NEUTRAL START FOR HYDROSTATIC TRANSMISSION

MISE EN MARCHE D'UN MOTEUR AVEC TRANSMISSION HYDROSTATIQUE AU POINT MORT

English Abstract

NEUTRAL START FOR HYDROSTATIC TRANSMISSION
Abstract of the Disclosure
A hydrostatic transmission including a pump and motor unit
wherein the pump unit is displaceable effectuated by an
operative member integral to the pump unit. A neutral start
switch communicating with a carrying machine is mounted in the
pump unit to contact the operative member in a manner causing
the neutral start switch to become operative only when the
operative member is assuming a neutral position.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. In a radial piston hydrostatic transmission including a
pump and motor unit in fluid communication, said pump unit
having a rotor carrying a plurality of radial piston balls, a
control ring pivotally mounted in a pump housing around said
rotor, a member pivotally received in a seat on said control
ring, a control shaft rotatably mounted in said pump housing
having a transversely extending linking arm slidably received in
said member such that rotation of said control shaft causes said
control ring to pivot, wherein the improvement comprises means
for detecting a neutral location of said control ring and for
providing resistance to creep of said control ring in said
neutral location, said means including said member having a
concavity form on one surface, and a switch having a contact
surface matingly sized to said concavity, said contact surface
of said switch to be received in said concavity when said
control ring occupies said neutral location.

Description

66
NEUTRAL START FOR llYDROSTATIC TRANSMISSION
Background of the Invention
This invention relates to radial piston hydros-tatic
transmissions and, more particularly, to a means of assuring a
neutral transmission settiny.
Radial piston hydrostatic transmissions are commonly used in
the smaller variety o~ of~-road vehicles such as small
tractors. Unlike a conventional gear transmission which is
positive engaging, a radial piston hydrostatic -transmision is
continuously engaged. As a result, the transmission control
linkage assemble must be able to position a control ring within
the hydrostatic transmission with greater precision in order to
achieve a true neutral transmission mode. Such control linkage
assemblies require frequent adjustment and are incapable of
assuring a neutral transmission mode.
Another problem encountered by radial piston hydrostatic
transmission occures as a result of control ring creep. Once
such transmissions are placed in a functional neutral mode, it
is not uncommon for the transmission control ring to creep
within the slack range of the control linkage assembly. Control
ring creep represents the unintended transmission of power.
Summary~ the Inventio_
It is an objective of the present invention to provide a
visual means of determining whether a radial piston hydrostatic
transmission is in a neutral mode.
It is a ~urther objective of the present invention to
present a means o~ preventing control ring creep.
A conventional radial piston hydrostatic transmission
includes a rotor containing a plurality oE radial ball piston.
A control ring is pivotably mounted within the transmission's
housing around the rotor and ball pistons. A pivot member
actuated by a control lever is seated in the control riny
responsible ~or positioning the control ring. A neutral start
switch is activated when the control ring enters th~ neutral
region and seat within a concavity in the pivot member when the
control ring
is in the neutral position. The s~itch also functions to resist
control ring creep.
4 ~ 1 ~ r~
o

~2~666
Brief De cription of the Drawings
FIG. 1 is a sectioned view of a hydrostatic transmission
pump and motor units employing radial ball pistons.
FIG. 2 is a sectioned view of -the radial ball fixed
displacement piston motor unit.
FIG. 3 is a sectioned view of the radial ball piston
hy~rostatic pump unit with a variably displaceable control rin~
and control lever.
Description of the Preferred Embodiment
Referring to FIGS. 1, 2 and 3, a conventional radial piston
hydrostatic transmission, generally indicated as 11, includes a
housing 13 containing a pump unit 15 and motor unit 17 in fluid
communication. The pump unit 15 consists of an input shaft 19
driving a rotor 21 containing a plurality of radial ball pistons
230 A control ring 27 is placed around the rotor 21 and pistons
23 pivotably mounted within the housing by pivot pin 2g. The
pump unit 15 consists of an output shaft 31 driven by rotor 33
carrying radial ball pistons 35.
The control ring 27 includes a seat 37 occupied by a pivot
member 39 in a manner allowing the member 39 to pivot. A
portion of a control lever 41 intrudes into the housing and is
rotatably mounted therein by any conventional means. The lever
41 has a linking pin 43 fixably mounted thereto by any
conventional means extending into the pivot member 39. It is
observed that by rotating the control lever 41 the communication
between the linking in 43 and pivot member 39 causes the control
ring 27 to pivotally displace about pin 29. A conventional
neutral start switch 47 is ~ixably mounted to the housing 13 to
extend within the housing having its contact surface 49 in
communication with the pivot member 39. The pivot member 39 has
formed therein a concavity 51 which receives the contact surface
49 of the neutral start switch 47 when the control ring is in a
neutral position, thereby placing the switch 47 in an operative
mode. Should the control ring 27 be in a position other than
neutral, the contact surface ~9 of switch 47 is in communication
with member 39 to place the switch 47 in an inoperative mode~
Further benefit is derived by a forced contract between contact
surface 49 and pivot member 39 and the release of the forced
contact when surface 49 is received by concavity 51 in that when
the surface 49 is received by concavity 51 in that when the
~0
- 2 -

iL21~66~
1 lrface 49 is received by concavity 51 the transmission 11 is
held in neutral to preven-t transmission creep.
The present invention has been described in its preferred
embodiment as it relates to a radial hydrostatic transmission.
The $ull scope of the invention should not`be thought as limited
by the preferred embodiment and applies to all equivalent
embodiments~ The fu].l scope of the present invention is defined
by the appended claim.
- 3 -