Coaxial push rod and hollow screw ball nut drive for master cylinder

• US 4,918,921 A
• Filed: 10/22/1987
• Issued: 04/24/1990
• Est. Priority Date: 10/22/1987
• Status: Expired due to Term

• Current Assignee: Luk Leamington Limited
• Original Assignee: Automotive Products PLC (Whitnash Plc)
• Inventors: Leigh-Monstevens, Keith V., Mabee, Brian D.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/111,294
• Time in Patent Office: 915 Days
• Field of Search: 60/538, 60/545, 60/582, 60/550, 74/388 R, 74/388 PS, 74/459, 310/93, 310/191, 310/209, 310/83, 180/79.1
• US Class Current: 60/545
• CPC Class Codes: B60T 13/745 acting on a hydraulic system, e.g. a master cylinder
• CPC Class Codes: F16D 2048/0212 Details of pistons for master or slave cylinders especially adapted for fluid control for other details of pistons in master or slave cylinders F16D2025/081 or F16D25/082
• CPC Class Codes: F16D 2125/10 Plural pistons interacting by fluid pressure, e.g. hydraulic force amplifiers using different sized pistons
• CPC Class Codes: F16D 2125/40 Screw-and-nut
• CPC Class Codes: F16D 2500/1024 combined with hydraulic actuation
• CPC Class Codes: F16D 2500/3026 Stroke
• CPC Class Codes: F16D 2500/5114 Failsafe
• CPC Class Codes: F16D 48/04 providing power assistance
• CPC Class Codes: Y10T 74/19535 Follow-up mechanism

Abstract

An electrically driven master cylinder assembly and various vehicle control systems utilizing the master cylinder assembly. Several forms of master cylinder assemblies are disclosed. In the preferred form, the assembly includes an electric DC motor directly coupled to a master cylinder unit with the central axis of the motor coaxial with the central axis of the bore of the master cylinder, a ball nut is positioned within the housing of the electric motor for rotation with the armature of the motor, and a ball screw is positioned on the axis of the motor and is driven linearly in response to rotation of the armature. The free end of the ball screw engages the piston of the master cylinder so that energization of the motor operates to move the piston of the hydraulic cylinder linearly within the bore of the hydraulic cylinder to discharge fluid from the outlet of the hydraulic cylinder for delivery to a slave cylinder to perform an appropriate vehicle control function such as engagement or disengagement of the vehicle clutch or actuation of the vehicle braking system.

Claims

1. An electric motor comprising:

(a) a housing;

(b) an annular armature mounted for rotation in said housing;

(c) a nut positioned within and mounted for rotation with said armature;

(d) an annular screw positioned within and threadably engaging said nut and defining a central bore;

(e) a push rod positioned concentrically and slidably within said annular screw bore and projecting out of one end of said screw bore; and

(f) one way drive means between said push rod and said screw driving said push rod linearly in response to linear movement of said screw in one direction while allowing relative axial movement between said push rod and said screw.

2. An electric motor comprising:

(a) a housing;

(b) an annular armature mounted for rotation in said housing;

(c) a nut positioned within and mounted for rotation with said armature;

(d) an annular screw positioned within and threadably engaging said nut and defining a central bore extending axially through said screw;

(e) a first push rod positioned concentrically within said annular screw bore, drivingly connected to said annular screw, and projecting at its outboard end out of one end of said screw bore; and

(f) a second push rod having its inboard end disposed within said screw bore in juxtaposition to the inboard end of said first push rod and projecting at its outboard end out of the other end of said screw bore.

3. A master cylinder assembly comprising:

(a) an electric motor including a housing and a hollow armature;

(b) a hydraulic master cylinder including a housing rigid with said motor housing, a cylinder defining an elongated bore, a piston movable linearly and slidably in said bore, inlet means in said cylinder for admitting hydraulic fluid into said bore from a reservoir, and an outlet fitting in said cylinder communicating with said bore and operative to convey hydraulic fluid out of said bore for delivery to a slave device in response to linear movement of said piston in said bore;

(c) nut means driven by said armature;

(d) an annular output shaft defining a bore extending axially therethrough and having a threaded portion threadably engaging said nut means so that rotation of said armature upon energization of said motor linearly advances said output shaft;

(e) a first push rod drivingly connected at its outboard end to said piston, having its inboard end disposed within said output shaft bore, and drivingly connected to said output shaft so that said piston is moved linearly in response to linear advancement of said output shaft; and

(f) a second push rod having its inboard end disposed within said output shaft bore in juxtaposition to the inboard end of said first push rod and extending at its outboard end out of the end of said output shaft remote from said master cylinder.