A series hydraulic hybrid system for a vehicle, comprising: a hydraulic circuit comprising a first hydraulic displacement unit in fluid communication with a second hydraulic displacement unit, a hydraulic actuator, a hydraulic accumulator assembly, at least one controllable circuit valve (12a, 12b, 13a, 13b), at least one controllable actuator valve (17a, 17b), a hydraulic working pump fluidly connected or selectively fluidly connected with the hydraulic actuator for selectively pressuring the hydraulic actuator, and a control unit configured to control the at least one actuator valve (17a, 17b) and the hydraulic displacement of the hydraulic working pump; wherein the hydraulic accumulator assembly is selectively in fluid communication with the hydraulic circuit by means of the at least one controllable circuit valve (12a, 12b, 13a, 13b), wherein the hydraulic accumulator assembly is selectively in fluid communication with the hydraulic actuator by means of the at least one controllable actuator valve (17a, 17b), such that the hydraulic accumulator assembly is configured to be selectively fluidly connected with and to be selectively fluidly disconnected from the hydraulic actuator by means of the at least one actuator valve (17a, 17b) independently of a control position of the at least one circuit valve (12a, 12b, 13a, 13b), and wherein the control unit is configured to control the at least one actuator valve (17a, 17b) and to control a hydraulic displacement of the hydraulic working pump and/or a rotational speed of the hydraulic working pump such that a flow of fluid flowing towards the hydraulic actuator and/or an actuator pressure acting on the hydraulic actuator remain/remains constant when the hydraulic accumulator assembly is fluidly connected with the hydraulic actuator and/or when the hydraulic accumulator assembly is fluidly disconnected from the hydraulic actuator. a hydraulic circuit comprising a first hydraulic displacement unit in fluid communication with a second hydraulic displacement unit, a hydraulic actuator, a hydraulic accumulator assembly, at least one controllable circuit valve (12a, 12b, 13a, 13b), at least one controllable actuator valve (17a, 17b), a hydraulic working pump fluidly connected or selectively fluidly connected with the hydraulic actuator for selectively pressuring the hydraulic actuator, and a control unit configured to control the at least one actuator valve (17a, 17b) and the hydraulic displacement of the hydraulic working pump; wherein the hydraulic accumulator assembly is selectively in fluid communication with the hydraulic circuit by means of the at least one controllable circuit valve (12a, 12b, 13a, 13b), wherein the hydraulic accumulator assembly is selectively in fluid communication with the hydraulic actuator by means of the at least one controllable actuator valve (17a, 17b), such that the hydraulic accumulator assembly is configured to be selectively fluidly connected with and to be selectively fluidly disconnected from the hydraulic actuator by means of the at least one actuator valve (17a, 17b) independently of a control position of the at least one circuit valve (12a, 12b, 13a, 13b), and wherein the control unit is configured to control the at least one actuator valve (17a, 17b) and to control a hydraulic displacement of the hydraulic working pump and/or a rotational speed of the hydraulic working pump such that a flow of fluid flowing towards the hydraulic actuator and/or an actuator pressure acting on the hydraulic actuator remain/remains constant when the hydraulic accumulator assembly is fluidly connected with the hydraulic actuator and/or when the hydraulic accumulator assembly is fluidly disconnected from the hydraulic actuator.