect to the tilted vane brake rotor of the present invention is as follows. In
This example is a comparison between a tilted vane brake rotor according to the present invention, and a perpendicular vane brake rotor of the prior art, being presented herein merely by way of exemplar illustration and not limitation.
The tilted vane disc rotor according to the present invention, similar to that of
The conventional perpendicular vane brake rotor, similar to that of
The following observations were made. The tilted vanes have a surface area about 12% larger than the perpendicular vanes. The tilted vane rotor effectively increased the frequency of the racking mode from 11 kHz over that of the perpendicular vane brake rotor to a frequency beyond human hearing (above about 18 kHz, possibly above about 22 kHz). The nodal diametrical modes were not clearly defined for the tilted vane brake rotor and were approximately 6% higher in frequency over the perpendicular vane brake rotor. Further, the V-shape of the tilted vane pairs allows counteraction of frictional forces in compression/tension, as opposed to pure bending as with conventional perpendicular vanes, and leads to a 10% increase in stiffness.
As discussed hereinabove, the normal coordinate analysis shows that brake rotors have three types of vibrational modes, namely node diametrical, compression, and racking. Table I shows the results of a normal coordinate analysis calculation of the normal modes of the conventional perpendicular vane brake rotor versus the tilted vane brake rotor, both of Example I.
In this example, “Mode #” refers to the vibration type and order; “Perpendicular Vane” refers to the convention perpendicular vane rotor (
As can be seen from Table I, the frequency shifts higher with the tilted vane brake rotor configured as depicted at
This effect can be seen clearly when comparing the displacement profiles of the node diametrical mode. The alignment of the vane affixments of the perpendicular vanes in the prior art brake rotor serves to facilitate the coupling of the local vibration modes in the brake rotor discs. In the present invention, the vane affixments of the tilted vanes are not aligned directly opposite of their counterpart on the opposing inside disc surfaces, thereby not facilitating the correlation between the local vibration modes within each rotor disc.
Table I is profiled in
All of the versions of the tilted vane rotors (i.e.,
To those skilled in the art to which this invention appertains, the above described preferred embodiments may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.
