E112 — Electric Motor Brake Booster — IBS Basic Core

E112DE — BGH X ZR 91/23 (Judgment of July 17, 2025)

Subject matter: Braking system with an electric motor-driven brake booster (claim for the device). The core invention is the control of the brake booster based on a displacement difference between the piston and the brake actuator — the basic principle of the IBS Basic displacement control according to measurement principle A2 — whereby a dead stroke (jump-in phase, Δs) is provided when the brake is not actuated.

Why the patent is patentable

a) Novelty over NK2 (closest prior art): The Federal Court of Justice (BGH) found that NK2 does not disclose essential features — in particular, the separate detection of the piston position and the resulting displacement difference are missing.

However, NK2 does not address whether the position of the piston is also detected by a sensor, as provided for in feature 6.1. Consequently, there is also a lack of disclosure of feature 6.3.

— BGH X ZR 91/23, paras. 91–92

Contrary to the opinion of the Patent Court, feature 7 is also not anticipated by NK2. […] Since NK2 does not provide for the detection of the piston's position and thus also does not detect the possible displacement difference between the piston and the brake actuator, the evaluation of this displacement difference for controlling the drive of the brake booster is also not disclosed.

— BGH X ZR 91/23, paras. 93–95

b) Inventive step — Subject matter not suggested by the prior art:

The subject matter of the contested patent is not suggested by the prior art. […] However, NK1 does not provide for a free stroke within the meaning of feature 10. The plaintiff does not demonstrate how the prior art could have provided an incentive to modify the braking system described in NK1 such that it exhibits such a free stroke in the unactuated state.

— BGH X ZR 91/23, paras. 98–100

There is no indication in the prior art that the braking system according to NK2 should be supplemented with a sensor for determining the piston position. […] Therefore, there is no suggestion to provide a sensor for determining the piston position and to control the brake booster in dependence on a possible displacement difference between the piston and the brake actuating device.

— BGH X ZR 91/23, paras. 102–105

Contrary to the plaintiff's view, it cannot be regarded as technically arbitrary whether a (single) sensor is used to detect relative movement between the plunger piston and the auxiliary piston […] or whether a combination of a sensor for detecting the piston position and a sensor for detecting the brake actuator is used for this purpose.

— BGH X ZR 91/23, para. 106

E112DE1 — BGH X ZR 134/23 (Judgment of September 18, 2025)

Subject matter: Method for controlling an electric motor-based brake force booster. The process patent protects the methodological steps of the IBS Basic Differential Travel Control: detect piston travel via a rotary encoder (= rotary encoder of the EC motor), detect the stroke of the actuator, determine the travel difference Δh, and use it for control — including the idle stroke Δs (jump-in phase).

Why the patent is valid

a) Novelty — NK5 does not disclose the two-sensor methodology:

Unlike what is provided for in Patent Claim 1, NK5 discloses neither the detection of the travel of the master cylinder piston nor the determination of the difference between the travel of this piston and the travel of the brake actuator by two sensors and their use to control the electric motor-driven brake force amplification.

— BGH X ZR 134/23, para. 88

b) Inventive step — No suggestion for modification:

NK1 provides no suggestion to modify the method provided for in NK5 — which involves using a single sensor to detect the relative movement between the plunger piston and the auxiliary piston and to use this for controlling the brake booster — to the effect that, instead, two sensors are used to determine, on the one hand, the piston stroke of the master cylinder and, on the other hand, the stroke of the brake actuator, and the data thus obtained is used to control the electric brake booster.

— BGH X ZR 134/23, para. 91

According to the NK5 doctrine, the position of the main brake cylinder piston is irrelevant for determining the assist force. Therefore, there is no basis for providing a sensor to determine the piston position and for controlling the brake booster based on a possible difference in travel between the piston and the brake actuator.

— BGH X ZR 134/23, para. 94

c) Admissibility of the method claim from the parent application:

Contrary to the plaintiff's view, it is sufficiently clear from BP2 that protection is claimed not only for a device but also for a method. In particular, the parent application already explains that the displacement difference is derived from the signals of the pedal stroke sensor and the rotation angle sensor, and that the values determined in this way are used to control the brake booster.

— BGH X ZR 134/23, paras. 98–99

E112DE2 — BGH X ZR 133/23 (Judgment of August 21, 2025)

Subject: Braking system with an electric motor-driven brake booster and specific ABS functionality. This patent expands the IBS Basic concept to include shunt-based pressure control in ABS operation (motor current proportional to pressure, no pressure sensor required) as well as specific ABS features (force application/adjustment of the actuator via spindle/piston). Special feature: The appeal was admissible but only partially justified — the main claim and auxiliary claim 1 failed because NK2 disclosed a dead stroke; only auxiliary claim 2, with the additional shunt features (current measurement for ABS without a pressure sensor), was successful.

Why the patent is valid

a) Original disclosure of the shunt features:

The parent application describes that, to simplify the system — particularly for ABS — the motor current can be measured via a shunt. The motor current is proportional to the motor torque and thus to the pressure. This makes it possible to dispense with redundant sensors.

— BGH X ZR 133/23, para. 85

b) Inventive step — subject matter not suggested by the prior art:

Contrary to the opinion of the Patent Court, the subject matter of Patent Claim 1 is not suggested by the prior art.

— BGH X ZR 133/23, para. 89

While there may have been braking systems in the prior art that disclose a combination of a sensor for determining the position of the piston and a sensor for determining the position of the brake actuator, there is no reason to modify the braking system described in NK2 accordingly.

— BGH X ZR 133/23, para. 99

According to NK2, the position of the piston is not relevant for determining the assist force. Neither the auxiliary piston nor the plunger piston can be classified as a piston within the meaning of Patent Claim 1. Therefore, there is no suggestion to provide a sensor for determining the piston position […] and to control the brake booster in dependence on a possible displacement difference between the piston and the brake actuator.

— BGH X ZR 133/23, para. 102