IPGATE AG – Patent Family E138c · Area-Switchable DAP Technology with Active Pressure Reduction

E138c – Area-Switchable DAP Technology
with Active Pressure Reduction

Dual-circuit DAP pressure supply with active pressure reduction via DAP return stroke. 3 independent inventions · 3 granted patents · US · DE · CN

Applicant	IPGATE AG, Churerstrasse 160B, 8808 Pfäffikon (CH)
Inventors	Heinz Leiber, Dr. Anton van Zanten, Dr. Thomas Leiber, Christian Köglsperger, Valentin Unterfrauner
Priority / Filing Date	August 13, 2014 (DE 10 2014 109 628.8)
PCT Application	PCT/EP2015/068696
Technology	Area-switchable DAP technology with active pressure reduction (dual-circuit pressure supply via DAP forward stroke / return stroke; active pressure reduction via DAP return stroke)
Innovations	3 independent inventions

Granted Patents

Jurisdictions

Independent Inventions

2014

Priority

IBS2 / B1

Technology Basis

Dual-Circuit DAP Pressure Supply
with Active Pressure Reduction

Patent family E138c describes an actuation system for vehicle brakes in which an electrically driven double-acting piston (DAP) supplies both brake circuits in a dual-circuit system — with each stroke direction directly assigned to one brake circuit — and actively reduces pressure without separate outlet valves.

The E138c (E138WO-TA1) patent family describes an actuation system in which the DAP serves as a complete two-circuit pressure source: the forward stroke and return stroke (working chambers 10a/10b) are each directly assigned to one brake circuit. A switching valve enables connection between the two chambers for area switching and pressure equalization. In addition, the DAP actively reduces pressure in the brake circuits — either only in the forward stroke or in both strokes — eliminating the need for separate outlet valves and supporting MUX operation and highly dynamic ABS control.

The E138c patent family comprises three granted patents in the jurisdictions US (US10,759,404 B2), DE (DE112015003240B4), and CN (CN107107890B). Together with E136, E138, E139, and E140, E138c forms the complete network of property rights for continuous DAP delivery technology in IP portfolio B1.

DE US CN

Development History

The E138c patent family was developed as a targeted extension of the basic double-acting piston (DAP) concept introduced in E136 and E138. While E136 and E138 established the fundamental principle of bidirectional pressure delivery, E138c addresses the specific requirement of dual-circuit supply from a single DAP unit — a prerequisite for fail-safe brake-by-wire systems at SAE L4/L5 autonomy levels.

The decisive insight was that by directly assigning the forward stroke to brake circuit 1 (BK1) and the return stroke to brake circuit 2 (BK2), an inherently redundant, fail-operational pressure supply is achieved without additional feed valves. The further integration of active pressure reduction via the DAP itself eliminates the need for separate outlet valves in ABS operation — reducing system complexity and improving pressure modulation dynamics.

Prior Art Limitation: Conventional single-acting pressure supply units require separate outlet valves for pressure reduction and cannot supply two brake circuits independently from a single piston unit — limiting fault tolerance and increasing system complexity.

E138c Solution: The DAP acts as a complete two-circuit pressure source. Stroke-direction-based circuit assignment enables fail-operational dual-circuit supply, while active pressure reduction via the DAP return stroke eliminates the need for dedicated outlet valves.

Three Independent Inventions

Each invention addresses a distinct functional aspect of the dual-circuit DAP architecture and is independently protected across US, DE, and CN.

Invention 1

Dual-Circuit DAP Pressure Supply

CN A1 · US A1

Actuation system with master cylinder (first pressure source) and DAP (second pressure source). DAP supplies BK1 in the forward stroke and BK2 in the return stroke; working chambers 10a/10b each assigned to one brake circuit. US A1 uses OR logic: either forward/return stroke OR working chambers assigned to circuits — broader formulation.

Invention 2

Active DAP Pressure Reduction

DE A1

Independent German claim: In addition to dual-circuit pressure supply, the DAP actively reduces pressure — either only in the forward stroke OR in both forward and return strokes. Eliminates separate outlet valves; supports MUX operation and highly dynamic ABS control without additional valve hardware.

Invention 3

DAP Pressure Build-Up / Reduction via Floating Piston

CN A23 · US A22 · DE A23

Method: Pressure in at least one brake circuit is changed via DAP movement. Pressure build-up and/or reduction in two circuits separated by floating pistons (SK) of the first pressure source. The floating piston provides hydraulic circuit separation — central prerequisite for two-circuit fail-safe operation. Essentially identical in all three jurisdictions.

Section 1 · Invention Overview

Categories, Descriptions & Keywords

All three independent invention concepts. The CN/US formulations differ in claim breadth for Invention 1; DE A1 provides an independent protection scope for active pressure reduction.

Invention	Cat.	Description	Keyword
E138c A1 CN A1 · US A1	Device	Actuation system with master cylinder (first pressure source) and DAP (second pressure source). DAP supplies BK1 in the forward stroke and BK2 in the return stroke; forward stroke/return stroke or working chambers 10a/10b each assigned to a brake circuit for dual-circuit pressure supply. Switching valve enables chamber connection for area switching and pressure equalization. US A1 is more broadly formulated with OR logic.	Dual-circuit DAP pressure supply
E138c DE A1	Device	Independent German claim: In addition to dual-circuit supply via stroke direction assignment, the DAP actively reduces pressure in the brake circuits — either only in the forward stroke or in both forward and return strokes. Eliminates need for separate outlet valves; enables MUX operation and highly dynamic ABS control.	Active DAP pressure reduction
E138c A23/A22 CN A23 · US A22 · DE A23	Method	Method of operation: Pressure in at least one brake circuit is changed by means of DAP movement. Pressure build-up and/or pressure reduction in two brake circuits separated by floating pistons (SK) of the first pressure source is achieved by movement of the DAP. The floating piston provides hydraulic circuit separation — a central prerequisite for two-circuit fail-safe operation. Essentially identical in CN, US, and DE.	DAP pressure control via floating piston

Section 1a · Family Overview

Jurisdictions & Status

All members of the E138c patent family as of February 2026. All three rights are granted.

File No.	Country	Status	Type	Application No.	Filed	Grant No.	Granted
E138CWOUS	US	Granted	Patent	15/503,554	Aug. 13, 2015	US10,759,404 B2	Sep. 1, 2020
E138CWODE	DE	Granted	Patent	112015003240.1	Aug. 13, 2015	DE112015003240B4	Feb. 9, 2023
E138CWOCN	CN	Granted	Patent	201580055031.X	Aug. 13, 2015	CN107107890B	Jan. 8, 2021