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Hydraulic Retarder with Accumulator

IP.com Disclosure Number: IPCOM000244926D
Publication Date: 2016-Feb-01
Document File: 3 page(s) / 163K

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Hydraulic Retarder with Accumulator

ABSTRACT

This invention relates to requesting a brake torque from a retarder. The torque rise time of the retarder may be improved by repeatedly supplying oil from the accumulator to the retarder when a braking torque is requested from the retarder. That is, oil is supplied from the accumulator to the retarder always when the braking torque of the retarder is to be increased, regardless of if the retarder is inactive prior to a torque request, or if the retarder is already active and the braking torque is to be increased.

BACKGROUND

A retarder is a device commonly used in heavy vehicles. The retarder is configured to slow down the vehicle and to maintain a steady speed of the vehicle as it travels downhill. Friction brakes of the vehicle may thus be used to a lesser extent. Brake fading is accordingly avoided and wear of the friction brakes is reduced.

In a hydraulic retarder, a rotor of the retarder is connected to a propeller shaft of the vehicle and a stator of the retarder is fixed in relation to a chassis of the vehicle. The rotor may be connected to the propeller shaft via an output shaft of a transmission of the vehicle. As hydraulic oil is supplied to the retarder, hydro dynamic braking forces between the rotor and the stator retard the propeller shaft and thus, brake the vehicle. The more oil the retarder is filled with, the larger a braking torque of the retarder will be.

In some hydraulic retarder systems, a gear pump mounted on a retarder axle fills the retarder with oil when the retarder is activated, i.e. when a control system of the retarder requests a braking torque from retarder. When the vehicle speed is low, the retarder axle rotates at a low speed and a long time is needed for the gear pump to fill the retarder with oil. Thus, it will take a long time before the requested braking torque is obtained from the retarder. Therefore, in some retarder systems oil is stored in an accumulator and supplied from the accumulator directly to the retarder when the retarder is activated.

Patent document US 5000300 discloses a hydraulic retarder. An accumulator is utilised for initial supply of oil to the retarder, see column 3, line 62 – column 4, line 4. Thereafter, oil is supplied from a torque converter to the retarder, see column 4, lines 46 - 49.

In some retarder systems, oil is supplied from the accumulator only once when the retarder is activated. That is, oil is not supplied from the accumulator when the retarder is already active providing a low braking torque and the braking torque is to be increased. For instance, oil is not supplied from the accumulator when a retarder braking torque of e.g. 500 Nm is to be increased to e.g. 3500 Nm.

Diagrams 1a and 1b illustrate the operation of a known retarder. At t1 a braking torque is requested by a control system of the retarder, as indicated by the broken line in Dia. 1a. Emptying of the accumulator is activated as indicated in Dia. 1b, and the ret...