Traveling hydraulic stepless transmission

Patent metadata

Field	Value
Publication number	US-11079014-B2
Application number	US-201916590069-A
Country	US
Kind code	B2
Filing date	Oct 1, 2019
Priority date	Oct 1, 2018
Publication date	Aug 3, 2021
Grant date	Aug 3, 2021

Abstract

A traveling hydraulic stepless transmission (“HST”), ensures stopping of a vehicle on a slope under high load conditions, maintains stopping the vehicle on flat ground under low load conditions, and enables smooth starting from a stop. The HST includes a neutral check valve (“NCV”) and an internal damping system (“IDS”). The NCV includes a first orifice that opens a first oil passage to a transaxle case when a pressure in the first oil passage is equal to or less than a predetermined pressure, and that connects the second oil passage to the transaxle case when a pressure in a second oil passage is equal to or less than the predetermined pressure. The IDS includes second orifices that connect a high pressure side of the oil passages to the transaxle case when a discharge rate of the hydraulic pump is equal to or less than a predetermined discharge rate.

First claim

What is claimed is:

1. A traveling hydraulic stepless transmission, comprising:
a hydraulic pump;
a movable swash plate disposed in the hydraulic pump;
a hydraulic motor;
a closed circuit that fluidly connects the hydraulic pump and the hydraulic motor comprising a first oil passage and a second oil passage; and
an internal damping system comprising:
a pair of pistons individually disposed in each of the first oil passage and the second oil passage;
a plate that cooperates with the movable swash plate and is in sliding contact with the pair of pistons;
a respective hole disposed on a surface of each of the pair of pistons in contact with the plate; and
a pair of grooves formed on a surface of the plate in contact with the pistons, each of the grooves formed in a portion of a path the hole disposed on each of the pistons traces on the surface of the plate when the plate is moved,
wherein the plate is configured to be attachable to and detachable from one of a pair of trunnion shafts.

2. The traveling hydraulic stepless transmission according to claim 1 , wherein the plate comprises a sealing part that seals the hole in the pistons when the plate is turned to a neutral position.

3. The traveling hydraulic stepless transmission according to claim 1 , wherein the movable swash plate is formed with a protrusion having a pair of protrusion-side flat portions parallel to a normal direction of the trunnion shafts of the movable swash plate,
wherein the plate is formed with a recess having a pair of parallel recess-side flat portions corresponding to the pair of protrusion-side flat portions, and
wherein the plate is attached to the movable swash plate by fitting the protrusion to the recess.

4. A traveling hydraulic stepless transmission, comprising:
a tank of hydraulic oil;
a hydraulic pump of a variable displacement type;
a capacity adjustment part disposed in the hydraulic pump;
a hydraulic motor;
a closed circuit that fluidly connects the hydraulic pump and the hydraulic motor in a closed circuit; and
a pair of neutral check valves configured for replenishment of hydraulic oil that are disposed individually in each of a first oil passage and a second oil passage of the closed circuit,
wherein each of the pair of check valves comprises:
a valve housing that is a cylindrical housing;
a first oil chamber formed on one end side of the valve housing in a cylinder axial direction;
a second chamber formed on another end side of the valve housing in the cylinder axial direction;
a communication hole connecting the first oil chamber and the second chamber;
an opening to fluidly connect the first oil chamber to the first oil passage or the second oil passage;
a first open hole to fluidly connect the second chamber to the tank;
a cylindrical body inserted through the communication hole to be displaceable in the cylinder axial direction, wherein the cylindrical body is formed with an oil hole passing through in a axial direction of the cylindrical body, an orifice opened on an outer peripheral surface of the cylindrical body and communicating with the oil hole, and a first seat surface formed at an end portion on a side facing the first oil chamber;
a spring member configured to bias the cylindrical body toward the first oil chamber; and

a valve body housed in the first oil chamber,
wherein the valve housing is formed with a second seat surface positioned on the first oil chamber side in the cylinder axial direction;

wherein when a pressure in either the first oil passage or the second oil passage is equal to or less than the biasing force acting on the cylindrical body, the valve body of the corresponding neutral check valve is brought into pressure contact with the first seat surface and separated from the second seat surface by the cylindrical body being displaced to the first oil chamber side, and the first oil passage and the second oil passage are made to fluidly communicate with the tank through the orifice, and
wherein when a pressure in the first oil passage or the second oil passage becomes higher than the biasing force of the spring member, the valve body of the corresponding neutral check valve is displaced to the second chamber side against the biasing force of the spring member, and is brought into pressure contact with the second seat surface, which shut off fluid communication between the a high pressure side of the first oil passage or the second oil passage and the tank.

5. The traveling hydraulic stepless transmission according to claim 4 , further comprising an internal damping system, comprising:
a pair of pistons individually disposed in the first oil passage and the second oil passage;
a plate connected to a control arm and in sliding contact with the pair of pistons;
a respective hole disposed on a surface of each of the pair of pistons in sliding contact with the plate; and
a pair of grooves formed on a surface of the plate in sliding contact with the pair of pistons, each of the grooves formed in a portion of a path the hole formed on each of the pistons traces on the surface of the plate when the plate is moved,
wherein the plate is configured to drain hydraulic oil from the first oil passage or the second oil passage to the tank through the groove when the groove is aligned with the hole, wherein oil is drained when the capacity adjustment part passes through a predetermined range extending beyond a neutral position.

Assignees

• Kanzaki Kokyukoki Mfg Co Ltd

Inventors

• Murashima Daisuke
• Tsukamoto Michio

Classifications

• B60K17/10

  of fluid gearing · CPC title

• F16H61/4026

  Control of low pressure · CPC title

• F16H61/4035

  Control of circuit flow · CPC title

• F16H61/439 Primary

  Control of the neutral position, e.g. by zero tilt rotation holding means · CPC title

• F16H39/06 Primary

  pump and motor being of the same type · CPC title