Shift lever assembly for minimizing jumpout

A directly mounted shift lever assembly (30) for a manually shifted vehicular transmission (16) for minimizing shift lever-induced jumpout. A counterweight (52) is mounted to the shift lever (31) in a forwardly extending manner to move the center of gravity (CG) of the resultant shift lever assembly forward of the shift lever Y--Y pivot axis (34).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to shift lever assemblies for manually 
shifted vehicular transmissions and, in particular, to shift lever 
assemblies for manually shifting vehicular transmissions which are 
specially configured to move the center of gravity of the assembly forward 
of the pivot axis of the shift lever to minimize the occurrence of shift 
lever-induced jumpout. 
2. Description of the Prior Art 
Manually shifted vehicular transmissions of the simple and/or compound 
types and of the synchronized, blocked and/or non-synchronized types are 
well known in the prior art, as may be seen by reference to U.S. Pat. Nos. 
5,000,060 and 5,390,561, the disclosures of which are incorporated herein 
by reference. 
The prior art manually shifted transmissions, especially as utilized for 
heavy-duty vehicles such as straight trucks and conventional (i.e., not 
cab-over-engine) tractor/semi-trailers, utilized a manually manipulated 
shift lever extending upwardly from a shift tower subassembly mounted 
directly on the transmission housing and interacting with a multiple-rail 
or single shift shaft shifting mechanism of the types shown in U.S. Pat. 
Nos. 4,455,883; 4,550,627; 4,920,815 and 5,272,931, the disclosures of 
which are incorporated herein by reference. 
While such transmissions are widely used and commercially successful, they 
are not totally satisfactory, as under certain severe road conditions, the 
transmissions may experience shift lever-induced jumpout (i.e., unintended 
disengagement of a gear ratio). This situation usually is associated with 
transmissions utilized in relatively heavy-duty vehicles (i.e., such as 
MVMA Class 5 and larger vehicles), which tend to have relatively long 
shift levers having relatively large shift knobs, often including master 
valving for controlling range and/or splitter shifts, at the ends thereof. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, the drawbacks of the prior art 
are minimized or overcome by the provision of a shift lever assembly for a 
manually shifted vehicular transmission having a directly mounted shift 
lever which will minimize or eliminate the occurrences of shift 
lever-induced jumpout. 
The foregoing is accomplished by the provision of a shift lever assembly 
for manually shifted transmissions having directly mounted shift levers 
which are configured to offset the center of gravity of the assemblies 
forward of the shift lever engagement (Y--Y) pivot axis. In one preferred 
embodiment, a forwardly extending counterweight is fixedly 
cantilever-mounted to the shift lever. Accordingly, it is an object of the 
present invention to provide a new and improved directly mounted shift 
lever assembly for manually shifted transmissions which will minimize 
shift lever whip-induced jumpout. 
This and other objects and advantages of the present invention will become 
apparent from a reading of the following description of the preferred 
embodiment taken in connection with the attached drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Certain terminology will be used in the following description of the 
preferred embodiment for convenience only and will not be limiting. The 
terms "upward," "downward," "rightward" and "leftward" will designate 
directions in the directions to which reference is made. The terms 
"forward" and "rearward" will refer, respectively, to the front and rear 
ends of the drive train components as conventionally mounted in the 
vehicle, being, respectively, to the left and right sides of the various 
drive train components, as illustrated in FIG. 1. The terms "clockwise" 
and "counterclockwise" will refer to rotational directions as viewed from 
the left side of the vehicle, as shown in FIG. 1. Said terminology 
includes the words above specifically mentioned, derivatives thereof and 
words of similar import. 
A typical vehicular powertrain system 10 utilizing the shift lever assembly 
of the present invention may be seen by reference to FIG. 1. Powertrain 10 
is of the type commonly utilized in heavy-duty vehicles, such as the 
conventional tractors of tractor/semi-trailer vehicles, and includes an 
engine, typically a diesel engine, 12, a master friction clutch 14 
contained within a clutch housing, a multiple-speed compound transmission 
16, and a drive axle assembly 18. The transmission 16 includes an output 
shaft 20 drivingly coupled to a vehicle drive shaft 22 by a universal 
joint 24 for driving the drive axle assembly, as is well known in the 
prior art. The transmission 16 is housed within a transmission housing 26 
to which is directly mounted the shift tower 28 of the shift lever 
assembly 30 of the present invention. 
FIG. 4 illustrates a typical shift pattern for a combined 
range-and-splitter-type compound transmission manually shifted by a 
manually operated shift lever. Briefly, the shift lever is movable in the 
side-to-side or X--X direction to select a particular ratio or ratios to 
be engaged and is movable in the fore and aft or Y--Y direction to 
selectively engage and disengage the various ratios. The shift pattern may 
include an automatic range shifting feature and manual splitter shifting, 
as is well known in the prior art. Transmissions utilizing shift 
mechanisms and shift patterns of this type are well known in the prior art 
and may be appreciated in greater detail by reference to aforementioned 
U.S. Pat. Nos. 5,000,060 and 5,390,561. 
Typically, the shift lever assembly 30 will include a shift finger or the 
like that shown) extending downwardly into a shifting mechanism 32, such 
as multiple-rail shift bar housing assembly or a single shift shaft 
assembly, as is well known in the prior art and as is illustrated in 
aforementioned U.S. Pat. Nos. 4,455,883; 4,550,627; 4,920,815 and 
5,272,931. 
In the prior art transmissions of the general type illustrated in FIG. 1 
but not incorporating the improved shift lever assembly of the present 
invention, it is known that annoying shift lever jumpout may occur if road 
conditions are severe. Briefly, shift lever jumpout is the unintended 
disengagement of the jaw clutches of a manually shifted transmission 
caused by shift lever oscillations in the Y--Y direction about the Y--Y 
pivot axis 34 of the shift lever assembly. it is the purpose of the shift 
lever assembly of the present invention to minimize the occurrences of 
such shift lever-induced jumpout. 
Referring to FIG. 1, in a typical heavy-duty vehicle powertrain, the 
engine-clutch-transmission assemblage will tend to move, during severe 
road conditions, in a vertical manner (as illustrated by arrow 36) and in 
a pivoting manner about a pivot point or axis 38 (usually located in the 
area of the vehicle clutch). As is indicated by arrow 40, an upward 
movement of the assemblage almost always is associated with a 
counterclockwise rotation of the assemblage around pivot axis 38, while, 
as indicated by arrow 42, a downward movement of the assemblage almost 
always is accompanied by a clockwise rotation of the assemblage about the 
pivot axis 38. As understood, shift lever-induced jumpout is forced by the 
inertial effects of excessive road-induced vibration in the vehicle drive 
train. This road-induced shock causes the engine-clutch-transmission 
assemblage to pitch on its mounts, as shown in FIG. 1. This pitching 
occurs at the natural frequency of the engine-clutch-transmission-mount 
system, usually between about 7 and 10 HZ. This pitching induces 
relatively high vertical, fore-aft and rotational accelerations on the 
transmission and, in particular, the shift lever assembly. The shift lever 
assembly then develops an inertial jumpout torque T.sub.J about its pivot 
34 as determined by the sum of the inertial torques thereon, as will be 
described in greater detail below and as schematically illustrated in FIG. 
2. It is noted that the typical rearward offset in transmission lever 
tends to increase the jumpout torque, whereas a forward offset tends to 
reduce jumpout torque 
As will be described in greater detail below and as is schematically 
illustrated in FIG. 3, jumpout torque T.sub.J is resisted by the shift 
rail or shift shaft detent force multiplied by its moment arm determined 
by the distance between the pivot 34 and the shift rail or shaft (i.e., 
detent torque T.sub.O). When the jumpout torque overcomes the detent 
torque, jumpout occurs. Detent force Fx may include the forces required to 
overcome a detent mechanism, torque lock in the engaged jaw clutches, and 
frictional forces in the shift mechanism. When the jumpout torque 
overcomes the detent torque, shift lever jumpout occurs. This tends to 
occur when the drive train has a very low torque, such as vehicle coast 
conditions, since the friction from so-called torque lock in the drive 
train during driving conditions tends to lock the engaged sliding clutch 
members in engagement and greatly overcomes any jumpout forces imposed 
thereon. 
As the shift lever assembly 30 itself is a dynamic system, it has its own 
natural frequency. Unfortunately, this also usually occurs between 7 and 
10 HZ. This frequency is determined by lever height, lever offset, tower 
height, and isolator stiffness. If the natural frequency of the 
engine-clutch-transmission assemblage matches that of the shift lever 
assembly, propensity for jumpout is greater because the engine-amplified 
inertial forces are amplified further by the lever resonance. 
In FIG. 2, 
T.sub.J =a.sub.X My-a.sub.Y Mx+I.varies. 
where: 
T.sub.J =Jumpout torque 
M=Mass of lever 
I=Moment of inertia of lever 
a.sub.X =Fore/aft acceleration 
a.sub.Y =Vertical acceleration 
.varies.=Angular acceleration of lever 
x=Distance between cg of lever and pivot 
y=Vertical distance between cg of lever and pivot 
cg=Center of gravity 
while in FIG. 3, 
T.sub.O =F.sub.X d 
where 
T.sub.O =Detent torque 
F.sub.X =Detent force 
d=Distance between pivot and rail. 
FIG. 2 illustrates a mathematical model for calculating the jumpout torque 
T.sub.J induced by shift lever whip. It is noted that jumpout torque will 
be applied in both the counterclockwise and clockwise directions about the 
shift lever pivot axis 34 but will tend to cause jumpout only in one of 
those two directions, depending upon the currently engaged gear ratio. In 
carefully studying this mathematical model, it may be seen that if the 
center of gravity (CG) of the shift lever assembly 30 is offset forward of 
the pivot point 34, then the upward vertical acceleration a.sub.Y of the 
shift lever assembly will produce a torque a.sub.Y Mx tending to 
counteract the torque resulting from the expected counterclockwise 
rotation of the shift lever assembly (I.varies.). Conversely, the torque 
resulting from downward acceleration of the shift lever assembly will 
produce a torque tending to counteract the torque resulting from a 
clockwise rotation of the shift lever assembly. Accordingly, Applicant has 
determined that the total jumpout torque T.sub.J resulting from shift 
lever oscillations due to the pitching of the engine-clutch-transmission 
assemblage may be reduced if the shift lever assembly is modified from its 
typical configuration such that the center of gravity of the shift lever 
assembly is offset in the forward direction from a plane 44 generally 
perpendicular to the axes of the output shaft 20 and containing the pivot 
axis 34 of the shift lever assembly. Similarly, any modification to the 
shift lever assembly which increases the forward offset of its center of 
gravity forwardly, even minimizing the rearward offset of the center of 
gravity, will tend to minimize the occurrences of shift lever-induced 
jumpout. 
Applicant has discovered that due to the tendency of the 
engine-clutch-transmission assemblage to rotate in a generally 
counterclockwise manner during upward vertical movements and to rotate in 
a generally clockwise manner during downward vertical movements about the 
pivot axis 38 of the assemblage, the inertial torque due to the vertical 
acceleration from road-induced vibration a.sub.Y Mx will tend to 
counteract the dominating torque (I.varies.) due to rotational 
acceleration, resulting in a much lower total jumpout torque about the 
pivot point. One method to accomplish this (see FIG. 7) would be to design 
the transmission 16A such that the shift tower 28A is moved rearwardly on 
the transmission such that the shift lever assembly 38 utilizes a shift 
lever 31 bent forwardly, which will tend to move the center of gravity 
thereof forwardly of a plane 44A containing the pivot axis of the shift 
lever. For many vehicle configurations, this solution may not be practical 
due to the layout of existing vehicles and the structure of existing shift 
mechanisms 32A. 
In FIGS. 1, 5 and 6; a preferred form of the present invention is 
illustrated, which is well suited for most, if not all, existing 
transmission and vehicle configurations and is well suited for 
retrofitting existing shift lever assemblies. In this preferred 
embodiment, a counterweight assembly 50 comprising a mass 52 fixedly 
cantilever-mounted to the existing shift lever 31 by a mounting means 54 
which will extend the mass forwardly of the plane 44 is provided. The mass 
of the counterweight member 52 and the length of the cantilever mounting 
means 54 is selected such that the center of gravity of the resulting 
shift lever assembly 30 will be such that the torque resulting from 
vertical accelerations will tend to counteract the torque resulting from 
pivotal accelerations. Referring to FIG. 2, this will provide best results 
in a situation where the length and mass are selected such that the 
resulting torque due to shift lever vertical acceleration, a.sub.Y Mx, 
will be generally equal to and opposed to the torque due to shift lever 
angular acceleration, I.varies.. 
FIGS. 5 and 6 show the structure of the counterweight assembly 50. Briefly, 
the mass 52 is attached to the mounting means 54, which comprises two 
separable pieces 56 and 58 defining aligned, cooperating, generally 
concave cavities 60 and 62, respectively, for clamping receipt of the 
shift lever 31 therebetween. A plurality of threaded fasteners, such as 
bolts 64 and 66, are provided for passage through through bores 68 and 70 
and threaded receipt in the interior threaded bores 72 and 74. The mass 52 
may be of a highly dense material and/or may have selectively variable 
inserts to vary the mass thereof. 
Accordingly, it may be seen that a new and improved shift lever assembly 
for manually shifted transmissions, especially manually shifted 
transmissions for heavy-duty vehicles, is provided which will minimize or 
eliminate the occurrences of shift lever-induced jumpout. 
Although the present invention has been described with a certain degree of 
particularity, it is understood that the description of the preferred 
embodiment is by way of example only and that numerous changes to form and 
detail are possible without departing from the spirit and scope of the 
invention as hereinafter claimed