A running control device of a vehicle executes a normal running mode with an engine coupled to drive wheels, a first inertia running mode with the engine stopped during running and an engine brake force reduced as compared to the normal running mode, and a second inertia running mode with the engine rotating during running and the engine brake force reduced as compared to the normal running mode. A determining portion determines a necessity of a brake negative pressure during the first or second inertia running mode. The necessity of the brake negative pressure is a condition for returning from the first inertia running mode and the second inertia running mode to the normal running mode. An upper limit value of the necessity of the brake negative pressure for returning from the first inertia running mode is smaller than that for returning from the second inertia running mode.

A running control device of a vehicle executes a normal running mode with an engine coupled to drive wheels, a first inertia running mode with the engine stopped during running and an engine brake force reduced as compared to the normal running mode, and a second inertia running mode with the engine rotating during running and the engine brake force reduced as compared to the normal running mode. A determining portion determines a necessity of a brake negative pressure during the first or second inertia running mode. The necessity of the brake negative pressure is a condition for returning from the first inertia running mode and the second inertia running mode to the normal running mode. An upper limit value of the necessity of the brake negative pressure for returning from the first inertia running mode is smaller than that for returning from the second inertia running mode.

An electric brake booster vacuum pump of a vehicle has a deactivation level determined according to a percentage of maximum available vacuum at the instant altitude of the vehicle. The activation level may be determined in the same way. The invention provides for earlier on-switching of a vacuum pump at altitude, while ensuring that the off-switching value is achievable at low atmospheric pressure.

An electric brake booster vacuum pump of a vehicle has a deactivation level determined according to a percentage of maximum available vacuum at the instant altitude of the vehicle. The activation level may be determined in the same way. The invention provides for earlier on-switching of a vacuum pump at altitude, while ensuring that the off-switching value is achievable at low atmospheric pressure.

In a hydraulic unit of a vehicle brake system having a first pump element, which is assigned to a first brake circuit, and a second pump element, which is assigned to a second brake circuit, the second pump element has a different delivery from the first pump element.

In a hydraulic unit of a vehicle brake system having a first pump element, which is assigned to a first brake circuit, and a second pump element, which is assigned to a second brake circuit, the second pump element has a different delivery from the first pump element.

A piston assembly for an unloader valve of an air compressor includes an unloader piston having an end portion with a first bore of a first bore diameter, an intermediate portion with a second bore of a second bore diameter and an opposite end portion with a third bore of a third bore diameter; a coil spring having a central opening, one end portion disposed in the second bore of the unloader piston and an opposite end portion extending into the first bore of the unloader piston; and a balance piston including a head portion having a diameter to be disposed in the first bore of the unloader piston, and a stem portion extending from the head portion into the central opening of the coil spring and having a diameter smaller than the diameter of the head portion. The diameter of the stem portion at an end portion facing away from the head portion substantially corresponds to an inner diameter of the central opening of the coil spring. The balance piston includes a heat protection element.

A piston assembly for an unloader valve of an air compressor includes an unloader piston having an end portion with a first bore of a first bore diameter, an intermediate portion with a second bore of a second bore diameter and an opposite end portion with a third bore of a third bore diameter; a coil spring having a central opening, one end portion disposed in the second bore of the unloader piston and an opposite end portion extending into the first bore of the unloader piston; and a balance piston including a head portion having a diameter to be disposed in the first bore of the unloader piston, and a stem portion extending from the head portion into the central opening of the coil spring and having a diameter smaller than the diameter of the head portion. The diameter of the stem portion at an end portion facing away from the head portion substantially corresponds to an inner diameter of the central opening of the coil spring. The balance piston includes a heat protection element.

When a leak occurs in one service circuit of a multi-circuit braking system, the leak can prevent replenishing the non-leaking service reservoir. To address this problem, a shared backup reservoir can be used to replenish the non-leaking service reservoir. A valve can be used to allow flow from the backup reservoir to whichever service reservoir is under higher pressure, as low pressure would indicate a leak. Additional valve(s) can be used to impede flow from the service reservoirs to the backup reservoir to prevent the service reservoirs from being drained if the backup reservoir is subject to a leak.

When a leak occurs in one service circuit of a multi-circuit braking system, the leak can prevent replenishing the non-leaking service reservoir. To address this problem, a shared backup reservoir can be used to replenish the non-leaking service reservoir. A valve can be used to allow flow from the backup reservoir to whichever service reservoir is under higher pressure, as low pressure would indicate a leak. Additional valve(s) can be used to impede flow from the service reservoirs to the backup reservoir to prevent the service reservoirs from being drained if the backup reservoir is subject to a leak.