Turning – Process of turning
Reexamination Certificate
2000-01-10
2001-04-17
Tsai, Henry (Department: 3722)
Turning
Process of turning
C082S112000, C082S118000, C082S151000
Reexamination Certificate
active
06216571
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an improved on-car brake lathe apparatus. More specifically, this invention relates to an apparatus and method for automatically compensating for the lateral runout of a lathe apparatus with respect to a vehicle hub. The invention further includes a novel runout measurement and control system that describes the runout of a disc brake assembly and directs a corrective signal to an automated control system for adjustment in order to effectively compensate of lateral runout. The novel runout apparatus and method may also be advantageously utilized in other practical applications in order to align two concentrically attached rotating shafts.
A brake system is one of the primary safety features in every road vehicle. The ability to quickly decelerate and bring a vehicle to a controlled stop is always critical to the safety of the vehicle occupants and those in the immediate vicinity. In this, a vehicle braking system is designed and manufactured to exacting specifications and rigorous inspection.
One of the main components of a brake system are the disc brake assemblies typically mounted on the front wheels of most passenger vehicles. Generally, the disc brake assemblies include a caliper (cooperating with a brake hydraulic system), brake pads, a hub, and a rotor. The caliper supports and positions a pair of brake pads on opposing sides of a brake rotor. In a hubless brake rotor (i.e. when the rotor and hub are separate components), the rotor is secured to the vehicle hub, via a rotor hat, with a series of bolts for rotation with the hub about a vehicle spindle axis. When a vehicle driver depresses a brake pedal thereby activating the hydraulic system, the brake pads are forced together and toward the rotor to grip the friction surfaces of the rotor.
Disc brake assemblies must be maintained to manufacturers specifications throughout the life of the vehicle in order to assure optimum performance and maximum safety. However, several problems have plagued the automotive industry since the inception of disc brakes.
A significant problem in brake systems is usually referred to as “lateral runout.” Generally, lateral runout is the side-to-side movement of the friction surfaces of the rotor as it rotates with the vehicle hub about a spindle axis. Referring to
FIG. 1
, for example, there is shown a rotor having friction surfaces on its lateral sides. A rotor is mounted on a vehicle hub for rotation about the horizontal spindle axis X. In an optimum rotor configuration, the rotor is mounted to rotate in a plane Y that is precisely perpendicular to the spindle axis X. Generally, good braking performance is dependant upon the rotor friction surfaces being perpendicular to the spindle's axis of rotation X and parallel to one another (“parallelism”). In the optimum configuration, the opposing brake pads will contact the friction surfaces of the rotor at perfect 90 degree angles and will exert equal pressure on the rotor as it rotates. More typically, however, the disc brake assembly will produce at least a degree of lateral runout that deviates from the ideal configuration. For example, a rotor will often rotate in a canted plane Y′ and about an axis X′ which is a few thousandths of an inch out of axial alignment with the spindle (shown in exaggerated fashion in FIG.
1
). In this rotor configuration, the brake pads, which are perpendicular to the spindle axis X, will not contact the friction surfaces of the rotor along a constant pressure plane.
The lateral runout of a rotor is the lateral distance that the rotor deviates from the ideal plane of rotation Y during a rotation cycle of the rotor. A certain amount of lateral runout is inherently present in the hub and rotor assembly. This lateral runout often results from defects in individual components. For example, rotor friction surface runout results when the rotor friction surfaces are not perpendicular to the rotor's own axis of rotation, rotor hat runout results when the hat connection contains deviations that produce an off center mount, and stacked runout results when the runouts of the components are added or “stacked” with each other. An excessive amount of lateral runout in a component or in the assembly (i.e. stacked runout) will generally result in brake noise, pedal pulsation, and a significant reduction in overall brake system efficiency. Moreover, brake pad wear is uneven and accelerated with the presence of lateral runout. Typically, manufacturers specify a maximum lateral runout for the friction surfaces, rotor hat, and hub that is acceptable for safe and reliable operation.
After extended use, a brake rotor must be resurfaced in order to bring the brake assembly within manufacturers specifications. This resurfacing is typically accomplished through a grinding or cutting operation. Several prior art brake lathes have been used to resurface brake rotors. These prior art lathes can be categorized into three general classes: (1) bench mounted lathes; (2) on-car caliper-mounted lathes; and (3) on-car hub mounted lathes. As discussed below, the on-car hub mounted lathes have proven to be the most reliable and accurate rotor refinishing lathes in the industry.
Bench mounted lathes, for example, that disclosed in U.S. Pat. No. 3,540,164 to Lanham, are inefficient and do not have rotor matching capabilities. In order to resurface a rotor on a bench mounted lathe, the operator is first required to completely remove the rotor from the hub assembly. The operator then mounts the rotor on the bench lathe using a series of cones or adapters. After the cutting operation, the operator remounts the rotor on the vehicle spindle. Even if the rotor is mounted to the lathe in a perfectly centered and runout free manner, runout between the rotor and hub is not accounted for in the bench lathe resurfacing operation. In addition, bench lathes are susceptible to bent shafts which introduce runout into a machined rotor. This runout is then carried back to the brake assembly where it may be added with hub runout to produced a stacked runout effect.
Similarly, caliper-mounted lathes, for example, that disclosed in U.S. Pat. No. 4,388,846 to Kopecko et al., have had limited success in compensating for lateral runout, but require time consuming manual operations. During a rotor refinishing procedure, the brake caliper must first be removed in order to expose the rotor and hub. Once removed, the caliper mounting bracket is freed and can be used to mount an on-car caliper-mount lathe. The caliper-mount lathes are wholly unacceptable for many reasons including the lack of a “rigid loop” connection between the driving motor and cutting tool and the inability to assure a perpendicular relationship between the cutting tools and the rotor. Moreover, the caliper-mount lathes do not have any reliable means for measuring and correcting lateral runout. Typically and in much the same manner as described below with reference to the hub mounted lathes, a dial indicator is utilized in determining the total amount of lateral runout in the disc assembly. This measurement technique is problematic in terms of time, accuracy and ability of automechanics to comfortably use the equipment.
On-car hub mounted lathes, for example, that disclosed in U.S. Pat. No. 4,226,146 to Ekman, assigned to the assignee of the instant application, and incorporated by reference into the disclosure herein, have proven to be the most accurate and efficient means for resurfacing the rotor.
Referring now to
FIG. 2
, there is shown an Ekman type on-car disc brake lathe
10
for mounting to the hub of a vehicle
14
. The lathe
10
includes a body
16
, driving motor
18
, adapter
20
, and cutting assembly
22
. The lathe is also provided with a stand and anti-rotation post (not shown), either of which can be used to counter the rotation of the lathe during a resurfacing operation. After the brake caliper is removed, the adapter
20
is secured to the hub of the vehicle
14
by using the wheel lug nuts. The lathe body
16
Newell Harold
Wiggins John
Fish & Richardson P.C.
Joseph B. Willey
Tsai Henry
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